Out of the following four assumptions used in the derivation of the equation for LMTD [LMTD = (Δt1 – Δt2)/ln(Δt1/Δt2)], which one is subject to the largest deviation in practice ?

A. Constant overall heat transfer co-efficient.
B. Constant rate of fluid flow
C. Constant specific heat
D. No partial phase change in the system