Refrigeration Evaporators: Functions, Types, Design Characteristics And Maintenance.

Evaporators are very important when it comes to refrigeration.


In this article, I will share with you the functions of refrigeration evaporators, their types, design characteristics and how one can maintain them.


Without wasting time, let me share what you need to know about these evaporators.


Functions of evaporators;

1. Absorb heat from the surrounding.

This is the first function of a refrigeration evaporator. As you already know the function of the refrigeration process is about cooling a hot body.


If you want to know more about how the refrigeration process works then I suggest you read the article below.


You might like this: Vapour Absorption Refrigeration System: Working Principle


The refrigeration evaporator contains the refrigerant that is used to absorb the heat from the surroundings to bring about cooling.


The heat is absorbed from the body being cooled by the evaporator, which in turn results in the decrease in temperature of the body being cooled.


The process of absorbing heat from the body being cooled is made possible due to the refrigerant that is usually inside the evaporator coiling.


That is not the only function of an evaporator. Here is the next function of the evaporator.


2. Provide the passage of the refrigerant.

The evaporator provides a passage of the refrigerant. You have to know that the refrigeration process won’t be complete without the refrigerant flowing through the entire refrigeration cycle.


This evaporator ensures that there is a passage for the refrigerant for the refrigeration process to be complete.


Without the refrigerant passing through the evaporator, the entire refrigeration process won’t work.


3. Provides temporary storage of the refrigerant.

The refrigerant will always be in the evaporator before it’s moved to the other parts of the refrigeration system.


Before the refrigerant absorbs heat from the body that is being cooled, it has to settle in the evaporator for a period.


Settling in the evaporator enables it to absorb heat effectively thus making the refrigeration process efficient.


So, we can all say that the evaporator provides temporary storage of the refrigerant. It has to be in the evaporator before it moves to other parts of the refrigerator.


Types of refrigeration evaporators;

1. Dry expansion evaporator.

This is the evaporator that only carries the amount of refrigerant that is needed by the refrigeration system.


In a dry expansion evaporator, the refrigerant is fed through the expansion valve so that it gets converted into gas before it reaches the end of the evaporator suction.


The right amount of refrigerant is fed through the expansion valve.


We are calling it a dry expansion evaporator because the refrigerant fed into the evaporator is of the right amount and it will already be in a gaseous state when it enters the evaporator.


This type of evaporator does not waste refrigerant at all because it uses the required amount of refrigerant.


The disadvantage of using a dry expansion evaporator is that the moment there is a leakage the entire refrigeration process will be affected since there will be no more refrigerant to compensate for the leakages.


2. Flooded evaporators.

This evaporator is called flooded because it’s covered with 10% liquid. The refrigerant in this evaporator is fed via the float valve to maintain a constant level of refrigerant in the evaporator.


This type of evaporator provides a rapid rate of cooling than the dry expansion evaporator because of the amount of refrigerant present in the evaporator.


The other thing is that the refrigerant is in liquid form thus energy transfer is very efficient compared to vapour refrigerant.


The issue is that you will have to maintain a constant level of refrigerant in this evaporator, without that the entire refrigeration process will be less effective.


Also, a flooded evaporator uses more refrigerant compared to a dry expansion evaporator, but I guess it’s worth it because of the rapid cooling it provides.


Design characteristics of refrigeration evaporators;

1. It should transfer enough heat through any size.

Since the entire refrigeration process depends on the amount of heat absorbed from a body, the evaporator should be able to transfer enough heat through any size.


Be it as big or small size as possible, it should be able to allow heat transfer without any issues.


That is what will result in the effective function of that evaporator.


If there are any limitations when it comes to heat transfer in the refrigeration system then this evaporator will be considered not fit for use in a refrigerator.


2. The liquid should not leave the evaporator.

This is another design characteristic that an evaporator should meet up.


The evaporator should not at any point allow the liquid to leave the evaporator to prevent wet compression.


As you know the rule of thumb when it comes to compression, liquids are in-compressible.


So, a liquid leaving the evaporator and entering the compressing unit will bring problems to the compression process.


This is whereby you will find that refrigeration uses a large amount of energy, shortages of oil in the compressor and the compressor will be very noisy during operation.


If the design of the evaporator can’t prevent the liquid from flowing in the compression unit, it’s not fit for use in a refrigeration system.


3. Liquid supply to the evaporator should be easy.

The process of supplying liquid to the evaporator should be easy. I mean if the liquid refrigerant can’t be easily supplied to the evaporator do you expect the refrigeration process to be efficient?


There should be no problem when it comes to the supply of refrigerant in the evaporator.


It doesn’t matter whether the liquid refrigerant is fed through the expansion valve or not.


The easy supply of the liquid in the refrigerant will make the entire refrigeration process easier.


So, the design characteristics of the refrigerant should be able to meet this factor.


Without it, the evaporator is not worth it to be used in the refrigeration system.


4. Corrosion and fouling should be minimum.

The design characteristics of the evaporator should be minimum on the outside.


When it comes to corrosion, we are talking about the material used to create the evaporator.


It should be corrosion-resistant to reduce the rate of corrosion on the outside.


If you have no idea of what fouling is; this is the process of formation of unwanted material deposits on the evaporator due to the process of heating exchange.


As you already know that the evaporator’s main function is to absorb heat, so the chances of fouling are pretty high.


The material used to create the evaporator should minimize that.


And what happens when the evaporator corrodes or fouls from the outside?


You have to know that corrosion and fouling will cover the external part of the evaporator thus minimizing heat transfer and this will render the refrigeration process ineffective.


5. The evaporator should be tight, compact and durable.

The evaporator being tight will aid in the effectiveness of heat transfer since the refrigerant will always be on the evaporator lining.


Being compact will help ease of its installation in the refrigeration system and occupy less space.


Durability is another factor that the evaporator should meet, you need a design that will render the evaporator for a long time.


For the evaporator to be durable, it has to have the correct design characteristics.


So in whatever way the evaporator is built, it should always ensure that it’s durable.


6. Evaporator maintenance.

Cleaning the outer surface of the evaporator to minimize corrosion and fouling. Doing this will increase the efficiency of heat absorption of the evaporator.


Also, frosting formation caused by changes in temperature between the inside and outside of the evaporator is a huge issue that minimizes heat transfer.


When frosting happens, the refrigerant temperature is usually lower than the anticipated temperature, this causes the water in the refrigerant to freeze thus negatively affecting heat transfer.


The main problem when it comes to evaporators is frosting formation on the surfaces of the evaporators. You can control this by using the following methods; water defrosting, pressure control defrosting and temperature control defrosting.


Final thoughts


If you understand the function of an evaporator then you are at a good starting point f understanding the refrigeration process.


I have tried my best to make this information easy to process and consume.


Dealing with the mechanical side of things sometimes can be super boring. I’m here to make it fun for you, easy to study and grasp the concept.


So, if you have any questions to do with evaporators just leave them in the comment section and I will do some research on it.


After all, I’m a mechanical nerd. Thanks for reading, and I hope to see you in my next article.


Related articles to check.

  1. Refrigeration Evaporators: Functions, Types, Design Characteristics And Maintenance.
  2. Two Stage Refrigeration Cycle Using A Flash Chamber: Working Principle
  3. Causes Of Vapour Compression Refrigeration System Failure +Solutions
  4. Vapour Absorption Refrigeration System: Working Principle
  5. Central Air Conditioning System: Components And Working Principle

Leave a Comment