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.

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 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.

A Flow Boiling Heat Transfer Investigation of FC-72 in a Microtube Using Liquid Crystal Thermography

2006 ◽  
Vol 129 (8) ◽  
pp. 977-987 ◽  
Author(s):  
R. Muwanga ◽  
I. Hassan
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Wall Temperature ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Test Facility ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Liquid Crystal Thermography

This paper presents experimental measurements of boiling heat transfer in a 1.067 mm inner diameter tube, using liquid crystal thermography for wall temperature measurement. The study was motivated by the two-phase microchannel pumped cooling loop, a recent technology proposed for thermal management of tomorrow's high-end electronics. The working fluid was FC-72, which is a dielectric coolant and measurements were obtained in a closed loop test facility. A unique flow boiling onset was observed whereby a large wall temperature gradient travels along the tube. During flow boiling conditions, wall temperature fluctuations have been observed. The use of a thermographic technique has added insight into the flow boiling characteristics and acts as a partial flow visualization method. Local heat transfer coefficients are presented and compared with correlations for both macro- and microchannels. The heat transfer coefficient is found to be influenced by the heat flux at a lower mass flux but only mildly at a higher mass flux.

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.

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.

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.

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.

1987 Max Jakob Memorial Award Lecture: Dynamics and Stability of Thin Heated Liquid Films

1990 ◽  
Vol 112 (3) ◽  
pp. 538-546 ◽  
Author(s):  
S. G. Bankoff
Keyword(s):  
Heat Transfer ◽  
Film Cooling ◽  
Heated Surface ◽  
Nucleate Boiling ◽  
Liquid Films ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Molecular Forces ◽  
Memorial Award ◽  
Film Heat Transfer

This review covers the dynamics and tendency toward rupture of thin evaporating liquid films on a heated surface. Very large heat transfer coefficients can be obtained. The applications include various boiling heat transfer and film cooling devices. A relatively new area for study is heat transfer through ultrathin films, which are less than 100 nm in thickness, and hence subject to van der Waals and other long-range molecular forces. Some recent work employing lubrication theory to obtain an evolution equation for the growth of a surface wave is described. Earlier phenomenological work is briefly discussed, as well as the connection between forced-convection subcooled nucleate boiling and thin-film heat transfer.

Nucleate Boiling and Critical Heat Flux From Protruded Chip Arrays During Flow Boiling

1993 ◽  
Vol 115 (1) ◽  
pp. 78-88 ◽  
Author(s):  
C. O. Gersey ◽  
I. Mudawar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Single Phase ◽  
Liquid Velocity ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Subcooled Flow

The effects of chip protrusion on the forced-convection boiling and critical heat flux (CHF) of a dielectric coolant (FC-72) were investigated. The multi-chip module used in the present study featured a linear array of nine, 10 mm x 10 mm, simulated microelectronic chips which protruded 1 mm into a 20-mm wide side of a rectangular flow channel. Experiments were performed in vertical up flow with 5-mm and 2-mm channel gap thicknesses. For each configuration, the velocity and subcooling of the liquid were varied from 13 to 400 cm/s and 3 to 36° C, respectively. The nucleate boiling regime was not affected by changes in velocity and subcooling, and critical heat flux generally increased with increases in either velocity or subcooling. Higher single-phase heat transfer coefficients and higher CHF values were measured for the protruded chips compared to similar flush-mounted chips. However, adjusting the data for the increased surface area and the increased liquid velocity above the chip caused by the protruding chips yielded a closer agreement between the protruded and flush-mounted results. Even with the velocity and area adjustments, the most upstream protruded chip had higher single-phase heat transfer coefficients and CHF values for high velocity and/or highly-subcooled flow as compared the downstream protruded chips. The results show that, except for the most upstream chip, the performances of protruded chips are very similar to those of flush-mounted chips.

Boiling Incipience in Narrow Channels

2000 ◽  
Author(s):  
M. S. Lakshminarasimhan ◽  
D. K. Hollingsworth ◽  
Larry C. Witte
Keyword(s):  
Flow Boiling ◽  
Heated Surface ◽  
Transition Process ◽  
Nucleate Boiling ◽  
Nucleation Theory ◽  
Hysteresis Phenomenon ◽  
Transfer Coefficients ◽  
Narrow Channels ◽  
Liquid Crystal Thermography ◽  
Boiling Incipience

Abstract Experiments were performed to investigate nucleate flow boiling and incipience in a flow channel, 1 mm high × 20 mm wide × 357 mm long, vertical, with one wall heated uniformly and others approximately adiabatic. Subcooled R-11 flowed upward through the channel; the mass flux varied from 60 to 4586 kg/(m2s). The inlet subcooling varied from 3.0 to 15.3 °C, and the inlet pressure ranged up to 0.20 MPa. Liquid crystal thermography was used to measure distributions of surface temperature from which the heat transfer coefficients on the heated surface were calculated. Observations of the boiling incipience superheat excursion and the hysteresis phenomenon are presented and discussed. In laminar flow, a boiling front was observed that clearly separated the region cooled by single-phase convection from the region experiencing nucleate boiling. A prediction for the wall temperature and heat flux at boiling incipience based on nucleation theory compared favorably with the data. An incipience turning angle was defined to describe the transition process from the point of incipience to fully developed nucleate boiling. Fully developed saturated nucleate boiling was correlated well by Kandlikar’s technique.

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