Cryogenic application

CRYOGENICS AND
ITS APPLICATIONS
Presented By-
SHABARISH M (RA1711002010067)

WHAT IS CRYOGENICS
▪ Cryogenics is the production and behaviour of
materials at very low temperatures.
▪ Cryogenic processes involve temperatures
below -180 Celsius (123 k)
▪ The extremely low temperatures are produced
using substances called cryogens.
▪ Liquid Nitrogen is the most commonly used
cryogen (LN2).
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Liquid Nitrogen (LN2), a colourless, low
viscosity liquid that is widely used as a
cryogen.
A cryogenic rocket engine that uses a
cryogenic fuel.

▪ The word cryogenics originates from the Greek
words ‘Cryo’ which means cold and ‘genics’
which means to produce.
▪ The cryogenic processes also have a unique
ability to recycle difficult to separate composite
materials.
▪ Cryogens are stored in vessels called as
Dewar flasks which provide good insulation.
 Liquid helium (LH2) is another commonly used
cryogen.
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A Compact thermal heat
switch for cryogenic space
applications operating near
100 k
AUTHORS- M. Dietrich, A. Euler, G. Thummes
PUBLICATION-Cryogenics, Volume 59, January-February 2018

THERMAL HEAT SWITCH
▪ A thermal switch is an electrical safety device
that interrupts electric current when heated to a
specific temperature.
▪ It is a device which opens at a high temperature
and re closes when the temperature drops.
▪ Thermal switches are used in power supplies in
case of overload, and also as thermostats in
some heating and cooling systems.
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A Thermal switch
Schematic symbol of thermal overload switch

CRYOCOOLERS
 A refrigerator designed to reach cryogenic temperatures is
often called a Cryocooler.
 The term is most often used for smaller systems, typically
table-top size, with input powers less than about 20 kW.
 In most cases cryocoolers use a cryogenic fluid as the working
substance and employ moving parts to cycle the fluid around a
thermodynamic cycle.
 The fluid is typically compressed at room temperature,
precooled in a heat exchanger, then expanded at some low
temperature
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▪ The returning low-pressure fluid passes through the heat
exchanger to precool the high-pressure fluid before
entering the compressor intake.
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HIGHLIGHTS
▪ A thermal heat switch has been developed intended for
cryogenic space applications operating around 100 K.
▪ The switch was designed to separate two pulse tube cold
heads that cool a common focal plane array.
▪ A construction based on the difference in the linear
thermal expansion coefficients (CTE) of different
materials was chosen.
▪ A simple design is proposed based on thermoplastics
which have one of the highest CTE known permitting a
relative large gap width in the open state
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▪ After a single switch was successfully built, a second double-
switch configuration was designed and tested.
▪ The long term performance of the chosen thermoplastic (ultra-
high molecular weight polyethylene) under cryogenic load is also
analyzed.
▪ The heat switch is a proof of concept for a redundant cryocooler
application.
▪ The creep of the used CTE material at cryogenics temperatures
was analyzed.
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INTRODUCTION
• Cryocoolers for space applications in the 77 K range are of
the pulse-tube type combined with a flexure bearing
compressor.
• As part of a research project studying various redundancy
concepts for satellite operations, a heat switch was
developed including two cold heads (CH1 and CH2) mounted
on a single focal plane array detector.
• The heat switch thermally connects an active cold head to
the FPA while increasing the thermal contact resistance to a
second cold head in stand-by mode, thus reducing the heat
load of the stand-by system to the active cold head.
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Schematic of the cold head assembly including heat switch and
FPA

WHY A CTE IS USED INSTEAD OF OTHER HEAT SWITCHES?
▪ There exist various kinds of heat switches for space
applications, each having their own advantages and
disadvantages.
▪ Most common are heat switches of the Gas-Gap and
CTE-based (CTE: linear thermal coefficient of expansion)
▪ In Gas-Gap switches the pressure of a gas in a small gap
is controlled. This can be done e.g. by use of absorbers or
valves connected to gas reservoirs. The
presence/absence of the gas in the small gap (typically
100 lm) enables/disables a thermal contact.
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▪ The CTE-based switches rely on the thermal expansion of
one or more components.
▪ When the temperature decreases the high CTE material
‘‘shrinks’’ and closes the gap between the two solids.
▪ Below a certain ‘‘switching temperature’’, the gap is fully
closed, thus providing a heat conduction path.
▪ By using thermoplastics with a high CTE, such as ultra-high
molecular weight polyethylene (UHMW-PE), in order to
circumvent the requirement of tiny gaps, the CTE-based
switch becomes superior compared to other designs with
respect to the required temperature range and standards
for space applications.
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THERMAL HEAT SWITCH CONCEPT
▪ The switch needs to serve as a support for the FPA, the contact
areas that are connected to the cold head and FPA must not
move upon switching.
▪ The switch should exhibit an on-state thermal conductivity of
more than 1 W/K at an operating temperature between 80 and
100 K and an off-state conductivity of less than 1 mW/K.
▪ Unfortunately, high thermal conductivity materials, such as
metals, exhibit a rather small CTE leading to a small gap sizes
which require careful manufacturing and increase the risk of
failure.
▪ This leads to a design where a thermoplastic is used as the
switching element only, bringing two metals with high thermal
conductivity into contact.
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▪ The graph below shows the CTE between 80 K and 300 K of
some metals and thermoplastics.
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▪ While most metals exhibit a CTE of 10–20 10^6 /K,
polytetrafluoroethylene (PTFE) for example has an order of
magnitude higher CTE compared to copper at room temperature.
▪ PTFE shows two solid–solid phase transitions near room
temperature with a maximum CTE of more than 500*10^-6/K.
▪ Measurements using liquid nitrogen revealed that ultra-high-
molecular-weight polyethylene (UHMWPE) has an even higher
thermal contraction than PTFE between room temperature and
77 K.
▪ When designing a CTE-based switch, one important parameter
is the gap width, which depends on the CTE material and the
desired switching temperature.
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▪ Two switches were built: a single switch connected to a single
cold head and heat load, which was used for initial testing.
▪ Later on, a second switch was built which has a T-form to
connect two cold heads to a single load located in the middle of
the switch.
▪ The part connected to the heat load (detector side) consists of
an inner shaft made of a solid copper cylinder (10 mm diameter)
with a flange on one end.
▪ The part connected to the cold head (PE-side) consists of a
copper flange with four integrated copper jaws that are
separated from the inner cylinder by the gap.
▪ The distribution of stress inside the switch components was
calculated using Hooke’s law.
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▪ The contact pressure of the jaws to the shaft at 100 K was estimated to be
1.4 MPa, while the maximum tensile stress in the UHMWPE was estimated to
be 5 MPa.
22
shows the compressive and tensile stresses in radial and tangential (= circumferential)
directions inside the switch components, calculated at an operating temperature of 100 K

▪ The test apparatus consists of a coaxial pulse tube cold head driven by
an AIM SL400 linear compressor to which the single switch is attached.
▪ During the measurement a constant heat load of 500 mW is being
applied to the detector side of the switch.
▪ The detector side of the switch maintains a constant temperature until
the switch closes at a temperature of about 220 K.
▪ After that, the detector side cools down quickly until it reaches the cold
head temperature.
▪ From there on, both temperatures further decrease until the base
temperature of 57 K is reached.
▪ At 2.5 h the compressor is turned off. Both temperatures start to rise
until the switch opening temperature of about 250 K is reached.
▪ From there on, the cold head temperature rises slower than the sensor
temperature because of the low thermal coupling in the off-state.
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▪ After 6 h the heater is switched off and after around 6.5 h the cooler
and heater are started again and the next cycle begins.
▪ There exists a small hysteresis of about 25 K due to the lag of the
UHMW-PE temperature with respect to the cold head temperature.
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Long term performance of UHMW-PE
▪ For long term satellite missions it is essential to know how the
materials used in the switch will degrade in their properties during
mission lifetime.
▪ It is known that thermoplastics tend to creep over time, which would
have a significant effect on the switch performance.
▪ Material pre-aging can significantly reduce long term creep, whereas
other methods like material-enforcement tend to reduce the CTE.
▪ Long term creep measurements for UHMW-PE have been studied for
room temperatures and above, mainly because of their application in
the medical sector
▪ A test apparatus was built for testing the creep of our UHMW-PE
samples at low temperatures using strain gauges (type Micro-
Measurements EK-13-250BF-10C/W)
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▪ The UHMW-PE samples were in form of a solid cube with an edge
length of 20 mm.
▪ The graph shows the compliance data under a compressive load of 1
MPa for several temperatures. Similar results are expected for tensile
stresses.
▪ After some initial relaxation processes on a time scale of less than
10,000 s, it appears that the material starts to creep linearly on a
logarithmic time scale.
▪ At least for the 100 K data this is in accordance with the research work
which used short term measurements near room temperature to
predict low temperature creep data for temperatures T < Tg , where
Tg = 130 K is the glass transition temperature of UHMW-PE.
▪ For a mission time of 10 years, a creep compliance of 0:2 GPa1 at 100
K can be roughly extrapolated
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Conclusions
▪ Two variants have been studied: a single and a double heat switch
configuration.
▪ The single switch showed a state change around 220 K, and an
on/off-state conductivity of more than 1 W/K and an 3 mW/K
respectively.
▪ The double switch was successfully tested in a two cooler
configuration and showed reliable switching characteristics over
several cycles.
▪ UHMW-PE, which was used as the high CTE material, shows a rather
high creep rate under uniaxial pressure at room temperature.
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▪ To estimate the degeneration of the material during switch operation at
cryogenic temperatures, creep tests were performed and extrapolated
for long term prediction.
▪ At 100 K, the compliance is estimated to be 0:2 GPa1 in 10 years
resulting in a 12% drop in contact pressure during on-state.
▪ The CTE-based thermal switch presented in this paper is a promising
concept.
▪ Further development will focus on mechanical properties as stability and
weight.
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OTHER APPLICATIONS OF CRYOGENICS
▪ Electric power transmission in big cities
▪ Frozen food
▪ Blood banking
▪ Infrared sensors
▪ Electronics
▪ Nuclear Magnetic Resonance
▪ Experimental research on certain physics phenomena.
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Astronomical instruments on the Very Large Telescope are equipped with
continuous flow cooling systems.

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Cryogenic gases delivery truck at a supermarket in Michigan

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Bruker 700 MHz nuclear magnetic resonance (NMR) spectrometer.

References
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11th international cryocooler conference; 2002. p. 637–48.
[2] Chan CK, Ross RG. Design and application of gas gap heat switches. Final report of phase II. Technical report NASA-
CR-187339. Washington, DC: National Aeronautics and Space Administration; 1990.
[3] Marland B, Bugby D, Stouffer C. Development and testing of an advances cryogenic thermal switch and cryogenic
thermal switch test bed. Cryogenics 2004;44(6–8):413–20 [2003 Space Cryogenics Workshop].
[4] Wang W, Yang an L, Yan T, Cai J, Liang J. Development of a cryogenic thermal switch, In: Miller SD, Ross Jr RG, editors.
Cryocoolers, vol. 14; 2007. p. 589–94
[5] Prenger FC, Stewart WF, Runyan JE. Development of a cryogenic heat pipe. In: Kittel Peter, editor. Advances in
cryogenic engineering. Advances in cryogenic engineering, vol. 39. US: Springer; 1994. p. 1707–14. ISBN: 978-1-
4613-6074-2
[6] You JG, Dong DP, Wang WY, Li ZW. Development and testing of a novel thermal switch. In: Proceedings of the 20th
ICEC. Elsevier Ltd.; 2005. p. 423–6.
[7] Catarino I, Bonfait G, Duband L. Neon gas-gap heat switch. Cryogenics 2008;48:17–25.
[8] NIST cryogenics technologies group. Material properties data base. Internet address; 2013. [accessed 01.06]
[9] Richard K Kirby. Thermal expansion of polytetrafluoroethylene (Teflon) from 190to +300. J Res Natl Bureau Stand
1956;57(2):91–4.
[10] Hartwig Günther. Polymer properties at room and cryogenic temperatures. New York: Plenum Publishing
Corporation; 1994
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Cryogenic application

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