Effects of surface orientation and heater material on heat transfer coefficient and critical heat flux of nucleate boiling

2018 ◽  
Vol 121 ◽  
pp. 632-640 ◽  
Author(s):  
Yong Mei ◽  
Yiqiong Shao ◽  
Shengjie Gong ◽  
Yechen Zhu ◽  
Hanyang Gu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Nucleate Boiling ◽  
Surface Orientation

Numerical and Parametric Investigation of the Effect of Heat Spreading On Boiling of a Dielectric Liquid for Immersion Cooling of Electronics

2021 ◽  
Author(s):  
Wei Tong ◽  
Alireza Ganjali ◽  
Omidreza Ghaffari ◽  
Chady Alsayed ◽  
Luc Frechette ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Surface Temperature ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Heat Removal ◽  
Nucleate Boiling ◽  
Input Power ◽  
Immersion Cooling

Abstract In a two-phase immersion cooling system, boiling on the spreader surface has been experimentally found to be non-uniform, and it is highly related to the surface temperature and the heat transfer coefficient. An experimentally obtained temperature-dependent boiling heat transfer coefficient has been applied to a numerical model to investigate the spreader's cooling performance. It is found that the surface temperature distribution becomes less uniform with higher input power. But it is more uniform when the thickness is increased. By defining the characteristic temperatures that represent different boiling regimes on the surface, the fraction of the surface area that has reached the critical heat flux has been numerically calculated, showing that increasing the thickness from 1 mm to 6 mm decreases the critical heat flux reached area by 23% at saturation liquid temperatures. Therefore, on the thicker spreader, more of the surface is utilized for nucleate boiling while localized hot regions that lead to surface dry-out are avoided. At a base temperature of 90 oC, the optimal thickness is found to be 4 mm, beyond which no significant improvement in heat removal can be obtained. Lower coolant temperatures can further increase the heat removal; it is reduced from an 18% improvement in the input power for the 1 mm case to only 3% in the 6 mm case for a coolant temperature drop of 24 oC. Therefore, a trade-off exists between the cost of maintaining the low liquid temperature and the increased heat removal capacity.

Effects of Heater Material and Surface Orientation on Heat Transfer Coefficient and Critical Heat Flux of Nucleate Boiling

2017 ◽  
Author(s):  
Yong Mei ◽  
Yechen Zhu ◽  
Botao Zhang ◽  
Shengjie Gong ◽  
Hanyang Gu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Orientation Angle ◽  
Nucleate Boiling ◽  
Copper Surface ◽  
Surface Orientation ◽  
Reactor Vessel

External reactor vessel cooling (ERVC) is the key technology for In-Vessel Retention (IVR) to ensure the safety of a nuclear power plant (NPP) under severe accident conditions. The thermal margin of nucleate boiling heat transfer on the reactor pressure vessel (RPV) lower head is important for ERVC and of wide concern to researchers. In such boiling heat transfer processes, the reactor vessel wall inclination effect on the heat transfer coefficient (HTC) and critical heat flux (CHF) should be considered. In this study, experiments were performed to investigate the effects of heater material and surface orientation on the HTC and CHF of nucleate boiling. Copper and stainless steel (SS) surfaces were used to perform boiling tests under atmosphere pressure. The orientation angle of both boiling surfaces were varied between 0° (upward) and 180° (downward). The experimental results show that the surface orientation effects on the HTC is slight for both the copper surface and the SS surface. In addition, the relationship of measured CHF values with the inclination angles was obtained and it shows that the CHF value changes little as the inclination angle increases from 0° to 120° but it decreases rapidly as the orientation angle increases towards 180° for both boiling surfaces. The material effect on CHF is also observed and the copper surface has higher CHF value than the SS surface. Based on the experimental data, a correlation for CHF prediction is developed which includes both the surface orientation effect and the heater material effect.

Enhancing Flow Boiling Heat Transfer in Microchannels Using Monolithically-Coated Silicon Nanowires

2011 ◽  
Author(s):  
Dan Li ◽  
Gensheng Wu ◽  
Wei Wang ◽  
Yunda Wang ◽  
Ronggui Yang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Silicon Nanowires ◽  
Flow Instability ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Variable Cross

Flow boiling in microchannels has been attractive for cooling of high power electronics. However, the flow instability hinders the heat transfer performance such as the premature initiation of the critical heat flux (CHF) and could result in device burnout. Numerous methods have been implemented to suppress the instability of flow boiling, including integrating micro pin fins in the channels [1] and inlet restrictors [2], as well as fabricating microchannels with variable cross-sectional areas [3]. Recently, Li et al [4] and Chen et al [5] explored the pool boiling enhancement using nanowires, which shows much more uniform bubble generation and a higher heat transfer coefficient and critical heat flux compared to plain surfaces. The work presented here is the very first effort to explor the impacts of nanowire coating on the flow boiling performance in parallel microchannels. We present here a monolithic integration process to fabricate silicon micro-channels coated with silicon nanowires and the flow boiling characterization of the microchannels. By comparing the flow boiling curves in the microchannels with and without nanowire coating, we show significant performance enhancement for a nanowire-coated microchannel, such as earlier ONB (onset of nucleate boiling), delayed OFO (onset of flow oscillation), enhanced HTC (heat transfer coefficient) and suppressed flow instability.

The Effect of Inlet Orifice on Critical Heat Flux and Flow Boiling Heat Transfer in Single Horizontal Microtube

2013 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Working Fluid ◽  
Flow Boiling Heat Transfer

Flow oscillation is a crucial issue for the development of flow boiling heat transfer in the applications. Inlet orifice has been proven be an option to eliminate the oscillation. However, the effects of inlet orifice on critical heat flux and flow boiling heat transfer coefficient are lack of study. In this work, the effects of inlet restriction on critical heat flux and heat transfer coefficient in single horizontal microtube under uniform heating condition is experimentally investigated using FC-72 as working fluid. A stainless steel microtube with an inner diameter of 889 μm is selected as main microtube. Two smaller microtubes are assembled at the inlet of main microtube to achieve the restriction configurations of 50% and 20% area ratios. The experimental measurement is carried out at mass fluxes ranging from 160–870 kg/m2·s and heat fluxes varying from 6–170 kW/m2. Two saturation pressures, 10 and 45 kPa, are tested. The experimental results of critical heat flux and two phase heat transfer coefficient obtained in the microtube without orifice are compared with the existing correlations. The addition of an orifice does not enhance the normal critical heat flux but increases the premature critical heat flux. In aspect of heat transfer, the orifice shows improvement on heat transfer coefficient at low mass flux and high saturation pressure.

scholarly journals Наножидкости для энергетики: механизм влияния диспергентов на тепловые параметры и кризисные явления при кипении

2020 ◽  
Vol 90 (2) ◽  
pp. 175
Author(s):  
В.Н. Морару ◽  
Б.И. Бондаренко ◽  
С.В. Сидоренко ◽  
Д.В. Комыш
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Direct Current ◽  
Sedimentation Stability ◽  
Boiling Crisis ◽  
Transfer Parameters ◽  
The Heat Transfer Coefficient

Abstract: The effect of dispersants organic (CTAB) and inorganic nature (sodium pyrophosphate and sodium silicate) on the critical heat flux (CHF) and heat-transfer coefficient (HTC) of boiling various aqueous nanofluids (NFs) under conditions of free convection is studied. It has been established that the addition of ionic dispersants to aluminosilicate NFs, increasing their aggregative and sedimentation stability, as a rule, worsens their heat-transfer parameters during boiling, causing a sudden pre-crisis heater burnout in a test unit powered by direct current. The mechanism of the phenomenon is revealed. On the contrary, the addition of dispersants and surfactants to carbon-containing NFs with high thermal conductivity, improving their stability, at the same time increases the heat transfer coefficient during boiling of NFs, but also cause pre-crisis heater burnout in the case of direct current heating. The effect of dispersants on crisis phenomena during boiling of water and NFs is analyzed and the causes of sudden pre-crisis heater burnout have been elucidated. Several mechanisms have been proposed for interpreting the observed effects, from which the expediency of using alternating heating current and non-ionic, non-foaming surfactants and dispersants to avoid an early onset of the boiling crisis in order to achieve higher values of the critical heat flux and the heat transfer coefficient during the NFs boiling.

Pool boiling performance of oxide nanofluid on a downward-facing heating surface

Kerntechnik ◽  
2022 ◽  
Vol 0 (0) ◽  
Author(s):  
Zhibo Zhang ◽  
Huai-En Hsieh ◽  
Yuan Gao ◽  
Shiqi Wang ◽  
Jia Gao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Roughness ◽  
Stainless Steel ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Heating Surface ◽  
Nano Particles

Abstract In this study, the pool boiling performance of oxide nanofluid was investigated, the heating surface is a 5 × 30 mm stainless steel heating surface. Three kinds of nanofluids were selected to explore their critical heat flux (CHF) and heat transfer coefficient (HTC), which were TiO2, SiO2, Al2O3. We observed that these nanofluids enhanced CHF compared to R·O water, and Al2O3 case has the most significant enhancement (up to 66.7%), furthermore, the HTC was also enhanced. The number of bubbles in nanofluid case was relatively less than that in R·O water case, but the bubbles were much larger. The heating surface was characterized and it was found that there were nano-particles deposited, and surface roughness decreased. The wettability also decreased with the increase in CHF.

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