STEAM JET REFRIGERATION

The steam at high pressure from the boiler known as motive steam expands through nozzle –ejector assembly as shown in the diagram, This high velocity sucks flash vapour from flash chamber and imparts momentum to vapour and carries along with motive steam through the ejector to the condenser. Cooling water is passed through the condenser and the latent heat for condensation is carried away by this cooling water. The resulting water after condensation is fed back to the boiler by means of a pump after excess water is purged to atmosphere as shown in the diagram.

The vapourisation of water from flash chamber causes the cooling of the remaining water in the chamber . The resulting chilled water is allowed to pass through the a heat exchanger and thus heating it up due to the thermal load .The hot water is sprayed back into the flash chamber as shown in the diagram. Make up water is supplied to the flash chamber through a level controllable float valve.The cycle is repeated.

Advantages:

1. Water is a good refrigerant with desirable properties. The large specific volume of water makes it suitable for jet refrigeration.

2. Direct cooling is possible inside the flash chamber by immersing the product to be cooled in the chilled liquid. The chilled fluid can be sprayed on the product also. This method is used in USA for chilling of vegetables before shipment. This method can be used in ships where steam is used for propulsion.

3. The system consists of one pump only and hence maintenance cost for the setup is less.

4. refrigeration system for cooling,

5. Above 75 ton refrigerating capacity ,the running cost is 50%less when compared to that of VCRS.

Limitations;

1. Useful only in places where chilling temperature is nearly 2 C as in the case of air conditioning and water coolers.

2. Large size Condenser is required since ejected steam and motive steam condences in it.

3. It I suitable due to the high volume of water vapour is required

VORTEX TUBE REFRIGERATION:

Figure 6.1 shows the working principle of vortex tube refrigeration.The atmospheric air is compressed and cooled in a heat exchanger and this cooled compressed air is allowed to enter a pipe tangentially as shown in the diagram. One end of the pipe is provided with a valve and other end is open.It is found that the central cool air leaves through section A and hot air leaves through section B. Thus, Vortex tube is a device which produces cooling at one end and heating at the other end as shown in Fig.6.1a. In Fig 6.1 b,central core of cooled air is surrounded with an outer part of hot air leaving from one end of the pipe.It was first developed by Ranqe and Hilsch ,hence vortex tube is known as Ranque or Hilsch Tube also.When the compressed air expands through the nozzle, a swirl motion of air is created. It is found that in the vortex motion the axial component of the velocity is much less than the tangential component for the entire length of tube. The air moves as a free vortex from the nozzle plane towards the valve end. When it reaches near the vave,the kinetic energy is converted to pressure energy forming a stagnation point. But this stagnation pressure is higher than the pressure in the nozzle plane.This results in a reversal in flow and this reversed flow comes in contact with the forward moving free vortex and results in a reversed vortex flow rotate with it. During the process of forced vortex flow the energy is supplied from the outer

moving layer.This supply of energy is insignificant compared to pumping of energy from the core to the outer layerdue to turbulent mixing in the centrifugal flow fields.Due to this there is a flow of cold core surrounded by a hot concentric flow field.

IIT Bombay have developed a Cascade system of vortex tube with a single stage R12 refrigeration system to develop temp as low as -100 C.

Advantages of vortextube:

Since air is the working medium,minor leakages are insignificant. Design is very simple No moving parts and hence life span is high and maintenance is

almost nil. Light in weight,quite compact,easy to cool even in complicated

space by admitting chilled air to that. Initial investment is less. No expert attendant is required for its operation.

Disadvantage;

Poor COP and hence not suitable for large capacity systems.

Applications:

Cooling of cutting tools where liquid coolant cannot be used. Some items can be cooled upto -50C by direct chilling. Used to condence natural gas.

Used for air suits .Such units are used by operators handling toxic gases during spray painting,maintenance of pressure vessels and coal mine workers.

Can be used for aircraft refrigeration. Used to cool turbine blades. Suited for all round airconditioning.

PULSE JET REFRIGERATION:

The basic idea of pulse tube was originated from Gifford in1961. In pulse tube sudden expansion and release of gas will give refrigerating effect. A schematic diagram to explain the working of pulse tube is shown in Fig.6.6. It consists of a high pressure gas source at a temperature close to ambient temperature. Here the receiver supplies the compressed air at ambient temperature to the pulse tube through a

suitable valve arrangement. During the pressure buildup,the high pressure gas enters the pulse tube and acts as a fictitious piston. Thus the gas present inside the pulse tube gets compressed resulting in increase in temperature varying from minimum value at left end to the maximum value at the right end as shown in Fig.6.6 (b). After that the heat transfer to the cooling medium reduces the temperature to a value Th which is the temperature of the cooling meium.