Numerical Investigation to Visualize the Flow Field Characteristics of a Cryogenic Turboexpander Manoj Kumar 1 , Debashis Panda 2 1,2 Ph.D. Scholars, Department of Mechanical Engineering, National Institute of Technology Rourkela, Odisha, India, 769008 Ranjit K. Sahoo 3 , Suraj. K. Behera 4 3,4 Professor, Department of Mechanical Engineering, National Institute of Technology Rourkela, Odisha, India, 769008 Abstract–The design and optimization of blade profile of cryogenic radial expansion turbine play a significant role in the development of an efficient turboexpander due to increasing demand of cryogenic fluids in research and industrial applications. The primary objective of the present studies is to propose an optimized blade profile for a radial turbine with nitrogen as a working fluid which is a part of turboexpander. Adequately designed turbine blade profile can increase the efficiency of the liquefaction unit. In this regard, the three- dimensional numerical analysis is performed using the shear stress transport turbulence model in ANSYS CFX. The pressure, velocity, temperature, static enthalpy and entropy are reported. With numerical results, the initial profile is optimized to enhance the efficiency of the turbine. The results obtained from the numerical analysis visualize the fluid flow physics inside the turbine. The designed model can predict turbine efficiency and power with an accuracy of ±16% of operating conditions. Keywords: Turboexpander, Fluid flow, Thermal behavior, CFD I. INTRODUCTION Cryogenic liquefaction system requires some essential components, such as expansion turbine, nozzle, diffuser, brake compressor, bearings, heat exchangers, etc. Out of which, expansion turbine plays a vital role to increase the efficiency of the turboexpander. In this regard, the computational study is essential to visualize the fluid flow characteristics. Researchers suggest that the radial turbine is ideally suited for these types of systems. In the design of turbo-expander for the liquefaction of various cryogenic gases, the design of turbine plays an important role, which affects the performance of the system. A two-stage expansion turbine was developed by Yang et al. [1] and performed the experiments to produce 1.5 l/hr of liquefied helium A small high-speed turboexpander operating at 600,000 rpm with externally pressurized gas bearings was designed by the National Bureau of Standards (NBS), USA [2]. The CFD analysis of helium and nitrogen turboexpander was performed by Sam and Ghosh [3] to develop a helium turboexpander with a variable flow capacity mechanism. In this paper, the design of a radial turbine and numerical analysis to visualize the flow field behavior are determined using nitrogen. Initially, the blade profile of a turbine is obtained from Blade-Gen using the operating conditions as mentioned in Table I. The computational grid is created using Ansys ICEM. Finally, the three-dimensional numerical simulation is performed to visualize the fluid flow and thermal characteristics of the turboexpander using the commercially available software ANSYS ® CFX. The pressure, Mach number, velocity, temperature, static enthalpy and entropy contours are obtained at different locations of the turboexpander. The development of an experimental set-up is under process in our laboratory. TABLE 1: SPECIFICATION OF THE DESIGNED TURBOEXPANDER Parameter Value Inlet Pressure 8 bar Temperature 150 K Pressure ratio 3.86 Turbine diameter 24.86 mm Turbine inlet blade height 1.36 mm Turbine outlet blade height 4.54 mm Axial length of the turbine 10.52 mm Number of turbine blades 13 Number of nozzles 17 Tip clearance 0.2 mm II. NUMERICAL SET-UP AND BOUNDARY CONDITIONS The three-dimensional Reynolds-averaged Navier-Stokes equation is used to investigate the flow field and thermal behavior of the turboexpander. The high-resolution scheme (second order) is used to discretize the convection term whereas spatial derivatives of diffusion terms are computed by shape functions using finite element approach. The fluid is assumed to be an ideal gas. The computational grid is generated using ANSYS ICEM software. Fig.1 shows the three-dimensional model of turboexpander and its mesh. International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 Published by, www.ijert.org AMDMM - 2019 Conference Proceedings Volume 7, Issue 03 Special Issue - 2019 1