What are the minimum flow requirements? How do I choose a fluid? Can the fluids be mixed? These questions and more are answered in our web exclusive sidebar.

Q: Is there a minimum flow requirement for a thermal fluid heater?
A: A minimum flow rate is required in order to maintain the appropriate velocities through the heater (typically 10 to 12 ft/sec). If the velocity is too low, the film temperature could increase, potentially destroying the fluid.

Q: What are the primary components in a thermal fluid system?
A: A typical system includes the heater, circulation pump, expansion tank and the user. Depending on the temperature requirements and the system design, control valves may also be used.

Q: How do I choose a thermal fluid?
A: The required operating temperature, along with the physical properties (specific heat, maximum operating temperature, vapor pressure, specific gravity and coefficient of thermal expansion) of the fluid, should be evaluated when choosing a thermal fluid. It is important to choose a fluid specifically designed for heat transfer as opposed to a multi-purpose or turbine oil.

Q: Can thermal fluids be mixed?
A: Mixing different fluids and subjecting them to high temperatures can have unpredictable results. In addition, once fluids have been mixed, the baseline analysis of the fluid is no longer applicable, making it difficult to perform an annual analysis of the fluid for degradation.

Q: Why is an expansion tank required?
A: All thermal fluids expand as they are heated. The amount of expansion is based on the operating temperature, system volume and the coefficient of thermal expansion of the fluid. An expansion tank must be provided to accommodate the increased system volume at operating temperature. Keep in mind that all fluids expand at a different rate.

Q: What types of materials (valves, piping, gaskets, etc.) should be used with thermal fluid systems?
A: Typically, thermal fluid systems should use either carbon or stainless steel components. Brass, bronze, cast iron and aluminum are incompatible with thermal fluid. Piping should be schedule 40 seamless SA 106 material. Valves should be cast steel or ductile iron with steel or stainless steel trim. Gaskets should be rated for the temperature and pressure of the system.

Remember that threaded connections larger than 1" should not be used in the flow circuit.

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