The Effects of Orifice Diameter and Valve Angle on the Performance of Ranque Hilsch Vortex Tube

The Effects of Orifice Diameter and Valve Angle on the Performance of Ranque Hilsch Vortex Tube 1 Onkar M. Kshirsagar, 2 V. V. Ankolekar, 3 V. N. Kapatkar 1 Master Student SCOE Pune, 2 Professor BSCOER Narhe, 3 Professor SCOE Pune Email: 1 onk_1112@yahoo.co.in Abstract An experimental is conducted to investigate effects of the cold orifice diameter, conical valve angle and inlet pressure on the performance of counter-flow vortex tube. A vortex tube of aluminum material having inner diameter 10mm were manufactured for experimentation. Four number of cold orifice and four number of hot end valve were manufactured for the experimentation, having diameter 2, 3, 4, 5mm and angle of 30, 45, 60, 75 respectively. In addition to this the effect of inlet pressure on the isentropic efficiency of vortex tube and cold air temperature was studied. From the data which obtained by experiment were used to propose the optimum values for cold orifice diameter and hot end valve angle to the VT for this experiment. Index Terms Experimental, Orifice, Performance, Vortex tube. I. INTRODUCTION Vortex tube is a device, which can cause energy separation of a compressed fluid. Its main components are of nozzle, vortex chamber, cold orifice, hot end valve, hot. No any moving part is required in the vortex tube. It requires compressed gas which is expanded in the nozzle and then high velocity gas inserted in to the vortex tube tangentially. This is caused to form vortex of gas into the tube. This inlet gas splits in to hot and cold temperature streams of low pressure, one of which, the peripheral gas, has a higher temperature than the initial gas, while the other, the central flow, has a lower temperature. Cold stream leaves at the cold orifice end which is near the nozzle and hot stream leaves the vortex chamber from valve end. The vortex tube was discovered by Ranque, a metallurgist and physicist who was granted a French patent for the device in 1932 and a United States patent in 1934. The initial reaction of the scientific and engineering communities to his invention was disbelief and apathy. Since the vortex tube was thermodynamically highly inefficient, it was abandoned for several years. Interest in the device was revived by Hilsch, a German engineer, who reported an account of his own comprehensive experimental and theoretical studies aimed at improving the efficiency of the vortex tube. He systematically examined the effect of the inlet pressure and the geometrical parameters of the vortex tube on its performance and presented a possible explanation of the energy separation process. After World War II, Hilschs tubes and instruments were uncovered, which were later studied. Indicative of early interesting the vortex tube is the comprehensive survey by Westley which included over 100 references. Other literature It consists of a principal tube, which a high pressure gas stream enters tangentially, and splits in two low pressure hot and cold temperature streams. Cold gas stream leaves the tube through a central orifice near the entrance nozzle, while hot gas stream flows toward regulating valve and leaves the tube. Vortex tube is also used for separating the gases. The ability to separate air into two streams of different temperatures is highly applicable to many areas of chemical engineering, particularly for refrigeration purposes. Moreover, to separate air efficiently without using any moving parts or power sources would be a through for the air conditioning industry as well as any other area that would require heating or cooling of compressed air. Another interesting application of the tube would be in areas where maintenance of equipment is difficult, costly or unsafe. Vortex tube finds several industrial applications such as cooling of machine parts, electric and electronic components; food items, ultrasonic weld, melt and quick solder setting etc. where efficient and localized cooling device is desirable. For its operation, dust free dehumidified compressed air in the range of 5 to 6 bars is injected into a cylindrical chamber (vortex chamber) tangentially through nozzles. Air swirls in the vortex chamber and accelerates towards cone end. A part of air at higher temperature escapes through the cone end and remaining air at lower temperature exits through cold orifice located at opposite end. This is an energy separation phenomenon which known as Ranque effect [4]. 36

Fig. 1 Schematic diagram of the counter flow RHVT [3]. II. WORKING PRINCIPLE OF VORTEX TUBE The theory of the Hilsch vortex tube, also known as the Ranque-Hilsch votex tube dates back to the 1930s where French physicist George Ranque invented an early prototype. Rudolf Hilsch, a German physicist improved Ranque's design to create a better version of the tube. The tube was named after the inventors, but most often is attributed to Hilsch, who made the more effective version [2]. and parallel flow vortex tube. By the literature review it is clear that counter flow vortex tube is more efficient than parallel flow vortex tube. So in this study, a counter flow vortex tube has been used. The setup used for the experimentation is as shown in the Fig. 3. Air is used as the working fluid which is supplied at desired pressure by using two-stage reciprocating air compressor. FRL unit is used to regulate the pressure of air. Then it is supplied to the vortex tube through the nozzle. The inlet pressure is measure by pressure gauge. Inlet and outlet flow rates are measured by air rotameter of the range 0-200 LPM. Thermocouple with three sensors was used to measure the inlet, cold exit and hot exit air temperature. The vortex tube is made up of aluminium metal for make it lighter and for reduction in cost. Due to less weight it is very suitable for jackets which are used for cooling purpose by mine workers. Here, the internal diameter of the vortex tube was 10 mm. Length of vortex tube was 18D. Diameter of the nozzle was 3mm. The cold orifice diameter (d) were varied as 2 mm, 3mm, 4 mm, 5 mm. Hot end valve angle varied as 30, 45, 60, 75. The inlet pressure variations are taken as 2 bar, 3 bar, 4 bar and 5 bar. The actual set up for this experimentation is shown in the Fig, 5 Fig.2 - Working of Vortex Tube [10] Working principle of the counter flow Ranque Hilsch vortex tube can be defined as follows compressible fluid which is tangentially introduced into the vortex tube from nozzles starts to make a circular movement in the vortex tube at high speeds because of the cylindrical structure of the tube depending on its inlet pressure and speed. Pressure difference occurs between tube wall and tube center because of the friction of the fluid circling at high speeds. Speed of the fluid near the tube wall is lower than the speed at the tube center because of the effects of wall friction. As a result, fluid in the center region transfers energy to the fluid at the tube wall depending on the geometric structure of the vortex tube. The cooled fluid leaves the vortex tube from the cold output side by moving towards an opposite direction compared to the main flow direction after a stagnation point. Heated fluid leaves the tube in the main flow direction from the other end as shown in Fig.1. Fig. 3 Schematic diagram of the experimental setup. III. EXPERIMENTAL STUDY Vortex tubes are mainly classified into two groups according to their direction of flow outlet as counter flow Fig. 4 Experimental Setup. 37

Fig. 5 shows the vortex tube, various orifices and hot end valves which are used for experimentation. All the parts of the tube are interchangeable so it is easy to change the parts such as cold orifice, hot end valve while conducting the experiment. The position of valve is adjusted by the screw. (4) Similarly normalised hot temperature rise is defined as (5) D. Cold orifice diameter Cold orifice diameter ratio ( ) is defined as the ratio of cold orifice diameter ( ) to vortex tube diameter ( ): Fig. 5 Vortex Tube with Different Cold Orifices and Hot end Valves. IV. DATA REDUCTION A. Cold flow mass ratio The cold flow mass ratio or cold mass fraction is the most important parameter indicating the vortex tube performance and the temperature/energy separation inside the RHVT. The performance of the RHVTs is evaluated based on the cold fraction. The cold mass fraction is the percentage of input compressed air that is released through the cold end of the tube. It is the mass flow rate of cold gas divided by mass flow rate of the inlet gas: where (1) represents the mass flow rate of the cold stream released, in represents the inlet or total mass flow rate of the pressurized inlet working fluid. Therefore, changes in the range. B. Cold and hot temperature difference Cold temperature difference or temperature reduction is defined as the difference in temperature between inlet flow temperature and cold flow temperature: (2) where is the inlet flow temperature and is the cold flow temperature. Similarly hot temperature difference is defined as C. Normalised temperature drop/rise Normalised cold temperature drop is defined as the ratio of cold temperature difference to inlet temperature: (3) 8.1.5 Isentropic efficiency Assuming the process inside RHVT as isentropic expansion, isentropic efficiency is. (6) (7) where is enthalpy at the inlet to vortex tube, cold exhaust enthalpy, and processes. For an ideal gas enthalpy after isentropic For an isentropic expansion, the exhaust temperature is Introducing Eq. (2) into Eq. (1) yields (8) (9) (10) where,, and are the isentropic efficiency, inlet air pressure, atmosphere pressure and specific heat ratio, respectively [8]. V. RESULTS AND DISCUSSION A. Effect of cold orifice diameter For observe the effect of cold orifice diameter on the cold air temperature difference ( T c ) the valve of angle 60 was selected and it was tested for different supply air pressure. Fig. 6 shows the effect of cold orifice diameter on the cold air temperature difference. From Fig. 6 it is observed that the maximum T c occurs at d/d = 0.2 and as the cold orifice diameter increases the cold temperature difference decreases. 38

Fig. 6 Effect of orifice diameter on Cold Air Temperature Difference ( T c ) at Valve angle 60. Fig. 7 indicates that isentropic efficiency of the vortex tube is higher for cold orifice diameter 2mm as compared to remaining diameters. Also it is observed from Fig. 7 that there very less effect of the cold orifice diameter on isentropic efficiency. C. Effect of supply air pressure The effect of inlet air pressure is investigated to find out an appropriate operating pressure for a vortex tube. It is observed form Fig. 6 that as supply air pressure increases the temperature difference in supply air and cold exit air increases. Fig. 9 shows the effect of inlet pressure on the cold exit temperature. It goes on decreasing as inlet air pressure increases. Fig. 9 Effect of Supply Air Pressure on Cold Air Temperature (T c ) for orifice diameter d= 2mm and 3mm at valve angle 60. VI. CONCLUSION Fig. 7 Effect of Cold orifice Diameter and Supply pressure on Isentropic Efficiency at Valve angle 60. B. Effect of hot end valve angle Four different values for the valve angle as mentioned above have been used for experimentation. The effect of the valve angle is tested for various values of the supply pressure. Fig. 8 shows that valve angle having less effect on the cold air temperature difference. However the valve of 30 and 60 angle gives best results. From the results of this experiment shows that the maximum temperature difference is occurred at d/d = 0.2 or at cold orifice diameter 2mm. While selecting the operating pressure it is necessary to consider requirement of the cold exit temperature. Also it is better to select the valve angle of 30 or 60. REFERENCES [1] K. Stephan, S. Lin, An investigation of energy separation in a vortex tube, International Journal of Heat and Mass Transfer 26 (3) (1983) 341-348. [2] Y.T. Wu, Y. Ding, Y.B. Ji, C.F. Ma, M.C. Ge Modification and experimental research on vortex tube International Journal of Refrigeration 30 (2007) 1042-1049. [3] K. Dincer S. Baskaya B. Z. Uysal, Experimental investigation of the effects of length to diameter ratio and nozzle number on the performance of counter flow Ranque Hilsch vortex tubes, Springer Heat Mass Transfer (2008) 44:367 373 Fig. 8 Effect of Vale angle on Cold Air Temperature Differance ( T c ) for orifice d = 3. [4] Sachin U. Nimbalkar, Micheal R. Muller, An experimental investigation of the optimum geometry for the cold end orifice of a vortex tube, 39

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