Use of the low temperature (less than 100°C) energy contributes to effective use of heat resources. The cost recovery by power generation is difficult by using an existing system (the binary cycle or the thermoel...Use of the low temperature (less than 100°C) energy contributes to effective use of heat resources. The cost recovery by power generation is difficult by using an existing system (the binary cycle or the thermoelectric conversion element), because the initial investment is large. The final purpose of this research is development of the low temperature difference drive engine supposing use in a hot-springs resort as a power source for electric power generation. In order that a traveler may look at and delight a motion of an engine, it is made to drive at low-speed number of rotations. An engine cycle of this study is aimed at the development of Stirling cycle engine which can maintain high efficiency in small size. This kind of engine has simple structure;it brings low cost, and it is easy to perform maintenance. However, it is difficult to obtain enough output by this type of engine, because of its low temperature difference. This paper deals with the heat transfer characteristic that the working fluid including a phase change material flows into the heating surface from the narrow path. In order to increase the amount of the heat transmission, Diethylether is added to the working fluid. Diethylether is selected as a phase change material (PCM) that has the boiling point which exists between the heat source of high temperature and low temperature. The parameters of the experiment are additive amount of PCM, rotational speed of the displacer piston and temperature of heat transfer surface. It is shown that it is possible to make exchange of heat amount increase by adding phase change material. The result of this research shows the optimal condition of the difference in temperature in heat processing, number of revolutions, and addition concentration of PCM.展开更多
The characteristics and microstructural changes of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlled low-cycle fatigue.The re- sults show that the cyclic softening...The characteristics and microstructural changes of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlled low-cycle fatigue.The re- sults show that the cyclic softening is featured in both steels hardened in different conditions under the strain controlled amplitude range of Δε_t/2=0.6-1.8×10^(-2).The softening effect mainly occurs in some initial cycles and the stress amplitude varies slightly in the sequential cycles,i.e.the softening effect is minified.No obvious stress saturation phenomenon was ob- served during the whole cyclic deformation.The TEM analysis shows that the cyclic softening is related to heterogenity of plastic deformation.The softening of the tested steels is caused by the formation of the dislocation cell structure with low density and low internal stress,and by the fragmentation and redissolution of fine carbides into matrix.展开更多
The preparation process of the CO gas sensor used at normal temperature is presented.The electric conductance of this type of sensor evolved oscillation from regularly when the sensor is exposed to low level CO gas.Th...The preparation process of the CO gas sensor used at normal temperature is presented.The electric conductance of this type of sensor evolved oscillation from regularly when the sensor is exposed to low level CO gas.The gas sensing mechanism was investigated by its crystalline structure.The mechanism of information sensing,which was the concurrence of the grain boundary barrier control and the crystal surface control,is discussed.展开更多
Due to the rapid development of China＇ s rail transportation equipment manufacturing industry and related international distribution, important material suppliers such as Baoshan Iron ＆ Steel Co., Ltd. carries on in...Due to the rapid development of China＇ s rail transportation equipment manufacturing industry and related international distribution, important material suppliers such as Baoshan Iron ＆ Steel Co., Ltd. carries on investigating the stability of material under extremely cold conditions. In this study, mechanical properties and secondary work embrittlement of weathering steel 05CuPCrNi were tested at low temperature. Compared to the mechanical properties at room temperature, the yield and tensile strength increase slightly with decreasing temperature. However, the variation of elongation is not obvious. The experimental results also show that the secondary work embrittlement transition temperature of 05CuPCrNi is lower than - 60 ℃. These results provide the basis for the use of this train body material in extremely cold regions.展开更多
Plasma boriding treatment was carried out at low temperature for the hot work die steel H13 assisted by surface nanocrystallization technology in this paper.At the same time,the thermal fatigue property of it was inve...Plasma boriding treatment was carried out at low temperature for the hot work die steel H13 assisted by surface nanocrystallization technology in this paper.At the same time,the thermal fatigue property of it was investigated through thermal fatigue testing with 3000 continuous cycles from room temperature to 700℃.The changes of structure and grain size in surface layer were characterized by high-resolution transmission electron microscopy(HRTEM).After plasma boriding at 580℃ for 4 h,the phase composition,morphology and in-situ nanomechanical property of boride layer were investigated by X-ray diffraction spectroscopy(XRD),scanning electron microscope(SEM),nanoindentation test,respectively.The results show that the boride layer with about thickness of 5μm is composed with two phases of Fe2B and FeB.The nanohardness of boride layer is as high as 21 GPa.Furthermore,thermal fatigue testing shows that the boride layer with excellent oxidation resistance and mechanical strength at elevated temperatures could effectively delay the crack initiation and impede the crack propagation.Therefore,the thermal fatigue property of H13 can be remarkably improved.展开更多
目的分析超声医生下背痛(low back pain,LBP)与相关缺勤发生影响因素,为防控LBP及其后果提供依据。方法采用分层整群抽样法抽取广东省内31家医院的超声医生作为研究对象,使用修订版北欧肌肉骨骼疾患问卷进行调查,并通过多因素logistic...目的分析超声医生下背痛(low back pain,LBP)与相关缺勤发生影响因素,为防控LBP及其后果提供依据。方法采用分层整群抽样法抽取广东省内31家医院的超声医生作为研究对象,使用修订版北欧肌肉骨骼疾患问卷进行调查,并通过多因素logistic回归分析LBP与相关缺勤发生的影响因素。结果共有512名超声医生的调查结果纳入分析,其LBP年发生率为55.5%,所致缺勤发生率为10.9%。妇幼保健院与综合医院的LBP发生率比较,差异无统计学意义(χ^(2)=0.477,P>0.05)。工龄>10~15年组的LBP发生率高于≤5年组(OR=3.34);月收入>10000元者LBP发生率高于月收入≤5000元者(OR=1.96);轮班引起LBP发生风险增加(OR=1.73)。工龄>10~15、>15~20、>20年组的LBP致缺勤发生率高于工龄≤5年组(OR=4.31、4.86、4.72);每天检查时间>8 h的LBP致缺勤发生率高于≤6 h者(OR=4.14)。结论超声医生的LBP发生率较高,其影响因素包括工龄、月收入和轮班情况,LBP致缺勤的影响因素包括工龄和每天超声检查时间,可考虑优先从工作组织管理措施减少LBP致缺勤发生。展开更多
文摘Use of the low temperature (less than 100°C) energy contributes to effective use of heat resources. The cost recovery by power generation is difficult by using an existing system (the binary cycle or the thermoelectric conversion element), because the initial investment is large. The final purpose of this research is development of the low temperature difference drive engine supposing use in a hot-springs resort as a power source for electric power generation. In order that a traveler may look at and delight a motion of an engine, it is made to drive at low-speed number of rotations. An engine cycle of this study is aimed at the development of Stirling cycle engine which can maintain high efficiency in small size. This kind of engine has simple structure;it brings low cost, and it is easy to perform maintenance. However, it is difficult to obtain enough output by this type of engine, because of its low temperature difference. This paper deals with the heat transfer characteristic that the working fluid including a phase change material flows into the heating surface from the narrow path. In order to increase the amount of the heat transmission, Diethylether is added to the working fluid. Diethylether is selected as a phase change material (PCM) that has the boiling point which exists between the heat source of high temperature and low temperature. The parameters of the experiment are additive amount of PCM, rotational speed of the displacer piston and temperature of heat transfer surface. It is shown that it is possible to make exchange of heat amount increase by adding phase change material. The result of this research shows the optimal condition of the difference in temperature in heat processing, number of revolutions, and addition concentration of PCM.
文摘The characteristics and microstructural changes of cyclic softening in hot-working die steels 5CrNiMo and 5Cr2NiMoVSi were studied under strain controlled low-cycle fatigue.The re- sults show that the cyclic softening is featured in both steels hardened in different conditions under the strain controlled amplitude range of Δε_t/2=0.6-1.8×10^(-2).The softening effect mainly occurs in some initial cycles and the stress amplitude varies slightly in the sequential cycles,i.e.the softening effect is minified.No obvious stress saturation phenomenon was ob- served during the whole cyclic deformation.The TEM analysis shows that the cyclic softening is related to heterogenity of plastic deformation.The softening of the tested steels is caused by the formation of the dislocation cell structure with low density and low internal stress,and by the fragmentation and redissolution of fine carbides into matrix.
文摘The preparation process of the CO gas sensor used at normal temperature is presented.The electric conductance of this type of sensor evolved oscillation from regularly when the sensor is exposed to low level CO gas.The gas sensing mechanism was investigated by its crystalline structure.The mechanism of information sensing,which was the concurrence of the grain boundary barrier control and the crystal surface control,is discussed.
文摘Due to the rapid development of China＇ s rail transportation equipment manufacturing industry and related international distribution, important material suppliers such as Baoshan Iron ＆ Steel Co., Ltd. carries on investigating the stability of material under extremely cold conditions. In this study, mechanical properties and secondary work embrittlement of weathering steel 05CuPCrNi were tested at low temperature. Compared to the mechanical properties at room temperature, the yield and tensile strength increase slightly with decreasing temperature. However, the variation of elongation is not obvious. The experimental results also show that the secondary work embrittlement transition temperature of 05CuPCrNi is lower than - 60 ℃. These results provide the basis for the use of this train body material in extremely cold regions.
基金Supported by Shanghai Leading Academic Discipline Project(S30107)
文摘Plasma boriding treatment was carried out at low temperature for the hot work die steel H13 assisted by surface nanocrystallization technology in this paper.At the same time,the thermal fatigue property of it was investigated through thermal fatigue testing with 3000 continuous cycles from room temperature to 700℃.The changes of structure and grain size in surface layer were characterized by high-resolution transmission electron microscopy(HRTEM).After plasma boriding at 580℃ for 4 h,the phase composition,morphology and in-situ nanomechanical property of boride layer were investigated by X-ray diffraction spectroscopy(XRD),scanning electron microscope(SEM),nanoindentation test,respectively.The results show that the boride layer with about thickness of 5μm is composed with two phases of Fe2B and FeB.The nanohardness of boride layer is as high as 21 GPa.Furthermore,thermal fatigue testing shows that the boride layer with excellent oxidation resistance and mechanical strength at elevated temperatures could effectively delay the crack initiation and impede the crack propagation.Therefore,the thermal fatigue property of H13 can be remarkably improved.
文摘目的分析超声医生下背痛(low back pain,LBP)与相关缺勤发生影响因素,为防控LBP及其后果提供依据。方法采用分层整群抽样法抽取广东省内31家医院的超声医生作为研究对象,使用修订版北欧肌肉骨骼疾患问卷进行调查,并通过多因素logistic回归分析LBP与相关缺勤发生的影响因素。结果共有512名超声医生的调查结果纳入分析,其LBP年发生率为55.5%,所致缺勤发生率为10.9%。妇幼保健院与综合医院的LBP发生率比较,差异无统计学意义(χ^(2)=0.477,P>0.05)。工龄>10~15年组的LBP发生率高于≤5年组(OR=3.34);月收入>10000元者LBP发生率高于月收入≤5000元者(OR=1.96);轮班引起LBP发生风险增加(OR=1.73)。工龄>10~15、>15~20、>20年组的LBP致缺勤发生率高于工龄≤5年组(OR=4.31、4.86、4.72);每天检查时间>8 h的LBP致缺勤发生率高于≤6 h者(OR=4.14)。结论超声医生的LBP发生率较高,其影响因素包括工龄、月收入和轮班情况,LBP致缺勤的影响因素包括工龄和每天超声检查时间,可考虑优先从工作组织管理措施减少LBP致缺勤发生。
