Experimental investigations into mixed convection about a horizontal cylinder. Part A: Heat transfer using digital speckle pattern interferometry

Mixed convection heat transfer is commonly found in many engineering applications and is particularly relevant to the cooling of electronic components but despite this, the physics of this heat transfer regime is not fully understood. This paper presents an experimental study into buoyancy opposing cross flow, a commonly found mixed convection regime. The experimental configuration comprised a long heated cylinder suspended in a glass walled enclosure. The airflow within the enclosure was controlled using a baffled axial fan to give Reynolds numbers in the range of 32 - 89. The mean Nusselt numbers were measured about the cylinder for Rayleigh numbers between 1.7E+04 - 4.0E+04. For the acquisition of full field data the optical techniques, digital speckle pattern interferometry (DSPI) and phase measurement interferometry (PMI), were employed. Buoyancy opposing cross flow created an unsteady flow field about the cylinder at low Reynolds numbers and steady state temperatures. DSPI enabled real-time interferograms to be recorded and results are presented in the form of instantaneous interferograms showing the high frequency fluctuations of the temperature field about the cylinder. Attention is focused on understanding the trend in mean heat transfer values resulting from an increased inertia force and thus providing a significant insight into unsteady mixed convection flow.