What is

a charge air cooler?

 

A charge air cooler is used to cool engine air after it has passed through a turbocharger, but before it enters the engine.
This is their main function. The idea is to return the air to a lower temperature,
for the optimum power from the combustion process within the engine.
More specifically, it is a heat exchange device used on turbocharged and supercharged (forced induction) internal combustion
engines to improve their volumetric efficiency by increasing intake air-charge density through isochoric cooling.
A decrease in air intake temperature provides a denser intake charge to the engine and allows more air and fuel to be
combusted per engine cycle, increasing the output of the engine. See our brilliant range of Charge Air Coolers here!

 

Our Charge air coolers

 

The charge air cooler is designed to cool the charged air from something in the region of 180°C
to 220°C, down to around 40°C. It achieves this by using cooling water.
Charge air coolers range in size depending on the engine. The smallest are most often referred to as intercoolers
and are attached to automobile or truck engines. The largest are often used on huge marine diesel engines
or in power plants. They can weigh several tonnes in these circumstances.

Most are still associated with diesel engines, but Vestas aircoil manufactures specialist air coolers for gas engines too.
The first marine diesel engine charge air cooler was built by Vestas aircoil A/S in 1956. Look at our history here.
The phrase “charge air cooler” is an all-encompassing term, meaning that
it cools the turbo’s charged air before it is routed into the engine.

 

More Information

Find it right here:

FUNCTIONS

 

A charge air cooler cools the combustion air after it has been compressed in the turbo charger.
The process of turbo charging involves compressing the air which introduces energy in the form of heat.
The air is cooled to the correct temperature for efficient use in the engine.

The air cooling is made possible by passing cool water (sea water or fresh water)
through the charge air cooler tubes. There are fins attached the tubes that have the effect of increasing
the surface area of the outer surface of the tube. This improves heat transfer.

The thermal design of an air cooler is of course critical. The engine performance could be badly affected if the charge
air cooler is incorrectly designed. This is vital at new building, but equally so when the time comes for replacement.

Using OEM approved Vestas aircoil to replace an air cooler gives the owner a distinct advantage
since the relationship Vestas has with the engine builders is historically strong. Access to
data is vital. With data, one can make certain the design will work in the engine.

Charge air coolers range in size depending on the engine. The smallest are most
often referred to as intercoolers and are attached to automobile engines or truck engines.
The largest are reserved for use on huge marine diesel engines and can weigh over 2 tonnes.

 

TEMPERATURE

 

The charge air cooler is designed to cool the charged air from something in the region of
180°C to 220°C, down to around 40°C. (A little higher on medium and high speed engines).

It achieves this by using cooling water either from the sea (25°C “ambient” or 32°C “tropical”) or a
central cooling water system with fresh water at around 32 degrees centigrade.

If your air cooler is under-performing, contact our aftermarket department for advice.

 

Thermal design – replacement air coolers

 

Often the engine for which the charge air cooler is to be fitted is already 10-15 years old. It’s running conditions
may not match those specified at its design stage. In addition, engines are often re-rated to suit the vessels
optimum performance efficiency. It is essential then to recognize that a poorly thought out copy of the original may not only cost
you more time and money, but that it might not be the correct solution to your current problem.

All air cooler designs, original and replacement, represent a trade-off between heat transfer and pressure drop characteristics.
Improved performance can be obtained by increasing turbulence. The optimum design should provide you with an acceptable performance with minimal pressure drop. The design of the fin and its thermodynamic characteristics is most important. The surface  
area of the fins alone is not as critical as you may think. The design of the fins that go to make up the surface area is a more
important factor. Other factors include, fin and tube density, tube geometry and material quality.

Check that the supplier has reviewed your coolers design and is proposing the correct thermal solution. There are suppliers who have
only one fin alternative and try to provide solutions for all engines with it. Clearly, they will be making design compromises
in order to win the order, so be careful and look for a company that has
design alternatives, not just one choice. Also, ask the supplier how he knows his proposed cooler design will satisfy
your thermal requirements. Has the fin arrangement been independently tested?

Our advice is that you should be as specific as possible about current operating parameters, that you take into
account the original design and lastly that you identify why you need to change the cooler i.e. what is the cause of the failure?  
If you tell the potential supplier the problem, he has a good chance to provide you with the solution!

THE DIFFERENCE

 

What is the difference between an intercooler, an aftercooler and a charge air cooler?
There is some confusion in terminology between aftercooler, intercooler, and charge-air cooler.

The inter prefix in the device name originates from historic compressor designs. In the past, aircraft engines
were built with Charge Air Coolers that were installed between multiple stages of supercharging, thus the designation of “inter”.

Likewise, the “after” prefix refers to cooler placed at the end of supercharging chain.
While multi-stage turbocharger systems are still in use today, the terms intercooler and aftercooler are most often used synonymously,
even in single stage cooling devices where a single cooler sits between the turbo and the engine. Both terms are used interchangeably.

Thus, since an intercooler or aftercooler commonly cools charged air, they are both referred to as a Charge Air Coolers.
Click here to find out the Functions of a charge air cooler or How charge air coolers work.

 

HOW DO THEY WORK?

 

The function of a charge air cooler is to cool engine inlet air after it has passed through a turbocharger, but before it enters the engine.
The idea is to return the air to a lower temperature, for the optimum power for the combustion process within the engine.
As the air is compressed it absorbs energy. Energy equals heat, so the temperature of the air increases as the pressure increases.

Over time, the heat would dissipate, but for the engine, the air is required immediately. For this reason, the intercooler is designed to
cool the air quickly using cold water. The heat (energy) is exchanged from the hot air to the cool water as the two mediums pass by each other in the charge air cooler.

The cool water passes thru multiple tubes within the unit. The tubes often have fins attached
to them that have the effect of extending the surface area of the outside of the tube. In this way, more of the outer surface of the tube is
in contact with the hot air. The heat energy passes from the air, into the fins, through the wall of the tube and into the water.

The tubes and fins are manufactured from material that is capable of conducting energy. It must also
withstand the water and the air, both of which often have contamination. Copper fins and copper nickel tubes are most often selected

Integral Support – charge air coolers

 

Fin & Tube heat exchangers – How to purchase a good quality air cooler
A working principle for charge air coolers:

A charge air cooler manufactured by Vestas aircoil will feature within it, a series of tube and fin elements. Fins are mechanically bonded to the outer surface of the tube. The principle is simple. By increasing the surface area, there is a consequent increase in the cooling surface, providing the bond between the tube and the fin is sufficiently strong to allow energy (heat) to pass. The same principle is used in reverse in a water heater (radiator).

The materials of construction are important: It’s all too easy to cut corners here. Of course, the prudent engineer wishes to
purchase at the best possible price, but consider the lifetime you expect from the replacement and how an air cooler company achieves your requirement.

You should expect, first of all, that the materials of construction are of suitable quality and that the supplier can prove the case. Copies
of material certificates should be available for inspection by you if you wish. 90/10 cooper nickel tubes are the optimum choice, but
there are higher grades too if appropriate. As for the fins, copper is the correct material. If a company offers aluminum fins, you can expect a very short operational life.

The replacement cooler should be constructed in a way, which accounts for all the physical stresses that it will encounter.
Of course, the cooler has no moving parts and is therefore often considered of less importance, but what
happens if the cooler begins to fall apart in your engine?

Its design should allow for the stress of uneven expansion and contraction caused by a temperature difference
in excess of 150 degrees C across it. It should also be rigid enough to withstand, sometimes, significant vibration.

A full tube support mechanism is therefore essential. Integral tube supports plates, positioned
at intervals along the length of the air cooler are recommended. These plates are in effect intermediate tube plates and allow every tube to be mechanically bonded to every other tube, not just at either end of the cooler but throughout its entire length. If individual tubes or rows of tubes are allowed to float free or simply clamped with bars on the outside face of the cooler fins, then there is nothing to stop early mechanical failure caused by vibration.
Our advice would be to question any potential supplier on this specific point in detail.

How are the fins attached to the tubes? There are two ways, and both are available from Vestas aircoil a/s. either by full
immersion of the finished elements in to a bath of tin (Tin coated); thus effectively turning the fins and tubes into one solid component.
Or: by expanding the diameter of the tube beyond its point of elasticity (Standard); thus gripping the fins to it. Both methods
are effective but the coated versions have advantages in contaminated environments.

There is a significant advantage if the number of separate components is kept to a minimum.
A “mono block” fin and tube element, encompassing as many tubes as possible is preferable.
The lifetime of the product will be longer where the possibility of separate components interacting against each other is removed.

Vestas has extended its maximum fin width to 77 tubes wide, big enough for almost all size of coolers – we call it a
“MonoBlock” element. A MonoBlock combined with a full integral support plate means there is effectively a one piece element.
Fewer components means a more robust air cooler. Perfect where there is vibration.