| Cryocoolers are generally defined as small refrigerators capable of achieving useful refrigeration below 120 K. The applications of cryocoolers are infrared sensors, cryopumps, shielding of magnetic resonance imaging systems, and cooling of semiconductor and superconducting circuits. Pulse tube refrigerators, a variation of the Stirling cycle, are a fairly recent development in cryocooler technology. The principal advantage of an orifice pulse tube refrigerator is that it has only one moving part, the compressor. The high mass flow rates in this refrigerator though result in greater heat loads on the regenerative heat exchanger.;The performance of regenerators in oscillating systems is not well understood, primarily due to the difficulty of making direct measurements of mass flow rates and temperatures in these systems. Therefore, it is difficult to develop accurate numerical models of regenerators, since no experimental measurements exist. This study was undertaken to help rectify these deficiencies by developing techniques to dynamically measure regenerator performance in an actually operating pulse tube refrigerator and develop a numerical model of a regenerator using the full set of conservation equations.;Durable yet sensitive sensors had to be developed capable of measuring mass flow rates and temperatures in a rapidly oscillating system at cryogenic temperatures. Specially designed constant temperature anemometers (CTA) and resistance temperature detectors (RTD) were developed with these capabilities. Both were constructed from 2 mm lengths of 3.8 ;In summary, this study has developed a method for dynamically measuring regenerator performance in an operating pulse tube refrigerator. A numerical model was also developed for predicting regenerator performance. Experimental results from this study will assist in improving the numerical model and in developing improved correlations for pressure drops and heat transfer in porous media for oscillating systems. This experimental and modeling work will help in the design of better regenerators and thus, better cryocoolers. |
