Showing papers by "Ranjit K. Sahoo published in 2019"

A methodology for the performance prediction: flow field and thermal analysis of a helium turboexpander

Abstract: Helium liquefaction systems are widely used in nuclear fission, superconductivity, space industries, and other scientific instruments. However, the efficiency of these systems is quite low due to the cryogenic operating temperature. In this regard, the one-dimensional design methodology of the helium turbine and nozzle (hereafter, renowned as turboexpander) is important to increase the efficiency of the system. This paper demonstrates the sensitivity analysis and optimal range of non-dimensional design variables on which the radial inflow turbine has maximum efficiency, minimum losses, and maximum power output using artificial intelligence techniques. On this basis, three turboexpander models are developed within the optimal range of predicted non-dimensional variables. After that, a comparative numerical study is carried out to highlight the flow field and thermal characteristics of helium fluid. The standard two equations $$k{-}\omega $$ SST model is used to solve the three-dimensional incompressible flow inside the computational domain. The numerical results are validated with the available experimental data from the existing literature. The variation of Mach number, Reynolds number, Prandtl number, static entropy, static enthalpy, temperature, and pressure inside the turboexpander is significantly affected by blade profile which is enormously affected by the design methodology. The study also demonstrates the flow separation region, vortex formation, tip leakage flow, secondary losses, and its reasons along with the spanwise location. The results highlight the importance of the design methodology, sensitivity analysis, the prediction capability of the artificial intelligence network, numerical methodology, and development of the helium turboexpander prototype models.

Preliminary design, flow field, and thermal performance analysis of a helium turboexpander: a numerical approach

Abstract: Most studies on cryogenic turboexpanders are focused on parametric studies and mean-line design to increase the performance of cryogenics liquefaction cycle without much attention to the splitter blades which are crucial for the stability of the flow field. This study focuses on a novel mean-line design methodology to develop the radial turbine and nozzle (hereafter renowned as turboexpander) to investigate the performance characteristics. Firstly, Sobol sensitivity analysis is performed to identify the effect of major non-dimensional design variables on isentropic efficiency of the turbine. Secondly, the non-dimensional design variables are optimized using artificial intelligence techniques. Thirdly, three turboexpander models with and without splitter blades are designed within the optimized range of non-dimensional variables. After that, the three-dimensional numerical analysis is carried out to visualize the effect of splitter blades on flow field and thermal characteristics of the turboexpander. It is noticed that the passage vortices and flow separation are minimized using the splitter blades. The numerical results are further validated with available data in the literature. A detailed comparative analysis of Mach number, pressure, temperature, velocity, static enthalpy, static entropy, etc., is carried out at different operating conditions. The results reveal that the use of splitter blades has a tremendous effect on the performance and flow field characteristics of the radial turbine. The proposed methodology specifies the insights for an optimum turbine design methodology of a cryogenic turboexpander, Sobol sensitivity analysis, prediction capability of artificial intelligence methods, numerical techniques to simulate the assimilating performance of turboexpander, as it is the most crucial and expensive component of turboexpander-based cryogenic system.

Numerical analysis of a single stage Gifford-McMahon type pulse tube refrigerator

Abstract: In this paper, a step by step design methodology has been proposed to design a single stage GM-Type pulse tube refrigerator. A numerical model has been developed that solves continuity, momentum and energy equations for fluid, and also energy equation for solid matrix, by using finite volume method. This numerical model predicts the mass flow rate, pressure history, temperature variations etc. in each discrete control volume. By using the information so obtained from the numerical model, a heat exchanger (shell and tube type) was designed by using e-NTU approach and then fabricated. Structural analysis was also performed to ensure the safety of various components of GM-type PTR, and to calculate the various forces for the design of flanges of regenerator and pulse tube. Numerical analysis shows that, the present setup can produce a refrigeration capacity up to 25.8 W @ 70 K and 12 W @ 40 K.

Design and Numerical Analysis to Visualize the Fluid Flow Pattern Inside Cryogenic Radial Turbine

Abstract: In this paper, the mean-line design and numerical analysis to visualize the flow field characteristics of the cryogenic radial turbine for the liquefaction of nitrogen are reported. The three-dimensional design of blade profile and a fluid passage is created using Blade-Gen©. The meridional plane, hub, and shroud layers are optimized to increase the efficiency, minimize the vortex formation, and losses in the fluid passage. Turbo Grid has been used to create the computational grid. Numerical simulations are carried out using shear stress transport turbulence model using CFX© to visualize the fluid flow behavior, high-pressure zone, heat transfer characteristics, vortex formation, pressure, velocity, Mach number, temperature, entropy generation, etc., using nitrogen as a working fluid. The blade-loading characteristics, blade thickness, and blade angle variation at leading and trailing edge are also being discussed.

Design and Numerical Investigation to Predict the Flow Pattern of Non-axisymmetric Convergent Nozzle: A Component of Turboexpander

Abstract: Current work proposes a novel design methodology using curve-fitting approach for a non-axisymmetric airfoil convergent nozzle used in small-sized cryogenic turboexpander. The curves used for designing the nozzle are based on a combination of fifth and third order curve at upper and lower surface respectively. Four different turbulence model such as k-ε, SST, BSL and SSG Reynolds stress turbulence model is used to visualize and compare the fluid flow characteristics and thermal behaviors at various cross-sections. It is interesting to observe that the Mach number obtained at the outlet of the nozzle is highest and temperature drop is maximum for SSG model under similar boundary conditions. It is also observed that the designed nozzle with curve fitting approach is appropriate for impulse type turbine with a small amount of reaction. The key feature of this implementation is to obtain subsonic velocity at the nozzle exit and reduce the irreversible losses through the nozzle, which can affect the performance of a turboexpander.

CFD Analysis of GM Pulse Tube with Functional Gradient Regenerator

Abstract: The present research aims to establish a stable and reliable simulation of GM pulse tube using commercially available CFD software. In line with aforementioned objective, three major tasks have been addressed in detail. First, a GM pulse tube has been taken from the literature for analysis. Unlike the present state of the art, the present analysis has been carried out using multi-component models in 3D environment. Various components involved in a pulse tube have been modelled, and the corresponding assembly model has been analysed. The proposed approach introduces tremendous amount of numerical complexities which have been addressed in detail. The numerical result agrees to lowest temperature achieved experimentally with 95% accuracy. In second, the thermoacoustic phenomena have been analysed regarding work done at various locations, which re-establishes the fact and phenomena which takes place in a double inlet GM pulse tube. At last, functionally gradient regenerator (FGR) has been proposed to enhance the performance of pulse tube. This particular task has two major sections. The first section enlightens the modelling of functionally gradient porous material (FGPM) for analysis, and the second section focuses on the realistic modelling from manufacturing point of view. Summarizing, the contribution establishes a practice to investigate a GM pulse tube in 3D component level together with an approach to the model functionally gradient regenerator.

Numerical Investigation to Visualize the Flow Field Characteristics of a Cryogenic Turboexpander

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 threedimensional 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.