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heater to the cooling tower during operation, thus narrowing the temperature difference
between the chiller-heater inlet and outlet.
(4) Absorber dilute solution temperature rises and the chiller-heater internal pressure becomes
higher.
If any one of the above phenomena is found, take preventive measures as early as possible for
the sake of the capacity and service life of the chiller-heater.
9.5.1 Mechanical cleaning
This method is effective in removing deposits and rust easily.
(1) Close the valves of water inlet and outlet piping and open the drain and air vent valves to
discharge water from the tubes and water boxes.
(2) Remove the covers of the water boxes on both sides and clean out the tube inner walls, side
plates, and water box interior with a brush.
(3) As the tubes are made of copper, use a soft bronze brush to clean the tubes. Clean the tubes
with it inserting the brush into each tube so that the tubes may not be harmed. Use of water is
more effective in cleaning. Never use a steel brush for cleaning.
(4) When cleaning is over, fit the water box covers after checking the following:
1) Checking if no corroded portions are found paying an attention to the vicinity of tube inlets,
joining parts of the tubes and side plates, and the flange contact faces of the side plates and
water boxes.
2) Check if deposits and other residuals such as brush, cloth and other foreign matters do not
remain inside the tubes and water boxes.
3) Check if the packing of the sluice plate and flange are not damaged and fitted correctly.
4) Check if the sluice plate is set in correctly between the tubes through the packing.
9.5.2 Chemical cleaning
Mineral scales forming a hard film on the tube walls, which are often hardly visible, may lower the
heat transfer performance greatly. The scales like calcium, carbonate, calcium sulfate and silicic
acid are invisible when the tubes are wet. Therefore, drain out water to dry up the inside of the
tubes before checking. Calcium scale is normally white. Silicic acid is hardly visible, but it can be
easily shaved off with a knife.
(1) The sort of scales to be deposited differs with the kind of water to be used (for example, river
water, city water, sea water.) The kind of chemical to remove the scale and cleaning method
depend upon the kind of scale deposited. This is because it is necessary to know the
composition of the scale deposited on the tubes, water boxes and pipes.
Generally, scales are classified as follows :
1) Deposit (calcium)
2) Iron rust
3) Mud
(2) Determination of chemical to be used and cleaning method
When the composition of scale is found, select the most effective chemical and cleaning
method. Generally, an inhibitor is mixed into the aqueous solution of hydrochloric acid.
General combinations are as follows :
1) Deposit ............... Week acid
It has a high calcium content and can be easily removed.
2) Iron dust ............ Strong acid and inhibitor
It is rather difficult to be removed because of its hardness. So, restrict corrosion by adding
inhibitor.
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