Flow Excursion-Induced Dryout at Low Heat Flux Natural Convection Boiling

1986 ◽  
Vol 108 (2) ◽  
pp. 425-432 ◽  
Author(s):  
M. Khatib-Rahbar ◽  
E. G. Cazzoli
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Natural Convection ◽  
High Heat ◽  
High Heat Flux ◽  
Two Dimensional ◽  
Boiling Process ◽  
Fast Breeder Reactors ◽  
Breeder Reactors ◽  
Saturated Boiling

Flow excursion-induced dryout at low heat flux natural convection boiling, typical of liquid metal fast breeder reactors, is addressed. Steady-state calculations indicate that low-quality boiling is possible up to the point of the Ledinegg instability, leading to flow excursion and subsequent dryout in agreement with experimental data. A flow regime-dependent critical heat flux relationship based upon a saturated boiling criterion is also presented. Transient analyses indicate that premature flow excursion cannot be ruled out and the boiling process is transient dependent. Analysis of a loss-of-flow transient at high heat flux forced convection shows a significantly faster flow excursion leading to dryout, which is in excellent agreement with the results of the two-dimensional THORAX code.

Transient Pool Boiling Heat Transfer—Part 1: Incipient Boiling Superheat

1977 ◽  
Vol 99 (4) ◽  
pp. 547-553 ◽  
Author(s):  
A. Sakurai ◽  
M. Shiotsu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Boiling Point ◽  
Boiling Heat Transfer ◽  
High Heat ◽  
The Other ◽  
High Heat Flux ◽  
The Heat Transfer Coefficient

Incipient boiling superheat for exponentially increasing heat inputs to a platinum wire supported horizontally in a pool of water was measured for exponential periods ranging from 5 ms to 10 s and for subcoolings ranging from 25 to 75K under atomospheric pressure. The heat transfer coefficient before the initiation of boiling was related to those by conduction and by natural convection. The heat flux at the incipient boiling point increased with the decrease in the period. The log-log plot of the heat flux against the superheat at the incipient boiling point had a single asymptotic line of slope 2 which was independent of subcoolings in the high heat flux region. On the other hand, as the heat flux decreased to zero, the superheat tended to approach to a constant value for each subcooling. This asymptotic superheat at zero heat flux was higher for higher subcooling. Transient incipient boiling superheat was reasonably explained by the combination of two kinds of incipient boiling models.

scholarly journals Boiling Heat Transfer Performance of Parallel Porous Microchannels

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2970
Author(s):  
Donghui Zhang ◽  
Haiyang Xu ◽  
Yi Chen ◽  
Leiqing Wang ◽  
Jian Qu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Boiling Process

Flow boiling in microporous layers has attracted a great deal of attention in the enhanced heat transfer field due to its high heat dissipation potential. In this study, flow boiling experiments were performed on both porous microchannels and a copper-based microchannel, using water as the coolant. As the heat flux was less than 80 W/cm2, the porous microchannels presented significantly higher boiling heat transfer coefficients than the copper-based microchannel. This was closely associated with the promotion of the nucleation site density of the porous coating. With the further increase in heat flux, the heat transfer coefficients of the porous microchannels were close to those of the copper-based sample. The boiling process in the porous microchannel was found to be dominated by the nucleate boiling mechanism from low to moderate heat flux (<80 W/cm2).This switched to the convection boiling mode at high heat flux. The porous samples were able to mitigate flow instability greatly. A visual observation revealed that porous microchannels could suppress the flow fluctuation due to the establishment of a stable nucleate boiling process. Porous microchannels showed no advantage over the copper-based sample in the critical heat flux. The optimal thickness-to-particle-size ratio (δ/d) for the porous microchannel was confirmed to be between 2–5. In this range, the maximum enhanced effect on boiling heat transfer could be achieved.

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