Numerical simulations of hotspot cooling with non-Newtonian power-law fluid in a minichannel having segmented elliptical pin fin arrays

Official URL: https://dx.doi.org/10.1016/j.icheatmasstransfer.2026.112449

In this study, flow and heat transfer in a minichannel with segmented elliptical pin-fin arrays were investigated using Newtonian and power-law fluids under two operating conditions, namely at fixed inlet flow rate and fixed generalized Reynolds number. The analysis systematically examined the coupled effects of shear-thinning rheology, segmented geometry, and flow constraints and provided new insights into their combined influence on the thermal-hydraulic performance. A fully developed inlet velocity profile was imposed in all simulations. The results show that the presence of pin-fins significantly modified both momentum and thermal transport by repeatedly disrupting boundary layer development across segmented heating zones. At a fixed flow rate, the thermal-hydraulic response is governed by the coupled influence of the fluid rheology and resulting variation in the generalized Reynolds number. An increase in the consistency index m, accompanied by a decrease in the power-law index n, led to higher pressure losses and reduced heat transfer, with approximately a 45% decrease in the average Nusselt number over the investigated range of n. This effect was marginal for the channel without pin-fins. In this case, streamwise variations were weak due to repeated redevelopment of the flow in each segment. At a fixed generalized Reynolds number, the behavior changed noticeably: both the pressure drop and Nusselt number had a non-monotonic dependence on n, which revealed a competition between shear-thinning effects and velocity scaling. The introduction of pin-fins significantly enhanced the heat transfer performance, as evidenced by substantially higher Nusselt numbers compared to the reference case without pin-fins. The thermal resistance was also considered as another performance index. Accordingly, the thermal resistance for the intermediate power-law index (n = 0.45) had a non-monotonic trend: an increasing trend at low Reg and pressure drop values and a decreasing trend at higher values due to enhanced convective transport. Furthermore, the thermal-hydraulic performance was evaluated using the Performance Evaluation Criterion (PEC) under a fixed flow rate. Water led to PEC values above 3, indicating strong overall enhancement, whereas all shear-thinning fluids yielded PEC < 1, which further decreased with decreasing power-law index and reflected a reduced thermal-hydraulic performance.