(C) 2006
Harry R Cripps |
## Principles of heat exchangers## Simplified heat exchanger conceptsHeat exchangers work because heat naturally flows from higher temperature to lower temperatures. Therefore if a hot fluid and a cold fluid are separated by a heat conducting surface heat can be transferred from the hot fluid to the cold fluid.
The rate of heat flow at any point (kW/m2 of transfer surface) depends on: - Heat transfer coefficient (U), itself a function of the properties of the fluids involved, fluid velocity, materials of construction, geometry and cleanliness of the exchanger
- Temperature difference between hot and cold streams
- Heat transfer surface area (A)
- Heat transfer coefficient
- Average temperature difference between the streams, strictly the log mean (DT
_{LM})
_{LM}
- But the larger the area the greater the cost of the exchanger
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