Abstract
This work presents and analyses the results of an experimental activity aimed at the characterization of stratified air–water flow conditions, which have been poorly analyzed in previous studies although they are significant for industrial applications. Tests were performed in a 24 m long, 60 mm inner diameter PMMA pipe; the superficial velocities ranged between 0.03 m/s and 0.06 m/s for the water and between 0.41 m/s and 2.31 m/s for air. The pressure gradient along the pipeline was determined and compared to the one obtained implementing two-fluid models available in the literature. Fair agreement with the models was found only at high values of the superficial gas velocities, i.e., above 1.31 m/s. Moreover, the void fraction was measured through a resistive probe and compared with the values predicted by available models. Since none of them was able to satisfactorily predict the void fraction in the whole range of superficial velocities, a drift flux model was successfully implemented. Eventually, with both the measured pressure gradient and the void fraction, a two-fluid model was implemented in order to determine the interfacial shear stress and to compare the outcome with the literature, emphasizing the influence of the operating conditions on the prediction performance.
Highlights
IntroductionFrom the 1970s onward, multiphase flow has been studied extensively in order to provide engineers with suitable design tools [1]
The global interest in the study of multiphase flow has progressively grown in the last century since multiphase mixtures are widely encountered nowadays in industrial processes and they represent a crucial matter to be analyzed for the development and the optimization of many industrial processes [1,2].In particular, from the 1970s onward, multiphase flow has been studied extensively in order to provide engineers with suitable design tools [1]
A significant aspect in the characterization of a multiphase flow is represented by the flow pattern, i.e., the variety of configurations taken by the two phases during the flow
Summary
From the 1970s onward, multiphase flow has been studied extensively in order to provide engineers with suitable design tools [1]. Different flow patterns strongly influence transport phenomena and they have been recognized and classified and integrated, where significant, within the models in order to achieve a consistent improvement in their accuracy. Regarding air–water adiabatic flows in horizontal ducts at atmospheric pressure, object of this paper, Mandhane et al [3] provided a useful map, identifying six different flow patterns as a function of the superficial velocities of the phases. This work analyses the stratified region of the flow map, corresponding to low superficial velocities of both gas and liquid phases, which is of particular interest in many industrial areas.
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