Pressure drop analysis of direct liquid cooled (DLC) rack

This study presents an experimental and numerical characterization of pressure drop in a commercially available direct liquid cooled (DLC) rack. It is important to investigate the pressure drop in the DLC system as it determines the required pumping power for the DLC system, which affects the energy efficiency of the data center. The main objective of this research is to assess the flow rate and pressure distributions in a DLC system to enhance the reliability and the cooling system efficiency. Other objectives of this research are to evaluate the accuracy of flow network modeling (FNM) in predicting the flow distribution in a DLC rack and identify manufacturing limitations in a commercial system that could impact the cooling system reliability. The main components of the investigated DLC system are: coolant distribution module (CDM), supply/return manifold module, and server module which contains a cold plate. Extensive experimental measurements were performed to study the flow distribution and to determine the pressure characteristic curves for the server modules and the coolant distribution module (CDM). Also, a methodology was described to develop an experimentally validated flow network model (FNM) of the DLC system to obtain high accuracy. The measurements revealed a flow maldistribution among the server modules, which is attributed to the manufacturing process of the micro-channel cold plate. The average errors in predicting the flow rate of the server module and the CDM using FNM are 2.5% and 3.8%, respectively. The accuracy and the short run time make FNM a good tool for design, analysis, and optimization for DLC systems. The pressure drop in the server module is found to account for 56% of the total pressure drop in the DLC rack. Further analysis showed that 69% of the pressure drop in the server module is associated with the module's plumbing (corrugated hoses, disconnects, fittings). The server cooling modules are designed to provide secured connections and flexibility, which come with a high pressure drop cost.