The Numerical Simulation And The Application Study Of The Flow Field And The Thermal Field In A Natural Draft Wet Cooling Tower

Natural draft counter-flow wet cooling tower is the main equipment of the power sector in our country, whose working efficiency greatly affects the economic benefits of thousands of electricity generating stations, even the energy conservation on a national scale. After a comprehensive survey and investigation, two widely-used theoretical models have been introduced, Merkel's model and Poppe's model, along with their respective advantages and disadvantages. It is found that although the original Merkel's model has its inaccuracy on computing air outlet temperature and air outlet humidity, it has a strong capability to calculate water outlet temperature accurately which is the foremost parameter. Moreover, its popularity results from its simplicity to implement. On the basis of the researches mentioned above, we employ the enthalpy potential method along with Merkel's model to build our platform of computation, respectively using FORTRAN language for 2D computation and FLUENT's User Defined Function for 3D computation.The program in this thesis for 2D computation is based on the one written by Pro. Dongtao Huang in the year of 2000. The main improvements include certain aspects as follows: Standard k ?εturbulence model has been implanted into the original program and the effect of the equivalent viscosity coefficient on the calculated water outlet temperature is discussed; Different inlet boundary conditions are investigated for the purpose of eliminating the resulting error caused by unreal boundary conditions.As for the 3D computation, VC++ compiled User Defined Functions, which is provided by the well-known CFD software FLUENT, is written to simulate the process of heat and mass transfer, using FLUENT to solve the Navier-Stokes equations at the same time. After eliminating the outcome's dependence on grid's density, it is revealed that the results of 3D computation have great priority over those of 2D's in accuracy. By using the 3D approach, this thesis analyze the effect of the supporting pillars on the cooling efficiency, concluding that the supporting pillars of cooling tower would reduce the water temperature drop by about 0.1℃. Moreover, significance of Merkel's assumption-ignoring the effect of evaporation on the water mass flow rate, is discussed. We conclude that assumption should be implanted into the computing programs before we use Merkel's model.