Interaction of vapor cloud and its effect on evaporation from microliter coaxial well

Abstract

The evaporation of volatile heavy hydrocarbon liquid from coaxial well configuration is studied to understand the vapor phase transport, vapor cloud interaction and its effect on the local evaporation rate of two evaporating coaxial cavities of microliter volume. The gap between the two coaxial cavities is varied without varying the dimensions (width and depth) of the coaxial cavities for studying the vapor cloud interaction. Digital holographic Interferometry (DHI) is used to decipher the vapor mole fraction field above the coaxial well. Gravimetric measurement has been carried out for measuring the evaporation rate. Diffusion-limited simulation of evaporation process has been carried out using COMSOL Multiphysics software to understand the role of convective motion. IR thermography measurement of liquid interface temperature has been carried out to correlate the vapor cloud interaction with local evaporation rate and evaporation induced cooling. A flat-disk shaped vapor cloud surrounds the coaxial cavities. Total evaporation rate measured from DHI shows good agreement with the gravimetric measurement having maximum deviation of 3%. Good match between the evaporation rate measured from gravimetry and holography with diffusion limited model is observed at low Grashof number. The mismatch in evaporation rate with the diffusion limited model is observed at high Grashof number due to higher radius of the coaxial cavity indicating the dominance of convective motion. The evaporation rate from individual well decreases when liquid simultaneously evaporates from the inner and outer coaxial cavities. This reduction in evaporation rate increases with decrease in gap between the two coaxial cavities due to increase in interaction between the vapor cloud. The decrease in local evaporation rate from individual cavity due to presence of a neighboring evaporating cavity correlates with the evaporative cooling effect using temperature measurement of the interface from IR thermography. Vapor cloud interactions of microliter volume coaxial cavities can influence the evaporation rate of individual coaxial cavity and the convection inside the liquid phase. The present study demonstrates the capability to precisely control the evaporation process by appropriate design of coaxial well configuration. The results from the present study can be useful for controlling the evaporation rate in several applications i.e. protein crystal growth, DNA/RNA sequencing and microfabrication etc. by suitable design of coaxial well.