Condensation inside tubes: condensate film coefficient for vertical downflow.
Abstract:ESDU 91024 presents a procedure for calculating the local (point) condensate film heat transfer coefficient at a prescribed vapour mass flux and the mean coefficient for the case when the saturation temperature is approximately constant over the entire condensing length. It applies to flow regimes in which the flow is controlled by vapour shear at the film interface or by gravity with either a wavy laminar film or a turbulent film. Criteria to establish the transition from mist-annular to annular flow and from annular to slug flow are included. The procedure applies to co-current downward flow; for reflux condensation ESDU 89038 should be consulted. The method depends on a correlation for the local coefficient extracted from the literature that was tested against experimental data also taken from the literature. No significant trends were seen with condensate or vapour phase Reynolds number, interfacial shear stress, vapour mass fraction or flow regime parameter (a parameter giving a non-dimensional gas phase velocity). Typical correlation plots illustrate that behaviour and show the data correlate within 30 per cent. The treatment of vapour desuperheating is considered, and the effect of condensate sub-cooling is treated. Step-by-step calculation procedures are presented and their use illustrated by a worked example.
|Data Item ESDU 91024