Heat transfer fluids (also known as hot oils or thermal liquids) are manufactured from highly refined petroleum, synthetically formulated hydrocarbons or siloxanes (silicone). Able to provide high temperatures at very low system pressures, heat transfer fluids offer safety, low maintenance and extended operating lifetimes as major benefits. In a tipsheet, Paratherm Corp., Conshohocken, Pa., offers some do's and don'ts when operating heat transfer fluid systems.
DO Clean New SystemsThere are many contaminants that can find their way into heat transfer systems. New systems are no exception. Hard contaminants such as weld slag and spatter as well as mill scale can damage pump bearings and seals and control valves. The mill scale can promote fluid oxidation. “Soft” contaminants such as protective lacquers and coatings, oils and welding flux are thermally unstable and can cause degradation of the fluid. While you can replace damaged fluid somewhat inexpensively, it's another matter to go through the cost and downtime of replacing mechanical seals, control valves and pumps. For these reasons, it is strongly recommend that your system be completely clean and dry before charging with heat transfer fluid.
DO Remove Water from Your SystemNo system we've seen has been entirely free of water. The more complex the system, the more water is usually present -- and the more difficult its removal. One proven method is to locate system low points having drain valves. Open each valve and drain a small quantity of fluid into a beaker.
If you see a phase separation (one liquid floating on top of another), keep draining until you draw pure fluid. Jog the pump, bringing “new” fluid to each low point. Continue the sampling and jogging procedure until no phase separation is observed (allow enough time for the water to work its way down to the low point).
Any remaining water can be “steamed off” by running the system at about 225oF (107oC) with all vents and the expansion tank warmup valve open. Once the vent system stops “steaming,” the system can be carefully taken to operating temperature safely.
Although hydro testing is a commonly accepted practice with heat transfer systems, we ask that you consider alternatives such as pressure-testing with inert gas or with the heat transfer fluid itself. Water in a system can cause pump cavitation and corrosion and, if trapped in a dead leg and hit by high-temperature oil, can flash to steam and literally blow the pipe or tubing apart. And if the pipe doesn't burst, the expansion can push a slug of hot oil out the expansion tank's vent -- a serious safety hazard.
DON'T Mix Heat Transfer FluidsMixing various hydrocarbons and subjecting the mixture to high temperatures and turbulence can be highly unpredictable. Compounding the potential problem are the possible catalytic effects of normal system contaminants and your system may be creating unknown and unwanted chemicals. We strongly suggest never mixing fluids.
For more information from Paratherm Corp., call (800) 222-3611; e-mail firstname.lastname@example.org or visit www.paratherm.com.