Study On Pool Boiling Heat Transfer With Mixed Wettable Cavity Structure Based On Solid-liquid Conjugate Heat Transfer Model

Boiling heat transfer,as an efficient energy transfer method accompanied by gas-liquid phase transition,has attracted extensive attention of scholars at home and abroad due to its characteristics of small heat transfer temperature difference and large heat flux.Boiling heat transfer is a phase change type of heat transfer where a large amount of heat is removed from the walls of the liquid during vaporization.The greater the amount of gas produced per unit time,the stronger the heat exchange capacity of the heat exchange surface.Therefore,by setting more nucleation sites on the heat exchange surface and an excellent liquid replenishment method,the performance of the heat exchange surface can be improved from the perspective of bubble dynamics.When exploring the dynamic behavior of bubbles,people often use numerical simulation to explore the flow of gas-liquid flow in the boiling process because of the deviation of the experiment and the difficulty in capturing the bubble movement.However,the lattice Boltzmann method at the mesoscopic scale can show the phase interface that other numerical simulation methods are poor to show at a small computational cost due to the particle characteristics under the statistical theory.In the third chapter of paper,based on the one component multiphase lattice Boltzmann method,different energy transfer rates of solid and liquid are successfully distinguished by tentatively introducing the physical parametersλ,c_pof solid and liquid into the temperature relaxation time,as a result,a novel solid-liquid conjugate boiling heat transfer LB model is proposed in this paper.After verifying the accuracy,stability and rationality of the model,boiling heat transfer at different wettability surfaces are simulated by the solid-liquid conjugate model and the original pseudo-potential model.The results show that the unintentional neglection of different heat transfer capacities of solid and liquid regions in the original pseudo-potential model leads to the appearance of large low-density phase transition region around the bubble root.The existence of low-density phase transition region produces additional interphase forces and greatly changes the wall contact angle of bubbles,temperature fields and heat flux distribution.However,for the solid-liquid conjugate heat conduction model,because the low-density phase transition region only appears in a very small range and at very low level,the actual bubble wall contact angles obtained by the conjugate heat transfer model are closer to the setting bubble contact angle,and the solid-liquid conjugate boiling heat transfer LB model can more accurately describe and display the actual microscopic process of boiling heat transfer.For other wettable surfaces except superhydrophilic surfaces,the maximum relative error of the actual contact angle obtained by the conjugate heat transfer model is 8.6%,which is 9.8%lower than that of the original pseudo-potential model,which demonstrates the solid-liquid conjugate heat transfer model.The thermal model is more realistically accurate under non-superhydrophilic conditions.This paper adopts a new solid-liquid conjugate boiling heat transfer LB pseudopotential model,the bubble detaching behavior and boiling heat transfer performance on the square cavity structure are analyzed through setting different contact angles of cavity surface and plane heating surface.The results show that the hydrophobic cavity surface can initialize bubble nucleation earlier and obviously increase the bubble detaching frequency because of its gas-bounding character,while the hydrophilic plane heating surface can restrict the expansion of bubbles and delay the appearance of film boiling.Besides,for uniform wettability surfaces,the bubble detaching period varies in quadratic equation with the surface contact angle due to the interaction of the wall force and buoyancy,and there is a minimum detaching period.While for the mixed wettability surfaces,the bubble detaching period also has a minimum value with the decrease of the contact angle of cavity surface,but the average bubble detaching diameter basically does not change with the cavity surface contact angle,moreover,the cavity surface contact angle corresponding to the minimum detaching period also increases with the increasing of plane heating surface contact angle.