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At the flow diagram
stage there are usually many variables, such as temperatures,
pressures, flow rates and the like, which can be changed within
limits. Later on, these factors become set as fixed quantities. It is
well to recognize during the design of the system that they do have an
influence on the size and cost of heat exchange equipment.
•Temperatures of heating and cooling media
A higher heating media temperature results in a smaller heat exchanger
for a given heating load. Limitations of materials must be kept in
mind here.
•Pressure drops permitted by the system affect heat exchanger size
The highest allowable pressure drop will result in substantial savings
in heat exchanger size.
•Length restriction sometimes affect heat exchanger costs
However, there are so many exceptions and limiting conditions that we
cannot simply say ‘‘the longer the cheaper."
•Materials of construction
Corrosive tendencies and purity requirements of fluids being handled.
Often, the choice here is based on reliable data and experience. |
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