Chapter 10 Cryogenics Chapter 10. Cryogenics Introduction - - PowerPoint PPT Presentation

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Jan 13, 2023 313 likes •627 views

Chapter 10 Cryogenics Chapter 10. Cryogenics Introduction Materials properties Refrigeration Insulation Insulation Cryostat design Cryogenic systems dolan swip 2009 1 Introduction "cryo" cryo cold = cold

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Chapter 10 Cryogenics Chapter 10. Cryogenics

Introduction Materials properties Refrigeration Insulation Insulation Cryostat design Cryogenic systems

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Introduction

"cryo" = cold cryo cold "genes" = that which generates 1877 90 liquefaction of N O 1877-90 liquefaction of N2, O2 1892-98 Dewar invented vacuum flask liquified H2 1908-11 H.K. Onnes liquefied He, discovered superconductivity 1934 Kapitza He liquefaction engine 1947 S.C. Collins liquefaction process

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Applications of Cryogenics Applications of Cryogenics

Industrial gas production Food preservation Food preservation Biomedical applications Bearings El t i Electronics Motors and generators Physics research Space technology Fusion research Magnets Magnets Neutral beams Vacuum pumps

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Mechanical Properties

Percent Elongation Mechanical ductility Elongation ductility yield stress modulus of elasticity f ti lif fatigue life Failure of welds at low T. “Ductile-to-brittle Transition temperature”

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Thermal Properties

Specific heat (J/mole-K): R = 8 314 J/mole-K R = 8.314 J/mole-K D = Debye Temperature D At T < 0 08  At T < 0.08 D, C = 233.8 (T/ D)3 St i l t l Stainless steel T(K) C (J/kg-K) 293 476 77 159 20 4.6

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Thermal Properties

T Enthalpy h = ho +  dT C(T)

Heat added per kg to raise temperature:

T2 T2 W/M =  dT C(T) = h2 – h1 T1 E l A il t i 100 t f C t bili Example: A coil contains 100 tonnes of Cu stabilizer. If the coil energy of 0.9 GJ is dissipated by a quench, By how much does the Cu temperature rise from 4 K? h = 0.9x109 J/105 kg = 9000 J/kg = 9 J/g Interpolating in Table we find T = 93 K

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Interpolating in Table, we find T 93 K.

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Enthalpy vs. Temperature

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Thermal Conductivity

structural supports coil  outside: d i l k desire low k Strength /k relative to SS-304 relative to SS 304

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Thermal Expansion

Example: SS-304, 4 K  300 K L/L ≈ 0.00303 Need to compute thermal stresses.

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Thermal Emissivity

293 K Used for radiant heat transfer in cryostats

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Electrical Resistivity

D d Depends on purity B & radiation damage  

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Vapor Pressures of Fluids

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From H. Neumann, FZK Summer School, 2008

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Cryogenic Liquids

Cannot be liquefied above “critical temperature”.

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How separate O2 from N2 ?

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Refrigeration and Liquefaction

Joule-Thomson Effect: If T<Tinversion, then If T Tinversion, then expansion  cooling T (H ) = 204 K Tinv(H2) = 204 K Tinv(He) = 20 K require precooling

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Expansion Engines

Ordinary expansion raises entropy, wastes energy Slow expansion into engine (piston or turbine)  cooling with less entropy rise, more efficient.  cooling with less entropy rise, more efficient.

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Collins Refrigeration System

25% 29K 50% 8K 25% 12%

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Insulation

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Heat Conduction Example

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Convection and Radiation

Small cells (styrofoam) or vacuum  convection  R di ti Radiation Stephen-Boltzmann Constant:  = 5.67x10-8 W/m2K4 Multilayer radiation barriers: 10 shields with e = 0.20  Prad = 0.003 as large Prad ≈ kapp A(T2-T1)/L

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Apparent Mean Thermal Conductivity

300K  77K Optimum spacing ~ 1 layer/mm Compaction  kapp 

app

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Vapor Shielding

77 K 293 K vapor LHe, 4.2 K LN2

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Cryostat Design

77 K Support JxB and gravity forces, low heat leak Styrofoam 77K  293 K

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Styrofoam 77K  293 K

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Heat Inflows

16 TF coils Bmax = 12 T

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Superinsulation Installation

Poor Better Best Best

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From H. Neumann, FZK Summer School, 2008

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Liquid Nitrogen Storage Dewar

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From H. Neumann, FZK Summer School, 2008

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MFTF-B Cryogenic System

During quench 10 m3 LHe 

7000 m3 gas  recovery bags.

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MFTF-B Cryogenic System

7 struts Diameter =27cm Thickness =2.9cm Each ~ 8 W

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MFTF-B Cryogenic Systems

Thermal stress limits cooling rate: 80K4K takes ~ 4-5 days.

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Summary

Cryogenic systems have many applications (industrial, food, biomedical, mechanical, electrical, physics, space, fusion). physics, space, fusion). Materials properties at low T limit performance (mechanical thermal electrical) (mechanical, thermal, electrical). Refrigeration technology well developed, but expensive. About 300 W input power per W of heat removed at 4 K. Multilayer aluminized plastic films in vacuum  low kapp Multilayer aluminized plastic films in vacuum  low kapp Structure dominates heat inflow.

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