Numerical investigation on heat transfer enhancement and surface temperature non-uniformity improvement of spray cooling

Heat dissipation and uniform temperature distribution are crucial to the operational reliability of electronic devices. In this study, the heat transfer enhancement and surface temperature non-uniformity (STNU) improvement of spray cooling are numerically investigated by CFD. The simulated results match well with experimental data under verification conditions with the maximum relative deviation below 7%, which demonstrates the numerical reliability of the two-phase flow model based on Euler-Lagrangian approach. The results of adjusting spray height reveal that there are different optimal spray heights for the heat transfer (4 mm) and the STNU (12.81 mm), indicating that the heat transfer enhancement and STNU improvement cannot be realized simultaneously. Based on this, two methods to enhance heat transfer and reduce STNU are developed. One method is to reduce the tangent angle theta and increase the tangent height H accordingly. It shows that the theta = 30 degrees, H = 27.59 mm case has a maximum enhancement of 24.03% in heat flux relative to the theta = 100 degrees, H = 6.21 mm case. Moreover, for all nozzles (theta = 30 degrees similar to 100 degrees), the lower STNU is attained at respective tangent heights. The other method is spray-array jets cooling, in which 132 micro-hole jets are added around the spray. It is found that the minimum STNU is obtained by spray-array jets cooling compared with all cases of spray cooling. In addition, it weakens the evaporation, but promotes the forced convection dramatically. Based on the analysis of several average liquid film microscopic characteristics and the droplet distribution, it is concluded that the mean film velocity, thickness and droplet coverage uniformity are the keys to determine heat transfer and STNU.