Problem 14-1 - Example 14-1 Air enters the inner tube of a...

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Example 14-1 Air enters the inner tube of a parallel flow double-pipe heat exchanger at 90°C with a mass flow rate of 0.03 kg/s. Water enters the outer tube through a duct of diameter 3 cm at a velocity of 8 m/s and a temperature of 10°C. The inside diameter of the inner tube is 4 cm and the overall heat transfer coefficient based on this diameter is 170 W/m 2 K. The length of the heat exchanger is 0.6 m. Find the outlet fluid temperatures. Solution: First find the heat capacity rates. For the cold (water) side C mA ρ = ± V () 2 2 3 kg m 1 m 999 8 1.5 cm ms 1 0 0 c m C m π ⎛⎞ = ⎜⎟ ⎝⎠ ± kg 5.65 C m s = ±
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, o kg J 5.65 4200 sk g C CC p C Cm c ⎛⎞ == ⎜⎟ ⎝⎠ ± o W 23730 C C C = For the hot (air) side , o kg J 0.03 1005 g C HH p H c ± o W 30.1 C H C = The smaller heat capacity rate is on the air side, min o W 30.1 C H min min ii i i UA U DL NTU π () 2 o W1 m 170 π 4cm 0.6 m m K 100 cm W 30.1 C NTU = 0.426 NTU = For a parallel flow double-pipe heat exchanger
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Problem 14-1 - Example 14-1 Air enters the inner tube of a...

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