Near wall temperature measurements and turbulent features in a water flow at transition Reynolds numbers in a square heated asymmetric cavity channel

Abstract

• Temperature profile and fluctuations in water flow in a heated cavity channel are measured at medium Reynolds numbers. • The conductive sublayer is clearly detected with a micro-thermocouple. • Temperature turbulent intensity shows peaks within the conductive sublayer with increasing magnitude along the channel. • Autocorrelation analysis reveals two trends in and outside the boundary layer attributed respectively to random turbulence and recirculation. • A slight peak in the Nusselt number distribution is observed in the centre of the channel as the Reynolds number increases. Passive cooling configurations are attracting an increasing interest in different thermal management applications. Nevertheless, a more efficient design requires deeper understanding of heat transfer and flow mechanisms. Among these, turbulence and convection play an important role. In particular, the so-called conductive sublayer close to the wall, where significant temperature gradients are present, is critical. Despite its importance, to the best knowledge of the authors only few experimental works have measured the temperature profile in the laminar sublayer of forced-convective turbulent flows. In the present work, measurements of the temperature profiles and temperature fluctuations in the boundary layer for water forced-convective flow in a heated cavity channel (for Reynolds number in the low turbulent regime [Re ≅ 3640-4970] and for different imposed heat fluxes [q w ≅ 9500, 13700, 19350 W/m 2 ]) were carried out using a micro-thermocouple at different streamwise positions. A new method is proposed for validating the temperature measurements. A minimum point in the temperature profile towards the inlet of the channel is observed which attributed to flow recirculation in the cavity. Increasing the fluid velocity resulted in a shift of the position of the minimum point towards the heated wall. An increase in heat flux led to a narrowing of the amplitude of the region around this minimum point. Peaks of temperature turbulence intensity with increasing magnitude along the streamwise direction were observed within the laminar sublayer. A slight peak in the Nusselt number distribution is observed at the centre of the channel as the Reynolds number was increased. Among the geometrical passive cooling configurations, the one presented in this work showed superior heat transfer performance.