The Study And Design Of Cylindrical Cavity Based On The Turbine Humidity Measurement

The humidity within turbine affects the efficiency,security and loss of power generation,hence it is essential to be measured.This paper firstly elaborates the theory of steam dampness measuring,using medium perturbation method,emphatically studying the effect about temperature and wavelength affecting to the permittivity of saturated water,and giving appropriate frequency range of measuring the permittivity.Closed at both ends of cavity and excited by rectangle waveguide,the cylindrical resonator is designed by mode chart,basing on the values of previous optimized parameters.Secondly,the analysis and calculation about the electromagnetic radiation from slots of both ends are presented by the relevant theory of microwave electromagnetic field,for instance, establishing the analysable cavity excitation source by the excitation source equivalence,resolving the cavity field is by green function method,considering the effect to the slots field affected by the annular slots using electromagnetic field equivalence, expounding the fields relation between cavity and slots by mode matching,etc.This paper emulates the radiation quantity from the slots by Matlab tool,and compares with the values of cavity model by HFSS tool,thus proves the correctness of analysis to the relevant field in cavity and radiation counting from the slots,and showing the regular pattern about radiation varying.Then utilizing the rules infered,and taking the patency of moist steam entering into consideration,this paper designs the annular slots with the numerical values of slots parameters.Next the paper proposes the lower limit of quality factor when the eigenmode of cavity was TE011,and investigates the effect of gap changing to quality factor.And the value of quality factor through the previous designing is given,which illustrates its performance meeting requirement.Finally, we calculate the humidity and its relative error by the designed cavity above.In fact,the saturated temperature is metabolic,and both temperature and humidity affect the resonant frequency offsetting,so the method of counting humidity above has certain error.Meanwhile,considering the permittivity of the formula in counting steam humidity,which corresponded to the frequency offsetting,being affected by the temperature and humidity complicatedly and nonlinear,this paper fits a relational optimizing expression of frequency shifting with temperature and humidity, and achieves the requirement of accuracy in steam measuring.Here, the error based on the expression is analyzed,and verified that the relative error within1%,which met the accuracy requirement.And the paper illustrates that the cavity model and humidity optimization expression both have the practicability.