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).

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

2003 ◽  
Author(s):  
Zoran V. Stosic ◽  
Vladimir D. Stevanovic
Keyword(s):  
Heat Flux ◽  
Residence Time ◽  
Pool Boiling ◽  
Three Dimensional ◽  
Heating Surface ◽  
Heat Fluxes ◽  
Heating Wall ◽  
Two Phase ◽  
Nucleation Sites ◽  
Phase Mixture

Prediction of nucleate boiling mechanisms and burnout conditions, when heat transfer coefficient sharply drops and the heating surface destruction could occur are one of the crucial topics in thermal design and safety analyses of various thermal equipment. Although these phenomena have been intensively investigated for decades, various influencing factors and complexity of coupled thermal and fluid dynamic processes have not yet been fully understood. The integral approach towards prediction of nucleate boiling and burnout conditions requires modelling and numerical simulation of micro level phenomena of bubble rise and departure at a numbers of nucleation sites, as well as macroscopic two-phase mixture behaviour on the heating surface. In this paper multidimensional numerical simulation of the atmospheric saturated pool boiling is performed under high heat fluxes, near to and at the occurrence of burnout conditions. Micro level phenomena on the heating surface are modelled with the key parameters of vapour generation on the heating wall, such as bubble nucleation site density, bubble residence time on the heating wall and certain level of randomness in the location of bubble nucleation. Heat flux is non-uniformly distributed on the heating surface with peaks at the nucleation sites. The nucleation sites are determined by a random function, while the mean number of nucleation sites is prescribed according to the material characteristics and roughness of the heating surface. The applied numerical grids are able to represent the nucleation sites on the heating wall for both fresh (polished) and aged (rough) heaters at the atmospheric pool boiling conditions. The macro level phenomena are modelled with two-fluid model of liquid-vapour flow. The interfacial drag is modelled with appropriate closure laws. The applied modelling and numerical methods enable full representation of the two-phase mixture behaviour on the heating surface with inclusion of the swell level prediction. In this way the integral conditions of nucleate pool boiling with the possibility of burnout are simulated and the critical heat flux conditions are predicted. The result of the three-dimensional numerical simulations and analyses are presented as the extension of the previously published two-dimensional numerical results. Here presented three-dimensional investigation is performed in order to take into account more realistically spatial effects of vapour generation and two-phase flow, such as phase dispersion within the two-phase mixture, than it was able with previously performed two-dimensional investigation. 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 several seconds from pool boiling initiation. A replenishment of the heating surface with water and partial surface wetting for lower heat fluxes is shown, while heating surface dry-out is observed 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. Also, the influence of the heat flux intensity on the pool boiling dynamics is analysed. 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).

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.

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.

Investigation of Cooling Performance of a Swirl Microchannel Heat Sink by Numerical Simulation

2011 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Numerical Simulation ◽  
Heat Flux ◽  
Heat Sink ◽  
High Heat ◽  
Heat Fluxes ◽  
Maximum Temperature ◽  
Microchannel Heat Sink ◽  
Irreversible Damage ◽  
Cooling Performance ◽  
Large Heat

High heat fluxes have been created by the semiconductor devices due to the high power generation and shrank size. The large heat flux causes the circuit to exceed its allowable temperature and may experience both working efficiency loss and irreversible damage due to excess in their temperatures. In this paper, a swirl microchannel heat sink is designed to dissipate the large heat flux from the devices. The numerical simulation is carried out to investigate the cooling performance. Uniform heating boundary condition is applied and single phase water is selected as coolant. The present micro heat sink applies multiple swirl microchannels positioned in a circular flat plate to enhance the heat convection by creating the secondary flow at high Reynolds numbers. Copper is selected as the material of heat sink. The channel depth and width are fixed as 0.5 mm and 0.4 mm, respectively. The heat is injected into the system from the bottom of heat sink at the heat fluxes from 10 to 60 W/cm2. Flow is supplied from the top of micro heat sink through a jet hole with a diameter of 2 mm and enters swirl microchannels at the volume flow rates varying from 47 to 188 ml/min. The cooling performances of swirl microchannel heat sinks with different curvatures and channel numbers are evaluated based on the targets of low maximum temperature, temperature gradient and pressure drop.

A FRACTAL MODEL FOR NUCLEATE POOL BOILING OF NANOFLUIDS AT HIGH HEAT FLUX INCLUDING CHF

Fractals ◽  
2010 ◽  
Vol 18 (04) ◽  
pp. 409-415 ◽  
Author(s):  
BOQI XIAO ◽  
SONGHUA GAO ◽  
LINGXIA CHEN
Keyword(s):  
Heat Flux ◽  
Volume Fraction ◽  
Pool Boiling ◽  
High Heat ◽  
Fractal Model ◽  
High Heat Flux ◽  
Nucleate Pool Boiling ◽  
Empirical Constant ◽  
Nucleation Sites ◽  
Proposed Model

A fractal model for nucleate pool boiling of nanofluids at high heat flux and critical heat flux (CHF) is developed based on the fractal distribution of nanoparticles and nucleation sites on boiling surfaces in this paper. The formula of calculating high heat flux and CHF for nanofluids in nucleate pool boiling is given by taking into account heat convection between nanoparticles and liquids due to the Brownian motion of nanoparticles in fluids. The proposed model is expressed as a function of temperature of nanofluids, the effective thermal conductivity of nanofluids, the average size of nanoparticles, the fractal dimension of nanoparticles and nucleation sites, the nanoparticles volume fraction of suspension, and physical properties of fluids. No additional/new empirical constant is introduced in this fractal model. An agreement between the proposed model predictions and experimental data is found. The validity of the fractal model for nucleate pool boiling of nanofluids at high heat flux and CHF is thus verified.

High Heat Flux Dissipation Using Symmetric Dual-Taper Manifold in Pool Boiling

2019 ◽  
Author(s):  
Aranya Chauhan ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pool Boiling ◽  
Heat Removal ◽  
Heating Surface ◽  
High Heat ◽  
Copper Surface ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Continuous Increase

Abstract The trend of miniaturization in electronics presents a great challenge in the thermal management of devices. The continuous increase in the number of transistors in the processor leads to high heat flux generation, limiting the performance of the device. Boiling heat transfer offers a great heat removal competency while maintaining the low chip temperatures. The critical heat flux (CHF) dictates the maximum heat removal ability, and heat transfer coefficient (HTC) defines the efficiency of the boiling process. This pool boiling study is focused on using a manifold containing a symmetric dual taper over the heating surface. The heat transfer performance of this configuration is evaluated for different taper angles in the manifold. The macro-convection assisted by vapor columns during boiling enhance the CHF and HTC limit significantly. A CHF of 287 W/cm2 with an HTC of 116 kW/cm2°C was achieved with a plain copper surface, representing greater than a 2-fold increases in each over a plain surface.

Dynamics of Pool Boiling on Plain and Nanotube Coated Silicon Surfaces

2010 ◽  
Author(s):  
Vijaykumar Sathyamurthi ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Flux ◽  
Surface Temperature ◽  
Chaotic Dynamics ◽  
Pool Boiling ◽  
Deterministic Chaos ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Test Fluid

Saturated pool boiling experiments are conducted over silicon substrates with and without Multi-walled Carbon Nanotubes (MWCNT) with PF-5060 as the test fluid. Micro-fabricated thin film thermocouples located on the substrate acquire surface temperature fluctuation data at 1 kHz frequency. The high frequency surface temperature data is analyzed for the presence of chaotic dynamics. The shareware code, TISEAN© is used in analysis of the temperature time-series. Results show the presence of low-dimensional deterministic chaos, near Critical Heat Flux (CHF) and in some parts of the Fully Developed Nucleate Boiling (FDNB) regime. Some evidence of chaotic dynamics is also obtained for the film boiling regimes. Singular value decomposition is employed to generate pseudo-phase plots of the attractor. In contrast to previous studies involving multiple nucleation sites, the pseudo-phase plots show the presence of multi-fractal structure at high heat fluxes and in the film boiling regime. An estimate of invariant quantities such as correlation dimensions and Lyapunov exponents reveals the change in attractor geometry with heat flux levels. No significant impact of surface texturing is visible in terms of the invariant quantities.

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