Comparative Estimation of the Effect from Using Different Coolants in Panel-Type Radiators of Spacecrafts

A radiant cooling heat exchanger is one of key components in a closed-cycle power installation and is the bulkiest structural part of a spacecraft. The most well-elaborated version of a cooler, known as a panel-type radiator (PR), is made according to the process arrangement of radiating panels. Selecting the optimal coolant is one of important issues in designing a PR. A liquid metal coolant in the form of molten Na–K mixture is presently regarded to be the most preferred one for these purposes. It features thermal stability, resistance to radiation, and a very high thermal conductivity. The main negative feature of Na–K melt is its explosion hazard when exposed to air, a circumstance due to which difficulties are encountered in experimentally perfecting the PR design under on-land conditions. We consider high-temperature organic coolants as an alternative to a liquid metal coolant. The aim of this study was to compare the effectiveness of using different coolants for the class of PR systems whose properties and geometrical characteristics are close to the prototypes developed at the State Scientific Center (SSC) Keldysh Research Center from composite materials on the basis of carbon fibers with high thermal conductivity. To this end, a mathematical model and relevant calculation procedure have been developed. The results from the performed calculations testify that, in view of a low specific heat of liquid metal coolant, its mass flow-rate should be a factor of 2–2.5 higher than the flowrate of high-temperature organic coolant, which entails essential loss of energy for pumping. Thus, the use of high-temperature organic coolants is more preferable for a certain class of PRs with parameters close to the considered ones. Turbulent flow of coolant is an important condition, due to which significant requirements are posed to its viscous characteristics. A diphenyl mixture can be regarded as the most efficient high-temperature coolant for the considered class of PRs.