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A survey of correlations for heat transfer and pressure drop during evaporation in plate heat exchanger
Abstract
With the increased regulations to move towards lower GWP refrigerants, natural fluids and their blends are becoming more favorable. Plate heat exchangers are being used in air-conditioning and refrigeration applications as well as a wide variety of other applications including food processing, chemical industry, and energy generation systems. Plate heat exchangers are favored because of their compactness, close approach temperature pure counter-flow operation, and enhanced heat transfer performance. Plate heat exchangers are increasingly utilized in two-phase flow operations due to their desirable characteristics. In order to achieve a better understanding of the current research status of two-phase flow in plate heat exchangers, this paper presents a literature review of available correlations for heat transfer and pressure drop calculations during evaporation in plate heat exchangers. Generally, research on evaporation heat transfer performance in plate heat exchangers is limited. Correlations on natural refrigerant mixtures are scarce. One recent correlationis proposed in literature for ammonia/water mixtures with specific conditions and mixture concentrations. A comparative evaluation of some of the existing correlations is presented in the light of their applicability to natural refrigerants. Overall, there is a significant gap in the literature regarding evaporation heat transfer and fluid flow characteristics of these types of exchangers.
... Eldeed et al. [1] surveyed refrigerant two-phase heat transfer and pressure drop correlations for BPHE applications. In particular they reviewed 17 boiling heat transfer correlations finding that the development of a sound calculation model requires a huge databank such as in Longo et al. [2] and in Amalfi et al. [ 3 , 4 ] procedures that seem to be the best state-of-the-art analyticalcomputational procedures for boiling inside BPHE. ...
... The Longo et al. [2] model consists of a non-dimensional forced-convection boiling correlation, developed from a wide database, and a nucleate boiling correlation, based on the Gorenflo [5] equation adapted to BPHE. h r = MAX ( h cb , h nb ) (1) h cb = 0 . 122 ( λ L / d eq ) R e eq 0 . ...
... Reynolds number, Re = G r d eq / μ L Re eq equivalent Reynolds number, Re eq = ( G r d eq / μ L ) [(1-X ) + X ( ρ L / ρ G ) 1 ...
This paper presents an Artificial Neural Network (ANN) model for predicting refrigerant boiling heat transfer coefficients inside Brazed Plate Heat Exchangers (BPHE). The model accounts for the effect of plate geometry, operating conditions and refrigerant properties. The model shows a fair agreement with a database of 1760 data points comprising 15 plate geometries and 16 refrigerants (including 4 natural refrigerants and 6 other low-GWP refrigerants). The Mean Absolute Percentage Error (MAPE) of the model predictions is 4.8%. The ANN model exhibits a better predictive capability than most of the state-of-the-art analytical-computational procedures for boiling inside BPHE available in the open literature. The characteristic parameters of the ANN model are fully reported in the paper.
... Unfortunately, the existing commercial plate type condenser simulation tools are not suitable for the iCond design under studied. They are mainly dedicated to plates without inner fins (chevron plates for instance) [2]. Hence, the goal of this study is to satisfy this need. ...
... By considering a simple characteristic element of the turbulator geometries, the laminar and turbulent boundary layer models were derived by performing simple force and energy balances. These models are then combined with the low flow asymptote using the form of Eqs.(1) and (2). The dimensionless numbers: Colburn factor and Fanning factor are defined by ...
An experimental and analytical study on the performance of a compact coolant-cooled condenser was conducted. The condenser design consists in stacked plates containing offset strip fins oriented transversally to the flow direction. Thermal performance and pressure drop data were obtained, using a heat exchanger test bench, at varying inlet conditions. These experimental data are used to develop a predictive heat exchanger model to size the condenser over a wide range of operating conditions, eliminating the need for expensive prototype development and testing.
... Eldeed et al. [1] surveyed two-phase heat transfer and pressure drop correlations of refrigerants for PHE applications. Amalfi et al. [ 2 , 3 ] and Tao and Infante Ferreira [4] focused their investigations on the boiling and condensation of refrigerants, respectively, in [5] model is capable of reproducing the Tao and Infante Ferreira [4] database with a Mean Absolute Percentage Error (MAPE) of approximately 25% and able to predict more than 93% of their data within ± 50%. ...
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.
... The heat transfer coefficients in single-phase zones of all heat exchangers are evaluated using the well-known Gnielinski correlation ( Admiraal and Bullard, 1993 ). To evaluate the boiling and condensation heat transfer coefficients of two-phase zones in the generator, evaporator and condenser, the correlations introduced by Yan and Lin and Yan et al. ( Eldeeb et al., 2016 ) are applied. ...
The dynamic behavior of the ejector refrigeration system (ERS) plays an important role in its performance prediction and control system design. This paper numerically and experimentally investigated ERS dynamic behavior by connecting generator, condenser and evaporator dynamic models into a single ERS dynamic model, as the heat exchangers dominate ERS thermal dynamics. The developed dynamic models of the heat exchangers were based on the moving boundary approach. A 1-D thermodynamic model of the ejector was also developed to evaluate the fluid behavior through the ejector. The pump and expansion valve were modeled using algebraic equations, as they were considered as steady state components in the system. The developed ERS dynamic model was validated experimentally by measuring the transient response to the step change of the pump speed. The validation studies revealed that the model is able to capture the refrigeration system's dynamics in terms of the pressures and outlet specific enthalpies of the heat exchangers, with relative errors of less than 3.78 and 0.5 %, respectively.
... The expansion of freezing water could cause stress and strain responsible of reduced performance and possible break-down of the HEX. Moreover, studies and CFD analysis on two-phase heat transfer in a PHE are scarce and this work could help in understanding the fluid behaviour inside the plates [8] [9]. The CFD model is used to better understand the heat transfer and pressure drop inside the BPHE in different conditions. ...
Energy use optimization is one of the numerous way to reduce the impact of the CO2 on the environment. The work presented in this paper explores the possibility to apply the Brazed Plate Heat Exchanger (BPHE) technology to enhance the heat transfer between an extremely cold liquid gas such as nitrogen or air and low-grade heat media such as hot water. BPHEs are known to be characterised by high turbulent flows and high heat transfer rate and thus are the best candidate to guarantee quick heat transfer between the two fluids. Particular concern in this application is given by the risk of freezing water inside the BPHE. Considering the high complexity in the internal structure of the BPHE, the work is based on its analysis using x-ray tomography and CFD via a commercial software. CFD analysis was carried out using a first simple geometry and physics to verify the feasibility of the study. Given the promising results (quick heat transfer and tempered water temperature), subsequent study will be focused on more complex geometry and realistic physics to acquire a comprehensive and exhaustive view of the problem.
... However, the majority of the correlations and measurement provide only estimations of the average heat transfer coefficient, which can be used for calculation methods such as the Number of Transfer Units (NTU) or Log Mean Temperature Difference (LMTD). Eldeeb, et al. (2016) give a good overview of some of the most well-known correlations for evaporation and condensation in BPHEs. ...
Brazed Plate Heat Exchangers (B PHEs) are increasingly used as evaporators for re frigeration and heat pump applications. Detaile d understanding of the underlying heat transfer phenomena is required for their effe ctive design and use. The number of correlations which are sui table for modeling t he dynamics of flow boiling within BPHEs is rath er low compared to other evaporator types. In this paper some correlations that in volve integral values of steam quality are evaluated for different set s of experimental data from literature. Modifications to the correlations are pres ented, which allow to predict the quasi-local heat transfer coefficient in each refrigerant ce ll. The cells equal finite volumes that are composed to a dynam ic model of a BPHE acting as evaporator. Heat transfer coefficient and heat flow rate from si mulation results are compared to those calculated from existing experimental data based on the same boundary conditions. The fine-tuned evaporator model is finally used to demonstrate effects of sudden load changes for the evaporator performance.
Plate heat exchangers are used regularly in the heating, ventilating,
air conditioning, and refrigeration industry. There is an urgent
need for detailed and systematic research regarding heat transfer
and the fluid flow characteristics of these types of exchangers.
As an initiative in this respect, a literature search is presented
on plate heat exchangers. New correlations for evaporation heat transfer
coefficient and friction factor are introduced, which are applicable
to various system pressure conditions and plate chevron angles. The
correlations are based on actual field data collected during several
years of installation and operation of chillers, and they are intended
to serve as design tools and perhaps as a starting point for future
research.
This paper deals with the design of plate heat exchangers for processes in single-phase, evaporation and condensation. Some results are given for the thermal and hydraulic performance of corrugated channels in single phase flow. The flow pattern is analysed to give some local information on the heat transfer and the velocity field. In two phase flows, the heat transfer coefficient and the pressure drop are correlated with models originally developed for smooth tubes. Some recommendations are proposed for future research.
Plate heat exchangers (PHE’s) are being used to an increasing extent as refrigerant evaporators but published information on their performance in this mode is rather limited. In this paper, two-phase heat transfer and pressure drop characteristics are presented for PHE’s when used as refrigerant liquid over-feed evaporators. Laboratory experiments were carried out with three industrial PHE’s having different chevron angle combinations, using refrigerant R134a and R507A. Measurements were made over ranges of mass flux, heat flux and corresponding outlet vapour qualities, and the effects of these parameters on the thermal and hydraulic performance of the evaporators were evaluated. Additional field test data of thermal performance were collected from ammonia and R12 water chillers, operating as thermosiphon evaporators. Based on all these data, empirical correlations are proposed for predicting the refrigerant boiling heat transfer coefficient and two-phase frictional pressure drop in PHE’s.
Plate heat exchangers are gaining acceptance in absorption refrigeration systems due to their high transfer rates, compactness, and low refrigerant charge. Nevertheless, boiling heat transfer and pressure drop studies with mixtures in plate heat exchangers (PHEs) are scarce.In this study, the experimental data of Táboas et al. (2010) on flow boiling of ammonia/water in a plate heat exchanger are compared with the predicted values using the correlations available in the open literature for the boiling heat transfer coefficient and pressure drop. In addition, this study proposes a new correlation based on a separate model by which to obtain the boiling coefficient. The new correlation uses a transition criterion, divided into an apparent nucleate boiling region where pure convective boiling cannot appear, and a region with competition between convective and apparent nucleate boiling. The correlation proposed can predict 98% of data from Táboas et al. (2010) within 20% error.
The evaporation heat transfer coefficient and pressure drop for refrigerant R-134a flowing in a plate heat exchanger were investigated experimentally in this study. Two vertical counterflow channels were formed in the exchanger by three plates of commercial geometry with a corrugated sine shape of a chevron angle of 60 deg. Upflow boiling of refrigerant R-134a in one channel receives heat from the hot down flow of water in the other channel. The effects of the mean vapor quality mass flux, heat flux, and pressure of R-134a on the el,evaporation heat transfer and pressure drop were explored. The quality change of R-134a between the inlet and outlet of the refrigerant channel ranges from 0.09 to 0.18. Even at a very low Reynolds number, the present flow visualization of evaporation in a plate heat exchanger with the transparent outer plate showed that the flow in the plate heat exchanger remains turbulent It is found that the evaporation heat transfer coefficient of R-134a in the plates is much higher than that in circular pipes and shows a very different variation with the vapor quality from that bl circular pipes, particularly in the convective evaporation dominated regime at high vapor quality. Relatively intense evaporation on the corrugated surface was seen from the flow visualization. Moreover, the present data showed that both the evaporation hear 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 evaporation heat transfer is clearly better only at the high quality. Raising the imposed wall heat flux was found to slightly improve the heat transfer, while at a higher refrigerant pressure, both the heat transfer and pressure drop are slightly lower. Based an the present data, empirical correlations for the evaporation heat transfer coefficient and friction factor were proposed.
Experiments on the evaporative heat transfer and pressure drop in the brazed plate heat exchangers were performed with refrigerants R410A and R22. The plate heat exchangers with different 45°, 35°, and 20° chevron angles are used. Varying the mass flux of refrigerant (13–34 kg/m2s), the evaporating temperature (5, 10 and 15 °C), the vapor quality (0.9–0.15) and heat flux (2.5, 5.5 and 8.5 kW/m2), the evaporation heat transfer coefficients and pressure drops were measured. The heat transfer coefficient increases with increasing vapor quality and decreasing evaporating temperature at a given mass flux in all plate heat exchangers. The pressure drop increases with increasing mass flux and quality and with decreasing evaporating temperature and chevron angle. It is found that the heat transfer coefficients of R410A are larger than those of R22 and the pressure drops of R410A are less than those of R22. The empirical correlations of Nusselt number and friction factor are suggested for the tested PHEs. The deviations between correlations and experimental data are within ±25% for Nusselt number and ±15% for friction factor.
Plate heat exchangers were first developed about 100 years ago but have won increasing interest during the last two decades, primarily due to the development of methods of manufacturing brazed plate heat exchangers. This type of heat exchanger offers very good heat transfer performance in single-phase flow as well as in evaporation and condensation. Part of the reason is the small hydraulic diameters, typically being less than 5 mm. Other advantages of plate heat exchangers are the extremely compact design and the efficient use of the construction material. In spite of their long use, the calculation methods for predicting heat transfer and pressure drop are not widely known. It is the purpose of this article to present such calculation methods for single-phase flow and for flow boiling and to discuss some of the specifics of this type of heat exchangers.
The evaporation heat transfer experiments were conducted with an oblong shell and plate heat exchanger without oil in the refrigerant loop using R-410A, a mixture of 50 wt% R-32 and 50 wt% R-125 that exhibits azeotropic behavior. An experimental refrigerant loop has been established to measure the evaporation heat transfer coefficient h r of R-410A in a vertical oblong shell and plate heat exchanger. Four vertical counter-flow channels were formed in the oblong shell and plate heat exchanger by four plates having a corrugated trapezoid shape of a 45° chevron angle. The upflow of the boiling R-410A in one channel receives heat from the hot downflow of water in the other channel. The effects of the refrigerant mass flux, average heat flux, refrigerant saturation temperature, and vapor quality of R-410A on the measured data were explored in detail. The results indicate that a rise in the refrigerant mass flux causes an increase in the h r . Raising the imposed wall heat flux was found to slightly improve h r . Finally, at a higher refrigerant saturation temperature, the h r is found to be lower. Based on the present data, an empirical correlation of the evaporation heat transfer coefficient was proposed.
Subcooled flow boiling heat transfer characteristics of refrigerant R-134a in a vertical plate heat exchanger (PHE) are investigated experimentally in this study. Besides, the associated bubble characteristics are also inspected by visualizing the boiling flow in the vertical PHE. In the experiment two vertical counterflow channels are formed in the exchanger by three plates of commercial geometry with a corrugated sinusoidal shape of a chevron angle of 60°. Upflow boiling of subcooled refrigerant R-134a in one channel receives heat from the downflow of hot water in the other channel. The effects of the boiling heat flux, refrigerant mass flux, system pressure and inlet subcooling of R-134a on the subcooled boiling heat transfer are explored in detail. The results are presented in terms of the boiling curves and heat transfer coefficients. The measured data showed that the slopes of the boiling curves change significantly during the onset of nucleate boiling (ONB) especially at low mass flux and high saturation temperature. Besides, the boiling hysteresis is significant at a low refrigerant mass flux. The subcooled boiling heat transfer coefficient is affected noticeably by the mass flux of the refrigerant. However, increases in the inlet subcooling and saturation temperature only show slight improvement on the boiling heat transfer coefficient.
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.