A method is presented to represent a curve by means of a polygonal. The curve, defined in a given interval, is divided into several arcs, and linear chords are drawn between the limits, such that the lines are close enough to the curve to satisfy a convergence criterion. The criterion states that the approximation is satisfactory if the ratio between the area under the curve arc and the area under the straight segment is equal to 1 within a prescribed error. The procedure is proposed to make a curve enthalpy-temperature relationship, usually encountered in condensation problems, behave as a set of linear legs of a polygonal. Hence, if the coolant enthalpy relationship is, or is assumed to be, linear in the whole interval, the nonlinear problem can be divided into a set of several linear ones, where local transfer equations can be posed and solved based on the local heat transfer coefficient and the local logarithmic mean temperature difference. The method was tested with good results in different condensation problems involving mixtures of vapors and pure vapors containing a noncondensing gas.
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