variavel0=<b>José R. Simões-Moreira</b> - jrsimoes@usp.br Escola Politécnica da Universidade de São Paulo
<b>P. S. G. Carvalho</b> - psgc@uol.com.br Escola Politécnica da Universidade de São Paulo
<b>Abstract.</b> It is important to know the water vapor content in many industrial processes such as combustion and process gases and particularly in atmospheric air. Several techniques and instruments can be used to measure the water vapor content, and the psychrometer is the most largely used because of its simplicity, low cost, and precision range within many practical applications. Its working principle is based on a simultaneous mass and heat transfer equilibrium process between a moist gas and the bulb of thermometer covered with a wet wick. The equilibrium temperature displayed by this thermometer is the Wet Bulb Temperature (WBT). Within certain operational conditions, the WBT is very close to a thermodynamic property of the moist gas known as Thermodynamic Wet Bulb Temperature (TWBT), which depends only on the thermodynamic state of the gas and can be used to determine the exact amount of water vapor in the gas. On the other hand, the WBT depends on many factors, including the bulb geometry, relative gas velocity, radiation effects, just to mention a few parameters. In this paper we investigate the operational conditions as well as the constructive geometry of the psychrometer and the Reynolds number range so that its temperature indication, i.e., WBT can be taken as the TWBT for any type of gas.
<b>Keywords.</b> wet, water vapor, humidity, moist, gas.