Experimental investigation and numerical simulation of the flow in the vortex tube

Master's Thesis of Mechanical Engineering - Energy Conversion

Abstract

The vortex tube is a simple mechanical device that has no moving parts and is one of the equipment used in the refrigeration system, in which a high-pressure fluid enters the vortex tube through inlet nozzles. and branches into two flows with a temperature lower and higher than the inlet temperature, thus temperatures up to -40 degrees Celsius can be created. As a local cooler and local heat generator, the vortex tube has a wide range of applications in the industry, such as: cooling plastic injection molds, gas dehumidification operations, thermal sealing operations, cooling the control cabin of electrical chambers, cooling camera lenses, adjusting adhesives and solders, and drying ink on labels and bottles. Although there have been many experimental studies on the performance of the vortex tube, the physical understanding of the flow and the mechanism of temperature separation of the gas or steam passing through it have not been fully deduced due to the complexity of the flow and the inconsistency of the experimental results. In this thesis, with the aim of recording hot and cold temperatures due to the phenomenon of temperature separation in terms of cold fraction, firstly, the performance of a sample of vortex tube laboratory equipment with model 433R made by P.A.Hilton company located in the United Kingdom has been investigated experimentally. The results of experimental investigation include cold and hot outlet static temperature diagrams according to the cold fraction, as well as the cold outlet pressure diagram according to the cold fraction. By using the cold and hot outlet static temperature, the graphs of the performance coefficient of the vortex tube heat generator and chiller, as well as the isentropic efficiency, have been presented according to the existing relationships. The uncertainty of the results of the experimental investigation is also calculated using Holman's empirical relationship and is drawn as an error bar on the graphs. In the following, using computational fluid dynamics methods available in ANSYS CFX14.5 software, the numerical simulation of steady state, compressible and three-dimensional flow has been done by creating a computational network with a regular and hexagonal structure, on the geometry of the vortex tube mentioned above and using fuzzy models such as standard and In addition, the applied cold inlet and outlet boundary conditions are in accordance with the laboratory conditions, while the warm outlet uses an artificial boundary condition. The study of grid independence has also been done by focusing on the static temperature difference between the hot and cold exit of the vortex tube. The description and how to perform the phenomenon of temperature separation and flow pattern is not discussed as the purpose of the simulation done in this thesis. At the end of the hot and cold outlet static temperature diagrams, performance coefficient and isentropic efficiency resulting from the results of numerical simulation are compared with the results of experimental investigation. Besides, the numerical simulation results are presented in the form of static temperature contours, stagnation temperature, Mach number density, velocity distributions, as well as the display of streamlines focusing on the position of the stagnation point and the secondary flow formation area. Keywords: vortex tube, experimental investigation, computational fluid dynamics, temperature separation, cold fraction, standard model,

1-1-Introduction to the vortex tube

The vortex tube[1], which is sometimes known as the Rank-Hilsch vortex tube or the Rank-Hilsch tube, is an innovative invention that was conceived by two French and German scientists named Georges Joseph Rank[2] and Rudolf Hilsch[3] independently during The years of World War II were introduced in Europe [1].

The vortex tube is a simple mechanical device that has no moving parts and is one of the equipment used in the refrigeration system, in which a high-pressure fluid enters the vortex tube through the inlet nozzles and is divided into two streams with a temperature lower and higher than the inlet temperature, (without any chemical reaction or the intervention of an external energy source) in this way, the temperatures can be It created up to -40 degrees Celsius. The vortex tube includes parts such as one or more inlet nozzles, a vortex chamber [4], an orifice at the cold end [5], a control valve at the hot end [6] and a pipe (Figure 1-1). When high-pressure fluid is tangentially injected into the vortex chamber by the inlet nozzles, a swirling flow is generated in the vortex chamber.As the fluid flow continues to rotate towards the center of the vortex chamber, the fluid expands and cools. In the vortex chamber, part of the fluid rotates towards the hot outlet and the other part of the fluid is directly in the cold outlet. Part of the gas in the vortex tube returns due to the axial component of the velocity and moves from the hot end to the cold end. In the hot outlet, the fluid leaves with a higher temperature, while in the cold outlet, the fluid has a lower temperature compared to the inlet temperature [2]. Compared to other devices in the refrigeration cycle, the vortex tube has advantages such as: simplicity, lack of moving parts, absence of electricity, no chemical reaction, easy maintenance, immediate supply of cold air, stable performance (due to the use of stainless steel and a clean working environment) and temperature regulation. Also, dependence on compressed gas and low thermal efficiency may limit some of its applications.

Figure 1?1: A diagram of a sample vortex tube [3]

1-2- Some applications of vortex tube

Although so far the proof It has not been decided about the mode of heat transfer inside the vortex tube and despite the incomplete understanding of this phenomenon, recently the vortex tube has been greatly developed with the use of local cooling devices on a small scale and commercially. Today, there are a significant number of manufacturing companies that use the vortex tube theory effectively and efficiently as a solution in industrial applications. Among these companies, we can mention Exair and ITW Vortec, both of which operate in the United States. These companies offer their products based on a wide range of applications and based on the following qualities of vortex tube technology:

Clean cooling

Easy maintenance - no moving parts

Stable outlet temperature

Cooling, without the need for electricity and Refrigerant

Reliable, compact and lightweight

Cheap price

Although there are many cases for vortex tube applications, as local cooling and heating (which will be explained later), innovative ideas about vortex tube applications can still be presented. Figure (1-2) shows an example of a commercial model of the vortex tube manufactured by Exair. rtl;">1-2-1-local cooling applications

Vortex tubes have a wide range of local cooling applications in machinery production lines and processes. An example of that is the cold air gun with a magnetic base, which is used as a substitute for the cooling agent in machining processes and is shown in Figure (1-3). [3]

Some other local cooling applications include the following:

Cooling plastic injection molds

Gas dehumidification operations

Heat sealing operations

1-1-1-    Heat generating applications Local

Using hot exhaust air, some applications of local heating include:

Setting adhesives and solders

Drying ink on labels and bottles

1-1-2-    Tube laboratory equipment Vortex

Laboratory equipment for use in the laboratory of thermodynamics and fluid mechanics is available in laboratory form by P.A.