The Ranque-Hilsch tube commonly known as a vortex tube is simply a grooved coupled pipe with no moving parts that can produce a cold air jet. It is a pure mechanical device that allows the possibility of both cooling and heating without using electricity. For the tube to work however, compressed air is required with pressure range of 5.5 bars- 6.9 bars. Using the centrifugal effect, the vortex tube splits the compressed air stream into two jets, one with a higher and one with a lower temperature than the inlet air. The absence of moving parts makes it reliable, durable and almost maintenance free.
Working of a Vortex Tube
Although the phenomenon is fairly complex to understand but an attempt has been made herein to explain the functionality of vortex tube in the most simplest terms possible.
The energy in a moving fluid can be divided into four components. They are Pressure energy, Kinetic energy, Potential energy, and Thermal Energy. The conservation of these energies is the basis of Bernoulli’s equation. In thermodynamics, the Pressure and the thermal energy are collectively termed “enthalpy”.
In a vortex tube, the Pressure energy is transformed into Kinetic energy first. High pressure air enters into the tube where the grooves force the flow to spin and swirl at almost 1,000,000 rpm. The kinetic energy than starts feeding off the thermal energy of the air. This results in the onset of separation of high and low thermal energy particles. The air next enters the tube portion where colder air particles (with low angular momentum and low energy) occupy the center of the air stream and the hotter air (high energy) swirls on the periphery of the tube.
The vortex tube has two outlets. The hot air is bled off from the annulus outlet at one end of the tube. The cold air stream bounces back after hitting the core and exits from the opposite end of the tube.
Some vortex tubes designed for industrial application can achieve a temperature differential of up to 71°C. According to a research published in Canadian Journal of Physics, the the maximum COP of the vortex tube effect for air is 2.5. Vortex tube can also be used with refrigerants to achieve a much higher COP.
Industrial Vortex Tubes
There are many suppliers that offer Industrial vortex tubes that are often made out of stainless steel. Their price depends upon the size and performance. A well designed vortex tube can raise the temperature of the inlet air stream by 93°C or reduce it by 71°C.
The tubes are available online from $100 to $200. They are rated by their cooling capacity (often specified in BTU) or the flow rate of cold stream (CFM). Most Industrial vortex tubes require compressed air at 100 PSI (6.9 bars)
The main application of vortex tube is in spot cooling. In spaces where cooling or heating is required and where electrical components may cause a safety hazard such as inside a cotton godown or warehouse with flammable material, vortex tube cooling can provide a safe solution.
They can be also used to spot cool soldered material. In a machining shop where compressed air in generally available, the vortex tubes are used in Milling/Lathe and CNC machines. The cold air stream from the tube helps the machining process by keeping the cutting tool cooler, thereby maintaining the tool’s hardness and also by blowing away chips and swarf. They are an effective replacement for much expansive liquid coolants used during machining which require a separate pumping and drain apparatus.
Compared to other refrigeration techniques, cooling through vortex tubes is the most environmentally friendly (as no refrigerants or chemicals are used) and is also one of the cheapest. When compared to cooling through Peltier effect (another solid-state cooling device), vortex cooling is much more efficient.
DIY Vortex Tube
A vortex tube can be easily made in a shed with a few tools in as little as $25 (20 pounds). Videos are available on YouTube that show the making of vortex tube from scratch using PVC pipe and standard fitting. It is advised that a Factor of safety must be incorporated in the design particularly when using high pressure air in PVC pipes.
Video Courtesy: Otto Belden
Home-made Electricity free Refrigerator / Air conditioner
Using the cold air stream from the Vortex tube, a refrigerator can be designed that uses no electricity. The five components required for this are as follows:
1.Propeller (mounted on a shaft that can be coupled with a compressor)
2.Compressor (without the electric motor)
3.Tubing (to hold compressed air)
5.Insulated box (can be made out of card board lined with Styrofoam)
All these components can be salvaged from local recycling centers. Propeller can be made using PVC pipes. The plan and schematics can be accessed from here.
It should be noted that propeller powered compressor are available commercially by the name of Wind-compressor.
1.The propeller would generate the torque required for the compressor to run.
2.The compressor would generate compressed air
3.The flexible tubing would supply the air to the vortex tube
4.The cold air stream from the vortex tube would be fed into the insulated box while hot air would be expelled to the ambient
5.Insulated box should have some degree of leakage and should not be hermetically sealed to ensure the flow of cold stream in the box.
The propeller with compressor should be mounted on a mast that is 3 to 10 meters high. The higher the propeller is, the more unperturbed wind it will receive.
This vortex tube refrigerator can help remote villages where grid electricity is unavailable and storing vaccines and medicines and food is a problem.
On a separate note, electricity can be generated using the Solar Stirling Plant. For details Click Here!
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