In today's world of expensive energy,
it is more vital than ever for heat exchange equipment to be kept free of
insulating deposits that promote high energy consumption. The four principal
sources of these deposits in the case of water cooled systems are: scale,
corrosion, biological growths and sludge. These factors are important for
another reason: they have a direct effect on equipment life.
Caused by the precipitation of calcium
and other salts of limited solubility, scale, in addition to its high insulating
value, progressively narrows pipe internal diameters and roughens tube surfaces,
thereby impeding proper flow.
In compression refrigeration systems,
scale translates into higher head pressures, hence an increase in power
requirements and costs. For example, 1/8" of scale in a 100 ton refrigeration
unit represents an increase of 22% in electrical energy compared to the
same size unit free of scale. Similarly, in absorption systems, scale creates
a higher back pressure on the concentrator, increasing energy expenditure.
While scale formation proceeds more
rapidly in open recirculating systems owing to the concentration effect
of evaporation, once-through systems are not exempt from scaling if high
temperatures are combined with silt and iron.