| Based on the existing research results at home and abroad, the experimental research of flow and heat transfer characteristics of air/steam-water two-phase flow in pipes under high gravity, the identification of flow pattern, and the development of the physical model and its numerical method were conducted. The obtained results are significant in developing airborne vapor cycle cooling system and can be added in the database in investigating the characteristics of gas-liquid two-phase flow and heat transfer.The rotating platform was established to simulate the dynamic load, on which a circular loop of air/steam-water two-phase flow circulation pipeline was installed and adjusted. The parameter measurement, data acquisition and processing, and the heating of air/steam-water two-phase flow under rotation condition were solved. The visual observation and real time record of flow pattern under high gravity were realized using visual technology. By changing the parameters, such as the orientation and inclination of the test pipe, rotating speed, inlet temperature, flow rate, and etc, the data of air/steam-water two-phase flow including its heat transfer under rotation condition for diffirent orientations and inclinations of the test pipe were obtained. By processing and analyzing the original data, the effects of acceleration on void fraction, flow rate, flow velocity, temperature, pressure and pressure drop of air/steam-water two-phase flow and the characteristics of the air/steam-water two-phase flow and boiling heat transfer under high gravity were obtained. The results show that the acceleration significantly influences the flow characteristic and boiling heat transfer of the two-phase pipe flow. As the direction of the dynamic load and the flow direction are opposite, the greater the dynamic load, the lower the flow rate, the higher the pressure drop and the flow resistance, and the more obvious the trend of blocking the fluid flow. The outside heat transfer coefficient increases with the increase in dynamic load. Therefore, the dynamic load will enhance heat dissipation and reduce the heat transferred to the two-phase fluid and the pipe wall temperature. Through visual technology, the novel flow patterns such as impact flow and impact mixing flow under high gravity were found in the present work.The physical models including centrifugal force and Coriolis force for gas-liquid two-phase flow with homogeneous fluid and separated fluid were developed. The non-dimensional analysis of governing equations were carried out. The mesh generation for two kinds of horizontal pipes were conducted and the finite volume method was used to discrete the equations. The equations were solved with the SIMPLE algorithm after setting the initial conditions and boundary conditions. The predicting results were compared with the experimental data and they agree well with each other. The computational results once again show that the outlet pressure and pressure drop increase with increasing acceleration,which are the monotonic increasing functions of the acceleration. However, the effective heat transferred to the fluid decreases with the increase in acceleration.The wavelet de-noising theory was applied to the pressure drop fluctuation signal de-noising processing of boiling steam-water two-phase flow in a horizontal pipe under high gravity. The wavelet packet transform was used to decompose the de-noising pressure drop fluctuation signal. The total energy of each band signal after the wavelet packet decomposition were used as the eigenvalue to construct and normalize the eigenvector. BP neural network and RBF neural network were used as gas-liquid two-phase flow pattern classifier. The different eigenvector matrixes which were used as the input parameters were input to the neural networks to identify the flow patterns. The experimental results show that this method can identify the flow patterns effectively and provide a new approach for the flow pattern identification. |
PDF Full Text Request