Question

Water (specific heat = 4 kJ/kg K) enters
a cross flow exchanger (both fluids
unmixed) at 15 degree Celsius and flows
at the rate of 7.5 kg/s. It cools air (C P =
1 kJ/kg K) flowing at the rate of 10 kg/s
from an inlet temperature of 120 degree
Celsius. For an overall heat transfer
coefficient of 780 kJ/m2 hr degree and
the surface area is 240 m2, determine
the NTU​

Answer 1

Answer:

Given,

the overall heat transfer coefficient (U) = 780 kJ/m2 hr

                                                  = (780 x 103/(3600))

                                                  = 216.67 w/m2 sec

Cmin.= mCp= 1x103 x10= 104

Surface area =  240 m2

NTU = U A/C min =  (216.67 x 240/ 104 )

                        = 5.2

Explanation: