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Evaporation and condensation phenomena play a significant role in many of the nuclear, biochemical, and thermal processes in industrial applications. It is a complicated phenomenon as it undergoes both heat and mass transfer processes along with the complexities involved in the interfacial regions of vapor and liquid phases. Several experimental works have been carried out in the recent past to understand the condensation process in detail. However, understanding the phenomenon using computational technique is more advantageous as the interfacial mass transfer between gas and liquid can be modelled accurately. In the present work, condensation of a saturated vapor bubble in the sub-cooled liquid is studied, and various factors that influence the bubble shape change and the bubble lifetime, are evaluated. The analysis is carried out using the ‘Multi-Fluid Volume of Fluid’ and ‘Thermal Phase Change’ (TPC) models implemented in ANSYS Fluent commercial CFD solver. A detailed study is performed to obtain the best approach for calculating interfacial area density using a ‘user-defined function’ (UDF), and the advantage of the node-based gradient calculation method is exhibited. The numerical results obtained for the history of bubble shape and bubble lifetime are validated against the experiment and previously published works with good accuracy. The paper also elaborates on how the initial bubble diameter, the subcooling temperature, and the system pressure affects the shape and lifetime of the bubble during the condensation process. Godkänd;2021;Nivå 0;2021-02-16 (johcin)

Open window buses without air-conditioning are a major mode of urban and inter-city transport in most countries. High occupancy combined with hot and humid conditions makes travel in these buses quite uncomfortable. In this study air flow through a bus has been studied that could be the basis for low cost and eco-friendly methods of increasing passenger comfort and possibly reduce drag. The aerodynamics of such a road vehicle has not been studied as previous investigations have been confined to vehicles with closed windows that present a smooth exterior to air flow. Using a 1:25 scaled Perspex model of an urban bus in Delhi, flow visualization was performed in a water channel. The Reynolds numbers were one-tenth of a real bus moving at 10 m/s. Smoke and tuft visualizations were also performed on an urban bus at 40 km/h. Numerical simulations were performed at the actual Reynolds number. Even though there were Reynolds number differences, the broad features were similar. Air enters the bus from the rear windows, moves to the front (relative to the bus) and exits from the front windows. Inside air velocity relative to the bus is about one-tenth of the free-stream velocity. The flow is highly three-dimensional and unsteady.