How cryocoolers work step-by-step | Description, Example & Application

Learn how cryocoolers work step-by-step. Discover the principles behind mechanical and non-mechanical cryocoolers, and their applications.

Cryocoolers: Introduction

Cryocoolers are specialized refrigeration systems that operate at very low temperatures. They are used in a variety of applications, including medical equipment, aerospace, and research laboratories. Cryocoolers work by removing heat from a system and transferring it to a heat sink. They are commonly used to cool superconducting magnets, which require temperatures below 10 K to operate. Cryocoolers can be classified into two categories: mechanical and non-mechanical.

Types of Cryocoolers

Mechanical Cryocoolers

Mechanical cryocoolers are the most common type of cryocooler. They work by using mechanical compression to transfer heat from a low-temperature reservoir to a high-temperature heat sink. There are several types of mechanical cryocoolers, including:

Stirling cryocoolers
Gifford-McMahon cryocoolers
Pulse-tube cryocoolers
Joule-Thomson cryocoolers

Stirling cryocoolers use a piston and cylinder to compress and expand a gas. The gas is then used to transfer heat from a low-temperature reservoir to a high-temperature heat sink. Gifford-McMahon cryocoolers use a mechanical compressor to compress and expand a gas. The gas is then used to transfer heat from a low-temperature reservoir to a high-temperature heat sink. Pulse-tube cryocoolers use a high-frequency oscillator to create pressure waves in a gas. The pressure waves are then used to transfer heat from a low-temperature reservoir to a high-temperature heat sink. Joule-Thomson cryocoolers use a throttling valve to expand a gas. The gas is then used to transfer heat from a low-temperature reservoir to a high-temperature heat sink.

Non-Mechanical Cryocoolers

Non-mechanical cryocoolers use a different method to transfer heat from a low-temperature reservoir to a high-temperature heat sink. They are typically more expensive than mechanical cryocoolers, but they are also more reliable and require less maintenance. There are several types of non-mechanical cryocoolers, including:

Dilution refrigerators
Adiabatic demagnetization refrigerators

Dilution refrigerators use a mixture of helium-3 and helium-4 to transfer heat from a low-temperature reservoir to a high-temperature heat sink. Adiabatic demagnetization refrigerators use the magnetocaloric effect to transfer heat from a low-temperature reservoir to a high-temperature heat sink.

In conclusion, cryocoolers are essential for many applications that require low temperatures. Mechanical cryocoolers and non-mechanical cryocoolers are the two main types of cryocoolers. Mechanical cryocoolers are the most common type and include Stirling cryocoolers, Gifford-McMahon cryocoolers, pulse-tube cryocoolers, and Joule-Thomson cryocoolers. Non-mechanical cryocoolers are typically more expensive than mechanical cryocoolers but are also more reliable and require less maintenance. They include dilution refrigerators and adiabatic demagnetization refrigerators.

Mechanical Cryocoolers: Working Principle

Mechanical cryocoolers work on the principle of the Stirling cycle, which involves compressing and expanding a gas to transfer heat from a low-temperature reservoir to a high-temperature heat sink. The Stirling cycle has four stages: compression, heat rejection, expansion, and heat absorption.

During the compression stage, the gas is compressed, and its temperature increases. The gas then flows through a heat exchanger where it releases heat to the environment. During the expansion stage, the gas expands, and its temperature decreases. The gas then flows through another heat exchanger where it absorbs heat from the low-temperature reservoir.

The Stirling cycle is used in several types of mechanical cryocoolers. In a Stirling cryocooler, a piston and cylinder are used to compress and expand the gas. In a Gifford-McMahon cryocooler, a mechanical compressor is used to compress and expand the gas. In a pulse-tube cryocooler, a high-frequency oscillator is used to create pressure waves in the gas, which then drives the compression and expansion.

Joule-Thomson cryocoolers work on a different principle than Stirling cycle-based cryocoolers. These cryocoolers use a throttling valve to expand a gas, which causes it to cool down. The cooled gas is then used to cool the low-temperature reservoir, and the expanded gas is returned to the compressor to be recompressed.

Non-Mechanical Cryocoolers: Working Principle

Non-mechanical cryocoolers use different principles than mechanical cryocoolers to transfer heat from a low-temperature reservoir to a high-temperature heat sink. These cryocoolers are typically more expensive than mechanical cryocoolers, but they are also more reliable and require less maintenance.

Dilution refrigerators use a mixture of helium-3 and helium-4 to transfer heat from a low-temperature reservoir to a high-temperature heat sink. The mixture of helium-3 and helium-4 is cooled by a heat exchanger to a temperature of about 100 mK. The mixture is then allowed to separate, with the helium-3 collecting at the bottom of the refrigerator. The helium-3 is then pumped out of the refrigerator, and the process is repeated.

Adiabatic demagnetization refrigerators use the magnetocaloric effect to transfer heat from a low-temperature reservoir to a high-temperature heat sink. These cryocoolers use a strong magnetic field to align the magnetic moments of the atoms in a material. The material is then thermally isolated, and the magnetic field is slowly decreased, which causes the atoms to become disordered and lose their magnetic alignment. This process absorbs heat from the material, which can then be used to cool a low-temperature reservoir.