Did you know there are many options to consider when selecting thermal fluids?

  1. Temperature is Everything – match your bulk temperature but also consider film temperature, heater type
  2. Controlling Oxidation – high temperature air exposure can destroy the wrong fluid quickly
  3. Maximizing Fluid Life – short-term or long-term use – invest wisely
  4. Availability is Critical – thermal fluids are often critical to production – how long can you wait for your thermal fluid to ship?
  5. Reliable Service & Support – thermal fluids are maintenance-intensive, but can your vendor help you if there are problem

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Expansion Tanks: How Big Should They Be?

Fluids expand when they’re heated, and all heat transfer systems need to account for this. Expansion tanks do just as their name suggests – they give that expanded fluid a place to go. But how do you determine the correct size for the tank?

First you need to know the Delta T. In this case, it’s basically the difference between your starting temperature and your desired system temperature. Multiply that by the fluid’s coefficient of thermal expansion.

So if you’re heating the fluid from an ambient temperature of 70°F to 300°F, the Delta T would be 230. For this example we’ll use Duratherm 450’s thermal expansion rate of 0.0564%/F. So the formula would basically look like this:

  • (300°F-70°F) x 0.0564 = 12.972 (expressed as a percentage)

Let’s say in in this case your system capacity is 100 gallons. That means you’d need an expansion tank to hold an additional 13 gallons because based on the formula above, your volume has increased to 113 gallons.

One more thing to keep in mind when sizing your tank: as a rule of thumb, it should typically be 1/3 full when cold and about 1/2 full when hot.

We hope this information helps. If you have any questions or comments, please let us know.

Michael Bates, Technical Director

1-800-446-4910 ext. 111