Should I use oil as a heat transfer fluid?

At higher temperatures, water ceases to become an effective heat transfer fluid. To continue to use water as a heat transfer fluid it may become necessary to pressurise the system, and substantial monitoring will be required to ensure safe operation. Water can also cause corrosion within the system.

Mineral and synthetic oils are suited for use as a heat transfer fluid at much higher temperatures, and do not need to be pressurised until the top end of the range is reached.

Although no heat transfer oil is capable of meeting all of the below factors evenly, the following factors should be considered, alongside the specifics of the application:

  • Low viscosity 
  • Good thermal stability 
  • High flash point 
  • Good heat transfer properties
  • Ease of waste disposal
  • Non-corrrosive
  • Non-toxic
  • Non-flammable

It is important that the viscosity of heat transfer oils is low, especially when operating at the lower end of the temperature range, as this will affect the operating conditions under which the chiller is able to function. If the oil becomes too viscous under lower temperatures, the system will not be able to start up, causing damage to the chiller. The operating viscosity of the heat transfer oil affects the flow properties within the pipes. The correct viscosity, combined with the associate optimum turbulent flow, enhances heat transmission.

The thermal stability of heat transfer oils makes a large contribution towards pump efficiency and the safe operation of the heat transfer system.

It is important to ensure that high quality heat transfer oils are used. Heat transfer oils are usually a mixture. It is essential that constituents with a low boiling point are removed, as they will begin to evaporate during normal operation of the chiller, their presence will reduce the viscosity and lower the flash point of the oil. If the operating temperature of the chiller rises with such constituents present, constituents with a much higher boiling point are cracked, resulting in a high-viscosity substance with deposits a sticky substance on pipes and surfaces.

When selecting a heat transfer oil, it is important to look at the heat transmission characteristics of the oil. The heat conductivity of the oil will give a good indication of how well heat will transfer from the film coating the pipe walls into the flowing heat transfer oil. The vapour pressure of the heat transfer oil will indicate whether the system will be able to be run without pressurisation. The thermal expansion-coefficient of the heat transfer oil will indicate whether the oil is compatible with the size of the expansion tank.

Applied Thermal Control Ltd.
39 Hayhill Industrial Estate, Barrow upon Soar, Leicestershire, LE12 8LD.
Telephone: +44 (0) 1530 83 99 98
E-Mail: sales@app-therm.com
Facebook Twitter YouTube LinkedIn
ISO 9001 ISO 14001