Critical Heat Flux on Curved Calandria Vessel of Indian PHWRs During Severe Accident Condition

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
P. K. Verma ◽  
P. P. Kulkarni ◽  
P. Pandey ◽  
S. V. Prasad ◽  
A. K. Nayak
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Nuclear Power ◽  
Cooling System ◽  
Severe Accident ◽  
Water Reactors ◽  
Curved Section

Abstract In pressurized heavy water reactors (PHWRs), during an unmitigated severe accident, the absence of adequate cooling arising from multiple failures of the cooling system leads to the collapse of pressure tubes and calandria tubes, which may ultimately relocate to the lower portion of the calandria vessel (CV) forming a debris bed. Due to the continuous generation of decay heat in the debris, it will melt and form a molten pool at the bottom of the CV. The CV is surrounded by calandria vault water, which acts as a heat sink at this scenario. In-vessel corium retention (IVR) through the external reactor vessel cooling (ERVC) is conceived as an effective method for maintaining the integrity of a calandria vessel during a severe accident in a nuclear power plant. Under the IVR conditions, it is necessary to ensure that the imparted heat flux due to melt is less than the critical heat flux (CHF) at the bottom of the calandria vessel wall. To evaluate the thermal margin for IVR, experiments are performed in a prototypic curved section of calandria vessel (25o sector) of calandria vessel to determine the CHF, heat transfer coefficient, and its variation along with the curvature of calandria vessel. The effect of moderator drainpipe on CHF and the heat transfer coefficient has also been evaluated. It has been observed that the imparted heat flux is much less than the CHF at the bottom of the calandria vessel.

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.

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.

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.

Effect of Particle Morphology on Pool Boiling From Surfaces Coated With Sintered Particles

2015 ◽  
Author(s):  
Suchismita Sarangi ◽  
Justin A. Weibel ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Particle Morphology ◽  
Wall Superheat

Immersion cooling strategies often employ surface enhancements to improve the pool boiling heat transfer performance. Sintered particle/powder coatings with different constituent particle sizes and total layer thicknesses have been commonly used on smooth surfaces to reduce the wall superheat and increase the critical heat flux during pool boiling. However, the role of the particle morphology on pool boiling has not been explicitly investigated. Since the morphology of the particles affects the pore shape, permeability, surface roughness, effective conductivity and diffusivity of the sintered coating, it will impact the heat transfer coefficient and critical heat flux during boiling. In this study, pool boiling of FC-72 is experimentally investigated using copper surfaces coated with a layer of sintered copper particles of irregular, dendritic and spherical morphologies. In order to isolate the effect of particle morphology, particles with the same effective diameter (90–106 μm) are sintered under controlled conditions that yield the same porosity (∼60%) and coating thickness (∼6 particle diameters) for all samples tested. The effects of particle morphology on the incipient wall superheat, nucleate boiling heat transfer coefficient, and critical heat flux are analyzed. The morphology of the pore structure in the coating formed by sintering is observed with SEM images; bubble nucleation and departure characteristics affecting the heat transfer performance of the coatings are qualitatively assessed with the aid of high-speed flow visualizations to corroborate the trends observed in the boiling curves. The irregular particles are observed to show the highest heat transfer coefficient, followed by dendritic and then spherical particles. The critical heat flux is found to be independent of the particle morphology.

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