Heat pipes cryogenic

W. L. Haskin, Cryogenic Heat Pipe, Report AFFDL-TR-025, Flight Dynamics Lab., Wright Patterson Air Force Base, Ohio, 1967. 

Vasiliev L.L., Kulakov A.G. (2003) Heat Pipe applications in sorption refrigerators, Low Temperature and Cryogenic Refrigeration. NATO Science Series II, Vol 99, Kluwer Academic Publishers, 401- 414. 

The considered experimented set - up can be applied in two different ways. The first one is to use is as a semiconductor sensor cooler with low heat dissipation to cool the sensor down to the ambient temperature. It is interesting to be applied in cryogenic range of temperatures. The second option is related with the cooler for high energy dissipation devices (for example laser diode cooler). The first set of experiments was performed with sorption heat pipe and ammonia as a working fluid to demonstrate the basic possibility to decrease the temperature of the heat loaded wall to compare with the temperature of this wall in the phase of loop heat pipe cooling mode. 

In the applications, industrial heat exchanges are mini-and-microscale heat transfers, miniature and micro heat pipes and heat transfer issues in cryogenic catheters are presented. Nanotechnology and heat transfer including heat transfer characteristics of silicon film irradiated by pico to femtosecond lasers are also introduced and discussed. 

Lee (2010) Thermal Design Heat Sinks, Thermoelectrics, Heat Pipes, Compact Heat Exchangers, and Solar CellshyK. Lee, John Wiley Sons, Inc., Hoboken NJ. This book focuses on thermal engineering but we mention it here because it discusses several topics that are relevant to IR detection thermal engineering and cryogenics (relates to our Chapter 12), and his chapter on solar cells covers radiation (like our Chapter 2 - Radiometry), semiconductor physics (relates to our Chapters 4 and 5). Lee covers these topics succinctly but in more detail than we can provide here. 

Piping or vessels blocked in while filled with liquid at or below ambient temperature, and subsequently heated by direct solar radiation. Cryogenic and refrigeration systems must particularly be examined in this respect. 

An opposite eflect of emitlance occurs when an attempt is made to use aluminum jackets on very cold (cryogenic) piping. In this case, heal reaching the surface from surroundings is reflected away so that the metal surface becomes so cold thal it will condense and freeze moisture from the air. To overcome this surface condensation and freezing hy use of thicker thermal insulation on the lines would require a very great increase in thickness over that needed if the jacket had heen made of a heat-absorbing material that would keep the surface above the dew point. 

To presume that thermal insulation is always necessary is false. For example, when cryogenic fluids arc transported from a supply suurce to a vessel, even in bright sunshine, it is usually most economical not to insulate the line at all. The reason for this Is twofold (I) lor the short time of transport the area of the pipe exposed to the surt is much smaller than the area that would be exposed if it were insulated and (2i the heat that would be in the insulation when the transport starts would have to be removed by the cryogenic fluid. The combination of these two factors often makes the use of insulation undesirable for this type of cold fluid transport system. Moreover, the rapid formation of ice crystals front moisture in the air constitutes a thermal insulation. 

Analyze the arrangement to assess the type(s) of heat transfer involved. The distance separating the hot and cold surfaces is small compared with the size of the surfaces. The approximation can thus be made that the furnace wall, the dense network of cryogenic piping, and the radiation shields are all infinitely extended parallel planes. This is a conservative assumption, since the effect of proximity to an edge is to introduce a source of moderate temperature, thus allowing the hot wall to cool off. Convection is omitted with the same justification. So the problem can be treated as pure radiation. 

Radiation differs from conduction and convection not only in mathematical structure but in its much higher sensitivity to temperature. It is of dominating importance in furnaces because of their temperature, and in cryogenic insulation because of the vacuum existing between particles. The temperature at which it accounts for roughly naif of the total heat loss from a surface in air depends on such factors as surface emissivity and the convection coefficient. For pipes in free convection, this is room temperature for fine wires of low emissivity it is above red heat. Gases at combustion-chamber temperatures lose more than 90 percent of their energy by radiation from the carbon dioxide, water vapor, and particulate matter. 

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