Thermo-fluid dynamic behaviour of a small length 3D printed lattice channel in a conjugated problem

The ever-smaller size of the electronic components and the ever-increasing thermal power to be removed, stimulate the possibility of studying the mini-cooling channels with internal porous structures, to increase the exchanged heat flow. The reduced dimensions in length imply the need to evaluate the behaviour of these lattice channels in the conjugate problem, i.e. with the development, from the inlet section, of both the thermal boundary layer and the fluid-dynamic boundary layer. The thermo-fluid dynamics characteristics of an aluminium 3D-printed reticular channel are studied experimentally and numerically in this work. The lattice shape of the unit cell can be defined as a double X or a double pyramidal truss with a common vertex. The test channel (TC) is 80 mm long and has a cross-sectional area, without internal lattice, of dimensions HxW, where H = 5 mm and W = 15mm. Pressure losses are measured and friction factors are calculated for different air volume flow rates, from 34 to 136 l/min. The flow regime varies from ReH=2305 to ReH=9570. Under steady-state conditions, constant heat flux is applied to the external surface of the lattice channel. Local Nusselt numbers are evaluated to understand the effect of the combined entry length problem. About the thermal performance, the main conclusion is that the tested lattice channel has average Nusselt numbers equal to 5 times the corresponding values of the smooth duct, without the truss, under the same operating conditions, i.e. conjugated problem and constant heat flux. Moreover, considering also the pressure drops in the overall evaluation of the reticular duct performance, the cooling efficiency is calculated by introducing both a COP coefficient and considering the thermal efficiency index NuHSD /f1/3HSD.