The objective of the short course is to present the latest developments in the theory and applications of PTC, Passive Thermal Control.
The lectures on relevant subjects will be presented by international experts who have first hand experience in the design and application of such sytems.
A passive thermal control system relies on conductive and radiative heat paths and has no moving parts or electrical power input. PTC is extensively used in the design of spacecrafts, satellites, electronic equipment, and similar objects where heating or cooling with active means, such as use of heaters, coolers, shutters, louvers, and cryogenic fluids, are either not practical or feasible for the required temperature ranges.
The techniques applied for PTC include phase change devices, coatings, insulation blankets, thermal doublers, and heat pipes.
Phase change devices absorb thermal energy by changing from a solid to a liquid. As the temperature decreases, the material re-solidifies. It is especially useful for electrical equipment that experiences short power spikes. The main disadvantage of phase change devices is that they are unable to absorb any more heat after melting, which allows the temperature to increase. A common type of phase change device is some type of wax in an aluminum container. These devices can be used between a cold plate and the primary heat dissipation device.
Thermal control coatings are surfaces, such as black and white paints, and gold, silver, and aluminum foils, that have special radiation properties. Coatings may be combined to obtain a more desirable average value for the radiative properties, absoptivity and emissivity (e.g.. a checker-board pattern). In general, it is desirable to have a high value of emissivity and a low value of absorptivity in order to maximize the heat rejection into space and to minimize the solar input. Thermal coatings are very efficient and lightweight. Unfortunately, they tend to degrade over time.
Multi layer insulation consists of closely spaced layers of aluminized Mylar or Kapton alternated with a course-net material. Insulation reduces the rate of heat flow per unit area between two boundary surfaces and prevents a large heat influx. Sensors and payloads can be wrapped in insulation blankets to thermally isolate them and reduce thermal control requirements.
Thermal doublers are heat sinks made of a highly conductive material placed in thermal contact with a component. Heat is conducted to the sink during an increase in temperature and then dispersed by radiation or conduction. The process also works in reverse and keeps components from experiencing severe cooling. They can also be used to spread heat out over radiator surfaces, and are frequently used to control the temperature of electrical equipment that has high dissipation of cyclical variation in power dissipation.
Heat pipe is a closed system in which heat is dissipated by evaporation and condensation. Thermal energy is absorbed by a liquid within the pipe. The liquid is turned into a gas which transports the heat to the other end of the pipe. The gas then condenses, cooling back into a liquid and releasing the heat to a radiator. The liquid returns to the hot area by way of capillary wicks. At room temperature, the pipe is usually made of Aluminum and the liquid is usually Ammonia. Heat pipes provide a highly conductive heat path and extremely high heat transfer rates. In addition, they are lightweight, can be used for a wide range of temperatures, and can have a variable conductance.