According to the condition NTU should be between 1.5 to 2. Therefore the above mean temperature value can be accepted.

 

TRIAL 1: To Calculate the Diameter of the Drier

Air entering the drier is 50723.27 lbs/h. But for designing purpose air is taken in excess so that the loss of heat from the drier is compensated.

Air entering the drier can be taken as ~ 51000 lb/hr.

Assume that the maximum superficial air mass velocity to be = 1000 lb/ (hr ft²)

D = (4*51.837/π)^0.5 = 8.07 ft = 2.46 m

Similarly length of the dryer can be calculated by using following equation

Q = U_a × S × Z × (ΔT)_M

Where,

Q = Total heat, Btu/Hr

Z = Length of drier, ft

S = heat transfer area, ft²

Before that we need to calculate the overall heat transfer coefficient from:

G_G = Maximum superficial air mass velocity, lb/ft² Hr

U_a = Overall heat transfer coefficient (volumetric), Btu/Hr ft³ ° F

D = Diameter of the drier in ft.

∴ Length of the drier

Z/D ratio check:

Which checks the condition that the Z/D ratio is between 3- 10. Therefore the above diameter and length can be accepted.