The Application of Hybrid Loop Heat Pipe System in Data Center Cooling

People nowadays use the Internet to make data centers leading to more and more waste heat in a cloud industry. Currently, the majority of cooling methods in data centers is air conditioning cooling (such as Google, Apple & Facebook), requiring to be located near the river or ocean to assist cooling. However, the efficiency of air-cooling is not sufficient enough due to the requirements of energy-consuming air conditioning systems or chillers. The cooling element can be roughly distinguished into two types: passive cooling element and active cooling element. Traditional Loop Heat Pipe system is a passive element, using phase-change effect to transfer heat without adding external power source when operating, while Hybrid Loop Heat Pipe system is an active cooling advice, designed to add the pump. These system uses a small amount of electrical power in exchange for exponential growth of heat transfer performance. From 2004, the US military cooperated with energy organizations to provide concepts of the combination of capillary force and liquid pump in two-phase circuits. In 2009, the same team discussed the influence of liquid pumps in loop heat pipes. In 2015, the professor Eduard Or considered with developing new cooling method, used in data centers in order to save energy. As a result, this study develops and manufactures Hybrid Loop Heat Pipe system by adding water pump and storage tank into a conventional loop type heat pipe system. Not only the capillary force but also pumping force provides the overall pressure drop of the system. The reservoir is able to keep sufficient working fluid to the wick structure from making it dry out. Therefore, further investigation of the effect of flowrate in Hybrid Loop Heat Pipe system is needed. Experimental results show that Hybrid Loop Heat Pipe system used Nickle as wick structure and water as working fluid, resulting in the maximum heat transfer capacity up to 1500W, 275%, better than traditional loop heat pipe, the thermal resistance from 0.226 ℃ / W down to 0.0788℃ / W; while using Nickle as wick structure and acetone as working fluid has the maximum heat transfer capacity up to 900W, 500% , better than traditional loop heat pipe, the thermal resistance from 0.35℃ / W down to 0.091℃ /W. In addition, this study used the same condition and controlled the temperature at 100℃ ± 1 ℃ to explore the effect of flowrate on performances. The results show that it is the flowrate of 0.9L / min which has the maximum heat transfer capacity of 600W and the lowest thermal resistance of 0.09 ℃ / W. Finally, this study used Hybrid Loop Heat Pipe system to demonstrate the cooling of the data center, showing the results that the extreme heat load is of 700W; operating temperature of 110 ℃; the lowest thermal resistance of 0.078 ℃ / W. Furthermore, It also has excellent performance of 500W within the limits of 100 ℃. In summary, this study can effectively enhance the heat-transfer performance of traditional loop heat pipe and significantly reduce the thermal resistance by pumping energy less than 50W. Hybrid Loop Heat Pipe system has extreme potential for high power density industrial such as cloud data centers.