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Experimental study of airflow and heat transfer above a hot liquid surface simulating a cup of drink

Laguerre, O., Osswald, V., Hoang, H.M., Souchon, I., Trelea, C., Hartmann, C., Flick, D.
Journal of food engineering 2017 v.197 pp. 24-33
air, air flow, air temperature, convection, evaporation, heat transfer, heat transfer coefficient, lead, odors, velocimetry, water temperature
This work was carried out to study the airflow and heat transfer above a cup of hot drink. The experiment was undertaken in a device in which the air temperature and velocity were controlled representing a room condition. The influence of heat exchange by convection and evaporation between the hot drink (at different temperatures) and air on the velocity and temperature fields above the cup is presented. An experimental methodology was developed to evaluate the heat transfer coefficient between the air and hot drink with and without evaporation.The airflow visualisation by PIV (Particle Imagery Velocimetry) above the cup shows that the flow is complex with unsteady plumes detachment and vortex formation. The combined convection and evaporation lead to upward airflow with temperature fluctuations which become significant for drink temperature above 55 °C. This can be explained by the non-linearity between saturated pressure of water and its temperature. This work could highlight how volatile aromas are released from hot drink.