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[Ash_jee]

How can we specify electric heater for fuel oil tank to mantain oil viscosity ? Anyone has any idea about calculation

[Art Montemayor]

You must first specify the duty (or heat transfer) expected of your electric heater. You must also specify the required temperature you want the fuel oil to achieve. You must know this since you know the type and specifications of your burner(s).

You alone know what type of “fuel oil” you have. We certainly don’t. There are various types of fuel oil and many qualities for each type. Some fuel oils are just outright corrosive and viscous and include a lot of water. You would be wise to insist on a consistent quality from your supplier and require a specified required viscosity for your burners as well as a specific heat value for the fuel oil. You should have a viscosity curve for your fuel oil.

From that curve you can read the required fuel oil temperature for your burner. It should normally be around 150 to 180 oF – all depending on the type and quality of fuel oil.

Electric fuel oil heaters work very well if specified accordingly. I’ve always used Chromalox immersion heaters on my boilers. For detailed technical information go to:

http://www.chromalox.com/default.aspx

http://www.chromalox...en/heat-sel.pdf

You should calculate the heat load for the fuel oil using the specific heat and the sensible heat equation. (Q = W Cp Delta T) The most important thing to bear in mind when specifying an electric heater is to work directly with a knowledgeable and experienced fabricator in order to get a reasonable and safe Watt Density to use in the design. This value is very important and is the heart of the electric heater design. The fabricator knows this value according to the alloy used, the fluid heated, the temperature range, and the application. That’s why I always resort to using an experienced supplier such as Chromalox.

Typical Watt Densities can run in the following estimated ranges:

Oil Heaters (Light Wt. oil) = 20 to 23 W/in2
Oil Heaters (Medium Wt. oil) = 15 W/in2
Oil Heaters (Heavy Wt. oil) = 6 to 10 W/in2

I hope this helps you out.