Numerical investigation of heat transfer performance and bubble behavior of nucleate pool boiling in a confined space under rolling conditions

Nucleate pool boiling process is widely used in heat exchangers because of its excellent heat transfer performance.With the gradual increase of applications,more and more equipments work in a non-static state,but there is little research under rolling conditions.Therefore,it is necessary to investigate the influence of rolling motion on the nucleate pool boiling process.In this study,a numerical investigation of the nucleate pool boiling process under static and rolling conditions is performed based on the volume-of-fluid(VOF)method.Physical fields and phase distribution under static state and rolling motion are compared to investigate the effect of rolling motion on the nucleate pool boiling process.The results show that rolling motion greatly influences the bubble behavior and void fraction owing to the differences between flow fields.The void fraction decreased by 11.84%,48.82%,and 56.87%as the maximum rolling angle increased from 15°to 45°,and by 11.84%,22.27%,and 21.81%as the rolling period increased from 1 s to 3 s.The void fraction decreased by 11.84%,48.82%,and 56.87%as the maximum rolling angle increased from 15°to 45°.The heat transfer coefficients of different cases are compared,and it is found that the effects of rolling motion on heat transfer coefficients can be ignored.

An Improved Treatment on the Apparent Contact Angle of a Single-Bubble in Consideration of Microlayer for Simulations of Nucleate Pool Boiling

Numerical simulation of single-bubble growth behavior during nucleate pool boiling was developed based on the volume of fluid method considering the thin liquid layer under the bubble(microlayer).However,the experimental values of apparent contact angle(the small region connecting the microlayer and bulk liquid)are crucial for the simulations.Reliance on experimental results limited the further application of such numerical method.In this study,a new method calculating the force balance,used to determine the interface shape near the apparent contact angle,was proposed instead of using the experimental values of the apparent contact angle.As a result,the good agreement was shown between the simulation results obtained based on the new and previous numerical methods.The simulation results were also in consistent with the experimental results.It can be concluded that the single-bubble behavior,including the heat transfer characteristics,during nucleate pool boiling can be simulated based on the proposed method.

Lattice Boltzmann Simulation of Nucleate Pool Boiling in Saturated Liquid

A thermal lattice Boltzmann method(LBM)for two-phase fluid flows in nucleate pool boiling process is proposed.In the present method,a new function for heat transfer is introduced to the isothermal LBM for two-phase immiscible fluids with large density differences.The calculated temperature is substituted into the pressure tensor,which is used for the calculation of an order parameter representing two phases so that bubbles can be formed by nucleate boiling.By using this method,twodimensional simulations of nucleate pool boiling by a heat source on a solid wall are carried out with the boundary condition for a constant heat flux.The flow characteristics and temperature distribution in the nucleate pool boiling process are obtained.It is seen that a bubble nucleation is formed at first and then the bubble grows and leaves the wall,finally going up with deformation by the buoyant effect.In addition,the effects of the gravity and the surface wettability on the bubble diameter at departure are numerically investigated.The calculated results are in qualitative agreement with other theoretical predictions with available experimental data.