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Passive Thermal Control System

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Heat transfer through MLI is a combination of solid conduction, radiation and, under atmospheric conditions, gaseous conduction. All of these forms are minimized in different ways. Interposing as many enclosing reflective surfaces (metallized sheets) as is practically possible between the object being insulated and its surroundings minimizes radiative heat transfer. One can minimize solid conduction heat transfer by minimizing the density of the low-conductance spacers between the reflective surfaces and making the blanket "fluffy" in order to minimize contact between layers. <ref name = "STC"/> <br \>
The heat transfer mechanisms operate simultaneously and interact with each other. Therefore, a useful technique is to derive either an apparent thermal conductivity, <math>K_{eff}</math>, or an effective emittance, <math>\varepsilon^*</math>, through the blanket. We can experimentally derive both the values for steady state heat transfer. <br \>
Theoretically, for a highly evacuated MLI system, the emittance <math>\varepsilon</math> for a blanket comprising of N non-contacting layers having emissivities <math>\varepsilon_1</math> and <math>\varepsilon_2</math> on opposite sides is computed as:<ref name = "STC"/>
[[File:PTC Equn.gif|frame|center]]
In satellite applications, the MLI is full of air at launch time. As the rocket ascends through the atmosphere, this air should be able to escape without damaging the blanket. Therefore, holes or perforations are required in the layers, even though this has an associated reduction in effectiveness. <br \>
== Surface Coatings and Paints ==
The Space Station has A satellite or a space station can have a variety of surface finishes because of the variance difference in thermal requirements from location region to locationregion. Thermal coatings and paints must be compatible with the environment and . They must also be resistant to both radiation and atomic oxygen that they will be constantly exposed to. <br \>
Different types of finishes are used to provide various degrees of thermal control for on-board equipment. Using coatings and paints with different emissivity and absorptivity with different characteristics allows the region or component to either be “warmed” or “cooled” as required. An example of this are radiators that use high emissivity and low absorptivity coatings to help radiate excess heat to space. <br \>
== Phase Change Materials ==
The This proposed technology will is expected to enable efficient thermal control by maintaining a constant temperature heat sink or heat source for a wide range of electronic components in rapidly changing thermal environments. The PCM Phase Change Material panel is being designed as a lightweight and flexible component. Even then, yet having it will have high thermal capacity. Thus, requiring it will require less mass and volume than currently presently used carbon-fiber and aluminum honeycomb composite panels. <ref>https://techport.nasa.gov/view/89663</ref><br \>ExExample:<ref>http: PCM //www.puretemp.com/pcmatters/pcm-briefing: Managing heat in low-orbit satellites 110</ref> <br \>Roccor LLC of Longmont, Colo., is using making use of phase change material in a device that is designed to manage internal heat in low-orbit satellites. A product with containing paraffin wax inside within a flat structure i is used. When the spacecraft is hot, it dumps heat into that the paraffin wax acts as a heat sink and turns that into a liquid — basically a store of energy. The Later on, the heat is later released into the satellite to keep temperatures stable. <br \>
PCM is one of the developing areas in efficient passive thermal control systems which acts as both a heat sink or a heat source based on the demand of the system.
[[File:PCMPCM2.jpgpng|frame|center|Principle of Phase Change material. Image inspired from [https://www.slideshare.net/prashantchikya/phase-changing-material here]]]
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== References==* http://pages.erau.edu/~ericksol/projects/issa/thermal.html* https://en.wikipedia.org/wiki/Spacecraft_thermal_control* Spacecraft Thermal Control Handbook Volume I: Fundamental Technologies, David G. Gilmore* http://www.esa.int/Our_Activities/Space_Engineering_Technology/Thermal_Control
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