Saturated Flow Boiling Heat Transfer Research Articles

Development of a New Correlation for Saturated Flow Boiling Heat Transfer in a Helically Coiled Tube

We have developed a heat transfer correlation for saturated flow boiling of water in a helically coiled tube. Initially, we collected experimental data encompassing a broad spectrum of thermal-hydraulic conditions and geometric configurations, and examined the influences of key dimensionless parameters, such as the convection number and the boiling number. The data analysis showed that the observed trend aligns with previous studies on boiling heat transfer within a straight tube. Also, we investigated the influence of centrifugal force acting on the fluid in a helically coiled tube and confirmed its significant impact on boiling heat transfer. Based on our findings, we propose a new heat transfer correlation that incorporates a dimensionless number of the centrifugal force divided by gravitational force. The basic structure of this correlation was adapted from the Kandlikar correlation for saturated flow boiling. The new correlation demonstrated enhanced accuracy compared to existing ones. Additionally, we showed its applicability to boiling heat transfer within a straight tube as well.

Saturated flow boiling heat transfer of R1233zd(E) in parallel mini-channels: Experimental study and flow-pattern-based prediction

The parallel channel is widely used in the two-phase flow boiling heat transfer due to its simple structure, but the existence of multiple flow patterns causes a complex and non-unified explanation of the heat transfer mechanisms. In this study, a saturated flow boiling experiment was designed in a parallel mini channel heat sink with R1233zd(E) as the working fluid. By controlling the vapor quality difference at the inlet and outlet to around 0.1–0.2, each single flow pattern was isolated and presented in the test section, and the corresponding variations of heat transfer coefficient (HTC) were discussed. The results showed that the flow pattern during the saturated flow boiling included bubbly flow, slug flow, wavy-annular flow and local dry-out. The transition boundaries between bubbly flow, slug flow and wavy-annular flow showed good agreement with the present criteria, while a modification was made on the transition from wavy-annular flow to local dry-out. The HTC showed a fast increase under low vapor qualities, then became stable and decreased with the increase of vapor quality. In addition, 6 correlations were selected to compare with the measured HTC classified according to the flow patterns. The comparison showed that the present correlations had different prediction accuracies on the HTC data under each flow pattern. The best prediction on the heat transfer during bubbly and slug flow was achieved by Liu and Winterton's model with the MAE of 16.4% and 12.9%, while Li and Wu's model showed the best agreement with the HTC data during wavy-annular flow with the MAE of 9.1%.

Dryout suppression and significantly enhanced flow boiling heat transfer through the two-tier vertically aligned carbon nanotube channel

It is crucial to design multi-functional structure to improve heat transfer characteristics. Here we report significantly enhanced saturated flow boiling heat transfer of water using the two-tier vertically aligned multiwalled carbon nanotube (VAMWNT) channel (tube diameter: 11.5 nm). The channel size is 10 × 10 × 2 mm3 (height: 2 mm). The tube aggregation-generated large voids act as micropores (10-200 µm) whereas the interstitial spaces between the tubes act as nanopores (< 72 nm). The microcavities at the periphery of aggregated nanotubes increase bubble nucleation sites while constraining bubble size. The high nanotube thermal conductivity induces more uniform bubble nucleation, and departed bubbles are swept away through the micropores. On the other hand, water is effectively replenished through the nanopores by high capillary pumping. Overall, the path separation of bubble departure and water replenish effectively prevents dryout and increases critical heat flux (CHF). The experiment is carried out at 3 different mass velocities (62, 83, and 104 kg m−2 s−1). The VAMWNT channel provides a high heat transfer coefficient (h = 100,666 W m−2 K−1 at 183 W cm−2), even before reaching CHF without any sign of local dryout, compared with microchannels and porous media in literature (under the similar heat flux and mass velocity). In contrast, the CHF condition is observed for a plain channel of the same size without the nanotubes, resulting in smaller h values than those of the VAMWNT channel. The novel two-tier structure separated liquid-vapor pathways, significantly enhancing heat transfer characteristics.

Deep learning-based assessment of saturated flow boiling heat transfer and two-phase pressure drop for evaporating flow

This work proposes new correlations as well as deep learning based modeling of saturated flow boiling heat transfer and two-phase pressure drops for evaporating flow. First, existing saturation flow boiling heat transfer correlations are compared to experimental database (2,500 data points) of numerous refrigerants for tube diameters ranging from 1 to 7 mm. The newly developed correlation for heat transfer outperformed the existing correlations resulting in an MAE =11.28%. For two-phase pressure drop of the evaporating flow, 1,954 measurement data points of 7 refrigerants were used, for the experimental tube diameter ranged from 0.509 to 14 mm. The newly developed correlation for pressure drop outperformed the existing correlations resulting in an MAE =19.07%. An optimal deep learning model (DL) was developed that further improved the accuracy of the prediction in terms of both heat transfer and pressure drop (R2=0.984 and MAE=4.5 % in terms of heat transfer and R2=0.994 and MAE=7.39 % in terms of two-phase pressure drop). The proposed correlations and deep learning models significantly improve microchannel prediction in terms of heat transfer and two phase pressure drop. Besides, explainable artificial intelligence highlights the dependence and interaction between various features affecting the heat transfer and pressure drop.

Flow boiling heat transfer of zeotropic mixture refrigerants R454B and R449A in a smooth horizontal tube

The paper reports an experimental investigation of local saturated flow boiling heat transfer of two environmentally-friendly zeotropic mixture refrigerants – R454B and R449A – in a horizontal 8.7 mm ID smooth tube, under high pressure and high heat-flux conditions. The test section is divided into five subsections to obtain quasi-local heat transfer and the refrigerants are heated by hot water in counter-current flow. For R454B, mass flux varied from 201 kg m−2 s−1 to 269 kg m−2 s−1 and the inlet pressure varied from 1.691 MPa to 3.282 MPa. For R449A, mass flux varied from 178 kg m−2 s−1 to 328 kg m−2 s−1 and the inlet pressure varied from 1.449 MPa to 3.244 MPa. The temperature glide and composition shift during flow boiling due to volatility difference between components were investigated. R454B and R449A displayed a temperature glide respectively from 1.12 K to 1.33 K and from 3.04 K to 4.61 K at the inlet of the test section in the present tests. During the process of saturated boiling, for R454B, mass fraction of the less volatile component, R1234yf, in liquid phase was over 7% more than that in vapor phase; For R449A, mass fractions of the less volatile components, R134a and R1234yf, in liquid phase were around 6% and 4% more than those in vapor phase. Thermal resistance and mass transfer resistance were discussed. Before the occurrence of partial dry-out, heat-transfer coefficients of R454B were mainly located between 6.5 kW m−2K−1 and 10 kW m−2K−1 while most of data of R449A lay in the range of 3.5 – 8 kW m−2K−1. The results of heat-transfer coefficient indicate that R454B exhibited greater heat transfer than R449A under close operating conditions. For both refrigerants, the heat transfer performance was locally enhanced in the region of near-zero vapor quality and gradually declines before intermediate vapor quality. After intermediate vapor quality, it tended to rise with vapor quality until a dramatic fall due to partial dry-out.

Flow boiling heat transfer and pressure drop of R245fa inside horizontal 1.62 mm and 2.43 mm tubes under hypergravity

Experimental investigation of refrigerant R245fa flowing inside horizontal 1.62 mm and 2.43 mm tubes under different gravity levels were carried out to study effects of gravity level, tube diameter, and heat flux on flow boiling heat transfer and pressure drop. The experimental parameter range is the mass flux of 351 kg m−2 s−1, heat fluxes of 32 and 64 kW m−2, system pressure of 217.8 kPa, average vapor qualities of 0.007–0.915, and gravity levels from 1 to 2.77 g. The flow boiling heat transfer and pressure drop of R245fa in different tube sizes under hypergravity are first reported. The results show that the heat transfer was enhanced significantly for both tubes when the turntable starts to rotate (from 1 to 1.04 g), which attributes to the fluid disturbance and secondary flow generated by the Coriolis force. With the further increase in hypergravity (from 1.04 to 2.77 g), the heat transfer coefficient may be enhanced or deteriorated. The reason is that the effect of centripetal acceleration, which increases much faster with increasing rotational speed of the turntable than the Coriolis acceleration, offsets the contributions made by the Coriolis force. The effect of heat flux on flow boiling heat transfer interacts with other factors. It is possible for the heat transfer coefficient at lower heat flux to be greater than that at higher heat flux due to the compound flow and heat transfer mechanisms. Under hypergravity, the pressure drop in the small tube is slightly larger than that under normal gravity, while in the large tube it may be smaller than that under normal gravity. The experimental data are compared with the predictions of existing correlations of saturated flow boiling heat transfer and frictional pressure drop, and those which can provide the most agreeable predictions are identified.

Saturation flow boiling characteristics of R290 (propane) inside a brazed plate heat exchanger with offset strip fins

An inclusive experimental study was conducted to explore the saturated flow boiling heat transfer coefficient (HTC) and frictional pressure drop (PDf) features of R290 in a brazed plate heat exchanger embedded with offset strip fins with an offset length of 2 mm, fin thickness of 0.3 mm, and fin height of 2 mm. The experiment was conducted at four different saturation temperatures (Ts = 5–20 °C), three mass fluxes (G =20–60 kg m−2 s−1), four heat fluxes (q = 7.5–15 kW m−2), and eight mean vapor qualities (Xm) at increasing inlet vapor quality (0.1–0.8). The findings revealed that nucleate boiling vanquished at lower Xm values, irrespective of the working conditions, despite the fact that at higher Xm, the boiling process was dominated by convection. There was a dry-out condition inside the heat exchanger at Xm = 0.42–0.63, except when G = 60 kg m−2 s−1. The result suggested that the HTC of R290 strongly depended on Xm and Ts compared with G and q. The PDf of R290 shows a strong dependence on Ts, G, and Xm, whereas it is less dependent on q. Moreover, PDf increases with an increase in G, Xm, and q values, and decreases with an increase in Ts. Furthermore, empirical correlations for Nusselt number and friction factor, which were developed for R290, accounted for the influence of equivalent and liquid Reynolds numbers and the liquid and vapor densities with a mean absolute error of 10% and 14%, respectively.

A relatively wide-ranged correlation of saturated flow boiling heat transfer within narrow rectangular channel for water

• Database of boiling heat transfer in narrow rectangular channel over a relatively wide parametric range obtained. • Corresponding transition of two-phase flow regimes with dominant heat transfer mechanisms observed and discussed. • A new, wide-ranged correlation proposed. A campaign of tests is performed for saturated boiling heat transfer characteristics of water in narrow rectangular channel. The test matrix covers a relative wide range of conditional parameters and 3142 test data are acquired, screened and selected for study. Meanwhile, visualization test has been conducted with three typical flow patterns, namely isolated bubbly, confined bubbly and irregular annular flows, being observed and identified, each pattern corresponding to a prevailing or a transitional combined boiling heat transfer mode. Study of the data trend indicates that two boiling heat transfer mechanisms, namely nucleate boiling and forced convective evaporation, are either one dominant or two combined transitional during different phases of saturated flow boiling within the channel. With the basic view obtained from the test campaign, and with related parametric effect and sensitivity study, as well as the existing correlation assessment with the test data, a new correlation for the saturated boiling heat transfer is proposed and regressed, which consists a modification factor composing the two basic boiling mechanisms and the transition function between. A preliminary assessment is performed for its statistical and predictive accuracy, from which a relatively satisfactory agreement is drawn. The new correlation applies to a heat flux range of 100 - 2300 k W / m 2 , a mass flux range of 500 2000 k g / m 2 · s , a system pressure range of 0.2 5.5 M P a and the equilibrium quality range of 0 0.72 . It might be used, in conjunction with the flow pattern and the related heat transfer mechanism, to predict the saturated boiling heat transfer coefficient over a wide range of heat flux, mass flux and pressures with better accuracy than previous correlations.

Assessment on R-410A saturated flow boiling heat transfer subject to periodic oscillating heat flux inside an annular duct

The objective of this study is concerned with assessing experimentally the heat transfer of time-dependent saturated flow boiling (TDSFB) for refrigerant R-410 A stemming from oscillations in the heat flux inside an annular duct with the gap of δ = 2 mm in order to improve the energy efficiency of heat exchanger system. The influences of operating parameters, such as mean applied heat flux q‾, heat flux oscillation amplitude Δq/q‾, mass flux of refrigerant G, oscillation period tp, and saturation temperature Tsat, on heat transfer characteristics of TDSFB are systematically explored. From the present experimental results, it is found that increasing mean applied heat flux enhances the average wall superheat and boiling heat transfer coefficient (BHTC, hr); while an increase in either Δq/q‾ or tp exerts very minor influence on the boiling curve and hr. As the q‾ oscillates in the triangular waveform, the wall temperature (Tw) varies in sinusoidal waves at the same frequency of q‾. At low, intermediate, and high q‾, three different flow patterns versus time are observed and named single-phase flow (SPF), intermittent boiling flow (IBF), and persistent boiling flow (PBF). The oscillation amplitudes of Tw and hr are increased with the increases of Δq/q‾. Enhancing either G or Tsat tends to result in a slight decrease in Tw, but an increase in hr. Moreover, the Tw does not fluctuate with the oscillation of lower q‾ under a shorter tp due to the tube thermal inertia, but oscillates significantly as the tp is raised. Finally, a correlation equation is presented to identify the bounds, distinguishing the three different flow patterns of R-410 A TDSFB subject to oscillatory heat flux inside horizontal annuli.

수직 원관에서의 메탄의 포화 유동 비등에 관한 수치해석적 연구

In this study, a numerical study on saturated flow boiling of methane is carried out in a smooth vertical pipe. The pipe has a diameter of 8 mm and length 1 m. The simulation is performed under the condition of mass flux of 52.36-150.31 kg/㎡s, heat flux range of 7,950.7-31,858.9 W/㎡, and outlet pressure of 0.7 MPa. The analysis for saturated flow boiling is implemented with taking into account the phase change process, wall boiling and inter-phase momentum transfer models. Simulation results are compared with the theoretical values and experimental results found in the literature. According to the simulation results, the vapor quality shown in the simulation is lower than that predicted by the theoretical values. However, the variation of the vapor quality with respect to heat flux shows similar trend to the theoretical value. The heat transfer coefficient is mainly dependent on the heat flux and not significantly affected by the mass flux. This means that the main mechanism of saturated flow boiling heat transfer is nucleate boiling.

High pressure saturated flow boiling of CO2 at the micro scale

Saturated flow boiling heat transfer of carbon dioxide (CO2) at the microscale was studied with pressures ranging from 2.4 MPa to 6 MPa (i.e., reduced pressure ranging from 0.3 to 0.81, respectively), mass fluxes ranging from 1199 kg/m2s to 2428 kg/m2s, mass qualities up to 0.94, heat fluxes up to 270 W/cm2, and ΔTsat up to 150 K. A maximum heat transfer coefficient (HTC) of about 150 kW/m2K, and a maximum critical heat flux (CHF) of about 200 W/cm2 was recorded. Comparison to established correlations were made and discussed based on a flow map of saturated flow boiling of carbon dioxide by Cheng et al. The map classified the flow into different patterns (i.e., bubbly, annular, dry-out, and mist flows), and provided insight about the observed HTC trends based on the mass quality. The Shah and the Cheng et al. correlations predicted the HTC reasonably well for mass qualities of up to 0.45 with mean average errors of about 23%, but for a mass quality of 0.94, the Kandlikar, the Shah, and the Cheng et al. correlations underpredicted experiments with mean average errors of 80%, 24%, and 98%, respectively. The critical heat flux condition was predicted well with different models, and the Katto et al. correlation provided the lowest mean average error of 23.0%.

Novel Saturated Flow Boiling Correlations for R600a and R717 Refrigerants

This research study provides a detailed analysis of the two-phase flow boiling heat transfer coefficients of R600a and R717. In addition, it proposes novel saturated flow boiling heat transfer correlations for these two refrigerants. In this context, 1306 experimental data points for R600a and 885 data samples for R717 are extracted from the literature works to develop new flow boiling models. Two different correlations are constructed under different forms of baseline frameworks for each refrigerant. The proposed flow boiling model for R600a utilizes the dimensionless numbers and operational parameters of the best performing literature correlations for this refrigerant while the model developed for R717 takes the advantage of piecewise continuous correlation form which successfully trace the tendencies of heat transfer coefficient with varying vapor qualities. It is found that the new model for R600a has a mean absolute error of 12.4% and mean relative error of 0.1, predicting 78.5% of the entire database within ±20.0% error band whereas the proposed correlation for R717 has an absolute error value of 17.3% having 65.3% of the data within ±20.0% error band, which are much better and accurate estimations compared to those obtained by the existing flow boiling models for R717 refrigerant.

A New Correlation of Heat Transfer Coefficients for Flow Boiling in Serrated Channels

Abstract Compact plate-fin heat exchangers with serrated channels have been widely used in a variety of industrial systems. However, few correlations for flow boiling heat transfer in serrated channels are available in the literature, and their prediction accuracy needs to be improved. This paper presents a database containing 1184 experimental data points of saturated flow boiling heat transfer in serrated channels, which is compiled from six sources covered by eight published articles involving four fluids. The parameter range it covers is the hydraulic diameters from 1.19 to 5.15 mm, mass fluxes from 12.5 to 210 kg/(m2 s), heat fluxes from 6 to 83.4 kWm2, saturation pressures from 101.3 to 800 kPa, and vapor qualities from 0 to 0.96. Based on the database, nine existing correlations of flow boiling heat transfer coefficient (HTC) developed for serrated channels were evaluated. There are only three having the mean absolute deviation (MAD) less than 100% against the database, among which the best one has an MAD of 26.0%. A new HTC correlation for flow boiling in serrated channels is developed, which has an MAD of 13.7% and predicts 78.7% of the database within ± 20%, far better than the best existing one.

Unsteady phenomena in saturated flow boiling heat transfer – An experimental study on oscillating refrigerant mass flux

The present work pertains to experimental studies on the unsteady phenomena in the saturated flow boiling of R407C stemming from the oscillatory refrigerant flow rate with the triangle shape in the horizontal slender annular channel. Attention is mainly paid to examine the effects of different parameters, including mean mass flux, amplitude and period of the oscillating mass flux, saturation temperature of R407C, input thermal flux, and gap size on the boiling diagrams and heat transfer coefficients. Firstly, the steady-state saturated flow boiling is studied as baseline cases. It was concluded that beyond the onset of nucleate boiling region, the mass flux of refrigerant has little influences on the boiling diagrams, which indicates that the fully developed nucleate boiling is the major mechanism. The saturated flow boiling heat transfer coefficient is enhanced as the gap size is reduced. Then, the experiment focuses on the temporal changes in the wall temperature Tw and the heat transfer coefficient hr stemming from oscillatory flow conditions. When the mass flux is oscillated periodically with the triangle shape, the Tw and hr are also oscillated temporally and enhanced with increasing in either the amplitude or frequency of oscillating mass flux. At higher input thermal flux, Tw decreases with the decreasing mass flux, which has opposite tendency compared to the single-phase convection with lower thermal flux. For intermediate exerted thermal flux, there is a negligible oscillation in the Tw and hr for most cases; the amplitudes of oscillations are lower than 0.2 °C. Besides, the significant oscillations in the wall temperature and heat transfer coefficient are noted the case with large period of the oscillating mass flux.

Experimental study on saturated flow boiling heat transfer of R1234yf in a horizontal 2.01 mm tube under hypergravity

Experiments on R1234yf flow boiling in a horizontal 2.01 mm copper tube under hypergravity are conducted to investigate the effect of gravity on two-phase flow boiling heat transfer coefficient (HTC). The experimental range of parameters is gravity levels of 1–3.16 g, mass fluxes of 365 and 570 kg m−2 s−1, saturation pressures of 0.62 and 0.70 MPa, heat fluxes of 47.6 and 97.5 kW m−2, and vapor qualities up to 0.985. Based on the experimental data, the effects of gravity, quality, heat flux, mass flux, and saturation pressure on the HTCs were analyzed. The results show that the HTCs increase with increasing gravity levels for the qualities up to around 0.7, and the gravity effects become indistinct and inconsistent when the quality is high (x > 0.8). The trends of the HTC variation with quality and the effects of the heat flux, mass flux and saturation pressure on the HTCs are similar under different gravity levels. When x < 0.6, the nucleate flow boiling mechanism dominates with the HTCs varying little with quality, and the HTCs increase significantly with increasing heat flux and negligibly with increasing mass flux and pressure. The critical heat fluxes occur when x > 0.7 or higher, and they occur earlier when the gravity level is higher. The comparison of the experimental data with existing saturated flow boiling HTCs for normal gravity shows that the Fang (2013b) correlation for R134a performs best with a mean absolute deviation (MAD), and that all of the top four correlations in prediction accuracy under-predict the experimental HTCs, which is consistent with the experimental results that hypergravity enhances flow boiling heat transfer.

Heat Transfer Coefficient, Pressure Gradient, and Flow Patterns of R1234yf Evaporating in Microchannel Tube

Abstract This paper presents the heat transfer coefficient, pressure gradient, and flow pattern of R1234yf in a microchannel tube. Both heat transfer coefficient and pressure gradient are presented against real saturation pressure, while flow pattern captures at the exit of data points are presented in the same plot. The experiment was conducted on a 24-port microchannel tube with an average hydraulic diameter of 0.643 mm. The experiment covers mass flux from 100 to 200 kg m−2s−1, heat flux from 0 to 6 kW m−2, vapor quality from 0 to 1, and inlet saturation temperature from 10 to 30 °C. Comparing the correlations to the HTC measurements at very low quality (about 0.1), Gorenflo, D., and Kenning, D. (2010, Pool Boiling, in: VDI Heat Atlas, 2nd ed, Springer, pp. 757–788) agree with the results. As vapor quality increases, pressure gradient increases. The adiabatic pressure gradient is a strong function of mass flux and saturation pressure (temperature). Flow patterns of R1234yf are also affected by mass flux and saturation pressure. The heat transfer coefficient is a strong function of mass flux and heat flux. The saturation temperature has a smaller effect on HTC in the condition range (10 – 30 °C). Under the test range, the accelerating pressure drop is insignificant compared to friction. Comparing to the results, Mishima, K., and Hibiki, T. (1996, “Some Characteristics of Air-Water Two-Phase Flow in Small Diameter Vertical Tubes,” Int. J. Multiph. Flow, 22(4), pp. 703–712) and Muller-Steinhagen, H., and Heck, K. (1986, “A Simple Friction Pressure Drop Correlation for Two-Phase Flow in Pipes,” Accessed March 1, 2018)., 20, pp. 297–308.) have small mean absolute error (MAE) to predict local pressure gradient. For the heat transfer coefficient, Sun, L., and Mishima, K. (2009, “An Evaluation of Prediction Methods for Saturated Flow Boiling Heat Transfer in Mini-Channels,” Int. J. Heat Mass Transf, 52(23–24), pp. 5323–5329) and Gungor, K. E., and Winterton, R. H. S. (1986, “A General Correlation for Flow Boiling in Tubes and Annuli,” Int. J. Heat Mass Transf, 29(3), pp. 351–358) have an MAE less than 30%.

Convective boiling heat transfer under microgravity and hypergravity conditions

The present paper concerns an experimental investigation of the gravitational effects on subcooled and saturated flow boiling heat transfer in a vertical 3.75 mm diameter aluminum tube, using perfluorohexane as working fluid. Experimental results obtained during parabolic flights are compared with data gathered in the same test facility for normal gravity. Results were obtained for mass velocities of 133, 252, 377 and 428 kg/m2s, heat fluxes up to 106 kW/m2 and vapor qualities up to 0.28. The assessments of prediction methods from literature for flow boiling heat transfer proposed for normal gravitational conditions were evaluated through comparisons of calculated and experimental results. In general, for either a mass velocity of 428 kg/m2s or a vapor quality lower than -0.2, the gravitational effects on the heat transfer coefficient were found as negligible. For lower mass velocities and saturated flow boiling, higher heat transfer coefficients were observed under hypergravity conditions. This behavior was associated to the fact that higher gravitational forces favor bubbles detachment. The method of Kanizawa et al. [1] provided reasonable predictions of the saturated flow boiling results under microgravity and hyper gravity conditions, predicting 100% of the data within an error band of ±30%.

An artificial neural network model to predict mini/micro-channels saturated flow boiling heat transfer coefficient based on universal consolidated data

Flow boiling in mini/micro channels is a very effective technique for meeting the high dissipating requirements of thermal management systems. However, accurate prediction of heat transfer coefficients remains an elusive task because of the complex fluid and thermal behavior in these two-phase systems. In this study, a machine learning based approach for predictingheat transfer for saturated flow boiling in mini/micro channels is proposed. A consolidated database of 16953 data points for flow boiling heat transfer in mini/micro-channels is amassed from 50 sources that includes 16 working fluids, reduced pressures of 0.0046 – 0.77, hydraulic diameters of 0.15mm – 6.5mm, mass velocities of 19 < G < 1608kg/m2s, liquid-only Reynolds numbers of 27 – 55270 and flow qualities of 0 – 1. An Artificial Neural Network (ANN) model is developed based on the universal consolidated database that was split into training data and test data, and used to predict the saturated flow boiling heat transfer coefficients. An optimization is conducted and ANN model architecture is selected which consists of dimensionless input parameters: Bd, Bo, Co, Frg, Frgo, Frf, Frfo, Prg, Prf, Reg, Rego, Ref, Refo, Sug, Suf, Weg, Wego, Wef, and Wefo, and hidden layers (75,70,60,50,30,20,10) that predicts the test data with an MAE of 14.3%. The ANN model is superior to universal correlations for saturated flow boiling heat transfer at predicting the test data, even predicting individual databases with high accuracy. The robustness of the ANN model was tested by excluding databases from the training datasets altogether and utilized to predict these excluded databases. The ANN model did extremely well when a working fluid data was included in the training dataset, and poorly when a working fluid data was excluded from training dataset. The use of a universal ANN model utilizing a consolidated database can become an extremely useful tool when it comes to predicting heat transfer coefficients for saturated flow boiling in mini/micro channels.

Investigation of flow boiling heat transfer and pressure drop of R134a in a rectangular channel with wavy fin

The saturated flow boiling heat transfer and pressure drop studies of R134a were experimentally investigated in a rectangular channel with wavy fin. Experiments were performed at mass flux range 30–50 kg m−2 s−1, heat flux range 11–18 kW m−2 and quality 0.26–0.8. The experimental data were obtained in a brazed test section. In preliminary step, single phase experiments were conducted to find out the j and f data of the wavy fin. In second step, two-phase flow boiling experiments were conducted to estimate the heat transfer and frictional coefficient based on experimental data. The trends of heat transfer and pressure drop with respect to mass flux, heat flux and quality were studied. Two-phase local boiling heat transfer coefficient is correlated in terms of Reynolds number factor F, and Martinelli parameter X. Pressure drop is correlated in terms of two-phase frictional multiplier, ϕf and Martinelli parameter, X.

Saturated flow boiling heat transfer: review and assessment of prediction methods

This paper presents a review of the correlations for saturated flow boiling heat transfer coefficients. Fifty correlations are systematically reviewed, which fall into seven categories. An experimental database for saturated flow boiling heat transfer was compiled from 67 sources. It contains 10,932 data points and covers 19 fluids, including eight pure halogenated refrigerants (R134a, R22, R123, R1234yf, R1234ze(E), R152a, R245fa, and R32), five refrigerant mixtures (R404A, R407C, R410A, R417A, and R507), four inorganic compounds (CO2, ammonia, water, and nitrogen), and two hydrocarbons (R290 and R600a). The parameter range of the database covers hydraulic diameters of 0.137–21 mm, mass fluxes of 20–1500 kg m−2 s−1, heat fluxes of 1.99–201 kW m−2, qualities of 0.001–0.999, and reduced pressures of 0.005–0.61. Fifty correlations of saturated flow boiling heat transfer coefficients are evaluated with the database, and the detail analysis of the evaluation results is performed. The work provides a guide to choosing a proper correlation for a given application and is helpful for understanding prediction methods of saturated flow boiling heat transfer coefficients.