Refrigeration is a prerequisite process these days. As shipping of goods from one place to another place is increasing at a tremendous rate, protecting the food products is becoming vital. But it is a not just food product that uses refrigeration process. In gas tankers, gas is kept under liquid state with the help of refrigeration process or Marine Refrigeration System. It becomes very vital for any seafarer to know about this process. So let’s see what this is all about.
What is Marine Refrigeration System?
This is the first and foremost question. Well we define Refrigeration as ‘Process in which the temperature of material or things is kept well below the outside or ambient temperature’. The uses of this process can be in any form like Air conditioning, Gas tankers etc. And now question arises why we do it? Purposes of refrigeration are many, but I have selected few main out of them.
1) Food stuff that are perishable in nature, are protected by means of it. Actually what happen is that due to lower temperatures, growth of bacteria reduces to several extents. So food can be kept for longer duration.
2) LNG carriers, gas are liquefied so that the pressure in the storage vessels do not increases to high levels.
3) There are several chemical that require Sub Zero temperature for their storage.
4) Removal of moisture from air, especially when this air is used as control air in control systems.
5) For air conditioning purposes.
Desirable Properties of Refrigerants used in Marine Refrigeration System
Refrigerants are liquids that are being used in refrigeration for creating refrigeration effect. For example water is like a refrigerant when it used in coolers. Following are some of the properties that are vital for any Refrigerants which are used in the refrigeration system. It should have low boiling point. Reason behind this is, if you are using high boiling point refrigerants, then you need to operate the machinery on high vacuum and it can prove harmful for the Marine Refrigeration System.
- Low condensing pressure and it eliminates the need making a heavy industry.
- Critical temperature of Refrigerants should be high.
- Low specific heat of the fluid as it will help in throttling process.
- It should be less corrosive and be chemically stable.
- It should be non inflammable and non explosive.
- Low specific volume of refrigerant.
- It should be ozone friendly.
Types of Refrigerant
Refrigerants are classified under two categories that are namely: Primary and secondary refrigerant. Primary refrigerant are defined as ‘Main fluid’ that flows in the machinery like compressor, expansion valve, condenser and evaporator. Commonly used primary refrigerant are Ammonia, CO2 etc. Secondary refrigerant are used in large industries. Primary refrigerant is used to provide cooling effect to secondary refrigerant. Most famous and common example can be seen home coolers in which air and water are two refrigerants.
Marine Refrigeration system
A Below diagrams shows the complete setup of basic Marine Refrigeration System that is being used in refrigeration process.
Process:
A cold refrigerant comes to the evaporator and here it takes heat from the material that has to be cooled down. Since it takes heat from the surrounding, refrigerant gets evaporated. After passing through the evaporator, the refrigerant reaches the compressor. Here it compressed back to the liquid form and passed on the condenser. Here at condenser the liquid is cooled down and passed on throttling valve. At throttling valve the fluid expands and it creates the cooling action. This cooling action is used at evaporator and hence the process is completed.
A cold refrigerant comes to the evaporator and here it takes heat from the material that has to be cooled down. Since it takes heat from the surrounding, refrigerant gets evaporated. After passing through the evaporator, the refrigerant reaches the compressor. Here it compressed back to the liquid form and passed on the condenser. Here at condenser the liquid is cooled down and passed on throttling valve. At throttling valve the fluid expands and it creates the cooling action. This cooling action is used at evaporator and hence the process is completed.
Evaporator-
It is a type of heat exchanger which is used to take heat from the items that has to be cooled down.
It is a type of heat exchanger which is used to take heat from the items that has to be cooled down.
Compressor-
Compresses the vapor form of refrigerant in to liquid form.
Compresses the vapor form of refrigerant in to liquid form.
Condenser–
All the heat in refrigerant is taken by cooling medium.
All the heat in refrigerant is taken by cooling medium.
Throttling valve- All types of expansion process takes place here. This is also called as the Thermal Expansion valve, and plays the role of creating cooling effect, as the liquid refrigerant is reduces to low pressure here, thus it produces the cooling effect.
So this was all from this article. Hope you would have liked it.
