A STUDY OF AIR-OIL TWO-PHASE FLOW IN A HORIZONTAL STRAIGHT PIPE

Abstract

<p>Air-oil flows are found in many industrial applications, including lubrication systems for high-speed machining and jet engines. Understanding the interaction of the two phases, and the effect flow characteristics have on pressure drop, are important to design lubrication systems. Applying pressure drop models without taking flow regime into account has been shown to result in large prediction errors.</p> <p>The overall objective of this research is to gain a better understanding of air-oil two-phase flow in a 1/2" ID horizontal straight pipe. The two key goals are to correct flow regime identification and pressure drop predictions. A new air-oil two-phase experimental facility was designed and commissioned. The facility can accommodate multiple test section geometries. Pressure drops for a wide range of test conditions were measured. Flow regimes were identified with the aid of a high-speed video camera.</p> <p>A capacitance sensor was developed to measure instantaneous void fraction and to obtain useful information to identify flow regimes. Three existing flow regime maps used for identification were evaluated using the current air-oil data. Significant errors in the prediction of the transitional boundaries of these maps were found. Corrections to the transitional boundaries to improve the overall prediction accuracy of the maps are suggested. The Mandhane et .al. (1974) flow regime map with suggested corrections was found to most accurately predict the transitional boundaries.</p> <p>Several existing pressure drop models were evaluated with data from the new test facility. The Chisholm (1973) and Martinelli (1948) models were found to have the highest accuracy with 40% RMSE. A correction factor was applied to the Martinelli model, resulting in 19% RMSE. Recommendations on the appropriate model for each identified flow regime are also made. Particular attention is paid to the prediction of pressure drop in the mist flow regime, due to the industrial applications of the regime.</p>