Because of the practical importance of two-phase instabilities, substantial efforts have been made to date to understand the physical phenomena governing such instabilities and to develop computational tools to model ...Because of the practical importance of two-phase instabilities, substantial efforts have been made to date to understand the physical phenomena governing such instabilities and to develop computational tools to model the dynamics. The purpose of this study is to present a numerical model for the analysis of flow-induced instabilities in forced-convection steam generator. The model is based on the assumption of homogeneous two-phase flow and ther- modynamic equilibrium of the phases. The thermal capacity of the heater wall has been included in the analysis. The model is used to analyze the flow instabilities in the steam generator and to study the effects of system pressure, mass flux, inlet temperature and inlet/outlet restriction, gap size, the ratio of do / di, and the ratio of qi / qo on the system be- havior.展开更多
A narrow annular test section of 1.5mm gap and 1800mm length was designed and manufactured, with good tightness and insulation. Experiments were carried out to investigate characteristics of flow instability of forced...A narrow annular test section of 1.5mm gap and 1800mm length was designed and manufactured, with good tightness and insulation. Experiments were carried out to investigate characteristics of flow instability of forced-convection in vertical narrow annuli. Using distilled water as work fluid, the experiments were conducted at pressures of 1.0~3.0MPa, mass flow rates of 3.0~25kg/h, heating power of 3.0~ 6.5kW and inlet fluid temperature of 20 oC, 40 oC or 60oC. It was found that flow instability occured with fixed inlet condition and heating power when mass flow rate was below a special value. Effects of inlet subcooling, system pressure and mass flow rate on the system behavior were studied and the instability region was given.展开更多
An experimental investigation is described for the characteristics of convective boiling flow instabilities in horizontally helically coiled tubes using a steam-water two-phase closed circulation test loop at pressure...An experimental investigation is described for the characteristics of convective boiling flow instabilities in horizontally helically coiled tubes using a steam-water two-phase closed circulation test loop at pressure from 0.5 MPa to 3.5 MPa. Three kinds of oscillation are reported: density waves; pressure drop excursions; thermal fluctuations. We describe their dependence on main system parameters such as system pressure, mass flowrate, inlet subcooling, compressible volume and heat flux. Utilizing the experimental data together with conservation constraints, a dimensionless correlation is proposed for the occurrence of density waves.展开更多
This study investigated the formation and development of a mesoscale convergence line （MCL） within the circulation of Typhoon Rananim （0414）, which eventually led to torrential rainfall over inland China. The stud...This study investigated the formation and development of a mesoscale convergence line （MCL） within the circulation of Typhoon Rananim （0414）, which eventually led to torrential rainfall over inland China. The study is based on satellite, surface and sounding data, and 20 km×20 km regional spectral model data released by the Japan Meteorological Agency. It is found that midlatitude cold air intruded into the typhoon circulation, which resulted in the formation of the MCL in the northwestern quadrant of the typhoon. The MCL occurred in the lower troposphere below 700 hPa, with an ascending airflow inclined to cold air, and a secondary vertical circulation across the MCL. Meso-/~ scale convective cloud clusters emerged and developed near the MCL before their merging into the typhoon remnant clouds. Convective instability and conditional symmetric instability appeared simultaneously near Diagnosis of the interaction between the MCL and kinetic energy and positive vorticity for its further the MCL, favorable for the development of convection. the typhoon remnant implies that the MCL obtained development from the typhoon remnant in the lower troposphere. In turn, the development of the MCL provided kinetic energy and positive vorticity at upper levels for the typhoon remnant, which may have slowed clown the decaying of the typhoon.展开更多
文摘Because of the practical importance of two-phase instabilities, substantial efforts have been made to date to understand the physical phenomena governing such instabilities and to develop computational tools to model the dynamics. The purpose of this study is to present a numerical model for the analysis of flow-induced instabilities in forced-convection steam generator. The model is based on the assumption of homogeneous two-phase flow and ther- modynamic equilibrium of the phases. The thermal capacity of the heater wall has been included in the analysis. The model is used to analyze the flow instabilities in the steam generator and to study the effects of system pressure, mass flux, inlet temperature and inlet/outlet restriction, gap size, the ratio of do / di, and the ratio of qi / qo on the system be- havior.
文摘A narrow annular test section of 1.5mm gap and 1800mm length was designed and manufactured, with good tightness and insulation. Experiments were carried out to investigate characteristics of flow instability of forced-convection in vertical narrow annuli. Using distilled water as work fluid, the experiments were conducted at pressures of 1.0~3.0MPa, mass flow rates of 3.0~25kg/h, heating power of 3.0~ 6.5kW and inlet fluid temperature of 20 oC, 40 oC or 60oC. It was found that flow instability occured with fixed inlet condition and heating power when mass flow rate was below a special value. Effects of inlet subcooling, system pressure and mass flow rate on the system behavior were studied and the instability region was given.
文摘An experimental investigation is described for the characteristics of convective boiling flow instabilities in horizontally helically coiled tubes using a steam-water two-phase closed circulation test loop at pressure from 0.5 MPa to 3.5 MPa. Three kinds of oscillation are reported: density waves; pressure drop excursions; thermal fluctuations. We describe their dependence on main system parameters such as system pressure, mass flowrate, inlet subcooling, compressible volume and heat flux. Utilizing the experimental data together with conservation constraints, a dimensionless correlation is proposed for the occurrence of density waves.
基金the National"973"Program of China under Grant No.2009CB421504the National Natural Science Foundation of China under Grant Nos.40730948,40675033,and 40975032the Key Project of the Chinese Academy of Meteorological Sciences under Grant No.2008LASWZI01.
文摘This study investigated the formation and development of a mesoscale convergence line （MCL） within the circulation of Typhoon Rananim （0414）, which eventually led to torrential rainfall over inland China. The study is based on satellite, surface and sounding data, and 20 km×20 km regional spectral model data released by the Japan Meteorological Agency. It is found that midlatitude cold air intruded into the typhoon circulation, which resulted in the formation of the MCL in the northwestern quadrant of the typhoon. The MCL occurred in the lower troposphere below 700 hPa, with an ascending airflow inclined to cold air, and a secondary vertical circulation across the MCL. Meso-/~ scale convective cloud clusters emerged and developed near the MCL before their merging into the typhoon remnant clouds. Convective instability and conditional symmetric instability appeared simultaneously near Diagnosis of the interaction between the MCL and kinetic energy and positive vorticity for its further the MCL, favorable for the development of convection. the typhoon remnant implies that the MCL obtained development from the typhoon remnant in the lower troposphere. In turn, the development of the MCL provided kinetic energy and positive vorticity at upper levels for the typhoon remnant, which may have slowed clown the decaying of the typhoon.
