ESDU 89039 provides a method for predicting pressure drop based on an empirical correction applied to the adiabatic pressure drop which is calculated in three components: the friction component following the method of Friedel, the gravity component for which the Premoli et al correlation is used, and the momentum component using homogeneous theory. The empirical factor is derived from a correlation of experimental data drawn from the literature, mainly for water but also for a number of refrigerants, hydrogen and pentane. A table gives the scope of the experimental results together with their sources, and there are over 5000 points for vertical tubes and over 2500 points for horizontal tubes. Tables present, as a function of the boiling number, the ratio of the liquid to vapour density and the quality, the number of data points available, their mean error from the predicted values, and their standard deviation. In addition, sketches compare the predicted values with the experimental in plots against Weber number. A detailed step-by-step calculation procedure is set out, and is illustrated by a worked example. Some guidance is given for dealing with tubes at other orientations and for estimating the pressure drop at inlet to and outlet from the tube and in 180 degree bends that interconnect the horizontal lengths of serpentine coils.

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