Capillary pumped thermal loops are very effective devices as the rejection system of waste heat from artificial satellites and space vehicles, since they can transfer the heat without external power and furthermore they are light weight, highly reliable and long life devices. They are, therefore, attractive devices for space engineering. The present paper describes theoretical evaluation method of the maximum heat transport capability of the capillary pumped thermal loops and simulation experiments to confirm the theoretical results and to observe stable operation of the loop by using of visible test loops. In addition, the means to increase the heat transport capacity of the loop has been discussed based on the estimation of the pressure loss in each process in the loop.
