| With the traditional energy shortage, the development of low carbon economyand energy saving have become the only way of the industry development. Thevariable speed hydrodynamic coupling has a remarkable energy-saving effect. In thecase of the increasing amount of the large-scale pumps and fans, the application of thehigh-power variable speed hydrodynamic coupling will generate enormous economicand social benefits. The variable speed hydrodynamic coupling has some superiorperformances such as achieving the smooth start, stepless speed adjustment andreducing the impulse and vibration. The speed of variable speed hydrodynamiccoupling is controlled by the use of slip, which can lead to the loss of energy. The lossof energy will change into heat energy and make the temperature of work liquid keeprising. If this heat can not get cooled timely, it will change the physical properties ofthe hydrodynamic transmission oil, such as density and viscosity reduction. Thereby itwill enable the transmission capacity decline. More seriously, it will result on theaging of the sealing elements and lead to the phenomenon of oil impregnate and oilleakage. According to the survey, it is one of the frequent troubles that thehydrodynamic transmission oil temperature is too high. To solve these problems whatare said above, supported by “Key Technology Research on Hydrodynamic VariableSpeed and Saving Energy of Large Pump and Fan(2007AA05Z256)” of the NationalHigh-tech Research Development Plan (863Plan), this thesis aims at the flow and theheat transfer characteristics of the working chamber of the high-power variable speedhydrodynamic coupling and the heat exchanger. This thesis carried out the numericalcalculation and experimental research to show the internal flow and heat transfer lawsaccurately, accordingly, and provided a theoretical basis for the optimizing design ofthe hydrodynamic coupling and the matching and optimization of the heat exchanger.This paper is mainly about the following aspects:1. Study on heat flow coupling of variable speed hydrodynamic coupling It is introduced that the control equations which conform the characteristics ofthe fluid flow and heat transfer in the hydrodynamic coupling,and the controlequations are transformed from the static coordinates to the rotating coordinates,andthe energy equation has been derived which can be represented by the flow fieldvariables,and points out the coupling relationship between the flow field andtemperature field.YOCQZ465variable speed hydrodynamic coupling was taken asthe study object. Flow and heat transfer of numerical calculation were carried out forthe working chamber of the fluid. Considering that the research object isthree-dimension viscous of two-phase unsteady turbulent flow, controlling equationsare composed of the continuity equation of mixed model, the momentum equation,energy equation and k εtwo equations of turbulence. In order to make thesimulation results more accurate and reliable, the whole flow field was as thecalculation region, divided by mixed element unstructured grid and sliding mesh. Themethod mentioned in this paper can be a theoretical reference for numericalsimulation on complex flow and heat transfer.2. Numerical calculation and analysis of heat-flow coupling for variablespeed hydrodynamic couplingThe maximum point of slip power loss for YOCQZ465variable speedhydrodynamic coupling of thermal power plant boiler feed-water pump is fluid-filledand0.667of speed ratio case through empirical formula calculation, that isqc=100%,i=0.667.Numerical calculation of flow and heat transfer was carried outfor fluid of working chamber at the operating point and typical traction operatingpoint, which is80%fluid filled and0.8of speed ratio. The results show that fluidtemperature is higher at the maximum slip power loss of operating point, whichproves that the empirical formula is correct. Through analysis and research onvelocity field, temperature field, pressure field and the liquid phase volumedistribution of the whole flow passage and flow passage section at the two operatingpoints of hydrodynamic coupling, it was revealed that flow and heat transfer law ofthe working chamber under full fluid filled and partially fluid filled. Through analysisand study on the cause of the characteristics of flow and heat transfer, the workingmechanism of variable speed hydrodynamic coupling was understood more deeply,which can guide optimization design of variable speed hydrodynamic coupling andimprove its performance. It has been proved that the fluid viscosity and the geometry shape in the working chamber have a great influence on the flow in the hydrodynamiccoupling and energy transfer by the analysis and study on the forming reasons of theheat transfer characteristics of flow, which has a certain guiding significance for theoptimal design of speed control type hydrodynamic coupling and improve their workperformance. On this basis, this paper drew torque curve of the hydrodynamiccoupling in different temperature under various working conditions. The comparisonsshow that the higher oil temperature can causes the drive performance declined.Therefore, maximum slip power loss of operating point should try to be avoided inpractical work in order to prevent working oil temperature rising.3. Heat exchanger flow and heat transfer numerical analysis and StructuralImprovementThis paper analyzed the cooling capacity of heat exchanger for YOCQZ465variable speed hydrodynamic coupling of thermal power plant boiler feed-water pumptheoretically. Three dimensional entity modeling was set up according toshell-and-tube heat exchanger and the numerical calculation of flow and heat transferin the whole flow area were carried out. The velocity fields and temperature fields ofheat exchanger shell and tube were obtained through numerical simulation, whichrevealed two working medium flow and heat transfer situation in the shell-and-tubeheat exchanger. This contributed to the further understand of heat transfer mechanismof shell-and-tube heat exchanger.The tube and shell structures of shell-and-tube heat exchanger were optimizedaccording to heat transfer enhancement technology and then the shell and tube heatexchanger volume decreased, anti-fouling ability enhanced and energy consumptionreduced after improving the structure. The original and the improved flow and heattransfer performance were analyzed by CFD numerical simulation software. Theresult shows that the heat exchanger performance significantly improved afteroptimization.4. Thermal balance test research of variable speed hydrodynamic couplingThermal balance test of YOCQZ465variable speed hydrodynamic coupling wasstudied. The temperature data of test points was acquired under without load on thebench and typical operating condition of thermal power plant. CFD numericalsimulation results and the oil temperature at the import and export of hydrodynamiccoupling of under typical working conditions in thermal power plant were in linebasically, which proved that the numerical method in this thesis is reliable. It has certain guiding significance for the complex flow and heat transfer. Modified groundswere provided for simplification for mathematical model and hypothesis condition inthe process of numerical research through analysis of experimental data for the energyloss without load. |
PDF Full Text Request