NUMERICAL INVESTIGATION OF JET PUMP WITH TWISTED TAPES

Arpita Srivastava Shaligram Tiwari and Mani Annamalai

Department of Mechanical EngineeringIndian Institute of Technology

Chennai, Tamil Nadu, India

ContentsIntroductionLiterature surveyBasic geometry of Jet PumpTape descriptionResults and discussionConclusionsReferences

Introduction Jet pump is used to transfer momentum from a

high velocity primary stream to a secondary stream that gets entrained. It is packaged with the advantage of geometrical simplicity without any moving parts.

Aim of the present study is to carry out three-dimensional numerical investigations of two phase flow jet pump in presence of twisted tapes under optimized conditions of the parameters such as upstream and downstream pressures, primary jet mass flow rate, entrained secondary stream mass flow rate, geometry of the ejector, etc.

Water and air have been used as fluids in the primary and secondary streams respectively. Nozzle profiles selected is conical. The mean diameter of nozzles are kept to be 4mm and 6mm.

Results in present study suggest that the momentum exchange achieved by the swirl causes increase in the efficiency of the jet pump.

Literature Survey Sharma in his work experimentally verified that, for

lower area ratio, nozzles having elliptical profile are capable of producing higher efficiency then nozzles with circular or conical profile. He experimented with different area ratio of nozzle. The geometrical design for the present study is taken from Sharma’s experiment.

Hansen and Kinnavy performed experiments on ejectors keeping different area ratio and then studied different parametric effect. It was concluded that area ratio has major role to play in ejector efficiency than any other parameter.

Abdus Samad investigated the influence of the introduction of swirl low performance of an ejector and concluded that it enhance the jet breakup resulting in higher suction rates at different optimized swirl angles.

Basic geometry of Jet Pump

Tape description

Pictorial representation of double twisted tape incorporated in primary nozzle

Numerical treatment the problem

For the present study CFD software ANSYS Fluent is used

This code solves the discretized equations in a segregated manner, with SIMPLE algorithm.

The first-order upwind scheme is taken for momentum, volume fraction, turbulent Kinetic energy and turbulent dissipation rate discretisation.

The solutions were assumed to have converged for the residual level of 10-4 for continuity, x-velocity, and y velocity and 10-6

for k -epsilon.

For performing the grid study, geometries with mesh size of 167231cells, 257111 cells, 430017 cells 707808 cells, 864906 cells, 1072648 cells and 1755598 cells were numerically analyzed.

Minimum orthogonal quality was kept at 0.5.The grid size was optimized by head difference. It was observed that for the geometries with higher mesh size, variation in head difference was almost negligible.

Since after 7.8lakhs grid size there was no such significant difference in pressure contours this was fixed as grid size for all the further simulations which include swirl generators also.

Boundary conditions used for each simulation are known static absolute pressure.

Turbulent intensity was selected 5 % and respective hydraulic diameters were used at each of the flow boundaries.

Results and Discussion On performing numerical studies, the ejector

incorporating double twisted tape is found to be highly efficient comparatively to other ejector combination.

It is also found that single twisted tape has the lesser efficiency than double twisted tape but better than without tape.

The Table 2.shows the comparative parametric studies carried out along with performance obtained.

The velocity, turbulent kinetic energy and vorticity magnitude graphs have been plotted against the length of the ejector

Efficiency of this arrangement is increased by 10% when compared with nozzle, without any tape.

Comparison Of Various Operating Parameters And Performance

Velocity profiles for jet pump with different twisted tape

Turbulent kinetic energy profiles for jet pump with different twisted tape

Vorticity magnitude profiles for jet pump with different twisted tape

Velocity contours at the mid plane for different Jet pumps

ConclusionsIt has been observed that there is

a change in flow behavior after the nozzle when twisted tapes are inserted in the upstream primary fluid and more pressure drops after the nozzle is observed due to high vorticity magnitude. This enhances the volume flow rate of the secondary air which ultimately results in better entrainment.

REFERENCES Pfleiderer, C., “Experiments on jet pump for its performance”, C.

Zeit, VDI, 58, 965 &1011. Martinelli, R.C., Boelter, L. M. K., Morrin, E. H., “Theoretical and

experimental analysis of ejectors Trans. ASME, 66, pp. 139-151. Senthil Kumar, R., Mani, A., Kumaraswamy, S. 2004, “Selection of

Pumps for Vacuum Desalination System Utilizing Ocean Thermal Energy, 31st National Conference on Fluid Mechanics and Fluid Power, Vol. 1, pp. 409–416.

Senthil Kumar, R., Mani,A., Kumaraswamy, S., 2007, “Experimental Investigation on Two-Phase Jet Pump used in Desalination System ” , Desalination, 204, pp. 437-447.

Hansen, A. G., and Kinnavy, R. 1965, “The design of water jet pumps part I – experimental determination of optimum design parameters”. ASME Paper 65-WA/FE-31.

Riffat, S. B., Gan, G., and Smith, S., 1996, Computational fluid dynamics applied to ejector heat pumps, Journal of Applied Thermal Engineering, 16, 291-297.

Riffat, S. B., and Omer, S. A. 2001, CFD modeling and experimental investigations of an ejector refrigeration system, Int. Journal on Energy Research, 25, 115-128.

Contd. Bartosiewicz, Y., Aidoun, Z., Mercadier, Y., 2006, “Numerical

assessment of ejector operation for refrigeration applications based on CFD”, Applied Thermal Engineering, n 26, pp.604–612.

Sharma, V. Kumar., Kumaraswamy, S., Mani, A. 2012, “Effect of Various Nozzle Profiles on Performance of a Two Phase Flow Jet Pump”. Int. Journal of Mechanical and Aerospace Eng,6, p.136-142.

Samad, A., Omar, R., Hewakandamby, B., Lowndes I., and Short, G. 2012, “Swirl Induced Flow Through a Venturi-Ejector,” ASME 2012 Fluids Engineering Division Summer Meeting (FEDSM2012), Puerto Rico, USA.

Neve, R. S. 1993, “Computational fluid dynamics analysis of diffuser performance in gas-powered jet pumps”, Int. Journal on Heat and Fluid flow, 14, 401-407.

Ouzzane, M., and Aidoun, Z. 2003, Model development and numerical procedure for detailed ejector analysis and design, Journal of Applied Engineering, 23, 2337-2351.

Thank you