MAJOR ASSIGNMENT

SUBMITTED BY : MAHENDRA PATEL (K10632)

SUBMITTED TO : MR. ADITAY MISHARA

STUDY 0F VORTEX TUBE USING A CFD MODEL

INTRODUCTION

The vortex tube was invented by a French physicist named Georges J. Ranque in 1931 when he was studying processes in a dust separated cyclone. It was highly unpopular during its conception because of its apparent inefficiency. The patent and idea was abandoned for several years until 1947, when a German engineer Rudolf Hilsch modifed the design of the tube. Since then, many researchers have tried to find ways to optimize its efficiency. Until today, there is no single theory that explains the radial temperature separation. Hundreds of papers have been published about the temperature separation in the vortex tube, with the greatest contribution being to the understanding of the Ranque–Hilsch vortex tube. 

Types Of Vortex Tube 1-Uni-flow vortex tube 2-Counterflow vortex tube

The Ranque-Hilsch vortex tube is a mechanical device operating as a refrigerating machine without any moving parts, by separating a compressed gas stream into a low total temperature region and a high one. Such a separation of the flow into regions of low and high total temperature is referred to as the temperature (or energy) separation effect

Working

The vortex tube, also known as the Ranque-Hilsch vortex tube, is a mechanical device that separates a compressed gas into hot and cold streams. The air emerging from the "hot" end can reach temperatures of 200 °C, and the air emerging from the "cold end" can reach -50 °C.[1] It has no moving parts.

  Pressurized gas is injected tangentially into a swirl chamber and

accelerated to a high rate of rotation. Due to the conical nozzle at the end of the tube, only the outer shell of the compressed gas is allowed to escape at that end. The remainder of the gas is forced to return in an inner vortex of reduced diameter within the outer vortex.

This approach is based on first-principles physics alone and is not limited to vortex tubes only, but applies to moving gas in general. It shows that temperature separation in a moving gas is due only to enthalpy conservation in a moving frame of reference.

  The main physical phenomenon of the vortex tube is the

temperature separation between the cold vortex core and the warm vortex periphery. The "vortex tube effect" is fully explained with the work equation of Euler,[2] also known as Euler's turbine equation, which can be written in its most general vectorial form as:

CFD MODEL

The ansys icem CFD is used for making the volume mesh for the vortex tube model. the standard k-epsilon turbulence model is used. Skye et al [6] investigate the RNG k-epsilon turbulence model but the result is not correlated with the experimental data, Reynolds stress equation also can’t be converge for this simulation walls are consider as no slip boundary condition. the 3D model is meshed with tria element in icem meshing tool, the velocity along the axial direction is the reason for creating the forced and free vortex zone inside the tube.

The present work is done using ansys fluent 14.5; it is the volume based solver. The solver used 3 dimensional steady, compressible, pressure based setup, density based solver diverged for this vortex tube problem, energy equation is on for capture the energy and temperature distribution. K-epsilon model is used 2equation model is used and for finding the wall friction on fluid standard wall function is used. Finding the heat dissipation between the layers can be captured by viscous heating function. Air is used as material body. Because the flow is considered as compressible flow ideal gas equation is used. No interaction between environment and computation domain.The inlet of the vortex tube is defined as a pressure inlet and cold outlet and hot outlet is defined as a pressure outlet and the atmospheric temperature is given as a input in the model. Wall is assumed as a adiabatic condition. The fluent package solved by mass, momentum and energy equation.

Nozzle (Generator)  The nozzles are of converging type, diverging type are converging-diverging type as per the design.

An efficient nozzle is designed to have higher velocity, greater mass flow, and minimum inlet losses Chamber is a portion of nozzle in the same plane of nozzle and facilitates the tangential entry of high velocity air stream into hot side. Generally, the chambers are not of circular form, but they are gradually converted into spiral form The main function of nozzle is to provide tangential entry of air into chamber which (tangential velocity of air) cause vortex (swirl) formation in vortex tube.

Diaphragm  A Diaphragm called cold orifice, with a suitable sized hole in its center is placed immediately to the

left of the tangential inlet nozzle. The compressed air is then introduced into the tube through this nozzle. After rebouncing of swirl air from the conical valve (hot outlet), cold air passes through the Centre of tube and finally comes out by diaphragm.

Valve  Valve obstructs the flow of air through hot side coming from nozzle and it also controls the quantity

of hot air through vortex tube. Conical valve at right end of the tube confines the exiting air to regions near the outer wall and restricts it to the central portion of the tube from making a direct exit

 

DETAILS OF VORTEX TUBE

Cold air side  he central part of the air flows in reverse direction from valve and makes exit

from the left end of the tube with sizeable temperature drop, thus creating a cold stream. Cold side is a cylindrical portion through which cold air is passed.

Hot air side Conical valve at right end of the tube confines the exiting air to regions near

the outer wall and restricts it to the central portion of the tube from making a direct exit. The outer part of the air near the wall of the tube escapes through the right end of the tube and is found to have temperature higher than that of inlet air.

Efficiency

Vortex tubes have lower efficiency than traditional air conditioning equipment. They are commonly used for inexpensive spot cooling, when compressed air is available

Vortex tube applications Commercial vortex tubes are designed for industrial applications to

produce a temperature drop of up to 71 °C (127 °F). With no moving parts, no electricity, and no Freon, a vortex tube can produce refrigeration up to 6,000 BTU/h (1,800 W) using only filtered compressed air at 100 PSI (6.9 bar). A control valve in the hot air exhaust adjusts temperatures, flows and refrigeration over a wide range.

Vortex tubes are used for cooling of cutting tools (lathes and mills, both manually-operated and CNC machines) during machining. The vortex tube is well-matched to this application: machine shops generally already use compressed air, and a fast jet of cold air provides both cooling and removal of the "chips" produced by the tool. This completely eliminates or drastically reduces the need for liquid coolant, which is messy, expensive, and environmentally hazardous.

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