Experimental and numerical approach for characterization and performance evaluation of cryogenic turboexpander under rotating condition

Abstract

A small-scale radial expansion turbine is distinguished by its ease of production, higher efficiency, and reliability. Such turbines have been successfully used in cryogenic turboexpander systems for refrigeration and liquefaction of the process gas. This paper presents a methodology for design optimization, numerical, and experimental investigation of a radial turbine and nozzle (turboexpander), the most necessary and extortionate component of a nitrogen liquefaction system based on Claude cycle. The initial investigation starts with the preliminary design of a turboexpander using an in-house developed Matlab® code. Then, a Sobol method-based optimization approach has been proposed to determine the normalized sensitivity index and optimal range of major non-dimensional and geometrical variables for the better off-design performance of the turboexpander. After that, different losses of the turbine have been determined using an optimum set of loss correlations which is incorporated into the preliminary design process. This approach can overcome the optimization issues caused by the high sensitive design parameters, which may not be addressed through conventional methods, and ameliorates the off-design performance of the turboexpander (improves power output, total-to-static efficiency, and diminishing the turbine losses by 14.28%, 3.89%, and 9.61% respectively) as compared to the initial design. Based on this, three turboexpander systems are designed and a comparative numerical study has been conducted to study the flow field phenomenon and their thermodynamic performance at three operating pressure and cryogenic temperature (16 bar & 150 K, 8 bar & 120 K, and 4.5 bar & 95 K) using ANSYS CFX®. Finally, the Claude cycle-based experimental facility has been established to determine the thermal performance of the turboexpander at various operating pressure (16 and 8 bar), rotational speeds (120,612, 102,419, and 80,914 rpm), inlet temperatures (150 and 120 K), and mass flow rates (0.01–0.10 kg/s). The results illustrate that the predicted performance from the numerical simulation shows good agreement with the experimental results. Additionally, error analysis of experimental parameters has also been discussed.