REFRIGERANT FLOW CONTROLS

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REFRIGERANT FLOW CONTROLS

Flow controls are fitted between the

condenser and the evaporator. These

produce the required pressure drop.

These also control the rate of flow of

refrigerant as per cooling required. There

are five types of refrigerant flow controls.

These are used in different applications.

FIVE TYPES

(i)  Capillary Tube

(ii)  Automatic Expansion Valve (AEV)

(iii)  Thermostatic Expansion Valve (TEV)

(iv)  Low Side Float Valve (LSFV)

(v)   High Side Float Valve (HSFV)

1)    Capillary tube

 The capillary tube is small diameter (0.5 to 2.25 mm) tube. It has no moving parts. Thus this is extremely simple and least expensive. Select Its length and diameter for the required pressure drop from condenser to evaporator.

Applications: Used for small refrigerating and air-conditioning systems.

(a)   Household refrigerators

(b)   Water coolers

(c)   Deep freezers

(d)   Window air-conditioners

(e)   Split air-conditioners

(f)    Small packaged air-conditioners

(g)  Display cabinets

2)  Automatic Expansion Valve (A.E.V.)

 Used in plants where cooling load is almost constant like in ice plants. These expansion valves are not suitable where cooling loads vary. It is because these increase the flow of refrigerant on less heat load on the evaporator. It decreases the flow of refrigerant through the evaporator when the heat load on the evaporator is high. These are very less in use.

3)      Thermostatic Expansion Valve (T.E.V.)

 It maintains a constant degree of super heat at the outlet of the evaporator. This is true for all types of heat loads on the evaporator It decreases the flow of refrigerant on decrease of heat load on the evaporator. This is the most commonly used expansion valve.

Its spring is set for a certain degree of super heat. (Ref Fig.)

(a) When cooling load on the evaporator increases, this in turn tends to increase the degree of super heat.

Refrigerant in the feeler bulb senses the higher degree of super heat. It opens the valve. This allows more refrigerant to enter the evaporator .Thus it keeps the preset degree of super heat.

(b) If the cooling load on the evaporator decreases, this in turn tends to decrease the degree of super heat.

Refrigerant in the feeler bulb senses the lower degree of super heat. It moves the valve in the closing direction. This allows less refrigerant  to enter the evaporator .Thus it keeps the preset degree of super heat.

Applications: Thermostatic expansion valves are used extensively in medium and large sized refrigerating and air-conditioning systems. They are used for  water chilling plants, brine chilling plants, packaged air-conditioners and central air-conditioning plants.

4)    Low Side Float Valve

The float valve is located in the evaporator itself. It is cheap and simple.

APPLICATION: Used only in big industrial units.

5)      High Side Float Valve

The float valve is located in the condenser itself. It is also cheap and simple.

APPLICATION

 Used only in big industrial units.