Effects of Dissolved Gas Content on Pool Boiling of a Highly Wetting Fluid

1995 ◽  
Vol 117 (3) ◽  
pp. 687-692 ◽  
Author(s):  
S. M. You ◽  
T. W. Simon ◽  
A. Bar-Cohen ◽  
Y. S. Hong
Keyword(s):  
Heat Transfer ◽  
Pool Boiling ◽  
Electronics Cooling ◽  
Horizontal Cylinder ◽  
Gas Content ◽  
Free Fluid ◽  
Dissolved Gas ◽  
Boiling Incipience ◽  
Wetting Fluid

Experimental results on pool boiling heat transfer from a horizontal cylinder in an electronic cooling fluid (FC-72) are presented. The effects on the boiling curve of having air dissolved in the fluid are documented, showing that fluid in the vicinity of the heating element is apparently liberated of dissolved gas during boiling. Dissolved gas was found to influence boiling incipience only with high gas concentrations (>0.005 moles/mole). For low-to-moderate concentrations, a larger superheat is required to initiate boiling and a hysteresis is observed between boiling curves taken with increasing and decreasing heat flux steps. Boiling, a very effective mode of heat transfer, is attractive for electronics cooling. The present experiment provides further documentation of the role of dissolved gas on the incipience process and shows similarities with subcooled boiling of a gas-free fluid.

Chaotic Mixing: A Sure Way for Optimal Thermal Conditions?

2010 ◽  
Author(s):  
M. F. M. Speetjens
Keyword(s):  
Heat Transfer ◽  
Thermal State ◽  
Electronics Cooling ◽  
Thermal Conditions ◽  
Laminar Flows ◽  
Chaotic Mixing ◽  
Asymptotic State ◽  
Driven Cavity ◽  
Time Periodic

Chaotic fluid mixing is generally considered to enhance fluid-wall heat transfer and thermal homogenisation in laminar flows. However, this essentially concerns the transient stage towards a fully-developed (thermally-homogeneous) asymptotic state and then specifically for high Pe´clet numbers Pe (convective heat transfer dominates). The role of chaos in the asymptotic state at lower Pe, relevant to continuously-operating compact devices as, for instance, micro-electronics cooling systems, remains largely unexplored to date. The present study seeks to gain first insight into this matter by the analysis of a representative model problem: heat transfer in the 2D time-periodic lid-driven cavity flow induced via non-adiabatic walls. The asymptotic time-periodic thermal state is investigated in terms of both the temperature field and the thermal transport routes. This combined Eulerian-Lagrangian approach enables fundamental investigation of the connection between heat transfer and chaotic mixing and its ramifications for temperature distributions and heat-transfer rates. The analysis exposes a very different role of chaos in that its effectiveness for thermal homogenisation and heat-transfer enhancement is in low-Pe asymptotic states marginal at best. Here chaos may in fact locally amplify temperature fluctuations and thus hamper instead of promote thermal homogeneity. These findings reveal that optimal thermal conditions are not always automatic with chaotic mixing and may depend on a more delicate interplay between flow and heat-transfer mechanisms.

Effect of Pressure, Subcooling, and Dissolved Gas on Pool Boiling Heat Transfer From Microporous Surfaces in FC-72

2003 ◽  
Vol 125 (1) ◽  
pp. 75-83 ◽  
Author(s):  
K. N. Rainey ◽  
S. M. You ◽  
S. Lee
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Nucleate Boiling ◽  
Gas Content ◽  
Absolute Pressure ◽  
Dissolved Gas ◽  
Test Conditions ◽  
Nucleate Boiling Heat Transfer ◽  
Surface Correlations

The present research is an experimental study of the effects of pressure, subcooling, and non-condensable gas (air) on the pool nucleate boiling heat transfer performance of a microporous enhanced and a plain (machine-roughened) reference surface. The test surfaces, 1-cm2 flat copper blocks in the horizontal, upward facing orientation, were immersed in FC-72. The test conditions included an absolute pressure range of 30–150 kPa, a liquid subcooling range of 0 (saturation) to 50 K, and both gas-saturated and pure subcooling conditions. Effects of these parameters on nucleate boiling and critical heat flux (CHF) were investigated. Results showed that, in general, the effects of pressure and subcooling on both nucleate boiling and CHF were consistent with the prevailing trends in the literature. For the present heater geometry, the effects of dissolved gas on the boiling performance were generally small, however, as the dissolved gas content increased (through either increased pressure or subcooling) more of the nucleate boiling curve was affected (enhanced). The enhancement of CHF from increased liquid subcooling was greater for the microporous surface than the plain surface. Correlations for both nucleate boiling and CHF were also presented.

The Effect of Chaotic Mixing on Heat Transfer in Continuous Thermal Processes at Low Peclet Numbers

2010 ◽  
Author(s):  
M. F. M. Speetjens
Keyword(s):  
Heat Transfer ◽  
Electronics Cooling ◽  
Thermal Conditions ◽  
Laminar Flows ◽  
Chaotic Mixing ◽  
Asymptotic State ◽  
Thermal Processes ◽  
Driven Cavity ◽  
Transfer Rates

Chaotic fluid mixing is generally considered to enhance fluid-wall heat transfer and thermal homogenisation in laminar flows. However, this essentially concerns the transient stage towards a fully-developed (thermally-homogeneous) asymptotic state and then specifically for high Pe´clet numbers numbers Pe (convective heat transfer dominates). The role of chaos at lower Pe under both transient and asymptotic conditions, relevant to continuous thermal processes as e.g. micro-electronics cooling, remains largely unexplored to date. The present study seeks to gain first insight into this matter by the analysis of a representative model problem: heat transfer in the 2D time-periodic lid-driven cavity flow induced via non-adiabatic walls. Transient and asymptotic states are investigated in terms of both the temperature field and the thermal transport routes. This combined Eulerian-Lagrangian approach enables fundamental investigation of the connection between heat transfer and chaotic mixing and its ramifications for temperature distributions and heat-transfer rates. The analysis exposes a very different role of chaos in that its effectiveness for thermal homogenisation and heat-transfer enhancement is in low-Pe transient and asymptotic states marginal at best. Here chaos may in fact locally amplify temperature fluctuations and thus hamper instead of promote thermal homogeneity. These findings reveal that optimal thermal conditions are at lower Pe not automatic with chaotic mixing and may depend on a delicate interplay between flow and heat-transfer mechanisms.

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