Heat transfer through multi-layer insulation (MLI)

Abstract Multi-layer insulation (MLI) is a crucial component to reduce a heat leak of a cryostat, and it is used for various applications in cryogenics. Its role is significant for the superconducting power transmission line (SCDC) mainly because the ratio of the surface to the volume is large for the conventional cryostat, and the heat leak is a principal source of the loss of SCDC. If we cannot reduce the heat leak to the cryogenic pipe of the SCDC, we will give up on developing the SCDC. Fortunately, we reached to the criteria of the heat leak in the Ishikari project. However, we need a lower heat leak for the next project because renewable energy (RE) will be a dominant energy source in this century, and the working rate of the RE is lower than that of the current power grid lines. To understand the processes of the heat leak through the MLI, we performed two different experiments and analyzed the data because the numerical simulation is not adequate for the heat transfer of the MLI. One way of the experiments is to measure the aluminum-coated thin film (ACTF) temperature of the MLI. It is useful to shorten the experimental time to test the different types of MLI. We tested three different kinds of spacers of the MLI experimentally. We also tested the weight effect of the MLI for the heat transfer process. The experimental results show that when the weight is high, the heat leak is high, and the analysis shows that it depends on the spacers' thermal conduction. Finally, we found that the Net type is an optimum spacer of the MLI in the present time.