MTS Water Quality Guide - Manual (Page 14)

Heat Exchanger Care and Water Quality Guide 14 Heat Exchanger Care
Fouling due to
accumulation of scale,
solids, and algae
Various compounds and marine growths present in cooling water will deposit a
film or coating on heat transfer surfaces. The film acts as an insulator, restricting
heat flow and protecting corrosive compounds. As a result of this insulating
effect, temperatures go up and corrosion increases.
• Scale is the result of dissolved minerals precipitating out of heat transfer
fluids. The solubility of these minerals is affected by changes in temperature
within the heat exchanger and chemical reactions between compounds
found in the cooling water. MTS has designed your HPU to have an
optimum fluid velocity based on the heat exchanger material and the heat
transfer needs of your system. This fluid velocity is normally sufficient to
keep the rate of precipitation low. If your fluid velocity decreases due to
fouling or clogging of the tubes, the rate of precipitation will increase.
Regular cleaning of the tubes and inlet filters will keep the fluid velocity
high enough to inhibit scaling.
• Suspended solids are usually found in the form of sand, iron, silt, or other
visible particles in one or both of the heat transfer fluids. If fluid velocities
are not high enough to keep them in suspension, particles settle out and
build up on the chamber walls. Suspended solids are very abrasive to
chambers and other heat exchanger parts. The proper use of filters and
screens for the cooling water and hydraulic fluid will reduce the presence of
abrasive particles in the fluid and protect your heat exchanger from erosion
damage.
• Algae and other marine growths are a serious problem if they get in the heat
exchanger. In many cases, the environment in the heat exchanger is
conducive to rapid proliferation of algae and other marine growths, which
restrict cooling water flow and impede heat transfer. A chemical algicide,
such as chlorine, is effective in controlling algae and other marine growths;
high fluid velocities also discourage them from proliferating.
How do I know when I have a heat exchanger failure?
The first indication of a hydraulic fluid-to-water heat exchanger failure is a milky
or cloudy coloration of the hydraulic fluid, indicating a water content greater than
0.2–0.3% by weight. Hydraulic fluid in the water discharge is also a sign of heat
exchanger failure. A corrosion failure starts as a small pin hole, which produces a
very low flow of water into the hydraulic fluid. Checking the hydraulic fluid
color on a daily basis will reduce the amount of water contamination and the
severity of the damage.