A bubble-assisted natural convection method achieves both the high cooling limit of the forced convection method in which the refrigerant is convected by the pump and the feature of the natural convection method achieving a low PUE of around 1.02. In our previous report, the characteristics were examined mainly based on simulation, but this time the potential of this cooling method was evaluated mainly from an experimental approach. Specifically, a fluorocarbon as a refrigerant and a silicone oil which has a low global warming potential and is expected to exhibit the similar cooling performance. In the natural convection method, the lower the viscosity of the refrigerant, the higher the cooling efficiency. However, the bubble assistance effect was more remarkable as the viscosity of the refrigerant becomes higher. As a result, even with silicone oil, a high cooling effect was demonstrated. In addition, with any of the refrigerants, high cooling properes of PUE 1.02-1.04 were demonstrated with bubble assistance. That is, when selecting a refrigerant, it is not necessary to consider only physical properes relating to convection such as viscosity as an evaluation value, and other physical properes such as cost and global warming coefficient can be considered as evaluation values. These results indicate that the bubble assisted convection technology exhibits promising potential for a practically useful cooling technology.
