Duo-CPU Liquid Cooling Loop Configuration: Parallel or Series?

Liquid-cooled cold plates for servers with high power density are raising interests. Despite many researches about optimizing the structure and parameters of each cold plate, rare researches are reported on configurations of the interconnections among them. This paper compares parallel and series configuration of the liquid cooling loops in duo-CPU server in the energy efficiency point of view. The analytical models of energy efficiency in parallel and series configuration are developed for liquid cooling system in a duo-CPU server. CPU work load distribution, heat transfer efficiency of cold plate design, and robustness under partial-blockage after use are taken into considerations when making comparison. Conclusions are: 1) Among all load distributions, series loop is at most as efficient as parallel loop due to pre-heat effect for two identical cold plates; 2) pre-heat effect will be severer as cold plate efficiency improves; 3) for different cold plates with efficiency proportional to friction, the most efficient point of load balance maintains unchanged only for parallel loop; 4) the parallel loop is efficient in more situations; 5) partial blockage causes significant change of optimal working point for parallel loop and possible significant degradation of energy efficiency.