The Basic Principles of Heat Exchanger Cleaning

Many different designs and applications of compact heat exchangers are used in military, commercial, and business aviation applications as well as ground support equipment. They primarily encompass water, oil, fuel, and air coolers as well as...

There are three primary types of solvents and cleaners that we use for various heat exchanger and other cleaning and degreasing processes.

  • Hydrocarbons are comprised of petroleum distillates, synthetic (paraffinic) hydrocarbons and Terpenes (distillates from plant oils). Hydrocarbons have a high solvency for “hard-to-clean” organic soils, including heavy oil, grease, and tar. They have a low liquid surface tension, which allows them to penetrate and clean small spaces. Many hydrocarbons are blends and less volatile components may be left on the parts after the bulk liquid has evaporated.
  • Hydrofluorocarbons, as with the chlorinated and now regulated CFC-113, CFC-11 and HCFC-141b solvents of the past. Today’s HFCs are used for precision cleaning, foam blowing, and refrigeration. HFCs target applications where non-VOC, low-toxicity, low-residue, and nonflammable solvents are required. HFCs high solvency and low boiling points make them an excellent choice for A/C flushing, where rapid evaporation by vacuum recovery leaves no solvent residue.
  • Aqueous cleaning and degreasing can be performed for a wide variety of cleaning applications. There is a primary environmental benefit of no VOCs and no ozone depletion, which is growing the applications of aqueous cleaning. However, some ferrous metals will exhibit flash rust in aqueous environments. Aqueous cleaners are usually a mixture of water, detergents, and other additives that promote the removal of organic and inorganic contaminants from a hard surface. Surfactants (surface action agents), provide detergency by lowering surface and interfacial tensions of the water so that the cleaner can penetrate small spaces better, get below the contaminant, and help lift it from a hard surface. Oil in water emulsifiers causes water immiscible contaminants, such as oil or grease, to become dispersed in the water.

It is always recommended that a commercial solvent chosen must be 100 percent volatile for it to completely evaporate and be removed. There are a lot of false claims being printed on the labels today, and this is why we emphasize the importance of studying and understanding the chemical product. Remember, you must be “Smarter than the label.”

Whatever chemical you choose to use, it is your professional responsibility to obtain a MSDS with sub component CAS numbers. It is extremely important you know what you’re using. Understand the effectiveness of both the chemical and physical properties of the product you choose to use. Know how and why this chemical will remove the undesirables (or paint). Know how this chemical will be removed from the system when cleaning is completed. Know if it is compatible with the metal and elastomer materials of the system, components, and the flushing equipment. Know the toxicity, hazard classification, flammability, combustibility, and proper handling. Know the local, state, and federal regulations regarding the use and disposal of the products you choose.

Basic physics
Now we can get to some basic physics principles. Complete and many times partially assembled systems cannot be flushed. You must always isolate the heat exchangers and flush through the most direct and unrestricted path to obtain the most satisfactory flushing results. You cannot flush through check valves, filters, orifices, or any device that would slow or restrict the heat exchanger flushing process and or solvent recovery and removal.

Some form of mechanical energy is almost always used to enhance a solvent cleaning process. Even the best suited chemicals for the job will produce poor results. If not introduced with the adequate energy necessary to defeat the “path of least resistance” rule, scrub the internals down into the corners and crevices; to dislodge trapped debris and carry it away. It is just like holding a dirty part under your parts washer outflow; you know the cleaning will be accelerated and improved when you add your elbow (energy) and a scrub brush.

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