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Cryogenics

Tyler Brewer

Overview

•History of cryogenics•Uses•Methods of Cooling•Materials Considerations•Vibration Issues

History

• “Cryogenics” is for approximately < ~150 C

• Greek – “Kryos” = frost– “-genic” = to produce

• 1887: Liquid oxygen produced (-183 C, 90K)

• 1892: Dewar invents the vacuum flask

• 1908: Liquid helium produced (4.2K)– Superconductivity discovered in 1911

thanks to this

• 1960: 1*10^-6 K attainablePhoto: The Worlds of David Darling

Industrial Uses

• Liquefied Natural Gas (LNG)• Liquid Hydrogen / Oxygen rocket fuel• Medicine

– Cryosurgery– Medical gases like O2

• Superconductivity– LHC at CERN

• Food preservation• Manufacturing

– Tight-tolerance part fitting

• Electronics– Detectors– Reduced thermal noise

Photo: CIMS Gas Products, LLC

Mechanics of Cooling

• Recuperative cycles– Gas is passed through heat exchanger to transfer energy– Continuous heat transfer

• Regenerative cycles– Cyclic process with low temperature stored in “Regenerator”– Requires large heat capacity due to alternating flow

Photo: European Space Agency

Joule-Thompson Liquifier

• Requires gas to be < 40 K• AKA Linde-Hampson Effect

1. Gas compressed2. Gas precooled 3. Gas passed through J-T valve

(cools down even more)4. Gas liquid at lowest pressure and temp,

removes heat from cold head5. “Exhaust” gas recycled to precool incoming gas,

sent back to reservoir

Hybrid Cascade JT cooler

P ~ 3 kPa ~ 0.01 atm

Other Regenerative Methods

• Claude Liquefier– 3 heat exchangers with expansion

engine

• Collins Cycle– Commonly used for mass

production of cryo-liquids– Complicated version of Claude

liquifier

Stirling Cycle Refrigerator

• Evolved from Stirling heat engine working in reverse

1. He compressed in upper chamber, hot

2. Displacer moves up, forcing He through Regenerator

3. Displacer and Compressor move up, isothermal expansion in lower chamber (extracts heat from R)

4. D and C move down, forcing He through R (removes more heat from R)

Gifford-McMahon Cycle

• Similar to Stirling cycle, but with cycling valves

1. Outlet valve closed, inlet valve opens, high pressure He fills R and space above D

2. Displacer moves up, gas passes through R, cooled isobarically

3. Inlet closes, outlet opens, gas expands, removes heat

4. D returns to initial position, gas warms isobarically

Considerations

• Temporary or long-term use• Owning and operating cost• Overall size

• Purchase liquid He, vent exhaust vapors– Small scale

• Purchase gaseous He, liquefy it, vent the exhaust– Depends on care and efficiency of system

• Purchase gaseous He, liquefy it, recover exhaust for reuse– Depends on care and efficiency of system

• Purchase gaseous He, run in closed-cycle refrigerator– More expensive startup

Magnetocaloric Effect

• When removed from a magnetic field, molecules become disorderly

• If isolated, energy to shift orientation comes from phonon collisions

• Results in reduced temperature• Can attain < 1 K using this technique in small scales• Gadolinium

Photo: Wikipedia

Properties of Materials

• Heat capacity changes as T → 0 K• Phonons contribute to heat capacity

at low T• Electron flow contributes to energy,

besides classical resistance, < 10 K• Thermal contraction, ~1% of

dimension– Thermal stress, tolerance considerations,

coupling

• Electrical Resistivity– Lowest resistivity depends on lattice

structure, purity

Properties of Materials

• Thermal conductivity– Nonlinearly dependent on T

• Lattice structures shift• Mechanical properties:

– Stress– Strain– Elasticity

• Superconductivity

Common Issues

• Vibrational travel up to 60 μm depending on hardware– Active vibration damping– System isolation– Montana Instruments: <5 μm

• Frost buildup– Design cold head so sample is

warmest object in the chamber

Photo: Montana Istruments

Questions

Sources

• Brittanica: http://www.britannica.com/science/cryogenics• CIMS Gas Products, http://www.cimsgas.com/cryogenics.html• Comic: http://xkcd.com/989/• Cooltech Applications,

http://www.cooltech-applications.com/magnetic-refrigeration-principle.html• David Darling: http://www.daviddarling.info/encyclopedia/D/dewar_flask.html• ESA: http://sci.esa.int/jwst/46831-cryocooler-for-miri/• Montana Instruments:

http://resources.montanainstruments.com/help/article/link/vibrations• Van Sciver, Steven W., Helium Cryogenics, 2nd Ed., Springer (2012)• Wikipedia: https://en.wikipedia.org/wiki/Magnetic_refrigeration