Towards a better understanding of heat transfer and flow mechanisms in a cavity channel with numerical simulations

In this work, both numerical simulations performed with ANSYS Fluent using the kT-kL-? turbulence model and experimental data are employed to investigate heat transfer in water flow in a uniformly heated (9500-19,350 W/m2) asymmetric channel for transitional Reynolds numbers ranging from about 3640 to 4970. The model predicts the experimental data mostly within about 15% and 16% respectively for the Nusselt number and pressure drops, with larger deviations for the Nusselt number occurring at the highest Reynolds numbers investigated. Simulations reveal the occurrence of a recirculation in the upper part of the channel. A new dimensionless parameter is introduced to characterize the strength of the recirculation with respect to the inertia flow which showed a distribution similar to the Nusselt number, thus suggesting an important role of the recirculation in enhancing the heat transfer. The thickness of both the thermal boundary layer and the conductive sublayer is determined both experimentally and numerically. While the former increases along the channel, the latter undergoes mostly a thinning, which can be attributed to the recirculation region. Peaks of negative turbulent heat flux are attributed to the flow recirculation and explain the minimum observed in the experimental temperature profiles. Among the RANS models, the kT-kL-? model resulted to be the best in predicting the experimental local Nusselt numbers. This work may aid in achieving a more efficient design of passive configurations for thermal management applications.