Introduction
The Vortex Tube is an interesting device in which a compressed gas (usually air) is divided into two streams at alower pressure.One of these streams is about 5OK colder,and the other is about 5OK hotter than the compressed gassupplied.
Although a hot gas stream is more conveniently produced byother methods, the Vortex Tube has few competitors wherea limited amount of cooling air is required in circumstancesin which its small size, relliability and freedom from electricalsupplies are of prime importance.
ln this unit,a modified industrlal Vortex Tube has beenincorporated into a test unit with all the controls andinstruments necessary to provide students with anappreciation of its characteristics and performance.This unit will be of interest to those concerned with
Refrigeration
Thermodynamics and Fluid Mechanics
Plant and Process Engineering
Experimental capabilities
Demonstration of the ability to produce hot and coldair from a device with no moving parts.
Production of performance curves for a vortex tube with
(a) Variation of inlet pressure
(b)Variation of hot and cold gas ratios
(clVariation of gas (if available)
Determination of refrigerating effect and comparisonof this with the estimated power needed to drivethe compressor.
Description
The Vortex Tube was invented by Georges Ranques,a Frenchman.in 1928 but initially it aroused little interest.In1946,Rudolph Hilsch published an article which was widelyread and which started the current interest in this unusualmethod of producing cooling air.
The Vortex Tube consists of two joined and concentriccylindricall chambers of different diameters,open at theirends.Spaced around the circumference of the larger chamber and close to the junction with the smaller chamber,are nozzles arranged to discharge tangentially into the cylinder.
When compressed gas is supplied to these nozzles, the jetsdischarge into the chamber at a near sonic velocity , and aforced vortex,rotating at approximately 500,000 rev/min,is created.The core of this vortex is cold and is extractedfrom the smaller end of the chamber,while the peripherywhich is hot, is extracted from the larger end.
The ratio of cold and hot gas flow rates can be varied by avalve which controls the hot gas discharge.
A number of theories have been put forward to explain theprocesses within the Vortex Tube and it is valuable for astudent to be confronted with a device which works, butabout which there is argument about how it works.
One theoryv due to c.D. Fulton is as follows.
Due to viscous forces, the vortex in the chamber rotates atconstant angular velocity (i.e. is a forced vortex) and itslinear velocity is proportional to the radius.
Since the momentum of the air leaving the nozzles is aconstant, the angular momentum of the core must havedecreased by the same amount as the angullar momentum ofthe periphery has increased.
Thus,the core, having done work, falls in temperature,while the periphery having had work done on it, increasesin temperature.
ln this unit,air (or any other safe gas if availablle) flows through a pressure regulator and filter,and is supplied to thevortex tube at up to700 kN m-2 gauge.After passing through the vortex, the cold air leaves from the upper endand the hot air from the lower end, both streams being atapproximately atmospheric pressure.
To avoid problems with frosting and flow meter errors,the hot and cold air streams are passed in opposite directionsthrough a concentric tube heat exchanger.The air streams,now close to ambient temperature,pass through variablearea flow meters to the atmosphere.
A "balance valve"" fitted in the outlet from the hot end ofthe vortex tube controls the proportions of the total airflow which passes from the "hot" and "cold"" ends.
Thermocouple sensOrs, with a selector switch and digital display allow the measurement of all important temperatures.Although no direct measurement of the refrigerating effectis made, the mass flow rate and the temperature of the
Thermocouple sensOrs, with a selector switch and digital
display allow the measurement of all important temperatures.Although no direct measurement of the refrigerating effectis made, the mass flow rate and the temperature of the
cold air stream are directly measured.It is assumed that anycooling which can be done by this cold air as it returns toambient temperature, is its refrigerating effect.
Typical performance curves obtained from this unit areshown below.
