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Two-Phase Cooling Coupled with Waste Heat Energy Capture for Data Center Environments: Investigation of Two-Phase Boiler Performance
Keywords: MIcrochannels, Boiling, Cooling
The goal of the Waste Energy Recovery Project is to assess, improve and demonstrate methods for collecting and reusing waste heat from data center servers. Recovery of waste heat from servers requires an efficient sub-system for absorbing, transporting, and transferring heat from the server to the energy conversion sub-system. Energy conversion sub-systems currently under consideration include Organic Rankine cycles and Absorption Refrigeration cycles. Two-phase liquid cooling is particularly well-matched to these energy-conversion sub-systems because the flow loop is nearly isothermal. As such, heat can be transferred to the energy conversion sub-system at the highest possible temperature, thereby minimizing exergy destruction and improving energy conversion efficiency. In this phase of the project, we are evaluating the performance of microchannel evaporative cold plates in both two-phase pumped and non-pumped flow loops using R-134a as the working fluid. A pumped two-phase flow loop was developed to experimentally characterize the cold plates with aspect ratios ranging from 1:1 to 6:1. The flow loop allows precise metered flow to be delivered to the device under test with precisely metered heat addition and controlled inlet flow conditions. Overall cold plate thermal resistance is calculated as the primary performance metric and the operating flow rate and inlet conditions are being optimized in order to maximize the boiler performance by minimizing the cold plate thermal resistance. A conjugate heat transfer model of the boiler was developed in order to better isolate and understand physical behavior and optimize the boiler geometric parameters, operating flow rate, and inlet conditions. 1-D flow boiling correlations were implemented in a MATLAB® finite difference model to solve the fluid side of the problem. A commercial finite element software, COMSOL®, was then used to solve a full 3-D FEA model in order to predict the temperature and heat flux distribution in each channel. The experimental data is used to validate the numerical model. The experimentally validated detailed cold plate model is integrated into a MATLAB based system model in order to simulate and optimize a rack based system for transporting heat from multiple servers simultaneously to the energy conversion sub-system.
Daniel Fritch, Graduate Research Assistant
Villanova University
Villanova, Pennsylvania

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