PREDICTION OF DIFFERENTIAL JOULE-THOMSON INVERSION CURVES FOR CRYOGENS USING EQUATIONS OF STATE Nupura Ravishankar 1 , P.M. Ardhapurkar 2 , M.D. Atrey 3 1 Sardar Vallabhbhai National Institute of Technology, Surat – 395 007 2 S.S.G.M. College of Engineering, Shegaon – 444 203 3 Indian Institute of Technology Bombay, Mumbai – 400 076 In many cryogenic applications, Joule–Thomson (J–T) effect is used to produce low temperatures. The isenthalpic expansion of gas results in lowering of temperature only if the initial temperature of the working fluid is below its characteristic temperature, called the inversion temperature. Inversion curves are helpful in studying the inversion temperatures. The prediction of inversion curves solely depends on the equation of state (EOS) for the working fluid. In the present work, various EOS are explored in order to predict the Joule–Thomson differential inversion curve for various commonly used cryogens viz. nitrogen, argon, carbon dioxide, helium, hydrogen and neon. The widely accepted EOS such as Van der Waals, Redlich–Kwong and Peng–Robinson EOS are used for this purpose. Key words: Inversion curve, Joule Thomson Effect, Van der Waal, Redlich Kwong, Peng Robinson INTRODUCTION The Joule-Thomson (J-T) effect has been widely investigated because of its importance for theoretical and practical purposes. It has many cryogenic applications and is widely used in gas liquefaction. The effect describes the temperature change of a gas or liquid when it is forced through a valve or porous plug under adiabatic conditions. The rate of change of temperature with respect to pressure in a J-T process (that is, at constant enthalpy) is called the differential Joule–Thomson coefficient, μJT and is given as,   =(   )  (1) The locus of points for which μJT =0 is called the differential inversion curve. The inversion curve divides the p-T plane into two zones as shown in Figure 1. The J–T coefficient is positive inside the inversion curve, while it is negative outside the curve.