The collapse of thin-walled micro-grooved heat pipes is a common phenomenon in the tube flattening process, which seriously influences the heat transfer performance and appearance of heat pipe. At present, there is no...The collapse of thin-walled micro-grooved heat pipes is a common phenomenon in the tube flattening process, which seriously influences the heat transfer performance and appearance of heat pipe. At present, there is no other better method to solve this problem. A new method by heating the heat pipe is proposed to eliminate the collapse during the flattening process. The effectiveness of the proposed method is investigated through a theoretical model, a finite element（FE） analysis, and experimental method. Firstly, A theoretical model based on a deformation model of six plastic hinges and the Antoine equation of the working fluid is established to analyze the collapse of thin walls at different temperatures. Then, the FE simulation and experiments of flattening process at different temperatures are carried out and compared with theoretical model. Finally, the FE model is followed to study the loads of the plates at different temperatures and heights of flattened heat pipes. The results of the theoretical model conform to those of the FE simulation and experiments in the flattened zone. The collapse occurs at room temperature. As the temperature increases, the collapse decreases and finally disappears at approximately 130 ℃ for various heights of flattened heat pipes. The loads of the moving plate increase as the temperature increases. Thus, the reasonable temperature for eliminating the collapse and reducing the load is approximately 130℃. The advantage of the proposed method is that the collapse is reduced or eliminated by means of the thermal deformation characteristic of heat pipe itself instead of by external support. As a result, the heat transfer efficiency of heat pipe is raised.展开更多
目的建立股骨头坏死(osteonecrosis of the femoral head,ONFH)不同保留角有限元模型进行生物力学分析,为以股骨头前侧保留角(anterior preserved angle,APA)和外侧保留角(lateral preserved angle,LPA)预测ONFH塌陷风险提供力学依据。...目的建立股骨头坏死(osteonecrosis of the femoral head,ONFH)不同保留角有限元模型进行生物力学分析,为以股骨头前侧保留角(anterior preserved angle,APA)和外侧保留角(lateral preserved angle,LPA)预测ONFH塌陷风险提供力学依据。方法选择1名健康成人左侧股骨头为研究对象,获取CT数据导入Mimics21.0软件,重建完整股骨近端模型以及构建3个体积相等、形态不同的ONFH模型,导入Solidworks 2022软件中分别构建APA为60°且LPA分别为45°、50°、55°、60°、65°、70°、75°的21个ONFH有限元模型,以及LPA为60°且APA分别为45°、50°、55°、60°、65°、70°、75°的21个ONFH有限元模型。根据生理状态下股骨头负荷情况,股骨远端设置完全固定,在股骨头表面负重区施加与股骨干成25°夹角、方向向下且大小为受试者3.5倍体质量的合力,利用有限元分析软件Abaqus 2021计算并观察股骨头表面、坏死区最大应力及股骨头负重区最大位移情况。结果研究建立的ONFH模型基本符合ONFH力学情况。在相同载荷条件下,3个不同形态相同体积的坏死区构成的42个ONFH不同保留角模型中,坏死区周围均有应力集中现象。APA为60°时,LPA<60°模型的股骨头表面、坏死区最大应力和股骨头负重区最大位移明显高于LPA≥60°模型(P<0.05);LPA≥60°模型间的各指标差异无统计学意义(P>0.05)。LPA为60°时,APA<60°模型的各指标明显高于APA≥60°模型(P<0.05);APA≥60°模型间的各指标差异无统计学意义(P>0.05)。结论从生物力学角度来看,当ONFH保留角小于临界值时,股骨头应力集中现象更为明显,提示此种状态下坏死股骨头发生塌陷风险更高。展开更多
基金supported by National Natural Science Foundation of China(Grant Nos. 50975096, 51175186)Guangdong Provincial Natural Science Foundation of China(Grant No. S2011010002225)+1 种基金Guangdong Provincial Science and Technology Planning Project of China(GrantNos. 2010A080802009, 2010A011300022, 2011B040300020)Fundamental Research Funds for the Central Universities of China(GrantNo.2012ZZ0053)
文摘The collapse of thin-walled micro-grooved heat pipes is a common phenomenon in the tube flattening process, which seriously influences the heat transfer performance and appearance of heat pipe. At present, there is no other better method to solve this problem. A new method by heating the heat pipe is proposed to eliminate the collapse during the flattening process. The effectiveness of the proposed method is investigated through a theoretical model, a finite element（FE） analysis, and experimental method. Firstly, A theoretical model based on a deformation model of six plastic hinges and the Antoine equation of the working fluid is established to analyze the collapse of thin walls at different temperatures. Then, the FE simulation and experiments of flattening process at different temperatures are carried out and compared with theoretical model. Finally, the FE model is followed to study the loads of the plates at different temperatures and heights of flattened heat pipes. The results of the theoretical model conform to those of the FE simulation and experiments in the flattened zone. The collapse occurs at room temperature. As the temperature increases, the collapse decreases and finally disappears at approximately 130 ℃ for various heights of flattened heat pipes. The loads of the moving plate increase as the temperature increases. Thus, the reasonable temperature for eliminating the collapse and reducing the load is approximately 130℃. The advantage of the proposed method is that the collapse is reduced or eliminated by means of the thermal deformation characteristic of heat pipe itself instead of by external support. As a result, the heat transfer efficiency of heat pipe is raised.
