Multiscale Entropy Analysis of Instantaneous Pressure Fluctuation in a Novel Jet Tank

Computational Simulation of Mixing Performance in the Circulating Jet Mixing Tank

Computational fluid dynamics (CFD) was used to investigate the turbulent mixing performance in a vertical CJT in the range of Re=3,668−18,342. Energy source of hot water was centrally placed just below the top of the tank and temperature instead of concentration measurements were used to quantify mixing performance. The 95 % criterion for temperature equilibrium was employed to evaluate the local mixing degree, and the global mixing performance was evaluated based on the ratio of well-mixed volume to total fluid volume. It was obviously observed from the axial distributions of t95 % that the macro-mixing times decreased slightly for z/H < 0.6 and a deep downward trends appeared with the increase of z/H with given r/R. The macro-mixing time in the jet mixing boundary layer were uniform which were a little longer than those in the bulk zones below z/H=0.5 and decreased sharply by 37.5−87.5 % than that in the bulk zone above z/H=0.5. The values of 95 % mixing time increased with the increase of r/R. The global t95 % decreased with the increasing Reynolds number, and a power correlation between the global t95 % values and Re was proposed. With the increasing logarithm of mixing time, the logarithm of segregation intensity rapidly decreased linearly in the slopes from –0.996 to –0.955. The segmentation intensity first decreased then increased with the increasing values of θ.

Investigation of the Effect of Outlet Structures on the Jet Flow Characteristics in the Circulating Jet Tank

A revised numerical model of circulating jet tank (CJT) was constructed by adding four momentum sources. The radial distribution tendency of total pressure predicted by large eddy simulation had a good agreement with experimental results. The axial velocities at the center of downcomers have parabolic attenuation tendency with the increasing axial positions. The inductive and restrictive effects of outlets on the jet flow performances were evaluated by the parameters, such as jet velocity decay, spreading rate and energy dissipation. The optimum factor of outlet structures was proposed based on the ratio of spreading rate to energy dissipation. Numerical results show that the downcomers equipped with four symmetrical rectangular outlets contribute more to reduce the decay of jet centerline velocity and make good use of the entrainment between the jet and bulk liquid to generate the largest spreading rate. Furthermore, a nearly plug flow pattern and the maximum value of optimum factor are attained compared with other types of outlets. The optimum factors of rectangular outlets firstly increase then decrease with the increasing ratios of width to diameter of the downcomers. Rectangular outlets induce the jet to expand and get the largest dimensionless jet length and spreading rate when the ratios of width to diameter w/D1 approach 0.08.