An experimental study of two-phase flow in idealised tube bundles

Abstract

This thesis reports on an experimental study of air-water mixtures flowing through idealized shell and tube, in-line and staggered heat exchangers. The measured void fractions in the maximum and minimum gaps between the tubes are reported at near atmospheric conditions, to give local variations for different tube diameters and tube bundle arrangements. The void fraction measurements were made using a gamma-ray densitometer. The pressure drops in the tube bundles are also reported. These data are compared with the correlations available in the open literatures to investigate the void fraction and pressure drop prediction methods for these heat exchangers. The in-line 38 mm tube bundle is shown to provide no significant effect on void fraction or drag force when compared with the 20 mm tube diameter bundle. A new void fraction model is therefore proposed by modifying the characteristic length of an existing slip ratio method. A new pressure drop model is presented. The acceleration pressure drop between the tubes from the separation to re-attachment is shown to be responsible for some of the frictional pressure drop with a liquid film on the tubes responsible for the remainder. The staggered bundle shows the bundle arrangement gives different void fraction and different pressure drop data when compared to the in-line bundle.