Falling film evaporation in vertical tubes.
Abstract:ESDU 98010 provides a guide to the design and operation of falling film evaporators under steady state conditions with pure component fluids. Correlations derived from an analysis of experimental data extracted from the literature are provided for predicting the local film heat transfer coefficient for flow inside plain vertical tubes of circular cross section. The background to the correlations is described fully, and a calculation procedure that predicts, using the new correlations, the tube length required for a particular duty is laid out and illustrated fully by a worked example. The effect of vapour shear is considered and limits due to minimum wetting rate and the onset of nuclear boiling are defined. The leading design details and practical operating characteristics of falling film evaporators are discussed. The mechanism of heat transfer is discussed, the various flow regimes that can occur in the annular film over the practical range of operating conditions and at specific locations within the evaporator are outlined and their effects on the film coefficients, for which equations are provided, are explained. The scope of the data bank that was used to derive the new correlations is stated and the performance of the new equation for Nusselt number against the data is illustrated graphically. A full bibliography is provided.
|Data Item ESDU 98010|