Heat Transfer Fluid – Questions and Answers [PDF Included]

The properties of heat transfer fluids have a great role in determining the efficiency of any system. The type of heat transfer fluid you should select depends on the application. Hence, you should know the specific purpose of the heat transfer fluid and the answers to some short questions before selecting the fluid.

Let’s jump into the short questions on Heat Transfer Fluid so that you can select them easily for your research field.

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Short Questions and Answers

Here are some questions on Heat Transfer Fluid. By studying all those questions and answers, you can enhance your knowledge in this field.

What is a heat transfer fluid?

Heat transfer fluid is a fluid by which heat is absorbed and then it stores or carries/transports the heat to another object/media of the process.

Why heat transfer fluid is used?

You must need higher efficiency for your application. For achieving high efficiency, you have to use heat transfer fluids. In thermal power plants, heat transfer fluid is water. Heat is transferred from the flue gas to the turbine. As a result, the turbine starts operating.

When the fuels are burnt inside the boiler, a huge amount of heat is generated. If water can absorb maximum heat out of it, it will easily be converted into steam that can drive the turbine easily. Thus, the heat transfer fluid enhances the efficiency of the system.

What are the properties of heat transfer fluids?

The heat transfer fluids should have the following basic properties:

The fluid should have very good thermal conductivity and heat capacity.

The fluid should not be corrosive.

It should have enough auto-ignition safety margin.

It should be hydrophobic.

It should have low viscosity, a wide range of service temperatures.

What are the different types of Heat Transfer Fluids?

Heat transfer fluids can be of three types based on the varieties in their chemical structures:

Synthetic Oil

Mineral Oil


Name some heat transfer fluids.

Therminol, Carbon nanotubes, etc.

The most commonly used heat transfer fluids are: Ethylene glycol and water solution

Propylene glycol and water solution.

Ionic Liquids (1-Ethyl-3-methylimidazolium methanesulfonate [C2mim][CH3SO3]

Molten Salt-Sodium Nitrate

Vegetable oil

What is therminol?

Therminol is an aromatic hydrocarbon. It is biphenyl-di phenyl oxide.

It can operate up to 400 degrees Celsius. It is an eutectic mixture of 73.5% diphenyl-oxide and 26.5% diphenyl.

The problem in using this fluid as a heat transfer fluid is that its’ freezing temperature is very high.

What are the properties of Carbon nanotubes (CNT)?

There are single-walled CNT, double-walled CNT, and multi-walled CNT.

CNT has a high thermal conductivity that helps them to create a network of conductive tubes.

The thermal conductivity of CNT is very high compared to copper and carbon fiber. It is more than 3000 W/m.k.

It is very hard to separate the CNT from the treated water.

It has a high affinity for bacterial growth. This problem can be avoided using the magnetic property of the CNTs.


A single-walled carbon nanotube consists of a layer of graphene.

The conductivity of SWCNT depends on the orientation of the graphene sheet.


MWCNT means a multi-walled carbon nanotube. It comprises multiple rolled layers of graphene sheets. Hence, it carries a complex structure.

Scientists face difficulties in obtaining a pure homogeneous and uniform sample of CNTs. Therefore, the mechanical and thermal properties of CNTs are yet to be measured by any means.

What are the general rules that you should know while selecting some fluids as HTF?

Avoid fluids that have kinematic viscosity is more than 60 centistokes at 40 degrees Celsius.

Avoid fluids that have a low boiling point and high freezing point. While exchanging the heat, the fluid should not change the phase.

Avoid the fluids that tend to corrode the pipe walls and thus it will increase the pressure drop within the pipeline.

Don’t opt for those fluids that have low thermal conductivity and low thermal diffusivity because these fluids reduce the rate of heat transfer.

How will you select the heat transfer fluid?

If the temperature of the heat transfer application is below 175 degrees Celsius, you should take the solution of water and inhibited glycols or any other inhibited glycol-based fluid.

If the temperature of the heat transfer application is above 175 degrees Celsius, you should take synthetic organic or silicon fluid.


I have given the answers to the short question on Heat transfer fluids which are very much necessary to know before picking up the fluid. I hope, these short questions and answers will help you in selecting the fluid for your application. If you have any queries on this topic, please don’t hesitate to write to us in the comment box. Wish you good luck!

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