Simultaneous investigation of flow and thermal fields inside a square duct with a built-in heated circular cylinder

Abstract

Air-based cooling methods are widely used for heat exchange and thermal management, due to their potential for heat removal with minimal complexity and operating costs. However, the physical mechanisms involved in these processes are not yet fully understood, due to the complexities involved in the many interacting underlying sub-processes pertaining to the energy transfer from the surface to the bulk fluid. When dealing with turbulent flows involving heat transfer, one needs to delineate the coupled effects of velocity and temperature to ascertain the heat transfer dynamics. Here, we present the first-ever application of an advanced methodology based on the concept of two-color laser-induced phosphorescence (2cLIP) and particle image velocimetry (PIV), elucidating the mechanisms involved in the heat transfer from the surface of a cylinder placed inside a confined square duct. The potential advantage of the technique is in measuring the whole-field velocity and thermal fields simultaneously by incorporating modifications to the conventional PIV systems through the usage of a single tracer (BAM:Eu+2) for measuring the velocity and temperature fields. This aids in reducing the costs and complexities involved in setting up separate systems for measuring the temperature field distributions. Measurements reported here, were performed for the Reynolds numbers of 270 and 360, and for the heat flux levels of 10, 12 and 15 W. Experimental observations revealed that, with an increase in the mass flow rate from 3.06×10-4 (kg/s) to 4.08×10-4 (kg/s), the heat removal rate from the surface of the cylinder was enhanced. Also, the heat transfer was witnessed to enhance in the rear portion of the cylinder, in the case of increased cylinder heat input at constant mass flow rate. Also, a local peak in the heat transfer coefficient was indicative of the flow separation from the cylinder surface. The spatio-temporally averaged Nusselt number (Nu¯D) was witnessed to be higher for higher mass flow rate and was seen to increase with increasing cylinder heat input at constant mass flow rate. To the best of the knowledge of the authors, the work reported is one of the first attempts to carry out the simultaneous, whole-field, non-intrusive measurements of flow and heat transfer in a confined channel fitted with a heated cylinder using Thermographic-PIV technique.