Structural Calculation And Simulation Analysis On Two-phase Flow Of Swirl Nozzle

In the falling-film evaporator of desalination project, high-performance liquid distribution device providing evenly liquid film, can keep the heat transfer efficient of evaporation tubes at a high rate. Therefore, a swirl nozzle pertaining to liquid distribution device is designed, and the two-phase flow through the nozzle is simulated and investigated by software FLUENT, in search for structural function of the nozzle and process characteristics of the jetting breakup.At first, the main structure and the relative position of the inlet and swirl chamber portion are designed by Maximum Flow Principle. Based on the main framework and the parameter relations derived by Momentum Equation Principle, the structure and size of the convergent-divergent outlet portion are calculated. At last, reference to the structure of related nozzles and experimental experience, the specific geometric curves are determined.The physical model representing the flow field of the nozzle is set up and then discretized. With the VOF method and RNG k-e model, the three-dimensional processes including the liquid rotation flow inside the nozzle, the breakup at the exit and the droplet dispersion in the small-scope field outside the nozzle are numerically simulated. Finally, the geometric parameters of the nozzle are objectively fixed and are compared to the original simulation circumstances.The simulation results show that the flow in the nozzle has spatial stability and circumferential asymmetry. The greatest resistance loss inside the nozzle is from the connection region between the swirl chamber and outlet portion, the second is from the region between the primary and sub-swirl chamber. The combination structure between swirl chamber and outlet portion hinders the symmetrical distribution of the liquid film, meanwhile causing the direction of the flow field strongly distorted, but it can make better use of swirl chamber to accelerate liquid. The convergent segment and the upper part of the throat in the outlet portion have accelerating effect on liquid film; The throat transfers the flow smoothly to reduce the loss of resistance; The flow velocity of the liquid is attenuated through the divergent segment, but the spray angle is restricted with the divergent segment long enough. At the nozzle exit, the way liquid film breaks has three forms:slice-shape, hole-shape and pillar-shape breakup, and which form liquid film tends to break into is related to the thickness and velocity of the jetting. The recommended value of section coefficient of this nozzle is in the range of0.5to0.55, and the spray cone angle can be adjusted from133o to168o as required with the recommended length of divergent segment about10mm.