科技论文写作作业xjtu.docx

键入文字键入文字英语科技论文实用写作方法作业 英语科技论文实用写作方法作业课程班级号：2学院：能动学院系别： 班级： ()Mail： An Experimental study on Evaporation/Boiling HeatTransfer in Sintered Porous WickSUN Zhen HONG Fang-Jun ZHENG Ping(School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China)Abstract We has designed and established an experimental apparatus to study the evaporation/boiling heat transfer in particle sintered porous wick under the working condition of heat pipe. The effects of particle size as well as the thickness and volumetric porosity of porous wick on evaporation/boiling heat transfer were investigated by using distilled water as working fluid. It was found that for the fixed particle size and porosity, there exists an optimal wick thickness corresponding to the maximum heat transfer coefficient. For the fixed thickness of porous wick, there is an optimal porosity when the heat flux is relatively low, however, the smaller the porosity is, and the higher the heat transfer coefficient is when heat flux is relatively high. An evaporation/boiling heat transfer model was also summarized to give plausible explanations of experimental results.Key words particle sintered; porous wick; evaporation/boiling; heat pipe键入文字键入文字0 Introduction The flat heat pipe is a high-performance thermal diffusion technology which connects the electronic chip (heat sauce) and the heat sink. It can be considered as a twodimension heat pipe from the direction of steam flow. The particle sintered porous wick is an important internal structure of the flat heat pipe. When the flat heat pipe is on the stable running period and the liquid level is lower than the upper surface of the porous wick, the phase transition occurs. To distinguish it from the pool boiling, this phase transition is called evaporation/boiling heat transfer. The evaporation and boiling heat transfer of refrigerant in and at the surface of porous wick is one of the important factors influencing heat pipes property. Although much literature about porous wick boiling heat transfer has been published (see paper 1, 2 and their references), much of the research was about pool boiling or one-dimension heat pipe, and little research was aimed at evaporation/boiling heat transfer in sintered 3-5 porous wick in flat heat pipe.Hanlon and Mal 3 examined the evaporation/boiling heat transfer of thick cooper (1.9mm) particle sintered porous wick, and they found that boiling would occur and bubbles appeared in wick which led to a decline of heat transfer when the heat flux was between 5-20w/cm2. The performance of heat transfer would decline with the increase of wicks thickness. Li, Peterson et al. 4, 5 studied the 0.37-1 mm (bubbles departure diameter) cooper wicks evaporation/boiling heat transfer. They found that the critical heat flux increased with the increase of wicks thickness, while the heat transfer coefficient changed little. They considered that the evaporation of liquid film on porous wicks surface was the main way of heat transfer, and also there existed an optimal porosity corresponding to the maximal critical heat flux. The optimal porosity was related to the thickness of porous wick and the size of the mesh: when the diameter of meshs cooper wire was fixed, the heat transfer coefficient decreased with the increase of porosity.From the research 3-5 above, the liquid level evened the surface of porous wick according to the overflow principle; meanwhile those experiments were conducted at the atmosphere pressure which didnt correspond to the heat pipe working condition. In this study, an experiment investigation in heat pipe (vacuum decompression) condition was done to characterize the effects from wicks diameter, type and porous wicks thickness (PM8PM2, PM6PM9PM3 at the condition of same heat flux. We can conclude that for the spray powder, when the porosity is fixed, there is an optimal thickness of wick which corresponds to the maximum heat transfer coefficient. The reason can be explained as below: the ways of porous wick evaporation/boiling heat transfer include the conduction between solids in wick, convection between liquids in liquid region and the film evaporation of liquid-vapor interface in and on the wick; the thick wick has a better diffusion effect and larger convection transfer area, then the liquid-vapor interface will increase after the formation of gas province; meanwhile thickening the wick will increase the thermal resistance in gas province and the vapors overflow resistance which causes an increase in liquids superheat. The interaction of the factors above makes the existence of optimal thickness of wick. It can be seen from Fig. 5 that when the thickness of wick increases, the maximum heat transfer coefficients heat flux decreases. That is the reason why the heat conduction in liquid region and the formation of gas province lead to a decline of heat transfer performance.2.4 Effects of wick thickness on evaporation/ boiling heat transfer (electrolysis powder)The Fig. 6 shows the influence by heat flux and thickness of wick on evaporation/boiling heat transfer coefficient for PM1, PM4 and PM7 electrolysis powder. With the increase of heat flux, the heat transfer coefficient increases first and then reduces like the spray powders situation. The heat transfer coefficients rank is PM7PM4PM1, and there isnt an optimal wick thickness. From the Table.1, the thickness range of PM1, PM4 and PM7 (0.35-0.45mm) is smaller than the range of PM2, PM5, PM8 (0.36-0.59mm) and the range of PM3, PM6, PM9 (0.37-0.81mm). The reason is probably that the optimal thickness isnt approached. If we expand the experimental rang, the optimal thickness might be approached by analyzing the mechanism of electrolysis powder.Fig.6 Effects of wick thickness on evaporation/boiling heat transfer (electrolysis powder)2.5 Effects of porosity on evaporation/boiling heat transferThe Fig.7 shows different samples PM1, PM2 and PM3s heat transfer performances. From Table.1 we can learn that the samples PM1, PM2 and PM3s thickness differences are very small ( PM1 PM2. When the heat flux is not so high, their heat transfer coefficients rank is PM1 PM2 PM3.Fig. 7 Effects of porosity on evaporation/boiling heat transferIt means that there must be an optimal porosity when wicks thickness is a constant. Its notable that sample PM1s different species from the other two samples might be the reason why sample PM1 has a better performance. We can find that the electrolysis cooper powder and spray cooper powder are both non-spherical irregular particles; however the electrolysis powder presents to be arborescent and has many micro pore structures. When the heat flux is relatively high (the heat transfer coefficient has declined), the minimum porosity of PM2 performs best. It can be seen that the little porosity has some advantage over the high heat flux, because the number of nucleation cores increases with the reinforcement of liquid driving force.3. Conclusions In this paper, we have studied the evaporation/boiling heat transfer phenomenon with electrolysis and spray powder particle sintered porous wick at the heat pipe condition (vacuum-sealed, evaporation temperature 45 C), and have obtained the conclusions below:1)With the increase of heat flux, the evaporation/boiling heat transfer coefficient first increases and then decreases.2)When the porosity is fixed, there is an optimal wicks thicknesses corresponding to the maximum heat transfer coefficient for the spray powder, and for the electrolysis powder, we havent find the optimal wick thickness owing to the limitation of experimental condition. Theoretically there is an optimal wicks thickness according to the evaporation/boiling model for electrolysis powder. 3)When the wicks thickness is fixed, there is an optimal porosity if the heat flux is not so high; on the other hand, if the heat flux is relatively high, the smaller porositys wick has a better heat transfer performance.References1 LIN Ruitai. Introduction to Heat and Mass Transfer in Porous Medium M. Tianjin University Press, 1995:286 (In Chinese)2 Brian D I, Tyler W D, Suresh V G. Heat and Mass Transport in Heat Pipe Wick Structure J. Journal of Thermophysics and heat Transfer, 2007, 21(2): 329-4043 Hanlon M A, Ma H B. Evaporation/ Boiling in Sintered Porous Media J. ASME J. Heat Transfer, 2003, 125: 644-6524 LI Chen, Peterson G P, WANG Yaxiong. Evaporation/Boiling in Thin Capillary Wick (1)- Wick Thickness Effects J. Journal of Heat Transfer, 2006, 128: 1312-13195 LI Chen, Peterson G P. Evaporation/ Boiling in Thin Capillary Wicks (II)Effects of Volumetric Porosity and Mess Size J. Journal of Heat Transfer, 2006, 128:1320-1328科技论文写作学习心得课程收获、体会A 课程整体收获在以前的英语学习中，接触到很多英语写作课程，但是科技论文写作还是第一次。以往的写作课着眼于记叙文议论文的写作指导，而科技论文更偏向于说明文，和其他的写作有很大的不同之处。通过本课程的学习，使我明白了一些关于科技论文写作的最基本的内容。首先，科技论文的本质是说明文，其最大的特点就是语言准确简洁。以前的英语写作过程中我们常常着眼于叙述语言的生动性、句式的多变性以及高级词汇的使用等等，但是在科技论文中，应该尽量避免过于繁杂的词汇、句式、语法。其次，科技论文叙述说明的目的性很强有特定的专业读者，因此往往开宗明义直入主题，叙述过程环环相扣逐步深入研究课题，而且还会直接省略一些相关定义解释的内容，默认读者已经了解。以上为科技论文写作和一般英语写作的主要不同之处。大二以后的课程基本都是专业课，英语学习相对减少甚至是停止英语学习。本课程使我重新开始巩固继续接触英语的学习，并且明确了以后因与学习的方向。从中学到本科的英语学习基本着眼于日常生活交际阅读的层面，进入研究生学习阶段后，英语的学习要更进一步于科研应用的层面。因此要转变英语学习的方向，从基本使用的方向转向科研技术的方向。另外，在学习过程中，使我逐渐了解了认真谨慎的科学作风。在着手写/翻译一篇科技论文时，先弄懂文章的思路整体内容，然后推敲字句的准确使用，而不是使用口语化模糊的字句，最后整体把握修改全文。B 翻译过程中具体收获科技论文的一个重要特点就是文章用词的准确性和句子、结构的简洁性。因此在写作中会有一些常用的功能性词汇和句型，它们的正确使用不仅有助于作者内容的明确表达，还有利于读者的理解。在上课过程中的论文讲评还有各个部分（导论、实验、结论等）经常会用的句型结构，对实际的写作有很大的帮助。在刚进入研究生阶段，接触的英文科技论文不多，读起来写作起来都相对吃力，觉得翻译时很多地方无从下手，但是掌握了一些常用词汇和句型会减少很多困难。文章中，时态的选择有时候也是个需要多加考虑的问题。比如前人所做的工作，实验过程，实验结果部分都会涉及到。同一种情况下，对于研究导向和论文导向的文章所选择的时态也会大有不同， 这些都是要斟酌的。在授课过程中，这些问题都在很多例子中涉及到。 另外，说明文中图和表的使用及表述方法也是很有讲究的。图表的格式，叙述图表中所要表达的内同都有要特定的原则。如果没有特别注意过这些东西，在翻译尤其是写作中会出现很多问题。当翻译写作整体基本完成的时候需要对全文整体进行再次检查修改。在翻译中，我出