In this article, I will share with you the working principle of a two-stage refrigeration unit that uses a flash chamber.
The two-stage refrigeration unit that uses a flash chamber is similar to a vapour compression refrigeration system.
They are similar since they all compress vapour, they have an evaporator and a condenser.
The main difference is that a two-stage refrigeration system uses a flash chamber, it has two throttling devices (expansion valves) and two compression chambers (two centrifugal compressors).
The other refrigeration components used in two stage refrigeration unit are just similar to the components used in the vapour compression system.
If you want to know the components used in the vapour compression refrigeration systems refer to the article below.
You might like this: Vapour Compression Refrigeration System: Components And Working Principle
Without wasting time, let me share with you how the two-stage refrigeration unit works.
Working principle of two-stage refrigeration unit using a flash chamber;
The working principle of two-stage refrigeration using a flash chamber is similar to VCR.
The only part that you will be new to is the flash chamber and the two stages of impeller compression.
Before I share with you the working principle of this refrigeration system there is something you need to know about the flash chamber.
Understanding how the flash chamber works will make it easier for you to connect the whole refrigeration cycle.
The flash chamber used in two stage refrigeration system is connected between the two throttling devices.
The main function of the flash cooler within the flashing chamber is to sub-cool the liquid refrigerant to a saturated temperature corresponding to the interstage pressure by vaporizing part of the liquid refrigerant.
You will understand deeply enough how the process works by reading the working principle.
Step by step of the working principle of a two-stage refrigeration unit;
The evaporator contains a mixture of liquid refrigerant and the vapour refrigerant that was initial flashed from the flash cooler.
The flashing action of the chamber forms a dry saturated vapour which is bled off to bypass the evaporator.
This dry saturated vapour is usually mixed with vapour refrigerant from the evaporator to increase the energy content of the gases being taken to the first stage impeller.
When the evaporator absorbs temperature from the medium to be cooled the liquid refrigerant changes its state from liquid to gas and it mixes with the dry saturated vapour from the flash chamber.
The vapour refrigerant leaves the evaporator and heads to the first stage impeller (centrifugal compressor).
The gases are compressed to the interstage pressure (compression ratio at each stage which is nearly the same at high (COP) coefficient of performance of refrigeration).
After the vapour, the refrigerant has been compressed its pressure increases and it leaves the first stage impeller via a tube that is connected to the second stage impeller.
The tube that connects the first stage impeller and second stage impeller is connected to the flash cooler which provides the evaporated refrigerant vapour from the flash cooler.
The compressed refrigerant vapour mixes with the evaporated vapour from the flash cooler as it goes to the second stage impeller for another compression.
The mixture of the evaporated vapour and the compressed refrigerant vapour enters the second stage impeller where it is compressed further thus increasing the pressure and the temperature of the refrigerant vapour.
The hot gases now enter the condenser where they are de-superheated and condensed to a liquid.
Sub-cooling also occurs to a small extent.
The sub-cooled refrigerant flows to the throttling device at the high-pressure side, and a small portion of the liquid refrigerant is released to the flash cooler where some are evaporated to the tube of the first stage impeller that connects to the second stage impeller.
The latent heat of evaporation lost through evaporation when the liquid refrigerant is in the flash cooler results in cooling the liquid refrigerant to the saturation temperature corresponding to the interstage pressure between the two compression chambers.
The remaining liquid refrigerant flows to the second throttling device.
The flashing action results in some of the dry saturated vapour bypassing the evaporator and left in between the evaporator and first stage impeller tube where later on it mixes with the vapour refrigerant from the evaporator, as I started earlier.
The throttling device reduces the pressure of the liquid refrigerant as it also controls its flow to the evaporator.
This refrigeration cycle is complete when the vapour refrigerant mixes with the dry saturated vapour that is in between the evaporator and first stage impeller and enters the first stage impeller.
And the process is repeated.
The flashing action of the flash cooler increases the efficiency of this refrigeration cycle since it aid the first stage impeller to do less work but with an increase of refrigerant energy content that is supplied by the evaporated liquid refrigerant in the flash cooler.
The two-stage refrigeration system is used in large plants that require higher cooling efficiency.
A hydronic air conditioning system uses this type of refrigeration unit since it requires a very higher efficiency.
The downside of this refrigeration system is that its initial cost is higher and it requires a large space to be installed.
If you have any questions about the working principle of this refrigeration system leave your comment.
Thanks for stopping by, see you in my next article.
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