The Role of Drops in Annular Gas-Liquid Flow: Drop Sizes and Velocities

Abstract

Methods of measurement and data obtained for drop sizes and velocity in annular gas/liquid flow have been reviewed. In particular, possible sources of bias of bias in the results have been examined. The interrelation of data from different sources is considered and regions where different behaviour predominates are identified. (Received 15 November 1987) 1. INTRODUCTION The occurrence of annular gas-liquid two-phase flow in many pieces of industrial equipment has resulted in it being the subject of a large number of studies over the last thirty years. Though the liquid film travelling on the channel walls received much early attention, it is only recently that developments in diagnostic equipment has permitted detailed measurement of the properties of the drops carried in the central gas core.Drops are important because they affect pressure drop, heat and mass transfer and processes like erosion, erosion/corrosion and corrosion. One primary effect of the existence of drops is that liquid is removed from the film. In pressure drop the film acts as rough surface over which the gas flows. If not all of the liquid travels in the film, allowance will have to be made for this in calculating the pressure drop. In heated systems, the formation of drops by entrainment or atomisation of liquid can result in the liquid film drying out well before all of the liquid is evaporated. This can occur because the entrainment rate is greater than the accompanying rate of redeposition. Dryout of the film results in a deterioration of heat transfer. In heat flux controlled systems, a sharp increase in wall temperature occurs and the vapour temperature rises above the saturation temperature causing the wall temperature to increase even further so as to maintain the temperature difference. Evaporation of the liquid drops keeps the vapour and wall temperatures down. The degree of temperature reduction depends on the size and velocities of the drops created in the annular flow region of the equipment. In the case of mass transfer, removal of dust or chemical species depends on the size of the drops and the

Drop size measurements for annular two-phase flow in a 20 mm diameter vertical tube

“…It is not surprising that the drop size equation developed by Tatterson et al (1977) gives poor predictions of the drop size data from this study. Perhaps more interesting, is that Tatterson's model gives good predictions of the data of Lopes which was shown by Azzopardi (1988) to have been taken at flow rates where the bag breakup mechanism would be expected. Azzopardi et al (1980) andlater, Lopes (1985) suggest that drop entrainment by the ligament break-up mechanism, is a two stage process.…”

Μελετη Δακτυλιοειδους Διφασικης Ροης Σε Οριζοντιο Αγωγο

“…Η μέση διάμετρος των σταγονιδίων εκτιμάται από έναν ημιεμπειρικό τύπο της βιβλιογραφίας (Εξ. 2.4-17) (Azzopardi, 1988) Αβεβαιότητα επικρατεί ακόμη σχετικά με την πραγματική κατανομή της ταχύτητας των σταγονιδίων και του αερίου, η οποία χρησιμοποιείται για τη μετατροπή των τοπικών πυκνοτήτων ροής σε συγκεντρώσεις σταγονιδίων. Η μεγαλύτερη απόκλιση ανάμεσα στα πειράματα και τις προβλέψεις του μοντέλου εμφανίζεται σε μεγάλες παροχές υγρού, όπου έχει διαπιστωθεί έντονη περιφερειακή ασυμμετρία των διαταραχών της υγρής στοιβάδας.…”