Thermic Fluid Heater is most popular in almost every industry, and it is being used for various heating applications due to unique advantage over other heating systems like steam heating, electrical heating, direct firing, air heating etc. In many of the applications, it is very cost effective and energy saving as it has an exceptional advantage over other industrial heating methods.
Thus, it is important to recognize various aspects of thermic fluid heating and significance of thermal oil temperature when thermic fluid circulate through tubes of heater. When fluid flowing inside the coils or tubes of the heater, it creates multiple layers of flow of the fluid along the tube periphery and this layer is almost stationery in a form of a film. This formation of film offers very high resistance to flow of heat from the heat source through heated metal surface to circulating thermic fluid. The level of resistance also depends on the velocity of thermic fluid flow and thickness of the film formed. Therefore, it is usual that more heat is passed through this film and transfer the heat in the bulk oil to gain bulk temperature of the fluid in the system. In this way, temperature at the film of the oil is always greater than bulk temperature of the thermic fluid. The bulk temperature is being established by the velocity of the thermic fluid in the heater coil.
To achieve optimum performance and longer life of the thermic fluid depends on the requirements of heat in your process and design parameters of the heater for the safe operation to meet the duty conditions. To ensure longer life of the thermic fluid without any deterioration, risk of fire or any damages, following are the care and requirements.
Considering the heater selection and load requirements are exactly as per the process, need to check the heater as it is operating as per the features envisaged at the time of selection. Ensure that heater works at prescribed heat load and thermic fluid flow velocity must be around three meters per seconds depending on viscosity of thermic fluid and the characteristic of thermic fluid pump, the correctness of flow velocity can be interpreted and hence checked by observing the pump circuit pressure. The user must be acquainted with the data, from manufacturer and observe the figures strictly. This care on part of users, will ensure the correctness of film thickness and hence the reliability on the correct interpretation of Bulk Temperature, in terms of safe working temperature at which the oil remains below cracking limit.
Another most significant issue is correctly selected the right thermic fluid for your unit. Now a days you can get best brand synthetic thermic fluids in the market at reasonable price, and You may get it tested or get the certificate of analysis to conform the specifications use as a reference document for future thermic fluid condition monitoring.
It is also recommended to retest the thermal oil from the system once in a year for a good synthetic thermic fluid or as may be recommended by the supplier. This is to ensure that all its properties are in good condition and not deteriorated. Periodical testing of thermal oil help to know the fluid is healthy and within reference values and parameters. All operating parameters of the heater system are to be monitored and controlled as per the requirement of safe working in the process load and to avoid any deterioration of thermic fluid and fouling in the system.
Any change in the operating parameters, fuel combustion or exhaust gas temperature, fouling in the system etc. are to be checked regularly and remedial measures should be implemented. Similarly, care must be taken to prevent any extraneous material or moisture or water etc. should not be entered into the expansion tank or thermic fluid circuit and also do not reuse the leakage thermic fluid from pump gland or spilled oils which can lead to the deterioration good thermal oil. It is advisable to top‐up the same grade of Thermic fluid in the system to ensure stability and longer life of thermic fluid in the system.
(Author is presently working as a Principal Consultant – Nirmal Encon Services, Director Technical ‐ Heatran Engineers Pvt Ltd, and Managing Director ‐ Nirmal Energy Limited & its associated companies, Ahmedabad and having more than three decades of experience in the similar fields.)