Flow Boiling in an In-Line Set of Short Narrow Gap Channels

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
D. Janssen ◽  
J. M. Dixon ◽  
S. J. Young ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Flow Boiling ◽  
Coefficient Of Performance ◽  
Narrow Gap ◽  
Transfer Coefficients ◽  
Data Set ◽  
Heat Transfer Fluids ◽  
Heat Transfer Coefficients ◽  
O 10

Heat transfer coefficients in a set of three symmetrically heated narrow gap channels arranged in line are reported at power densities of 1 kW/cm3 and wall heat flux of 3–40 W/cm2. This configuration emulates an electronics system wherein power dissipation can vary across an array of processors, memory chips, or other components. Three pairs of parallel ceramic resistance heaters in a nearly adiabatic housing form the flow passage, and length-to-gap ratios for each pair of heaters are 34 at a gap of 0.36 mm. Novec™ 7200 and 7300 are used as the heat transfer fluids. Nonuniform longitudinal power distributions are designed with the center heater pair at 1.5X and 2X the level of the first and third heater pairs. At all levels of inlet subcooling, single-phase heat transfer dominates over the first two heater pairs, while the third pair exhibits significant increases because of the presence of flow boiling. Reynolds numbers range from 250 to 1200, Weber numbers from 2 to 14, and boiling numbers from O(10−4) to O(10−3). Exit quality can reach 30% in some cases. Overall heat transfer coefficients of 40 kW/m2K are obtained. Pressure drops for both Novec™ heat transfer fluids are approximately equal at a given mass flux, and a high ratio of heat transfer to pumping power (coefficient of performance (COP)) is obtained. With a mass flux of 250 kg/m2s, heater temperatures can exceed 95 °C, which is the acceptable limit of steady operation for contemporary high performance electronics. Thus, an optimal operating point involving power density, power distribution, mass flux, and inlet subcooling is suggested by the data set for this benchmark multiheater configuration.

Flow Boiling in an In Line Set of Short Narrow Gap Channels

2013 ◽  
Author(s):  
D. D. Janssen ◽  
J. M. Dixon ◽  
S. J. Young ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Flow Boiling ◽  
Coefficient Of Performance ◽  
Narrow Gap ◽  
Transfer Coefficients ◽  
Data Set ◽  
Heat Transfer Fluids ◽  
Heat Transfer Coefficients ◽  
O 10

Heat transfer coefficients in a set of three symmetrically heated narrow gap channels arranged in line are reported at watt densities of 1 kW/cm3. This experimental configuration emulates an electronics system wherein power dissipation can vary across an array of processors, memory chips, or other components. Three pairs of parallel ceramic resistance heaters in a nearly adiabatic housing form the flow passage, and length-to-gap ratios for each pair of heaters is 34.1 at a gap of 0.36 mm. Novec™ 7200 and 7300 are used as the heat transfer fluids. Non-uniform longitudinal power distributions are designed with the center heater pair at 1.5X and 2X the level of the first and third heater pairs. At all levels of inlet sub-cooling, single-phase heat transfer dominates heat transfer over the first two heater pairs, while the third pair exhibits significant increases because of the presence of flow boiling. Reynolds numbers range from 250 to 1200, Weber numbers from 2 to 15, and boiling numbers from O(10−4) to O(10−3). Exit quality can reach 30 percent in some cases. Overall heat transfer coefficients of 40 kW/m2K are obtained. Pressure drops for both Novec™ heat transfer fluids are approximately equal at a given mass flux, and a high coefficient of performance is obtained. With a mass flux of 250 kg/m2s, heater temperatures can exceed 95 °C, which is the acceptable limit of steady operation for contemporary high performance electronics. Thus, an optimal operating point involving power density, power distribution, mass flux, and inlet sub-cooling is suggested by the data set for this benchmark multi-heater configuration.

Flow Boiling in a Short Narrow Gap Channel

2013 ◽  
Author(s):  
D. D. Janssen ◽  
J. M. Dixon ◽  
S. J. Young ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Small Scale ◽  
Narrow Gap ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
O 10

Heat transfer coefficients in sub-cooled flow boiling in symmetrically heated narrow gap channels are reported at power densities of 1 kW/cm3 and greater. A pair of parallel ceramic resistance heaters in a nearly adiabatic housing forms the flow passage with length-to-gap ratios of 16:1 and 34:1. Water, Novec™ 7200 and 7300 are used as the heat transfer fluids at a mass flux of 100 to 1000 kg/m2s. Reynolds numbers range from ∼200 to ∼5600, Weber numbers range from ∼0.75 to ∼173, and boiling numbers from O(10−4) to O(10−2). Flow regimes span single-phase convection to nucleate flow boiling depending on mass flux and inlet sub-cooling, and exit quality can reach 40% in some cases. Results include overall two-phase heat transfer coefficients, wall temperature, exit quality and coefficient of performance. The initiation of flow boiling demonstrates that mean heater temperatures can be maintained below 95 °C over a wide range of power density and up to and exceeding 1 kW/cm3. A super position principle is suggested as an analytical framework to estimate exit quality and heat transfer coefficients. Highly favorable coefficients of performance across the data set indicate that the pumping power penalty within the heated zone is very small. Thus convective boiling in which the mechanism is nucleate boiling appears to hold the greatest potential to increase heat transfer coefficients, especially in small scale, inter-chip cooling strategies.

Flow Boiling Heat Transfer, Pressure Drop, and Flow Pattern for CO2 in a 3.5mm Horizontal Smooth Tube

2009 ◽  
Vol 131 (9) ◽  
Author(s):  
Chang Yong Park ◽  
Pega Hrnjak
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flow Pattern ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

Abstract C O 2 flow boiling heat transfer coefficients and pressure drop in a 3.5mm horizontal smooth tube are presented. Also, flow patterns were visualized and studied at adiabatic conditions in a 3mm glass tube located immediately after a heat transfer section. Heat was applied by a secondary fluid through two brass half cylinders to the test section tubes. This research was performed at evaporation temperatures of −15°C and −30°C, mass fluxes of 200kg∕m2s and 400kg∕m2s, and heat flux from 5kW∕m2 to 15kW∕m2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients indicated the nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes at a mass flux of 200kg∕m2s. However, enhanced convective boiling contribution was observed at 400kg∕m2s. Surface conditions for two different tubes were investigated with a profilometer, atomic force microscope, and scanning electron microscope images, and their possible effects on heat transfer are discussed. Pressure drop, measured at adiabatic conditions, increased with the increase of mass flux and quality, and with the decrease of evaporation temperature. The measured heat transfer coefficients and pressure drop were compared with general correlations. Some of these correlations showed relatively good agreements with measured values. Visualized flow patterns were compared with two flow pattern maps and the comparison showed that the flow pattern maps need improvement in the transition regions from intermittent to annular flow.

Two-Phase Pressure Drop and Boiling Heat Transfer in a Single Horizontal Microchannel

2006 ◽  
Author(s):  
Cheol Huh ◽  
Moo Hwan Kim
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Local Flow ◽  
Heat Transfer Coefficients ◽  
Phase Pressure

With a single microchannel and a series of microheaters made with MEMS technique, two-phase pressure drop and local flow boiling heat transfer were investigated using deionized water in a single horizontal rectangular microchannel. The test microchannel has a hydraulic diameter of 100 μm and length of 40 mm. A real time observation of the flow patterns with simultaneous measurement are made possible. Tests are performed for mass fluxes of 90, 169, and 267 kg/m2s and heat fluxes of from 100 to 600 kW/m2. The experimental local flow boiling heat transfer coefficients and two-phase frictional pressure gradient are evaluated and the effects of heat flux, mass flux, and vapor qualities on flow boiling are studied. Both the evaluated experimental data are compared with existing correlations. The experimental heat transfer coefficients are nearly independent on mass flux and the vapor quality. Most of all correlations do not provide reliable heat transfer coefficients predictions with vapor quality and prediction accuracy. As for two-phase pressure drop, the measured pressure drop increases with the mass flux and heat flux. Most of all existing correlations of two-phase frictional pressure gradient do not predict the experimental data except some limited conditions.

Low Mass Quality Flow Boiling in Microtubes at High Mass Fluxes

2011 ◽  
Vol 3 (4) ◽  
Author(s):  
Mehmed Rafet Özdemir ◽  
Alihan Kaya ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
High Mass ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Wall Superheat

In this article, an experimental study on boiling heat transfer and fluid flow in microtubes at high mass fluxes is presented. De-ionized water flow was investigated over a broad range of mass flux (1000 kg/m2s–7500 kg/m2s) in microtubes with inner diameters of  ∼ 250 μm and ∼685 μm. The reason for using two different capillary diameters was to investigate the size effect on flow boiling. De-ionized water was used as working fluid, and the test section was heated by Joule heating. Heat transfer coefficients and qualities were deduced from local temperature measurements. It was found that high heat removal rates could be achieved at high flow rates under subcooled boiling conditions. It was also observed that heat transfer coefficients increased with mass flux, whereas they decreased with local quality and heat flux. Moreover, experimental heat flux data were compared with partial boiling correlations and fully developed boiling correlations. It was observed that at low wall superheat values, there was only a small inconsistency between the experimental data and the conventional partial boiling prediction method of Bergles, while the subcooled and low quality fully developed boiling heat transfer correlation of Kandlikar could fairly predict experimental results at high wall superheat values.

Flow Boiling Heat Transfer of CO2 at Low Temperatures in a Horizontal Smooth Tube

2005 ◽  
Vol 127 (12) ◽  
pp. 1305-1312 ◽  
Author(s):  
Chang Yong Park ◽  
Pega S. Hrnjak
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Smooth Tube ◽  
High Mass ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

Flow boiling heat transfer coefficients of CO2 are measured in a horizontal smooth tube with inner diameter 6.1mm. The test tube is heated by a secondary fluid maintaining constant wall temperature conditions. Heat transfer coefficients are measured at evaporation temperatures of −15 and −30°C, mass flux from 100to400kg∕m2s, and heat flux from 5to15kW∕m2 for qualities (vapor mass fractions) ranging from 0.1 to 0.8. The characteristics of CO2 flow boiling are explained by CO2 properties and flow patterns. The measured CO2 heat transfer coefficients are compared to other published data. Experiments with R22 were also conducted in the same system and the results show that the heat transfer coefficients for CO2 are 40 to 150% higher than for R22 at −15°C and low mass flux of 200kg∕m2s mostly due to the characteristics of CO2 nucleate boiling. The presented CO2 heat transfer coefficients indicate the reduction of heat transfer coefficient as mass flux increases at low quality regions and also show that dryout does not occur until the high quality region of 0.8, for mass fluxes of 200 and 400kg∕m2s. The Gungor and Winterton correlation gives a relatively good agreement with measured data; however it deviates more at lower evaporation temperature and high mass flux conditions.

Fully Developed Nucleate Boiling in Narrow Vertical Channels

2004 ◽  
Vol 127 (8) ◽  
pp. 941-944 ◽  
Author(s):  
M. S. Lakshminarasimhan ◽  
Q. Lu ◽  
Y. Chin ◽  
D. K. Hollingsworth ◽  
Larry C. Witte
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Mass Flux ◽  
Flow Boiling ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
Vertical Flow ◽  
Transfer Coefficients ◽  
Liquid Crystal Thermography ◽  
Heat Transfer Coefficients

Experiments were performed to investigate nucleate flow boiling and incipience in a vertical flow channel, 20mmwide×357mmlong, with one wall heated uniformly and others approximately adiabatic. Three channel spacings, 2, 1 and 0.5mm, were investigated. Initially subcooled R-11 flowed upward through the channel; the mass flux varied from 60to4586kg∕(m2s), and the inlet pressure ranged up to 0.20MPa. Liquid crystal thermography was used to measure distributions of surface temperature from which the heat transfer coefficients on the heated surface were calculated. Fully developed saturated nucleate boiling was correlated well by a modification of Kandlikar’s technique.

CO2 Flow Boiling Heat Transfer and Flow Pattern at Low Temperatures in Horizontal Smooth Tubes

2006 ◽  
Author(s):  
C. Y. Park ◽  
P. S. Hrnjak
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Mass Flux ◽  
Low Temperatures ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Boiling Heat Transfer

In this study, flow boiling heat transfer coefficients and flow patterns CO2 are examined in horizontal smooth tubes with inner diameter 6.1 and 3.5 mm at low temperatures. In order to measure the heat transfer coefficients, the test tube was heated by two brass pieces maintained a higher temperature than CO2 by a secondary fluid. Flow visualization was carried out at adiabatic conditions. This research was performed at evaporation temperatures of -15 and -30 °C, mass flux from 100 to 400 kg/m2 s, and heat flux from 5 to 15 kW/m2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients for the 6.1 and 3.5 mm tubes had nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes. However, enhanced convective boiling contribution was presented for the 3.5 mm tube at 400 kg/m2 s. The presented heat transfer coefficients indicated the reduction of heat transfer coefficient as mass flux increased at low quality regions and also showed that dryout did not occur until the high quality region of 0.8, for mass fluxes of 200 and 400 kg/m2 s. The measured heat transfer coefficients were compared with predicted values with some general correlations to predict flow boiling heat transfer coefficients. The pictures of visualized flow patterns were presented and the flow patterns were compared with a flow pattern map. They were used to explain the relation between the flow boiling heat transfer coefficient and vapor quality at the mass flux of 100 kg/m2 s.

Heat Transfer Characteristics of Flow Boiling of R134a in Uniformly Heated Horizontal Circular Microtubes

2010 ◽  
Author(s):  
Saptarshi Basu ◽  
Sidy Ndao ◽  
Gregory J. Michna ◽  
Yoav Peles ◽  
Michael K. Jensen
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Mass Flux ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Nucleate Boiling ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

An experimental study of two-phase heat transfer coefficients was carried out using R134a in uniformly heated horizontal circular microtubes with diameters of 0.50 mm and 1.60 mm. The effects of mass flux, heat flux, saturation pressure, and vapor quality on heat transfer coefficients were studied. The flow parameters investigated were as follows: exit pressures of 490, 670, 890, and 1160 kPa; mass fluxes of 300–1500 kg/m2s; heat fluxes of 0–350 kW/m2; inlet subcooling of 5, 20, and 40 °C; and exit qualities of 0 to 1.0. The parametric trends presented in the study are consistent with published literature. Heat transfer coefficients increased with increasing heat flux and saturation pressure while they were independent of variations in mass flux. Vapor quality had a negligible influence on heat transfer coefficients. For the conditions studied, the trends indicated that the dominant heat transfer mechanism was nucleate boiling. The experimental data was compared to three microchannel correlations — the Lazarek-Black, the Kandlikar, and the Tran Correlations. None of the correlations predicted the experimental data very well, although they all predicted the correct trend within limits of experimental error.

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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