In order to provide guideline for choosing a suitable tube-wall thickness(d)for the micro-jet methane diffusion flame,the effect of tube-wall thickness on the blow-off limit is investigated via numerical simulation in...In order to provide guideline for choosing a suitable tube-wall thickness(d)for the micro-jet methane diffusion flame,the effect of tube-wall thickness on the blow-off limit is investigated via numerical simulation in the present work.The results show that the blow-off limit of micro-jet methane diffusion flame firstly increases and then decreases with the increase of tube-wall thickness.Subsequently,the underlying mechanisms responsible for the above non-monotonic blow-off limit are discussed in terms of the flow filed,strain effect and conjugate heat exchange.The analysis indicates that the flow field is insignificant for the non-monotonic blow-off limit.A smaller strain effect can induce the increase of the blow-off limit fromd=0.1 to 0.2 mm,and a worse heat recirculation effect can induce the decrease of the blow-off limit fromd=0.2 to 0.4 mm.The non-monotonic blow-off limit is mainly determined by the heat loss of flame to the tube-wall and the performance of tube-wall on preheating unburned fuel.The smallest heat loss of flame to the tube-wall and the best performance of tube-wall on preheating unburned fuel result in the largest blow-off limit atd=0.2 mm.Therefore,a moderate tube-wall thickness is more suitable to manufacture the micro-jet burner.展开更多
The operating range of the flow rate or flow velocity for the micro-jet flame is quite wide,which can be used as the heat source.In order to optimize the micro-jet tube combustor in terms of the solid material,the pre...The operating range of the flow rate or flow velocity for the micro-jet flame is quite wide,which can be used as the heat source.In order to optimize the micro-jet tube combustor in terms of the solid material,the present paper numerically investigates the impact of thermal conductivity(λs)on the operating limit of micro-jet flame.Unexpectedly,the non-monotonic blow-off limits with the increase ofλs is found,and the corresponding generation mechanisms are analyzed in terms of the thermal coupling effect,flow field,and strain effect.At first,the lower preheating temperature of the fuel and larger heat loss amount to the environment lead to a larger blow-off limit at a largerλs.After that,the smaller local flow velocity in the vicinity of flame root and smaller strain effect slightly increase the blow-off limit with the continuously increasingλs.Therefore,it is deduced that the applied performance of micro-jet combustor with a smaller thermal conductivity is better in terms of the blow-off limit.展开更多
The occurrence of Lean Blowout(LBO)is a disadvantage that endangers a stable operation of gas turbines.A determination of LBO limits is essential in the design of gas turbine combustors.A semiempirical model is one of...The occurrence of Lean Blowout(LBO)is a disadvantage that endangers a stable operation of gas turbines.A determination of LBO limits is essential in the design of gas turbine combustors.A semiempirical model is one of the most widely used methods to predict LBO limits.Among the existing semiempirical models for predicting LBO limits,Lefebvre’s LBO model and the Flame Volume(FV)model are particularly suitable for gas turbine combustors.On the basis of Lefebvre’s and FV models,the concept of effective evaporation efficiency is introduced in this paper,and a Flame Volume-Evaporation Efficiency(FV-EE)model is derived and validated.LBO experiments are carried out in a model combustor with 23 different structures and 10 different sprays.The prediction uncertainty of the FV-EE model is less than±13%for all of these 33 structures and sprays,compared with±50%for the FV model and±60%for Lefebvre’s model.Furthermore,the prediction uncertainty of the FV-EE model is also less than±13%for other combustors from available literature.展开更多
目的运用动量参数探讨老年人执行身体前倾动作时,年龄差异对动态平衡机制的影响。方法16位健康老年人为老年组,16位健康大学生为年轻组,组内男女各半。受试者站立于测力板上,随机进行自然站立与双脚并拢的前倾动作各10次,并以5台红外线...目的运用动量参数探讨老年人执行身体前倾动作时,年龄差异对动态平衡机制的影响。方法16位健康老年人为老年组,16位健康大学生为年轻组,组内男女各半。受试者站立于测力板上,随机进行自然站立与双脚并拢的前倾动作各10次,并以5台红外线摄影机同步纪录;以MATLAB计算质心线动量与角动量,并以SPSS进行检验。结果执行身体前倾动作时的动态平衡能力,老年人与年轻人在不同支撑面下的质心线动量和角动量存在显著差异(P<0.05);线动量与角动量显著相关(r=0.947),且与压力中心偏离度(r=0.877 vs 0.720)、质心偏离度(r=0.923 vs 0.814)、倾斜角(r=0.671 vs 0.557)等参数呈正相关,而与安全限界(r=-0.819 vs-0.695)呈负相关。结论利用动量参数可以作为评价老年人动态平衡的手段,而促进老年人动态平衡提升,应以训练动态稳定极限位置的质心速度控制能力为优先考虑。展开更多
基金Project(51876074)supported by the National Natural Science Foundation of China。
文摘In order to provide guideline for choosing a suitable tube-wall thickness(d)for the micro-jet methane diffusion flame,the effect of tube-wall thickness on the blow-off limit is investigated via numerical simulation in the present work.The results show that the blow-off limit of micro-jet methane diffusion flame firstly increases and then decreases with the increase of tube-wall thickness.Subsequently,the underlying mechanisms responsible for the above non-monotonic blow-off limit are discussed in terms of the flow filed,strain effect and conjugate heat exchange.The analysis indicates that the flow field is insignificant for the non-monotonic blow-off limit.A smaller strain effect can induce the increase of the blow-off limit fromd=0.1 to 0.2 mm,and a worse heat recirculation effect can induce the decrease of the blow-off limit fromd=0.2 to 0.4 mm.The non-monotonic blow-off limit is mainly determined by the heat loss of flame to the tube-wall and the performance of tube-wall on preheating unburned fuel.The smallest heat loss of flame to the tube-wall and the best performance of tube-wall on preheating unburned fuel result in the largest blow-off limit atd=0.2 mm.Therefore,a moderate tube-wall thickness is more suitable to manufacture the micro-jet burner.
文摘The operating range of the flow rate or flow velocity for the micro-jet flame is quite wide,which can be used as the heat source.In order to optimize the micro-jet tube combustor in terms of the solid material,the present paper numerically investigates the impact of thermal conductivity(λs)on the operating limit of micro-jet flame.Unexpectedly,the non-monotonic blow-off limits with the increase ofλs is found,and the corresponding generation mechanisms are analyzed in terms of the thermal coupling effect,flow field,and strain effect.At first,the lower preheating temperature of the fuel and larger heat loss amount to the environment lead to a larger blow-off limit at a largerλs.After that,the smaller local flow velocity in the vicinity of flame root and smaller strain effect slightly increase the blow-off limit with the continuously increasingλs.Therefore,it is deduced that the applied performance of micro-jet combustor with a smaller thermal conductivity is better in terms of the blow-off limit.
基金co-supported by the National Science and Technology Major Project,China(No.2017-III-0007-0032)the Key Laboratory Fund,China(No.6142702180306).
文摘The occurrence of Lean Blowout(LBO)is a disadvantage that endangers a stable operation of gas turbines.A determination of LBO limits is essential in the design of gas turbine combustors.A semiempirical model is one of the most widely used methods to predict LBO limits.Among the existing semiempirical models for predicting LBO limits,Lefebvre’s LBO model and the Flame Volume(FV)model are particularly suitable for gas turbine combustors.On the basis of Lefebvre’s and FV models,the concept of effective evaporation efficiency is introduced in this paper,and a Flame Volume-Evaporation Efficiency(FV-EE)model is derived and validated.LBO experiments are carried out in a model combustor with 23 different structures and 10 different sprays.The prediction uncertainty of the FV-EE model is less than±13%for all of these 33 structures and sprays,compared with±50%for the FV model and±60%for Lefebvre’s model.Furthermore,the prediction uncertainty of the FV-EE model is also less than±13%for other combustors from available literature.
文摘目的运用动量参数探讨老年人执行身体前倾动作时,年龄差异对动态平衡机制的影响。方法16位健康老年人为老年组,16位健康大学生为年轻组,组内男女各半。受试者站立于测力板上,随机进行自然站立与双脚并拢的前倾动作各10次,并以5台红外线摄影机同步纪录;以MATLAB计算质心线动量与角动量,并以SPSS进行检验。结果执行身体前倾动作时的动态平衡能力,老年人与年轻人在不同支撑面下的质心线动量和角动量存在显著差异(P<0.05);线动量与角动量显著相关(r=0.947),且与压力中心偏离度(r=0.877 vs 0.720)、质心偏离度(r=0.923 vs 0.814)、倾斜角(r=0.671 vs 0.557)等参数呈正相关,而与安全限界(r=-0.819 vs-0.695)呈负相关。结论利用动量参数可以作为评价老年人动态平衡的手段,而促进老年人动态平衡提升,应以训练动态稳定极限位置的质心速度控制能力为优先考虑。
