Vapor evolution and condensation dynamics in a differentially-heated immiscible DCM-water layer system: High speed videography and IR measurements

The present study is concerned with the experimental investigation of boiling and condensation characteristics of one of the high volatile fluids as it undergoes phase change in a differentially-heated two-fluids system. The vertically stratified immiscible-fluids system is realized with dichloromethane (DCM), the more volatile component, as the (heavier) bottom fluid and water as the top fluid layer. Phase change in the bottom DCM layer is affected through localized heating using a transparent ITO-coated borofloat glass substrate, triggering nucleate boiling. Synchronized high-speed videography and infrared thermography are employed to investigate the coupled vapor transport and condensation processes occurring within the immiscible fluid system. An energy balance framework is developed to quantify local heat storage, lateral conduction, natural convection, radiation at the top plate. The analysis shows that lateral conduction within the copper plate constitutes the dominant heat dissipation pathway during condensation. Spatio-temporal variations in surface heat flux around the impact region highlight the influence of localized phase-change events on transient thermal transport. Comparison of the total estimated dissipated energy with the theoretical latent energy corresponding to a pure vapor bubble reveals that the entrapped volume carries a lower effective vapor content. It is thus inferred that the entrapped vapor bubble therefore consists of a composite liquid–vapor mixture, with the liquid fraction estimated to be approximately 28–44% across the tested heat flux range. The presence of this encapsulated liquid layer explains the stability of the rising entrapped volume, which undergoes almost negligible condensation while traversing through the water layer. The insights obtained enhance the understanding of vapor transport and condensation mechanisms in immiscible fluid systems and offer guidance for the development of passive, high-performance thermal management schemes.