Cross Flow Boiling in Micro-Pin Fin Heat Sinks

2007 ◽  
Author(s):  
Santosh Krishnamurthy ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Cross Flow ◽  
Flow Patterns ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Convective Boiling ◽  
Surface Heat Fluxes ◽  
Pin Fins

Flow boiling of water across a bank of circular staggered micro pin fins, 250 μm long and 100 μm diameter with pitch-to-diameter ratio of 1.5, was experimentally studied for mass fluxes ranging from 346 kg/m2s to 794 kg/m2s and surface heat fluxes ranging from 20 W/cm2 to 350 W/cm2. The local two-phase heat transfer coefficients were measured using thermistors located along the flow path of the channel. The flow was visualized and classified as vapor slug and annular flow patterns. Based on the observed flow patterns, the dominant heat transfer mechanism during boiling process was assumed to be convective boiling.

Reduced Pressure Boiling Heat Transfer in Rectangular Microchannels With Interconnected Reentrant Cavities

2005 ◽  
Vol 127 (10) ◽  
pp. 1106-1114 ◽  
Author(s):  
Ali Koşar ◽  
Chih-Jung Kuo ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Convective Boiling ◽  
Reduced Pressure ◽  
Exit Pressure ◽  
Mass Fluxes ◽  
Mechanism Transition ◽  
Two Phase Heat Transfer

Boiling flow of deionized water through 227μm hydraulic diameter microchannels with 7.5μm wide interconnected reentrant cavities at 47 kPa exit pressure has been investigated. Average two-phase heat transfer coefficients have been obtained over effective heat fluxes ranging from 28 to 445W∕cm2 and mass fluxes from 41 to 302kg∕m2s. A map is developed that divides the data into two regions where the heat transfer mechanisms are nucleation or convective boiling dominant. The map is compared to similar atmospheric exit pressure data developed in a previous study. A boiling mechanism transition criterion based on the Reynolds number and the Kandlikar k1 number is proposed.

Numerical Simulation of Forced Convective Boiling in a Microchannel

2018 ◽  
Vol 10 (4) ◽  
Author(s):  
Yun Whan Na ◽  
J. N. Chung
Keyword(s):  
Numerical Simulation ◽  
Two Phase Flow ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Simulation Method ◽  
Flow Patterns ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Two Phase ◽  
Convective Boiling

Forced convective flow boiling in a single microchannel with different channel heights was studied through a numerical simulation method to investigate bubble dynamics, two-phase flow patterns, and boiling heat transfer. The momentum and energy equations were solved using a finite volume (FV) numerical method, while the liquid–vapor interface of a bubble is captured using the volume of fluid (VOF) technique. The effects of different constant wall heat fluxes and different channel heights on the boiling mechanisms were investigated. The effects of liquid velocity on the bubble departure diameter were also analyzed. The predicted bubble shapes and distribution profiles together with two-phase flow patterns are also provided.

Flow Boiling in Mini and Microchannels

2004 ◽  
Author(s):  
M. Cortina Di´az ◽  
H. Boye ◽  
I. Hapke ◽  
J. Schmidt ◽  
Y. Staate ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Outer Wall ◽  
Local Heat ◽  
Constant Heat Flux ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Convective Boiling ◽  
Inconel 600

Flow boiling heat transfer characteristics of water and hydrocarbons in mini and microchannels are experimentally studied. Two different test section geometries are employed; a circular channel with a hydraulic diameter of 1500 μm, and rectangular channels with height values of 300–700 μm and a width of 10mm. In both facilities the fluid flows upwards and the test sections, made of the nickel alloy Inconel 600, are directly electrically heated. Thus the evaporation takes place under the defined boundary condition of constant heat flux. Mass fluxes between 25 and 350 kg/(m2s) and heat fluxes from 20 to 350 kW/m2 at an inlet pressure of 0.3 MPa are examined. Infrared thermography is applied to scan the outer wall temperatures. These allow the identification of different boiling regions, boiling mechanisms and the determination of the local heat transfer coefficients. Measurements are carried out in initial, saturated and post-dryout boiling regions. The experimental results in the region of saturated boiling are compared with available correlations and with a physically founded model developed for convective boiling.

Flow Boiling in Microchannels

2005 ◽  
Author(s):  
Kathleen H. Peters ◽  
Francis A. Kulacki
Keyword(s):  
Flow Boiling ◽  
Heat Fluxes ◽  
Nickel Plate ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Convective Boiling ◽  
Data Set ◽  
Heat Transfer Coefficients ◽  
Micro Channels ◽  
Constant Wall Heat Flux

Experiments are reported on convective boiling of water in a system of parallel micro-channels with a constant wall heat flux and highly sub-cooled inlet flow. The test section comprises a nickel plate containing ∼388 micro-channels along the center-plane with a mean hydraulic diameter of 145 μm with and a mean separation of 35 μm. The data set spans wall heat fluxes from 94 to 152 kW/m2, 8 < G < 24 kg/m2-s, and 2 < Re < 40. These parameters produce Weber, capillary and boiling numbers one to two orders of magnitude below those of the current published database. Overall heat transfer coefficients in flow boiling are estimated in the range 65 to 325 kW/m2-K. The present experiments more nearly emulate conditions for practical micro-channel heat exchangers compared to those of reported studies using artificially induced two-phase flows and either one or several micro-channels.

Evaporation of Ammonia in a Smooth Horizontal Tube: Heat Transfer Measurements and Predictions

1999 ◽  
Vol 121 (1) ◽  
pp. 89-101 ◽  
Author(s):  
O. Zu¨rcher ◽  
J. R. Thome ◽  
D. Favrat
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Two Phase

Experimental test results for flow boiling of pure ammonia inside horizontal tubes were obtained for a plain stainless steel tube. Tests were run at a nominal saturation temperature of 4°C, nine mass velocities from 20–140 kg/m2 s, vapor qualities from 1–99 percent and heat fluxes from 5–58 kW/m2. Two-phase flow observations showed that the current test data covered the following regimes: fully stratified, stratified-wavy, intermittent, annular, and annular with partial dryout. The Kattan-Thome-Favrat flow boiling model accurately predicted the local heat transfer coefficients measured in all these flow regimes with only two small modifications to their flow map (to extend its application to G < 100 kg/m2 s). Their flow boiling model was also successfully compared to the earlier ammonia flow boiling data of Chaddock and Buzzard (1986). The Gungor-Winterton (1987) correlation instead gave very poor accuracy for ammonia.

Flow Boiling of R134a in Circular Microtubes—Part I: Study of Heat Transfer Characteristics

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Saptarshi Basu ◽  
Sidy Ndao ◽  
Gregory J. Michna ◽  
Yoav Peles ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Heat Fluxes ◽  
Average Error ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Two Phase Heat Transfer

An experimental study of two-phase heat transfer coefficients was carried out using R134a in uniformly heated horizontal circular microtubes with diameters from 0.50 mm to 1.60 mm over a range of mass fluxes, heat fluxes, saturation pressures, and vapor qualities. Heat transfer coefficients increased with increasing heat flux and saturation pressure but were independent of mass flux. The effects of vapor quality on heat transfer coefficients were less pronounced and varied depending on the quality. The data were compared with seven flow boiling correlations. None of the correlations predicted the experimental data very well, although they generally predicted the correct trends within limits of experimental error. A correlation was developed, which predicted the heat transfer coefficients with a mean average error of 29%. 80% of the data points were within the ±30% error limit.

Flow Boiling in a Microchannel Heat Sink

2005 ◽  
Author(s):  
Dong Liu ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Transfer Model ◽  
Microchannel Heat Sink ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Convective Boiling ◽  
Saturated Boiling

Flow boiling heat transfer in a microchannel heat sink is experimentally investigated. The microchannels considered are 275 μm wide and 636 μm deep, and the experiments are conducted at inlet water temperatures in the range of 66 to 95°C and mass fluxes of 341 to 936 kg/m2s. Convective boiling heat transfer coefficients are measured and compared to predictions from correlations proposed for larger channels. While an existing correlation was found to provide satisfactory prediction of the heat transfer coefficient in subcooled boiling in the microchannels, saturated boiling was not well predicted by the correlations for macrochannels. A new heat transfer model is developed to correlate the data in the saturated boiling regime. Good agreement with the experimental measurements indicates that this correlation is suitable for use in the design of two-phase microchannel heat sinks.

Upflow Boiling and Condensation in Rectangular Minichannels

2003 ◽  
Author(s):  
V. V. Kuznetsov ◽  
S. V. Dimov ◽  
P. A. Houghton ◽  
A. S. Shamirzaev ◽  
S. Sunder
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Section ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients

When boiling or condensation occurs inside very small and non-circular channels, capillary forces influence two-phase flow patterns, which in turn determine heat transfer coefficients and pressure drop. A better understanding of the underlying phenomena would be beneficial from the perspective of optimizing the design of compact evaporators and condensers. The thrust of this study was to understand the nature of up-flow boiling and condensation heat transfer in channels with a small gap. It consisted of two parts. The first part included observation of two-phase flow patterns with refrigerant R21 in a test section containing plain fins. The shape of the channels formed between fins was close to rectangular. The test section was placed in a closed refrigerant loop, and it was fabricated with a transparent wall to allow observation of the flow. An electrically heated coil was used to introduce liquid and vapor at the needed quality into the test section. Regimes of slug, froth, annular and cell flow patterns were recognized and the areas of flow pattern were determined. The second part included up-flow boiling and condensation heat transfer measurement with refrigerant R21 in a set of vertical mini-channels consisting of plain fins. An aluminum fin pad was bonded to two dividing aluminum sheets by dip brazing. Heat was supplied to the test section from a thermoelectric module, which utilized the Peltier effect. A thick copper plate was placed between the dividing sheet on each side of the fin passage and the respective Peltier module to establish a uniform wall temperature. Heat transfer coefficient measurements were done under forced flow conditions. Data are obtained for mass flow rates of 30 and 50 kg/m2s under both boiling and condensation modes with wall superheats ranging from 1 to 5K. The dependence of heat transfer coefficient from wall superheat was not observed both for boiling and condensing modes. It shows the primary role of evaporation from thin films in a confined space when the mass flux is small. At low vapor quality the boiling heat transfer coefficients are considerably higher than that for condensation. A high heat flux in ultra thin liquid film area near the channel corner or in the vicinity of liquid-vapor-solid contact line (after the film rupture) supports the high total heat transfer coefficient in evaporation mode. In contrast with evaporation mode, at upflow condensation mode the heat transfer coefficient is strongly dependent on vapor quality. At plug flow regime the vapor velocity determines the condensing heat transfer.

Characteristics of Two-Phase Flow Heat Transfer of R-22 and R-290 in Horizontal Circular Small Tube

2016 ◽  
Vol 819 ◽  
pp. 181-185
Author(s):  
Agus Sunjarianto Pamitran ◽  
Ulfi Khabibah ◽  
Normah Mohd-Ghazali ◽  
Robiah Ahmad ◽  
Kiyoshi Saito
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Experimental Result ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
Small Tube

Hydrocarbon refrigerants have been widely used to replace HFCs. As hydrocarbon, R-290 has no ODP (Ozone Depletion Potential) and negligible GWP (Global Warming Potential). This paper presents flow boiling heat transfer in small tube with R-290 and R-22. The test tube has inner diameter of 7.6 mm and length of 1.07 m. In order to determine the heat transfer coefficient, experiments were carried out for heat fluxes ranging from 10 to 25 kW/m2, mass fluxes ranging from 204 to 628 kg/m2s, and saturation temperatures ranging from 1.87 to 11.9o C. The study analyzed the heat transfer through the local heat transfer coefficient along the flow under the variation of these different parameters. In comparison with R-22, R-290 provides higher heat transfer coefficients. In the prediction of the heat transfer coefficients of R-22 and R-290, the correlation of Shah (1982) and Choi et.al. (2009) best fitted the present experimental result, respectively.

Forced Convective Boiling of Refrigerant HCFC123 in a Mini-Tube

2010 ◽  
Author(s):  
Koichi Araga ◽  
Keisuke Okamoto ◽  
Keiji Murata
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Pool Boiling ◽  
Constant Heat Flux ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Convective Boiling ◽  
Frictional Pressure Drop ◽  
Heat Transfer Coefficients

This paper presents an experimental investigation of the forced convective boiling of refrigerant HCFC123 in a mini-tube. The inner diameters of the test tubes, D, were 0.51 mm and 0.30 mm. First, two-phase frictional pressure drops were measured under adiabatic conditions and compared with the correlations for conventional tubes. The frictional pressure drop data were lower than the correlation for conventional tubes. However, the data were qualitatively in accord with those for conventional tubes and were correlated in the form φL2−1/Xtt. Next, heat transfer coefficients were measured under the conditions of constant heat flux and compared with those for conventional tubes and for pool boiling. The heat transfer characteristics for mini-tubes were different from those for conventional tubes and quite complicated. The heat transfer coefficients for D = 0.51 mm increased with heat flux but were almost independent of mass flux. Although the heat transfer coefficients were higher than those for a conventional tube with D = 10.3 mm and for pool boiling in the low quality region, they decreased gradually with increasing quality. The heat transfer coefficients for D = 0.30 mm were higher than those for D = 0.51 mm and were almost independent of both mass flux and heat flux.

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