Heat Transfer Augmentation in Convecting Film Flows

The manifestation of unsteady heat transfer in incompressible forced convecting flows, such as film flows, is of direct practical interest to a large number of important industrial applications, such as film evaporators and reactors. In this paper an attempt is made to improve our fundamental understanding of unsteady heat transfer in these flows, and to predict this phenomenon by developing a reduced model of the specific case of a film flow over a heated solid. A time-varying heat transfer fluctuation is imposed, caused by a feature or disturbance that convects freely with the flow. The energy equation is solved to obtain the fluid’s thermal development, while a conjugate boundary condition comprising a one-dimensional thermal interaction between the fluid and the contacting solid substrate is imposed. Two heat transfer behaviours are found, which are referred to as “under-damped” and “damped”. Their characteristics with regards to the thermal development of the investigated flows are studied, including a consideration of heat transfer “augmentation” (relative to equivalent steady flows). Augmentation is found to remain negative for all investigated conditions.