Experiments on isothermal and non-isothermal evaporation from partially filled, open-topped vertical tubes

Experiments were performed to provide a critical test of analytical/numerical models for predicting evaporation from an open-topped vertical tube partially filled with a liquid. Separate apparatuses were used to achieve evaporation under either isothermal or non-isothermal conditions. The experiments were performed for water evaporating into air which contained water vapor. The experimental work was supplemented by the numerical implementation of the models using the ambient conditions of the experiments as input. Excellent agreement was found to prevail between the experimentally determined and numerically predicted Sherwood numbers. This finding, along with other comparisons, validated the models. For isothermal evaporation, the validation established that account must be taken of natural convection in the gas-vapor space above the liquid surface and that pure diffusion is an insufficient description of the transport process. For non-isothermal evaporation, it was established that in addition to natural convection in the gas-vapor space, it is necessary to account for thermal radiation at the bounding surfaces of the space and for natural convection in the liquid pool.