Passive Thermal Control System - Revision history

Yash at 13:21, 22 February 2018

2018-02-22T13:21:26Z

Yash: /* Phase Change Materials */

2018-02-22T13:21:06Z

‎Phase Change Materials

Yash: /* Surface Coatings and Paints */

2018-02-22T13:13:48Z

‎Surface Coatings and Paints

Yash: /* Working of MLI */

2018-02-22T13:09:24Z

‎Working of MLI

Yash at 13:08, 22 February 2018

2018-02-22T13:08:24Z

Yash: /* Working of MLI */

2018-02-22T13:07:26Z

‎Working of MLI

Yash at 11:41, 22 February 2018

2018-02-22T11:41:36Z

Yash at 11:34, 22 February 2018

2018-02-22T11:34:57Z

Yash: /* Multi Layer Insulation (MLI) */

2018-02-22T11:34:36Z

‎Multi Layer Insulation (MLI)

Yash at 11:33, 22 February 2018

2018-02-22T11:33:47Z

← Older revision		Revision as of 13:21, 22 February 2018
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	== References ==		== References ==
−
−	~~== 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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 == Phase Change Materials ==
-The proposed technology will enable efficient thermal control by maintaining a constant temperature heat sink or heat source for a range of electronic components in rapidly changing thermal environments. The PCM panel is being designed as a lightweight and flexible component, yet having high thermal capacity, requiring less mass and volume than currently used carbon-fiber and aluminum honeycomb composite panels. <br \>
+This proposed technology is expected to enable efficient thermal control by maintaining a constant temperature heat sink or source for a wide range of electronic components in rapidly changing thermal environments. The Phase Change Material panel is being designed as a lightweight and flexible component. Even then, it will have high thermal capacity. Thus, it will require less mass and volume than presently used carbon-fiber and aluminum honeycomb composite panels. <ref>https://techport.nasa.gov/view/89663</ref><br \>
-Ex: PCM briefing: Managing heat in low-orbit satellites <br \>
+Example:<ref>http://www.puretemp.com/pcmatters/pcm-briefing-110</ref> <br \>
-Roccor LLC of Longmont, Colo., is using phase change material in a device designed to manage internal heat in low-orbit satellites. A product with paraffin wax inside a flat structure i used. When the spacecraft is hot, it dumps heat into that paraffin wax and turns that into a liquid — basically a store of energy. The heat is later released into the satellite to keep temperatures stable. <br \>
+Roccor LLC of Longmont, Colo., is making use of phase change material in a device that is designed to manage internal heat in low-orbit satellites. A product containing paraffin wax within a flat structure is used. When the spacecraft is hot, the paraffin wax acts as a heat sink and turns into a liquid — basically a store of energy. Later on, the heat is 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:PCM.jpg|frame|center|Principle of Phase Change material]]
+[[File:PCM2.png|frame|center|Principle of Phase Change material. Image inspired from [https://www.slideshare.net/prashantchikya/phase-changing-material here]]]
 ----
 If you are done reading this page, you can go back to [[Mechanical Subsystem]]
 == References==

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 == Surface Coatings and Paints ==
-The Space Station has a variety of surface finishes because of the variance in thermal requirements from location to location.  Thermal coatings and paints must be compatible with the environment and must be resistant to radiation and atomic oxygen that they will be constantly exposed to.  <br \>
+A satellite or a space station can have a variety of surface finishes because of the difference in thermal requirements from region to region.  Thermal coatings and paints must be compatible with the environment. 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 \>

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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:
+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 \>

@@ Line 20: / Line 20: @@
-=== Multi Layer Insulation (MLI)<ref>Spacecraft Thermal Control Handbook
+=== Multi Layer Insulation (MLI)<ref name = "STC">Spacecraft Thermal Control Handbook
 Volume I: Fundamental Technologies, David G. Gilmore
 </ref> ===
@@ Line 30: / Line 30: @@
 Imagine a 1 <math>mm^2</math> surface in outer space, at 400 K. Assume that its emissivity is 1. Also assume that it is facing away from the sun (i.e. in the direction opposite to the sun) or other heat sources. Using the Stefan–Boltzmann law, we can show that this surface will radiate 1452 watts. Now if we place a thin (but opaque) layer 1 cm away from the plate (thermally insulated from it), and also with an emissivity of 1, then this layer will cool until it is radiating 726 watts from both its sides. Once this point is reached, everything will be in balance. The new layer gets 1452 watts from the plate, out of which 726 watts is radiated back, and 726 watts is radiated to space. The original plate still radiates 1452 watts, but gets 726 back from the new layer, which makes the net loss to be 726 watts. So overall, the radiation losses have been halved by adding the new layer. <ref>https://www.revolvy.com/main/index.php?s=Multi-layer+insulation&uid=1575</ref> <br \>
 MLI is composed of multiple layers of low-emittance films. <br \>
-The MLI construction, in its simplest form, is a layered blanket which is assembled from thin embossed Mylar sheets. Each sheet has, on one side, a vacuum-deposited aluminum finish. Because of the embossing, the sheets come in contact at only a few points, thereby minimizing the conductive heat paths between layers. The layers have an aluminum finish on one side only so that the Mylar can act as a somewhat low-conductivity spacer. A construction which gives higher performance is composed of Mylar film metalized (with aluminum or gold)  on both sides.  These have silk or Dacron net as the low-conductance spacers. <ref name = "ref4">https://books.google.co.in/books?isbn=188498911X</ref> <br \>
+The MLI construction, in its simplest form, is a layered blanket which is assembled from thin embossed Mylar sheets. Each sheet has, on one side, a vacuum-deposited aluminum finish. Because of the embossing, the sheets come in contact at only a few points, thereby minimizing the conductive heat paths between layers. The layers have an aluminum finish on one side only so that the Mylar can act as a somewhat low-conductivity spacer. A construction which gives higher performance is composed of Mylar film metalized (with aluminum or gold)  on both sides.  These have silk or Dacron net as the low-conductance spacers. <ref name = "STC"/>
-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 = "ref4"/> <br \>
+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:

@@ Line 28: / Line 28: @@
 [[File:MLI4.jpg|thumb|300px| Multi Layer Insulation Close-Up view. Image reproduced from [https://commons.wikimedia.org/wiki/File:MultiLayerInsulationCloseup.jpg here]]]
 Lets understand this with an example.
-Imagine a square meter of a surface in outer space, at 400 K, with an emissivity of 1, facing away from the sun or other heat sources. From the Stefan–Boltzmann law, this surface will radiate 1452 watts. Now imagine placing a thin (but opaque) layer 1 cm away from the plate, thermally insulated from it, and also with an emissivity of 1. This new layer will cool until it is radiating 726 watts from each side, at which point everything is in balance. The new layer receives 1452 watts from the original plate. 726 watts is radiated back to the original plate, and 726 watts to space. The original surface still radiates 1452 watts, but gets 726 back from the new layers, for a net loss of 726 watts. So overall, the radiation losses have been reduced by half by adding the additional layer. <br \>
+Imagine a 1 <math>mm^2</math> surface in outer space, at 400 K. Assume that its emissivity is 1. Also assume that it is facing away from the sun (i.e. in the direction opposite to the sun) or other heat sources. Using the Stefan–Boltzmann law, we can show that this surface will radiate 1452 watts. Now if we place a thin (but opaque) layer 1 cm away from the plate (thermally insulated from it), and also with an emissivity of 1, then this layer will cool until it is radiating 726 watts from both its sides. Once this point is reached, everything will be in balance. The new layer gets 1452 watts from the plate, out of which 726 watts is radiated back, and 726 watts is radiated to space. The original plate still radiates 1452 watts, but gets 726 back from the new layer, which makes the net loss to be 726 watts. So overall, the radiation losses have been halved by adding the new layer. <ref>https://www.revolvy.com/main/index.php?s=Multi-layer+insulation&uid=1575</ref> <br \>
 MLI is composed of multiple layers of low-emittance films. <br \>
-The simplest MLI construction is a layered blanket assembled from thin embossed Mylar sheets, each with a vacuum-deposited aluminum finish on one side. As a result of the embossing, the sheets touch at only a few points, and conductive heat paths between layers are thus minimized. The layers are aluminized on one side only so that the Mylar can act somewhat as a low-conductivity spacer. Higher-performance construction is composed of Mylar film metalized (with aluminum or gold) on both surfaces with silk or Dacron net as the low-conductance spacers. <br \>
+The MLI construction, in its simplest form, is a layered blanket which is assembled from thin embossed Mylar sheets. Each sheet has, on one side, a vacuum-deposited aluminum finish. Because of the embossing, the sheets come in contact at only a few points, thereby minimizing the conductive heat paths between layers. The layers have an aluminum finish on one side only so that the Mylar can act as a somewhat low-conductivity spacer. A construction which gives higher performance is composed of Mylar film metalized (with aluminum or gold)  on both sides.  These have silk or Dacron net as the low-conductance spacers. <ref name = "ref4">https://books.google.co.in/books?isbn=188498911X</ref> <br \>
-Heat transfer through MLI is a combination of radiation, solid conduction, and, under atmospheric conditions, gaseous conduction. These forms of heat transfer are minimized in different ways. Radiative heat transfer is minimized by interposing as many enclosing reflective surfaces (metalized sheets) as is practical between the object being insulated and its surroundings. Solid-conduction heat transfer is minimized by keeping the density of the low-conductance spacers between the reflective surfaces as low as possible and making the blanket "fluffy" to minimize contact between layers. <br \>
+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 = "ref4"/> <br \>
-Because the heat transfer mechanisms operate simultaneously and interact with each other, a useful technique is to refer to either an apparent thermal conductivity, <math>K_{eff}</math>, or an effective emittance, <math>\varepsilon^*</math>, through the blanket. Both values can be derived experimentally during steady-state heat transfer.  <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 \>
-In theory, for highly evacuated MLI systems, the emittance <math>\varepsilon</math> for a blanket of N non-contacting layers of emissivities <math>\varepsilon_1</math> and <math>\varepsilon_2</math> on opposite sides is computed as:
+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:
 [[File:PTC Equn.gif|frame|center]]
-In satellite applications, the MLI will be full of air at launch time. As the rocket ascends, this air must be able to escape without damaging the blanket. This may require holes or perforations in the layers, even though this reduces their effectiveness. <br \>
+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 \>
-MLI blankets are constructed with sewing technology. The layers are cut, stacked on top of each other, and sewn together at the edges. Seams and gaps in the insulation are responsible for most of the heat leakage through MLI blankets. A new method is being developed to use polyetheretherketone (PEEK) tag pins (similar to plastic hooks used to attach price tags to garments) to fix the film layers in place instead of sewing to improve the thermal performance. Traditionally, MLI blankets are sewn together; the multi-layered blanket being held together by stitches. However, any kind of hole that punches through the layers tends to degrade the overall thermal performance of the blanket. Another method, of using tag-pins - the small nylon "I" looking pins that are used to hook price tags to clothes in stores - to fix the layers in place, has been mentioned in the literature, see paper by R. Hatakenaka, here). That way you don't need to punch as many holes as when you are sewing, and tagging - a few inches between tags - is faster and less error-prone than sewing around the whole perimeter of the blanket. Moreover, the tag-pins allow you to fasten the layers together without compressing them, which reduces stress around the holes. Lastly, the blankets tend to contract in the direction of sewing which might lead them to be to small if not oversized properly. <br \>
+MLI blankets are traditionally constructed with sewing technology. The layers are cut, then stacked on top of each other, and finally sewn together at the edges. Seams and gaps in the insulation are the cause of most of the heat leakages through MLI blankets. A new method is being developed to use polyetheretherketone (PEEK) tag pins (similar to plastic hooks used to attach price tags to garments) to fix the film layers in place instead of sewing to improve the thermal performance.<ref>https://en.wikipedia.org/wiki/Multi-layer_insulation</ref> <br \>
-In some applications the insulating layers must be grounded, so they cannot build up a charge and arc, causing radio interference. Spacecraft also may use MLI as a first line of defense against dust impacts. <br \>
+In some applications the insulating layers must be grounded, so that they do not build up a charge and arc, which cause radio interference. Satellites may also use MLI as a first protection against dust impacts. <br \>
 == Surface Coatings and Paints ==

@@ Line 23: / Line 23: @@
 Volume I: Fundamental Technologies, David G. Gilmore
 </ref> ===
-Multilayer Insulation (MLI) is used to minimize temperature gradients throughout the spacecraft and to control heat transfer rates. MLI blankets prevent both excessive heat loss from a component and excessive heating from environmental fluxes, rocket plumes, and other sources. Most spacecraft flown today are covered with MLI blankets, with cutouts provided for areas where radiators reject internally generated waste heat. Single-layer radiation barriers are sometimes used in place of MLI where less thermal insulation is required, since they are lighter and cheap to manufacture. <br \>
+Multilayer Insulation (MLI) is used to minimize temperature gradients throughout the satellite and to control heat transfer rates. MLI blankets work in both ways: they prevent both excessive heat loss from a satellite component and also prevent excessive heating from the external environmental fluxes, and other sources. Most satellites today are covered with MLI blankets. Cutouts are provided at places for radiators to reject internally generated waste heat. If lesser thermal insulation is required, single layer radiation barriers may be used, in place of MLI, since they are cheap to manufacture and also lighter. <br \>
-In practice, simply increasing the  number of layers past a certain value will not improve performance. As the no. of layers increases, radiative heat transfer becomes small compared with conductive “shorts” between layers and other losses. Taking all these factors into account, about 25 layers usually suffice to obtain a minimum overall conductance value.
+In practice, just by increasing the  number of layers beyond a certain value, performance cannot be improved. As the number of layers increases, radiative heat transfer becomes small compared to conductive “shorts” between layers and other losses. About 25 layers are usually sufficient to obtain a minimum overall conductance value.
 ==== Working of MLI ====
 [[File:MLI4.jpg|thumb|300px| Multi Layer Insulation Close-Up view. Image reproduced from [https://commons.wikimedia.org/wiki/File:MultiLayerInsulationCloseup.jpg here]]]

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-Passive thermal control systems involve no mechanical moving parts or fluids. There is no power consumption which ensures its low mass and cost. It is highly reliable due to its design simplicity, implementation and testing. The only drawback of PTCS is its low heat transport capability except for heat pipes when compared with ATCS. <br \>
+Passive thermal control systems involve no mechanical moving parts or fluids. There is no power consumption which ensures its low mass and cost. It is highly reliable due to its design simplicity, implementation and testing. The only drawback of PTCS is its low heat transport capability except for heat pipes when compared with ATCS.<ref>https://en.wikipedia.org/wiki/Spacecraft_thermal_control</ref> <br \>
 PTCS includes the following components:
 ==Thermal Insulations ==
-=== Introduction ===
+=== Introduction <ref>https://books.google.co.in/books?isbn=0470501960</ref> ===
-Thermal insulations consist of low thermal conductivity materials
+Thermal insulations comprise of low thermal conductivity materials which are combined in a manner such that the system has an even lower thermal conductivity. Conventionally, in
-combined to achieve an even lower system thermal conductivity. In conventional
+fiber-type, powder-type and flake-type insulations, throughout an air space, the solid material is finely dispersed. To characterize such systems, an effective thermal conductivity is used, which depends on both the thermal conductivity and surface radiative properties
-fiber-, powder-, and flake-type insulations, the solid material is finely dispersed
+of the solid material, and also the characteristics and volumetric fraction of the void or air
-throughout an air space. Such systems are characterized by an effective thermal conductivity,
+space. Bulk density (solid mass/total volume) is a special parameter of the system,
-which depends on the thermal conductivity and surface radiative properties
+which is very highly dependent on the manner of packing of the materials.
-of the solid material, as well as the nature and volumetric fraction of the air or void
+If small hollow spaces or voids are formed as a result of bonding or fusing portions of the
-space. A special parameter of the system is its bulk density (solid mass/total volume),
+solid material, a rigid matrix will be created. A system is referred to as cellular insulations if such spaces are sealed from each other. Foamed systems, those made from plastic and glass materials in particular, are an example of such rigid insulations. Reflective
-which depends strongly on the manner in which the material is packed.
+insulations comprise of parallel, multilayered, thin sheets or foils which have a high reflectivity. These sheets or foils are spaced to reflect radiant energy back to its source. The foil spacing is designed to restrict air motion, and it is evacuated in high-performance
-If small voids or hollow spaces are formed by bonding or fusing portions of the
+insulations. The air in the void space reduces the effective thermal conductivity of the system in all kinds of insulations.
-solid material, a rigid matrix is created. When these spaces are sealed from each
+Please note that heat transfer through any insulation system
-other, the system is referred to as a cellular insulation. Examples of such rigid insulations
+may consist of several modes: conduction through the solid materials; conduction or convection through the air in the void spaces; and radiation between the
-are foamed systems, particularly those made from plastic and glass materials. Reflective
+surfaces of the solid matrix. Effective thermal conductivity accounts for all of
 these processes.
 === Multi Layer Insulation (MLI) ===