Developments in Humidity Standards and the Psychrometer Equation  

作　　者：Ian C.Kemp Carl-Gustav Berg 

机构地区：[1]Hyprotech UK Aspen Technology, Gemini Building, Fermi Avenue, Harwell Business Centre, Didcot, Oxfordshire OX11 0QR, U.K.,Process Design Laboratory Faculty of Chemical Engineering, Abo Akademi University, Biskopsgatan 8, FIN-20500 Abo, FINLAND

出　　处：《Chinese Journal of Chemical Engineering》2004年第6期792-800,共9页中国化学工程学报（英文版）

摘　　要：Determination of the wet-bulb temperature at the surface of a material is the basis of one class ofhumidity measuring instruments, and is important in industrial applications such as dryer modelling and simula-tion. The psychrometer equation is a frequently used method of estimating wet-bulb temperature, and contains apsychrometer 'constant'. Analysis shows that this is in fact a variable coefficient affected by temperature, pressure,radiation and conduction effects, and the identity of the gas and vapour. Radiation and conduction affect the dif-ference between adiabatic saturation temperature and indicated wet-bulb temperature. Inconsistencies in currentlyrecommended values for the psychrometer coefficient, including published international standards, are identifiedand explained. Particular problems arise when the enhancement factor is applied to vapour pressure to accountfor non-ideality of gases. Special considerations are also needed for wet-bulb temperatures approaching the boilingpoint, where the psychrometer coefficient tends to zero. Self-consistent recommendations recently published in thenew British Standard BS1339 are given, which cover both the air-water system and a general vapour-gas system.Determination of the wet-bulb temperature at the surface of a material is thebasis of one class of humidity measuring instruments, and is important in industrial applicationssuch as dryer modelling and simulation. The psychrometer equation is a frequently used method ofestimating wet-bulb temperature, and contains a psychrometer ''constant''. Analysis shows that this isin fact a variable coefficient affected by temperature, pressure, radiation and conduction effects,and the identity of the gas and vapour. Radiation and conduction affect the difference betweenadiabatic saturation temperature and indicated wet-bulb temperature. Inconsistencies in currentlyrecommended values for the psychrometer coefficient, including published international standards,are identified and explained. Particular problems arise when the enhancement factor is applied tovapour pressure to account for non-ideality of gases. Special considerations are also needed forwet-bulb temperatures approaching the boiling point, where the psychrometer coefficient tends tozero. Self-consistent recommendations recently published in the new British Standard BS1339 aregiven, which cover both the air-water system and a general vapour-gas system.

关 键 词：psychrometry humidity STANDARDS CONVECTION DIFFUSION enhancement factor 

分 类 号：O642[理学—物理化学]