Calculation of evaporation of chemicals into air

Calculation of the rate of evaporation of volatile chemicals exposed to air is needed in many situations to determine environmental impact and need for mitigating actions such as providing ventilation. Such situations include emission sources in industrial manufacturing operations such as open surface tanks, container filling, indoor spills, spills occurring in transportation and from bulk storage facilities. There have been a number of experimental studies to measure rate of evaporation of chemicals from horizontal surfaces. A number of theoretical and empirical prediction methods have been proposed. However, there has been no evaluation of various prediction methods with a database consisting of data from many sources covering a wide range of properties and conditions so that the best methods could be identified. This research was done to fulfil this need. Data for 21 chemicals with very diverse properties exposed to air at a wide range of velocities and temperatures were compared to available general correlations. These included empirical and semi-theoretical correlations as well as the analogy between heat and mass transfer. Data were from tests done under natural convection as well as with forced convection. Air velocity ranged from 0 to 5.1 m/s, air temperature from 5 to 61 °C, evaporating liquid temperature −1 to 64 °C, and liquid saturation pressure 0.01 to 61 kPa. A simplified formula was derived for natural convection evaporation using the analogy between heat transfer which shows excellent agreement with data. The results of this research are presented and recommendations are made regarding the most suitable correlations under various conditions.