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A cross-flow type air heater has an area of 50 m2. The overall transfer coefficient is 100 W/m2 K; and heat capacity of the stream, be it hot or cold, is 1000 W/K. What is the NTU?

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  1. 500
  2. 50
  3. 5
  4. 0.5

Answer (Detailed Solution Below)

Option 3 : 5
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Detailed Solution

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Concept:

NTU is a measure of the effectiveness of the heat exchanger.

The NTU is a measure of the heat transfer size of the exchanger; larger the value of NTU, the closer the heat exchanger approaches its thermodynamic limit.

Cmin is the minimum heat capacity between the hot and cold fluid

Calculation:

Given:        

A = 50 m2, U = 100 W/m2 K,

Cmax = Cmin = 1000 W/K

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