Evaporator and Selection

Evaporator is another main equipment in refrigeration system that is crucial for function. The right solutions of evaporator, therefore, plays an important part in refrigeration system. Apart from preserving goods and expanding shelf life, it also saves cost of electricity bill.

 

1. Heat Transfer

Solutions and calculation of evaporator have two main points which are heat transfer by conduction and convection.

1.1 Conduction

To transfer the cool from copper pipes which are a source of the cool to finned evaporator.

1.2 Convection

To transfer the cool from the finned evaporator to a chamber by using air as a medium.

Evaporators use a principle of both conduction and convection. In composing the evaporator, another vital module is calculation of heat transfer area.

SA =[2/Sfin/1000] x [Sh x Sd – π/4 x[dT² + n x dh²]] x r + π x dT/1000
and
Total Surface Area = SA x Ifin x [N° Tubes High + N° of Tubes Deep]

It is being said that an evaporator is an insignificant tool. Its main duty is cool down the area – which is a false statement. Genuinely, the effective evaporator is derived from the right solution and calculation in engineering. In industries that have several models of evaporators, relevant personnel should be aware differences in each category although it all function as a part of refrigeration system. The hidden agenda could be energy difference, cost of electricity, durability, and safety. Should there occur errors in the evaporator, storage inside the refrigerators would be greatly affected. Certainly, the cost of deficit would be higher than the cost of acquiring the effective evaporator.

 

2. Eurovent Certified

In choosing the right equipment, one should consider its standard and certification. Because well recognised standards are a guarantee of that product or services as well as an indicator that customers would receive great benefits and convenience. For evaporators, a main part in refrigeration system, in both business and commercial, it should also be certified. One of the most well known organisation in Europe is EUROVENT CERTIFIED which guarantees specifications of evaporators. Users can find out for warranties at http://www.eurovent-certification.com Products that are certified by the organisation is a support that shows confidence in the selection.

 

3. Pipes Construction

Because the source of cool in evaporator generated in refrigeration pipes by evaporating the refrigerants at low pressure, the pipes are then being cooled, therefore, they are important in conduction and convection. Nowadays, the refrigerant pipes in evaporators were developed to create turbulent so that the refrigerants can convect and conduct within the pipes effectively, resulting in better function in the evaporator as total.

The quality pipes should have thick walls to strengthen of the evaporator; also, to prevent leakage and cracks. In production of the evaporator, the expansion of the pipes should be durable to withstand pressure and torque in action.

 

4. Finned Evaporator Solution

The finned evaporators play important part in convection and conduction into a chamber. The solution of effective finned evaporators must have turbulent ventilation as it increase capability to convect and conduct. However, if turbulent is too strong, the pressure will drop and should be fixed by increasing the fan power in order to overcome the pressure drop in the evaporator.

Therefore, the review of solutions in finned evaporator as aforementioned should be core of the objective. Another tool that greatly aids the design and analyse is Finite Element Method (FEM) Programming.

“The design of finned evaporator – materials that being used should be thick enough to prevent damage from the embed. Therefore, in some thick evaporator, the embed enhance convection and conduction while taking less surface of finned evaporator. The compare some specific elements of evaporator such as surface of evaporator, air volume, number of fans, and others of one to another is improper because those elements are a component in evaporators that can produce the cool. Therefore, cooperation should consider quality of refrigeration because each model of evaporator has different finned design, pipes alignment, pipe types, air volume, wind speed, and others.

 

5. Unfreeze by Using Electricity Solution

In subzero freezer, it is unavoidance to see ice crystals at the evaporator, resulting in a drop of effectiveness in cooling. Ice crystals therefore become an inevitable obstacle in refrigeration. Solution to this problem is to melt the ice crystals.

To unfreeze the ice crystals, there are several methods such as by an electric radiator, hot gas, hot water, and others. For small to medium freezer, it is usually solved by an electric radiator. The radiator in an evaporator can melt the ice crystals effectively only when heat is being transfer from the radiator to a finned evaporator. Some evaporator is equipped with radiator sleeve where the outer shell is connected to the finned evaporator and the inner sleeve is for the electric radiator.

Once the radiator is on its process, heat is transferred to the finned evaporator which makes the ice crystals melt rapidly throughout. However, in some non-sleeve radiator, there could be some issue such as the ice crystals do not melt completely, or the electric radiator is broken or overloaded of electric radiator.

 

6. Fan Selection

Air is medium that transfer the cool to storage by passing through an evaporator. Therefore, it is important to choose the right equipment in order to produce the right amount of air. Fan is vital to the system as it can cause success or failure in the system.

There is a misconception in choosing evaporators by comparing different model of evaporators and contrast size and numbers of fans. Those are one of indicators in evaporator construction. Solutions from each enterprises and models are differ. Some evaporator consists of smaller fans but effective. On a contrary, some evaporator needs many fans in order to produce the right temperature for refrigeration.

In summary, to compare and contrast evaporators, number of fans is not an absolute measurement.

 

---

 

Written by Dr. Sukit Litikorn
Engineering Support Director, Refrigeration System
Harn Engineering Solutions Pcl.