Based on nuclear power plant(NPP) best-estimate transient analysis with RELAP5 / MOD3 code,the reactor point kinetics model in RELAP5 / MOD3 code is replaced by the two-group,3-D space and time dependent neutron kinet...Based on nuclear power plant(NPP) best-estimate transient analysis with RELAP5 / MOD3 code,the reactor point kinetics model in RELAP5 / MOD3 code is replaced by the two-group,3-D space and time dependent neutron kinetic model,and two-fluid model is replaced by drift flux model.A coupled three-dimensional physics and thermal-hydrodynamics model is used to develop its corresponding computing code,thus simulating natural circulation of single-phase flow for the PWR.In this paper,we report the forward and reverse flow distribution in the inverted U-tubes of the steam generator(SG) under some typical operating conditions in the natural circulation case, and analyze the influence of main coolant pump resistance on the forward and reverse flow distribution.The calculation results show that,the pressure drop between SG inlet and outlet plenum decreases,and the SG inlet and outlet mass flow decrease with an increased main coolant pump resistance,but net mass flux of reverse flow in inverted U-tubes,and the ratio of mass flow in all reverse flow tubes to that of main coolant pipeline increase, meanwhile,the secondary steam load is invariable in this process.展开更多
With net zero carbon emissions targets approaching over the next 20 to 30 years, the water industry must act now to develop energy efficient techniques and designs to reduce emissions and reduce the carbon footprint o...With net zero carbon emissions targets approaching over the next 20 to 30 years, the water industry must act now to develop energy efficient techniques and designs to reduce emissions and reduce the carbon footprint of water utility providers. There is also the potential for significant energy and therefore financial savings to be realised from the adoption of more energy efficient designs approaches. Water utility providers account for a significant proportion of national electricity consumption. The purpose of this research is to determine if, over the long term, opting for a larger diameter pipe at design stage can lead to significant financial and emissions savings for water utility providers when considering pumping mains. Pumping mains are widely used throughout the water and wastewater industry where a gravity solution is not possible. 72 hypothetical water main design scenarios were analysed and the long term financial and environmental impact of each hypothetical water main was assessed. It was found across all design scenarios that larger diameter water mains were capable of delivering the same rate of flow of smaller diameter pipes at a much reduced velocity and requiring reduced pumping power. It was concluded that pumped mains of larger diameters can ultimately be more energy efficient and cost effective over the long term when selected in favour of smaller diameter pumped mains in otherwise identical design scenarios.展开更多
Objective：To obtain early results of off-pump coronarE~ artery bypass grafting（OPCAB） in patients with significant left main coronary artery（LMCA） and triple vessels stenosis by comparing with those of a similar ...Objective：To obtain early results of off-pump coronarE~ artery bypass grafting（OPCAB） in patients with significant left main coronary artery（LMCA） and triple vessels stenosis by comparing with those of a similar group undergoing conventional coronary artery bypass surgery（CCAB）. Methods：Data for patients with significant LMCA and triple vessels stenosis who underwent CCAB or OPCAB were collected retrospectively between January 1999 and May 2006. Non-randomized, retrospective data analysis included demo- graphic and preoperative risk factors, operative details, clinical outcome and early follow-up. Results： The number of distal anastomo- sis and grafts varied from 3 to 6. The average number per patient was similar in the two groups （OPCAB group：3.76 ± 0.98, CCAB group：3.81 ± 1.02）. Thirty-day mortality occurred to one patient in the OPCAB group whereas two early deaths were observed in the CCAB group but did not reach statistical significance （P 〉 0.05）. The frequency of atrial fibrillation （AF）, IABP usage, mediastinitis, re-operation for bleeding （or tamponade） were similar in the two groups （P 〉 0.05）. Postoperative inotropic requirements, peak CKMB, ventilation time, blood loss, FFP, RBC transfusion need and the length of ICU-stay were all significantly lower in the OPCAB group compared with CCAB group（P 〈 0.05）.Conclusion： Significant LMCA and triple-vessel stenosis can safely and effectively undergo myocardial revascularization using OPCAB surgery. LMCA should no longer be seen as a contraindication to perform OPCAB grafting.展开更多
The influence of the axial mount position of the guide vane on the pressure fluctuation in a nuclear pump(AP1000)is investigated.The characteristics of the three-dimensional flow inside the nuclear pump are analyzed b...The influence of the axial mount position of the guide vane on the pressure fluctuation in a nuclear pump(AP1000)is investigated.The characteristics of the three-dimensional flow inside the nuclear pump are analyzed by means of numerical simulation.Results indicate that when the axial relative distance between the guide vane and the pumping chamber is reduced,in conditions of“small flow,”the efficiency of the pump increases,the pressure inside the pumping chamber decreases,while the losses related to the guide vane grow.Under large flow conditions,as the efficiency of the pump decreases,the losses for the guide vane and the pumping chamber increase.The pressure fluctuation in the annular pumping chamber is basically determined by the rotation frequency and the blade passing frequency.The magnitude of these fluctuations is affected by the guide vane axial position.In particular,the smallest possible amplitude is obtained when the outlet central plane of the guide vane coincides with the outlet axis of the pumping chamber.展开更多
文摘Based on nuclear power plant(NPP) best-estimate transient analysis with RELAP5 / MOD3 code,the reactor point kinetics model in RELAP5 / MOD3 code is replaced by the two-group,3-D space and time dependent neutron kinetic model,and two-fluid model is replaced by drift flux model.A coupled three-dimensional physics and thermal-hydrodynamics model is used to develop its corresponding computing code,thus simulating natural circulation of single-phase flow for the PWR.In this paper,we report the forward and reverse flow distribution in the inverted U-tubes of the steam generator(SG) under some typical operating conditions in the natural circulation case, and analyze the influence of main coolant pump resistance on the forward and reverse flow distribution.The calculation results show that,the pressure drop between SG inlet and outlet plenum decreases,and the SG inlet and outlet mass flow decrease with an increased main coolant pump resistance,but net mass flux of reverse flow in inverted U-tubes,and the ratio of mass flow in all reverse flow tubes to that of main coolant pipeline increase, meanwhile,the secondary steam load is invariable in this process.
文摘With net zero carbon emissions targets approaching over the next 20 to 30 years, the water industry must act now to develop energy efficient techniques and designs to reduce emissions and reduce the carbon footprint of water utility providers. There is also the potential for significant energy and therefore financial savings to be realised from the adoption of more energy efficient designs approaches. Water utility providers account for a significant proportion of national electricity consumption. The purpose of this research is to determine if, over the long term, opting for a larger diameter pipe at design stage can lead to significant financial and emissions savings for water utility providers when considering pumping mains. Pumping mains are widely used throughout the water and wastewater industry where a gravity solution is not possible. 72 hypothetical water main design scenarios were analysed and the long term financial and environmental impact of each hypothetical water main was assessed. It was found across all design scenarios that larger diameter water mains were capable of delivering the same rate of flow of smaller diameter pipes at a much reduced velocity and requiring reduced pumping power. It was concluded that pumped mains of larger diameters can ultimately be more energy efficient and cost effective over the long term when selected in favour of smaller diameter pumped mains in otherwise identical design scenarios.
基金This work was supported by the Fund of Social Development in Jiangsu province(NO:BS2006013)
文摘Objective：To obtain early results of off-pump coronarE~ artery bypass grafting（OPCAB） in patients with significant left main coronary artery（LMCA） and triple vessels stenosis by comparing with those of a similar group undergoing conventional coronary artery bypass surgery（CCAB）. Methods：Data for patients with significant LMCA and triple vessels stenosis who underwent CCAB or OPCAB were collected retrospectively between January 1999 and May 2006. Non-randomized, retrospective data analysis included demo- graphic and preoperative risk factors, operative details, clinical outcome and early follow-up. Results： The number of distal anastomo- sis and grafts varied from 3 to 6. The average number per patient was similar in the two groups （OPCAB group：3.76 ± 0.98, CCAB group：3.81 ± 1.02）. Thirty-day mortality occurred to one patient in the OPCAB group whereas two early deaths were observed in the CCAB group but did not reach statistical significance （P 〉 0.05）. The frequency of atrial fibrillation （AF）, IABP usage, mediastinitis, re-operation for bleeding （or tamponade） were similar in the two groups （P 〉 0.05）. Postoperative inotropic requirements, peak CKMB, ventilation time, blood loss, FFP, RBC transfusion need and the length of ICU-stay were all significantly lower in the OPCAB group compared with CCAB group（P 〈 0.05）.Conclusion： Significant LMCA and triple-vessel stenosis can safely and effectively undergo myocardial revascularization using OPCAB surgery. LMCA should no longer be seen as a contraindication to perform OPCAB grafting.
基金supported by the National Natural Science Foundation of China(No.51469013).
文摘The influence of the axial mount position of the guide vane on the pressure fluctuation in a nuclear pump(AP1000)is investigated.The characteristics of the three-dimensional flow inside the nuclear pump are analyzed by means of numerical simulation.Results indicate that when the axial relative distance between the guide vane and the pumping chamber is reduced,in conditions of“small flow,”the efficiency of the pump increases,the pressure inside the pumping chamber decreases,while the losses related to the guide vane grow.Under large flow conditions,as the efficiency of the pump decreases,the losses for the guide vane and the pumping chamber increase.The pressure fluctuation in the annular pumping chamber is basically determined by the rotation frequency and the blade passing frequency.The magnitude of these fluctuations is affected by the guide vane axial position.In particular,the smallest possible amplitude is obtained when the outlet central plane of the guide vane coincides with the outlet axis of the pumping chamber.
