How To Clean A Heat Transfer System - Part I

Even under the best conditions, a heat transfer fluid will eventually degrade. Commonly this happens over time due to a process known as oxidation — the chemical reaction that takes place between a fluid and oxygen. It’s an inevitability that ultimately brings the fluid’s useful life to an end. But it also happens due to contaminants, overheating and numerous other conditions have deleterious effects on the lifespan of a fluid.

You cannot completely prevent a fluid from eventually degrading, but you can slow its progression. With proper fluid maintenance, you can significantly prolong the service life of your fluids, reducing maintenance costs and downtime, and providing better protection for equipment.

Fluid analysis offers a convenient way to monitor a fluid’s oxidation rate and other conditions, helping ensure that fluid remains in service only during its useful service life — no shorter (which is wasteful) and no longer (which is dangerous to equipment).

System Fill

Whenever your heat transfer fluid is replaced, it is a good time to consider changing out the fluid filters. Filtration will extend the service life of the fluid and reduce system maintenance costs. These benefits increase as the system operating temperature increases.

A side-stream filtration system is recommended for systems with centrifugal pumps. With a side-stream configuration, the optimal flow rate through the filter is 10 percent of full system flow. At a minimum, circulate at least three percent of the full system flow through the side-stream filter.

1. Heat transfer fluids should be charged first via the system expansion tank. Open all high point vents and valves to the various system users
2. Fill the system through the lowest points to dislodge trapped light-ends. 
3. Light-ends or moisture escaping could cause a spike in the system pressure or small puffs of steam or vapor as it leaves the vent from the expansion tank
4. Continuously fill and drain the expansion tank slowly while replenishing the system with new fluids
5. After replenishing the system, any residue of light-ends or moisture should be vented through the bleeder valve at the high points of the system
6. With the system’s fluids refilled and nitrogen expelled, you can turn on the circulation pump

In liquid phase thermal systems, the expansion tank volumes should be approximately 26% – 30% of the total estimated volume of thermal fluid in the thermal system. A properly sized expansion tank should be approximately 1/4 full at startup temperatures and 3/4 full at operating temperatures. Don’t forget to blanket the expansion tank with an inert gas if your system specifications call for that. Always follow your system manufacturer’s guidelines on Nitrogen blanketing.

Continue to part II