Pulse-tube Refrigerators can be operated over a wide range of temperatures. These units can be used in numerous space and commercial refrigeration applications, including food refrigerator/freezers, laboratory freezers, and freeze dryers. Pulse-tube Refrigerators can also be used to cool detectors and electronic devices.

Pulse-tube Refrigerators can be operated over a wide range of temperatures. These units can be used in numerous space and commercial refrigeration applications, including food refrigerator/freezers, laboratory freezers, and freeze dryers. Pulse-tube Refrigerators can also be used to cool detectors and electronic devices.

Pulse-tube Refrigeration, a variation of the Stirling cycle, is a relative newcomer compared to other refrigeration cycles.

The Pulse-tube Refrigerator is the first unit applied to the temperature range and load level needed for typical food freezers and laboratory freezers.

The design of the Pulse-tube Refrigerator unit was based on the Orifice Pulse-tube concept. First, the gas is compressed in the compressor. Next, it flows through the compressor aftercooler, where heat is rejected to a water-cooling loop. Then the gas flows through the regenerator, which is basically an economizer, conserving cooling from one cycle to the next. The gas then enters the cold-end heat exchanger where heat is added to the gas from the surroundings.

The gas finally enters the Pulse Tube, orifice, and reservoir. These three components produce the phase shift of the mass flow and pressure, which is necessary for cooling. The gas shuttles back and forth between the hot and cold ends rather than circulating continuously around a loop, as in some refrigeration cycles. Heat is lifted against the temperature gradient and rejected at the hot-end heat exchanger, which is also water-cooled.

The compressor designed and built for this unit is a dual-opposed-piston type. The displacement of these two pistons is 180° out of phase, to reduce vibrations. The compressor, which can be operated over a wide range of frequencies, is designed for operation at a nominal 60 Hz.

The compressor pistons are supported by helical mechanical springs which assist in producing harmonic motion and return the pistons to the needed null positions before startup. The pistons are supported inside the cylinders on dry lubricated, low-friction sleeve bearings. Each piston is attached to a separate moving coil, which is formed by wrapping copper wire around the end of a spool. When voltage is applied to a coil, the resulting current produces a force on the coil.

Optical encoders provide real-time readout of all piston positions. These encoders use a noncontacting interrupter scale between a light-emitting-diode source and sensors to detect motion. A tachometer pulse and direction signal are generated.

The cold-end and hot-end heat exchangers consist of fine mesh copper screens, fabricated in-house using proprietary techniques.

After design and fabrication, the Pulse-tube Refrigerator unit was subjected to numerous tests. A temperature of -45 °C was reached, which is well below the temperature required for food freezers.

Pulse-tube Refrigerators offer increased reliability, fewer moving parts, and much lower cold-end vibration than other spacecraft or commercial refrigeration concepts.

This work was done by W.G. Dean of Dean Applied Technology Co. for Marshall Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com  under the Machinery/Automation category, or circle no. 166 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Dean Applied Technology, Inc.
1580 Sparkman Drive #103
Huntsville, AL 35816
(205) 721-9550

Refer to MFS-26440, volume and number of this NASA Tech Briefs issue, and the page number.