The thesis has changed the heat and moisture exchange curves of Swiss Luwa air washer into double efficiency formulas which are widely used in our country with a computer, and also worked out the regression formula of...The thesis has changed the heat and moisture exchange curves of Swiss Luwa air washer into double efficiency formulas which are widely used in our country with a computer, and also worked out the regression formula of heat transfer efficiency(X). This has created favourable condition for us to use computer in our calculation of Luwa air washer.展开更多
A theoretical study has been conducted to investigate the effects of mass transfer on heat transfer in moisture exchange across a membrane and a mathematical model describing the heat transfer process with considerati...A theoretical study has been conducted to investigate the effects of mass transfer on heat transfer in moisture exchange across a membrane and a mathematical model describing the heat transfer process with consideration of the heat of sorption was established. A dimensionless variable, Ψ =JLλ /δ (T <SUB>10</SUB>−T <SUB>20</SUB>), which controls the effect of the heat of sorption on the heat transfer in membrane process, was obtained through theoretical analysis, and the effects of Ψ on the heat transfer process were analyzed. Results showed that in the case that the temperature gradient and mass transfer are in the same direction, the effective heat flux changes the direction at Ψ=1. For Ψ【1, the heat transfers from high to low temperature sides through the membrane, and the total thermal resistance increases with increasing the moisture flux across membrane or reducing the temperature difference between the bulk flows on the two sides of membrane. For Ψ】1, the overall effect of the heat and mass transfer is that the effective heat flux points from low to high temperature sides and the total thermal resistance decreases with increasing the mass flux or reducing the temperature difference. In the case that the temperature gradient and mass transfer are in the opposite directions, the existence of the heat of sorption acts to enhance the heat transfer from high to low temperature sides, causing a reduced total thermal resistance, and the greater the mass flux or the smaller the temperature difference, the smaller the total thermal resistance.展开更多
A theoretical study was conducted to investigate the effects of mass transfer on heat transfer in the process of moisture exchange across a membrane and a mathematical model describing the heat transfer with considera...A theoretical study was conducted to investigate the effects of mass transfer on heat transfer in the process of moisture exchange across a membrane and a mathematical model describing the heat transfer with consideration of the effect of mass transfer was developed.A dimensionless variable,ψi,which presents the degree to which the mass transfer affects the heat transfer,was proposed through theoretical analysis.With calculating of this dimensionless variable,the heat transfer coupled with mass transfer can be converted into a conventional heat transfer,making the heat transfer calculation simpler and more easily to understand.On the basis of theoretical analysis,the effects of mass transfer on heat transfer were numerically studied.The results show that,in the case that the temperature gradient and mass transfer are in the same direction,ψi is greater than unity,and the mass transfer acts to enhance the heat transfer;in the case that the temperature gradient and mass transfer are in opposite directions,ψi is less than unity,and the mass transfer works to hinder the heat transfer.When the mass flux is small,the effect of the mass transfer is weak.When the mass flux is large,the heat flux carried by the mass flux has a considerable impact on the heat flux,and ψi,deviates from unity significantly.展开更多
On the basis of non-equilibrium thermodynamic theory,the coupling phenomena of heat and mass transfer during the process of moisture exchange across a membrane were studied and the relevant physical and mathematical m...On the basis of non-equilibrium thermodynamic theory,the coupling phenomena of heat and mass transfer during the process of moisture exchange across a membrane were studied and the relevant physical and mathematical models were established.Formulae for calculating the four characteristic parameters included in the non-equilibrium thermodynamic model were derived,and the dependences of these parameters on the temperatures and concentrations on the two sides of the membrane were analyzed,providing a basis for calculating the heat and mass fluxes.The effects of temperature and concentration differences between the two sides of membrane and the membrane average temperature on the transmembrane mass and heat fluxes were investigated.The results show that for a given membrane average temperature,a larger concentration difference or a smaller temperature difference leads to a higher mass flux.For fixed concentration and temperature differences and with the mass flux predominantly caused by the concentration difference,a higher membrane average temperature yields a higher mass flux.The ratio of the heat of sorption induced by mass flow to total heat relates not only to the temperature and concentration differences between the two sides of membrane but also to the membrane average temperature and the ratio increases when the temperature difference is reduced.展开更多
文摘The thesis has changed the heat and moisture exchange curves of Swiss Luwa air washer into double efficiency formulas which are widely used in our country with a computer, and also worked out the regression formula of heat transfer efficiency(X). This has created favourable condition for us to use computer in our calculation of Luwa air washer.
基金the National Natural Science Foundation of China(Grant No.50576040)
文摘A theoretical study has been conducted to investigate the effects of mass transfer on heat transfer in moisture exchange across a membrane and a mathematical model describing the heat transfer process with consideration of the heat of sorption was established. A dimensionless variable, Ψ =JLλ /δ (T <SUB>10</SUB>−T <SUB>20</SUB>), which controls the effect of the heat of sorption on the heat transfer in membrane process, was obtained through theoretical analysis, and the effects of Ψ on the heat transfer process were analyzed. Results showed that in the case that the temperature gradient and mass transfer are in the same direction, the effective heat flux changes the direction at Ψ=1. For Ψ【1, the heat transfers from high to low temperature sides through the membrane, and the total thermal resistance increases with increasing the moisture flux across membrane or reducing the temperature difference between the bulk flows on the two sides of membrane. For Ψ】1, the overall effect of the heat and mass transfer is that the effective heat flux points from low to high temperature sides and the total thermal resistance decreases with increasing the mass flux or reducing the temperature difference. In the case that the temperature gradient and mass transfer are in the opposite directions, the existence of the heat of sorption acts to enhance the heat transfer from high to low temperature sides, causing a reduced total thermal resistance, and the greater the mass flux or the smaller the temperature difference, the smaller the total thermal resistance.
基金supported by the National Natural Science Foundation of China (Grant No. 50576040)
文摘A theoretical study was conducted to investigate the effects of mass transfer on heat transfer in the process of moisture exchange across a membrane and a mathematical model describing the heat transfer with consideration of the effect of mass transfer was developed.A dimensionless variable,ψi,which presents the degree to which the mass transfer affects the heat transfer,was proposed through theoretical analysis.With calculating of this dimensionless variable,the heat transfer coupled with mass transfer can be converted into a conventional heat transfer,making the heat transfer calculation simpler and more easily to understand.On the basis of theoretical analysis,the effects of mass transfer on heat transfer were numerically studied.The results show that,in the case that the temperature gradient and mass transfer are in the same direction,ψi is greater than unity,and the mass transfer acts to enhance the heat transfer;in the case that the temperature gradient and mass transfer are in opposite directions,ψi is less than unity,and the mass transfer works to hinder the heat transfer.When the mass flux is small,the effect of the mass transfer is weak.When the mass flux is large,the heat flux carried by the mass flux has a considerable impact on the heat flux,and ψi,deviates from unity significantly.
基金supported by the National Natural Science Foundation of China (50576040)
文摘On the basis of non-equilibrium thermodynamic theory,the coupling phenomena of heat and mass transfer during the process of moisture exchange across a membrane were studied and the relevant physical and mathematical models were established.Formulae for calculating the four characteristic parameters included in the non-equilibrium thermodynamic model were derived,and the dependences of these parameters on the temperatures and concentrations on the two sides of the membrane were analyzed,providing a basis for calculating the heat and mass fluxes.The effects of temperature and concentration differences between the two sides of membrane and the membrane average temperature on the transmembrane mass and heat fluxes were investigated.The results show that for a given membrane average temperature,a larger concentration difference or a smaller temperature difference leads to a higher mass flux.For fixed concentration and temperature differences and with the mass flux predominantly caused by the concentration difference,a higher membrane average temperature yields a higher mass flux.The ratio of the heat of sorption induced by mass flow to total heat relates not only to the temperature and concentration differences between the two sides of membrane but also to the membrane average temperature and the ratio increases when the temperature difference is reduced.
