Heat transfer to oil-water flow in horizontal and inclined pipes: Experimental investigation and ANN modeling Milad Boostani a , Hajir Karimi a, * , Sadra Azizi b a Department of Chemical Engineering, Yasouj University, Yasouj 75914-353, Iran b Young Researchers and Elite Club, Yasouj Branch, Islamic Azad University, Yasouj, Iran article info Article history: Received 19 February 2016 Received in revised form 12 June 2016 Accepted 6 September 2016 Keywords: Heat transfer Oil-water flow Flow pattern Inclined pipe Artificial neural network abstract In this work, local heat transfer coefficients (HTC) and different flow patterns of oil-water two-phase flow in a horizontal and slightly upward inclined (þ4  and þ7  ) pipe were investigated. The test section was an 11 mm inner diameter (ID) copper pipe with a length to diameter ratio of 164. Water and diesel fuel (2.49 mPa s viscosity and 798 kg/m 3 density) were selected as immiscible liquids and high speed photography technique was used for the flow pattern identification. The superficial Reynolds numbers ranged from 1350 to 13,700 for water and 300e3700 for oil. The experimental results indicated that the oil-water heat transfer is dependent on the inclination angle and flow pattern. As the pipe inclination angle increases averaged HTC values for each flow pattern increases. It was found that the effect of the flow pattern on the oil-water HTCs is higher than the pipe inclination. In addition, an artificial neural network (ANN) model was developed for predicting the HTC of oil-water two-phase flow in the studied different inclination angles of pipe. Superficial oil Reynolds number (Re so ), superficial water Reynolds number (Re sw ), inclination angles (IA) and some numbers appropriated for each flow pattern (FPN) were selected as input variables, whereas two-phase HTC (h TP ) values were selected as output variables. The ANN was trained, validated and tested against the experimental data. The obtained optimal ANN model had good prediction for all of the positions and all flow patterns. Mean absolute percent error (MAPE) of 1.98% and correlation coefficient (R) of 0.993 for testing data set and MAPE of 1.81% and R value of 0.995 for all data sets were achieved. © 2016 Elsevier Masson SAS. All rights reserved. 1. Introduction The oil-water two-phase flow in pipes is commonly observed in many industries, such as petrochemical processes, extraction pro- cesses, tubular reactors, heat exchangers and crude oil production and transportation through both horizontal and inclined pipes. Estimating heat transfer rate is demanding in all of the above processes for economical design and optimized operation. It is of great interest to know how the two-phase heat transfer rate varies with flow rates, flow pattern and pipe inclination. Therefore, it is very important to test the various factors affecting the oil-water flows and develop new models to gives accurate prediction. Most of the reported two-phase heat transfer studies concern gas-liquid heat transfer. For instance, the influences of flow pattern, velocity of each phase and pipe inclination on the gas-liquid heat transfer have been studied experimentally by several researchers [1e6]. The characteristics of oil-water flow are generally different from gas-liquid flow, because of lower density difference between the two phases, lower viscosity ratio and more complex interfacial forces [7]. The complexity in oil-water two-phase flow makes it harder to predict the heat transfer rate. Limited studies on heat transfer to oil-water flow in pipes have been performed compared with the gas-liquid heat transfer. Some methods for calculating the heat transfer of oil-water flow in hor- izontal pipes have been published, such as developing the empirical correlations [8,9] and theoretical models [10e12]. However, there is no model applicable for predicting the heat transfer coefficient for a variety of flow patterns and pipe inclination angles. In addition, some of these methods cannot be employed in situations when high accuracy is required. The understanding of the oil-water flow behaviour is very important in field development and in oil production. The tem- perature difference between the hydrocarbon fluids and the seawater results in wax deposition blockage [6]. In addition, owing * Corresponding author. E-mail address: hakar@yu.ac.ir (H. Karimi). Contents lists available at ScienceDirect International Journal of Thermal Sciences journal homepage: www.elsevier.com/locate/ijts http://dx.doi.org/10.1016/j.ijthermalsci.2016.09.005 1290-0729/© 2016 Elsevier Masson SAS. All rights reserved. International Journal of Thermal Sciences 111 (2017) 340e350