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Heat is generated whenever fluid
flows change from high to low pressure without producing mechanical
work. Even with good system design, 25 to 30% of the prime
mover is converted into heat.
Well designed electro-hydraulic
servo valve or proportional valve systems may convert 60 to
80% of input horsepower into heat.
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The two primary issues concerning
a plate
heat exchanger design are surface area and turbulation.
Quite simply, the more surface
area, with cold fluid on one side and hot fluid on the other,
the more cooling.
The second and equally important issue is turbulation. Turbulent
flow is critical to efficient heat transfer. As oil cools
it becomes more viscous. Thick oil tends to coagulate on the
cooling surface acting as an insulator, prohibiting heat transfer.
By varying internal baffle spacings, adding fins or turbulators,
heat exchangers can be designed to eliminate this insulating
boundary layer increasing heat transfer. In summary, the surface
area is only effective when the hot and cold fluids are allowed
to come into direct contact with it.
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