Flow And Heat Transfer Analysis Of Flue Gas In Flue Composite Wall In Northern Ruralareas

The rural areas in northern China have a large population and those rural buildings cover a large area.The energy consumption of building heating in northern rural areas in winter far exceeds that of urban areas.One of the reasons for the high building energy consumption is that the poor thermal insulation performance of those enclosure structures.The energy loss caused by the heat transfer through the external wall is large and the wall is prone to condensation and mildew.The second reason is that the large exhaust smoke and excessive combustion losses of the Kang system which is used for heating in northern rural areas.To solve the problem of excessive energy consumption in northern rural buildings,it is necessary to take into account both the architectural characteristics of rural houses and the economic conditions of farmers.Therefore,this paper puts forward a new flue composite wall,which can not only achieve the purpose of heat preservation and reduce the energy consumption of buildings but also do not increase the economic burden of farmers.This paper proposes a new flue composite wall that uses the flow and heat transfer of high temperature flue gas in the flue to achieve the thermal insulation and moisture isolation of the wall and recovery the waste heat resources.Therefore,this paper uses both the thermal performance test and numerical simulation method to study the characteristics of the wall by strengthening the convection heat transfer on the gas-solid surface to recover the waste heat of the flue gas and heat insulation and moisture isolation.This paper also gives the calculation method of the related thermal performance parameters for the rational optimization and analysis of the flue structure of the wall,which provides a scientific basis for using the flue to carry out the recovery of the waste heat and heat preservation and dehumidification.The multi-function composite wall test bench was used to test the flow and heat transfer conditions of the flue composite wall.The main thermal performance test parameters are the transient temperature and the surface heat flux density of the surface of the wall.The temperature of the surface of the measuring wall continued to rise to295.59 K during the heating period,and the temperature of the wall rose to the peak value of 298.83 K after 80 minutes.Then the wall came into the cooling stage,and the final wall surface temperature was reduced to 292.83 K after 640 min.The average heat flux on the surface of the wall decreased to-29.8 W/m2 firstly and then rose to-6.87W/m2 during the operation.The test results show that the flue composite wall can hold moisture and recover the residual heat resources of the flue gas.By establishing the three-dimensional unsteady coupled turbulent flow and radiative heat transfer model of the flue composite wall,the thermal performance of the flue composite wall is simulated.By comparing the simulation results of the temperature and heat flux of the measured points of the wall with the measured data,the mean error of the simulated calculation is only 5.42%.It shows that the mathematical model can be used to describe the thermal performance of the wall.In order to obtain the reasonable flue structure and its size parameters,the influence of different flue structure,insulation thickness,cavity thickness,the baffle width and the inlet velocity on the thermal performance of the wall is simulated.The heating and thermal insulation performance of the wall is better when the flue type is cross-tunnel,the thickness of the insulation layer is 60-80 mm,the thickness of the cavity is 60-40 mm,the width of the smoke baffle is 20-80 mm,and the inlet velocity of flue is 0.95-1.55m/s.The range of the reasonable operating parameters of the flue composite wall and the optimization of different flue structures provide basis and reference for the thermal design and maintenance of flue composite wall for northern rural houses.