## 1 Introduction  
Multiphase flows are considered as complicated flow phenomena compared to a single flow [1]. There are essential features of multiphase flows whose modeling outcome is contentious and structural explanation is still unexplored. The most common type of multiphase flow in almost all chemical, petroleum, and production industries is the two-phase gas/liquid flow [2, 3]. Different forms of flow patterns may be observed when two or more phases flow simultaneously [2]. In pipe cross-sections, unpredictable turbulent flow structures generating highly asymmetric volume distribution are a challenge in experiential investigations [4, 5]. This kind of unstable flow condition complicates the measurement process and may create difficulties in capturing actual flow conditions. There are also instances where the existing theoretical solution or experimental results cannot describe specific physical properties [1, 6]. Flow regimes or patterns are amongst the most significant aspects of multiphase flow. The structural flow distribution of different phases in a pipe is known as the flow pattern or flow regime. The flow regime depends on the inertia force, buoyancy force, flow turbulence, and surface tension, which are altered by fluid properties, flow rates, pipe diameter, and pipe predilection [7, 8]. Different forms of flow patterns may be observed when two phases of gas/Newtonian and gas/non-Newtonian flow simultaneously. Some of the conventional distributions are stratified flow, where the liquid and gas phase is separated, and the gas flows on top as it is lighter than the liquid; bubbly flow, where there is a dispersion of small-sized bubbles within the liquid; slug flow, in which each gas bubble forms a large slug shape (often a bullet shape); and annular flow where liquid flows as a film on the wall of the pipe. For gas/Newtonian and gas/non-Newtonian flow, several flow maps exist to predict the flow patterns. The Taitel and Dukler [7] and [PERSON] et al. [9] flow maps for gas/Newtonian flow, and the Chhabra and Richardson [10] flow map for gas/non-Newtonian flow are the most frequently used. Among the flow regimes, slug flow is the most frequent two-phase flow phenomena experienced in horizontal or near horizontal pipelines in practical applications [11, 12, 13]. The presence of slug flows in a pipeline can trigger a great range of design and operational problems, including the exertion of kinetic force on fittings and fittings, pressure cycling, control instability, and inadequate phase separation. If the flow rate is raised, much of the liquid is swept out, and the liquid handling capacity of the receiving facilities may be overwhelmed. In the case of a slug greater than the slow catcher capacity, the facilities can be flooded and destroyed. Therefore, multiple operational problems, such as pipeline network instability and damage to equipment due to high-pressure fluctuation or vibration of the system, can be caused by slug flow [14, 15]. This can also be termed a water hammering effect. Therefore, slug flow and slug frequency analysis has been one of the primary research interests in multiphase flow. To measure the hydrodynamic behavior of multiphase flow, it is essential to understand flow pattern under specific flow conditions [2, 16]. Two-phase flow implies gas and liquid flow through a pipeline system, simultaneously. The gas and liquid interface is deformable, so it is hard to predict the region occupied by a gas or liquid phase [17]. When two phases flow through a pipeline, different types of interfacial distribution can form. The variety of flow patterns mostly depends upon the input flux of the two phases, the size and assembly of the pipe, the physical properties of the fluid, etc. Many experimental studies on gas/Newtonian or solid/Newtonian fluid flow have been conducted [18, 19, 20, 21, 22, 23, 24]. Nevertheless, a limited number of studies have observed non-Newtonian multiphase flow [25, 26].