This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,...This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,mass fluxes between 198 and 305 kg/m^(2)s,and heat fluxes from 9.77 to 20.18 kW/m^(2),yielding 99 sets of local heat transfer coefficient data.The results show that increasing heat flux and mass flux enhances the heat transfer coefficient,although the rate of enhancement decreases with increasing vapor quality.Conversely,higher saturation temperatures slightly reduce the heat transfer coefficient.Additionally,the experimental findings reveal discrepancies in the accuracy of existing pressure drop and heat transfer coefficient prediction models under the studied conditions.This study recommends using the Kimand Mudawar correlation to predict pressure gradients within the tested range,with aMean Error(ME)of−5.24%observed in this study.For heat transfer coefficients,the Cooper and Kandlikar correlations are recommended,achieving a Mean Absolute Error(MAE)of approximately 22%.This research provides value for performance prediction and parameter selection of micro-channel technology in broader application scenarios within heating,ventilation and air-conditioning fields.展开更多
In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 k...In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 kg/(m2 s),saturation temperatures of 293,298,and 303 K,and inlet sub-cooling of 5,10,and 15 K.The analysis of the experimental results provides the following conclusions:a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall;conversely,an elevated saturation temperature results in a reduced amount of superheat at the boiling inception wall.Furthermore,an increase in sub-cooling and saturation temperature will enhance heat transfer efficiency.The wall temperature is mostly influenced by variations in saturation temperature and is minimally related to changes in mass flux and subcooling degree.An increase in mass flux results in a greater pressure drop attributed to heightened frictional pressure loss.The variation in pressure drop with respect to sub-cooling is minimal,while an increased saturation temperature correlates with a reduced pressure drop due to the formation of smaller bubbles and lowered frictional pressure loss at high saturation pressures.This study thoroughly examines and summarizes the effects of mass flow rate,saturation temperature,and subcooling on the flow-boiling heat transfer and pressure drop characteristics of R1234yf.Furthermore,the new correlation has 93.42%of the predicted values fall within a 15%mean absolute error,exhibiting a mean absolute error of 5.75%.It provides a superior method for predicting the flow-boiling heat transfer coefficients of R1234yf in the heat sink of parallel microchannels compared to existing correlations.展开更多
Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.Ho...Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.However,the continuous rise in power density of electronic components imposesmore stringent requirements on the heat transfer capability of microchannel flow boiling.HFE-7100,a dielectric coolant with favorable thermophysical properties,has become a focal point of research for enhancing flow boiling performance in open microchannels.The flow boiling heat transfer performance ofHFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology.Based on visualization results,a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micronano structured open microchannels(MNSOMC)and smooth-surface open microchannels(SSOMC),to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels.The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure.Moreover,bubbles in the channel tended to coalesce along the flow direction,forming elongated slug bubbles with high aspect ratios,which enabled efficient thin film evaporation in conjunction with intense nucleate boiling,thereby significantly enhancing flow boiling heat transfer.Under the experimental conditions of this study,the maximum enhancements in the heat transfer coefficient(HTC)and critical heat flux(CHF)of HFE-7100 inMNSOMC were 33.4%and 133.1%,respectively,with the CHF reaching up to 1542.3 kW⋅m^(−2).Furthermore,due to the superior wettability and capillary wicking capability of the micro-nano composite structures,the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.展开更多
Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of th...Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of the geometric and system parameters on heat transfer characteristics in helically coiled tubes are investigated by collecting large amounts of experimental data and analyzing the heat transfer mechanisms. The existing correlations are divided into two categories,and they are calculated with the experimental data.The Dn factor is introduced to take into account the effect of a complex geometrical structure on flow boiling heat transfer.A new correlation is developed for predicting the flow boiling heat transfer coefficients in the helically coiled tubes,which is validated by the experimental data of R134a flow boiling heat transfer in them;and the average relative error and root mean square error of the new correlation are calculated.The results show that the new correlation agrees well with the experimental data,indicating that the new correlation can be used for predicting flow boiling heat transfer characteristics in the helically coiled tubes.展开更多
This paper proposed a new experimental rig of testing flow boiling heat transfer of refrigerant and lubricant oil mixture. The quantity of oil in the test section can be controlled and regulated conveniently and accur...This paper proposed a new experimental rig of testing flow boiling heat transfer of refrigerant and lubricant oil mixture. The quantity of oil in the test section can be controlled and regulated conveniently and accurately by connecting separate lubricant oil circuit with test section in parallel. It was built up by retrofitting a multiple air-conditioner and installing three oil-separators in serials at the compressor outlet. And so the lubricant oil in the discharged refrigerant gas of compressor can be removed completely.The refrigerant flow rate through test section can be bypassed by the by-path circuit of indoor unit.This experimental rig has advantages such as on-line and continuous oil injection, short time of obtaining stability, flexible operation, simple control, which lead to high efficiency in the research of flow boiling heat transfer of refrigerant and lubricant oil mixture.展开更多
Fouling of heat transfer surfaces during subcooled flow boiling is a frequent engineering problem in process industries. It has been generally observed that the deposits in such industrial systems consist mainly of ca...Fouling of heat transfer surfaces during subcooled flow boiling is a frequent engineering problem in process industries. It has been generally observed that the deposits in such industrial systems consist mainly of calcium carbonate （CaCO3）, which has inverse solubility characteristics. This investigation focused on the mechanism to control deposition and the morphology of crystalline deposits. A series of experiments were carried out at different surface and bulk temperatures, fluid velocities and salt ion concentrations. It is shown that the deposition rate is controlled by different mechanism in the range of experimental parameters, depending on salt ion concentration. At higher ion concentration, the fouling rate increases linearly with surface temperature and the effect of flow velocity on deposition rate is quite strong, suggesting that mass diffusion controls the fouling process. On the contrary, at lower ion concentration, the fouling rate increases exponentially with surface temperature and is independent of the velocity, illustrating that surface reaction controls the fouling process. By analysis of the morphology of scale, two types of crystal （calcite and aragonite） are formed. The lower the temperature and ion concentration, the longer the induction period and the higher the percentage of calcite nreciDitated.展开更多
The surfactant additive octadecylamine (ODA) was used to enhance the flow boiling heat transfer of water in vertical copper tube, and the effects of the aqueous solution properties, mass fraction of ODA, mass flux and...The surfactant additive octadecylamine (ODA) was used to enhance the flow boiling heat transfer of water in vertical copper tube, and the effects of the aqueous solution properties, mass fraction of ODA, mass flux and heat flux etc. on flow boiling heat transfer were investigated. In order to analyze the mechanism of enhancement on boiling heat transfer with ODA, the copper surface was detected by XPS, and the diagram of binding energy was obtained. The results show that ODA can be adsorbed on the surface of the copper wall, and affects the properties of the heating surfaces and enhances the flow boiling heat transfer of water. Only in low heat flux and in a suitable range of concentration, can ODA aqueous solution enhance flow boiling heat transfer, and the suitable mass fraction of ODA is in the range of 1×10 -5 5×10 -5 . In addition, compared with water, ODA aqueous solution does not increase the flow drag under the same experimental conditions.展开更多
Flow boiling heat transfer of nitrogen at high subcritical pressure conditions in a single vertical mini-channel with the diameter of 2.0 mm was experimentally investigated.The tested mass flux varied from 530 to 830 ...Flow boiling heat transfer of nitrogen at high subcritical pressure conditions in a single vertical mini-channel with the diameter of 2.0 mm was experimentally investigated.The tested mass flux varied from 530 to 830 kg/(m^2·s),the inlet pressure ranged from 630 to 1080 kPa,and the heat flux ranged from 0 to 223.2 kW/m^2.Effects of the mass flux and the inlet pressure on the nitrogen boiling curve were examined.Results showed that within the limited test conditions,the merging of three boiling curves indicates the dominance of nucleate boiling and the inlet pressure has a positive enhancement on heat transfer performance.Three heat transfer trends were identified with increasing heat flux.At low heat fluxes,the heat transfer coefficient increases first and then decreases with vapour quality.At intermediate heat fluxes,the heat transfer coefficient versus the vapour quality presents an inverted"U"shape.At high heat fluxes,a double valley shape was observed and the partial dry-out in intermittent flow and annular flow helps to interpret the phenomenon.The increasing inlet pressure increases the heat transfer coefficient over a wide range of vapour quality until the partial dry-out inception.The lower surface tension and lower latent heat of evaporation enhance the nucleate boiling for higher inlet pressure.A modified experimental correlation(mean absolute error(MAE)=19.3%)was proposed on the basis of the Tran correlation considering both the nucleate boiling and the partial dry-out heat transfer mechanism.展开更多
Experiments on subcooled flow boiling have been conducted using water in a rectangular flow channel.Similar to the coolant channel in internal combustion engines(IC engines),the flow channel in this experiment was asy...Experiments on subcooled flow boiling have been conducted using water in a rectangular flow channel.Similar to the coolant channel in internal combustion engines(IC engines),the flow channel in this experiment was asymmetrically heated.Bubble images were captured using a high speed camera from the side view of the channel.The experimental conditions in terms of bulk temperature,bulk velocity,pressure and heat flux ranged from 65°C–75°C,0.25 m/s–0.75 m/s,1–1.7 bar and 490 kW/m2–700 kW/m2,respectively.On the basis of these tests,a statistical analysis of the bubble size has been conducted considering a population of 1400 samples.It has been found that the mean Sauter bubble diameter increases with the decrease of subcooling,bulk velocity,pressure and increased heat flux.A modified correlation has been finally proposed to predict the mean Sauter bubble diameter under subcooled flow boiling conditions upstream of the onset of significant void,which shows good accuracy with the experimental results.展开更多
This paper reports the influence of heat transfer surface treatment on the formation of calcium sulphate de-posit during flow boiling heat transfer. The surface of several test heaters was treated by surface modificat...This paper reports the influence of heat transfer surface treatment on the formation of calcium sulphate de-posit during flow boiling heat transfer. The surface of several test heaters was treated by surface modification techniques, such as dynamic mixing magnetron sputtering [DLC (diamond-like carbon), DLC-F (diamond-like carbon-fluorine) and AC (amorphous carbon)] and polishing to reduce surface energy. The results showed that heat transfer surface with low surface energy experienced significant reduction of formation of CaSO4 deposit. (1) Magnetron sputtering stainless steel heat transfer surface with DLC, DLC-F and plasma arc sputtering with AC did not change the surface roughness, but they reduced surface energy and improved heat transfer coefficient, so hindered CaSO4 deposit formation significantly. The DLC-F surface performed better than the DLC surface. (2) Surface energy played an important pole in improving heat transfer coefficient. The less the surface energy the more significant the heat transfer coefficient improved with other ex-perimental conditions identical. (3) The polished surface improved the roughness of the heater, but owing to the high sur-face energy it was not better than the DLC-F surface for a long-term consideration on improving the heat transfer coeffi-cient.展开更多
Al2O3/R141b ＋ Span-80 nanorefrigerant for 0.05 wt.% to 0.4 wt.% is prepared by ultrasonic vibration to investigate the influence of nanoparticle concentrations on flow boiling heat transfer of Al2O3/R141b ＋ Span-80...Al2O3/R141b ＋ Span-80 nanorefrigerant for 0.05 wt.% to 0.4 wt.% is prepared by ultrasonic vibration to investigate the influence of nanoparticle concentrations on flow boiling heat transfer of Al2O3/R141b ＋ Span-80 in micro heat exchanger by direct metal laser sintering. Experimental results show that nanoparticle concentrations have significantly impact on heat transfer coefficients by homogeneity test of variances according to mathematical statistics. The heat transfer performance of Al2O3/R141b ＋ Span-80 nanorefrigerant is enhanced after adding nanoparticles in the pure refrigerant R141b. The heat transfer coefficients of 0.05 wt.%, 0.1 wt.%, 0.2 wt.%, 0.3 wt.% and 0.4 wt.% Al2O3/R141 b ＋ Span-80 nanorefrigerant respectively increase by 55.0% 72.0%, 53.0% 42.3% and 39.9% compared with the pure refrigerant R141b. The particle fluxes from viscosity gradient, non-uniform shear rate and Brownian motion cause particles to migrate in fluid especially in the process of flow boiling. This migration motion enhances heat transfer between nanoparticles and fluid. Therefore, the heat transfer performance of nanofluid is enhanced. It is important to note that the heat transfer coefficients nonlinearly increase with nanoparticle concentrations increasing. The heat transfer coefficients reach its maximum value at the mass concentration of 0.1% and then it decreases slightly. There exists an optimal mass concentration corresponding to the best heat transfer enhancement. The reason for the above phenomenon is attributed to nanoparticles deposition on the minichannel wall by Scanning Electron Microscopy observation. The channel surface wettability increases during the flow boiling experiment in the mass concentration range from 0.2 wt.% to 0.4 wt.%. The channel surface with wettability increasing needs more energy to produce a bubble. Therefore, the heat transfer coefficients decrease with nanopartide concentrations in the range from 0.2 wt.% to 0.4 wt.%. In addition, a new correlation has been proposed by fitting the experimental data considering the influence of mass concentrations on the heat trans- fer performance. The new correlation can effectively predict the heat transfer coefficient.展开更多
The drag reducing effect of polymer additive aqueous solution was investigated in flow boiling, and the polymer additives were two kinds of polyacrylamide (PAM) with relative molecular mass about 2.56×10 6 and 8....The drag reducing effect of polymer additive aqueous solution was investigated in flow boiling, and the polymer additives were two kinds of polyacrylamide (PAM) with relative molecular mass about 2.56×10 6 and 8.55×10 6. The frictional pressure drop was calculated according to the measured total pressure drop. The results show that the flow drag of flow boiling is reduced by adding a small amount of PAM to water when heat flux is in the range of 15.1 kW·m -2 to 47.0 kW·m -2 , when the mass fraction of PAM is higher than 2.0×10 -5 , the drag reducing effect is obvious. Drag reducing effect of PAM, whose relative molecular mass is 8.55×10 6, is slightly better than that of 2.56×10 6 at the same mass fraction, and the greater the flow rate of the additive solution, the better the effect of the drag reduction.展开更多
The purpose of this study is to conduct the dryout point and heat transfer correlation for subcooled boiling flow in narrow annuli. First, the dryout point of subcooled flow boiling of water was measured in narrow ann...The purpose of this study is to conduct the dryout point and heat transfer correlation for subcooled boiling flow in narrow annuli. First, the dryout point of subcooled flow boiling of water was measured in narrow annular channels under the working condition of pressure ranging from 0.1 to 0.3 MPa and low mass flow rate from 6 to 60 kgm^-2 s^-1. Experimental test channels were annular and heated bilaterally with the channel gap of lmm and 1.5mm, and heated length of 1500mm.The location of the dryout was observed and measured by experiment with investigating the various system parameter effects on dryout point, and the results show that the location of dryout point is basically stable and repeating and the heat transfer coefficient increased with heat flux, mass flux and pressure, however, decreases with the gap size. Next, new correlations of CHF and critical vapor quality for narrow annular channels was proposed and calculation results shown a good agreement with the experimental data.展开更多
Flow boiling in microchannels with porous walls has received extensive attention in recent years. Compared with the emphasis on heat transfer, there is a lack of research on the effect of the porous wall structures on...Flow boiling in microchannels with porous walls has received extensive attention in recent years. Compared with the emphasis on heat transfer, there is a lack of research on the effect of the porous wall structures on the pressure drop characteristics. In this study, systematic experiments are performed to measure the pressure drop of water-vapor two-phase flow in five microchannels with copper foam fins, which consist of nine or six channels and fins of copper foam. The porosities of the foam fins range from0.78 to 0.82 and ratios of fin width to channel width range from 0.5 to 2. The channels are approximately 0.5 or 1 mm in width and 1 mm in height. Both adiabatic and flow boiling experiments are conducted with water at mass fluxes ranging from 66 to 407 kg/(m^(2)s). In the adiabatic experiments, the average quality in channels is between 0.017 and 0.846. In the flow boiling experiments, the outlet quality of channels is between 0.040 and 0.863. Slug flow, churn flow, annular flow, and wispy-annular flow are observed in adiabatic experiments. A two-phase frictional pressure drop correlation based on the Lockhart-Martinelli model is developed for copper foam fin microchannels by introducing the effects of the mass flux, porosity, ratio of fin width to channel width, and heating condition step by step. The mean absolute percentage errors of the new correlation are 7.53% for 325data points under adiabatic conditions and 5.51% for 268 data points under flow boiling conditions, respectively. This work provides insight into the correlations of frictional pressure drop in microchannels with porous walls.展开更多
With the advancement of micro machining technology,the high-heat-flux removal from miniature electronic devices and components has become an attractive topic.Flow boiling in micro-channels is an optimal form of heat t...With the advancement of micro machining technology,the high-heat-flux removal from miniature electronic devices and components has become an attractive topic.Flow boiling in micro-channels is an optimal form of heat transfer and has been widely employed in high-heat-flux cooling applications.This comprehensively-reviewed article focused on the available recent literatures of experimental investigation regarding the flow boiling heat transfer and unstable behaviors of the fluid with lower boiling point in micro-channels.The thermal-fluid characteristics and potential heat transfer mechanisms of low-boiling-point fluids flow boiling in different narrow passages were summarized and discussed.The literatures regarding the pressure drop and occurrence of the unstable phenomena existing in two-phase flow boiling process were also discussed.The emphasis was given to the heat transfer enhancement methods as well as instability elimination,and various methods such as modification of surface and channel flow geometries were considered.Some future researches in the field of micro-scale flow boiling were suggested.展开更多
Microchannel flow boiling heat transfer has the advantages of strong heat dissipation capacity,good temperature uniformity,and compact structure.It is an excellent way to thermally manage electronic devices,but when t...Microchannel flow boiling heat transfer has the advantages of strong heat dissipation capacity,good temperature uniformity,and compact structure.It is an excellent way to thermally manage electronic devices,but when the heat flux exceeds CHF(Critical Heat Flux),the heat transfer performance deteriorates as the working fluid dries out.Non-azeotropic mixtures have the potential to effectively delay or avoid dry-out during the boiling process due to their temperature slide characteristics which causes the mass transfer resistance.To understand the influence of non-azeotropic mixtures on microchannel flow boiling,using the phase-change microchannel heat sink as the research object,the experiments on the flow boiling heat transfer performance of R245fa/R134a mixtures under different working conditions were carried out,and the characteristics of flow boiling heat transfer were obtained under the different working conditions,and comparison was developed with those of pure substance R245fa.The results demonstrated that a small amount of low-boiling-point components in the high-boiling-point working fluid inhibited boiling heat transfer to some extent,and lowered the average heat transfer coefficient under the non-dryout condition slightly lower than that of the pure substance;however,it also effectively delayed the onset of local dry-out and prevented significant deterioration in thermal transfer performance under the lower mass flow rate and higher heat flux,which could enhance the heat sink's stability.展开更多
Flow boiling in microchannels has attracted wide attention due to its excellent heat transfer capability,but flow boiling instability is a huge challenge limiting its application.Instability can lead to a series of pr...Flow boiling in microchannels has attracted wide attention due to its excellent heat transfer capability,but flow boiling instability is a huge challenge limiting its application.Instability can lead to a series of problems,such as uneven flow distribution,temperature and pressure drop oscillations.This work proposes a novel asymmetric check microvalve(ACMV)structure,exhibiting high ratio of resistance between the reverse and forward flow.The results show the reverse pressure drop of the ACMV structure is 2.06 times that of the forward pressure drop,and the forward flow resistance of the ACMV structure is 16%smaller than that of the conventional inlet restrictor.In addition,bubble dynamics of an isolated bubble in the generated channel under dual outlet condition was numerically investigated.It is found that the bubble grows symmetrically in the rectangular channel upstream and downstream.The distance of bubble movement downstream in the microchannel with ACMV is three times that of the microchannel with inlet restrictor.The microchannel with ACMV can suppress the backflow of isolated bubble better than microchannel with inlet restrictor.Moreover,the growth of the bubble downstream extends the effective evaporation domain,which contributes to the enhanced bubble growth rate.The ACMV is expected to be a potential replacement for the conventional inlet restrictor,which provides a novel and efficient solution for future heat dissipation from high power devices.展开更多
This research explores the characteristics of boiling in inclined pipes,a domain of great importance in engineering.Employing an experimental visualization technique,the boiling dynamics of deionizedwater are examined...This research explores the characteristics of boiling in inclined pipes,a domain of great importance in engineering.Employing an experimental visualization technique,the boiling dynamics of deionizedwater are examined at varying inclination angles,paying special attention to the emerging flow patterns.The findings demonstrate that the inclination angle significantly impacts flow pattern transitions within the 0°to 90°range.As the heat flux rises,bubbles form in the liquid.The liquid’s inertia extends the bubble-wall contact time,thereby delaying the onset of bulk bubble flow.Beyond a 90°inclination,however,the patterning behavior is more influenced by the fluid velocity.At low speeds,incomplete pipe filling results in a large liquid plug hindering flow,while high speeds lead to full pipe filling.In general,gravity,inertia,buoyancy forces,and capillary forces are themain influential factors in the considered problem.However,an analysis of the heat transfer coefficient and boiling curve for different inclination angles reveals that the observed variations are essentially due to corresponding changes in the flow pattern.Finally,an optimal mass flux and inclination angle,able to minimize total entropy generation and improve heat transfer efficiency,are determined by means of an entropy generation analysis.展开更多
To solve the heat dissipation problem of electronic devices with high heat flux hotspots,a diamond microchannel heat sink consisting of 37 parallel triangular microchannels with channel lengths of 45 mm and hydraulic ...To solve the heat dissipation problem of electronic devices with high heat flux hotspots,a diamond microchannel heat sink consisting of 37 parallel triangular microchannels with channel lengths of 45 mm and hydraulic diameters of 280|im was designed.The flow boiling heat transfer characteristics of ammonia in the microchannels were investigated under high heat fluxes of 473.9-1000.4 W/cm^2.Saturated flow boiling experiments with saturation temperatures of 25℃,30℃,and 35℃ and mass fluxes of 98-1200 kg/m^2s were conducted,as well as subcooled flow boiling with inlet subcooling of 5℃ as a comparison.The temperature and pressure drop measurements were analyzed.The main conclusions below can be drawn.(1)At a given heat flux,the heat source temperature first decreased and then increased with the mass flux,and there existed an optimum mass flux to optimize the cooling performance of the heat sink.(2)The heat transfer performance under the saturated inlet condition was obviously better than that under the subcooled inlet condition.(3)A larger saturation temperature leaded to weakening of both the heat transfer capacity and the stability of the microchannel heat sink.Notably,with the high heat diffusion ability of the diamond substrate and the great heat transfer capacity of ammonia flow boiling in microchannels,the heat sink can achieve a heat removal capacity of up to 1000.4 W/cm^2.展开更多
The present study reports an experimental evaluation of heat transfer characteristic of R134a flow boiling in mi- cro-channel heat sink. The heat sink is composed of 30 parallel rectangular micro-channels with cross-s...The present study reports an experimental evaluation of heat transfer characteristic of R134a flow boiling in mi- cro-channel heat sink. The heat sink is composed of 30 parallel rectangular micro-channels with cross-sectional dimensions of 500μm width and depth, as well as total length 30ram. Experiments were conducted with heat flux up to 80.212 W/cm2, mass velocity ranging from 373.33 to 1244.44 kg/m2s, vapor quality ranging from 0.06 to 0.9. The wall temperature of heat sink heated could be controlled at around 50℃. Heat transfer coefficient could be up to 180 kW/mZK. Two dominating flow patterns were observed by analyzing boiling curves. The heat trans- fer characteristics of nucleate boiling and convective boiling were presented in the study. Revised correlations of R134a flow boiling in micro-channel heat sink were carded out with the consideration of nucleate boiling and convective boiling mechanisms.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.52306026)the State Key Laboratory of Air-Conditioning Equipment and System Energy Conservation Open Project(Project No.ACSKL2021KT01)The APC was covered by the Special Innovation Project Fund of the the State Key Laboratory of Air-Conditioning Equipment and System Energy Conservation Open Project(Project No.ACSKL2021KT01).
文摘This study investigates the flow boiling heat transfer coefficient and pressure gradient of refrigerant R410A inmicro-channel flat tubes.Experiments were conducted at saturation temperatures ranging from 25℃ to 30℃,mass fluxes between 198 and 305 kg/m^(2)s,and heat fluxes from 9.77 to 20.18 kW/m^(2),yielding 99 sets of local heat transfer coefficient data.The results show that increasing heat flux and mass flux enhances the heat transfer coefficient,although the rate of enhancement decreases with increasing vapor quality.Conversely,higher saturation temperatures slightly reduce the heat transfer coefficient.Additionally,the experimental findings reveal discrepancies in the accuracy of existing pressure drop and heat transfer coefficient prediction models under the studied conditions.This study recommends using the Kimand Mudawar correlation to predict pressure gradients within the tested range,with aMean Error(ME)of−5.24%observed in this study.For heat transfer coefficients,the Cooper and Kandlikar correlations are recommended,achieving a Mean Absolute Error(MAE)of approximately 22%.This research provides value for performance prediction and parameter selection of micro-channel technology in broader application scenarios within heating,ventilation and air-conditioning fields.
基金supported by the Beijing Municipal Science&Technology Commission(Z231100006123010).
文摘In this study,the flow boiling characteristics of R1234yf in parallel microchannels were experimentally investigated.The experiments were conducted with heat flux from 0 to 550 kW/m^(2),mass flux of 434,727,and 1015 kg/(m2 s),saturation temperatures of 293,298,and 303 K,and inlet sub-cooling of 5,10,and 15 K.The analysis of the experimental results provides the following conclusions:a reduced mass flux and lower subcooling correspond to a diminished degree of superheat at the boiling inception wall;conversely,an elevated saturation temperature results in a reduced amount of superheat at the boiling inception wall.Furthermore,an increase in sub-cooling and saturation temperature will enhance heat transfer efficiency.The wall temperature is mostly influenced by variations in saturation temperature and is minimally related to changes in mass flux and subcooling degree.An increase in mass flux results in a greater pressure drop attributed to heightened frictional pressure loss.The variation in pressure drop with respect to sub-cooling is minimal,while an increased saturation temperature correlates with a reduced pressure drop due to the formation of smaller bubbles and lowered frictional pressure loss at high saturation pressures.This study thoroughly examines and summarizes the effects of mass flow rate,saturation temperature,and subcooling on the flow-boiling heat transfer and pressure drop characteristics of R1234yf.Furthermore,the new correlation has 93.42%of the predicted values fall within a 15%mean absolute error,exhibiting a mean absolute error of 5.75%.It provides a superior method for predicting the flow-boiling heat transfer coefficients of R1234yf in the heat sink of parallel microchannels compared to existing correlations.
基金funded by the National Natural Science Foundation of China(Grant No.52276047)the Open Fund of NationalKey Laboratory of SpacecraftThermal Control(Grant No.NKLST-JJ-202401011)the Beijing Municipal Science&Technology Commission(Grant No.Z231100006123010).
文摘Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.However,the continuous rise in power density of electronic components imposesmore stringent requirements on the heat transfer capability of microchannel flow boiling.HFE-7100,a dielectric coolant with favorable thermophysical properties,has become a focal point of research for enhancing flow boiling performance in open microchannels.The flow boiling heat transfer performance ofHFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology.Based on visualization results,a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micronano structured open microchannels(MNSOMC)and smooth-surface open microchannels(SSOMC),to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels.The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure.Moreover,bubbles in the channel tended to coalesce along the flow direction,forming elongated slug bubbles with high aspect ratios,which enabled efficient thin film evaporation in conjunction with intense nucleate boiling,thereby significantly enhancing flow boiling heat transfer.Under the experimental conditions of this study,the maximum enhancements in the heat transfer coefficient(HTC)and critical heat flux(CHF)of HFE-7100 inMNSOMC were 33.4%and 133.1%,respectively,with the CHF reaching up to 1542.3 kW⋅m^(−2).Furthermore,due to the superior wettability and capillary wicking capability of the micro-nano composite structures,the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.
基金The National Natural Science Foundation of China(No.50776055,51076084)
文摘Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of the geometric and system parameters on heat transfer characteristics in helically coiled tubes are investigated by collecting large amounts of experimental data and analyzing the heat transfer mechanisms. The existing correlations are divided into two categories,and they are calculated with the experimental data.The Dn factor is introduced to take into account the effect of a complex geometrical structure on flow boiling heat transfer.A new correlation is developed for predicting the flow boiling heat transfer coefficients in the helically coiled tubes,which is validated by the experimental data of R134a flow boiling heat transfer in them;and the average relative error and root mean square error of the new correlation are calculated.The results show that the new correlation agrees well with the experimental data,indicating that the new correlation can be used for predicting flow boiling heat transfer characteristics in the helically coiled tubes.
文摘This paper proposed a new experimental rig of testing flow boiling heat transfer of refrigerant and lubricant oil mixture. The quantity of oil in the test section can be controlled and regulated conveniently and accurately by connecting separate lubricant oil circuit with test section in parallel. It was built up by retrofitting a multiple air-conditioner and installing three oil-separators in serials at the compressor outlet. And so the lubricant oil in the discharged refrigerant gas of compressor can be removed completely.The refrigerant flow rate through test section can be bypassed by the by-path circuit of indoor unit.This experimental rig has advantages such as on-line and continuous oil injection, short time of obtaining stability, flexible operation, simple control, which lead to high efficiency in the research of flow boiling heat transfer of refrigerant and lubricant oil mixture.
基金Supported by the Special Funds for Major State Basic Research Projects of China (G2000026304)
文摘Fouling of heat transfer surfaces during subcooled flow boiling is a frequent engineering problem in process industries. It has been generally observed that the deposits in such industrial systems consist mainly of calcium carbonate （CaCO3）, which has inverse solubility characteristics. This investigation focused on the mechanism to control deposition and the morphology of crystalline deposits. A series of experiments were carried out at different surface and bulk temperatures, fluid velocities and salt ion concentrations. It is shown that the deposition rate is controlled by different mechanism in the range of experimental parameters, depending on salt ion concentration. At higher ion concentration, the fouling rate increases linearly with surface temperature and the effect of flow velocity on deposition rate is quite strong, suggesting that mass diffusion controls the fouling process. On the contrary, at lower ion concentration, the fouling rate increases exponentially with surface temperature and is independent of the velocity, illustrating that surface reaction controls the fouling process. By analysis of the morphology of scale, two types of crystal （calcite and aragonite） are formed. The lower the temperature and ion concentration, the longer the induction period and the higher the percentage of calcite nreciDitated.
基金The Natural Science Foundation of Tianjin(No.94220)
文摘The surfactant additive octadecylamine (ODA) was used to enhance the flow boiling heat transfer of water in vertical copper tube, and the effects of the aqueous solution properties, mass fraction of ODA, mass flux and heat flux etc. on flow boiling heat transfer were investigated. In order to analyze the mechanism of enhancement on boiling heat transfer with ODA, the copper surface was detected by XPS, and the diagram of binding energy was obtained. The results show that ODA can be adsorbed on the surface of the copper wall, and affects the properties of the heating surfaces and enhances the flow boiling heat transfer of water. Only in low heat flux and in a suitable range of concentration, can ODA aqueous solution enhance flow boiling heat transfer, and the suitable mass fraction of ODA is in the range of 1×10 -5 5×10 -5 . In addition, compared with water, ODA aqueous solution does not increase the flow drag under the same experimental conditions.
基金the National Natural Science Foundation of China(No.11872373)。
文摘Flow boiling heat transfer of nitrogen at high subcritical pressure conditions in a single vertical mini-channel with the diameter of 2.0 mm was experimentally investigated.The tested mass flux varied from 530 to 830 kg/(m^2·s),the inlet pressure ranged from 630 to 1080 kPa,and the heat flux ranged from 0 to 223.2 kW/m^2.Effects of the mass flux and the inlet pressure on the nitrogen boiling curve were examined.Results showed that within the limited test conditions,the merging of three boiling curves indicates the dominance of nucleate boiling and the inlet pressure has a positive enhancement on heat transfer performance.Three heat transfer trends were identified with increasing heat flux.At low heat fluxes,the heat transfer coefficient increases first and then decreases with vapour quality.At intermediate heat fluxes,the heat transfer coefficient versus the vapour quality presents an inverted"U"shape.At high heat fluxes,a double valley shape was observed and the partial dry-out in intermittent flow and annular flow helps to interpret the phenomenon.The increasing inlet pressure increases the heat transfer coefficient over a wide range of vapour quality until the partial dry-out inception.The lower surface tension and lower latent heat of evaporation enhance the nucleate boiling for higher inlet pressure.A modified experimental correlation(mean absolute error(MAE)=19.3%)was proposed on the basis of the Tran correlation considering both the nucleate boiling and the partial dry-out heat transfer mechanism.
基金the National Natural Science Foundation of China(Grant No.51576116)the National Natural Science Foundation of Shandong Province(Grant No.ZR2019MEE041)。
文摘Experiments on subcooled flow boiling have been conducted using water in a rectangular flow channel.Similar to the coolant channel in internal combustion engines(IC engines),the flow channel in this experiment was asymmetrically heated.Bubble images were captured using a high speed camera from the side view of the channel.The experimental conditions in terms of bulk temperature,bulk velocity,pressure and heat flux ranged from 65°C–75°C,0.25 m/s–0.75 m/s,1–1.7 bar and 490 kW/m2–700 kW/m2,respectively.On the basis of these tests,a statistical analysis of the bubble size has been conducted considering a population of 1400 samples.It has been found that the mean Sauter bubble diameter increases with the decrease of subcooling,bulk velocity,pressure and increased heat flux.A modified correlation has been finally proposed to predict the mean Sauter bubble diameter under subcooled flow boiling conditions upstream of the onset of significant void,which shows good accuracy with the experimental results.
基金Supported by the Special Fund for Excellent Talents from Beijing Communist Party Organization Division, fund for Excellent Talents Reinforce Education Plan for Universities under Beijing City Administration (Z03-16).
文摘This paper reports the influence of heat transfer surface treatment on the formation of calcium sulphate de-posit during flow boiling heat transfer. The surface of several test heaters was treated by surface modification techniques, such as dynamic mixing magnetron sputtering [DLC (diamond-like carbon), DLC-F (diamond-like carbon-fluorine) and AC (amorphous carbon)] and polishing to reduce surface energy. The results showed that heat transfer surface with low surface energy experienced significant reduction of formation of CaSO4 deposit. (1) Magnetron sputtering stainless steel heat transfer surface with DLC, DLC-F and plasma arc sputtering with AC did not change the surface roughness, but they reduced surface energy and improved heat transfer coefficient, so hindered CaSO4 deposit formation significantly. The DLC-F surface performed better than the DLC surface. (2) Surface energy played an important pole in improving heat transfer coefficient. The less the surface energy the more significant the heat transfer coefficient improved with other ex-perimental conditions identical. (3) The polished surface improved the roughness of the heater, but owing to the high sur-face energy it was not better than the DLC-F surface for a long-term consideration on improving the heat transfer coeffi-cient.
基金Supported by the National Natural Science Foundation of China[21276090]
文摘Al2O3/R141b ＋ Span-80 nanorefrigerant for 0.05 wt.% to 0.4 wt.% is prepared by ultrasonic vibration to investigate the influence of nanoparticle concentrations on flow boiling heat transfer of Al2O3/R141b ＋ Span-80 in micro heat exchanger by direct metal laser sintering. Experimental results show that nanoparticle concentrations have significantly impact on heat transfer coefficients by homogeneity test of variances according to mathematical statistics. The heat transfer performance of Al2O3/R141b ＋ Span-80 nanorefrigerant is enhanced after adding nanoparticles in the pure refrigerant R141b. The heat transfer coefficients of 0.05 wt.%, 0.1 wt.%, 0.2 wt.%, 0.3 wt.% and 0.4 wt.% Al2O3/R141 b ＋ Span-80 nanorefrigerant respectively increase by 55.0% 72.0%, 53.0% 42.3% and 39.9% compared with the pure refrigerant R141b. The particle fluxes from viscosity gradient, non-uniform shear rate and Brownian motion cause particles to migrate in fluid especially in the process of flow boiling. This migration motion enhances heat transfer between nanoparticles and fluid. Therefore, the heat transfer performance of nanofluid is enhanced. It is important to note that the heat transfer coefficients nonlinearly increase with nanoparticle concentrations increasing. The heat transfer coefficients reach its maximum value at the mass concentration of 0.1% and then it decreases slightly. There exists an optimal mass concentration corresponding to the best heat transfer enhancement. The reason for the above phenomenon is attributed to nanoparticles deposition on the minichannel wall by Scanning Electron Microscopy observation. The channel surface wettability increases during the flow boiling experiment in the mass concentration range from 0.2 wt.% to 0.4 wt.%. The channel surface with wettability increasing needs more energy to produce a bubble. Therefore, the heat transfer coefficients decrease with nanopartide concentrations in the range from 0.2 wt.% to 0.4 wt.%. In addition, a new correlation has been proposed by fitting the experimental data considering the influence of mass concentrations on the heat trans- fer performance. The new correlation can effectively predict the heat transfer coefficient.
文摘The drag reducing effect of polymer additive aqueous solution was investigated in flow boiling, and the polymer additives were two kinds of polyacrylamide (PAM) with relative molecular mass about 2.56×10 6 and 8.55×10 6. The frictional pressure drop was calculated according to the measured total pressure drop. The results show that the flow drag of flow boiling is reduced by adding a small amount of PAM to water when heat flux is in the range of 15.1 kW·m -2 to 47.0 kW·m -2 , when the mass fraction of PAM is higher than 2.0×10 -5 , the drag reducing effect is obvious. Drag reducing effect of PAM, whose relative molecular mass is 8.55×10 6, is slightly better than that of 2.56×10 6 at the same mass fraction, and the greater the flow rate of the additive solution, the better the effect of the drag reduction.
基金This work is supported by the Project of National Natural Science Foundation of China （No. 50076014） and the Project of Major State Basic Research Program （No. G2000026303）.
文摘The purpose of this study is to conduct the dryout point and heat transfer correlation for subcooled boiling flow in narrow annuli. First, the dryout point of subcooled flow boiling of water was measured in narrow annular channels under the working condition of pressure ranging from 0.1 to 0.3 MPa and low mass flow rate from 6 to 60 kgm^-2 s^-1. Experimental test channels were annular and heated bilaterally with the channel gap of lmm and 1.5mm, and heated length of 1500mm.The location of the dryout was observed and measured by experiment with investigating the various system parameter effects on dryout point, and the results show that the location of dryout point is basically stable and repeating and the heat transfer coefficient increased with heat flux, mass flux and pressure, however, decreases with the gap size. Next, new correlations of CHF and critical vapor quality for narrow annular channels was proposed and calculation results shown a good agreement with the experimental data.
基金supported by the National Natural Science Foundation of China(Grant No.51876102)the Tsinghua University Initiative Scientific Research Program。
文摘Flow boiling in microchannels with porous walls has received extensive attention in recent years. Compared with the emphasis on heat transfer, there is a lack of research on the effect of the porous wall structures on the pressure drop characteristics. In this study, systematic experiments are performed to measure the pressure drop of water-vapor two-phase flow in five microchannels with copper foam fins, which consist of nine or six channels and fins of copper foam. The porosities of the foam fins range from0.78 to 0.82 and ratios of fin width to channel width range from 0.5 to 2. The channels are approximately 0.5 or 1 mm in width and 1 mm in height. Both adiabatic and flow boiling experiments are conducted with water at mass fluxes ranging from 66 to 407 kg/(m^(2)s). In the adiabatic experiments, the average quality in channels is between 0.017 and 0.846. In the flow boiling experiments, the outlet quality of channels is between 0.040 and 0.863. Slug flow, churn flow, annular flow, and wispy-annular flow are observed in adiabatic experiments. A two-phase frictional pressure drop correlation based on the Lockhart-Martinelli model is developed for copper foam fin microchannels by introducing the effects of the mass flux, porosity, ratio of fin width to channel width, and heating condition step by step. The mean absolute percentage errors of the new correlation are 7.53% for 325data points under adiabatic conditions and 5.51% for 268 data points under flow boiling conditions, respectively. This work provides insight into the correlations of frictional pressure drop in microchannels with porous walls.
基金supported by the National Natural Science Foundation of China (No.U2141219)。
文摘With the advancement of micro machining technology,the high-heat-flux removal from miniature electronic devices and components has become an attractive topic.Flow boiling in micro-channels is an optimal form of heat transfer and has been widely employed in high-heat-flux cooling applications.This comprehensively-reviewed article focused on the available recent literatures of experimental investigation regarding the flow boiling heat transfer and unstable behaviors of the fluid with lower boiling point in micro-channels.The thermal-fluid characteristics and potential heat transfer mechanisms of low-boiling-point fluids flow boiling in different narrow passages were summarized and discussed.The literatures regarding the pressure drop and occurrence of the unstable phenomena existing in two-phase flow boiling process were also discussed.The emphasis was given to the heat transfer enhancement methods as well as instability elimination,and various methods such as modification of surface and channel flow geometries were considered.Some future researches in the field of micro-scale flow boiling were suggested.
基金supported by the National Natural Science Foundation of China(No.52076185)the Natural Science Foundation of Zhejiang Province(No.LZ19E060001)the Open Project of Shanghai Key Laboratory of Multiphase Flow and Heat Transfer in Power Engineering(No.KF2019-02)。
文摘Microchannel flow boiling heat transfer has the advantages of strong heat dissipation capacity,good temperature uniformity,and compact structure.It is an excellent way to thermally manage electronic devices,but when the heat flux exceeds CHF(Critical Heat Flux),the heat transfer performance deteriorates as the working fluid dries out.Non-azeotropic mixtures have the potential to effectively delay or avoid dry-out during the boiling process due to their temperature slide characteristics which causes the mass transfer resistance.To understand the influence of non-azeotropic mixtures on microchannel flow boiling,using the phase-change microchannel heat sink as the research object,the experiments on the flow boiling heat transfer performance of R245fa/R134a mixtures under different working conditions were carried out,and the characteristics of flow boiling heat transfer were obtained under the different working conditions,and comparison was developed with those of pure substance R245fa.The results demonstrated that a small amount of low-boiling-point components in the high-boiling-point working fluid inhibited boiling heat transfer to some extent,and lowered the average heat transfer coefficient under the non-dryout condition slightly lower than that of the pure substance;however,it also effectively delayed the onset of local dry-out and prevented significant deterioration in thermal transfer performance under the lower mass flow rate and higher heat flux,which could enhance the heat sink's stability.
基金support from the National Natural Science Foundation of China with Grant No.52276070the Fundamental Research Funds for the Central Universities with Grant No.30922010903。
文摘Flow boiling in microchannels has attracted wide attention due to its excellent heat transfer capability,but flow boiling instability is a huge challenge limiting its application.Instability can lead to a series of problems,such as uneven flow distribution,temperature and pressure drop oscillations.This work proposes a novel asymmetric check microvalve(ACMV)structure,exhibiting high ratio of resistance between the reverse and forward flow.The results show the reverse pressure drop of the ACMV structure is 2.06 times that of the forward pressure drop,and the forward flow resistance of the ACMV structure is 16%smaller than that of the conventional inlet restrictor.In addition,bubble dynamics of an isolated bubble in the generated channel under dual outlet condition was numerically investigated.It is found that the bubble grows symmetrically in the rectangular channel upstream and downstream.The distance of bubble movement downstream in the microchannel with ACMV is three times that of the microchannel with inlet restrictor.The microchannel with ACMV can suppress the backflow of isolated bubble better than microchannel with inlet restrictor.Moreover,the growth of the bubble downstream extends the effective evaporation domain,which contributes to the enhanced bubble growth rate.The ACMV is expected to be a potential replacement for the conventional inlet restrictor,which provides a novel and efficient solution for future heat dissipation from high power devices.
基金supported by the National Natural Science Foundation of China(Project No.52166004)the National Key Research and Development Program of China(Project No.2022YFC3902000)the Major Science and Technology Special Project of Yunnan Province(Project Nos.202202AG050007,202202AG050002).
文摘This research explores the characteristics of boiling in inclined pipes,a domain of great importance in engineering.Employing an experimental visualization technique,the boiling dynamics of deionizedwater are examined at varying inclination angles,paying special attention to the emerging flow patterns.The findings demonstrate that the inclination angle significantly impacts flow pattern transitions within the 0°to 90°range.As the heat flux rises,bubbles form in the liquid.The liquid’s inertia extends the bubble-wall contact time,thereby delaying the onset of bulk bubble flow.Beyond a 90°inclination,however,the patterning behavior is more influenced by the fluid velocity.At low speeds,incomplete pipe filling results in a large liquid plug hindering flow,while high speeds lead to full pipe filling.In general,gravity,inertia,buoyancy forces,and capillary forces are themain influential factors in the considered problem.However,an analysis of the heat transfer coefficient and boiling curve for different inclination angles reveals that the observed variations are essentially due to corresponding changes in the flow pattern.Finally,an optimal mass flux and inclination angle,able to minimize total entropy generation and improve heat transfer efficiency,are determined by means of an entropy generation analysis.
文摘To solve the heat dissipation problem of electronic devices with high heat flux hotspots,a diamond microchannel heat sink consisting of 37 parallel triangular microchannels with channel lengths of 45 mm and hydraulic diameters of 280|im was designed.The flow boiling heat transfer characteristics of ammonia in the microchannels were investigated under high heat fluxes of 473.9-1000.4 W/cm^2.Saturated flow boiling experiments with saturation temperatures of 25℃,30℃,and 35℃ and mass fluxes of 98-1200 kg/m^2s were conducted,as well as subcooled flow boiling with inlet subcooling of 5℃ as a comparison.The temperature and pressure drop measurements were analyzed.The main conclusions below can be drawn.(1)At a given heat flux,the heat source temperature first decreased and then increased with the mass flux,and there existed an optimum mass flux to optimize the cooling performance of the heat sink.(2)The heat transfer performance under the saturated inlet condition was obviously better than that under the subcooled inlet condition.(3)A larger saturation temperature leaded to weakening of both the heat transfer capacity and the stability of the microchannel heat sink.Notably,with the high heat diffusion ability of the diamond substrate and the great heat transfer capacity of ammonia flow boiling in microchannels,the heat sink can achieve a heat removal capacity of up to 1000.4 W/cm^2.
基金supported by National Natural Science Foundation of China(No.51376019)
文摘The present study reports an experimental evaluation of heat transfer characteristic of R134a flow boiling in mi- cro-channel heat sink. The heat sink is composed of 30 parallel rectangular micro-channels with cross-sectional dimensions of 500μm width and depth, as well as total length 30ram. Experiments were conducted with heat flux up to 80.212 W/cm2, mass velocity ranging from 373.33 to 1244.44 kg/m2s, vapor quality ranging from 0.06 to 0.9. The wall temperature of heat sink heated could be controlled at around 50℃. Heat transfer coefficient could be up to 180 kW/mZK. Two dominating flow patterns were observed by analyzing boiling curves. The heat trans- fer characteristics of nucleate boiling and convective boiling were presented in the study. Revised correlations of R134a flow boiling in micro-channel heat sink were carded out with the consideration of nucleate boiling and convective boiling mechanisms.
