Characteristics Of Heat And Mass Transfer In The Sonic Nozzles

The sonic nozzle is one of the traditional flow sensors with corresponding ISO9300 standard.As the mechanism of the sonic nozzle is complicated,there are still many problems to be solved.In this paper,in-depth study on the heat and mass transfer characteristics of the “thermal effect” and “condensation phenomenon” of the sonic nozzle was carried out started from the temperature distribution.The “thermal effect” is mainly related to “heat transfer”,and “condensation phenomenon” has the characteristics of “heat transfer” and “mass transfer”.The main research work and results in this paper are as follows:In view of heat transfer process of the “thermal effect”,the basic principle of thermal effect was analyzed firstly,including the thermal boundary layer and thermal expansion properties.Then the dynamic wall temperature distribution was obtained,and temperature distribution of nozzle axial cross-section was interpolated by the Kriging interpolation algorithm.It was found that the temperature distribution is similar “U” with high in amphi and low in middle.The maximum observed temperature drop of the sonic nozzle wall was up to 16.5?.Then the numerical model was established based on the fluid-structure interaction heat transfer and fluid flow.Combining the simulation and the experiment results,it was found the shock wave separation made a backflow zone,which would heat the wall in the rear of the separation point.Thus,the sonic nozzle wall is divided into three regions,front heating zone,cooling zone and rear heating zone respectively,and the cut-off points are the throat and shock wave separation point respectively.At last,the characteristics of the shock wave were the studied.It was shown that with the nozzle pressure ratio increases,the shock wave moves to the nozzle outlet and the location is closer to the throat than the theoretical value.In view of the heat and mass transfer process of “condensation”,the steady state moisture condensation model was established firstly.The effects of relative humidity,temperature and pressure of the nozzle inlet on the condensation onset point and intensity were analyzed.Secondly,the unsteady state spontaneous condensation viscous model of water vapor was established.The relationship of supercooling degree of inlet with the frequency of self-excitation oscillation and the variation of flow rate were studied.According to the motion mode of aerodynamic shock wave generated by condensation,the condensation self-excited oscillation can be divided into three different modes.The influence of condensation “unsteady state” on flow field,flow rate and stability was analyzed.In this study,the minimum correction factor of the influence of the self-excitation oscillation on the flow rate is 0.988,that is,the maximum variation of flow rate is 1.2%.In addition,the experiment platform for the condensation was set up.Some results of steady and unsteady condensation were obtained which verified the theoretical and simulation results.