Two-phase flow pressure drops through thin and thick orifices have been numerically investigated with air–water flows in horizontal pipes. Two-phase computational fluid dynamics (CFD) calculations, using the Eulerian–Eulerian model have been employed to calculate the pressure drop through orifices. The operating conditions cover the gas and liquid superficial velocity ranges Vsg = 0.3–4 m/s and Vsl = 0.6–2 m/s, respectively. The local pressure drops have been obtained by means of extrapolation from the computed upstream and downstream linearized pressure profiles to the orifice section. Simulations for the single-phase flow of water have been carried out for local liquid Reynolds number (Re based on orifice diameter) ranging from 3 × 104 to 2 × 105 to obtain the discharge coefficient and the two-phase local multiplier, which when multiplied with the pressure drop of water (for same mass flow of water and two phase mixture) will reproduce the pressure drop for two phase flow through the orifice. The effect of orifice geometry on two-phase pressure losses has been considered by selecting two pipes of 60 mm and 40 mm inner diameter and eight different orifice plates (for each pipe) with two area ratios (σ = 0.73 and σ = 0.54) and four different thicknesses (s/d = 0.025–0.59). The results obtained from numerical simulations are validated against experimental data from the literature and are found to be in good agreement.
SUMMARYTheoretical studies have been made to determine the pressure drops caused by abrupt flow area expansion/contraction in small circular pipes for two-phase flow of air and water mixtures at room temperature and near atmospheric pressure. Two-phase computational fluid dynamics (CFD) calculations, using Eulerian-Eulerian model (with the air phase being compressible for pipe contraction case) are employed to calculate the pressure drop across sudden expansion and contraction. The pressure drop is determined by extrapolating the computed pressure profiles upstream and downstream of the expansion/contraction. The larger and smaller tube diameters are 1.6 and 0.84 mm, respectively. Computations have been performed with single-phase water and air, and two-phase mixtures in a range of Reynolds number (considering all-liquid flow) from 1000 to 12 000 and flow quality from 1.2×10 −3 to 1.6×10 −2 . The numerical results are validated against experimental data from the literature and are found to be in good agreement. The expansion and contraction loss coefficients are found to be different for single-phase flow of air and water, and they agreed reasonably well with the commonly used theoretical predictions. Based on the numerical results as well as experimental data, correlations are developed for two-phase flow pressure drops caused by the flow area contraction as well as expansion.
Purpose -The purpose of this paper is to compute the pressure drop through sudden expansions and contractions for two-phase flow of oil/water emulsions. Design/methodology/approach -Two-phase computational fluid dynamics (CFD) calculations, using Eulerian-Eulerian model, are employed to calculate the velocity profiles and pressure drops across sudden expansions and contractions. The pressure losses are determined by extrapolating the computed pressure profiles upstream and downstream of the expansion/contraction. The oil concentration is varied over a wide range of 0-97.3 percent by volume. The flow field is assumed to be axisymmetric and solved in two dimensions. The two-dimensional equations of mass, momentum, volume fraction and turbulent quantities along with the boundary conditions have been integrated over a control volume and the subsequent equations have been discretized over the control volume using a finite volume technique to yield algebraic equations which are solved in an iterative manner for each time step. The realizable per phase k-1 turbulent model is considered to update the fluid viscosity with iterations and capture the individual turbulence in both the phases. Findings -The contraction and expansion loss coefficients are obtained from the pressure loss and velocity data for different concentrations of oil-water emulsions. The loss coefficients for the emulsions are found to be independent of the concentration and type of emulsions. The numerical results are validated against experimental data from the literature and are found to be in good agreement.Research limitations/implications -The present computation could not use the surface tension forces and the energy equation due to huge computing time requirement. Practical implications -The present computation could compute realistically the two-phase pressure drop through sudden expansions and contractions by using a two-phase Eulerian model and hence this model can be effectively used for industrial applications where two-phase flow comes into picture. Originality/value -The original contribution of the paper is in the use of the state-of-the-art Eulerian two-phase flow model to predict the velocity profile and pressure drop through industrial piping systems.
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