TABLE OF CONTENTS Various military, commercial, and scientific projects require cooling of infrared (IR) sensors and spectrometers, optical elements, low-noise amplifiers, superconducting devices, and other instruments over a range of temperatures from below 10 K to more than 150 K. Many of these projects require the use of cryocoolers to meet mass, volume, life, or cost requirements. As a result, a wide range of cryocoolers is under development, and these coolers use a number of different thermodynamic cycles to meet project requirements.
This chapter reviews some of the basic principles of thermodynamics and the basic equations used to define cryocooler performance. Broad classifications of cryocoolers applicable to spaceborne systems are also defined, and an overview of the status, availability, and flight history of various cryocoolers is provided. In Chapters 8 through 13, industry experts discuss the details of each of the major cryocooler cycles under development, including characteristics, performance, applications, design issues, and hardware availability.
The Carnot cycle is used as a standard of comparison for heat-engine cycles because it has the highest efficiency for a given temperature range. Similarly, the reversed-Carnot cycle serves as the standard for refrigeration engines because for a given temperature range, it has the highest coefficient of performance (COP).
Figure 7.1 shows the reversed-Carnot cycle on a temperature-entropy (T-S) diagram. The cycle consists of two compression cycles and two expansion cycles. Heat absorbed during the process corresponding to the line with endpoints 1 and 4...
