The rapidly expanding use of very low temperatures in research and high technology during the last several decades and the concurrent high degree of activity in cryogenic engineering have mutually supported each other, each improvement in refrigeration technique making possible wider oppor tunities for research and each new scientific discovery creating a need for a refrigerator with special features. In this book, Professor Walker has provided us with an excellent exposition of the achievements of this period, the fundamental principles involved, and a critical examination of the many different cryogenic systems which have led to a new era of low-level refrigeration. I feel fortunate to have had a part in the developments discussed in this book. During the early 1930s I constructed several rotary engines using leather vanes. Their performance was not good, but I was able to liquefy air. I had been impressed by the usefulness of leather cups in tire pumps and in Claude-type engines for air liquefaction. I was trying to find a way to avoid that part of the friction generated by a leather cup as a result of the radial force of the working gas on the cylindrical part of the cup. During the 1950s I built two efficient helium liquefiers in which essentially leather pistons were used.

Inhaltsangabeof Part 2.- 8 Heat Exchangers in Cryocoolers.- Nomenclature.- Heat Exchangers in Cryocoolers.- Types of Heat Exchangers Used in Cryocoolers.- Recuperative Exchangers.- Tubular Exchanges.- Plate-Fin Exchangers.- Perforated Plate Exchangers.- Fundamentals of Recuperative Theory.- Exchanger Effectiveness.- Design of Recuperative Heat Exchangers.- Maldistribution of Flow.- Axial Heat Conduction.- Friction Effects.- Transient Response of Heat Exchangers.- Oscillatory Flow Systems.- Enhanced Heat Transfer Surfaces.- Regenerative Heat Exchangers.- Dynamic Regenerative Exchangers.- Static Regenerative Exchangers.- Common Theory for Static and Dynamic Types.- Advantages and Disadvantages of Regenerative.- Exchangers.- A Low-Temperature Problem: The Regenerator Material.- Heat Capacity.- Heat Regenerator.- Hausen Regenerator.- Presentation of Performance Data: Reduced-Length-Reduced-Period Method.- NTU-Effectiveness Method.- Application of Theory to Regeneration in Stirling-Type Engines with Oscillatory Flow.- Regenerator Design for Stirling Engines.- Experimental Performance.- Heat-Transfer and Fluid-Friction Characteristics of Dense-Mesh Wire Screens.- Regenerative Annulus.- Heat Pipe.- Heat Exchangers for Very Low Temperature.- References.- 9 Some Aspects of Design.- Target Definition.- Reliability.- Coldfinger Design.- Conduction Heat Leakage.- Cooldown.- Regenerator.- Shuttle Heat Transfer.- Balancing.- Case 1: Single Revolving Mass.- Case 2: Several Masses Revolving in the Same Plane.- Case 3: Several Masses Rotating in Several Planes.- Reciprocating Masses.- Partial Primary Balancing.- Secondary Inertia Forces.- Multiple Reciprocating Forces.- Design Guidelines for Engine Balancing.- Perfect Dynamic Balance.- Bearings.- Fluid-Lubricated Bearings.- Oil or Gas Lubrication.- Grease-Lubricated Bearings.- Ball and Roller Bearings.- Gas Bearings.- Gas-Lubricated Pistons.- Gas Bearings on Shafts and Flat Surfaces.- Dry-Rubbing Bearings.- Seals.- Static Seals.- Dynamic Seals.- Piston Side Thrust.- Hermetic Seals.- Close Tolerance Seals.- Materials.- Significant Properties.- Mechanical Properties.- Physical Properties.- Fluorocarbons.- Closure.- Cooling.- Air Cooling.- Water Cooling.- Spacecraft Radiative Cooling.- Electrial and Electronic Systems.- Drive Motors.- Brushless dc Motors.- Electric Controls.- References.- 10 Practical Problems in Cryocooler Design and Operation.- Comparison of Cryocooler Types.- Integral Stirling.- Split Stirling.- Integral Vuilleumier (VM).- Split Vuilleumier.- Giflford-McMahon (GM).- Design Considerations and System Trade-OfTs.- Heat Rejection.- Microphonics.- Thermophonics.- Special Problems Related to Cryocooler Operation.- Gas Contamination.- Helium Gas Retention.- Rubber O-Ring Seals.- Casting Leaks.- Metal Porosity.- Weld Joints.- Seal Problems.- References.- 11 Fundamentals of Alternate Cooling Systems.- Thermodynamic Considerations.- Ideal Refrigeration Cycles.- Interaction of Force with System.- Entropies and Refrigeration Principles of Various Systems.- Helium-4 and CCl2F2.- Other Gas-Liquid-Solid Systems.- Electron Systems.- Phonon Systems.- Other Solid Systems.- Magnetocaloric Systems.- Electrocaloric Systems.- Chemical Systems.- Mixtures.- Photon Systems.- How Much Entropy is Enough?.- Alternate Means to Eliminating Mechanical Parts.- References.- 12 Very-Low-Temperature Cooling Systems.- He3 Refrigerators.- Properties of He3.- Single-Cycle He3 Refrigerators.- Continuous He3 Refrigerators.- He3-He4 Dilution Refrigerators.- Properties of Liquid He3-He4 Mixtures.- Principles of Dilution Refrigerators.- Examples of Dilution Refrigerators.- Multiple Mixing Chambers.- He4 Circulating Dilution Refrigerators.- Pomeranchuk Cooling.- Properties of He3 on the Melting Curve.- Examples of Pomeranchuk Cooling.- Magnetic Refrigerators.- Electron-Spin Systems.- Nuclear-Spin Systems.- Hyperfine Enhanced Nuclear-Spin Systems.- Combined Systems.- Dynamic Nuclear Polarization.- References.- 13 Cryogenic Engineeri