Vortex tubes, also known as Ranque-Hilsch tubes, are mechanical devices that separate pressurized air or any noble gas into hot and cold streams.
There are no moving parts of the vortex tubes. The compressed air is pushed towards a “generator” which allows the air to rotate at very high speeds.The air turns and moves towards the other end of the tube. A conical plug at this end ensures that the outer part of the air is thrown out. The remaining air is forced back through the smaller inner diameter vortex and through the center hole of the ureter. The vortex tube is considered to make the “inside-out” motion of the air inside. In other words, the inner air layer has the same rotation rate as the outer layer, that is, the same angular velocity. Often, the rigid body rotation movement is caused by friction between the inner and outer air flows that separate in the vortex tube. To explain, due to the centrifugal force, the outward air flow is exposed to more pressure from the air remaining inside. While the internal and external air currents are rotating in the same direction and at angular velocity, the current inside loses the angular momentum value. The reduction in angular momentum causes kinetic energy transfer to the external airflow. Thus, the supply air is separated into hot and cold air streams. For this reason, the temperature of the air flow on the outer surface is higher than the inside. According to flow characteristics, there are parallel and counter flow, adiabatic and nonadhyabatic vortex tubes according to design specifications. Although the vortex tubes are subjected to different classifications, the working principle of all devices is the same.
Working principle of the vortex tube
The counterflow vortex tube operating principle is shown above. The compressed air enters through point (A). The air begins to rotate around itself at very high speeds with the help of the generator in the tube. Air traveling along the hot tip out of the hot air then turns to the opposite side and consists of two air streams (B) and (C) running in opposite directions. The airflow advancing towards the hot tip heats up and is thrown out at point (D). The air in the middle section cools down and exits from point (E). The temperature and the capacity can be adjusted with the plug at point (D) or by using different generators. (B), (C) hot air outlet, (D) hot air outlet, and (E) cold air outlet.
When the vortex tubes are evaluated in terms of the yield, the temperature reduction between the entering air and the air leaving the cold side is taken into consideration, generally depending on the cooling rate. The cooling rate is expressed by the ratio of the amount of cold air output to the total input air amount. In other words, in a vortex tube with a cooling rate of 60, 60% of the air is from the cold air side, and 40% is from the hot air side. The air temperature from the cold end depends on the inlet air temperature. For example, if the inlet air temperature is -12.2 ° C at a pressure of 6.9 bar, virtually all vortex tube producers guarantee a temperature of -70 ° C with a cooling rate of 40%. As the cooling rate is reduced, the temperature difference between inlet and outlet cold air will increase and lower temperatures will be achieved. For example, if the temperature difference between inlet and outlet air at 80% cooling rate (6.9 bar) is 30 ° C, it is 47 ° C at 50% cooling rate (6.9 bar) 68 ° C.
Obtaining a lower temperature at the end of the tube does not always mean that it will be the most cooling effect. As the cooling rate in the vortex tubes changes, the temperature at the cold end is affected in the reverse direction. The cooling effect is obtained by balancing the temperature value and the air flow. The cooling capacity of the vortex tube should be taken into account first when selecting the vortex tube. In addition, as the air pressure entering the vortex increases and the dryness level increases, the vortex tube increases its efficiency. The use of filter media in the pressurized air intake is a very important parameter to increase the efficiency. Vortex tubes are used where spot cooling is required.