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A.
Installation instructions for PWO coolers
OLAER Fawcett Christie PWO coolers are designed
for a dynamic working pressure of 14 bar. In static conditions,
they can be suited up to 25 bar.
Inlets and outlets are clearly identified
on the OLAER sticker affixed to the front of the unit. In doubt,
oil connections are usually larger than water connections, and
fitted with a parallel thread. Water connections use taper threads.
The maximum tightening torque on the connectors is 200Nm.
The nominal cooling efficiency is achieved
by cross flowing through the plates, the oil inlet and water
inlet being located on a diagonal. (i.e. C1 oil in, C3 oil out,
C4 water in, C2 water out).
The cooler may be mounted in any position.
However, requirements for draining the circuits must be taken
into consideration.
The PWO coolers must not be installed into
a rigid frame. Use the OLAER purpose made brackets (or “armaflex”
equivalent) to provide a “soft, elastic installation”.
All piping should be done in such a way as to minimize the machine
vibrations to the cooler. When installed on the circuit return
line, the cooler must be connected using flexible hoses. Failure
to comply with mounting instructions may void the OLAER warranty.
B.
Factors effecting fouling
Temperature, turbulence, velocity, flow distribution,
surface finish and water quality all effect fouling in a cooler.
C.
Primary causes of fouling
Laminar flow is formed when the velocity in
the flow channel is uneven with low velocity next to the heat
transfer surface. When the fluid passes through a tube the highest
velocity will be at the centre of the tube, The fluid velocity
is reduced the closer it gets to the tube wall, creating a stagnant
film of low flow velocity next to the tube wall. The tube wall
has no turbulence to keep particles in the fluid in motion.
In laminar flow particles collect on the tube wall causing fouling
of the heat transfer surface. Conventional cooler types are
very sensitive to low velocities and easily get into the laminar
area.
The opposite of laminar flow is turbulent
flow. Operating with turbulent flow is the best way to avoid
fouling in coolers.
PWOs impart a high degree of turbulence to the fluid. This turbulence
keeps particles moving in the fluid and actually performs a
scouring action to keep the heat transfer surface clean. This
is accomplished by the unique design of PWOs. As the fluid passes
through the channel it is constantly changing direction, disturbing
the boundary layer and insuring turbulent flow even at extremely
low velocities. In OLAER PWO coolers water flow rate will always
be turbulent.
D.
Cleaning
Measuring of inlet and outlet temperatures
of the cooler indicates if fouling has occurred.
Fouling of the heat transfer surface decreases the heat transfer,
resulting in temperature differences lower than specified. Another
way to determine fouling is by measuring pressure drop over
the cooler. Since fouling restricts the passages and thus increasing
the velocity, this will be shown as increased pressure drop.
When using these methods make sure that the water flow rate
is as specified as changes in flow rate, of course, also effect
temperature and pressure drop.
E.
Methods of cleaning
If cleaning of the cooler is required, back-flush
with water will remove most soft deposit. If fouling appears
in shape of hard deposit, circulate a weak acid through the
cooler in reverse direction to the normal water flow. Use 5%
phosphoric acid or, for frequent cleaning, 5% oxalic acid or
similar weak acid. Afterwards rinse with a large quantity of
water to flush all acid from the cooler before starting up the
system again. Never wait until the cooler is completely clogged
before cleaning.
F.
Filters or strainers
When there are particles in the fluid that
could clog the cooler, filters or strainers should be used.
Particles up to 1mm diameter will not cause any problems.
When the water is chemically treated, please contact OLAER .
Sea water cannot be used in PWOs. For sea water applications
PWOs with titanium plates or Shell&Tubes coolers are recommended.
Ammonia cannot be used in PWOs.
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