建筑环境与能源应用工程专业英语5讲课教案.ppt

建筑建筑环境与能源境与能源应用工程用工程专业英英语5 5heat transfer equipment 传热设备传热设备 heat exchanger 热交换器热交换器boiler 锅炉锅炉 condenser 冷凝器冷凝器 radiator 散热器散热器 refrigerator 冰箱冰箱solar collector 太阳能集热器太阳能集热器 heat transfer rate 传热传热(速速)率率temperature difference 温差温差 factor of safety 安全系数安全系数experimental error 实验误差实验误差 operating condition 运行条件运行条件heat transfer coefficient 传热系数传热系数under these adverse conditions 在最不利工况下在最不利工况下three forms of heat transfer:conduction 传导传导 convection 对流对流 radiation 辐射辐射heat transfer equipment 传热设备传热设备 heat exchanger 热交换器热交换器boiler 锅炉锅炉 condenser 冷凝器冷凝器 radiator 散热器散热器 refrigerator 冰箱冰箱solar collector 太阳能集热器太阳能集热器 heat transfer rate 传热传热(速速)率率temperature difference 温差温差 factor of safety 安全系数安全系数experimental error 实验误差实验误差 operating condition 运行条件运行条件heat transfer coefficient 传热系数传热系数under these adverse conditions 在最不利工况下在最不利工况下three forms of heat transfer:conduction 传导传导 convection 对流对流 radiation 辐射辐射Heat Sensible Heat Latent Heatdue to molecular thermal motionSolidificationfusionLiquefactionevaporationConductionConvectionRadiationThree forms of heat transfertemperature gradientcross-sectional area normal to flowthermal conductivityheat flow rateEquation(1)states that the heat flow rate q in the x direction is directly proportional to the temperature gradient dt/dx and the cross-sectional area A normal to the heat flow.The proportionality factor is the thermal conductivity.The minus sign indicates that the heat flow is positive in the direction of decreasing temperature.Conductivity values are sometimes given in other units,but consistent units must be used in Equation(1).(1)The fundamental equation for unsteady-state conduction in solids or fluids in which there is no substantial motion iswhere thermal diffusivity is the ratio/cp;is thermal conductivity;,density;and cp,specific heat.If is large(high conductivity,low density and specific heat,or both),heat will diffuse faster.Is there any mistakes?Heat transfer involving motion in a fluid due to the difference in density and the action of gravity is called natural convection or free convection.Heat transfer coefficients associated with gases for natural convection are generally much lower than those for forced convection.Forced air coolers and heaters,forced air-or water-cooled condensers and evaporators,are examples of equipment that transfer heat primarily by forced convection.When fluid flows over a flat plate,a boundary layer forms adjacent to the plate.The velocity of the fluid at the plate surface is zero and increases to its maximum free stream value just past the edge of the boundary layer.Radiation,one of the basic mechanisms for energy transfer between different temperature regions,is distinguished from conduction and convection in that it does not depend on an intermediate material as a carrier of energy but rather is impeded by the presence of material between the regions.The rate of thermal radiant energy emitted by a surface depends on its absolute temperature.A surface is called black if it can absorb all incident radiation.The total energy emitted per unit time per unit area of black surface Wb to the hemispherical region above it is given by the Stefan-Boltzmann law.where Wb is the total rate of energy emission per unit area,and is the Stefan-Boltzmann constant 5.670 108 W/(m2 K4).Infiltrationzero energy buildinglow energy buildingTypical Features Increased ceiling and wall insulation Radiant barrier Low air infiltration rate High-performance windows Engineered HVAC Tight duct installation All-fluorescent lighting Photovoltaic(PV)solar-electric system1.1.Introduction heat transfer problems encountered in practice (1)rating (2)sizing two kinds of approach for the study of heat transfer (1)experimentally (2)analytically2.2.Modeling in Heat Transfer modeling in heat transfer and the problems encountered a very accurate but complex model a simple but not-so-accurate model3.3.Engineering Software Packages Neither will engineering software packages replace the traditional engineering courses.And why?1.The heat transfer problems encountered in practice can be considered in two groups:(1)rating and(2)sizing problems.2.However,this approach is expensive,time-consuming,and often impractical.3.the size of a heating system of a building must usually be determined before the building is actually built on the basis of the dimensions and specifications given.encountered in practice:现实中遇到的现实中遇到的rating problem:速率问题速率问题 sizing problem:容量选择的问题容量选择的问题time-consuming:耗时的耗时的 dimension:规模尺寸、维规模尺寸、维 3-D：？：？specification:（工程）说明书（工程）说明书4.the results obtained are subject to the accuracy of the assumptions and idealizations made in the analysis.5.In heat transfer studies,often a good compromise is reached by reducing the choices to just a few by analysis,and then verifying the findings experimentally and doing some fine-tuning.subject to:受受支配，取决于支配，取决于 make a assumption(idealization)in:在在中作了假设（理想化）中作了假设（理想化）reach a compromise:达到一种折衷或平衡达到一种折衷或平衡fine:细微地细微地,精巧地精巧地 tune:调整调整fine-tuning：？：？6.In the limiting case of infinitesimal or differential changes in variables,we obtain differential equations that provide precise mathematical formulations for the physical principles and laws by representing the rates of changes as derivatives.7.The equation itself is very instructive as it shows the degree of dependence of some variables on others,and the relative importance of various terms.infinitesimal:无穷小、无穷小的无穷小、无穷小的 infinite:无穷大、无穷大的无穷大、无穷大的variable:变量变量 constant:？differential equation:微分方程微分方程 integral：积分、积分的：积分、积分的calculus:微积分微积分 derivative:派生的事物，导数派生的事物，导数instructive:指导性的指导性的 various terms:不同变量不同变量8.Many processes that seem to occur in nature randomly and without any order are,in fact,being governed by some visible or not-so-visible physical laws.9.This is where the power of analysis lies.10.An analyst working on an engineering problem often finds himself or herself in a position to make a choice between a very accurate but complex model,and a simple but not-so-accurate model.occur randomly:随机发生随机发生 without any order:无序无序 not-so-visible:不不（那么）可见的（那么）可见的 not-so-+adjlie:存在存在 The solution lies in research.?make a choice between:在在之间作出选择（抉择）之间作出选择（抉择）11.For example,the process of baking potatoes or roasting a round chunk of beef in an oven can be studied analytically in a simple way by modeling the potato or the roast as a spherical solid ball that has the properties of water.12.For example,when purchasing a heat exchanger that will handle hard water,we must consider that some calcium deposits will form on the heat transfer surfaces over time,causing fouling and thus a gradual decline in performance.modelas:将将模型化为模型化为，将，将视为视为 spherical:球形的球形的hemi-:“半半”hemispherical:?hemisphere:?calcium deposits:钙的沉积物钙的沉积物 calcium carbonate:碳酸钙碳酸钙fouling:结垢结垢 decline in performance:性能的降低性能的降低13.At the minimum,the model should reflect the essential features of the physical problem it represents.At the minimum:至少至少 essential features:基本特征基本特征14.There are many significant real-world problems that can be analyzed with a simple model.real-world problem:实际问题实际问题15.But it should always be kept in mind that the results obtained from an analysis are as accurate as the assumptions made in simplifying the problem.16.Therefore,the solution obtained should not be applied to situations for which the original assumptions do not hold.hold:使有效、可行或真实使有效、可行或真实The theory holds.This is an observation that still holds true.be kept in mind:牢记牢记17.A solution that is not quite consistent with the observed nature of the problem indicates that the mathematical model used is too crude.18.Thus any solution to a problem should be interpreted within the context of how that problem is formulated.19.After all,almost all the heat transfer problems we are likely to encounter in practice can be solved using one of several sophisticated software packages readily available in the market today.be consistent with:与与一致一致 crude:粗略的，天然的、未加工的粗略的，天然的、未加工的crude oil:?crude salt:?software package:软件包软件包 readily:容易地容易地interpret:解释、说明解释、说明 context:上下文、背景上下文、背景formulate:用公式表示用公式表示20.These software packages not only give the desired numerical results,but also supply the outputs in colorful graphical form for impressive presentations.21.It is unthinkable to practice engineering today without using some of these packages.impressive:给人印象深刻的给人印象深刻的 presentation:表达、表现表达、表现practice:从事从事 engineering:工程（学）工程（学）the College of Civil Engineering:?Built Environment and Service Engineering:?the Chinese Academy of engineering:?the Chinese Academy of Sciences:?the Chinese Academy of Social Sciences:?22.This tremendous computing power available to us at the touch of a button is both a blessing and a curse.at the touch of a button:按一下按键按一下按键 23.In the hands of poorly educated people,these software packages are as dangerous as sophisticated powerful weapons in the hands of poorly trained soldiers.poorly educated：未受过良好教育的未受过良好教育的 highly educated:受过良好教育的受过良好教育的sophisticated:尖端的、先进的尖端的、先进的 poorly trained:未受过良好培训的未受过良好培训的 24.If it were true that the engineering students do not need all these fundamental courses they are taking because practically everything can be done by computers quickly and easily,then it would also be true that the employers would no longer need high-salaried engineers since any person who knows how to use a word-processing program can also learn how to use those software packages.engineering students:工科学生工科学生 science students:理科学生理科学生arts students:文科学生文科学生 high-salaried:高薪的高薪的word-processing program:文字处理程序文字处理程序25.But the statistics show that the need for engineers is on the rise,not on the decline,despite the availability of these powerful packages.26.We should always remember that all the computing power and the engineering software packages available today are just tools,and tools have meaning only in the hands of masters.statistics:统计数字统计数字 统计学统计学 mathematical statistics:?theory of probability:?show:显示、表明显示、表明 results show that:结果表明结果表明how to translate?27.Having the best word-processing program does no make a person a good writer,but it certainly makes the job of a good writer much easier and makes the writer more productive.make 注意用法注意用法how to translate?28.That is,more time will be spent in the classrooms discussing the physical aspects of the problems in greater detail,and less time on the mechanics of solution procedures.mechanics:技巧，技巧，机械学、力学机械学、力学29.Neither will engineering software packages replace the traditional engineering courses.30.They will simply cause a shift in emphasis in the courses from mathematics to physics.traditional:传统的传统的 conventional:?traditional method traditional model traditional approachshift:转变、轮（换）班转变、轮（换）班,轮班职工轮班职工;轮班工作时间轮班工作时间an eight-hour shift:八小时的工作班八小时的工作班work in three shifts of eight hours:每班八小时的三班制每班八小时的三班制the day shift:日班日班 the night shift:夜班夜班worked the night shift:值夜班值夜班31.All these marvelous and powerful tool available today put an extra burden on todays engineers.32.They must still have a thorough understanding of the fundamentals,develop a“feel”of the physical phenomena,be able to put the data into proper perspective,and make sound engineering judgments,just like their predecessors.put an burden on:增加负担增加负担physical phenomenon:物理现象物理现象perspective:观点、看法观点、看法33.The engineers in the past had to rely on hand calculations,slide rules,and later hand calculators and computers.hand calculations:手工计算手工计算 slide rules:计算尺计算尺 hand calculators:计算器计算器34.The easy access to such power and the possibility of a simple misunderstanding or misinterpretation causing great damage make it more important today than ever to have a solid training in the fundamentals of engineering.35.In this text we make an extra effort to put the emphasis on developing an intuitive and physical understanding of heat transfer phenomena instead of on the mathematical details of solution procedures.access to:有权使用有权使用 solid:坚实的坚实的make a effort to do:努力去做某事努力去做某事put the emphasis on:将重点放在将重点放在，强调，强调此课件下载可自行编辑修改，仅供参考！此课件下载可自行编辑修改，仅供参考！感谢您的支持，我们努力做得更好！谢谢感谢您的支持，我们努力做得更好！谢谢