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 [(T_sat-t1)/(T_sat-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.   

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Introduction | Combined heat transfer process | Heat transfer in cooling tower | Variables affecting performance of CT heat transfer | Heat transfer within cooling system (heat exchanger) | Types of heat exchanger | Basic design procedure and theory | Designing a test heat exchanger | Log Mean Temperature difference | L.M.T.D. Correction factors | Overall heat transfer coefficient | Elaborated method for calculating U values | Effect of scale formation | Condensation of steam | Condenser, where the hot fluid temperature varies | Significance of pressure | Significance of flow rate | Methods of checking steam condenser performance | Common conversion factors