Numerical Study On Flow Field And Heat Transfer Characteristics In Porous Material Layer Of Exhaust Air Insulation Wall

With the increasing demand for living and working environment,the original housing structure can no longer meet the current needs.Multifunctional architecture is increasingly respected by this society.However,from the perspective of the contact area between the entire building and the outside world,the exterior wall is undoubtedly the most important part of the whole enclosure structure.Therefore,the analysis of energy-saving transformation and thermal comfort of exterior walls has become the research focus of the whole society.A strong thermal performance of the wall must generally meet the thermal comfort and thermal insulation performance is prominent.In this large environment of energy-saving transformation and development,a new type of composite wall structure which meets the needs of today's environment has emerged as the times require —— exfiltration thermal insulation.The exfiltration thermal insulation is a new type of energy-saving wall which combines enclosure structure with exhaust heat recovery system.Its core point is that the airflow seeps in the porous material layer,taking away the load that is transmitted to the indoor from the outdoor,so that the temperature of the surface of the indoor side wall can be infinitely close to the indoor temperature,reducing the energy consumption of the air conditioner,and returning to the heat of the exhaust air.At the same time,it can also take away the polluted gas that is stranded,clean the air,and improve the thermal comfort of the indoors.In the early stage of my research group,basic,liner type,sandwich ventilation have been studied and analyzed.It is clear that the exhaust air insulation wall has superior thermal insulation performance compared with other walls.The Previous studies on all heat transfer characteristics,load characteristics and thermal insulation performance of walls are based on the numerical model established by our research group.However,the model is not entirely in line with the actual situation.In order to simplify equation and save calculation time,we have related simplifications and assumptions about the model.As for the rationality of this hypothesis and its impact on the actual situation,there is no detailed study so far.In view of the above realities,this paper establishes CFD model to investigate the effects of different factors on the flow field and heat transfer characteristics of basic and liner type walls.As to how to verify the rationality of the simplification of the previous model,we quantitatively analyze the accuracy of the three hypotheses of horizontal flow,uniform permeation and horizontal heat transfer by using velocity angle,mass flow rate and inner surface temperature as assessment variables,and simulate the influence of different cavity layer factors,structure layer factors and permeability layer factors on these three hypotheses respectively.Through the above simulation analysis,the research results show that the airflow of the basic exhaust air insulation wall is mainly concentrated in the middle and lower part of the flow.the vertical heat transfer can be neglected.And the liner type airflow mainly concentrates on the bottom and top flow.the vertical heat transfer phenomenon exists and can be completely suppressed by the change of external conditions,and neither type of wall flows completely in the horizontal direction.The results of this study also provide the best external conditions for different wall types to meet the simplified assumptions,and provide a theoretical basis for later numerical model modification and the application of exhaust air insulation engineering.