Pressure Reducing Test And Numerical Analysis On The Flow Characteristics Of Surfactant In Pipeline

Using surfactant solution in heating and cooling system and long distance transportation pipeline could depress the turbulent friction, reduce pumping power and increase system transmission efficiency. The research of surfactant drag-reducing flow at present mainly on straight pipe flow and lack of research on elbow pipe flow in heating system.Low and medium concentration of surfactant solutions got the shear thinning characteristics, thus Carreau-Bird model could be used to fit four different concentration of surfactant solutions’ shear viscosity variation curve of shear rate. Adj. R-square for four different concentration of surfactant solution are 0.9428, 0.9626, 0.9958, 0.9945,and the ideal fitting result show that numerical simulation of surfactant flow with Carreau-Bird model is reliable.The improper setting of operating pressure in heating system will cause operating pressure change ups and downs. High pressure in pipe not only give rise to water and electric waste,but also cause pipe network leakage and damage. Furthermore, high pressure of return water from high-rise buildings in directly connected heating system also need to be reduced. The pressure reducing device can effectively lower the pressure in pipelines by setting the opening degrees of fence structure. We calculated decompression efficiency of the pressure reducing device through model test. The results shows that decompression efficiency of the pressure reducing device increased with the openging degree of fence structure increased and reached the maximum value at 30° when inner side and out side become centrosymmetric. On the contrary, the decompression efficiency of pressure reducing device decreased with Reynolds number increased.CFD software FLUENT is implemented to conduct numerical simulation of water and different concentration of surfactant flow when passed through pressure reducing device, natural compensator and square compensator in heating system. Surfactant flow lower the turbulent intensity where section changes greatly when passed through pressure reducing device, the decompression efficiency of surfactant flow decreased 7.47% ~ 16.95% compared with water flow, and the inhibition rate of surfactant solution increased first and then decreased with concentration increased. The velocity recovery zone length of surfactant flow after pressure reducing device were shorter than water ranges from 10.67% to 16.52%, which illustrated the surfactant flow enhanced transport ability.Surfactant flow lower the secondary flow and vortex intensity which formed at elbow part of compensator so that the energy loss caused by them could be reduced. Numerical simulation results show that the local loss interactive coefficient of surfactant flow first increased and then decreased with its concentration increased, indicating that the surfactant solution got a optimum drag reducing concentration.The local loss interactive coefficient of surfactant flow ranges from 0.79 to 0.81 when passed through Z type compensator, and the figure ranges from 0.62 to 0.68 when passed through square type compensator, which is slightly greater than water flow.With the length of straight transition part increased, the coverage of core high speed area expanded and up forward when fluid flow passed through the third elbow in square type compensator. Surfactant flow changed the distribution of velocity field and the coverage of core high speed area of surfactant flow is larger than that of water in the same working condition.