Cryogenic Systems Group

Cryogenic Q & A

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Table of Contents

1. What is cryogenics?
2. How is it done?
3. What is it used for at BNL?
4. Who benefits from it?
5. When was the Cryogenic Group formed?

What is cryogenics?

The production of low temperatures or the study of low-temperature phenomena. The process of refrigerating a gas to a temperature below its critical temperature so that liquid can be formed.

How is it done?

Many gases can be put into a liquid state at normal atmospheric pressure by simple cooling; a few, such as nitrogen and helium require pressurization as well.

Gas liquefaction is a special case of gas refrigeration. The gas is first compressed to an elevated pressure in an ambient-temperature compressor. This high-pressure gas is passed through a countercurrent heat exchanger to a throttling valve or expansion engine. Upon expanding to the lower pressure, cooling may take place, and some liquid may be formed. The cool, low-pressure gas returns to the compressor inlet to repeat the cycle. The purpose of the countercurrent heat exchanger is to warm the low-pressure gas prior to recompression, and simultaneously to cool the high-pressure gas to the lowest temperature possible prior to expansion. Both refrigerators and liquefiers operate on this same basic principle.

An important distinction between refrigerators and liquefiers is that in a continuous refrigeration process, there is no accumulation of refrigerant in any part of the system. This contrasts with a gas-liquefying system, where liquid accumulates and is withdrawn. Thus, in a liquefying system, the total mass of gas that is warmed in the countercurrent heat exchanger is less than the gas to be cooled by the amount that is liquefied, creating an unbalanced flow in the heat exchanger. In a refrigerator, the warm and cool gas flows are equal in the heat exchanger. This results in balanced flow condition. The thermodynamic principles of refrigeration and liquefaction are identical. However, the analysis and design of the two systems are quite different due to the condition of balanced flow in the refrigerator and unbalanced flow in liquefier systems.

The prerequisite refrigeration for gas liquefaction is accomplished in a thermodynamics process when the process gas absorbs heat at temperatures below that of the environment. A process for producing refrigeration at liquefied gas temperatures usually involves equipment at ambient temperature in which the gas is compressed and heat is rejected to a coolant. During the ambient-temperature compression process, the enthalpy and entropy, but usually not the temperature of the gas, are decreased. The reduction in temperature of the gas is usually accomplished by heat exchange between the cooling and warming gas streams followed by an expansion of the high-pressure stream. This expansion may take place either through a throttling device (isenthalpic expansion) where there is a reduction in temperature only (when the Joule-Thomson coefficient is positive) or in a work-producing device (isentropic expansion) where both temperature and enthalpy are decreased. (From Answers.com)

What is it used for at BNL?

At BNL the cryogenic process is used for a number of projects. From The Medical Department, with it's MRI to here at C-AD where at the Relativistic Heavy Ion Collider (RHIC) the process is use to keep the 2.5 mile ring of superconducting magnets at approximately -452F or 4.5K. At the Alternating Gradient Synchrotron (AGS) it is used for projects such as the AGS cold snake magnet and The Energy Recovery Linac (ERL). Both of which, like RHIC, have superconducting magnets. In the past it has been used for the R&D of new superconducting magnets at the magnet test facility and at the AGS it was used on beam line experimental targets and the largest superconducting magnet at the time, the Muon g-2 storage ring.

Who benefits from it?

At BNL we use a considerable amount of electricity. The operating cost of a superconducting magnet is cheaper then that of a conventional magnet.  With superconducting magnets being cost efficient, more funding can go to into the physics, upgrades or even to the ever higher electric costs.

When was the Cryogenic Group formed?

By 1998 a group of engineers and technicians from the Magnet Division, National Synchrotron Light Source and the Alternating Gradient Synchrotron were combined to form what is now called The Cryogenic Systems Group.

Bernard. Yatauro
Copyright © 2001  CAD Cryogenic Group. All rights reserved.
Revised: 05/18/11.

Last Modified: May 18, 2011
Please forward all questions about this site to: Bernard Yatauro

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation of State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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