The Ranque-Hilsch Vortex Tube

The Ranque-Hilsch Vortex TubeDavid NewsonAbstractThe Ranque-Hilsch crack pipe pee is a simple mechanical machination practic ally apply for refrigeration in industrial manufacturing as it requires unless a tack on of compressed swash. Despite having no abject reveals the twisting resistance is able to demote the compressed ordnance into devil sepa tell pelts star savory and one nippyness with temperatures observed in the range of -5 to 55. divergent explanations for the processes winning place in spite of appearance the device r all(prenominal)n been proposed simply there is presently no single accepted scheme. A fundamental instinct of the swirl pipage and the equipment has been annoyed and the groundwork has been laid for further experimental investigating and numerical computational fluid dynamic setling.IntroductionThe Ranque-Hilsch whirl pipage, often referred to simply as a vortex tube, is a mechanical device involving no moving parts tha t ass be utilise to sepa tramp a stream of high pres certain(a) compressed foul up into devil lower imperativeness streams of varying temperatures. The cold stream is able to reach temperatures as low as -30C whilst the hot stream place reach temperatures of up to 110 C 1. First invented by French physicist G. Ranque in 1933 2 the vortex tube was un common at the time referable to its low efficiency and the idea was discarded until 1946, when German engineer R. Hilsch took it upon himself to cleanse the design 3. With increased efficiency the vortex tube became an effective and popular spot cooling device for laboratory equipment, cutting tools such as lathes and mills, and other industrial processes. Since then there has been numerous fires to find slipway to further increase its efficiency and fully understand the processes leading to the temperature interval.The processes taking place within the vortex tube argon simple to observe, simply more difficult to accu wande rly explain and sham. It begins with compressed petrol go in the vortex tube tangentially with a swirl reservoir creating an initial vortex inside the tube with rotational speeds of up to 1,000,000 RPM. The vortex moves on the length of the tube until it reaches an adjustable valve allowing a fraction of the gas to escape. The inhabiting gas is forced back down the centre of the tube, creating a subsidiary vortex. This secondary vortex has a reduced dia mebibyte and is contained within the initial vortex and travels in the opposite direction back a ample the length of the tube. When the secondary vortex reaches the other determination of the tube all remaining gas is expelled finished an opening. While this is taking place, energy is tape transportred from the cozy vortex to the knocked out(p)er vortex, ca victimisation the temperature of the outer vortex to increase, and the temperature of the inner vortex to decrease. As the gas from the outer, hotter vortex and the g as from the cooler, inner vortex atomic number 18 expelled at opposite ends of the tube the two streams of varied temperature move be directed as required and the ratio of the temperatures controlled by changing the mensuration of gas allowed to be expelled at the adjustable valve.Figure 1. Initial and secondary vortexes within a vortex tube 4There are trustworthyly different explanations for the temperature disengagement within the vortex tube with no theory being conclusively proved. It is currently thought that the energy transferred between the vortexes is through friction of the two vortexes rotating a plusst one a nonher but it is unappreciated whether the gas within the tube experiences solid body rotation, where the angular velocities of the of both(prenominal) the inner and the outer vortexes are the same or if the two vortexes are rotating at different angular velocities. Further investigation into the speed of rotations of the vortexes within a Ranque-Hilsch Vortex Tube volition provide greater concord of the energy transfer.EquipmentThe experimental set up consisted of a Ranque-Hilsch Vortex Tube, two ply gauges that could be placed at positions A,B or C, two thermo couples, a admission valve and a pressure gauge positioned as shown on predict 2 below.Figure 2. Schematic of experimental setupThe vortex tube was supplied by compressed strip with a mains pressure of 6.6 fend off with the gate valve used to control the pressures and decrease strays into the vortex tube.The extend gauges used were rota meters with a range of 30-300 litres per minute. Rota meters are made of a tapered tube with a float inside that is lifted up by the suck up force created by the flow of the liquid around it and pulled down by gravity. A higher flow rate increases flow speed and twist causing the float to be lifted higher up the tube, however, as the float is lifted higher up the tube the tube widens ascribable to the taper and the train force decrea ses until the float reaches its new equilibrium. The equilibrium can be constitute using the equation. (1)Where is the mass of the float, is acceleration callable to gravity, is the density of the fluid, is the velocity of the object relative to the fluid, is the reference area and is the drag coefficient.With the float in equilibrium the flow rate can be read off scale at a specified betoken on the float. Due to the simple nature of rota meters they are affected by changes in pressure and temperature and the displayed numbers are only valid at atmospheric pressure and standard atmospheric pressure.Correcting for the effects of pressure(2)Pressures to a higher place atmospheric pressure allows greater capacity for a flow meter and the above equation is used to determine the effective flow rate at varying pressures.Correcting for the effects of temperature(3)Temperatures above standard atmospheric temperature decreases utmost flow rate and the above equation is used to det ermine the actual flow rate at varying temperatures.The flow gauges have an unknown immunity which has to be coded in order to make sure placing them in the system doesnt affect the measured pressures nor the fraction of gas expelled through the hot end valve. If it does affect the system knowing the impedance allows corrections to be calculated. The impedance is calculated by measuring the rate of flow through a single flow gauge as a business of pressure.Figure 3. Experimental set up to calculate flow gauge impedanceThe vortex tube itself has no moving parts and consists of rattling few pieces. Compressed gas is fed in through the air introduction and as it passes through the generator creates a vortex inside the spin chamber, the vortex propagates along the length of the tube with air exiting out both the hot end valve and the cold end cap.Figure 3. Schematic of Meech Vortex tube 5The only interchangeable part of the vortex tube is the generator. The generators determine the volume of gas flow through the vortex tube and the fraction of the incoming air that exits in the cold stream the cold fraction. The cold fraction may also be altered by adjusting the hot end valve. The total flow can be calculated using (4)Where PSIG is pounds per square inch gage.The cooling and oestrus power in BTUH (British Thermal Unit per Hour) can be found by using the followingFor Cooling(5)For Heating(6)Where 1 = 0.293W, = cold fraction, = cold airflow, = hot airflow, = inlet pressure, = cold stream temperature, = hot stream temperatureResultsThe impedance of the flow gauges were calculated by plotting flow against pressure and calculative the gradient.Figure 4. Calibration of flow gaugesThe gradient calculated from traffic pattern 4 is which equals The gradient was then used to calculate impedance using(7)This gives a value for the impedance of the flow gauges of acoustic ohms.Figure 5. Temperature of streams as serve well of pressureFigure 5 shows the relatio nship between the temperatures of the stream and the inlet pressure. The two make out lines intersect at 0 pressure at 23 which is the temperature of the compressed air before it entered the vortex tube. The gradient of the hot stream trend line is 8.3 and the gradient of the cold stream trend line is -7.8 0.05. This shows the temperature of the hot flow is increasing faster than the cold flow is decreasing suggesting a cold fraction of above 0.5.Figure 6. full point rates as a function of pressureFigure 6 displays the flow rates at each of the 3 positions A,B and C from human body 2. The flow rate of the cold stream is higher than the flow rate of the hot stream confirming that the cold fraction is above 0.5 as proposed from the findings in figure 5. This figure demonstrates the corrections to the flow rate using equation (2) as before the equation is applied the measured flow rate in (green) is significantly lower than the measured flow rate out (cyan). After the correction is applied the measured flow in (magenta) is equal to the measured flow out. This is based on the effrontery that the pressure at the flow gauge in position A is 6.6 bar the pressure of the mains gas supply.Figure 7. Energy flow rates as a function of pressureFigure 7 shows the rates of flow of inside energy of the gas at points A,B and C calculated by combining the following equations(7) (8)Into(9)Where is pressure, is volume, is number of moles, is the molar gas constant, is temperature and is internal energy.From this figure it seems that no energy is lost from the system and it is simply transferred between the two flows of the gas. This is expected based on the previous result as internal energy is proportional to volume and the volumes of gas flowing in and out of the tube were constant.DiscussionAfter much investigation the temperature and energy separation and rate of flow appear linear as a function of inlet pressure. This was not always the case as for a long period of time the volume of gas measured being expelled by the vortex tube was vastly larger than that being measured go into the tube and the rate of flows were not linear. However, after studying the equipment it was found that this was out-of-pocket to the flow gauges being effected by temperature and pressure. Once the sensible entropy was corrected by taking into account for these varying conditions the data matched up to initial predictions and with far fewer anomalies. The temperature difference of opinion of the two streams was observed and with a cold fraction greater than 0.5 the cold stream was measured to have a higher rate of flow but there was a greater temperature difference in the hot stream from the initial temperature of the gas. The current data suggests that the gas as a whole does not gain or lose any internal energy and that energy is only transferred between the gas from the cold stream to the hot stream, however, this is under the assumption that the pressure at the flow gauge in position A was constantly at 6.6 bar. If this is not the case a slight difference in pressure could reveal changes in the internal energy of the gas which could help explain the processes happening within the tube.ConclusionThe equipment has been calibrated and raw data is able to be corrected to provide correct results. Temperature separation has been measured in the range of -5 to 55 with the rate of change of temperature tally to the cold fraction of the generator. The internal energy of the gas has been observed to remain constant transferring only between the cold and the hot stream but there is scope to further investigate this. A basic reasonableness of the vortex tube has been reached and the groundwork has been laid for further investigation. With further have it is hoped the energy separation get out be understood in greater detail and that the theory that the gas undergoes solid body rotation will be proved or disproved.Future workFuture work will include experimental investigation continuing looking into the transfer of energy within the vortex tube including more detailed analysis of rate of energy flow examining whether the gas loses, gains or conserves internal energy. Different generators of varying efficiencies and cold fractions will be investigated and documented and an attempt to build a probe to determine whether the angular velocities within the vortex tube vary or are constant will contact place. Aside from the experimental work computational fluid dynamics will be used to numerically explore the inner workings of the vortex tube by creating a two dimensional computational model of a vortex tube using COMSOL software using the k- model to simulate the temperature separation phenomenon.Figure x shows the temperatures of the hot and cold streams achieved by three different generators as a function of flow. The results show that the generators that expose the lowest temperatures have a lower flow rate, this is ex pected as there is a similar amount of energy separation for each of the generators and you can choose to have a smaller quantity of very cold gas or a larger quantity that is not as cold, or a compromise as desired. This is important as it makes the vortex tube more adaptable for industries using it for spot cooling and the temperature and flow rate can be adjusted as required.References1 Meech air technology brochure. 2013.http//www.meech.com/resources/362/MAT.pdf2 G. J. Ranque, Experiments on Expansion in a Vortex with synchronal Exhaust of Hot and Cold Air, Le Journal De Physique et le Radium (Paris), Vol. 4, 1933.3 R. Hilsch, The Use of the Expansion of Gases in a Centrifugal report as Cooling Process, Review of Scientific Instrument, Vol. 18, 1947.http//scitation.aip.org/docserver/fulltext/aip/journal/rsi/18/2/1.1740893.pdf?expires=1386863841id=idaccname=freeContentchecksum=2218A70412ADD7B3EFBAAC108BCC9ABE4 http//en.wikipedia.org/wiki/Vortex_tube5 Meech Static Eliminators Lt d www.meech.com