Heat Exchanger Duty (U·A·LMTD)
Heat Exchanger Duty (U·A·LMTD)
Once the LMTD is known, the exchanger’s heat duty follows from its surface area and overall heat-transfer coefficient.
The heat duty is Q = U·A·ΔT_lm. where U is the overall heat-transfer coefficient, A the area and ΔT_lm the log-mean temperature difference.
Inputs
U := 500 W/(m^2·K)=500 kg/K/s^3
A := 12 m^2=12 m^2
dT_lm := 34 K=34 K
Multiply coefficient, area and driving temperature difference.
Q := U·A·dT_lm=204000 W
Results
Rearranged as A = Q/(U·ΔT_lm), the same relation sizes the exchanger for a required duty. A higher U (clean surfaces, turbulence) shrinks the area needed.
Assumptions & limitations
- Constant U over the surface.
- Steady state.
- LMTD valid for the flow arrangement.