Experimental performance study of cryogenic turboexpander by using aerodynamic thrust bearing Subrata K. Ghosh a, * , Ranjit K. Sahoo b , Sunil K. Sarangi b a Department of ME & MME, Indian School of Mines, Dhanbad, Jharkhand, India b National Institute of Technology, Rourkela, Orissa, India article info Article history: Received 19 June 2008 Accepted 2 February 2010 Available online 23 February 2010 Keywords: Turboexpander Aerodynamic thrust bearing Instrumentation abstract An indigenous programme on design and development of a small high speed cryogenic turboexpander has been taken up at NIT, Rourkela. This paper aims at the development of a small high speed cryogenic turboexpander in Indian condition by using aerodynamic thrust bearings. Attention has been paid to the study of the performance of turboexpander and the effect of stability on the vibration of bearings. Series of tests were conducted to confirm the findings. The maximum rotational speed obtained was 200,000 rpm and a temperature drop of 30  C. The outcome may help the designers, researchers and manufacturer of these components. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction A medium or large cryogenic system needs many components, e.g. compressor, heat exchanger, expansion turbine, instrumenta- tion, vacuum vessel, etc. One needs to be self reliant in this vital technology. While all other components are indigenously available to some extent; but whole cryogenic liquid plants are being imported due to the lack of availability of the turboexpander. The longitudinal section of designed and developed turboexpander is shown in Fig. 1 . We have used [1] gas lubricated aerodynamic thrust bearing and aerodynamic tilting pad journal bearing. Thrust bearing supports the thrust load comprising of the rotor weight and the difference of pressure between the turbine and the compressor ends. The radial load arises primarily due to the rotor imbal- ance and is taken up by a pair of aerodynamic journal bearings. The most important and very unpleasant task from the designer's point of view, in case of aerodynamic bearings, is that even relatively short contact of sliding surfaces causes heavy damage, due to the absence of lubricant. Therefore it is essential to use very reliable methods of calculation of bearing properties, especially of the dynamic characteristics, and suit- able materials of bearing surfaces [2]. Many researchers adop- ted Lund's assembly method to analyze, optimize and design tilting pad journal bearings for improving rotor dynamic performance [3]. 2. Turboexpander test rigs The main motive of the present test is to study the performance of the turboexpander under varying operating conditions. The process compressor takes air from the atmosphere through a filter, compresses it and sends to a storage vessel, where it is maintained above the required pressure of 0.6 MPa. The schematic diagram of the turboexpander experimental test rig is shown in Fig. 2. A high pressure line connects from the vessel to the inlet of turbine. The exhaust gas from the turbine returns back to the inlet of the process compressor. There are pressure gauges to measure the pressure at the vessels, inlet and outlet of the turbine. A brake compressor is installed on the same shaft as the turbine operates in a closed circuit. The gas is coming through the nozzle to the inlet of the brake compressor and compressed by the brake compressor. The compressed gas leaving the brake compressor is cooled in a heat exchanger by water and recirculated in the brake compressor. To reduce the heat transfer rate, cold end housing is totally detached from the atmosphere by evacuating the vessel of cold end housing. One vacuum pump is connected to this vessel to create vacuum. 3. Selection of equipment The following are the specifications of the various equipment, instruments and other accessories in building the experimental test set up. * Corresponding author. Tel.: þ91 9430187029; fax: þ91 326 2296563. E-mail address: subratarec@yahoo.co.in (S.K. Ghosh). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2010.02.017 Applied Thermal Engineering 30 (2010) 1304e1311