| As a kind of low-grade heat recovery and water treatment equipment,the tube multi-effect evaporation water system plays a great role in the shortage era of energy and drinking water resources.The tube evaporator and the vapor-liquid separator are the key parts of the multi-effect evaporation system,which are of great importance to improve energy efficiency and quality of the production of water.The present work adopt numerical stimulation,which considered the heat transfer enhancement of tube with vortex generator in the evaporator part of the multi-effect evaporation water system and the influence of structure of cyclone in the separation charmer part on flow field and separation efficiency.Further,experiment and numerical simulation under cold condition for single-effect evaporation water system were conducted to analyze the influence of inlet air volume flow rate(the volume of steam separation treatment per hour)on flow field.The main contents and conclusions were list as follows:1)A kind of vortex generator inserted into the tube was proposed,which was curved surface blade in structure.Numerical simulation was done using the RNG k-? turbulent model and enhanced wall treatment(EWT)in FLUENT,the cone angle,flow direction(cone pointing downstream and upstream),vortex generator installation position(center and eccentric)and the single pitch ratio(p)were considered to analyze the velocity field and temperature field distribution under the condition of constant wall temperature and the Reynolds number(Re)from 25953 to 51906.The heat transfer enhancement of the vortex generator installed for different types were studied by calculating the Nusselt number(Nu),friction factor(f)and comprehensive performance evaluation criterion(PEC).The results showed that the inserted vortex generator had the function of heat transfer enhancement.If there were two vortex generators with cone,when eccentric installed under p=150mm the Nu was largest,170 bigger than that of smooth tube;when single vortex combine with cone upstream and eccentric the PEC was largest.2)The cyclone structure was designed with the numerical simulation.The FLUENT Reynolds Stress Turbulent Model(RSM)and Multiphase flow model(VOF and DPM)was used to analyze the influence of inlet form(single entrance,double symmetric entrance and up-down double entrance)and inlet length on the cyclone flow field and the separation effect.Results showed the symmetrical double entrance type cyclone separator had the characteristics of more stable symmetry flow field and the best separation efficiency.When the inlet length c was 1.25D/2 of cyclone,the full development of flow field was formed andno longer affected by entrance length.The particles with diameter larger than 5 μm could be completely separated when inlet velocity and volume concentration equaled to 10 m/s and2%,respectively.3)The study on the single-effect evaporation water system was performed by the experimental and numerical analysis.According to the above simulation results,a cold experimental set of single-effect evaporation water system was built.Under different inlet air volume flow rates(the volume of steam separation treatment per hour),the influence of different underflow pipe diameters of built-in cyclone on the pressure drop,the suck-back height and the flow field were analyzed.The results showed that the pressure drop and the suck-back height both increased with the increase of inlet velocity.However,the stability of the flow field decreased.The pressure drop of the system and the suck-back height of the underflow tube with small diameter were bigger than those with large diameter.The numerical simulations were consistent with experimental studies with the errors less than10%.Meanwhile,the internal flow field of built-in cyclone had the characteristics of double spiral flow and classical "Rankine vortex" model,which agreed with the flow field of independent cyclone separator discussed in chapter 4.Therefore,the separation efficiency of the system could be acquired by calculating that of the independent cyclone.The current research could offer a reference for the design of the multi-effect evaporation water system. |
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