Fluid dynamics and thermal performance of double-sided plate heat exchanger with streamwise periodic variable cross section Z-shaped flow channel

A novel microchannel flow structure characterized by a double-sided plated heat exchanger with streamwise periodically variable cross-sections (SPVCS-Z) was proposed in this paper. And a comprehensive investigation by analytical and numerical approach is then conducted to explore the fluid dynamics and thermal performance by varying two dimensionless geometry parameters:γ, ζ— the inclined angle and the slot width of the slant baffle-plates, respectively. The Reynolds number range based on channel width was set to 400–12800 and the uniform heat flux was set to 250000 W/m². The GEKO-turbulence model was utilized and calibrated by DNS data of a baseline forward-facing step flow and the free parameters C_SEP, C_NW and C_CORNER was modified respectively to their best-fitting values to 0.6, 0.5 and 1.0 at near wall turbulence in 2D domain. The investigation into the entrance effect of the flow channel reveals which can be minimized when ζ is around 0.125. In addition, based on the continuity assumption and morphology setup, a virtual streamline function for proposed corner flows within a characteristic volume-cell was derived. Furthermore, relevant semi-empirical analytical expressions for the convective heat transfer coefficient and Nusselt number were obtained. Notably, the contribution of the Reynolds number to heat transfer deviates significantly from the commonly observed constant-exponent relationship (about 0.2 ∼ 0.4). Instead, it exhibits a subtle dependence on the flow pattern. We fitted the exponent term of Reynolds number to 0.4-γζ/5, which shows nice agreement with the results obtained by numerical simulation. Compared to the flat plate turbulent boundary layer flow, the proposed SPVCS-Z design exhibits remarkably enhanced thermal performance under the geometric configuration optimized for maximizing the inclination angle and minimizing the scale of the baffle plate's slot. It natively supports double-sided cooling without the need to worry about the unevenness of flow dispersion. The study's findings offer profound insights into the analysis of fluid flow and heat transfer mechanisms of the SPVCS-Z structure, presenting detailed investigation of factors affecting heat transfer performance, along with an in-depth discussion on the trade-off relative to pressure loss. The derivation of the heat transfer expression facilitates the achievement of ultimate cooling performance for engineering practice in double-sided electronics cooling.