Simulation of vortex tube using natural gas as working fluid with application in city gas stations

The work has been done on a 3D model of vortex tube and the governing equations have been solved using ANSYS– FLUENTTM software. Simulations were performed using density based solver and k-ε turbulence model. After validating some results of present study with available data, the effects of geometrical parameters and air/natural gas flow in a vortex tube with 6 and 2 tangential nozzles was examined. The performance of vortex tube with 6 nozzles was better when compared with 2 nozzles which is in satisfactory agreement with previous experiments, so we only show the results for the 6 nozzles vortex tube. There is a little difference between air and natural gas as a working fluid. We found that the temperature difference between hot and cold ends for air flow was little more than natural gas. Based on the results obtained in this work it is concluded that vortex process based on pressurized natural gas can be used in C.G. S as a heat exchanger for high efficiency operation and energy saving purposes. INTRODUCTION Vortex tube is a device, which can separate a higher pressure input gas into two lower-pressure flows with different temperatures. One flow has a higher temperature than the input gas temperature while the other has a temperature lower than that. The vortex tube has numerous advantages such as its low volume, ease of production and maintenance, a high safety factor, lack of any movable parts, and simple structure. Among the experimental studies, results of the work by Cockrill [1] indicated that the performance and efficiency of counter-flow vortex tubes are better than those of the uni-flow vortex tubes. Figure (1) depicts a counter-flow (or standard) vortex tube. Figure 1 standard counter-flow vortex tube In this research, a counter-flow vortex tube (or a standard vortex tube) was used. This device was discovered by Ranque, the French physicist and metallurgist [2]. Several years later, studies of vortex tubes were continued by a German scientist named Hilsch [3]. After Hilsch, broad experimental and theoretical research was conducted on vortex tubes by various scientists and researchers. Ahlborn et al. [4] examined flow inside a vortex tube. They considered the presence of a secondary swirl flow in a vortex tube. Comparison between the performance predicted by a computational fluid dynamic (CFD) model and experimental measurements taken using a commercially available vortex tube reported by Skye [5]. Other researchers such as Selek [6] and Dincer [7] conducted experimental research on flow and temperature in a vortex tube. Aljuwayhel et al. [8] used a numerical model to examine the principles of energy separation in a vortex tube. Frohlingsdorf [9] modelled flow in a vortex tube using a CFX code. Khait et al. [10] studied air flow in a vortex tube. They used various models to simulate turbulent flow. Oliver et al. [11] modeled turbulent air flow inside a Ranque–Hilsch vortex tube in three dimensions using ANSYS-CFX. Their findings stress the significance of meshing especially in the cold region. Zein et al. [12] studied the effect of the ratio of vortex tube length to diameter on simulation of vortex tube flow. According to their findings, the inertia point inside a vortex tube is independent of vortex tube length. Reynolds [13], and Deissler and Perlmutter [14] considered energy separation a result of friction and turbulence. There are always limitations on experimental studies which result from limitations of test devices. However, with Computational Fluid Dynamics (CFD) it is possible to eliminate these limitations. One of the CFD studies on pressure is the study by Ameri and Behnia [15], who indicated that with an increase in the inlet pressure the efficiency decreases. Poshernev and Khodorkov [16] used natural gas as the working fluid and turned it into liquid using a vortex tube. Comparison between the performance predicted by a computational fluid dynamic (CFD) model and experimental measurements taken using a commercially available vortex tube In this research, the fluid flow is analysed inside a vortex tube and the effects of various factors (such as geometry, inlet gas boundary conditions, and size of inlet gas nozzle) on performance of vortex tube is studied to determine the appropriate conditions for performance of the vortex tube. Distribution of temperature is analysed as the main variable, and distribution of velocity is studied as another variable. This is because temperature distribution in a vortex tube depends on velocity distribution. Therefore, the system dimensions and dimensionless parameters, which are dependent on system dimensions, are selected such that feasibility of application of this system as a heater in the C.G. S (City Gate Station) is studied in practice. For this purpose, numerical inputs of the software, in 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics