Correlations of Nucleate Boiling Heat Transfer and Critical Heat Flux for External Reactor Vessel Cooling

Abstract

Four types of steady-state boiling experiments were conducted to investigate the efficacy of two distinctly different heat transfer enhancement methods for external reactor vessel cooling under severe accident conditions. One method involved the use of a thin vessel coating and the other involved the use of an enhanced insulation structure. By comparing the results obtained in the four types of experiments, the separate and integral effect of vessel coating and insulation structure were determined. Correlation equations were obtained for the nucleate boiling heat transfer and the critical heat flux. It was found that both enhancement methods were quite effective. Depending on the angular location, the local critical heat flux could be enhanced by 1.4 to 2.5 times using vessel coating alone whereas it could be enhanced by 1.8 to 3.0 times using an enhanced insulation structure alone. When both vessel coating and insulation structure were used simultaneously, the integral effect on the enhancement was found much less than the product of the two separate effects, indicating possible competing mechanisms (i.e., interference) between the two enhancement methods.

Measurement of Critical Heat Flux in a Candu End Shield Consisting of a Vertical Surface Abutting a Packed Bed of Steel Shielding Balls

“…Finally, several experimental programs have examined the feasibility of IVR for externally flooded LWR pressure vessels under severe accident conditions. These include both flat [13] and curved [3,6], surfaces. Some indication of relevant trends may be taken from the results, particularly the angular dependence of CHF for large surfaces in the SULTAN experiments [13] and the impact of a "baffle" to direct water flow in the ULPU experiments [3]; however, the potential for significant deviation from these results due to the presence of the steel shielding balls cannot be discounted.…”

“…The main boundaries constituting the CV walls are the cylindrical shell and the 2 calandria tubesheets that separate the CV from the end shields packed with steel balls. CHF in geometries resembling the cylindrical shell has been studied as part of investigations of IVR in the light water reactor (LWR) community [3][4][5][6][7][8][9][10][11][12][13][14]. In contrast, CHF has not been studied in geometries analogous to the surface of the calandria tubesheet facing the coarse porous medium constituted by steel balls and the end shield.…”

Effect of grooves on nucleate boiling heat transfer from downward facing hemispherical surface

“…The key technology is to ensure that the critical heat flux (CHF) on the downward facing surface is greater than the heat flux from the core molten debris. Various methods have been proposed for enhancing ERVC performance, including using structured surface, nanofluids (Pham et al, 2012;Angayarkanni and Philip, 2015) and thermal insulation (Yang et al, 2005;Noh and Suh, 2013). The structured surfaces include porous coating (Yang et al, 2006;Jun et al, 2016;Tetreault-Friend et al, 2016;Sohag et al, 2017;Wang et al, 2018), pin fins (Chu et al, 2013;Zhong et al, 2015), micro channels (Bai et al, 2016;Hou et al, 2017;Zhong et al, 2018aZhong et al, , 2018b, honeycomb porous plates (Mt Aznam et al, 2016;Fogaça et al, 2018), and spherical porous bodies (Mori et al, 2018), and so on.…”

Research progresses and future directions on pool boiling heat transfer

“…Saturated pool boiling curve for water on a temperature controlled thin copper strip using Couple Map Lattice method in non-linear spatio-temporal chaos dynamics was reproduced [54]. Experiments were conducted to investigate the efficiency of two distinctly different heat transfer enhancement methods using a thin vessel coating and an enhanced insulation structure for external reactor vessel cooling under severe accidental conditions [55]. Nucleate pool boiling characteristics during pool boiling of sub-cooled water on very small wires were studied [56].…”