EXPERIMENTAL STUDY ON DRAG REDUCTION CHARACTERISTICS OF DIUTAN GUM SOLUTION BY SLIT INJECTION

Diutan gum (DG) is a new type of polymer additive that can greatly reduce turbulence resistance. Compared with PEO, PAM and other flexible polymers, DG has significant shear resistance. However, there are relatively few studies on its drag reduction performance at present. In this paper, the relationship between the rheological characteristics of DG and its drag reduction behavior is analyzed by testing the rheological characteristics of DG, the law of drag reduction by in-tube injection and the process of spray diffusion, and the reasons for the change of its drag reduction law are explained from the perspective of spray diffusion. The results show that DG solution is a shear thinning fluid. The viscosity - elastic transition occurs and the transition point is independent of temperature, only moves forward with the increase of concentration. The drag reduction effect of DG increases firstly and then decreases with The Reynolds number, and increases monotonically with the injection rate. Compared with pure water injection, DG solution diffuses slowly in the flow field, and the higher the injection rate, the more obvious the agglomeration near the wall surface. Combined with the observation of jet diffusion of DG solution, it can be seen that when the flow rate is small, DG solution is not fully diffused, but in an uneven aggregation state, which does not give full play to its turbulence inhibition effect and has weak drag reduction. With the increase of flow velocity, the flow shear rate increases, the diffusion of DG is gradually uniform, the turbulence inhibition effect is enhanced, and the drag reduction rate increases. However, when the flow rate is too high, the concentration of DG is seriously diluted, and the shear rate in the near wall area is too high, which may cause the fracture of long chain molecules, resulting in the decrease of drag reduction effect.