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Condensation heat transfer within horizontal tubes
Abstract
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.)
... According to the studies on the flow pattern, many correlations [6][7][8][9][10][11][12] for predicting the heat transfer coefficient and pressure drop were proposed. They took surface tension, shear force, gravity, viscosity et al. into consideration and were certified with the experiment. ...
... They took surface tension, shear force, gravity, viscosity et al. into consideration and were certified with the experiment. For example, the Shan [6], Akers et al. [7], Thome [8], Dobson and Chato [9] and Cavallini et al. [10] correlations were presented based on the experimental data from tubes with inner diameter larger than 3 mm, and the Wang et al. [11] and Yan and Lin [12] correlations were proposed based on the heat transfer characteristics for the mini-tube. ...
... Condensation heat transfer characteristics of all types refrigerant inside the horizontal smooth tube have been studied for years and many correlations have been developed, meanwhile, continuous improvement of correlations has also been made for various alternative refrigerants and new type heat exchangers. In this experimental analysis, six well-known correlations by Cavallini et al. [38], Shah [6], Thome et al. [39], Akers et al. [7], Dobson and Chato et al. [9] and Jung et al. [40] were applied to compare the heat transfer coefficient of smooth tubes. Comparisons of the heat transfer coefficient between the predictive values and experimental values varying with mass velocity are shown in Figure 11, and Table 5 lists the deviation of various correlations against experimental heat transfer coefficient. ...
The condensation heat transfer coefficient of R134a was experimentally studied inside two smooth and four micro-fin tubes. The working conditions and structural parameters of the test tubes were selected as the influencing factors, and the experiment was conducted under mass velocities of 400–1100 kg·m⁻²·s⁻¹, condensation temperatures of 35–45 °C and water-testing Reynolds numbers of 8000–22,000, with an inlet superheat of 1–2 °C and outlet subcooling of 1–2 °C at the test section for the refrigerant. Experimental results indicate that the heat transfer coefficient increases with increasing mass velocity and decreasing condensation temperature and water-testing Reynolds number. The heat transfer coefficient of the micro-fin tube with a helix angle of 28° is the highest and that of smooth tube is the lowest for test tubes with the same inner diameter. Tube diameter has a small influence on the heat transfer coefficient for the smooth tubes while the heat transfer coefficient increases with decreasing tube diameter for the micro-fin tubes. The heat transfer coefficient inside the test tube was compared with some well-known existing correlations, and results show that correlations by Cavallini et al., Thome et al., Shah and Akers et al. can estimate the experimental data with mean absolute deviation of less than 30%, and correlations of Dobson and Chato et al. and Jung et al. cannot be used to capture the heat transfer coefficient with mean absolute deviations of 140.18% and 146.23%, respectively. While the Miyara et al. correlation overestimates the heat transfer coefficient, correlations of Cavallini et al., Koyama et al. and Oliver et al. all underestimate the experimental data for the micro-fin tube. Their deviations are from 25 to 55% for micro-fin tubes 3 and 4, while their deviations keep to within 30% for micro-fin tubes 5 and 6. Finally, to improve the correlation prediction accuracy, a dimensionless parameter was introduced to the correlations of Dobson and Chato et al. and Jung et al., and correlations of Cavallini et al., Koyama et al. and Oliver et al. were modified by enhancing the turbulence effect. The prediction accuracy of all modified correlations can be controlled to within 30%.
... These effects contribute to the steeper HTC gradients with increasing quality noticed for HCs compared to R134a. (Longo et al., 2017) verified in their experiments, that the heat transfer factor, J h , a modified version of the Colburn J factor (Kern, 1950), can be well-correlated by plotting it against the (Akers et al., 1959) equivalent Reynolds number, Re eq . Therefore, in the present study an attempt of adjusting a prediction method for the HTC through correlating Re eq and J h based on the pure fluids database is performed. ...
... 3.1.1. Comparison to earlier prediction methods Fig. 6 displays boxplots built in MATLAB (MATLAB 2015) for the relative errors presented by the prediction methods ( (Akers et al., 1959;Cavallini et al., 2006;Cavallini and Zecchin, 1974;Chang et al., 2000;Dobson and Chato, 1998;Haraguchi et al., 1994;Jaster and Kosky, 1976;Jung et al., 2003;Koyama et al., 2003;Moser et al., 1998;Shah, 1979Shah, , 2009Soliman et al., 1968;Tandon et al., 1995;Thome et al., 2003;Traviss et al., 1973) and the new correlation) when compared to the pure HCs data obtained in the present study. Fig. 6 shows that accurate 2 predictions are obtained by the flow-pattern based methods of (Thome et al., 2003;Dobson and Chato, 1998;Haraguchi et al., 1994;Tandon et al., 1995;Cavallini et al., 2006), by the strictly empirical ones of (Cavallini and Zecchin, 1974;Shah, 1979;Shah, 2009) and the new correlation, and the one of (Moser et al., 1998) based on Colburn analogy. ...
... For R600a/R290 and G≥200 kg m− 2 s− 1 the effect of Rmass, which shows values lower than for R600a/R1270, is negligible. 4 A new empirical prediction method is suggested, based on the pure fluids database by correlating the heat transfer factor (Kern, 1950), Jh, with the equivalent Reynolds number, Reeq, (Akers et al., 1959). 5 In general, higher accuracy is observed using various known methods when predicting the results for pure HCs. ...
The present paper concerns an experimental investigation about the heat transfer coefficient during convective condensation of hydrocarbons and their zeotropic mixtures. Experiments were performed in a horizontal smooth channel, with internal diameter of 9.43 mm for R600a, R290, R1270, R600a/R290 (70/30 molar fraction) and R600a/R1270 (75/25 molar fraction), for mass velocities ranging from 50 to 250 kg m−2 s−1, vapor qualities from unity to zero, heat fluxes from 5 to 60 kW m−2 and a saturation temperature of 35°C. Experiments were also performed for R134a. In general, higher heat transfer coefficients were obtained for the hydrocarbons compared to R134a. The heat transfer process was dominated by shear effects for the hydrocarbons regardless of the mass velocity. At low mass velocities (below 100 kg m−2 s−1), both mixtures provided lower heat transfer coefficients than the pure fluids. At high mass velocities a reduction of the heat transfer coefficient compared to the pure fluid was noticed only for R600a/R1270 at high qualities. The experimental data is compared against prediction methods from literature and based on the pure fluids database, a new strictly empirical prediction method is proposed, which performs better for both pure fluids and mixtures database. For the mixtures, the performance of the methods was improved when considering a correction for the mass transfer effects associated to the concentration gradients near the liquid/vapor interface.
... The new correlations are developed depending on the equivalent Reynolds number concept [62]. ...
... The definition of the equivalent Reynolds number ( ) is given below [62] (18) ...
... where the equivalent mass flux ( ) is defined as [62] [( ...
A numerical investigation of the condensing flow of isobutane inside microchannel has been performed. Impact of mass flux, hydraulic diameter, and vapor quality on the heat transfer rate and pressure drop is determined. To this purpose, steady-state numerical simulations of condensation flow of isobutane have been performed at mass fluxes ranging from 200 to 600 kg/m²s inside a single circular microchannel with varying diameter. Similar to the usual operation conditions, the simulations have been conducted for constant saturation temperature and constant wall heat flux as the thermal boundary condition. The proposed model has been based on the volume of fluid approach, which is an interface tracking method. The Lee model has been used to model the phase change mass transfer at the interface. A verification study has been performed by comparing the proposed model results with the experimental and visual data available in the literature. The currently available correlations are assessed by comparisons with the simulation results. Based on the presently validated simulations, a new correlation has been proposed for the heat transfer coefficient and pressure drop of isobutane condensing flow inside small-scale channels. This is a novel aspect of the present paper, since such a correlation does not yet exist.
... This may lead to certain deviation between the results of this study and those predicted by his model. Furthermore, the highest deviation between the measured data and model outcomes corresponds to the correlations proposed by Bohdal et al. (2012) and Akers et al. (1958) , with AARE values 278.93 % and 134.15 %, respectively, which have not been reported in the Table. These values indicate poor capabilities of these models for estimating the HTC for fluid condensation in horizontal pipes. ...
... This figure shows that the correlations by Dorao and Fernandino (2018) and Shah (2019) are the most consistent with the experimental data. On the other hand, the results generated by the correlations of Bohdal et al. (2012) , Dobson and Chato (1998) , and Akers et al. (1958) are not shown in Fig. 3 due to the large deviations between the experimental results and those calculated based on these correlations. ...
... The models highly deviate from experimental data. The calculated AARE values for Dorao and Fernandino (2018) , Cavallini et al. (2006) , Shah (2009) , Bohdal et al. (2012 , Shah (2019) , Crosser (1955) , Dobson and Chato (1998) , and Akers et al. (1958) are 24.41%, 32.47%, 34.64%, 278.93%, 30.15%, 45%, 64.72%, and 134.15%, respectively. ...
A new general explicit correlation is proposed to predict the heat transfer coefficient of fluids condensing in conventional and mini channels. The expression has been developed by correlating the Numix number with Remix, Prmix, phase density ratio, Pres, WeGT, and FrL using genetic programming for the two-phase flow. The model has been validated with a big dataset consisting of 6521 data samples, covering a wide range of fluids used in refrigeration and heat pump industries, cross-sectional geometries (different diameters), mass fluxes, and saturation temperatures. The new generalized correlation fits the wide range of data points used with an average relative error of 17.82 %. The same database has been used to compare predictions of eight correlations available in the literature, but they failed to give a reasonable estimation of the present experimental results.
... 5) и применима для неоднородного Arrhenius [62] McAdams и др. [10] Davidson et al. [63] Akers et al. [49] Cicchitti и др. ...
... 6. Измеренные [57] (точки) и рассчитанные (линии) значения градиента потерь давления в зависимости от массового паросодержания при различных расходах теплоносителя. генного потока представляют собой стабильные расчетные данные с MARD ≈ 56%, за исключением соотношений из [48,49,64]. Средние значения абсолютных относительных отклонений данных из этих работ превышают 80%. ...
... Средние значения абсолютных относительных отклонений данных из этих работ превышают 80%. Можно видеть, что формулы из работ [49,64] дают наибольшие откло-нения, когда массовый расход 200 кг/(м 2 · с), в то время как при использовании методов из [46] получаются худшие расчетные результаты, если массовый расход больше 800 кг/(м 2 · с). Очевидно, что наилучшей из всех формул является предложенная в данной работе, за ней следуют Cicchitti et al. ...
Расчет потерь давления в двухфазном потоке необходим для решения задач в различных областях тех-
ники. Несмотря на проведенные исследования, некоторые вопросы, относящиеся к этой теме, все еще
требуют уточнения. Цель данной работы – изучение зависимости потерь давления от гидравлического
сопротивления (трения) в двухфазном потоке и вязкости смеси. Новая формула для расчета потерь
давления на трение в двухфазном потоке разработана с использованием модели гомогенного потока.
Исходное уравнение получено на основе аналогии между вязкостью смеси двухфазных потоков и теп-
лопроводностью пористой структуры. Новая формула тестировалась на 846 экспериментальных точ-
ках, заимствованных из литературы для труб круглого сечения. Экспериментальные данные получены
на разных рабочих жидкостях, таких как R1234ze(E), R32, R-600a, R717, R134a, R410A и диоксид угле-
рода (CO2), при различных значениях внутреннего диаметра труб и массового расхода. Точность пред-
ложенной новой формулы оценивалась с помощью относительной погрешности, выраженной в про-
центах, и плотности распределения вероятности (PDF – от англ. probability density function). Значения,
полученные при расчете по новой формуле и другим соотношениям, взятым из литературы, сравнива-
лись с имеющимися экспериментальными данными. Обнаружено, что новая формула имеет среднее
относительное значение абсолютных отклонений расчетных значений от экспериментальных данных
30%, и показано, что она может быть использована для прогнозирования значений потерь давления в
трубах круглого сечения, мини- и микроканалах.
... Using a one dimensional transport analogy between thermal conductivity in porous media and viscosity in two-phase flow, new definitions for two phase viscosity will be introduced. These definitions for two-phase viscosity Correlation for two-phase viscosity Arrhenius [62] McAdams et al. [10] Davidson et al. [63] Akers et al. [49] Cicchitti et al. [11] Owens [64] Dukler et al. [46] Beattie and Whalley [47] Lin et al. [48] Fourar and Bories [65] García et al. [66,67] Awad and Muzychka [12] ...
... Figure 10 presents comparison between the new correlation and other correlations based on independent experimental data against different mass flux. All homogeneous correlations present stable predictions with MARDs around 56% except the Owens [64], Akers et al. [49] and Lin et al. [48] correlation whose MARD exceeds 80%. It can be seen that Owens [64] and Akers et al. [49] correlations have the biggest deviations when mass flux is 200 kg/(m 2 s), while Dukler et al. [46] methods give the worst predictions when mass flux is larger than 800 kg/(m 2 s). ...
... All homogeneous correlations present stable predictions with MARDs around 56% except the Owens [64], Akers et al. [49] and Lin et al. [48] correlation whose MARD exceeds 80%. It can be seen that Owens [64] and Akers et al. [49] correlations have the biggest deviations when mass flux is 200 kg/(m 2 s), while Dukler et al. [46] methods give the worst predictions when mass flux is larger than 800 kg/(m 2 s). Obviously, the best one is the new correlation in all of the correlations, the next one is Cicchitti et al. [11] and Awad and Muzychka [12]. ...
The calculation of pressure drop in pipes two-phase flow is essential in different areas. Even though
several studies concerning this issue have been conducted, an accurate correlation is still required. The objective
of the paper is to develop correlations for two-phase friction pressure drop and mixture viscosity. The new correlation
can be used to compute the friction pressure drop for two phase flow in homogenous approach modeling.
The original equation is generated from a similitude between the mixture viscosity for two-phase flows and
the thermal conductivity of the porous structure. The new correlation is evaluated against 846 experimental data
of friction pressure drop collected from literature on circular pipes; the experimental data including different
working fluids such as R1234ze (E), R32, R-600a R717, R134a, R410A and carbon dioxide (CO2) at different
hydraulic inner diameters and mass flux. Models are assessed based on the relative percentage error and the
probability density function (PDF). The predictions by the new correlation and other correlations from the literature
are compared based on some experimental data. It is found that new correlation has a mean absolute relative
deviation (MARD) of 30%. It is proved that these new correlations of two-phase flow pressure drop can be
used to predict the experiment measurements of pressure drop, on circular pipes, minichannels and microchannels.
... We selected four correlations for the heat transfer coefficient comparison. One of them is an early and widely used correlation developed by Akers et al. [44] for annular flow in a horizontal tube, including a definition of an equivalent Reynolds number Re eq , accounting for the vapor core and the interfacial shear stress: ...
... Their correlation depends on two heat transfer regions divided by the equivalent Reynolds number and includes the effect of the presence of superheated vapor in the condensation process based on the Webb model [46]. Among the four correlations, Yan et al. [12] and Würfel and Ostrowski [18] correlations were developed based on the mean values of test data along the channel, while Akers et al. [44] and Longo et al. [45] correlations were developed aiming to predict the local heat transfer coefficient. Therefore, we applied the average values of experimental data for the heat transfer process to calculate the predicted values by the former two correlations and applied numerical integration along the channel to compute the average heat transfer coefficient by the latter two correlations. ...
... For the frictional pressure drop (see Fig. 9), we compared experimental results with predictions by two existing pressure drop correlations by Hsieh and Lin [47] and Khan et al. [48]. Vakili-Farahani Predicted values calculated from Akers et al. [44] R134a ...
The fundamental understanding of the thermal–hydraulic performance of working fluids during condensation is important for the optimal design of the condenser in various thermodynamic cycles. This paper is aimed at obtaining flow condensation heat transfer and pressure drop characteristics in a plate heat exchanger during the working conditions of the condenser of either organic Rankine cycle power systems or heat pump units. The selected working fluids are two hydrofluorocarbons, R134a and R245fa, as well as their hydrofluoroolefin replacements, R1234ze(E) and R1233zd(E). Measurements of heat transfer coefficients and pressure drops were carried out with varying saturation temperature, mass flux, and liquid Reynolds number, ranging from 30 �C to 70 �C, 16 kg/m2s to 90 kg/m2s and 65 to 877, respectively. Based on commonly used existing correlations, new heat transfer and pressure drop correlations were developed, including the effect of the surface tension. The experimental data indicate that different heat transfer mechanisms occur at low liquid Reynolds number with the different working fluids. The results suggest higher heat transfer coefficients and pressure drops for R1234ze(E) and R1233zd(E) than for R134a and R245fa at the same working conditions. The new correlations enable significantly better prediction accuracies for the experimental results in this study than existing correlations, indicating that the surface tension is a suitable parameter to consider in mini and micro-scale condensation heat transfer.
... Several correlations of heat transfer coefficients, which were developed for smooth and micro-fin tubes have been published in the literature, such as [7,26,[31][32][33][34][35]. Figure 9 and Table 3 show the summary comparison of experimental condensation heat transfers with the existing correlations. ...
... Figure 9 and Table 3 show the summary comparison of experimental condensation heat transfers with the existing correlations. The Aker [31], Tang [34], Kedzierski, and Goncalves [26] correlations give the acceptable predictions with measurement data. Aker [31] and Tang [34] proposed correlations of heat transfer coefficient in the case of forced convection condensation, which were developed for annular flow pattern. ...
... The Aker [31], Tang [34], Kedzierski, and Goncalves [26] correlations give the acceptable predictions with measurement data. Aker [31] and Tang [34] proposed correlations of heat transfer coefficient in the case of forced convection condensation, which were developed for annular flow pattern. It under predicted the experimental data with almost all data lay in the annular regime, but in other flow regime shows over prediction. ...
An experimental study of condensation heat transfer characteristics of flow inside horizontal micro-fin tubes is carried out using R410A, R22, and R32 as the test fluids. This study especially focuses on the influence of heat transfer area upon the condensation heat transfer coefficients. The test sections were made of double tubes using the counter-flow type; the refrigerants condensation inside the test tube enabled heat to exchange with cooling water that flows from the annular side. The saturation temperature and pressure of the refrigerants were measured at the inlet and outlet of the test sections to defined state of refrigerants, and the surface temperatures of the tube were measured. A differential pressure transducer directly measured the pressure drops in the test section. The heat transfer coefficients and pressure drops were calculated using the experimental data. The condensation heat transfer coefficient was measured at the saturation temperature of 48°C with mass fluxes of 50–380 kg/(m²s) and heat fluxes of 3–12 kW/m². The values of experimental heat transfer coefficient results are compared with the predicted values from the existing correlations in the literature, and a new condensation heat transfer coefficient correlation is proposed.
... The new correlations were formulated based on the concept of the equivalent Reynolds number (Re eq ) [52], whose expressions can be found in Equations (15) and (16). ...
... where the equivalent mass flux (G eq ) is defined as follows [52]: ...
A CFD simulation of the condensation flow of R600a and R290 within microchannels was conducted to explore the effect of mass flux, hydraulic diameter, and vapour quality on heat transfer rate and pressure drop. Data obtained from CFD simulations were used to develop new heat transfer and pressure drop correlations for the condensation flows of R600a and R290, which are climate-friendly refrigerants. Steady-state numerical simulations of condensation flow of refrigerants were carried out inside a single circular microchannel with diameters varying between 0.2 and 0.6 mm. The volume of fluid approach was used in the proposed model, calculating the interface phase change using the Lee model. The CFD simulation model was validated via a comparison of the simulation results with the experimental data available in the literature. It is found that the newly developed Nu number correlation shows a deviation, with an Ave-MAE of 11.16%, compared to those obtained by CFD simulation. Similarly, the deviation between friction factors obtained by the newly proposed correlation and those obtained by CFD simulation is 20.81% Ave-MAE. Widely recognized correlations that are applicable to the condensation of refrigerants within small-scale channels were also evaluated by comparing newly developed correlations. It is concluded that the newly proposed correlation has a higher accuracy in predicting the heat transfer coefficient and pressure drop. This situation can contribute to the creation of a sustainable system via the use of microchannels and climate-friendly refrigerants, like R600a and R290.
... Corrélation d' Akers (1959) Parmi les différentes méthodes qui ontété proposées pour la condensation contrôlée par les masses (i.e. gravité et inertie) et le cisaillementà l'intérieur des tubes horizontaux, l'approche d'Akers et al. [4] s'appuie uniquement sur un nombre de Reynolds tubulaireéquivalent défini par : ...
... Corrélation d' Akers (1959) Parmi les différentes méthodes qui ontété proposées pour la condensation contrôlée par les masses (i.e. gravité et inertie) et le cisaillementà l'intérieur des tubes horizontaux, l'approche d'Akers et al. [4] s'appuie uniquement sur un nombre de Reynolds tubulaireéquivalent défini par : ...
The heat powers dissipated by the electronic systems in the satellites are in continuous increase over the years. The emissive areas of the satellites become thus insufficient to evacuate these heat fluxes. One solution to this problem is to develop a heat pump coupled with the classical heat pipes in order to increase the temperature of the radiative panels without degrading that of the equipments. The present work is carried out in this issue with a focus on the condensation zone in microgravity. For this purpose, an experimental study was conducted on the hydrodynamic and thermal behaviors of the condensation flows at low mass velocities inside channels having hydraulic diameters less than one millimeter. This study highlighted three main flow zones: annular, intermittent and spherical bubbles. The transitions between the flow patterns were analyzed and the hydraulic and thermal parameters were determined for each zone. Finally, the impact of the hydrodynamic coupling between several micro-channels mounted in parallel on the flow and heat transfer laws was highlighted and studied. In parallel to this experimental study, a heat pump (at scale 1) was dimensioned and realized with the different partners of the project in which this thesis is positioned.
... It's total AARD values of 40.77% is not acceptable for prediction of heat transfer coefficient in coiled tubes. The Akers et al. [22], Shah (2009Shah ( , 2013Shah ( , 2016 [19][20][21], Dorao and Fernandino [18] and Hosseini et al. [14] correlations for straight tubes have almost the same results with AARD of 39.43%, 31.16%, 31.23%, ...
... = h I + h Nu If neither of the above conditions is satisfied. h I and h Nu are calculated similar to Shah (2009) correlation.General correlation for condensation in all orientations of straight tubes.Akers et al.[22] ...
There are several experimental studies on heat transfer during condensation in coiled tubes. But there is no well-verified method for calculating of heat transfer coefficient. In this study, a general non-linear correlation for estimation of heat transfer coefficient during flow condensation in different orientations of smooth coiled tubes is proposed. The correlation has been obtained by correlating the Nusselt number with two-phase Reynolds number, reduced pressure, Froude number, tube to coil diameter ratio, and inclination angle of coil axis to horizontal using Genetic programming (GP). This model has been validated with 503 experimental data points from 9 sources, which include different tube diameters, coil diameters, inclination angles, orientations, working fluids, mass fluxes and saturation temperatures. The new correlation predicts experimental data points with an excellent value of average absolute relative deviation (AARD) of 9.20%. The same database is also compared to 9 available correlations for straight and coiled tubes. Their deviations are significantly higher than the present correlation. In addition, impact of each input parameter on heat transfer coefficient in coiled tubes has been discussed.
... Shin and Kim [8,9] provided a unique experimental apparatus for measuring the condensation heat transfer coefficients of R-134a two-phase flow inside the sub-millimeter hydraulic diameter within single channel and the deviations of their measurements ranged from 3.5% (low mass flux) to 19.9% (high mass flux). Compared with the correlations by Shah [7], Akers et al. [10], and Friedel [11], the fluctuations at low mass flux were effectively reduced. Kim and Mudawar [12,13] summarized a consolidated database consisting of thousands of data points from published articles. ...
... The two-phase condensation heat transfer coefficient (h tp ) in the rectangular micro-channel heat sink in comparison with empirical correlations is illustrated in Fig. 4(b) and Table 5. The correlations proposed by Akers et al. [10], Koyama et al. [32] and Kim and Mudawar [12] underestimate the h tp , and the correlation summarized by Bohdal et al. [33] significantly overestimates the h tp due to the different order of hydraulic diameter. Besides, the predicted error by Shah [7] is much more accurate under small mass flux, yet the error becomes Table 4 Comparison of two-phase friction pressure loss between experimental data and correlations summarized in literatures. ...
This study experimentally investigates the condensation of dielectric fluid HFE-7100 in a micro-channel heat sink with the hydraulic diameter of 1.21 mm. Tests are conducted at a fixed pressure of 110 kPa, with vapor mass quality (xin) ranging from 0.1 to 0.9, mass fluxes (G) from 150 to 250 kg·m−2·s−1, inclined angle (θ) from −90° to +90°. A novel trapezoid drainage design is proposed to enhance the condensation heat transfer by effectively entraining condensation film. When G is lower than 200 kg·m−2·s−1, the two phase heat transfer coefficient (htp) for the trapezoid drainage design exceeds the conventional rectangular micro-channel heat sink by 10–26% while the corresponding pressure drop is about 22–45% lower. When G is increased to 250 kg·m−2·s−1, the drainage design can still dramatically decrease the pressure drop, however, it shows a negative effect on htp
when the xin is greater than 0.2. With inclined arrangements, the pressure drop would dramatically increase due to gravity effect. Besides, at the conditions of θ = −45° and −90°, the trapezoid drainage channel can improve the htp by 43–45% when G is lower than 200 kg·m−2·s−1. On the contrary, with the arrangement of θ = +45° and +90°, the trapezoid drainage channels may decrease the htp by 8–15%. This phenomenon is especially pronounced at a high xin. In addition, the heat transfer enhancement and deterioration are both analyzed based on stress distribution at vapor phase and condensation film.
... Proof of this is the increase of pressure drops (∆p/L) x with a reduction of the minichannel internal diameter. Own experimental results of the local heat transfer coefficient α x were compared with the calculation results of the correlation of other authors: Shah [18], Akers [2], Thome [22] and Tang end all [21]. Results of this comparison are showed in fig.8 and fig.9. ...
... Results of this comparison are showed in fig.8 and fig.9. [2], b) Thome [22], c) Tang [21]. ...
The paper presents the results of experimental investigation of Novec 649 refrigerant condensation in tube minichannels. This is a low-pressure refrigerant. This investigations are basis for flow structures visualization during condensation in pipe minichannels. The local and the average values of pressure drop (Δp/L) and heat transfer coefficient α in the whole range of the changes of vapour quality (x = 1 ÷ 0) were calculated. On the basis of the obtained test results there was illustrated the influence of the vapour quality x, the mass flux density G and the inner diameter of channel d changes on the studied parameters. These results were compared with the calculation results based on the dependencies of other authors.
... Applications of aluminum (Al) alloys have expanded across numerous industries due to their desirable properties, including their light weight, high heat conduction, and favorable electrical and mechanical characteristics [1]. One typical applications for an Al alloy is as a heat exchanger in an air conditioner [2][3][4][5]; notably, Al is a commonly used material for heat exchange because of its high formability, good specific strength, low density, and high thermal conductivity [6,7]. In addition, it is a more economical material than copper, which is the original material that is used in heat exchanger applications. ...
... In other words, the formation of Al3Zr IMPs is not an important factor in the galvanic corrosion of an Al alloy. Consequently, the sum of current from the Al matrix was decreased according to the following situations: (1) the small size of IMPs; (2) decreasing the number of IMPs; and (3) a lower difference in the corrosion potential between the Al matrix and the IMPs. ...
Corrosion resistance of Zr that has been added to an Al alloy (U1070) is higher than that of a commercial Al alloy (A1070). A decreasing number and size of Al3Fe intermetallic particles (IMPs) were observed by electron microprobe analysis and transmission electron microscopy. Based on the numerical corrosion simulation, it was confirmed that decreasing the number and size of IMPs was favorable for improving the corrosion resistance of the Al alloy due to the reduction of the galvanic effect. In addition, Al3Zr was found to be insignificant in promoting galvanic corrosion within the Al matrix. Thus, Zr is an advantageous alloying element for improving the corrosion resistance of the Al alloy.
... Moreover, the available condensation correlations, which are commonly used for ORC simulation, can be obtained from the investigations of Cavallini et al. [26], Akers et al. [27], Shah et al. [28], Qian [29], Han et al. [30], and Longo et al. [31]. Correlations from [26][27][28][29] can be used if the condenser is a shell-and-tube heat exchanger, while another correlation from [28] as well as from [30] and [31] are suitable for plate heat exchangers. ...
... Moreover, the available condensation correlations, which are commonly used for ORC simulation, can be obtained from the investigations of Cavallini et al. [26], Akers et al. [27], Shah et al. [28], Qian [29], Han et al. [30], and Longo et al. [31]. Correlations from [26][27][28][29] can be used if the condenser is a shell-and-tube heat exchanger, while another correlation from [28] as well as from [30] and [31] are suitable for plate heat exchangers. General information about these correlations is summarized in Tables 3 and 4. ...
Organic Rankine Cycles (ORCs) are an effective way to produce electricity from low-grade heat sources, which cannot be effectively obtained using conventional high-temperature Rankine cycles. Due to the lack of available information regarding the real Organic Rankine Cycle units on industrial level, off-design simulation under diversified operating conditions plays a significant role for both the system performance prediction and control strategy design. This paper summarizes the theoretical basis, modeling approaches and tools for ORC off-design simulations. Firstly, a review was conducted on the individual state-of-the-art convective heat transfer correlations and void fraction models. Secondly, different kinds of modeling approaches and simulation tools were proposed, highlighting their relevant characteristics, and were categorized for their specific applications. Moreover, an in-depth analysis of technical challenges related to various applications and focusing on the model accuracy and complexity, computational efficiency, as well as the model compatibility were extensively described and discussed. Finally, the current research trends in this field and the development for further investigations were presented.
... where Re eq is the equivalent Reynolds number of the organic fluid, and it is evaluated as [97,99]: ...
The work presents an integrated system for combined heat and power generation based on a topping biodiesel internal combustion engine (ICE) and a bottoming transcritical organic Rankine cycle (TORC). A 0D/1D mathematical model is developed to evaluate the performance of the innovative biodiesel system in design and off-design conditions for a wide range of rated power and organic fluids. The analysis highlights that the TORC integration improves the total full load electric power by more than 12%, and the engine size significantly influences the integrated system performance. The total electric efficiency increases from 35.0% to 47.9%, whereas the thermal efficiency decreases from 27.2% to 19.8% when the ICE's nominal power moves from 10 kWel to 500 kWel. Afterward, a multi-objective investigation is carried out to define the most suitable power of the proposed biodiesel system and its capability to satisfy the energy request of specific users. A thermal self-consumption equal to 100%, an electric self-consumption larger than 94%, and a payback time of 5.2 years are found. Lastly, a sensitivity analysis demonstrates the economic feasibility of the proposed biodiesel integrated system for a wide range of prices of energy vectors and system components.
... The model showed an acceptable agreement with the heat transfer coefficient data, with an overall mean absolute error MAE of 27.5% (60.5% and 97.4% of the data falling within ±30% and ±50%). Lee et al.1 compared the experimental data taken during condensation of FC-72 in microgravity in the 7.1 mm I.D. tube with the predictions of well-known correlations for the condensation heat transfer coefficient (Akers et al.56 , Cavallini and Zecchin 57 , Shah 58 , Dobson and Chato 42 , Wang et al. 59 , Koyama et al. 60 , Kim and Mudawar 61 ). The smallest mean absolute deviation between predicted and experimental heat transfer coefficients was obtained with Kim and Mudawar 61 model (MAE = 21.8%, with 69.2% of points falling within ±30%), followed by the correlations of Shah 58 (MAE = 27.6%) and Wang et al. 59 (MAE = 28.9%). ...
In the present paper, a thorough review of the experimental and numerical studies dealing with filmwise and dropwise condensation under microgravity is reported, covering mechanisms both inside tubes and on plain or enhanced surfaces. The gravity effect on the condensation heat transfer is examined considering the results of studies conducted both in terrestrial environment and in the absence of gravity. From the literature, it can be inferred that the influence of gravity on the condensation heat transfer inside tubes can be limited by increasing the mass flux of the operating fluid and, at equal mass flux, by decreasing the channel diameter. There are flow conditions at which gravity does exert a negligible effect during in-tube condensation: predictive tools for identifying such conditions and for the evaluation of the condensation heat transfer coefficient are also discussed. With regard to dropwise condensation, if liquid removal depends on gravity, this prevents its application in low gravity space systems. Alternatively, droplets can be removed by the high vapor velocity or by passive techniques based on the use of condensing surfaces with wettability gradients or micrometric/nanometric structuration: these represent an interesting solution for exploiting the benefits of dropwise condensation in terms of heat transfer enhancement and equipment compactness in microgravitational environments. The experimental investigation of the condensation heat transfer for long durations in steady-state zero-gravity conditions, such as inside the International Space Station, may compensate the substantial lack of repeatable experimental data and allow the development of reliable design tools for space applications.
... Predictive abilities most of correlations were improved. The smallest MARD was found for Akers and Rosson correlation [33] (14%), than Shah et al. [34] (20%), Cavallini and Zecchin [35] (21%), Dorao and Fernandino [36] and Huang et al. [37] (24%). A new prediction model with the MARD of 13.91% was developed and presented by authors. ...
This paper is an introduction to the cycle proposed by the authors related to research directions concerning the problems of condensation of zeotropic refrigerant mixtures. For over a hundred years, research has been conducted on the search for new working fluids in the cycles for cooling devices and heat pumps. Initially, the natural refrigerants used were replaced with homogeneous synthetic refrigerants, followed by mixtures of two or more refrigerants. Among the mixtures, there are azeotropic and zeotropic mixtures. In the case of an azeotrope mixture, a liquid solution of two or more chemical compounds is in thermodynamic equilibrium with the saturated vapor resulting from this mixture. The chemical composition of the liquid and vapor is identical. A zeotropic mixture is a liquid-vapor system in which the composition of a liquid mixture (solution) of two or more chemical compounds is always different from that of the saturated vapor generated from this liquid. This is due to the different boiling and condensation temperatures of the individual components of the mixture at the same pressure. There is a so-called temperature glide. The phase transformations of individual components do not run simultaneously, which means that the boiling or condensation phase transition temperature changes during the process being carried out. This raises a number of computational, design, and operational problems for power equipment. Today, however, zeotropic mixtures find an alternative to refrigerants with a high GWP potential. Despite the disadvantage of temperature glide, they also have advantages. These include ecological, energy, and economic indicators. As a result, they are increasingly used in the energy economy. This prompts researchers to conduct further research in the field of a detailed description of the phenomenon of boiling and condensation phase transformations of zeotropic mixtures under temperature glide, searching for new computational relationships, new design solutions, and applications. It is still an insufficiently recognized research problem. Bearing the above in mind, the authors made an attempt to review the state of knowledge in this area. Particular attention was paid to the progress in modeling the condensation phenomenon of zeotropic mixtures for application in compact heat exchangers. Miniaturization of cooling devices creates great application possibilities in this area.
... Analysis and the experimental studies of the authors of this study has shown that unstable interactions negatively affect the efficiency of boiling and the condensation phase transitions of refrigerants [25][26][27][28][29][30]. ...
This paper presents experimental research and mathematical modeling data concerning the impact of unit dynamic instabilities on the phase-transition condensation processes of the zeotropic mixtures R404A and R448A and azeotropic R507A refrigerants in pipe minichannels. The R507 refrigerant is currently used as a temporary substitute for R404A, whereas R448A is a sustainable prospective substitute for R404A. The study presents experimental testing data for the condensation processes of these refrigerants in pipe minichannels and a proposal for the use of dimensional analysis, including the Π-Buckingham theorem, to determine the regression relationship explaining the propagation of unit dynamic instabilities. Based on the experimental studies performed, regression computational models were developed and showed satisfactory agreement in the range of 20% to 25%. They give the possibility to identify, in a utilitarian, way the speed of propagation of temperature and pressure instabilities during the liquefaction of refrigerants. The study was carried out on pipe minichannels with an internal diameter of di = 3.3, 2.3, 1.92, 1.44 and 1.40 mm.
... Önerilen modellerin çoğu, Dittus ve Boelter'in tek fazlı zorlanmış konveksiyon korelasyonunun modifikasyonları niteliğindedir. [3] Örneğin Cavallini ve Zecchin [5] Akers ve arkadaşları [4], ve Shah [6] tarafından önerilen modellerle, Dittus ve Boelter'in [2] korelasyonlarının çoğu değiştirilmiştir. ...
ZET Sanayinin birçok alanında, değişik türde ve çeşitte soğutucu akışkanların kullanılıyor olmasının yanı sıra, literatüre de birbirinden farklı özelliklere sahip birçok yeni akışkan eklenmiştir. Her soğutucu akışkan için literatürde bulunan mevcut yoğuşma ısı transfer korelasyonlarıyla ısı transfer katsayısı hesabı yapmak, birçok hatayı beraberinde getirmektedir. Bu makalede birçok soğutucu akışkana yer verilmiş ve literatürde bulunan en popüler korelasyonlardan 9 korelasyon ile deneysel veriler karşılaştırılmıştır. Akışkan türleri, kütle akış hızları, sıcaklıkları ve boru çapları gibi parametreler değiştirilerek ısı transfer sonuçları Java Crimson Editör ile hesaplanmıştır. Isı transfer katsayı sonuçları grafiksel analiz metotları ile karşılaştırmalı olarak irdelenmiştir. ABSTRACT In many areas of Industry, as well as using different types and varieties of refrigerants, many new fluids with different properties have also been added to the literature. Calculating the heat transfer coefficient with the existing condensation heat transfer correlations found in the literature for each refrigerant leads to many errors. Many refrigerants are included in this article. Experimental data were compared with 9 correlations of the most popular correlations found in the literature, heat transfer results were calculated using Java Crimson editor by comparing and changing parameters such as fluid types, mass flow velocities, temperatures and pipe diameters. The heat transfer coefficient results were examined comparatively with graphical analysis methods.
... Akers et al. 48 ...
In this paper, an Artificial Neural Network soft matrix correlation to estimate the pressure drop of air-water two-phase flow is developed. The applicability of the model is extended by using dimensionless physical numbers as inputs (Air-Reynolds number, Water-Reynolds number, and the ratio of Air Inertial Forces to Water Inertial Forces), so the model can be implemented for vertical pipes with the proper combination of diameter-velocity-density-viscosity allowing estimations of dimensional numbers within the range of: Air-Reynolds numbers (430–6100), Water-Reynolds number (2400–7200), and Air-Water-Inertial forces ratio (1.6–1834), including the diameter range from 3 to 28 mm. Experimental measurements of frictional pressure drop of water-air mixtures are determined at different conditions. A search of the most suitable density, viscosity, and friction models was conducted and used in the model. The performance of the proposed ANN correlation is compared against published expressions showing good approximation to experimental data; results indicate that the most used correlations are within a mean relative error ( mre) of 23.9–30.7%, while the proposed ANN has a mre = 0.9%. Two additional features are discussed: i) the applicability and generality of the ANN using untrained data, ii) the applicability in laminar, transitional, and turbulent flow regimen. To take the approach beyond a robust performance mapping, the methodology to translate the ANN into a programmable equation is presented.
... The review of the previous study in this area according to [1,5,9,13,14,20,25,26,[31][32][33][34][35][36][37][38] showed that most investigations on condensation within smooth tubes focused on both vertical and horizontal configurations at mass fluxes typically higher than 200 kg/m 2 s and less than or equal to 1 000 kg/m 2 s. Other findings of [4,33,[39][40][41][42][43][44][45] noted that at low mass fluxes, the coefficient of transfer of heat was dependent on the difference in temperature. ...
The focus of this research article is to provide a state of the art review on smooth and inclined tubes condensation with particular emphasis on low mass fluxes. The most relevant experimental investigations are explained with a view to identifying the gaps in the literature. Overall, it could be deduced that at low mass fluxes, there needs to be a fundamental understanding between the relationship between difference in temperature and inclination on transfer of heat and pressure drops to enable designers optimize heat exchangers.
... In the basic homogeneous model the two-phase viscosity μ tp is considered equal to the liquid viscosity μ l . Different improved models have been formulated, where μ tp is calculated by means of more complex relations between the vapour and liquid properties [25][26][27][28][29][30] . Yamamoto et al. [21] compared their data to the basic homogeneous model and found that the model predicts the data well for the 2 mm ID tube, but the prediction level drops for the smaller tube sizes of 1 mm ID and 0.5 mm ID respectively. ...
The thermal management of most of the silicon pixel detectors at the heart of the Large Hadron Collider experiments at CERN relies on boiling carbon dioxide inside compact heat exchangers of small hydraulic diameter at saturation temperatures between +15 ∘C and −30 ∘C. Due to the current lack of suitable predictive models, a long-term study has been launched to create a consistent and reliable experimental database studying the peculiarities of boiling carbon dioxide in mini- and micro-channels. This study presents results on the total pressure drop of boiling carbon dioxide at low vapour quality (0 < x < 0.4) in 200 mm-long stainless steel tubes with an inner diameter of 2.15 mm, 1 mm and 0.5 mm. By means of a dedicated test setup equipped with high precision sensors, a wide range of saturation temperatures (+15 ∘C to −25 ∘C) and mass fluxes (100 to 1800 kg/m²s) have been explored and diabatic tests were carried out for heat fluxes from 5 to 35 kW/m². The data presented focus on the influence of the saturation temperature on the two-phase pressure drop. It is suggested that the combination of shifting physical properties of carbon dioxide and different confinement conditions causes a change in the phenomenological behaviour of the flow and that a transition between macro- and micro-scale most likely occurs within the range of test parameters. It is further shown that a shift in the applicability of existing prediction methods is caused by those effects and no correlation is able to predict the experimental data and trends in the whole temperature range. A selective approach to the use of existing correlations is also proposed.
... The experiment was carried out using different mini-channels of 0.31 mm to 3.3 mm HD with saturation temperature varying from 303 K to 313 K. The MF was varied from 100 kg/m 2 s to 1300 kg/m 2 s while VQ was varied from 0 to 1.The results of models were compared with the experimental results and it was found that the Akers et al. model [21] and Shah et al. model [6] showed better agreement for the HTC while the Friedel et al. model [22] and Garimella et al. model [23] show better agreement for FPD. Condensation of R134a, R236ea and R410a inside multi-port mini-channel of 1.4 mm hydraulic diameter was studied by Cavallini et al. [24] with wide range of reduced pressure.The experimental HTC compared with the HTC predicted by various models available in the literature and it was observed that results of all predictive models under study do not match with experimental results. ...
The present study aims to investigate the effect of working fluid, mass flux, vapour quality and saturation temperature on local condensation Heat Transfer Coefficient (HTC) and local Frictional Pressure Drop (FPD) in a horizontal circular mini-channel. The refrigerants HFO-1234yf and HFC-R134a have been used as a working fluids. The mass flux was varied from 200 to 800 kg/m² s whereas two distinct saturation temperatures were used: 35 °C and 40 °C. The experimental analysis was carried out using horizontal circular single port mini-channel of hydraulic diameter 1 mm. During experiment, inlet condition of refrigerant was maintained to be saturated vapour. The results show that HTC and FPD increases with increase in vapour quality and mass flux whereas decreases with increase in saturation temperature. The experiment results of present study and previously published results are compared with various predictive models. Models which show minimum deviation from experimental results were used to develop new modified model to predict HTC with MARD of ± 15 % and FPD with MARD of ± 10 %.
... Woking fluid Geometry Flow direction Akers et al. (1959) Not limited Round tube Horizontal Ananiev et al. (1961) Water Round tube Horizontal Boiko and Kruzhilin (1965) Water Round tube Vertical Cavallini and Zecchin (1974) Not ...
Direct steam generation coupled with solar energy is a promising technology which can reduce the dependency on fossil fuels. It has the potential to impact the power-generation sector as well as industrial sectors where significant quantities of process steam are required. Compared to conventional concentrated solar power systems, which use synthetic oils or molten salts as the heat transfer fluid, direct steam generation offers an opportunity to achieve higher steam temperatures in the Rankine power cycle and to reduce parasitic losses, thereby enabling improved thermal efficiencies. However, this is associated with non-trivial challenges, which need to be addressed before such systems can become more economically competitive. Specifically, important thermal-energy processes take place during flow boiling, flow condensation and thermal-energy storage, which are highly complex, multi-scale and are multi-physics in nature that involve phase-change, unsteady and turbulent multiphase flows in the presence of conjugate heat transfer. This paper reviews our current understanding and ability to predict these processes, and knowledge that has been gained from experimental and computational efforts in the literature. In addition to Rankine cycles, organic Rankine cycle applications, which are relevant to lower operating temperature conditions, are also considered. This expands the focus to beyond water as the working fluid and includes refrigerants also. In general, significant progress has been achieved, yet there remain challenges in our capability to design and to operate effectively high-performance and low-cost systems with confidence. Of interest are the flow regimes, heat transfer coefficients and pressure drops during the thermal processes present in direct steam generation systems including those occurring in the solar collectors, condensers and relevant energy storage schemes during thermal charging and thermal discharging. A brief overview of some energy storage options are also presented to motivate the inclusion of thermal energy storage into direct steam generation systems.
... The second method is to develop new correlation and computational models based on theoretical or experimental studies performed using minichannels. Correlations useful in the calculation of the heat transfer during condensation in the conventional channel, and applicable for minichannels, include: Akers et al. [1,2], Dobson and Chato [7], Shah [18], Cavallini and Zecchin [8], Tang et al. [21], Thome et al. [22,23], Tandon et al. [20], Moser et al. [18], and Wilson et al. [25]. When using any correlation concerning condensation in minichannels, one must always refer to the source material of its origin and compare the parameters of the process and the scope of its verification. ...
Investigations of refrigerant condensation in pipe minichannels are very challenging and complicated issue. Due to the multitude of influences very important is mathematical and computer modeling. Its allows for performing calculations for many different refrigerants under different flow conditions. A large number of experimental results published in the literature allows for experimental verification of correctness of the models. In this work is presented a mathematical model for calculation of flow resistance during condensation of refrigerants in the pipe minichannel. The model was developed in environment based on conservation equations. The results of calculations were verified by authors own experimental investigations results.
Two-phase flow is widely occurring in various engineering entities ranging from power plants, petroleum refineries to process industries. The potential to precisely predicts the drop in two-phase flow pressure is crucial and varies depending on the number of variables such as phase mass flux, channel orientation, channel cross-section, and channel size. The work gives an investigational examination of adiabatic air–water two-phase flow in minichannels. Horizontally kept circular transparent tubes of 1.0, 1.5, 2.0, 2.5, and 3.0 mm diameter were used for experimentation. Variation of mass flux used was from 307 to 7883 kg/m2 s for these experiments. Some of the available correlations from open literature were compared with experimental pressure drop data. The assessment revealed that known correlations are insufficient to infer experimental data. A new empirical correlation encompassing fluid properties was built based on evidence from trials. The new correlation made a decent fit to the present experimental results. It was noticed that majority of the data is lying within the ±35% error range.KeywordsAdiabatic flowAir–water flowTwo-phase flowPressure dropMinichannelsEmpirical correlationExperimental studyCircular tubes
Owing to the current crisis of environmental degradation generated from various sectors, many efforts have been tried out to commensurate the ecological cycle of the earth. The main contributors causing the environmental degradation are the industrial, transportation, and power plant sectors. Diesel engines are mostly used as a prime mover in those sectors to generate power owing to their superior thermal efficiency. However, at the same time, they also give off deleterious pollutants (like smoke, oxides of nitrogen, unburnt hydrocarbons, etc.). In order to reduce those deleterious pollutants, the present research study is focused to amend the diesel fuel properties on mixing the multi-walled carbon nanotubes (MWCNTs) as fuel-borne additives along with ordinary water methodically. Ordinary water (in prefixed volume percentage, say 2% and 4%) in presence of MWCNT and surfactants was employed to prepare the MWCNT unified water-diesel emulsions methodically and eventually tested for stability. The MWCNT blended water-diesel emulsions were examined in a CI engine to assess the working feature traits. It was established that MWCNT+ water mixture with the diesel, the emissions, and performance traits of the CI engine were ameliorated. It was noted that due to the existence of MWCNT in the water-in-diesel fuels, the secondary atomization effects could have influenced during the combustion period, and thereby caused the reduction in the magnitude of emissions (oxides of nitrogen, unburnt hydrocarbons, and smoke in particular).KeywordsMWCNTEmulsionStabilityPerformanceEmissionsDiesel engine
The study on gas-liquid two-phase flow characteristics of heaving oscillation is of great significance for the safe operation of offshore floating nuclear power platform. In this work, the frictional pressure drop of gas-liquid two-phase flow in vertical and inclined upward tubes under heaving oscillation was studied experimentally. The oscillation frequency was sequentially varied through values of 0.21, 0.42, 0.7 and 0.98 Hz, whereas the oscillation amplitude was 100, 150 and 180 mm. The diameter of the tube was 15, 20 and 25 mm, whereas the inclination angle was 60, 70, 80 and 90°. In total, 579 experimental data points were obtained and used to verify the 24 existing models of frictional pressure drop. The results showed that the existing models had relatively large errors in the calculation of frictional pressure drop under heaving oscillation. Considering the influence of additional force, the calculation method of liquid-phase conversion coefficient was improved, and the new model for the frictional pressure drop in gas-liquid two-phase flow for vertical and inclined upward tubes under heaving oscillation was established. It was found that the model established in this paper can greatly improve the accuracy of frictional pressure drop calculations under heaving oscillation.
The study of refrigerant condensation in minichannels is a very wide and complicated issue. An important aspect due to the range of the two-phase changes is mathematical and computer modelling. It allows providing calculation of heat transfer coefficient and pressure drops for many different refrigerants under different flow conditions. A mathematical model for the calculation of heat transfer coefficient and pressure drop during condensation of refrigerants in pipe minichannels is presented in this work. The model was obtained in MATLAB software based on conservation equations. The results of the calculations were verified by the authors’ own experimental investigations data and experimental data from the literature. This article concerns the results of R404A, R410A and R407C refrigerants condensation modeling.
Experiments were performed to investigate the heat transfer coefficient (HTC) of R134a and R410A condensing in rectangular, parallel microchannels with hydraulic diameter [Dh] between 0.66 and 1 mm. Three microchannels MC-1, MC-2, and MC-3 with aspect ratios of 0.5, 0.7, and 1 respectively, were selected while keeping the constant channel length (30 cm), base area (63 cm²), and channel depth (1 mm). Tests were conducted for mass flux 200 < G < 600 kg/m²s, vapour quality 0.05 < x < 0.83, and saturation temperatures of 30 and 40 °C. It was observed that as the refrigerant mass flux and vapour quality increased, the condensation HTC of R134a and R410A increased, but the same decreased as the saturation temperature increased. Data demonstrates that R134a has a higher condensation HTC than R410A, with the maximum value of condensation HTC attained in MC-1 with an aspect ratio of 0.5, followed by MC-2 and MC-3 with an aspect ratio of 0.7 and 1, respectively. Data received from the current experimental research was compared to existing condensation HTC correlations developed for conventional channels and mini/micro channels. A novel correlation has also been proposed for condensation HTC in microchannels, and the resulting correlation agreed to the experimental data with an MAE of 5.40% and predicts the data almost within the 20% error band.
Sanayinin birçok alanında, değişik türde ve çeşitte soğutucu akışkanların kullanılıyor olmasının yanı sıra, literatüre de birbirinden farklı özelliklere sahip birçok yeni akışkan eklenmiştir. Her soğutucu akışkan için literatürde bulunan mevcut yoğuşma ısı transfer korelasyonlarıyla ısı transfer katsayısı hesabı yapmak, birçok hatayı beraberinde getirmektedir. Bu makalede birçok soğutucu akışkana yer verilmiş ve literatürde bulunan en popüler korelasyonlardan 9 korelasyon ile deneysel veriler karşılaştırılmıştır. Akışkan türleri, kütle akış hızları, sıcaklıkları ve boru çapları gibi parametreler değiştirilerek ısı transfer sonuçları Java Crimson Editör ile hesaplanmıştır. Isı transfer katsayı sonuçları grafiksel analiz metotları ile karşılaştırmalı olarak irdelenmiştir.
The present study has focused on thermally performance modeling and designing of microchannel condenser (MC-C). It is aimed at contributing to new MC-C designs for refrigeration applications working with isobutane (refrigerant R600a). To this purpose, a novel thermal simulation model has been developed as a design tool to predict the heat capacity,outlet temperature and pressure of the MC-C. The existing correlations in the literature about heat transfer and pressure drop of refrigerant flow inside the microchannel have been evaluated to improve the accuracy of the thermal simulation model. A new heat transfer coefficient correlation has been employed in the model with the purpose of further improvement of the accuracy. An experimental study has been performed to validate thermal simulation model results. It is found that the model predicted isobutane temperature at the outlet of the MC-C and heat transfer capacity with deviations in the range of ± 2% and ± 1%, respectively. The model has an average of 6.8% MAE for the prediction of the isobutane pressure at the outlet of the MC-C The theoretical air-cooled MC-C designs have been performed to investigate the effect of hydraulic diameter microchannels and pass arrangement on heat transfer performance. The theoretical air-cooled MC-C designs have been modeled and discussed with the experimentally validated thermal simulation model for refrigeration applications. According to the model results, although the heat transfer coefficient inside microchannels increases as the hydraulic diameter decreases, heat transfer capacity decreases. When the pass arrangement is modeled, it is concluded that the designs with high tube numbers in the passes at which vapor quality is still high exhibit higher heat transfer capacity in the MC-C.
This article presents a proposal for a regressive model describing dynamic pressure vp and temperature vT impulsive instabilities during condensation of R134a refrigerant and isomers R1234yf and R1234ze(E) in minichannels. The model was verified in relation to the obtained experimental results. In the development of the model, a dimensionless analysis using Buckingham's Π theorem was applied to obtain the dependence on dimensionless values of the propagation velocities of the pressure instability vp⁺ related to the acoustic speed vp and of the temperature instability vT⁺ related to the condensation front vFC. Experimental studies were carried out with the use of miniature tubes of circular cross-section with hydraulic internal diameter dh = 3.30, 2.30, 1.92, 1.44, and 1.40. The comparison of the computational results obtained from the model with experimental results showed a satisfactory compliance of ±25%.
Three micro-finned and two smooth multiport tubes having the same tube width and height with the microfin tubes were tested using R-410A. For the smooth multiport tube, the tube with smaller hydraulic diameter yielded both higher heat transfer coefficients and larger pressure drops. However, for the microfin tube, results suggested that, fin configuration (number of fins per channel, fin height, etc.) has to be considered in addition to hydraulic diameter. The trend of the pressure drop generally followed the hydraulic diameter – smaller hydraulic diameter tube yielded larger pressure drop. Data are compared with the predictions by existing correlations.
This paper consists of the analysis of research on refrigerant condensation in minichannels and compact heat exchangers cooled with either water or air. An analysis of the state of knowledge of the research on refrigerant condensation in minichannels and mini-heat exchangers, so-called multiports, was performed. Directions for further research in this field were indicated. The authors present results for the condensation of refrigerants R134a, R404A, R407C and R410A in a pipe containing minichannels with internal diameters of di = 0.5,0.64,0.7,1.2,1.6,2.0, and 2.5 mm; and mini-condensers constructed in the form of two bundles of tubular stainless steel minichannels with an internal diameter d = 0.64 mm and length L = 100 mm. Exchanger M4 contained four minichannels and M8 contained 8 minichannels. In each case the average values of the heat transfer coefficient and frictional pressure drop throughout the condensation process (x = 1–0) were designated. The impact of the vapour quality of the refrigerant and the mass flux density on the intensity of heat transfer and flow resistance were illustrated. A correlation was proposed to determine the local value of the heat transfer coefficient over a wide range of changes in the heat-flow parameters of the refrigerant. A comparative analysis of test results for various refrigerants in both minichannels and mini-heat exchangers was made. Experimental studies have shown that the value of the heat transfer coefficient αx depends on the value of the heat flux density q on the cooled surface. This relationship is particularly noticeable in the case of large changes in the value of the heat flux density (q = 500–35,000 W • m⁻²). It was also confirmed that the per-channel intensity of heat exchange in multiports is lower than in the case of a single minichannel with the same internal diameter.
Corrosion of the aluminum multi-port extrusion (MPE) leads to heat exchanger leakage. Corrosion of the 1xxx series aluminum MPE tubes proceeds continuously along Al13Fe4, which is the precipitation phase of Fe impurity. The continuous corrosion behavior along Al13Fe4 rapidly propagates into the aluminum MPE tube, thereby reducing the penetration life. In this study, Zr was added in order to control the dispersion of Al13Fe4 precipitates in an attempt to improve the corrosion resistance of A1070 aluminum MPE tubes for heat exchangers. The refinement and dispersion of Al13Fe4 phase was controlled by the addition of Zr, which is a highly insoluble element in aluminum. Zr plays a role in increasing nucleation and inhibiting the growth of the surrounding Al13Fe4 phase during the precipitation to Al3Zr phase. As a result, the size of the Al13Fe4 phase became finer and more dispersed, and the continuous corrosion tendency was decreased. Therefore, corrosion propagation of aluminum MPE tube progressed uniformly and penetration was suppressed.
Two-Phase Flow, Boiling, and Condensation - by S. Mostafa Ghiaasiaan January 2017
Cambridge Core - Thermal-Fluids Engineering - Two-Phase Flow, Boiling, and Condensation - by S. Mostafa Ghiaasiaan
This paper presents the results of an experimental investigation on heat transfer and pressure drop characteristics for R134a in multiport flat tubes (MPFT). In order to perform a fundamental analysis, an experimental facility has been set up to determine both the heat transfer coefficient and the pressure drop value in the two-phase flow regime inside extruded MPFT (d=0.91−0.77mm) with either rectangular channels or including an axial fin structure. The operating parameters have been varied within a broad range to ensure a high degree of reliability and comparability to heat transfer and pressure drop correlations. A very good agreement of the pressure drop data with the Friedel (1979) and Jige et al. (2016) correlations can be confirmed. The heat transfer coefficient can be predicted well for the MPFT with rectangular channels using the Jige et al. (2016) correlation, but only poor agreement can be achieved for the MPFT including the fin structure for all correlations taken into consideration.
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