Experimental Investigations on 20 K Stirling-Type Two-Stage Pulse Tube Cryocooler with Inline Configuration

Multistaging in a Stirling-type Pulse Tube Refrigerator (PTR) is employed to reach the temperature range of 20 K and below. Various configurations of two-stage PTRs can be used, where the former stage provides precooling for the next stage. There are several candidate twostage configurations, each with advantages and limitations. These include: inline, ‘U’ type, coaxial, and combinations of these. In addition to the above, the configuration can be of integral or split type, depending if the compressor is directly attached to the pulse tube assembly or is remote. The present work describes experimental investigations carried out on an integralconfiguration Stirling-type two-stage PTR with inline pulse tubes for both stages. This pulse tube configuration is thermodynamically advantageous as it involves the least dead space and flow resistance. Inertance tubes are used as the phase shift mechanism for both stages. The secondstage alone has an added double-inlet valve along with the inertance tube. A linear compressor is used to provide the PV power to the PTR and is maintained at 350 W. The investigations are carried out for different operating conditions. INTRODUCTION The development of low temperature cryocoolers has been initiated to fulfill the need for low temperatures in several space missions. These requirements include the cooling of electronic devices such as infrared sensors, or the precooling of Joule-Thomson refrigerators. Under the given constraints on the cryocoolers for space applications in terms of reliability, lifetime, and generated vibration, pulse tube cryocoolers with no moving parts at the cold end are an attractive technology to satisfy the same. Multistaging is used to achieve such low levels of temperatures, where the former stage serves as a precooling stage for the next one. The two stages can be coupled in two different ways. The gas-coupled design contains the same gas in both the stages with the same pressure and the same frequency. On the other hand, a thermally-coupled design can have two different gases, different pressures and frequencies, and different compressors for each stage. Yang and Thummes [1] have reported a minimum temperature of 20.02 K for the input power of 200 W using a Leybold Polar SC7 compressor. The design is of the gas-coupled type. Nguyen et al. [2] E Two-Stage Pulse Tube Cryocooler with Inline Configuration M.V. Tendolkar , K.G. Narayankhedkar , M.D. Atrey 1 1 Indian Institute of Tech. Bombay, Powai, Mumbai-400076, India 2 xperimental Investigations on 20 K Stirling-Type Veermata Jijabai Tech. Institute, Matunga, Mumbai-400019, India