![]() ![]() When heat is transferred as a result of a change of phase like condensation or evaporation the temperature of the primary or secondary fluid remains constant. AMTD will in general give a satisfactory approximation for the mean temperature difference when the smallest of the inlet or outlet temperature differences is more than half the greatest of the inlet or outlet temperature differences. T so = secondary outlet temperature ( oF, oC)Ī linear increase in the secondary fluid temperature makes it more easy to do manual calculations. T si = secondary inlet temperature ( oF, oC) T po = primary outlet temperature ( oF, oC) T pi = primary inlet temperature ( oF, oC) AMTD (or DT AM) - Arithmetic Mean Temperature DifferenceĪMTD = (t pi + t po) / 2 - (t si + t so) / 2 (2)ĪMTD = Arithmetic Mean Temperature Difference ( oF, oC).Arithmetic Mean Temperature Difference - AMTDĪn easier but less accurate way to calculate the mean temperature difference is the The Logarithmic Mean Temperature Difference is always less than the Arithmetic Mean Temperature Difference. LMTD = Logarithmic Mean Temperature Difference ( oF, oC)ĭt i = t pi - t si = inlet primary and secondary fluid temperature difference ( oF, oC)ĭt o = t po - t so = outlet primary and secondary fluid temperature difference ( oF, oC)ĭt i = t pi - t so = inlet primary and outlet secondary fluid temperature difference ( oF, oC)ĭt o = t po - t si = outlet primary and inlet secondary fluid temperature difference ( oF, oC) LMTD = (dt o - dt i) / ln(dt o / dt i) (1) LMTD (or DT LM) - Logarithmic Mean Temperature Difference. ![]() A logarithmic mean temperature difference is termed The rise in secondary temperature is non-linear and can best be represented by a logarithmic calculation. Logarithmic Mean Temperature Difference - LMTD The temperature profile in the primary fluid is not dependent on the direction of flow. With saturation steam as the primary fluid the primary temperature can be taken as a constant since the heat is transferred as a result of a change of phase only.
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