Afshin J. Ghajar | afshin.ghajar@okstate.edu
School of Mechanical and Aerospace Engineering, Oklahoma State University
Stillwater, OK 74075 USA
Abstract: Non-boiling gas-liquid two phase flow phenomenon finds its wide application in engineering processes pertaining to petroleum, nuclear, refrigeration and chemical industries. The two phase flow parameters such as flow patterns, void fraction, pressure drop and heat transfer are the important elements in design of any engineering process involving two phase flow. The non-boiling gas-liquid two phase flow in vertical upward pipe orientation is extensively studied in past few decades while little attention has been paid to the two phase phenomenon in vertical downward pipe orientation. The central complexity involved in the gas-liquid two phase flow is the compressibility nature of the gas phase and a significant influence of varying flow patterns on the process design parameters such as void fraction, pressure drop and heat transfer. The change in the pipe orientation is observed to have a prominent effect on the general appearance and occurrence of the flow patterns and on the pressure drop and heat transfer characteristics of the two phase flow.
The objective of this keynote lecture is to compare and contrast the flow patterns, void fraction, pressure drop and convective heat transfer in vertical upward and vertical downward pipe orientations. The similarities and differences observed in these two phase flow parameters will be discussed with reference to the interaction of buoyancy, gravity and inertia forces. Two phase flow models available in the literature for predicting void fraction, pressure drop and heat transfer in vertical upward and downward orientations will be reviewed. The validity of application of Reynolds analogy to predict non-boiling heat transfer in vertical upward and downward two phase flow will also be discussed. Further, the performance of a recent void fraction correlation developed at the Oklahoma State University's Two Phase Flow Laboratory will be verified against a comprehensive data set and the performance of other competent correlations. Finally, to assist design engineers in selecting right correlation for a specific range of two phase flow conditions, the top performing correlations to predict pressure drop and non-boiling heat transfer in vertical upward and downward orientation will be recommended.
Keywords: Non-boiling two phase flow, flow patterns, void fraction, pressure drop, heat transfer, Reynolds analogy