| In the field of energy technology research with huge potential and wide application such as catalytic cracking of biomass tar and heavy oil, the feed nozzle for the high viscosity liquid is a hot issue. For tar and other liquid fuel, nozzle is the core of feed technology, the quality of nozzle performance directly affect the reaction results and its own lifespan of nozzle as well as related to the stability of reaction process operation of the project. Atomization mechanism and the atomizing feed nozzles adapted are of urgent need to be researched and developed.Firstly, viscosity-temperature characteristics empirical formula of the four liquid, including biomass tar were obtained through viscosity-temperature characteristic experiment, the viscosity of tar dropped from12.6to2.7mPa·s.6nozzles with different structural parameters, atomizing cone angle and pressure for biomass tar were designed according to the design and performance requirements.Experimental study about swirl nozzle atomization characteristics was carried out to find that reduced viscosity and the increased pressure made average particle size of the droplet become small, and its size distribution range gradually change narrow, the droplet size distribution becomes uniform. The influence of tar viscosity on the quality of atomization can be summarized with cell number Z. The average axial velocity of jet droplet increased with the increase in pressure and decrease in viscosity of the working fluid, all of the experimental values of the spray cone angle were smaller than the design value, and the atomizing cone angle gradually increased as the pressure increased, and tend to close to the design value. The greater the viscosity, the smaller the angle of the spray cone, the influence of viscosity on the spray cone angle is not obvious. It can conclude by experiments that the nozzle6#is with the best structure designed under the conditions of this work, which generated droplets with SMD as small as35.5μm, meeting the requirement.It was found through the numerical simulation of the flow field inside the velocity of the liquid got larger when into the vortex chamber, and its speed gradually got larger in the swirl chamber until into the orifice, where its speed decreased. The internal flow field was in accordance with the swirling motion theory and there is a transition zone between the free vortex region and the forced vortex zone of the swirl chamber, but the transition region did not exist in he injection hole. The radial velocity of the nozzle hole was positive, and that in the swirl chamber was negative, and the radial velocity of each cross-section was not evenly distributed. Air cone was formed close to the axis because of the negative pressure inside the forced vortex. The closer to the axis, the smaller static pressure was, distribution of dynamic pressure was similar to the speed. The distribution of total pressure in the forced vortex region was like a quadratic curve, and logarithmic in semi-free vortex region. Turbulent kinetic energy loss at entrance of the vortex chamber and region near the wall of nozzle was the main energy loss sources. The liquid temperature in the swirl chamber is almost unchanged, while the closer to the axis, the lower temperature was in nozzle hole.Prediction equation for SMD was proposed and it fitted well with the experimental results. Fitting equation for SMD and T of2#and6#nozzle under given operating conditions was obtained on the basis of experimental data. This study accomplished atomization of highly viscous liquid and will provide theoretical basis and experimental data for further optimization of swirl nozzle and improvement of the atomization quality. |
PDF Full Text Request