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Heat transfer and pressure drop during HFC refrigerant saturated vapour condensation inside a brazed plate heat exchanger
Abstract
This paper presents the heat transfer coefficients and the pressure drop measured during HFC refrigerants 236fa, 134a and 410A saturated vapour condensation inside a brazed plate heat exchanger: the effects of saturation temperature (pressure), refrigerant mass flux and fluid properties are investigated. The heat transfer coefficients show weak sensitivity to saturation temperature (pressure) and great sensitivity to refrigerant mass flux and fluid properties. A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 20 kg/m2s that corresponds to an equivalent Reynolds number around 1600–1700. At low refrigerant mass flux (Gr < 20 kg/m2s) the heat transfer coefficients are not dependent on mass flux and are well predicted by the Nusselt [20] analysis for vertical surface: the condensation process is gravity controlled. For higher refrigerant mass flux (Gr > 20 kg/m2s) the heat transfer coefficients depend on mass flux and are well predicted by Akers et al. [21] equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 25–30% increase for a doubling of the refrigerant mass flux.The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on mass flux.HFC-410A shows heat transfer coefficients similar to HFC-134a and 10% higher than HFC-236fa together with frictional pressure drops 40-50% lower than HFC-134a and 50–60% lower than HFC-236fa.
... The super-heated-vapor HTCs were from 5% to 10% higher than those of saturated vapor under the same refrigerant mass flux. Longo et al. [80] investigated the condensation HTCs and the pressure drop characteristics of R-236fa, R-134a, and R-410A inside a brazed plate heat exchanger. R-410A exhibited similar condensation HTCs to R-134a, while the condensation HTCs of R-236fa were 10% lower than R-410A. ...
... Pressure drops of various refrigerants inside the plate heat exchanger. Rectangular, circular, and triangular upward solid connected lines present the Longo [75], Longo and Zilio [76] and Longo et al. [77] study respectively, triangular forward solid connected line presents the Longo [80] study, and the remaining symbols present the Longo [78] study. ...
... Figure 18. Condensation HTC of various refrigerants inside the plate heat exchang circular, and triangular upward solid connected lines present the Longo[75], Long and Longo et al.[77] study respectively, triangular forward solid connected line pre[80] study, and the remaining symbols present the Longo[78] study. 18. Condensation HTC of various refrigerants inside the plate heat exchanger. ...
In this study, the nucleate boiling heat transfer performance for R-1234ze(E) subject to lubricant oil is reported. The viscosity grade ranges from low viscosity (68 cSt) to high viscosity (220 cSt) and the tested POE oils include POEA-68, POEA-170, POEC-170, POEA-220, and POEC-220 on a horizontal smooth copper tube. The 30 different refrigerant-oil mixtures were prepared by varying the oil mass concentration ranging from 1 % to 10 % and the corresponding saturation temperatures are 10 °C, 0 °C, and − 6 °C with heat flux ranging from 10 to 90 kW/m2. The results showed that all grades of POE oils are compatible and completely miscible with low GWP refrigerant R-1234ze(E) in the given test range. The present study reveals that the heat transfer characteristics of each refrigerant-oil mixture very much depend on the saturated temperature, heat flux, oil mass concentration, and operating pressure. The highest mass concentration (10 %) consistently deteriorates the heat transfer coefficient (HTC). However, the degradation of HTC with R-1234ze(E) is comparatively less severe than that of R-134a/POE mixture. It is found that a 3 % oil concentration is regarded as the threshold concentration for the highest enhancement in the HTC when compared to the pure refrigerant. The performances of other oil concentrations such as 1 % and 5 % are subject to saturation temperature, heat flux, and evaporator pressure. In terms of the influence of saturation temperature on HTC of the mixture, it was observed that among all the grades of oil, POEC-170 oil shows peculiar behavior and its performance is independent of saturation temperature.
... A literature review based on the properties of the evaporation and condensation of several LGWP refrigerants on brazed plate heat exchangers (PHEs) were presented by Shon et al. [5]. The HTCs and frictional pressure decrease during vaporization of the LGWP refrigerant on brazed PHEs were the subject of significant study by Longo et al. [6][7][8][9][10]. One of the most significant advantages of the azeotropic (hydrofluorocarbon (HFC) + hydrofluoroolifin (HFO) blend) R-513A is that it is fully non-flammable (A1 class) with comparable properties that may be used to replace R-134a systems with ease. ...
... A literature review based on the properties of the evaporation and condensation of several LGWP refrigerants on brazed plate heat exchangers (PHEs) were presented by Shon et al. [5]. The HTCs and frictional pressure decrease during vaporization of the LGWP refrigerant on brazed PHEs were the subject of significant study by Longo et al. [6][7][8][9][10]. ...
... The above literature shows that previous investigations reported specific results under limited conditions, including the working fluid (refrigerants), evaporation within the tubes and micro-channels [11][12][13], evaporation inside and outside of enhanced surfaces [14], and plate heat exchangers [8,9,[15][16][17]. Some of the results are not in line with each other. ...
This review presents the nucleate/convective boiling performance for a variety of important low global warming potential (LGWP) alternatives to commonly used high-global warming potential (GWP) refrigerants (such as R-134a, R404A, and R-410A, etc.). Efforts are stressed on the assessment of their evaporation pressure drop and heat transfer coefficient (HTC) characteristics. These alternatives include R-1234ze(Z), R-1234ze(E), R-1233zd (E), R-1234ze(E), R-410A, R-1234yf, and R-513A. The authors investigated the thermo-fluid properties within and outside a tube, mini-channel, micro-fin tube, and plate heat exchanger. The investigation of the numerical, experimental, and simulated results revealed that the evaporation pressure drop and HTC characteristics were dependent on a variety of variables. These factors include the working fluid’s thermodynamics and transport properties, the refrigerant’s mass flux, heat flux, saturation temperature, the vapor quality, the conditions and flow patterns, the orientation of the heating surface, and the geometry (shape, size, and surface area smooth/enhanced) of the heating surface. An expanded LGWP refrigerants, surfaces, and conditions database is needed. Mechanistic models may assist. These models can optimize boiling, anticipate heat transfer, and develop high-performance geometries.
... The super-heated-vapor HTCs were from 5% to 10% higher than those of saturated vapor under the same refrigerant mass flux. Longo et al. [80] investigated the condensation HTCs and the pressure drop characteristics of R-236fa, R-134a, and R-410A inside a brazed plate heat exchanger. R-410A exhibited similar condensation HTCs to R-134a, while the condensation HTCs of R-236fa were 10% lower than R-410A. ...
... Pressure drops of various refrigerants inside the plate heat exchanger. Rectangular, circular, and triangular upward solid connected lines present the Longo [75], Longo and Zilio [76] and Longo et al. [77] study respectively, triangular forward solid connected line presents the Longo [80] study, and the remaining symbols present the Longo [78] study. ...
... Figure 18. Condensation HTC of various refrigerants inside the plate heat exchang circular, and triangular upward solid connected lines present the Longo[75], Long and Longo et al.[77] study respectively, triangular forward solid connected line pre[80] study, and the remaining symbols present the Longo[78] study. 18. Condensation HTC of various refrigerants inside the plate heat exchanger. ...
In this review, the condensation HTCs (heat transfer coefficients) and pressure drop characteristics of some major low-global-warming-potential (GWP) refrigerants alternative to R-134a such as R-1234ze(E), R-1234ze(Z), R-1234yf, R-513A, and R-450A are reviewed. The thermofluids’ characteristics inside/outside a tube, minichannel, microfin tube, and plate heat exchanger are examined. In addition, several other refrigerants attributed to low GWP are also included in the present review. The experimental/numerical/simulation results’ analysis reveals that condensation HTCs and pressure drop characteristics depend on several parameters such as thermodynamics and transport properties of the working fluid, mass flux of the refrigerants, heat flux, saturation temperature, vapor quality, flow patterns, flow conditions, orientation of the condensing geometry, and condensation geometry (shape, size, and smooth/enhanced).
... Mass flux, G Longo (2010aLongo ( , 2010b experimentally studied the effects of mass flux on the condensation HTCs for HFCs (R236fa, R134a and R410A) and hydrocarbons (R600a, R290 and R1270). For all the investigated refrigerants, at small mass flux the HTCs are mass flux independent, while at larger mass flux the HTCs increase with mass flux. ...
... The HTCs decrease with increasing mass flux at first, and then keep almost constant for larger mass fluxes. The transition mass flux is similar to Longo (2010aLongo ( , 2010b: 15 kg · m −2 · s −1 . The equivalent Reynolds number for two-phase flow, Reeq, is given in the study by Akers et al. (1958): ...
... When the equivalent Reynolds number is used to classify the flow, the transition values of Longo (2010aLongo ( , 2010b are 1650 for both types of refrigerants. At small mass flux, condensation is mainly governed by gravity. ...
This study presents a literature review of work related to the two-phase flow patterns of vertical downward flow in plate heat exchangers with corrugated chevron plates. An understanding of these flow patterns is crucial for developing accurate models of plate heat exchangers functioning as condensers or absorbers. Flow pattern maps of the previous studies are combined and translated to dimensionless forms. One of the proposed flow pattern maps is based on ReL versus FrTP,hor/Λ0.5 and performs better than other representations. This map is compared with the map of tubes and shows general agreements in terms of the pattern positions, but the separating lines between flow patterns fit poorly. Influencing factors of condensation mechanisms are presented, among which mass flux and vapor quality are dominant. The preferred flow pattern map explains the transition of condensation mechanisms qualitatively when variations of mass flux and vapor quality are considered. Recommendations are given to come to more uniform flow pattern maps in plate heat exchangers with chevron corrugations.
... The friction factor f is used to evaluate the fluid flow resistance or pressure drop in the channel. The testing pressure drop P exp includes five parts [13], inlet local pressure loss P in (deceleration), inlet pipe friction pressure loss P in−p , outlet local pressure loss P out (acceleration), outlet pipe friction pressure loss P out−p and the friction pressure loss ...
... The empirical correlation can predict 90% test data with the errors within ±15%. The detail comparison for the prediction Nu using the regression equation (13) and the test data is described in Fig. 12. The empirical correlation application must be strict in the range Re = 200-7000 and Pr = 2.0-12.0. ...
... Mean absolute error : E m.ab For the empirical correlation (13), the average error of this equation is −1.7%, mean absolute error is 9.7% for all the data. ...
This paper experimentally investigates the thermal hydraulic characteristics for three types of fluid on plate heat exchanger surfaces. The three types of fluid are R245fa, glycol and water. The characteristics of heat transfer coefficient Nu and friction factor f are given. The concept of pump power is provided to overall evaluate the enhanced heat transfer. The dimensionless correlation equations of Nu and f factors are provided using multiple regression method. The mean absolute errors for the Nu and f factor are 9.7 and 6.8% in the whole test range.
... The development of the new computational procedure was based on the analysis of a wide set of experimental data on pure or near azeotropic refrigerants saturated vapour condensation inside a commercial herringbone-type BPHE previously obtained by the authors which includes 338 data points on HFC refrigerants (HFC236a, HFC134a, HFC410A) [8], HC refrigerants (HC600a-Isobutane, HC290-Propane, HC1270-Propylene) [9] low Global Warming Potential HFO refrigerants (HFO1234yf, HFO1234ze(E)) [10,11]. Fig. 1 plots these data points in non-dimensional co-ordinates showing the heat transfer factor [12] ...
... where the characteristic constant 1.875 and the exponent 0.445 on the equivalent Reynolds number were obtained by a best-fitting procedure on the data previously obtained by the authors [8][9][10][11]. ...
... This new model for saturated vapour forced-convection condensation was also applied, coupled with the model developed by Webb [15], to forced-convection condensation of super-heated vapour: Comparison between experimental and calculated saturated vapour condensation heat transfer coefficient by Nusselt [14] analysis (Eq. (7)): data in gravitydominated region (Re eq < 1600) by the authors [8][9][10][11]. 9)): data in forcedconvection condensation region (Re eq > 1600) by the authors [8][9][10][11]. ...
... The development of the new computational procedure was based on the analysis of a wide set of experimental data on pure or near azeotropic refrigerants saturated vapour condensation inside a commercial herringbone-type BPHE previously obtained by the authors which includes 338 data points on HFC refrigerants (HFC236a, HFC134a, HFC410A) [8], HC refrigerants (HC600a-Isobutane, HC290-Propane, HC1270-Propylene) [9] low Global Warming Potential HFO refrigerants (HFO1234yf, HFO1234ze(E)) [10,11]. Fig. 1 plots these data points in non-dimensional co-ordinates showing the heat transfer factor [12] ...
... where the characteristic constant 1.875 and the exponent 0.445 on the equivalent Reynolds number were obtained by a best-fitting procedure on the data previously obtained by the authors [8][9][10][11]. ...
... This new model for saturated vapour forced-convection condensation was also applied, coupled with the model developed by Webb [15], to forced-convection condensation of super-heated vapour: Comparison between experimental and calculated saturated vapour condensation heat transfer coefficient by Nusselt [14] analysis (Eq. (7)): data in gravitydominated region (Re eq < 1600) by the authors [8][9][10][11]. 9)): data in forcedconvection condensation region (Re eq > 1600) by the authors [8][9][10][11]. ...
This paper presents a new computational procedure for refrigerant condensation inside herringbone-type Brazed Plate Heat Exchanger (BPHE). A transition point between gravity controlled and forced convection condensation was found for an equivalent Reynolds number around 1600. At low equivalent Reynolds number (<1600) the heat transfer coefficients are not dependent on mass flux and are well predicted by a simple model based on the Nusselt (1916) equation for vertical surface. For higher equivalent Reynolds number (>1600) the heat transfer coefficients depend on mass flux and condensate drainage is controlled by the combined actions of gravity and vapour shear. A new model was developed for predicting the heat transfer coefficients in the forced convection condensation region. This new model was also applied to super-heated vapour condensation by using the equation of Webb (1998) to account for super-heating effects. The new computational procedure was compared against data from the literature: the mean absolute percentage deviation between experimental and calculated heat transfer coefficients was lower than 16%.
... Longo et al. [67] conducted a comparative study, akin to [68], assessing heat transfer coefficients and pressure drops in a heat exchanger for R600a, R290, and R1270 as HFC refrigerant alternatives. Notably, R290 demonstrated similar performance to R22 in heat transfer with a 50% lower pressure drop. ...
... IR thermography confirmed convective boiling dominance for both refrigerants, with outlet vapor superheating degrading average boiling heat transfer coefficients. Experimental data validated author-proposed models [68]. Additionally, Longo et al. provided local heat transfer coefficients for R32 and R410A [77], [80], showing fair agreement with Longo et al. 's correlations [74], [75]. ...
... Fig. 2 and Table 2 give the main geometrical characteristics of the BPHE tested, whereas Table 3 outlines the main features of the different measuring devices in the experimental rig. A detailed description of the experimental rig, the measurement devices and the operating procedures was reported by [12]. The experimental results were reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. ...
... Figs. 7 and 8 show the comparison between present HFO-1234ze(Z) saturated vapour condensation heat transfer coefficients and frictional pressure drop and those of HFC-134a, HFC-236fa, HFO-1234ze(E) and HC-600a previously measured by present authors [12,20,21] inside the same BPHE under the same operating conditions. HFO-1234ze(Z) exhibits heat transfer coefficients much higher than those of all the other refrigerants considered and frictional pressure drop similar to HC-600a. ...
This paper presents the experimental heat transfer coefficients and pressure drop measured during refrigerant HFO-1234ze(Z) saturated vapour condensation inside a commercial Brazed Plate Heat Exchanger (BPHE) and compares this data with similar measurements previously obtained for refrigerant HFC-236fa, HFC-134a, HC-600a, HFO-1234ze(E) in order to experimentally assess refrigerant HFO-1234ze(Z) for high temperature heat pumps. HFO-1234ze(Z) exhibits heat transfer coefficients much higher than those of all the refrigerants now used in heat pumps and frictional pressure drop similar to HC-600a at the same refrigerant mass flux. Therefore, considering also its thermodynamic properties, HFO-1234ze(Z) seems to be a very promising low GWP refrigerant for high temperature heat pumps with a potential capability similar to refrigerant CFC-114 that dominated this type of application before Montreal Protocol.
... In addition, plate heat exchangers are gaining popularity in the refrigeration and air conditioning technical fields Due to their compact design and high thermal efficiency with the extension of their application as two-phase heat exchangers such as an evaporator and condenser. Many researchers have focused on the condensation and evaporation heat transfer coefficient in a plate heat exchanger but most of the existing literature on this subject only deals mainly with the overall heat transfer coefficient [2][3]. However, even if some recent studies have attempted to describe the characteristics of local heat transfer, such as Longo et.al [4] studied the behavior of local heat transfer, nevertheless, the local heat transfer coefficient has not been properly clarified. ...
This study presents experimental investigation of evaporation local heat transfer characteristics of CF3I in a vertical brazed plate heat exchanger. To do this a test section which contains a total of 8 stainless steel plates is designed to measure the local heat transfer coefficient of the refrigerant. Two of them were constructed herringbone for the refrigerant flow channel the other two flat plats are processed for the cooling plate for the refrigerant, and the another is for cooling water flow channel. To measure local heat transfer coefficient, 20 thermocouples were set in the test section. These 20 thermocouples are installed to measure the refrigerant wall temperatures, water side temperature and saturation temperature of the refrigerant. Recording these measurements makes it possible to calculate the local heat transfer coefficient at different positions in the test section. The refrigerant flow channel and the water flow channels are countercurrent in the test section. The refrigerant flow channel is in the middle, and it is sandwiched by two water channels from outside. In evaporation, the flow direction of the refrigerant is upwards in the test section. The experiment was carried in the condition of vapor qualities from 0.0 to 1.0 at certain saturation temperature and masse flux. In evaporation experiment, local heat transfer coefficient indicates maximum value near refrigerants inlet position and minimum value at end face position of cross section of the channel with the same phenomena as [1] for pure R32. The heat transfer coefficient for mass flux 50kg/m2s is almost 1.2 times higher than that for mass flux 20 kg/m2s at high quality vapor.
... Based on literature review, a summary can be arrived that most of previous studies on PHEs were carried out on GPHEs [ 5 , 7-10 , 24-27 ], while research on BPHEs was almost in two-phase flow [28][29][30][31][32][33][34][35][36][37][38][39][40][41] and very few investigations regarding PHEs were reported for single-phase flow [ 11-13 , 42 , 43 ]. Furthermore, most of numerical investigations were executed by modeling of a small portion of PHEs [ 18 , 19 , 44-50 ], while inlet and outlet regions including ports have significant effects on flow pattern and distribution. ...
Effect of chevron angle on thermofluids characteristics of Brazed Plate Heat Exchangers (BPHEs) are studied experimentally and numerically. The simulations include the effects of brazing joints and inlet/outlet port distribution that were normally overlooked in the existing literature. Four types of non-mixed BPHEs are considered with various chevron angles: L (35°), M (50°), H (65°), and LH (35°/65°). These four types of non-mixed BPHEs are combined in order to produce four types of mixed BPHEs: L+M, M+H, L+H, and LH+H. Results show that rise of chevron angle leads to the augmentation of Nusselt number and friction factor. Hence, type H and type L have the maximum and the minimum Nusselt numbers and friction factors among all non-mixed and mixed BPHEs. However, type H has the worst performance based on volume goodness factor method, while type M has the best performance among all modeled BPHEs followed by type L+M. Detailed flow study illustrates that rise of chevron angle leads to change in flow pattern from chevron angle direction to zig-zag or straight direction, which causes increase in heat transfer rate and pressure drop. Correlations are developed for Nusselt number and friction factor of non-mixed and mixed BPHEs in a wide range of Reynolds number between 50 and 10,000 with mean deviations of 9%.
... As mentioned before, infrared thermography has been used in order to study this phenomenon mainly in air to refrigerant heat exchangers, because its relatively easy access to the frontal area. ( Bowers et al., 2010 ), or ( Longo, 2010a( Longo, , 2010b used thermography in microchannel heat exchangers to visualize the two-phase flow region for different outlet vapor qualities and superheats of 5 and 10 K and to outline a methodology to quantify both refrigerant maldistribution and effective usage of the heat exchanger respectively. ...
The refrigerant distribution in a brazed plate heat exchanger evaporator with distributor has been studied with a thermographic camera working under different conditions of inlet vapor quality, superheat, and water temperature drop. The thermographies have shown a clear uneven thermal distribution except when superheat is null. In most of the cases, they show that a great part of the liquid accumulates at the end channels of the evaporator. The degradation of the evaporator performance is higher when the water temperature drop has a similar or higher value than the superheat. On the other hand, when the superheat is significantly higher than the water temperature drop, the evaporator performance is very similar to situations in which there is an even distribution of the refrigerant. The registered evaporation temperatures are much lower for the case of 13 K of water temperature drop, highlighting the importance of the influence of this parameter on the evaporator performance. This research is described in two parts, Part A (present paper) including the description of the experimental campaign, the obtained experimental results and the results discussion and Part B including an analysis of the degradation of the evaporation temperature due to the refrigerant maldistribution as well as a deeper analysis of the registered temperatures and of the causes for the great degradation observed when the water temperature drop is increased.
... They also showed that in a straight or wavy channel with a smaller wave amplitude to wavelength ratio longer elongated bubbles are formed, which blocks the path and increases the pressure drop. Longo [40] experimentally investigated the heat transfer and pressure drop of hydrofluorocarbon saturated vapor in a gasket plate heat exchanger with wavy channels in different saturated vapor temperatures and refrigerant flow rates. He showed that the heat transfer coefficient is not much sensitive to the temperature but it strongly depends on the mass flow. ...
The effect of different geometrical parameters of wavy and strip fins in a three-fluid plate-fin compact heat exchanger on the condensation heat transfer in the middle heat exchanger has been experimentally investigated. The three-fluid heat exchanger consisted of three heat exchangers with strip and wavy fins. In the examined system, the hot and cold fluids flowed through the adjacent heat exchangers (strip channels), while the middle heat exchanger (wavy channels) was occupied with a single-component two-phase flow (condensed vapor). The Nusselt number, the friction factor, the heat transfer surface contribution between the middle heat exchanger and each of the adjacent heat exchangers, and the thermal performance factor were calculated using the measured data at the inlets and outlets of the heat exchangers, and by using the thermal balance equations between the fluids passing through the heat exchangers. In the examined heat exchanger, the hot and cold flows had a cross-direction with the two-phase fluid flow. The two-phase Reynolds number, the vapor quality, and the heat transfer surface contribution of the middle heat exchanger with the adjacent heat exchangers were 50–4800, 0.1–0.67, and 0.19–0.7, respectively. The results show that the two-phase flow pattern in the wavy channels of the middle heat exchanger is stratified and wavy. According to the findings, a higher thermal performance factor is observed when the ratio of the wavy channel heat transfer surface to the heat transfer surface of the cold or hot flows is closer to 1. Also, with higher wave amplitude to wavelength ratios, lower pitch to height ratio of the fins, the lower wavelength to the fin length ratios, and lower fin pitch to wave amplitude ratios are obtained a higher thermal performance factor.
... The model was further validated by the experimental data from three PHEs with varied geometrical characters. Longo and his co-workers conducted a great deal of experiment on condensation heat transfer in brazed PHE with diverse refrigerants, namely R134a [10,11], R410a [12], isobutene, propane and propene [13], R236fa [14], R1234yf [15], R1234ze [16] and R152a [17]. A detailed review of earlier research work and a discussion on the thermal-hydraulic performance of condensation in PHEs can be found in the book by Wang et al. [18]. ...
Plate heat exchangers are widely used for two-phase heat transfer in the industrial applications, and recently more attention has been paid to the plate heat exchangers with enhanced surface due to their better heat transfer performance. In this paper, the local condensation heat transfer coefficients are studied using R134a in a micro-structured plate heat exchanger. In order to obtain a more accurate prediction model, a series of measurements are conducted under various operating conditions. The mass flux of R134a varied from 47 kg/m ² s to 77 kg/m ² s, the saturation pressure in the condenser ranged from 6.32 bar to 8.95 bar, and the value of the heat flux was between 13 kW/m ² and 22 kW/m ² . The local two-phase Nusselt number increases with the increase of the mass flux. As the saturation pressure increases, the local two-phase Nusselt number increase at the beginning of the condensation and decrease at the end of the condensation. However, the effect of heat flux on local heat transfer is irregular, due to the interaction of these parameters in the experiment. Comparing with the unstructured plate heat exchanger, R134a condenses faster at the beginning of the process in the micro-sturctured plate heat exchanger, and the local heat transfer performs better when the vapor quality is lower. Combing with the phenomenon that the overall heat flux in micro-structured plate is larger under the same working conditions, it shows that the overall heat transfer of the micro-structured plate is improved, but the local heat transfer uprades only at lower vapor qualities. A new correlation is developed, it predicts all the experimental data within the root mean square error 10%, and a new correlation for the waterside is suggested as well.
... The authors of the present paper carried out in the past an extensive measurement campaign on refrigerant boiling [4][5][6][7][8][9][10] and condensation [11][12][13][14][15][16][17][18] inside a commercial BPHE. Several traditional HFC refrigerants (R134a, R410A, R236fa, R404A), HydroCarbon (HC) refrigerants (R600a, R290, R1270), low-GWP HFC refrigerants (R152a, R32), HydroFluoroOlefin (HFO) refrigerants (R1234yf, R1234ze(E), R1234ze(Z)) and a HydroChloroFluoroOlefin (HCFO) refrigerant (R1233zd(E)) were tested. ...
This paper presents a Gradient Boosting Machines (GBM) model for predicting refrigerant two-phase frictional pressure gradient inside Brazed Plate Heat Exchangers (BPHE) based on an extensive database that includes 1624 boiling data-points, 925 condensation data-points, 16 different plate geometries, and 16 different refrigerants (including 4 natural refrigerants and 6 other low-GWP refrigerants). The model accounts for the effect of plate geometry, operating conditions and refrigerant properties. The model is able to reproduce the whole database with a Mean Absolute Percentage Error (MAPE) of 6.6%. The GBM model exhibits a better predictive performance than the state-of-the-art analytical-computational procedures for two-phase pressure drop inside BPHE available in the open literature. The characteristic parameters of the GBM model are thoroughly reported in the paper.
... The authors of the present paper had carried out in the past an extensive analysis of refrigerants condensation and vaporisation inside a commercial Brazed Plate Heat Exchanger (BPHE) [5,6]. The traditional HFC refrigerants (R134a, R410A, R404A, R236fa), HydroCarbon (HC) refrigerants (R600a, R290, R1270), low GWP HFC refrigerants (R152a, R32), HydroFluoroOlefin (HFO) refrigerants (R1234yf, R1234ze(E), R1234ze(Z)) and also a HydroChloroFluoroOlefin (HCFO) refrigerant (R1233zd(E)) were considered. ...
This paper presents the heat-transfer assessment of different low GWP substitutes for traditional HydroFluoroCarbon (HFC) refrigerants obtained by applying both an experimental analysis based on the direct measurement of thermal (heat transfer coefficients) and hydraulic (pressure drops) performances and a theoretical analysis based on a specific Performance Evaluation Criteria (PEC), the Total Temperature Penalisation (TTP), in the specific case of boiling and condensation in a commercial Brazed Plate Heat Exchanger (BPHE). The results of both the experimental and the theoretical assessment confirm that the refrigerant R32 has comparable heat transfer characteristics to R410A. Similarly the refrigerants R290 and R1270 exhibit superior heat transfer performance to R404A; the refrigerants R152a, R1234yf and R1234ze(E) show heat transfer characteristics comparable to R134a and R1234ze(Z) exhibits superior heat transfer performance to R236fa. The coupling of experimental and theoretical assessments provides a sound procedure for the heat-transfer assessment of the low GWP alternatives for traditional HFC refrigerants.
... This is still a topic that could do with further study. Longo et al. (2004) and Longo (2010Longo ( , 2011 conducted studies that looked at condensation in PHX, and from these studies it can be seen that at low equivalent Reynolds number (Re eq < 1750), the j -factor is nominally constant at a value of 60, and above that, it is linear with equivalent Reynolds number, so the j -factor can be given by ...
Packaged air conditioning (AC) units, called Environmental Control Units (ECUs), are being increasingly used by the U.S. military, especially in hot ambient temperature climates. The compact packaging of ECUs resembles unitary-type rooftop or room AC systems, and they are used to cool personnel and equipment in enclosed spaces such as shelters, vehicles, and containers. Despite these similarities, ECUs have distinctive features that aren’t found in commercial packaged AC units. An ECU is designed to sustain harsh and extreme weather conditions up to 51.7 °C (125 °F) which is a design set-point by the military. As the outdoor temperature increases, both the cooling capacity and coefficient of performance (COP) of ECUs drop dramatically. In addition, the compact design degrades airflow uniformity due to air maldistribution across evaporator coil, which results in further performance degradation. Therefore, the goal of this study is to identify ways to improve the component as well as the system performance of the ECUs in the field at high ambient temperatures.
A passive solution was evaluated to compensate for the degradation in performance of ECU evaporators, known as the interleaved circuitry method. The interleaved circuitry method, where the refrigerant from a circuit with high air flow is routed to a circuit with low air flow and vice-versa, has been investigated to determine its effectiveness in reducing the air maldistribution effect. Air velocity measurements in front of the ECU’s evaporator have been conducted in psychrometric chambers and the measurement locations have been defined by the log-Tchebycheff rule. The velocity profile was obtained by the Lagrange Interpolation method as percentage values. The system performance after interleaved circuitry implementation was compared to the baseline system at different operating conditions up to 51.7 °C (125 °F). The results showed that the interleaved circuitry method increased the superheat uniformity of the individual circuits and improved the cooling capacity and COP up to 16.6% and 12.4%, respectively. Furthermore, the tuned model predicted the evaporator cooling capacity within a mean absolute error of approximately ±10%.
Moreover, vapor injection (VI) with economization, where cool gas is injected to the compressor at an intermediate stage to absorb the heat generated during the compression process, has been experimentally and numerically assessed to significantly improve system performance. The ECU has been retrofitted with an economized vapor injection (EVI) system and experimentally characterized in side-by-side psychrometric chambers. The performance of the EVI system for superheated and saturated injection conditions were compared to the case of without injection at different operating conditions. The results showed that the EVI system reduced the compressor discharge temperature by up to 5 °C, and improved the cooling capacity and COP by up to 12.7% and 3.1%, respectively. The experimental data have been used to develop, tune, and validate a detailed steady-state cycle model. The predictions of suction and injection mass flow rates, compressor power consumption, and system COP were within a mean absolute error of approximately ±5%. At last, the model has been employed to optimize the economizer geometry in order to maximize the system COP at designed ambient condition of 51.7 °C (125 °F). The optimization process resulted in maximum improvements in compressor discharge temperature, cooling capacity, and COP of 8.5 °C, 22.3%, and 17.3%, respectively.
... Nous développons ici la méthode utilisée par (Longo, 2008) et (Longo, 2010) pour établir une corrélation du coefficient d'échange en condensation avec surchauffe de la vapeur en entrée du condenseur. ...
This research work examines at the global and local scales the thermo-hydraulic characteristics of plate heat exchangers with corrugated chevron plates, for single-phase and condensation flows. The study is divided into two parts:
Part 1: The first part concerns the analysis of flow structures for single-phase flows. After its validation using the results of the experimental campaign, the simulation tool, based on observables carefully selected, allows to identify quantitatively the coexistence of two flows structures. These results highlight the joint role of the mass flux and the chevron angle on the dominance of either of the flow structures. This new understanding of the flows has led to the proposal of a generalized model for pressure drop. Owing to its simplified form and depending mainly on the plate geometrical parameters, this model is considered as an optimization tool for plate heat exchangers.
Part 2: The second part concerns the study of convective condensation with and without vapor superheating at the inlet of the heat exchanger. For this work, a specific experimental setup has been developed allowing precise control of the boundary conditions. Otherwise a specific metrology has been set to the point, based on infrared thermography, in order to determine certain local quantities as the fluids temperatures profiles and the vapor quality along the condenser. With relative deviation in the order of 20 % between the global and local approaches, the results on heat transfer calls into question certain assumptions of the literature. Thus, we observe a high and wide variability of the heat transfer coefficients and the heat flux density along the condenser, and the superheating of the vapor tends to increase the heat transfers.
These additional measures question some assumptions of the literature on the development of heat transfer correlations in condensers. The study has been conducted with and without vapor superheating at the inlet of the condenser.
... Longo [9][10][11] performed a series of condensation experiments on the R134a, the R410A and the R236fa in a commercial brazed plate heat exchanger (BPHE) (b = 65°, b = 2 mm, P = 8 mm). Although different refrigerant was applied, two conclusions on condensation regime were identified: (1) the gravitational regime (for G < 20 kg/m 2 Ás), where the mean HTC was irrelevant to the mass velocity, and (2) the viscous regime (for G > 20 kg/m 2 Ás), where the mean HTC increased with the mass velocity. ...
... To allow for the possibility of evaporating flow at high quality, the Shah chart correlation for boiling heat transfer has also been included and it can be chosen optionally by the user [36]. The heat transfer coefficient correlation for condensing flow used in the model refers to the study conducted by Longo on condensing refrigerant flow in PHEX [37]. Note that no general two-phase heat transfer correlations have been implemented for two-component mixtures. ...
Despite the increasing interest in organic Rankine cycle (ORC) systems and the large number of cycle models proposed in the literature, charge-based ORC models are still almost absent. In this paper, a detailed overall ORC simulation model is presented based on two solution strategies: condenser subcooling and total working fluid charge of the system. The latter allows the subcooling level to be predicted rather than specified as an input. The overall cycle model is composed of independent models for pump, expander, line sets, liquid receiver and heat exchangers. Empirical and semi-empirical models are adopted for the pump and expander, respectively. A generalized steady-state moving boundary method is used to model the heat exchangers. The line sets and liquid receiver are used to better estimate the total charge of the system and pressure drops. Finally, the individual components are connected to form a cycle model in an object-oriented fashion. The solution algorithm includes a preconditioner to guess reasonable values for the evaporating and condensing temperatures and a main cycle solver loop which drives to zero a set of residuals to ensure the convergence of the solution. The model has been developed in the Python programming language. A thorough validation is then carried out against experimental data obtained from two test setups having different nominal size, working fluids and individual components: (i) a regenerative ORC with a 5 kW scroll expander and an oil flooding loop; (ii) a regenerative ORC with a 11 kW single-screw expander. The computer code is made available through open-source dissemination.
... -1 , the results show two different tendencies of the heat transfer variation with respect to the mass flux: 1/ the heat transfer coefficient decreases with the mass flux until 2/ it reaches a "plateau" whose value depends on the fluid and the working pressure. This trend was obtained by [13] on condensation of pure fluids (pentane, butane and propane) inside BPHE (β = 45°, b = 5 mm), and by [14] and [15], on condensation of R-236fa, R-410A or R-134a inside BPHE (β = 65°, b = 2 mm), where β and b are the angle and the amplitude of the BPHE corrugation, respectively. The authors explain this behavior by a change in the condensation mode between the gravity controlled regime (described by Nusselt theory) and the inertial regime (dominated by the vapor/liquid interfacial shear). ...
The existing technologies of brazed plate heat exchanger (BPHE) must be improved in order to face the new challenges of the energy transition, whether in energy recovery of systems, or in the efficiency of thermodynamic machines. To establish predictive methods of BPHE performance, it is necessary to bring new information on the understanding of the BPHE thermo-hydraulic transfers. In this study, the intended application is related to heat pumps, whose performance is sensitive to the heat transfer in the condenser. At the condenser inlet, the vapor superheating can reach 30 K. In this work, we present an analysis of a superheated vapor effect on the mean heat transfer coefficient in the condenser.
The tested BPHE prototype consists of 3 plates, thus 2 channels, and pentane is used as the working fluid. IR metrology is used to distinguish the different fluid state distributions which are representative of different heat transfers. The IR thermography shows a significant impact of the vapor superheat, depending on the mass flux, on the fluid distribution at the channel inlet. The condensation heat transfer coefficient has been measured at a mean constant saturation temperature of 36.5°C (1.029 bars), while varying the vapor superheat between 2 and 25 K and the pentane mass flux between 8 and 18 kg.m-2.s-1. The results show:1/ an increase in the heat transfer coefficient with the vapor superheat reaching 50% for the lowest mass flux, 2/ a decrease in the heat transfer coefficient with increasing the mass flux, highlighting the gravity mode condensation.
... Consequently, quantitative predictions of the flow boiling heat transfer coefficient were obtained through experimental investigations and expressed by empirical correlations such as the ones of Yan Lin for R141a[10], of Ayub[6]for ammonia and R22, of Sterner and Sunden for ammonia[11]and the correlation of Han at al. for R22 and R422A[12]. Research carried out in[13]investigated the effect of refrigerant mass flow rate , saturation temperature (pressure) and fluid properties on pressure drops and heat transfer during the saturated vapor condensation of R236fa, R134a and R410A for a brazed plate heat exchanger that used water as hot stream. The analysis resulted in a great influence of fluid properties and refrigerant mass flow rate and a feeble effect of saturation temperature on the heat transfer coefficient. ...
This paper analyzes the performances of an evaporator for small scale waste heat recovery applications based on bottoming Organic Rankine Cycles with net output power in the range 2-5 kW. The heat recovery steam generator is a plate heat exchanger with oil as hot stream and an organic fluid on the cold side. An experimental characterization of the heat exchanger was carried out at different operating points measuring temperatures, pressures and flow rates on both sides. The measurement data further allowed to validate a numerical model of the evaporator whereas heat transfer coefficients were evaluated comparing several literature correlations, especially for the phase-change of the organic fluid. With reference to a waste heat recovery application in industrial compressed air systems, multiple off-design conditions were simulated considering the effects of oil mass flow rate and temperature on the superheating of the organic fluid, a key parameter to ensure a proper operation of the expansion machine, thus of the energy recovery process.
... where J H is the heat transfer factor. For the condensation process a constant friction factor of 2.0 is assumed for all fluids [14]. The flat plate heat exchanger design model was verified in the single-and two-phase regions using an example outlined in Coulson et al. [11]. ...
Organic Rankine cycle turbogenerators are a promising technology to transform the solar radiation harvested by solar collectors into electric power. The present work aims at sizing a small-scale organic Rankine cycle unit by tailoring its de-sign for domestic solar applications. Stringent design criteria, i. e., compactness, high performance and safe operation, are targeted by adopting a multi-objective optimization approach modeled with the genetic algorithm. Design-point thermo-dynamic variables, e. g., evaporating pressure, the working fluid, minimum al-lowable temperature differences, and the equipment geometry, are the decision variables. Flat plate heat exchangers with herringbone corrugations are selected as heat transfer equipment for the preheater, the evaporator and the condenser. The results unveil the hyperbolic trend binding the net power output to the heat exchanger compactness. Findings also suggest that the evaporator and condens-er minimum allowable temperature differences have the largest impact on the system volume and on the cycle performances. Among the fluids considered, the results indicate that R1234yf and R1234ze are the best working fluid candidates. Using flat plate solar collectors (hot water temperature equal to 75 °C), R1234yf is the optimal solution. The heat exchanger volume ranges between 6.0 and 23.0 dm 3 , whereas the thermal efficiency is around 4.5%. R1234ze is the best working fluid employing parabolic solar collectors (hot water temperature equal to 120 °C). In such case the thermal efficiency is around 6.9%, and the heat ex-changer volume varies from 6.0 to 18.0 dm 3 .
... 316L. The calculation of the convection coefficient of the refrigerant fluid is made by the correlation provided byLongo (2010), which uses a Nusselt correlation for film condensation for vertical surfaces.Based on the mass flux it is observed that heat transfer is controlled by film condensation and the effects of forced convection are small. For water, the correlation proposed byHan et al. (2003) is used, which is a function of the Reynolds and Prandtl numbers and the plate corrugation angle . ...
The present work main objective was to create a mathematical model, using the
VBA™ language, for a Bosch Air-Water Heat Pump. The model analyses its behaviour on different
ambient conditions. The set of equations is solved with the Broyden method improved with the
Sherman-Morrison formula.
The model includes energy and heat transfer balances for the Evaporator and Condenser, to
simulate the heat exchanges and the work of the compressor and Evaporator Fan. The Compressor
performance is predicted through the system’s evaporating and condensing temperatures.
Different changes on the vapour compression cycle are analysed, phase separation and the
introduction of an internal heat exchanger to the system. The influence of the Fan’s power is
evaluated as well as modifications of the Evaporator’s geometry with the purpose of maximizing the
coefficient of performance (COP).
The conceived model is able to predict the real installation operation, producing identical
results from the case study presented. For equal input conditions the internal heat exchanger cycle
produces more heat and the higher COP.
The study revealed that the evaporator Fan is over dimensioned for obtaining the highest
COP. Geometry changes indicate a limited grow of COP with the heat transfer area and air flow rate.
L’objectif de ce projet de recherche est d’approfondir les connaissances actuelles sur les mécanismes mis en jeu lors de la condensation de diazote (pur ou en présence d’incondensables), en vue d’arriver, à terme, à développer des corrélations et/ou une approche théorique permettant de mieux modéliser ces phénomènes. Ces connaissances conduiront à proposer des voies d’optimisation de la conception des équipements en condition industrielle. Pour ce faire, un dispositif expérimental permettant l’étude du coefficient d’échange local de chaleur par condensation, dans des conditions contrôlées (et pertinentes pour les procédés visés), sera monté.
Plate heat exchanger (PHE) has been wildly used as the condenser of the organic Rankine cycle (ORC). As a potential zeotropic working fluid of ORC system, it is of great significance to study the condensation heat transfer of the mixture of R245fa/R141b and lubricating oil in PHE for the development of ORC system. In this paper, an experimental study on the condensation heat transfer coefficient (HTC) of a mixture of R245fa/R141b (0.5/0.5 by mass) and polyester oil (POE) in a plate heat exchanger (PHE) has been carried out. In addition, the results were compared with those of R245fa and R141b. The parameters in the experiment range from 0 to 0.9 for vapor quality, 0%–4% for oil concentration and 20 to 60 (kg·m⁻²·s⁻¹) for mass flux. The results showed a 20% reduction in HTC for R245fa/R141b with 4% oil concentration compared to oil-free refrigerant. In addition, the HTC of R245fa/R141b-POE mixture was between that of R245fa/POE and R141b/POE. The oil enhancement factor of different refrigerant/POE mixtures was less than 1.0, which could be well predicted by the Eckels correlation with a maximum mean absolute deviation (MAD) of 13.4%. The product of the predicted enhance factor and HTC predicted by the Jung et al. correlation agreed well with the tested HTC of different refrigerant/POE mixtures in the PHE. The maximum MAD of different refrigerant/POE mixtures was 20.6%, and 96.3% of predicted results were within ±30% deviation. A new correlation with a maximum MAD of 15% was proposed, which predicted the condensed HTC of refrigerant/POE mixture by using its physical properties.
This paper presents the local heat transfer coefficients of R32 and R410A complete condensation inside a Brazed Plate Heat Exchanger (BPHE). A new test section, with one channel on the refrigerant-side and two channels on the water-side, was specifically designed and manufactured for measuring the local heat transfer coefficient in refrigerant two-phase heat transfer in BPHE. The test section includes two thick corrugated plates instrumented with 36 copper-constantan thermocouples for measuring the plate surface temperature, the heat flux and the heat transfer coefficient in 9 different positions along the refrigerant channel. The experimental tests were carried out at a saturation temperature around 30°C, in the refrigerant mass velocity range 10 − 39 kg m⁻²s⁻¹ with an inlet vapour quality around 1.00 and an outlet vapour quality ranging from 0.04 to 0.27. A transition point between gravity controlled and forced convection condensation was found for a refrigerant mass velocity around 20 kg m⁻²s⁻¹. The experimental data was compared against theoretical models: Nusselt (1916) analysis for vertical surface predicts very well the data in gravity controlled condensation, while Longo et al. (2015) model shows a fair agreement with the forced convection condensation data.
Plate heat exchangers with an enhanced surface are attracting continuous attention as a smart option to acquire a more efficient heat transfer performance. Despite of a large number of research dedicated to the two-phase heat transfer, the understanding of condensation heat transfer mechanisms is still defective. In this paper, the experimental results of the quasi-local heat transfer coefficient and the two-phase frictional pressure drop during condensation of R1234ze(E) and R134a are reported in a micro-structured plate heat exchanger with mixed plates showing a chevron angle of 27°/63° and a hydraulic diameter of 5.5mm. The measurements were carried out with 110 groups of data for pure R1234ze(E) and 163 groups of data for pure R134a respectively. The mass flux and saturation temperature range from 34.08 to 70.64 kg/m²s, 22.51 to 40.84°C (corresponding to psat = 4.62 - 7.84 bar, pr = 0.13 - 0.22) for R1234ze(E), and 46.39 to 77.9 kg/m²s, 24.93 to 38.03°C (psat = 6.64 - 9.64 bar, pr = 0.16 – 0.24) for R134a. The effect of mass flux and saturation pressure is discussed, the experimental results indicate that the condensation in the micro-structured plate heat exchanger is shear-controlled, the transition from partial film flow to full film flow occurs at x ≈ 0.35-0.45. The characteristics of the two-phase frictional pressure drop for the mixed 27°/63° plates is similar to soft plates. Based on existing correlations, the experimental results are compared with predictive results by existing empirical correlations, and new correlations with better accuracies are developed by taking the influence of different parameters into consideration.
This study investigates the condensation flow patterns and heat transfer characteristics of a low global warming potential refrigerant R-1234ze(E) for downward flow in a plate heat exchanger through flow visualization. An asymmetric flow aspect for downward condensation is characterized by vapor- and liquid-preferred paths owing to the effect of gravity. Flow patterns for downward condensation are classified into two regimes: steady film flow without intermittent flooding and pulsating film flow involving intermittent flooding. Additionally, the condensation heat transfer coefficient and frictional pressure drop were analyzed considering flow patterns. Intermittent flooding is hardly related to the heat transfer performance. A frequency analysis of the pressure drop exhibited a considerable difference in periodic characteristics between the flow regimes with and without intermittent flooding. Finally, the visualization data coincided with the flow pattern map proposed by the existing study, and an empirical correlation for predicting the flow transition between pulsating and steady film flow was developed in terms of the Weber number.
The pressure drop in the two-phase condensing flow of air-steam mixture inside channels of plate heat exchanger (PHE) with different geometries of corrugations is studied based on experiments and one-dimensional mathematical modelling. The experiments were made with five samples of the PHE channel. In three of them plates with corrugations inclination angles 30, 45 and 60 degrees at the same height of corrugations 5 mm. The other two plates corrugations height was 7.5 and 10 mm at the same pitch to height ratio and inclination angle of 60 degrees. The correlation of pressure drop data for all experimental samples by average process parameters is not able to give acceptable accuracy. The correlation for local pressure gradients in two-phase condensing flow is identified using a developed one-dimensional mathematical model. The model of separated flows of phases is employed for channel zones close to air-steam mixture entrance. Further on channel length with an increase of liquid phase quantities, its combination with the dispersed annular flow structure model is used. The proposed equations can be included in the mathematical model when designing PHE and optimising the geometrical form of corrugations on its plates for steam condensation processes from an air-steam mixture.
This paper investigates the dynamic behavior of dual vapor compression Refrigeration (VCR) chillers, considering nine ecofriendly refrigerants such as R134a, R32, R1234yf, R1234ze(E), R717, R600, R600a, R290, R410a and compared to R22. Disturbances are introduced to the secondary loop of the VCR as sudden and ramp increases of the inlet cooling and chilled water temperatures and their impact on the dynamic responses of the condensing, evaporating and chilled water outlet temperatures, and Coefficient of Performance (COP) are discussed. The duration of the dynamic responses, the rise in temperatures and the change in COP are used as criteria to evaluate the fluids through a combination of rank-ordering and multi-criteria assessment approaches. R290 and R410a exhibit lower transient response time than the other options. Refrigerants R290 and R717 exhibit the lowest rise in the condensing temperature, R717 exhibits the minimum rise in the evaporating temperature, whereas R717 and R1234yf indicate the lowest rise in the chilled water temperature among others. R717 further exhibits very low change in COP under disturbances, whereas it exhibits the optimum trade-offs among all fluids between robustness in dynamic operation and steady-state efficiency. It is recommended to introduce disturbances in a ramp manner instead of a sudden increase.
In this study, we analyzed the effects of heat flux, mass flux, condensation pressure, and mean vapor quality on the condensation heat transfer and friction pressure drop characteristics of R-1234ze(E) and R-1233zd(E) in plate heat exchangers with different chevron angles. When the mean vapor quality increased, the heat transfer coefficient and frictional pressure drop increased. Both increased with increasing the mass flux and with decreasing the condensation pressure. Unlike the heat transfer coefficient, the frictional pressure drop was hardly affected by the heat flux. R-1233zd(E) showed a larger heat transfer coefficient and frictional pressure drop than R-1234ze(E) owing to the differences in thermodynamic properties. The Nusselt number correlation and friction coefficient correlations were derived for various chevron angles from the experimental results. The ratio of the Nusselt number and pressure drop according to the equivalent Reynolds number was compared. It is concluded that R-1234ze(E) has a higher energy performance parameter than R-1233zd(E), which means that R-1233zd(E) has an advantage in terms of heat transfer, but the loss due to the increased pressure drop is relatively large. It is also confirmed that the result from the simple relative economic evaluation agree well with that from the energy conversion performance evaluation.
This paper presents an Artificial Neural Network (ANN) model for predicting refrigerant condensation heat transfer coefficients inside herringbone-type Brazed Plate Heat Exchangers (BPHE). The model accounts for the effect of plate geometry, operating conditions and refrigerant properties both in the saturated and in the superheated vapour condensation regimes. The model predictions demonstrate good agreement with a database of 1884 data points comprising 12 plate geometries and 16 refrigerants (including 4 so-called natural refrigerants and 6 other low-GWP refrigerants). The Mean Absolute Percentage Error (MAPE) of the model predictions is 3.6%. The results demonstrates that the ANN model presented herein is capable of better predictive capability than most of the state-of-the-art BPHE analytical-computational models presented in the open literature. The characteristic parameters of the ANN model are reported in the paper.
Plate heat exchanger (PHE) is popularly used as the condenser. The condensation heat transfer along the plate in a conventional plate condenser (CPC) is unavoidably worsened due to condensate accumulation. In this paper, the liquid-separation condensation is applied to plate condenser (LPC) by removing the condensate for heat transfer enhancements. The working principles and the structure of LPC are described in details. A mathematical model is established. With focus on a simple LPC, the refrigerant side performance is identified by the performance evaluation parameter (PEC), while its overall performance integrating water side is evaluated by the exergy efficiency (η). Results show that in LPC, PEC and η reach to their maximum values simultaneously when the path length ratio (PLR k ) and corrugation amplitude ratio (CAR k ) are at 0.4 and 0.72, respectively. With the optimized configuration of LPC, the initial refrigerant mass flow rate (ṁ r,1 ) and inlet vapor quality (x r,in,1 ) are parametrically investigated. Their increments benefit LPC performance that is mainly contributed by the second path. LPC has magnitudes of PEC always greater than one, indicating the effectiveness of liquid-separation condensation. LPC performance is superior to CPC in terms of a higher heat load (Q r ) and an improved exergy efficiency (η).
In this study, condensation heat transfer performance and frictional pressure drop in plate heat exchanger using a low GWP refrigerant R-1233zd(E) as a working fluid are experimentally analyzed. Experiments on single phase water-to-water are also conducted in the tested plate heat exchanger, and the heat transfer coefficient correlation of the cooling water side is derived by applying the modified Wilson plot technique. In the refrigerant-to-water experiments, the influences of heat flux, refrigerant mass flux, and saturation pressure on the heat transfer and pressure drop in the tested plate heat exchanger are analyzed with varying the mean vapor quality. Experimental results show that the heat transfer coefficient increases with increasing the heat flux, mean vapor quality, and the mass flux while it decreases with increasing the saturation pressure. On the other hand, the frictional pressure drop increases with increasing the mass flux and mean vapor quality while it decreases with increasing the saturation pressure. Experimental correlations for predicting Nusselt number and friction factor of R-1233zd(E) in plate heat exchanger are developed and compared against other correlations from literature.
In recent years, research on economized vapor injected (EVI) compression systems showed potential improvements to both cooling capacity and coefficient of performance (COP). In addition, the operating range of compressors can be extended by reducing the discharge temperature. However, the optimum operation of such systems is directly related to the amount of refrigerant charge, which often is not optimized. Therefore, an accurate charge estimation methodology is required to further improve the operation of EVI compression systems. In this paper, a detailed cycle model has been developed for the EVI compression system. The model aims to predict the performance of EVI systems by imposing the amount of required refrigerant charge as an input. In the cycle model, the EVI compressor was mapped based on the correlation of Tello-Oquendo et al. (2017), whereas evaporator, condenser and economizer heat exchanger models were constructed based on the available ACHP models (Bell, 2015). With respect to charge inventory, the two-point regression model from Shen et al. (2009) was used to account for inaccurate estimation of refrigerant volumes, ambiguity in slip flow model, and solubility of refrigerant in the lubricating oil. The cycle model has been validated with experimental performance data taken with a 5-ton Environmental Control Unit (ECU) that utilizes EVI technology. The developed cycle model showed very good agreement with the data with a MAE in COP of less than 5%. Furthermore, the estimated charge inventory has been compared to the one-point regression model. Results showed that the former method allowed to predict the charge inventory with an MAE of less than 0.2%.
A numerical analysis model using a flow network approach is developed to evaluate the performance of a plate heat exchanger (PHE). In order to consider complex flows in PHEs in the model, the flow paths in the channels are represented by a flow network consisting of nodes and branches. This model is able to evaluate the node-average local properties of the working fluids of each channel in a PHE. Several empirical correlations for the pressure drop and the heat transfer are evaluated against various experimental data to implement the selected correlations into the numerical analysis model according to the flow conditions and geometry of the heat transfer plates used. The pressure drop and heat transfer capacity of a PHE were experimentally measured with a range of operating parameters and the measured values were then compared with the prediction by the numerical analysis model. The predictions of the heat transfer capacity are in good agreement with the experimental data within a discrepancy of 10%, whereas the prediction of the pressure drop significantly deviated from the experimental data. The analysis also demonstrates that the total heat transfer rate varies little whereas the pressure drop increases sharply as the maldistribution of the flow is intensified.
Most of the energy consumed in cooling cycles comes from fossil fuels, whose reserves are becoming depleted. The aim of this article is to show the potential benefits of using ejectors in cooling systems to improve its energetic efficiency. A review of different configurations of ejector cooling systems has been carried out for being compared against a conventional compressor cycle. The same cooling capacity and working conditions were imposed by using refrigerants R134a, R1234yf and R600a. The results showed that the Coefficient of Performance could increase up to 26%. Ejectors have been characterised by correlations of entrainment ratio and a new definition of ejector compression efficiency. Those correlations have been obtained by means of a pseudo-one dimensional method of ejector analysis. Ejector cooling systems were proven to be a potential alternative to conventional vapour compression cycles.
Centrifugal intensification of condensation heat transfer in the rotor–stator cavities of a stator–rotor–stator spinning disc reactor (srs-SDR) is studied, as a function of rotational velocity ω, volumetric throughflow rate ɸv, and average temperature driving force ∆T. For the current range of ω, heat transfer from the vapor bubbles to the condensate liquid is limiting, due to a relatively low gas–liquid interfacial area aGL. For ɷ > 84 rad s⁻¹, a strong increase of aGL, results in increasing the reactor-average condensation heat transfer coefficient hc from 1600 to 5600 W m⁻² K⁻¹, for condensation of pure dichloromethane vapor. Condensation heat transfer in the srs-SDR is enhanced by rotation, independent of the vapor velocity. The intensified condensation comes at the cost of relatively high energy dissipation rates, indicating condensation in the srs-SDR is more suited as a means to supply heat (e.g. in an intensified reactor-heat exchanger), rather than for bulk cooling purposes. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3784–3796, 2016.
Plate Heat Exchangers (PHEs) are used in a wide variety of applications including heating, ventilation, air-conditioning, and refrigeration. PHEs are characterized by compactness, flexible thermal sizing, close approach temperature, and enhanced heat transfer performance. Due to their desirable characteristics, they are increasingly utilized in two-phase flow applications. Detailed research on heat transfer and fluid flow characteristics in these types of exchangers is required to design and use plate heat exchangers in an optimal manner. This paper reviews the available literature on the correlations for heat transfer and pressure drop calculations for two-phase flow in PHEs as an initial process step in order to understand the current research status. Comparative evaluations for some of the existing correlations are presented in the light of their applicability to different refrigerants. Overall, there is a significant gap in the literature regarding two-phase heat transfer and fluid flow characteristics of these types of exchangers. © 2016 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.
Plate heat exchangers (PHE), compact and energy-efficient, are used as condensers in various industrial applications to recover and recycle heat energy. The condenser optimization still represents a challenge. Due to complex thermo-hydraulic couplings inside three-dimensional PHE geometry, most of the literature studies are correlatives based on hypothesis as uniform heat flux or heat transfer coefficient along the condenser. In this article, some new information on the analysis of condensation heat transfer along the PHE is highlighted. The experimental study focuses on complete condensation of saturated pentane inside a PHE of 4.4 mm hydraulic diameter placed vertically with a descending flow of the refrigerant. The global and local thermo-hydraulic characteristics, as the vapor quality, the heat flux density and the heat transfer coefficient, were identified along the PHE based on the infrared thermography, and the effect of mass flux, between 9 and 30 kg m-2 s-1, on these characteristics is analysed. The results show a significant variation, of the heat transfer coefficient and the heat flux density, between the inlet and the outlet of the condensation region for most of the mass fluxes. In our operating range, the heat flux rate decreases till 400% between the PHE inlet and outlet, while the condensation heat transfer coefficient decreases by 5-10 times. The PHE mean heat transfer coefficients, calculated from the local values are then 10-20% higher than the ones calculated from the literature assumption of uniform heat fluxes or the assumption of constant heat transfer coefficient. Moreover, the variation of the mean heat transfer coefficient with pentane mass flux allowed the identification of two condensation regimes, from gravity mode to a mix gravity/convection mode, with a transition limit around 15 kg m-2 s-1. Condensation flow analysis was conducted based on pressure drop measurements and calculations. Hence the global pressure drop measured experimentally and the local profile deduced from infrared images, are compared to the results obtained by models from the literature. The comparison shows that the homogeneous model and the Lockhart-Martinelli (1949)'s model predict with good agreement the experimental results.
In this paper, flow boiling heat transfer in a plate heat exchanger at the low mass flux condition was investigated for low temperature lift heat pump applications. The effects of vapor quality, heat flux, evaporation pressure, and mass flux were studied. The current study shows that the influence of convective boiling heat transfer is suppressed under given test conditions, and the effect of boiling heat transfer was dominant. This is evident from the insignificant effect of vapor quality on flow boiling heat transfer coefficient. It showed a dominant effect of nucleate boiling heat transfer. When heat flux was increased, the flow boiling heat transfer coefficient increased which is an indication of nucleate boiling heat transfer. Excess temperature was also studied, which closely relates to nucleate boiling regime. As evaporation pressure was decreased, it became easier for vapor bubbles to generate, which can be explained with a lower excess temperature. Furthermore, a more rigorous bubble movement at a low excess temperature range involved in this study enhanced heat transfer across the surface, so that flow boiling heat transfer coefficient increased. For the effect of mass flux, the flow boiling heat transfer coefficient increased slightly as the mass flux was increased. This means that convective boiling heat transfer is present, but it just played a minor role in the evaporation heat transfer because of a low fluid mass flux.
This paper presents the experimental heat transfer coefficients and pressure drops measured during refrigerant HFC32 condensation inside a commercial Brazed Plate Heat Exchanger (BPHE) and compares this data with similar measurements previously obtained for refrigerant HFC410A to assess its capability as low GWP substitute for HFC410A in medium size chillers and heat pumps. The effects of saturation temperature, refrigerant mass flux, and vapour super-heating are investigated. HFC32 exhibits heat transfer coefficients much higher and frictional pressure drop slightly higher than those of HFC410A. Therefore, considering that HFC32 exhibits a GWP just one-third that of HFC410A, taking into account also its good thermodynamic properties, it seems to be a very promising low GWP substitute for HFC410A in medium size chillers and heat pumps.
This study experimentally quantified the change in heat transfer and pressure drop associated with tilting a compact brazed plate heat exchanger from the intended vertical position. Both clockwise and counterclockwise rotations within a plane perpendicular to the fittings were examined. A SWEP B15 {times} 36 was tested as an R-22 evaporator and condenser under fixed refrigerant state conditions suitable to high-efficiency water-source heat pumps. This study showed that a substantial performance penalty occurred when the evaporator was rotated past 30{degree} from the vertical. The evaporator heat transfer in the horizontal position was 60--75% of the vertical value. For a rotation angle of 30{degree}, the degraded heat transfer was within 5% of the vertical value. Rotation direction and entering refrigerant state had little effect on the performance of the evaporator for rotation angles less than 60{degree}. Only when the evaporator was rotated to the horizontal position did rotation direction and refrigerant state have much effect. At the horizontal position, a subcooled-entering refrigerant and a counterclockwise rotation both tended to lessen the evaporator heat transfer degradation. Rotation of the condenser to the horizontal position improved the overall heat transfer coefficient by approximately 17--30%. Rotation direction had a negligible effect on the performance of the condenser for angles less than 60{degree}. Both the evaporator and condenser pressure drops were influenced by flow distribution changes as the heat exchangers are rotated.
This article presents a study on heat transfer in condensation of pure and mixtures of hydrocarbons in a compact welded plate heat exchanger. Three pure fluids (pentane, butane, and propane) and two mixtures (butane + propane) have been used. The operating pressure ranges from 1.5 to 18 bar. For pure fluids, two heat transfer mechanisms have been identified. For low Reynolds numbers, the condensation occurs almost filmwise and the heat transfer coefficient decreases with increasing Reynolds number. For higher values of the Reynolds number, the heat transfer coefficient increases gently. The transition between the two regimes is between Re = 100 and 1,000 and depends on the operating conditions. For mixtures, the behavior is different. For low Reynolds numbers, mass transfer affects heat transfer and reduces the heat transfer coefficient by a factor of up to 4. Correlations for filmwise and in-tube condensation do not predict the results accurately, and a specific correlation is proposed for pure fluid condensation. For mixtures, the condensation curve method does not allow mass transfer effects to be taken into account, and more work is required to establish an accurate predictive model.
Experimental heat transfer and isothermal pressure drop data for single-phase water flows in a plate heat exchanger (PHE) with chevron plates are presented. In a single-pass U-type counterflow PHE, three different chevron plate arrangements are considered: two symmetric plate arrangements with β = 30 deg/30 deg and 60 deg/60 deg, and one mixed-plate arrangement with β = 30 deg/60 deg. For water (2 < Pr < 6) flow rates in the 600 < Re < 10â´ regime, data for Nu and f are presented. The results show significant effects of both the chevron angle β and surface area enlargement factor Ï. As β increases, and compared to a flat-plate pack, up to two to five times higher Nu are obtained; the concomitant f, however, are 13 to 44 times higher. Increasing Ï also has a similar, though smaller effect. Based on experimental data for Re ⥠1000 and 30 deg ⤠β ⤠60 deg, predictive correlations of the form Nu = Câ(β) Dâ(Ï) Re{sup p1(β)} Pr¹³ (μ/μ{sub w}){sup 0.14} and f = Câ(β) Dâ(Ï) Re{sup p2(β)} are devised. Finally, at constant pumping power, and depending upon Re, β, and Ï, the heat transfer is found to be enhanced by up to 2.8 times that in an equivalent flat-plate channel.
This paper experimentally investigates HFC-410A vaporisation inside a commercial brazed plate heat exchanger: the effects of heat flux, refrigerant mass flux, saturation temperature and outlet conditions are evaluated. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show great sensitivity to heat flux and outlet conditions and weak sensitivity to saturation temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on the refrigerant mass flux. The experimental heat transfer coefficients are compared with two well-known equations [Cooper, M.G., Heat flows rates in saturated pool boiling – a wide ranging examination using reduced properties, in: J.P. Hartnett, T.F. Irvine Jr. (Eds.), Advanced in Heat Transfer, Academic Press, Orlando, FL, 1984, pp. 157–239; D. Gorenflo, D. Pool boiling, in: E.U. Schlünder (Ed.), VDI Heat Atlas, Dusseldorf, Germany, 1993 (Ha1-25).] for nucleate boiling and a correlation for frictional pressure drop is proposed.
Concern for the environmental effects of HFC-refrigerants as well as the use of flammable refrigerants has resulted in a need of decreasing the refrigerant charge in refrigeration and heat pump systems. This paper discusses the possibility of such reductions, both at the systems- and the component level. It is shown that a move towards indirect systems, using secondary refrigerants, on both the cold and the hot side of the system may result in considerable reduction of charge. However, this reduction may come at the cost of slightly reduced system performance, which in itself is detrimental from an environmental point of view. At the component level, it may be shown that the main contents of refrigerant is usually contained in the heat exchangers. By selecting compact designs the charge may be reduced to extremely low levels. Specifically, mini-channel heat exchangers can be used for reaching low charge. With proper selection of heat exchangers, the system performance should not be influenced by the reduction of charge. For indirect systems, the amount of refrigerant solved in the compressor oil may be comparable to the amount in the (compact) heat exchangers. A possible solution to reduce this amount is to use compressors with less oil. With components selected for minimum charge, the system design may be different than what is usual. Instead of a high pressure receiver and a thermostatic expansion valve, a capillary tube may be used in combination with a minimal low pressure receiver, similar to the system design used in household refrigerators.
This paper presents the experimental tests on HFC-134a condensation inside a small brazed plate heat exchanger: the effects of refrigerant mass flux, saturation temperature and vapour super-heating are investigated.A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 20kg/m2s. For refrigerant mass flux lower than 20kg/m2s, the saturated vapour heat transfer coefficients are not dependent on mass flux and are well predicted by the Nusselt [Nusselt, W., 1916. Die oberflachenkondensation des wasserdampfes. Z. Ver. Dt. Ing. 60, 541–546, 569–575] analysis for vertical surface. For refrigerant mass flux higher than 20kg/m2s, the saturated vapour heat transfer coefficients depend on mass flux and are well predicted by the Akers et al. [Akers, W.W., Deans, H.A., Crosser, O.K., 1959. Condensing heat transfer within horizontal tubes. Chem. Eng. Prog. Symp. Ser. 55, 171–176] equation. In the forced convection condensation region, the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8–10% higher than those of saturated vapour and are well predicted by the Webb [Webb, R.L., 1998. Convective condensation of superheated vapour. ASME J. Heat Transfer 120, 418–421] model. The heat transfer coefficients show weak sensitivity to saturation temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on the refrigerant mass flux.
This paper presents the heat transfer coefficients and the pressure drop measured during HFC-410A condensation inside a commercial brazed plate heat exchanger: the effects of saturation temperature, refrigerant mass flux and vapour super-heating are investigated. The heat transfer coefficients show weak sensitivity to saturation temperature and great sensitivity to refrigerant mass flux and vapour super-heating. At low refrigerant mass flux (20 kg/m²s) the saturated vapour condensation heat transfer coefficients depend on mass flux and are well predicted by Akers et al. [W.W. Akers, H.A. Deans, O.K. Crosser, Condensing heat transfer within horizontal tubes, Chem. Eng. Prog. Symp. Series 55 (1959) 171-176] equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8-10% higher than those of saturated vapour and are well predicted by Webb [R.L. Webb, Convective condensation of superheated vapor, ASME J. Heat Transfer 120 (1998) 418-421] model. A simple linear equation based on the kinetic energy per unit volume of the refrigerant flow is proposed for the computation of the frictional pressure drop. (author)
Adiabatic pressure drop in chevron and two styles of bumpy plate heat exchangers were investigated for vertical upward flow with R134a. Qualities ranging from sub-cooled liquid to superheated vapor were investigated. Mass fluxes ranged from 16kg/m2s (for superheated vapor) to approximately 300kg/m2s (for sub-cooled liquid). The pressure drop experiments were conducted for 10°C and 20°C inlet temperatures. A two-phase pressure drop model, based on the kinetic energy of the flow, was developed in order to relate the two-phase pressure drop data to the single-phase data. The model predicts two-phase pressure drop within 15% of experimental measurements.
Experimental heat transfer and pressure drop results for two brazed plate heat exchangers (BPHE) of different sizes are presented in this article. The BPHEs are a type of compact plate heat exchanger with parallel corrugated plates that are brazed together in series. Water and a glycol/water mixture in the liquid phase were passed through the heat exchangers in a counter flow configuration, and relevant experimental data were collected. The Wilson technique was then used to obtain the single-phase heat transfer coefficient in the corrugated passages. The BPHEs were subsequently installed in a simple refrigeration cycle and the heat transfer coefficients and pressure drops during condensation of R-134a were measured. Empirical correlations for this type of plate heat exchangers were developed, plotted, and compared with relevant published results.
The effects of vapor velocity, liquid loading, and physicai properties
of the fluid on the condensing coefficient of a vapor in a horizontal tube were
investigated. The data, presented in graphs, were obtained in tests in which the
aversge condensing coefficient was determined as a function of the mass flow of
the vapor in the tube at constant tube wall temperature and constant pressure.
(J.R.D.)
Heat transfer and associated frictional pressure drop in the condensing flow of the ozone friendly refrigerant R-410A in a vertical plate heat exchanger (PHE) are investigated experimentally in the present study. In the experiment two vertical counter flow channels are formed in the exchanger by three plates of commercial geometry with a corrugated sinusoidal shape of a chevron angle of 60°. Downflow of the condensing refrigerant R-410A in one channel releases heat to the upflow of cold water in the other channel. The effects of the refrigerant mass flux, imposed heat flux, system pressure (saturated temperature) and mean vapor quality of R-410A on the measured data are explored in detail. The results indicate that the R-410A condensation heat transfer coefficient and associated frictional pressure drop in the PHE increase almost linearly with the mean vapor quality, but the system pressure only exhibits rather slight effects. Furthermore, increases in the refrigerant mass flux and imposed heat flux result in better condensation heat transfer accompanying with a larger frictional pressure drop. Besides, the imposed heat flux exhibits stronger effects on the heat transfer coefficient and pressure drop than the refrigerant mass flux especially at low refrigerant vapor quality. The friction factor is found to be strongly influenced by the refrigerant mass flux and vapor quality, but is almost independent of the imposed heat flux and saturated pressure. Finally, an empirical correlation for the R-410A condensation heat transfer coefficient in the PHE is proposed. In addition, results for the friction factor are correlated against the Boiling number and equivalent Reynolds number of the two-phase condensing flow.
The characteristics of evaporation heat transfer and pressure drop for refrigerant R134a flowing in a plate heat exchanger were investigated experimentally in this study. Two vertical counter flow channels were formed in the exchanger by three plates of commercialized geometry with a corrugated sine shape of a chevron angle of 60°. Upflow boiling of refrigerant R134a in one channel receives heat from the hot downflow of water in the other channel. The effects of the heat flux, mass flux, quality and pressure of R134a on the evaporation heat transfer and pressure drop were explored. The preliminary measured data for the water to water single phase convection showed that the heat transfer coefficient in the plate heat exchanger is about 9 times of that in a circular pipe at the same Reynolds number. Even at a very low Reynolds number, the present flow visualization in a plate heat exchanger with the transparent outer plate showed that the flow in the plate heat exchanger remains turbulent. Data for the pressure drop were also examined in detail. It is found that the evaporation heat transfer coefficient of R134a in the plates is quite different from that in circular pipe, particularly in the convective evaporation dominated regime at high vapor quality. Relatively intense boiling on the corrugated surface was seen from the flow visualization.
More specifically, the present data showed that both the evaporation heat transfer coefficient and pressure drop increase with the vapor quality. At a higher mass flux the pressure drop is higher for the entire range of the vapor quality but the heat transfer is only better at high quality. Raising the imposed wall heat flux was found to slightly improve the heat transfer. While at a higher system pressure the heat transfer and pressure drop are both slightly lower.
Two-phase flow analysis for the evaporation and condensation of refrigerants within the minichannel plate heat exchangers is an area of ongoing research, as reported in the literatures reviewed in this article. The previous studies mostly correlated the two-phase heat transfer and pressure drop in these minichannel heat exchangers using theories and empirical correlations that had previously been established for two-phase flows in conventional macrochannels. However, the two-phase flow characteristics within micro/minichannels may be more sophisticated than conventional macrochannels, and the empirical correlations for one scale may not work for the other one. The objective of this study is to investigate the parameters that affect the two-phase heat transfer within the minichannel plate heat exchangers, and to utilize the dimensional analysis technique to develop appropriate correlations. For this purpose, thermo-hydrodynamic performance of three minichannel brazed-type plate heat exchangers was analyzed experimentally in this study. These heat exchangers were used as the evaporator and condenser of an automotive refrigeration system where the refrigerant R-134a flowed on one side and a 50% glycol–water mixture on the other side in a counter-flow configuration. The heat transfer coefficient for the single-phase flow of the glycol–water mixture was first obtained using a modified Wilson plot technique. The results from the single-phase flow analysis were then used in the two-phase flow analysis, and correlations for the refrigerant evaporation and condensation heat transfer were developed. Correlations for the single-phase and two-phase Fanning friction factors were also obtained based on a homogenous model. The results of this study showed that the two-phase theories and correlations that were established for conventional macrochannel heat exchangers may not hold for the minichannel heat exchangers used in this study.
This paper presents the experimental work carried out to apply “cross-grooved” surfaces to refrigerant vaporisation and condensation inside plate heat exchangers (PHE) with herringbone macro-scale corrugation. This paper also investigates the effect of an increase in the surface roughness of the plate on refrigerant two-phase heat transfer inside PHE. The enhanced surfaces are experimentally evaluated both in vaporisation and condensation tests with refrigerant 22, and compared against a PHE with a smooth surface. The experimental results show that the “cross-grooved” surface is useful both in vaporisation and condensation, whereas the increase in surface roughness is useful only in vaporisation. The “cross-grooved” surface gives an increase in the heat transfer coefficient from 30% to 40% in vaporisation to 60% in condensation with respect to a PHE with a smooth surface. The enhancement in heat transfer coefficient is higher than the simple increase in heat transfer surface area. A fair agreement was found between present experimental data and semi-empirical correlations both for condensation and vaporisation inside PHE.
This paper presents the experimental heat transfer coefficients and pressure drop measured during HFC refrigerant 134a, 410A and 236fa vaporisation inside a small brazed plate heat exchanger: the effects of heat flux, refrigerant mass flux, saturation temperature, outlet conditions and fluid properties are investigated. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show great sensitivity to heat flux and outlet conditions and weak sensitivity to saturation temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow. HFC-410A shows heat transfer coefficients 40–50% higher than HFC-134a and 50–60% higher than HFC-236fa and frictional pressure drops 40–50% lower than HFC-134a and 50–60% lower than HFC-236fa. The experimental heat transfer coefficients are compared with two well-known equations for nucleate boiling [M.G. Cooper, Heat flows rates in saturated pool boiling – a wide ranging examination using reduced properties, Advanced Heat Transfer, Academic Press, Orlando, Florida, 1984, pp. 157–239; D. Gorenflo, Pool boiling, in: E.U. Schlünder (Ed.), VDI Heat Atlas, Dusseldorf, Germany, 1993, Ha1-25] and a correlation for frictional pressure drop is proposed.
Performances of brazed plate heat exchanger set in heat pump
- T Dutto
- J C Blaise
- T Benedic
T. Dutto, J.C. Blaise, T. Benedic, Performances of brazed plate heat exchanger
set in heat pump, in: Proceedings of the 18th Int. Congr. Refrig., Montreal,
Canada, 1991, pp. 1284-1288.
Plate heat exchangers and their design theory, Heat Transfer Equipment Design, Hemisphere
- R K Shah
- W W Focke
R.K. Shah, W.W. Focke, Plate heat exchangers and their design theory,
Heat Transfer Equipment Design, Hemisphere, Washington, 1988, pp. 227-254.
Refrigerant properties computer code, REFPROP 7
NIST, Refrigerant properties computer code, REFPROP 7.0, 2002.