Heat transfer modelling of dropwise condensation behaviour of magnesium vapours in the electrothermal production of magnesium

Abstract

During the extraction of magnesium by the electrothermal process, the condensation of magnesium vapours in the condenser is critical to achieve operational efficiency. In the present work, a mathematical heat transfer model has been developed to predict the growth rate of a single liquid metal drop during dropwise condensation (DWC) of magnesium vapours in the electrothermal process. Homogeneous DWC model has been developed considering negligible thermal resistance at the liquid-vapour interface for a single cycle of liquid magnesium layer formed at vapour-liquid interface. The heterogeneous DWC has been modelled taking into account all possible thermal resistances. The role of constriction resistance on transient droplet growth behaviour has been studied and the parametric sensitivity analysis has been conducted. Parameters i.e. degree of undercooling (Delta T), contact angle (theta), thickness of condenser wall (delta )and constriction effect cause (beta) has been studied for droplet growth behaviour. Heat transfer and specially the constriction resistance was found to be quite significant for heterogeneous DWC of magnesium metal vapours. Alongwith other parameters, the thermally inactive region (beta) on the condenser surface inversely affects the growth. The model-based predicted Mg droplet growth profiles during condensation have been validated with published data on similar DWC studies.