SEMINAR PRESENTATION ON EXPANSION DEVICES

SUBMITTED By- NAME

CONTENT:- INTRODUCTION TYPE OF EXPANSION DEVICE DESCRIPTION FUNCTION IN REFRIGERATION CYCLE ADVANTAGES AND DISADVANTAGES APPLICATION AND FUNCTION OF EXPANSION DEVICES CONCLUSION

INTRODUCTION :- The basic functions of an expansion device used in refrigeration systems are……..

Reduce pressure from condenser pressure to evaporator pressure.

The control functions which may involve the supply of liquid to the evaporator at the rate at which it is evaporated. This determines the efficiency with which evaporator surface is utilized.

It controls the mass floe rate of refrigerant according to the load on the evaporator.

Decrease the pressure and temperature of flowing refrigerant .

TYPES OF EXPANSION DEVICES :-1. Capillary Tubes 2. Constant pressure or Automatic Expansion Valve

(AEV)3. Thermostatic Expansion Valve (TEV)4. Hand (manual) expansion valves 5. Float type Expansion Valve a) High Side Float Valve b) Low Side Float Valve6. Electronic Expansion Valve

DescriptionNot use one flow control, or metering, of

the refrigerant is accomplished by use of a temperature sensing bulb, filled with a similar gas as in the system, that causes the valve to open against the spring pressure in the valve body as the temperature on the bulb increases. As the suction line temperature decreases, so does the pressure in the bulb and therefore on the spring causing the valve to close. An air conditioning system with a TX valve is often more efficient than other designs that do

Function in Refrigeration CycleExpansion valves are flow-restricting devices that cause

a pressure drop of the working fluid. The valve needle remains open during steady state operation. The size of the opening or the position of the needle is related to the pressure and temperature of the evaporator. There are three main parts of the expansion valve that regulate the position of the needle. A sensor bulb, at the end of the evaporator, monitors the temperature change of the evaporator. This change in temperature creates a change in pressure on the diaphragm……FOR EX..-

if the temperature in the evaporator increases, the pressure in the diaphragm increases causing the needle to lower

Automatic expansion valve :- This works in response to the pressure changes in the

evaporator due to increase in load( pressure increase) or due to decrease in load (pressure decreases).

This valve maintains a constant pressure throughout the varying load on the evaporator controlling the quantity of refrigerant flowing into Evaporator.

The automatic expansion valve opens and closes to either increase or decrease the amount of refrigerant feeding into the evaporator in response to the pressure of the refrigerant in the evaporator.

Application of automatic expansion valve:-

The automatic expansion valves are used wherever constant temperature is required, for example, milk chilling units and water coolers .

• These are also used in home freezers and small commercial refrigeration systems where hermetic compressors are used.

CAPILLARY TUBE:-

A capillary tube is a long, narrow tube diameter. of constant. The refrigerant has to overcome the frictional resistance offered by tube walls. This leads to some pressure drop.

Advantages and disadvantages :- It is inexpensive. It does not have any moving parts hence it does not

require maintenance . It cannot adjust itself to changing flow conditions in

response to daily and seasonal variation in ambient temperature and load. It is susceptible to clogging because of narrow bore of the tube.

It cant operated efficiently at other condition .

Thermostatic Expansion Valve (TEV) :-• Thermostatic expansion valve controls the flow of refrigerant

through the evaporator I such a way that the quality of the vapour leaving the evaporator will always in superheated condition.

• Its operation is used for maintaining a constant degree of superheat at the evaporator outlet.

Advantages and disadvantages :- It provides excellent control of refrigeration capacity as

the supply of refrigerant to the evaporator matches the demand

It ensures that the evaporator operates efficiently by preventing starving under high load conditions .

It protects the compressor from slugging by ensuring a minimum degree of superheat under all conditions of load, if properly selected

The feeler bulb must always be in good thermal contact with the refrigerant tube.

TEV cannot be used since very small extent of superheating

Electronic Type Expansion Valve :- An electronic expansion valve consists of an orifice and a

needle in front it. The needle moves up and down in response to magnitude

of current in the heating element. If the refrigerant will superheat the resistance offered by heat element will be less so it increases the mass flow rate of refrigerant. If less then it will decrease the mass flow rate of refrigerant.

An expansion valve is used to control the superheat of the refrigerant exiting the evaporator and is designed to maintain a set superheat in normal operating conditions.

It reduces the high pressure liquid refrigerant to low pressure liquid refrigerant .

It control the flow of refrigerant according to the load . Expansion devices available to suit many different

domestic, commercial and light industrial refrigeration and air conditioning applications.

Advantages and function of expansion devices :-

Hand operated expansion valve :-

A manual valve expansion is that it makes no automatic adjustments in accordance with changes in system of cooling load.

It must be opened or closed manually each time you change the load on the system. Equipment operator must be on hand at each change of the load on the system. When automatic control is required,.

Float type expansion valves are normally used with flooded evaporators in large capacity refrigeration systems. A float type valve opens or closes depending upon the liquid level.

Float type expansion valves :-

Low-side float valves:- A low-side float valve maintains a constant liquid level in

a flooded evaporator or a float chamber attached to the evaporator. When the load on the system increases or decreases.

High-side float valves :- In the this type float chamber is placed on the high

pressure side between the condenser and the evaporator.

The refrigerant condensed in the condenser moves to the float valve. As the level of the refrigerant rises the float ball moves up and opens the float valve that allows for the passage of the refrigerant through needle valve. 

The level of the refrigerant coming from the condenser reduces when there is less load on the plant. When the level of the refrigerant drops down thus reducing the flow of the refrigerant through it. 

Thank you for your attention…!!!