Critical Evaluation of Friction Pressure-Drop Prediction Methods for Gas-Liquid Flow in Prediction Methods for Gas-Liquid Flow in Horizontal Pipes Available data for friction pressure drop in horizontal, two-phase flow are used to compare and to evaluate 16 correlations and models. In a proposed two-step prediction method, an expected flow pattern is predicted on the basis of the system variables. The correlation I recommended for use with that flow regime is used to predict the friction pressure drop. Introduction A large number of correlations and models exist in the literature for dealing with various aspects of the flow of gas-liquid mixtures in pipes. One of the purposes of this paper is to help ease the task of the designer who must paper is to help ease the task of the designer who must ultimately select one of these methods for use in a particular problem. It reports the results of a detailed particular problem. It reports the results of a detailed comparison study of correlations and models for predicting friction pressure drop in horizontal gas-liquid flow. The results of other studies carried out to evaluate flow pattern maps and liquid holdup prediction methods for two-phase flow in horizontal and upward-inclined pipes are reported elsewhere. Previous Evaluation Studies Previous Evaluation Studies In 1964, Dukler et al. presented a critical comparison of the correlations of Baker, Bankoff, Chenoweth and Martin, Lockhart and Martinelli, and Yagi. Predictions by these methods were compared with culled Predictions by these methods were compared with culled experimental data contained in the AGA/API Data Bank that was compiled at the U. of Houston. The Lockhart and Martinelli correlation was found to give the best over-all agreement with the data. However, even this method was not consistently good, and it was concluded that a definite improvement could be made. The result of their study led Dukler et al. to propose a new correlation for two-phase friction pressure drop based on similarity analysis. Recently, Hernandez and Brill compared the correlations of Beggs and Brill, Dukler et al., Eaton et al.; and Guzhov et al. with the experimental data of Eaton and Beggs. Perhaps not too surprisingly, they found that the Eaton et al. correlation was in the best agreement with Eaton's data and the Beggs and Brill correlation was in the best agreement with Beggs' data. However, the Dukler et al. correlation was found to be in the best over-all agreement with all the data used in their study. Approach Followed in This Study The approach followed in this study is similar to that outlined in detail in an earlier paper dealing with liquid holdup correlations. A brief summary of the approach follows.About 10,500 friction pressure-drop observations contained in the U. of Calgary Multiphase Pipe Flow Data Bank were used as a basis for evaluating the accuracy of the correlations considered in this study.The data were grouped by predicted flow pattern using the Mandhane et al. flow pattern map as a basis.Each correlation was then tested against all the data points contained within each flow pattern grouping. points contained within each flow pattern grouping.After examining the values of five different error parameters, a correlation was selected for each predicted parameters, a correlation was selected for each predicted flow pattern as being in best over-all agreement with the corresponding experimental data. (In this paper, we have multiplied error parameters appropriately to avoid decimal numbers. The multipliers are given in the Nomenclature.) JPT P. 1348