Effect of geometry on flow field and oil/water separation in vertical deadlegs

Purpose - Corrosion in deadlegs occurs as a result of water separation due to the very low flow velocity. The present work aims to investigate the effect of geometry on flow field oil/water separation in deadlegs in an attempt for obtaining the conditions for avoiding formation of deadleg. Design/methodology/ approach - The investigation is based on the solution of the mass and momentum conservation equations of an oil/water mixture together with the volume fraction equation for the secondary phase. A fluid flow model based on the time-averaged governing equation of 3D turbulent flow has been developed. An algebraic slip mixture model for the calculation of the two immiscible fluids (water and crude oil) is utilized. Findings - Results are obtained for different lengths of the deadleg. The inlet flow velocity is kept unchanged (1.0 m/s) and the deadleg length to diamter ratio (L/D_B) ranges from 1 to 7. The considered fluid mixture contains 90 percent oil and 10 percent water (by volume). The results show that the size of the stagnant fluid region increases with the increase of L/D_B 1≈3D_B. Practical implications - Deadlegs should be avoided whenever possible in design of piping for fluids containing or likely to contain corrosive substance. When deadlegs are unavoidable, the length of the inactive pipe must be as short as possible to avoid stagnant or low-velocity flows. Originality/value - The model solves the continuity and momentum equations for the mixture, and the volume fraction equation for the secondary phase utilizing an algebraic expression for the relative velocity.