The present work introduces experimental investigations of a real reverse osmosis (RO) plant. Flowrate and pressure measurements have been performed. The pump pressure fluctuations at different flowrates and the permeate pressure of RO membrane at different seawater salinities have been measured experimentally. The results of the present experimental measurements and some of the previously published experimental results of RO membrane have been compared with the corresponding theoretical results of the plant theoretical model in order to validate the simulation program (presented in part 1 of this paper). In the present work the validated simulation model has been used to carry out prediction study to investigate the dynamic characteristics of the plant axial piston pump and the RO membrane performance under normal and abnormal operating conditions. The RO plant simulation model has been used to present a proposed operational chart for the investigated desalination plant in case of working under different feed water salinity and temperature.
Vortex formation and shedding downstream obstructions may be assumed to be one of the main sources of flow induced vibration and noise in pipes, ducts, and control valves. The level of the produced noise depends on the size of the formed vortex and its shedding frequency hence, controlling the size of the formed vortex may be one of the main factors that help in attenuation of the generated noise. The vortex size may be estimated from the reattachment length of the separated flow downstream these obstructions. In the present work, vortex formation downstream a single orifice and two orifices in series in a rectangular duct have been investigated numerically and experimentally. A numerical solution has been coded to solve the flow governing equations in the primitive variables using the finite difference technique. The solution has been carried out for laminar, 2-D and incompressible flow field at Reynolds number ranges from 50 to 400 for orifice height to duct height ratio of 0.5 and for the inter distance between the two orifices from 0.2H to 7H. The velocity field, the streamlines, and the vorticity field have been determined. The code is written in visual C-language to achieve low computational time and lower number of iterations. An experimental investigation has been carried out on 2-D laminar flow visualization table. The streamlines of water flow throughout the single orifice and two orifices in the rectangular duct have been visualized for various Reynolds number and orifice height to duct height ratio, D/H, values. The experimental and the theoretical results showed a considerable agreement. The results showed a minimum vortex size as well as lowest circulation in case of using an inter distance of about (1-D/H). Finally, the results showed that the control of the inter distance between the two orifices or similarly between any two obstructions in a rectangular duct may be of special interest to reduce the size of the generated vortex and consequently to attenuate the vibration and noise.
Marine risers used to convey oil from the sea bed to the sea level, marine cables, heat exchanger pipes, civil engineering structures and aircraft wings vibrate due to the formation of the vortex streets behind these structures. The interactions between the flow oscillations and the structure give rise to complicated vibrations of the structure which could cause structural damage due to the fatigue. Numerical simulation of the vortex-induced vibrations on circular cylinders is used to investigate the possibility of suppressing these vibrations for different engineering applications. The unsteady, incompressible, two-dimensional Navier-Stokes equations are solved numerically on a structured grid using the finite difference method. The effect of flow control using the boundary layer suction for fixed or moving cylinder is investigated by applying the appropriate boundary conditions on the cylinder surface. In the current study, natural motion of the cylinder is not considered. Flow oscillations are investigated only for fixed cylinder and for forced motion of the cylinder. The results indicate that the flow oscillations are completely damped for a fixed cylinder using suction on the cylinder surface. For forced motion of the cylinder, the vortex shedding from the surface is eliminated using the boundary layer suction. The flow oscillates only due to the forced motion of the body vibrations which means that the flow oscillations can be damped completely if the cylinder is left to oscillate naturally.
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