Condensation of Steam

Steam is frequently used as heating medium. The mean temperature difference is given here:  A pure, saturated, vapour will condense at a fixed temperature, at constant pressure. For an isothermal process such as this, the simple LMTD can be used in equation 1.3; no correction factor for multiple passes is needed. The LMTD will be given by:

ΔT m =            (t2 – t1)               (eq. 1.34)

ln [(Tsat-t1)/(Tsat-t2)]

Where T sat  =     saturation temperature of the vapour,

t1     =     inlet coolant temperature,

t2     =     outlet coolant temperature.

When the condensation process is not exactly isothermal but the temperature change is small; such as where here is a significant change in pressure; the LMTD can still be used but the temperature correction factor will be needed for multipass condensers. The appropriate terminal temperatures should be used in the calculation.