Study Of Pool Boiling Heat Transfer On Copper Foam Surface Under Different Gravity Conditions

As a common porous material,metal foam has a good boiling heat transfer enhancement effect under normal gravity condition.Particularly,copper foam with super-hydrophilic surface has superior boiling heat transfer performance.Aiming at the microgravity environment in aerospace engineering,the bubble's dynamic behavior and heat transfer performance on copper foam surface under microgravity condition was studied.Numerical simulation method was used to study the effect of copper foam's parameters,such as porosity and pore size,on pool boiling heat transfer performance and bubble behavior.A pool boiling experimental platform suitable for drop tower equipment was set up,and the experimental study on pool boiling heat transfer on copper foam under microgravity conditions was carried out.The fluorinated liquid FC-72 was used as the working liquid.The results showed that three typical bubble departure behaviors were observed in pool boiling under microgravity.Compared with the smooth surface,the bubble departure frequency of the copper foam surface under microgravity condition was increased,and the bubble departure diameter was reduced.Compared with untreated copper foam,the super-hydrophilic copper foam increased the bubble departure frequency by 40%,and the average bubble departure diameter was decreased by 10.1%at the same heat flux(q?15W/cm~2).After entering the microgravity environment,the test block's temperature was increased,and the heat transfer performance was deteriorated.The exponential fitting of the experimental data showed that the heat transfer coefficient of the untreated copper foam surface was 86.1%higher than that of the smooth surface at the end of microgravity condition,and the heat transfer performance of the super-hydrophilic copper foam was 12.9%higher than that of the untreated copper foam.The existing multi-relaxation-time(MRT)pseudopotential lattice Boltzmann method(LBM)was improved,both the inter-particle interaction force model and source term model for adjustable thermodynamic consistency was applied to improve the thermal consistency of lattice Boltzmann model.The finite-difference method was used to solve the temperature field.The thermodynamic consistency of the present lattice Boltzmann model was verified,and the model parameters were adjusted to improve the model's accuracy.Laplace's law,surface wettability,and d~2law for droplet evaporation were verified respectively to confirm the reliability in simulating multiphase flow and phase change heat transfer.The grid independence of the model was also verified to improve the model's numerical accuracy.The copper foam was regarded as a porous medium,and a two-dimensional physical model of the porous medium was established.An improved thermal lattice Boltzmann method was used to study the pool boiling heat transfer on the porous media based on mesoscopic scale.The results show that,compared with smooth surface,the pool boiling heat transfer performance of porous media was increased by about two times,and the range of heat flux for high heat transfer performance was extended.Porous media with low porosity/pore size had a stronger resistance to bubble departure behavior,the bubble departure frequency was reduced,and the vapor release rate was reduced,the boiling heat transfer performance was better,but the heat transfer performance was severely suppressed under high heat flux condition.The porous media with high porosity/pore size had a weaker heat transfer performance,but its heat transfer performance was less affected by the increase of heat flux.With the increase of relative surface area,the real heat transfer coefficient(RHTC)in boiling regime showed a downward trend.Under high porosity condition(?>89%),the dominant factor influencing pool boiling heat transfer performance was heat transfer area rather than bubble departure resistance.