Technology Transfer

Refrigeration System Is Environmentally Friendly

A NEW, ENVIRONMENTALLY FRIENDLY PULSE-tube refrigeration system has been developed for NASA to use aboard the Space Shuttle and the International Space Station. This system offers many applications to commercial users, including increased reliability, fewer moving parts and much lower cold-end vibration than designs previously used both commercially and on spacecraft.

Working for Marshall Space Flight Center in Huntsville, Alabama, William G. Dean of Dean Applied Technology, Inc., has invented a pulse-tube refrigeration unit that offers a viable alternative to units that use ozone-destroying chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerant fluids. The pulse-tube refrigerators use helium—nontoxic to humans and harmless to the environment—as the working fluid.

Pulse-tube refrigerators can operate over a wide range of temperatures. The technology can be used in food refrigerators and freezers, laboratory freezers and freeze dryers. Pulse-tube refrigerators also can be used to cool electronic devices and detectors. It is the first unit applied to the temperature range and load level needed for typical food and laboratory freezers.

The pulse-tube refrigerator unit's design is based on the orifice pulse-tube concept. Gas is compressed in the compressor. It flows through the compressor's after-cooler, in which the heat is rejected to a water-cooling loop. Helium then flows through the regenerator, which is essentially an economizer, conserving cooling from one cycle to the other.

Next, the gas enters the cold-end heat exchanger, in which heat is added to the gas from the surroundings. In the final stage, the gas enters the pulse tube, orifice and reservoir, which, together, produce the phase shift between the mass flow and pressure necessary for cooling.

The gas moves repeatedly between the hot and cold ends rather than circulating continuously around a loop, as is found in some other types of refrigeration systems. Heat is lifted and rejected at the hot-end heat exchanger, which is also cooled by water.

The new unit's compressor uses dual-opposed pistons displaced 180 degrees out of phase to minimize vibration. This is of great importance to NASA because vibrations can affect sensitive experiments being performed aboard the Space Shuttle and the International Space Station.

For more information, contact Bob Lessels at Marshall Space Flight Center.
Call: 256/544-6539, Fax: 256/544-3151, E-mail: Bob.Lessels@msfc.nasa.gov
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The nontoxic, environmentally friendly working fluid in this pulse-tube refrigeration system offers more commercial applications than previous designs used in space and on Earth.