Working of the refrigeration system (VCRS) in ship | Working of the sensing bulb and thermostatic expansion valve|
Processes involved in refrigeration:
There are four different process involved in the main components of a refrigeration system.
- In compressor – isentropic compression
- In evaporator – Isobaric heat rejection/ condensation
- In thermostatic expansion valve – Isenthalpic expansion
- In evaporator –Â Isobaric heat absorption
Working of the refrigeration system (VCRS):
The air inside the room is sucked into the evaporator and it exchanges the heat with the refrigerant which allows the air in the room to cool down and this air is circulated continuously. This heat converts the refrigerant into a gas or vapour state. This low temperature low pressure super-heated refrigerant vapour is sucked by the compressor and compressed to a high temperature and high pressure super-heated vapour.
After compression, this gas goes into the condenser for releasing the heat of the gas and turned into liquid. The condenser is a type of a heat-exchanger which has seawater lines in it. At first when the refrigerant goes into the condenser, the temp drops a little bit as the refrigerant was super-heated, then the refrigerant changes into high pressure slightly low temp liquid refrigerant. After that this high-pressure refrigerant fluid goes through the drier and here all moisture will be absorbed.
When this high-pressure fluid goes through the thermostatic expansion valve orifice its pressure suddenly drops due to the its volume increases, refrigerant drops to a very low temp low pressure and it becomes into a mixture of liquid plus vapour refrigerant and then it goes into the evaporator.
At the initial point of the evaporator pipe refrigerant temperature is low but the temperature continuously increases from absorbing the heat and converting refrigerant liquid to gas by the latent heat of vaporisation process. After the evaporator sensing bulb senses the temperature of vapour to control the thermostatic expansion valve regulator. When the gas temperature is very high it means more refrigerant is required in the evaporator for cooling and the whole cycle continues.
Two pressure zones are present in the total cycle. From the delivery side of the compressor to the thermostatic expansion valve, the orifice is a high-pressure line after the orifice to the suction of the compressor is the low-pressure line.
Working of Sensing bulb:
In the refrigeration system the sensing bulb is fitted at the discharge line of the evaporator which senses the temp of the refrigerant coming from the evaporator. The sensing bulb has the same refrigerant in a confined space that flows in the main system, when the degree of superheat of the refrigerant is more then the sensing bulb senses it. The refrigerant in the sensing bulb vapourises which increases the pressure in it and as we know that the fluid flows from high pressure to low pressure region. The refrigerant in the sensing bulb flows through the capillary tube to the TEV.
Working of Thermostatic Expansion Valve:
The components of a thermostatic expansion valve are:
- The diaphragm
- The pin
- The orifice
- The poppet valve
- The spring
When degree of superheat of refrigerant is more:
If the superheat of the refrigerant is more than the pressure in the sensing bulb will increase and the refrigerant will flow towards the TEV through the capillary tube and will hit the diaphragm. The diaphragm will push the pin situated below, the pin will push the poppet valve and the spring, when the poppet valve goes down it will open the orifice and the flow of refrigerant increases.
When degree of superheat of refrigerant is less:
If the superheat of the refrigerant is less then the pressure will decreases in the sensing bulb and the spring in the TEV will push the poppet valve up due to which the the orifice will close which will restrict the flow of refrigerant into the evaporator.
Note:
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