how is heat exchanger design calculate?

Q = U x A x ΔTm = The log mean temperature difference ΔTm is:

ΔTm = (T1 – t2) – (T2 – t1)

= °F. Where:

T1 = Inlet tube side fluid temperature; t2 = Outlet shell side fluid temperature;

ln (T1 – t2) (T2 – t1)