Core-technology advances extend maintenance-free operating life of coolers to more than 50,000 hours.
A Stirling cooler is a mechanical system that approximates the ideal gas cycle. Often associated with airborne or portable cooling applications that require compact design and low input power, Stirling coolers are suitable for such applications because of their high efficiency. Compared to Gifford-McMahon and Joule-Thomson cycles, Stirling offers more than twice the cooling performance in the capacity range from 1-100 W. The coolers have a variety of military and commercial applications in infrared receivers and thermal imaging equipment.
Although Stirling coolers have been widely adopted for these applications, the cooler's life, typically less than 7500 hours, has prevented broad commercial use. Stirling Technology Company (STC) has developed a family of long-life coolers based on flexure bearings, clearance seals, and low-cost linear drive motors. Two NASA SBIR contracts, with Marshall Space Flight Center (solicitation year 1994) and Goddard Space Flight Center (solicitation year 1994) provided funding to advance the core technologies used in these coolers. A low-cost linear drive compressor and flexure bearings serve as the technology platform for STC's BeCOOL™ cryogenic coolers, capable of more than 50,000 hours of continuous operation with no maintenance.
The special features that provide low-cost manufacturing and maintenance-free operation that were realized in this program are the following:
- Moving iron motor: The linear motor mover is iron and the magnets are integrated into the stationary motor stator. In this configuration, the magnets are not exposed to cyclic motion that can induce cyclic stresses and cause demagnetization over time.
- Flexure bearings and clearance seals: The linear motor mover is supported by flexure bearings (see Figure 2). The flexures align the compressor piston along the longitudinal axis while preventing radial misalignment. This technique allows for the use of a clearance seal between the piston and the compressor housing. By using a very small clearance seal instead of a rubbing seal, there is no contact between the power piston and the compressor housing.
- Low-cost manufacturing: The linear drive compressor uses standard electric motor materials and fabrication methods. This technology is mature and very low in cost.
This work was done by
Stirling Technology Company
4208 W. Clearwater Ave.
Kennewick, WA 99336