a b s t r a c tCooling of datacenters is estimated to have an annual electricity cost of 1.4 billion dollars in the United States and 3.6 billion dollars worldwide. Currently, refrigerated air is the most widely used means of cooling datacenter's servers, which typically represents 40e45% of the total energy consumed in a datacenter. Based on the above issues, thermal designers of datacenters and server manufacturers now seem to agree that there is an immediate need to improve the server cooling process. The goal of the present study is to propose and simulate the performance of a novel hybrid two-phase cooling cycle with micro-evaporator elements (multi-microchannel evaporators) for direct cooling of the chips and auxiliary electronics on blade server boards (savings in energy consumption of over 60% are expected). Different working fluids were considered, namely water, HFC134a and a new, more environmentally friendly, refrigerant HFO1234ze. The results so far demonstrated that the pumping power consumption is on the order of 5 times higher for the water-cooled cycle. Additionally, a case study considering the hybrid cooling cycle applied on a datacenter and exploring the application of energy recovered in the condenser on a feedwater heater of a coal power plant was also investigated (modern datacenters require the dissipation of 5e15 MW of heat). Aspects such as minimization of energy consumption and CO 2 footprint and maximization of energy recovery (exergetic efficiency) and power plant efficiency are investigated.

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