Investigation On The Flow And Heat-Exchange Characteristics Of One Novel Vortex-tube Air-to-air Cooler For The 2MW Wind Turbine

In recent years,the installed capacity of wind power generator has been gradually increased with the development of the wind-power technology,so that the heat amount produced by the wind power generator would enhanced considerably.The high temperature and poor heat dissipation of wind turbines will cause the corresponding equipment to be damaged and shorten its service time.Therefore,it is urgent to explore one low-cost,simple and convenient measure that can dissipate effectively heat from a wind turbine.In this thesis,a air-to-air cooler for the 2MW wind turbine is chosen as a reference prototype.It is proposed to replace the plain tube with a new type of vortex-shaped heat exchange enhancement tube.Furthermore,the flow and heat transfer process is simulated for the novel vortex-tube air-to-air cooler.Then,the enhanced heat transfer capacity and flow resistance characteristics are analyzed in detailed.In this thesis,firstly,the geometry model of the vortex-shaped heat transfer enhancement tube is established based on the theory of the structural mechanics.Then the heat exchanger unit is selected and the corresponding model is established for the air-to-air cooler of the 2MW wind turbine.The 3D numerical simulations are carried out to explore the behaviors of the heat transfer and flow of the vortex-tube and plain-tube air-to-air coolers by using the SST k-ω turbulence model.Additionally,the difference of flow and heat transfer characteristics between the two cooler tubes is identified by combining the velocity field with the temperature field.The numerical results show that the heat transfer capabilities inside and outside the tube are enhanced to the different extents after replacing the plain tube with the vortex tube due to the existence of the vortex structure arranged periodically in the axial and circumferential directions.In the calculated range of Re,the vortex-tube air-to-air cooler has the much superior integrated comprehensive performance factor inside and outside the tube,up to 1.9 and 1.17,respectively.At the same time,the temperature drop of the hot fluid in the shell side increases from 4.3-10 K to 8-15.5K,which improves the cooling capacity of the generator,reduces the temperature rise of the generator and is beneficial to prolong its service time.Moreover,it is found that compared to the plain tube air-to-air cooler,the vortex tube air-to-air cooler can save about 42% of the volume on the condition of cooling the same heat amount,which can reduce the cost and improve the economic efficiency of the whole system.In order to further improve the heat transfer enhancement in the shell side of the vortex-tube air-to-air cooler,the influences of the different structural parameters on the performance in the shell side are analyzed.It is found that at the same inlet flowrate of the hot air,the comprehensive heat exchange performance in the shell side of the vortex-tube air-to-air cooler can be significantly improved by one effective measurement which can be that the wind deflector is placed far away from the cooling tube outlet,or the transverse tube spacing is reduced,or the longitudinal tube spacing is increased appropriately or the length-to-diameter ratio is relatively small.