Numerical Simulation Of Heat And Moisture Convection Characteristic In Multi-media Indoor Air

Indoor air environment is influenced by the process of air flow,heat and moisture transfer.The simulation of indoor air heat and moisture transportation is an important way to understand and evaluate the quality of indoor air environment.It is of great significance to understand heat and moisture transfer in electronic equipment and building thermal storage wall by conducting the research of double diffusive convection in enclosures filled with air,solid and porous medium.This paper investigated the fluid flow,heat and moisture transfer in enclosures filled with air,solid and porous medium both analytically and numerically.The influence of parameters(Rayleigh number,buoyancy ratio and Darcy number)on the heat and moisture transportation is mainly considered.Firstly,numerical simulation and scale analysis were carried out to investigate the effect of solid blocks with two configurations on natural convection heat transfer in the enclosure.Based on a large number of numerical results,the correlation between the average heat transfer rate of the two configurations is obtained.The increase of Rayleigh number and thermal conductivity will promote the heat transfer in the cavity,while solid-to-fluid volume ratios and the number of solid blocks would weaken the heat transfer rate.Especially,when the number of solid blocks reaches the critical value,the flow in the gap between solid blocks will be gradually stagnant.Scale analysis was used to derive an analytical expression for the minimum number of obstacles required for the phenomenon of flow decay inside gaps to take place.Secondly,the influence of solid wall on heat and moisture transportation in an inclined rectangular enclosure was studied.Based on the assumption of parallel flow,the analytical solutions under different conditions were obtained.The heat and moisture transfer rates in the enclosure obtained the minimum when the buoyancy ratio was-1.The presence of solid wall could inhibit the heat and moisture transfer rates,which shows that the thicker solid wall decreased the Nusselt number and Sherwood number.The combined effect of opposed buoyancy ratio and negative angle of inclination was similar to that of cooperate buoyancy ratio and positive angle.The comparison between analytical and numerical results showed that the parallel flow assumption was valid in most situations.Futhermore,multiple steady flow solution branches in the vicinity of N =-1 have been numerically obtained,which are the upward solutions from buoyancy ratio increasing from-2 to 0,the downward solutions of the buoyancy ratio decreasing from 0 to-2,and the rest solutions of the motionless states.When considering the superposition of fluid layer and porous layer,the effects of two configurations of porous layer and the presence of Soret effect and Dufour effect on heat and moisture transportation and entropy generation were discussed.On one hand,the heat and moisture transportation of two different configurations of porous layers in a square enclosure was studied analytically and numerically.The average heat and moisture transfer rates increased with higher Rayleigh number and buoyancy ratio.Thermal and solutal buoyancy forces in these two enclosure were always cooperated such that only these situations of N > 0 should be considered in future.A good agreement of Sherwood number was obtained between the analytical and numerical results,while the scale analysis may overpredict the average heat transfer rates in two configurations.On the other hand,the effects of porous layer under Soret effect and Dufour effect on double diffusion convection and entropy generation were considered.Soret effect had no significant effect on the heat transfer rate,but the moisture transfer rate would be enhanced by stronger Soret effect.Dufour effect had a positive effect on heat transfer rate and would weaken the moisture transfer rate.In addition,the increase of Soret parameter could enhance the entropy generation induced by heat transfer and fluid viscosity,while all entropy generation would be decreased due to the positive effect of Dufour parameter on heat and moisture transfer process.In addition,when solid-to-fluid volume ratio was low,the heat transfer rate of square solid blocks was higher than that of rectangular solid blocks,and the opposite result was obtained for the higher solid-to-fluid volume ratio.On the basis of these results,the influence of internal heat generated porous layer on the double diffusion convection in an enclosure was discussed.The average heat and moisture transfer rates increased with the increase of Rayleigh number and buoyancy ratio,while the Darcy number and thermal conductivity of porous block had little effect on the moisture transfer rate.The presence of magnetic field inhibited the convection effect in this enclosure,and the stronger magnetic field would lower the heat and moisture transfer rates.On the other hand,the maximum values of average Nusselt number and Sherwood number were located at the inclination angles of-10 and 30,respectively.Finally,heat and moisture transportation in an enclosure with a composite layer consisting of an internal heat generated porous layer and a solid layer was simulated.In the convection dominant region,the average heat transfer rate increased with the increase of Darcy number in the solutal-driven flow,but decreased in the thermal-driven flow,and the average moisture transfer rate increased monotonously.The thermal conductivity of composite layer could promote the heat transfer in the enclosure,and had no significant impact on the moisture transfer.The average heat transfer rate as a function of inclination angle,when N > 0,was presented like a sinusoid where the maximum is near at 45° and 135° and the minimums is located at 90°.