Thermal analysis of liquid immersed electronics for data centres

Data centres have racks that include servers which support digital services. The growing demand on digital services such as streaming content, web services, telecommunications, financial and social media has led to an unprecedented growth in data centres and therefore their electrical power consumption. A significant portion of data centre energy is consumed by the cooling systems within data centres. Energy consumption of data centres can be reduced by improving their cooling systems. Some data centres are cooled by air cooling while others are cooled by liquid. The liquid cooling approach has greater opportunities for efficient cooling, particularly in high density data centres. The liquid cooling methods can be classified as rack heat exchanger, in server and on chip heat exchangers and total liquid immersion. The liquid immersed concept submerges the server in a dielectric liquid. This liquid is in direct contact with all of the microelectronics and it has properties that do not cause any electrical discharge. The heat from server components, such as the CPU, is transferred via natural convection in the dielectric liquid to water channels, which transport the heat. The main interest of this thesis is to study liquid immersed microelectronics for data centres. The thesis starts with validation of numerical and experimental work to develop the correct physics for immersed server simulation model. Investigations for optimal heat transfer within the servers include varying the fin height and cold plate height and the adoption of baffles on the server water jackets (similar to a cold plate). How such servers can be integrated into a data centre is also investigated. The overview results show that the heat transfer performance when immersing servers is improved when heights of the heat sink fins and distances of the cold plate are optimised. Baffles with a rectangular cross sectional area attached to the water jacket demonstrated the best results where the heat transfer can be improved by up to 71% compared to water jackets with no baffles. Extending these results into a data centre scenario showed that increasing the rack occupancy had a positive effect on the Power Usage Effectiveness (PUE), which indicates an improvement in the cooling system.