湿度标准及湿度计量之进展

• 来源期刊: 中国化学工程学报（英文版）
• 学科: 工学
• 关键词: psychrometry humidity standards convection diffusion enhancement factor
• 年，卷（期）: 2004,（6）
• 页码范围: 792-800
• 页数: 9页
• 分类号: TQ0
• 语种: 英文

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.