Master's thesis in the field of energy conversion mechanics
Abstract
In this study, by using the computational fluid dynamics technique, it has been tried to obtain the optimal dimensions for the vortex tube injection nozzles. For this purpose, numerical simulation has been performed for different values ??of length, width, and height of injection nozzles, and other dimensions of the modeled vortex tubes have been considered the same for all models, which are the dimensions of the vortex tube device of Sky et al. Numerical results for turbulent and compressible flows have been obtained using the standard k-? turbulence model. The main goal of this numerical study is to obtain the minimum possible temperature in the cold outlet by changing the dimensions of the injection nozzles. In the present study, the pressure in the rotation chamber and its relationship with the temperature of the cold outlet of the device were investigated, and finally, for certain values ??of the dimensions of the injection nozzles, better energy separation has been achieved. Finally, some results obtained from the numerical work have been compared with the experimental results, and there is an acceptable agreement between them. style="direction: rtl;">Chapter One
Introduction
The vortex tube is an innovative invention of two scientists named George Joseph Ranquio and Rudolf Hilsch, who separately built this device during the war in the 1940s.[1] For this reason, the vortex tube is also called Rankio-Hilsch vortex tube [1] in honor of these two.
The vortex tube divides the gas flow entering the tube into two separate flows: one is hotter and the other is colder than the inlet. The interesting thing to note about this device is the absence of any moving parts, electrical or chemical parts, or work input to it. Although the vortex tube geometry is simple, the process of fluid dynamics and thermodynamics is very complex. So far, many experimental, theoretical and numerical works have been done to investigate the phenomenon of temperature separation [2] in the vortex tube. It is clear that by using the technique of computational fluid dynamics [3], the complications and costs related to experimental work can be reduced. A pipe can be made to work by opening and closing a small valve. The valve should automatically open when a molecule of hot water reaches it and close when a molecule of cold water reaches it.[2] This imaginary device could be used as a source to obtain hot and cold fluids at the same time. This device, which was first called Maxwell's Jenny Tube, became a reality a century later and is known today as Vortex Tube. Figure 1-1 shows a schematic design of this device that divides the incoming dense air into two streams of colder and warmer air. The attraction of this device for researchers, as mentioned, is the absence of any moving tools or work input to it.
As mentioned, the vortex tube is originally known by the names of two scientists, the first one is a Frenchman named Ranquio who discovered the vortex tube completely by accident in 1933, and the second one is a German named Rudolph Hilsch. who in 1946 successfully built and tested the device by doing comprehensive laboratory work and publishing articles in this field. The research of these two people will be discussed in more detail below.
1-2 Ranquio's research
One ??of the most comprehensive articles with detailed analysis of how the vortex tube was discovered was published by Fulton [1] shortly after its discovery by Ranquio, in which it is pointed out that Ranquio confused the stagnation temperature [4] with the static temperature [5] and that is why The vortex tube made by him did not work properly. Figure 1-2 shows the vortex tube designed by Rankio[4].
Today's modern vortex tubes in terms of structure and design are similar to what is shown in Figure 1-3, which is accompanied by its exploded view. This vortex tube is made by Exair company.
The first article published in the field of vortex tube is related to Rankio in 1931. In this article, he showed that the air inlet can be tangential and include one or more injection nozzles [6]. He also explained how to achieve the desired cooling rate by adjusting the diameter of the cold outlet or changing the area of ??the hot outlet. He also concluded that if the hot outlet is closed, the temperature on the pipe wall [7] reaches its maximum value and also that the temperature of the cold outlet decreases as the pressure increases. The summary of Rankio's theory is that the rotating gas flow expands in a thick sheet on the wall, and the inner layers of this sheet press on the outer layers by a centrifugal force, compressing them and thus heating them. At the same time, the internal layers expand and cool down, and the friction between the layers also reaches its lowest value. [4]
1-3 Hilsch's research
Hilsch[6] published an article in 1946, and in it he briefly used Rankio's work in 1933 as the main source. He took this idea and came up with a similar design for his Vortex Tube. He wrote in this article that the air expands through the orifice in a centrifugal field from the high pressure area in the pipe wall to a low pressure area near the pipe axis. During this expansion, the air gives a significant part of its kinetic energy to the surrounding layers through increased friction. Therefore, these layers face an increase in temperature. Internal friction causes energy to flow from the tube axis to its environment and tries to reach a single and uniform angular velocity on the entire surface of the tube. [6]
It is worth mentioning that the vortex tube classification is based on the location of the cold air outlet in two types. The first one is vortex tube with opposite flow [9], which according to Figure 1-4, this device includes an inlet part with a series of nozzles with a central hole, a hot tube and a conical valve. Compressed gas enters the nozzles with high pressure and speed. With the expansion of the air inside the tube, rapid vortices are formed, which can be changed by adjusting the cone valve, and finally the gases that pass around the hole are cooled and the rest is heated. The difference is that the cold air exits concentrically with the warm air. Its operation is also similar to the opposite flow mode. A schematic of this type of vortex tube is shown in Figure 5-1.
After Hilsch, almost everyone has used the counter-flow vortex tube design rather than its parallel-flow variant. This is because the design and construction of the vortex tube is easier with the opposite flow type, and two separate hot and cold flows are obtained at the two outlets facing each other. In this thesis, work is also done on the vortex tube with the opposite flow.
In this type of vortex tube that can be seen in Figure 6-1, the tube or tube of the vortex tube has a divergence angle of about 4 to 7 degrees. This type of vortex tube has a shorter working length compared to the conventional types and is used for special applications. they become