3. Temperature Data
Define the Temperature variables as:
t1 = Entering Water Temperature
T1 = Entering Air Temperature
t2 = Exiting Water Temperature
T2 = Exiting Air Temperature
89.6 ° °F
4. 1st Law Energy Balance
Q = ma2o Cp_H2O (ATH20) = mair Cp_air (ATair)
a) Q - heat transferred from H2O to air (Btu/hr).
b) Airflow (CFM)
5. As - Calculating the Surface Area of the Heat Exchanger
Using the dimensions of the Heat Exchanger from Page 1, calculate the surface area of the
water side. The flattened tubes are so thin that only their width (W) needs to be considered.
6. ATLM - Calculating the Log Mean Temperature Difference
Crossflow Heat Exchangers use a Counter Flow heat exchanger model, to determine the Log
Mean Temperature Difference (LMTD) or ATtM, the best method to determine the average
Temperature difference between the two fluids from one end of the heat exchanger to the
LMTD = in
7. Correction Factor - Fc
Using the Table below, Calculate the correction factor.
1.0 .0.8.0.6.0.4 0.2
T1 - T2
t2 - ty
(c) Single-pass cross-flow with both fluids unmixed
1 - inlet
t - tube side
T - shell side
8. U - Calculating the Heat Exchanger Coefficient
Q = U As (ATLM) Fc
Calculate the Heat Exchanger Coefficient U in Btu/hr*ft²*F.
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