scholarly journals Thermal efficiency of metal foams on pool boiling

2021 ◽  
Vol 2116 (1) ◽  
pp. 012005
Author(s):  
L L Manetti ◽  
A S Moita ◽  
E M Cardoso
Keyword(s):  
Nickel Foam ◽  
Pool Boiling ◽  
Heating Surface ◽  
High Heat ◽  
Heat Fluxes ◽  
Vapor Flow ◽  
Maximum Enhancement ◽  
Fin Efficiency ◽  
Nickel Foams ◽  
Similar Area

Abstract This paper presents an experimental work on pool boiling using HFE-7100 at saturated conditions, under atmospheric pressure, and copper and nickel foams as the heating surface with four different thicknesses varying between 0.5 mm and 3 mm, followed by an analysis of the effect of foam fin-efficiency based on Ghosh model. All foams showed a better heat transfer coefficient (HTC) than the plain surface; however, as the heat flux increased, the HTC from the thicker nickel foams decreased due to the bubble vapor flow inside the foam. On the other hand, the thinner nickel foam showed better HTC at high heat fluxes with a maximum enhancement of 120%. The foam efficiency presented a similar tendency with the HTC, i.e., as the thickness decreases the efficiency increases; however, as compared with copper foams with a similar area but different porous diameter, the copper foams are 40% more efficient than the nickel ones due to the foam material, which has a thermal conductivity 4.5 times higher.

scholarly journals Numerical prediction of nucleate pool boiling heat transfer coefficient under high heat fluxes

2016 ◽  
Vol 20 (suppl. 1) ◽  
pp. 113-123 ◽  
Author(s):  
Milada Pezo ◽  
Vladimir Stevanovic
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pool Boiling ◽  
Heating Surface ◽  
High Heat ◽  
Bubble Nucleation ◽  
Heat Fluxes ◽  
Two Phase ◽  
Boiling Heat Transfer Coefficient

This paper presents CFD (Computational Fluid Dynamics) approach to prediction of the heat transfer coefficient for nucleate pool boiling under high heat fluxes. Three-dimensional numerical simulations of the atmospheric saturated pool boiling are performed. Mathematical modelling of pool boiling requires a treatment of vapor-liquid two-phase mixture on the macro level, as well as on the micro level, such as bubble growth and departure from the heating surface. Two-phase flow is modelled by the two-fluid model, which consists of the mass, momentum and energy conservation equations for each phase. Interface transfer processes are calculated by the closure laws. Micro level phenomena on the heating surface are modelled with the bubble nucleation site density, the bubble resistance time on the heating wall and with the certain level of randomness in the location of bubble nucleation sites. The developed model was used to determine the heat transfer coefficient and results of numerical simulations are compared with available experimental results and several empirical correlations. A considerable scattering of the predictions of the pool boiling heat transfer coefficient by experimental correlations is observed, while the numerically predicted values are within the range of results calculated by well-known Kutateladze, Mostinski, Kruzhilin and Rohsenow correlations. The presented numerical modeling approach is original regarding both the application of the two-fluid two-phase model for the determination of heat transfer coefficient in pool boiling and the defined boundary conditions at the heated wall surface.

Ultrasonic augmentation in pool boiling heat transfer over external surfaces: A review

2020 ◽  
pp. 095440622095035
Author(s):  
Abhishek Swarnkar ◽  
Vikas J Lakhera
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
High Heat ◽  
Ultrasonic Field ◽  
Ultrasonic Waves ◽  
Heat Fluxes ◽  
Surface Topology

Boiling heat transfer is known for high heat fluxes at relatively small temperature differences. However, over the decades, technological innovations have demanded further augmentation in heat fluxes associated with boiling. Among the various active and passive methods, use of ultrasonic waves in boiling liquid has emerged as a proven technique for the required heat transfer improvement as demonstrated by a number of researchers. The present article reviews the application of ultrasonic waves in enhancing the heat transfer in various regimes of pool boiling. It has been found that the use of ultrasonic field is more promising in case of sub-cooled boiling as compared to saturated condition. Along with ultrasonic field of lower frequency and higher power, the usage of various passive techniques of surface improvement such as micro channel, surface topology, nano coatings etc. leads to further augmentation of heat transfer. Also, the relative placement of heating surface in ultrasonic wave field must be considered inevitably while designing an ultrasonic field assisted pool boiling system. It requires further investigations to conduct more parametric studies such as effect of pressure along with the usage of ultrasonic waves during sub- cooled boiling. Also during ultrasonic assisted pool boiling, various nano fluids can be tested for improving the heat transfer characteristics particularly in the saturated nucleate boiling regime.

Multi-Dimensional Numerical Simulation of Burnout on Horizontal Surface in Pool Boiling

2002 ◽  
Author(s):  
Zoran V. Stosic ◽  
Vladimir D. Stevanovic
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Residence Time ◽  
Pool Boiling ◽  
Heating Surface ◽  
High Heat ◽  
Heat Fluxes ◽  
Heating Wall ◽  
Nucleation Sites ◽  
Vapour Generation

Multidimensional numerical simulation of the atmospheric saturated pool boiling is performed under high heat fluxes, near to and at the occurrence of burnout conditions. Heat flux through the vessel bottom wall is varied and its influence on the pool boiling dynamics is analysed. Dynamics of vapour generation on the heating wall is modelled through the density of nucleation sites and the bubble residence time on the wall. The nucleation sites are determined by a random function. The applied numerical grid is able to represent the nucleation sites on the heating wall for both fresh (polished) and aged (rough) heaters at the atmospheric pool boiling conditions. Results are presented for short time period after the initiation of heat supply and vapour generation on the heating surface, as well as for quasi steady-state conditions after two seconds from pool boiling initiation. The results show a replenishment of the heating surface with water and partial surface wetting for lower heat fluxes, while heating surface dry-out is predicted for high heat fluxes. The influence of the density of nucleation sites and the bubble residence time on the wall on the pool boiling dynamics is investigated. Numerical simulations show that decrease of the density of nucleation sites and increase of bubble residence time on the heating surface (characteristics pertinent to fresh-polished heaters) lead to the reduction of critical heat flux values. Obtained results are in excellent agreement with the recent experimental investigations of the upward facing burnout conditions on the horizontal heated plate. Details of the developed numerical procedure are presented. The introduced method of random spatial and temporal generation of the vapour at the heated wall is a new approach. It enables the macroscopic representation of the population of microscopic vapour bubbles, which are generated at nucleation sites on the heater wall, and which burst through liquid micro-layer in thermal-hydraulic conditions close to the burnout. The applied numerical and modelling method has shown robustness by allowing stable calculations for wide ranges of applied modelling boiling parameters (density of nucleation sites and bubble residence time).

Film Boiling in a Scaling Liquid

1976 ◽  
Vol 98 (2) ◽  
pp. 173-177 ◽  
Author(s):  
L. C. Farrar ◽  
E. Marschall
Keyword(s):  
Calcium Sulfate ◽  
Heating Surface ◽  
Sulfate Solution ◽  
High Heat ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Saturated Liquid ◽  
Experimental Heat ◽  
Experimental Heat Transfer ◽  
Heating Surfaces

Film boiling experiments were carried out in an aqueous-calcium sulfate solution. The experimental results indicate that scale formation on heating surfaces during evaporation of a calcium sulfate solution can be avoided under carefully controlled conditions. Experimental heat transfer results for both distilled water and aqueous calcium solutions compare very well with analytical predictions. In addition, for high heat fluxes, contact between liquid and heating surface was found to exist during stable film boiling in a quiescent, saturated or almost saturated liquid.

Pool Boiling Using Thin Enhanced Structures Under Top-Confined Conditions

2006 ◽  
Vol 128 (12) ◽  
pp. 1302-1311 ◽  
Author(s):  
Camil-Daniel Ghiu ◽  
Yogendra K. Joshi
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
Pool Boiling ◽  
Single Layer ◽  
Temperature Limit ◽  
Heat Fluxes ◽  
The Other ◽  
Vapor Flow ◽  
Maximum Heat ◽  
Maximum Heat Flux

An experimental study of pool boiling using enhanced structures under top-confined conditions was conducted with a dielectric fluorocarbon liquid (PF 5060). The single layer enhanced structures studied were fabricated in copper and quartz, had an overall size of 10×10mm2, and were 1mm thick. The parameters investigated in this study were the heat flux (0.8-34W∕cm2) and the top space S(0-13mm). High-speed visualizations were performed to elucidate the liquid/vapor flow in the space above the structure. The enhancement observed for plain surfaces in the low heat fluxes regime is not present for the present enhanced structure. On the other hand, the maximum heat flux for a prescribed 85°C surface temperature limit increased with the increase of the top spacing, similar to the plain surfaces case. Two characteristic regimes of pool boiling have been identified and described: isolated flattened bubbles regime and coalesced bubbles regime.

Sign in / Sign up

Export Citation Format

Share Document