| Energy is the fundamental of socioeconomic development,also an important part of human production and life.The three major energy resources,coal,petroleum and natural gas,are not renewable,and the products of combustion pollute the environment,so the clean energy needs to be developed urgently.Nuclear power catches wide attention for its advantages of rich nuclear fuel,convenient transportation and storage,low pollution and low electricity generation cost.The narrow rectangular channel,with compact structure and good heat transfer effect,has been applied to nuclear power system.However,the structural property of narrow rectangular channels makes the flow process quite different to that in the traditional circular channel,and the study of flow pattern transformation is mostly focused on the single side visual experimental channel.Though the size of narrow side is only a few millimeters,the density of heat flow there is very high,where more boiling cores can be provided,so its influence on the flow pattern can not be ignored.Changes of the flow pattern will inevitably lead to the change of the pressure drop characteristic.Accurate pressure drop calculation can provide more safety and economy security for the system.In this work,the flow pattern transition and pressure drop characteristics of a narrow rectangular channel heated by three sides are studied by an experimental study of a three narrow rectangular channel.In this paper,a narrow rectangular experimental channel heated by three sides was designed on the basis of a test bench for high pressure gas-liquid two phase flow,on which visualization experiment was carried out.The flow pattern changes in the channel were recorded by high speed camera,and the change process of the flow pattern with different flow rate and inlet under-cooling degree in the channel was observed.Comparative analysis was carried out,and the flow pattern with the measurement data was plotted.The variation of differential pressure between the two ends of the channel under different working conditions was measured and the fluctuation characteristic of differential pressure was analyzed.In the study of the flow pattern changing process,five flow patterns were observed,like separating bubbly flow,combined bubbly flow,slug flow,stirring flow and gas film slug flow.The change process of the flow pattern was described in detail.The flow pattern changing process of the three-side heated channel was compared with that of the single side heated channel and the adiabatic channel,and it was found that the variation was dramatic.We found the slug flow and film slug flow in the three-side channel,but did not found annular flow.In addition,the flow pattern map was also analyzed,and the effect of mass velocity and heatflux on the transformation lines in the flow pattern map was studied.It was found that when the bubbly flow was turned into slug flow or stirring flow,the super-facial velocity of liquid phase decreased with the increment of super-facial velocity of gas phase;when the slug flow or stirring flow was transformed into gas film slug flow,with the increasing of the super-facial velocity of gas phase,the super-facial velocity of liquid phase increased firstly and then decreased.When the mass velocity was the same,the heat flux increased,the transformation delayed,the corresponding conversion of gas superficial velocity increased with the liquid superficial velocity decreased.Compared and analyzed with the flow pattern of single side heating channel and the adiabatic channel with similar channel size,we found that,there were big differences in the flow pattern of non heating channel,the trend of the transformation line of the bubbly flow changed into the slug flow and the slug flow changed into the stirring flow are opposite to our experimental data.Compared with the single side heating channel,the flow pattern transition line had a great inclination angle and the flow pattern transition was more advanced.In the study of pressure drop characteristics,the fluctuation of the two section pressure drop of the experimental section in a short time was analyzed with different outlet void fraction.The effects of the outlet void fraction,mass velocity and inlet subcooling on the total boiling pressure drop and pressure drop of other part were also analyzed,in the end,the calculated values of the pressure difference formula were compared with the experimental results,found the more suitable pressure difference formula for this experiment. |
PDF Full Text Request