On the evaluation of transport properties for droplet evaporation problems

This article presents an improved method to evaluate the average gas phase fluid properties to more accurately predict the evaporation rate of liquid droplets. Compared to the current widely applied method (known as the one-third rule), the new method is shown to reduce the evaporation rate errors from potentially in excess of 14% with an average of 6.1%, to within 3.5% and with an average of 1.4%. The method is derived analytically by equating the solution with constant transport properties and the solution with transport properties proportional to the square-root of temperature. Therefore, this method has a theoretical foundation and is not based on any fitting parameters or empirical coefficients. This work provides an essential link between the well-known constant property solution to droplet evaporation, and the more complex numerical solution with variable properties. The presented method allows the computational speed and simplicity of constant properties, while approaching the high accuracy of variable fluid properties.