Research paper Opposed piston linear compressor driven two-stage Stirling Cryocooler for cooling of IR sensors in space application Virendra Bhojwani a,⇑ , Asif Inamdar a , Mandar Lele b , Mandar Tendolkar c , Milind Atrey d , Shridhar Bapat d , Kisan Narayankhedkar e a Jaywantrao Sawant College of Engineering, Pune, Maharashtra, India b MIT College of Engineering, Pune, Maharashtra, India c VJTI, Matunga, Mumbai, India d Indian Institute of Technology, Bombay, Mumbai, India e MGM CET, Navi Mumbai, India article info Article history: Received 1 December 2016 Received in revised form 20 February 2017 Accepted 3 March 2017 Available online 6 March 2017 Keywords: Cryocooler Two-stage Stirling Cycle Opposed piston linear compressor Flexure bearing abstract A two-stage Stirling Cryocooler has been developed and tested for cooling IR sensors in space application. The concept uses an opposed piston linear compressor to drive the two-stage Stirling expander. The con- figuration used a moving coil linear motor for the compressor as well as for the expander unit. Electrical phase difference of 80 degrees was maintained between the voltage waveforms supplied to the compres- sor motor and expander motor. The piston and displacer surface were coated with Rulon an anti-friction material to ensure oil less operation of the unit. The present article discusses analysis results, features of the cryocooler and experimental tests conducted on the developed unit. The two-stages of Cryo-cylinder and the expander units were manufactured from a single piece to ensure precise alignment between the two-stages. Flexure bearings were used to suspend the piston and displacer about its mean position. The objective of the work was to develop a two-stage Stirling cryocooler with 2 W at 120 K and 0.5 W at 60 K cooling capacity for the two-stages and input power of less than 120 W. The Cryocooler achieved a min- imum temperature of 40.7 K at stage 2. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction The most attractive feature of Stirling Cycle cryocoolers is its high COP. Stirling machines with linear motor drive are compact and require no valves for operation. Stirling coolers can be oper- ated at high speeds and high pressures (cooling capacity being pro- portional to speed and pressure). This leads to a reduction in the specific mass (mass of cooler per unit cooling capacity). The use of very high effectiveness regenerative heat exchanger (with very large area density) also contributes to the compactness. The sys- tem operates on Closed Thermodynamic cycle using Helium or Hydrogen as working fluid [1]. Cyclic Analysis proposed by Atrey et al. [2] was used to simulate the performance of the proposed. Thermoaccoustic theory to optimize the system operating and structure parameters. The Cryocooler achieved a minimum tem- perature of 27.6 K and cooling power of 78 W at 40 K with an elec- tric input of 3.2 kW. Alan Caughley et al. [4] discuss a novel concept for free piston Stirling Cryocooler using pair of metal diaphragms to seal and suspend the displacer. The diaphragm allows the displacer to move without rubbing resulting in reduced friction and improved life. The Cryocooler achieved a minimum temperature of 56 K and 29 W of cooling at 77 K. de Jonge et al. [5] discussed analysis and optimization of linear motor for linear compressor, the said analysis has been used to design the linear motor for the present application. Cryocooler in the present work. Cyclic analysis divides the Stir- ling Cycle in equal number of intervals pressure and volume of the compressor and expander vary with each interval. The ideal com- pressor power per cycle is estimated by integrating Compressor PV area for one cycle. The ideal cooling power is estimated by inte- grating PV area for the expansion process. Various losses (Pumping loss, Temperature swing loss, Shuttle conduction loss, regenerator loss, Pressure drop loss) are considered to predict actual Compres- sor power and cooling power. Xiaotao Wang et al. [3] discusses development of a two-stage high capacity free piston Stirling Cry- ocooler driven by linear compressor for HTS application. The paper The thermal analysis was carried out using Cyclic presents results from a numerical model based on http://dx.doi.org/10.1016/j.cryogenics.2017.03.001 0011-2275/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: bhojwanivk@gmail.com (V. Bhojwani). Cryogenics 83 (2017) 71–77 Contents lists available at ScienceDirect Cryogenics journal homepage: www.elsevier.com/locate/cryogenics