Coolant vs Refrigerant: 7 Important Factors Related To It

Coolant and refrigerant are not entirely different. This article discusses about the topic Coolant vs Refrigerant in detail.

Coolant is a broad term and refers to a fluid that absorbs heat from the system. This way the temperature of the system can be regulated. When the temperature needs to be reduced below ambient temperature, then the coolant is referred as a refrigerant. Hence, all refrigerants are coolants in broader sense.

Definition of coolant

As discussed above, coolant can be any fluid that is used to remove heat from the system and reduce the temperature of the system.

The coolant can work without changing its phase (whether liquid or gas) or by changing its phase (liquid to gas and gas to liquid).

Uses of Coolant

A coolant is used in places where the temperature needs to be regulated. Excess heat can create a lot of problems in engines, machine components etc.

Different places where coolant is used are-

  • Inert gases are used as coolants in nuclear reactors.
  • Vehicle engines use cooling fluid/ water jackets around engine to absorb the excess heat generated in the cylinder.
  • Rocket engine nozzles have small tubes through which liquid oxygen is passed that cools the nozzle to a desired temperature, without which the metals used in nozzle wouldn’t have survived the high temperature generated because of exhaust gases.

Types of coolant

Coolant comes in various forms and phases. It is important to know the nature of coolant because an improper coolant will not be able to regulate the temperature of the system to required value.

The different types of coolants used in industry are-

  • Gaseous- Hydrogen, Boron, Sulfur Hexafluoride are commonly used gas coolants. Hydrogen is used in turbogenerators, Boron in nuclear reactors and Sulfur Hexafluoride in switches, transformers or other kind of circuit breakers etc.
  • Two phase- These types of coolants uses both the phases of coolant that is liquid and gas. These coolants are usually used in applications where desired temperature is below ambient temperature. These coolants are called as refrigerants.
  • Liquids- Water is the most common liquid coolant. But it cannot be used while dealing with metals due to corrosive nature of metals. Various mineral oils are used as coolant in place of water to cool machine components. For example, special oil is used to cool the job while machining on lathe.

Definition of refrigerant

Refrigerants are the coolants that are used in low temperature applications. Refrigerants use their latent heat of vaporization to reduce the temperature to significantly low value.

Refrigerants bring with them a lot of environmental concerns which is why there are many rules and regulations of refrigerants.

Image: Refrigerant

Image credit: Stephanie~commonswiki, Can of DuPont R-134a refrigerantCC BY-SA 3.0

How do refrigerants cool the system?

Refrigerants absorb heat and change their phase to achieve the desirable temperature. Some gas cycles may use only one phase of the refrigerant for example Bell Coleman cycle or Reverse Brayton cycle.

In a typical refrigeration cycle, the refrigerant enters the system in liquid form. It absorbs the heat from the system and gets converted into gaseous form. Later on, the gaseous refrigerant is converted back to liquid state so that it can be used again.

Coolant Vs Refrigerant
Image: The observed stabilization of HCFC concentrations (left graphs) and the growth of HFCs (right graphs) in earth’s atmosphere.

Image credits: Wikipedia

What are desirable properties of refrigerants?

The use of refrigerants is regulated due to their toxic and inflammable nature. They also give out green house gases which are harmful for ozone layer.

Due to above reasons, some refrigerants are banned. An ideal refrigerant has following properties-

  • Non toxic
  • Non corrosive
  • Non flammable
  • No green house gas emission and ozone layer depletion potential.
  • Freezing point below the target temperature.

Is AC coolant and engine coolant same?

Both AC coolant and engine coolant are used for cooling. But their applications and mechanism differ from each other.

Water is typically used as engine coolant. It cools down the engine by absorbing heat and transferring it to the outside air and also transfers heat to the cabin of the vehicle when vehicle heating feature is turned ON. It is mixed with anti freeze substances so that the water does not get frozen. AC coolant is used for absorbing heat from the cabin and emitting out to the atmosphere. The AC coolant will change its phase from liquid to gas and back to liquid.

Hence, the major difference between the two is the application (one is used to cool engines and other is used to cool the cabin) and other difference is the mechanism of cooling (engine coolant does not change its phase whereas AC coolant switches its state from liquid to gas time to time).


I, Abhishek Khambhata, have pursued Btech in Mechanical Engineering. Throughout four years of my engineering, I have designed and flown unmanned aerial vehicles. My forte is fluid mechanics and thermal engineering. My fourth year project was based on performance enhancement of unmanned aerial vehicles using solar technology. I would like to connect with like minded people.

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