| With recent rapid development in both fluid flow and heat and mass transfer in micro and nano scale,the gas particle fluid in micro scale,such as micro solid energy system,has attracted considerable attentions.However,the micro particles were usually treated as the macro one in the previous studies,which ignored the non-equilibrium momentum and energy exchange at the gas-particle interface.Thus,based on the issues as mentioned above,the present study was carried out which includes the following three parts: 1.Study on unconfined gas particle flow and heat transfer characteristics in the slip regime.A numerical model was established to investigate the flow and heat transfer characteristics between gas and particle in the slip regime,in which the gas compressibility and variable properties were considered.In the modeling,the velocity slip and temperature jump boundary conditions were implemented on the particle surface to characterize the rarefication effects between gas and particle.It shows that with increasing the Knudsen number,the velocity slip on the particle surface increases,which leads to a decrease of drag force.Meanwhile,the Nusselt number decreases with the increase of the Knudsen number due to temperature jump between gas and particle,which inhibits the heat transfer process.As gas variable properties were considered in present numerical model,the drag force will increase and the Nusselt number between gas and particle will decrease with increasing the particle temperature,which are caused by the increase of gas viscosity and conductivity,respectively.Therefore,the gas compressibility and variable properties cannot be neglected in the numerical model.Based on the numerical results,the flow and heat transfer correlations were proposed which consider the effects of micro scale and particle temperature.2.Study on confined gas-particle flow and heat transfer characteristics in the slip regime.Based on the previous study,a three dimensions numerical model was developed to study flow and heat transfer characteristics between gas and particle in a confined space,in which the gas was treated as compressible/variable fluid.In order to characterize the rarefication effects between gas-solid interfaces,the velocity slip and temperature jump boundary conditions were implemented on the particle surface and solid wall.The results show that drag coefficient and Nusselt number will decrease with increasing the Knudsen number.And with the increase of particle temperature,the drag coefficient and Nusselt number will increase and decrease,respectively.Moreover,comparing with the unconfined results,the enhanced heat transfer effect of confined space can be observed as the blockage ratio is larger than 1/8.3.Study on micro scale gas particle fluid in the confined space.Based on the Euler-Lagrangian approach,a two-dimensions numerical model was established to study gas particle fluid in the confined space.It was found that the gas rarefication effects on the particle surface will decrease the drag force,which leads to a slower movement of the micro particles compared to the macro scale ones.Besides,the particles with small Stokes number respond to the variation of flow quickly,while the particles with large Stokes number fail to characterize the evolutions of flow field due to the dominant inertial force effect.Moreover,the thermophoretic force has an important effect on micro particle trajectory in the confined space.And the side wall particle capture efficiency increases with the increase of the internal cylinder temperature. |
