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1、精選優(yōu)質(zhì)文檔-傾情為你奉上2. Conduction(導(dǎo)熱) The best heat-insulating solids own their insulating properties to the air or to other gases contained in cells within the material.(最好的隔熱材料在空氣和材料細(xì)胞中擁有自己的絕熱性能。) These cells cause the heat to flow through the solid material through a long tortuous passage. (這些細(xì)胞使熱量需要通過一
2、個(gè)漫長曲折的通道才能流過這個(gè)堅(jiān)實(shí)的固體。) In addition, the available cross-sectional area of the solid material is much less than the projected area. (另外,見識(shí)的固體材料可用的橫截面面積比投影面你少得多。) Experimental evidence shows that many small unicellular pockets of gas are much more effective than a series of connected cells having the s
3、ame total volume in giving insulating value to a substance. (試驗(yàn)表明,一個(gè)物體在給定的總量上具有相同的絕熱值上,許多小口袋氣體單細(xì)胞比的一系列連通細(xì)胞更加有效)There may be considerable variation in the thermal conductivity of any given insulating material because the conductivity depends on its density, the size and number of its air cells, and i
4、ts absorbed moisture.(在任何給定的絕熱材料的導(dǎo)熱系數(shù)方面有很大的差異,這是因?yàn)閷?dǎo)熱系數(shù)取決于它的密度,空氣細(xì)胞的大小和數(shù)量,和它吸收的水蒸氣。)3. Natural Convection(自然對流) Consider heat transfer by natural convection between a cold fluid and a hot surface.(考慮到冷流體和熱表面之間的自然對流換熱。) The fluid in immediate contact with the surface is heated by conduction, becomes l
5、ighter and rises because of the difference in density of the adjacent fluid. (流體在表面直接接觸通過傳導(dǎo)加熱,將變的更輕,也會(huì)上升,這是由于相鄰流體的密度差異。) The motion is resisted by the viscosity of the fluid. (這種運(yùn)動(dòng)會(huì)被流體的粘度所抵制)The heat transfer is influenced by(傳熱的影響): (1) gravitational force due to thermal expansion, (2) viscous drag
6、 and (3) thermal diffusion.(由于熱力膨脹的引力,粘性阻力和熱擴(kuò)散。) It may be expected to depend on the gravitational acceleration g, the coefficient of thermal expansion ,the kinematic viscosity (=/), and the thermal diffusivity =(/cp). (這是可以預(yù)測的,這取決于引力加速度,g,熱膨脹系數(shù),運(yùn)動(dòng)粘度(=/),和熱擴(kuò)散系數(shù)=(/cp)。) These variables can be express
7、ed in terms of dimensionless number(這些熱量可以早無量綱方面表示): the Nusselt number, Nu, is a function of the product of the Prandtl number, Pr, and Grashof number, Gr, which, when combined, depend on the fluid properties, the temperature difference between the surface and the fluid, t, and the characteristic l
8、ength of the surface, L. (努謝爾特?cái)?shù),Nu;普朗特?cái)?shù)推導(dǎo)的函數(shù),Pr,和格拉曉夫數(shù);Gr,在混合條件下,取決于流動(dòng)的特性,溫差取決于流體和表面溫度的不同,t;表面特征長度,L。) The constant c and exponent n depend on the physical configuration and nature of flow.(系數(shù)c和指數(shù)n取決于不同的物理構(gòu)造和流動(dòng)性質(zhì)。)Natural convection can affect the transfer coefficient in the of weak forced convectio
9、n. (自然對流可以影響現(xiàn)存在的微弱的受迫對流的傳導(dǎo)系數(shù)。) As the forced convection effect , i.e. , the Reynolds number, increases, the “mixed convection ”(superimposed forced-on-free convection) gives way to the pure forced convection regime.(對于受迫對流的影響,即雷諾數(shù),增加,“混合對流”(加上自然對流影響的受迫對流)被單純的受迫對流區(qū)域所替代。) Since the heat transfer coeff
10、icient in the mixed convection region is often larger than calculated based on the natural or forced convection heat transfer.(由于在混合對流區(qū)域的傳熱系數(shù)往往大雨基于自然對流或受迫對流的換熱計(jì)算結(jié)果。) The reference given before summarizes natural, mixed, and forced convection regimes for vertical and horizontal tubes.(在作出參考之前總結(jié)了縱向和橫向
11、管段的自然、混合和受迫對流區(qū)域。) Local conditions influence the values of the convection coefficient in a mixed convection regime, but the references permit locating the pertinent regime and approximating the convection coefficient.(當(dāng)?shù)貤l件影響了在混合對流區(qū)域的對流系數(shù)的值,但是可引用當(dāng)?shù)貐^(qū)域相關(guān)允許值和近似得到對流換熱系數(shù)。) 6. Fundamentals of industrial Ve
12、ntilation(工業(yè)通風(fēng)的基礎(chǔ))In essence this boils down to heat transfer and mass transfer between the incoming air and air the already within the building.(從本質(zhì)上講,這歸結(jié)于進(jìn)入的空氣和已經(jīng)在建筑物內(nèi)的空氣的傳熱和傳質(zhì)。) If owing to excessive internal heat production the temperature of the air in the building tends to exceed the specified
13、 norms, cooler air is introduced and mixed with the indoor air; the temperature of the air (owning to heat transfer) then remains at the norm. (這是由于建筑物內(nèi)部產(chǎn)熱過多導(dǎo)致空氣的溫度往往超過規(guī)定的指標(biāo),引入冷的空氣引入與室內(nèi)空氣混合(由于傳熱),使空氣溫度保持不變。)If harmful gases or vapours are released, their concentration is heldwithin specified limits
14、by dilution with the clean incoming air.(如果有害揮發(fā)性氣體被釋放掉,它的濃度將會(huì)被在一定范圍內(nèi)通過引入室外清潔空氣來稀釋。)7. Natural Ventilation Fields of Application (自然通風(fēng)的應(yīng)用領(lǐng)域)The time has long passed when it was necessary to demonstrate the benefits of natural ventilation and justify its application. The proofs were simple and very co
15、nvincing.(時(shí)間已經(jīng)過去很久了當(dāng)它有必要去表明自然通風(fēng)的好處和證明它的可用性。) They were based on comparisons of mechanical ventilation and natural ventilation. (這是基于自然通風(fēng)和機(jī)械通風(fēng)的比較。) In hot shops where all the emphasis was laid on mechanical ventilation, and natural air change, being regarded as unimportant, was not taken into account
16、 at all.(在熱的車間里,所有的重點(diǎn)是機(jī)械通風(fēng),自然通風(fēng)被認(rèn)為是無足輕重的,沒有被重視到的。) It was found in all the tests that the volume of natural air change many times exceeded the volume of mechanical ventilation. (很多測試表明,自然通風(fēng)的換氣量幾倍于機(jī)械通風(fēng)的換氣量。) This revealed the negligible role of general mechanical ventilation despite its heavy install
17、ation and running costs. (這表明,全面的機(jī)械通風(fēng)是不會(huì)估計(jì)到它的很大的裝備和運(yùn)行花費(fèi)。)Mechanical ventilation in these cases was best used as a corrective to natural ventilation, in the form of air curtains and local air supply or extraction.(在這些情況下,機(jī)械通風(fēng)最好是自然通風(fēng)的一個(gè)補(bǔ)救措施,以空氣幕的形式和當(dāng)?shù)乜諝獾墓?yīng)和提取。)9. Comfort and Discomfort(舒適與不舒適) A parti
18、cular example is the range effect.(一個(gè)特別的例子這個(gè)范圍的影響。) When an observer experiences a range of stimuli and is asked to rate them on category scale, he tends to rate them by putting the stimuli from the middle of the range into the central categories of the rating scale.(當(dāng)一個(gè)測試員經(jīng)歷了一定范圍的刺激并且要求把他們分為不同類別范圍的
19、等級,他傾向于從評定列表范圍的中間到中央類別投入的刺激來分類。) This has been clearly demonstrated in experiments on the acceptability of noise. (這已經(jīng)清楚的表明對噪音的可接受性的實(shí)驗(yàn)。)Subjects exposed to a range of sound levels tend to place the boundary between acceptable and unacceptable noise at the centre of the range of noise which they have
20、 been exposed. (受驗(yàn)者暴露在聲音等級的范圍,往往已經(jīng)規(guī)定了在噪音范圍的中央的可接受與不可接受噪音的邊界。) Thus people who have only been exposed to low noise levels. (因此, 人們只暴露在低噪聲等級的水平范圍內(nèi)。) The range effects do not apply only to the range of stimuli provided by the experimenter.(范圍內(nèi)的影響并不只適用于實(shí)驗(yàn)者提供的刺激范圍。) People carry their own standards with
21、them, based on their general experience, with which they compare a new stimulus. (根據(jù)一般的經(jīng)驗(yàn),人們具有自己的評價(jià)標(biāo)準(zhǔn)來比較新的刺激。) Thus, the meaning of the words comfortable or uncomfortable will not have an absolute value, but will be relative to his experience and expectation. (因此,舒服或不舒服的含義,沒有一個(gè)絕對的值,而是相對于他們的經(jīng)驗(yàn)和期望。) W
22、hen Gagge et al. (1976) put young men in an environmental chamber at 48, the subjects reated the environment as slightly uncomfortable.(當(dāng)Gagge et al.將青年男子放于48的環(huán)境實(shí)驗(yàn)室中,受驗(yàn)者感覺環(huán)境稍不舒適。) There is little doubt that the equivalent environment in an office would be regarded as intolerable. (毫無疑問,在辦公室里的等效環(huán)境將被認(rèn)
23、為是不能容忍的。) However, the subjects knew they were in a physiological laboratory, were expecting to sweat, and did not object strongly to the experience. (但是,受試者知道他們在勝利實(shí)驗(yàn)室,他們期待汗水,并沒有強(qiáng)烈反對這種經(jīng)驗(yàn) 。)11. Efficiency Is Fashionable Again(效率又流行起來了)Two basic types of cogeneration systems are available(熱電聯(lián)產(chǎn)系統(tǒng)的兩個(gè)基本類
24、型是可用的): (1) topping system, which produces electricity and exhausts thermal energy which is used for district heating or comparable functions.(一流的系統(tǒng),生產(chǎn)電力和廢氣熱能,這是用于區(qū)域供熱或類似功能。) (2) bottoming system, which produces thermal energy for an industrial process or district heating and part of the thermal ene
25、rgy is withdrawn to generate electricity. (底部系統(tǒng),產(chǎn)生熱能用于工業(yè)或區(qū)域供熱,以部分的熱能要轉(zhuǎn)回產(chǎn)生熱能。) Each system has particular equipment requirements. (每個(gè)系統(tǒng)都有特定的設(shè)備要求。) Which system is used depends on the special need sand situation of the user.(使用哪種系統(tǒng)取決于用戶需求和情況。)12. Refrigeration (制冷)It is convenient to classify the appl
26、ications of refrigeration into the following categories(可以把制冷的應(yīng)用很方便的分為以下幾類): domestic, commercial, industrial, and air conditioning.(住宅,商業(yè),工業(yè)和空調(diào)。) Sometimes transportation is listed as a separate category.(有時(shí)候,交通被列為單獨(dú)的一類。) Domestic refrigeration is used for food preparation and preservation, ice mak
27、ing, and cooling beverages in the household.(家用制冷是用于視頻加工和保鮮,制冰,和在家庭中的冷卻飲料。) Commercial refrigeration is used in retail stores, restaurants, and institutions, for purposes the same as those in the household.(商用制冷是用于零售商店,餐館和機(jī)構(gòu),目的是和家用制冷相同。) Industrial refrigeration in the food industry is needed in pro
28、cessing, preparation, and large-scale reservation.(在食品工業(yè)方面的工業(yè)制冷是滿足加工,制備,和大型預(yù)定方面的需求。) This includes use in food chilling and freezing plants, cold storage warehouses, breweries, and dairies, to name a few.(這包括在食物中的冷卻和冷凍廠,冷藏倉庫,釀酒,乳制品等方面的應(yīng)用。) Hundreds of other industries use refrigeration; among them a
29、re ice making plants, oil refineries, pharmaceuticals.(數(shù)以百計(jì)的行業(yè)使用制冷,其中有制冰廠,煉油廠,制藥廠。) Of course ice skating rinks need refrigeration.(當(dāng)然,溜冰場也需要制冷。)The most widespread method of producing mechanical refrigeration is called the vapor compression system.(機(jī)械制冷生產(chǎn)的最有效的方法就是所謂的蒸汽壓縮系統(tǒng)。)The equipment may be sep
30、arate or of the unitary (also called self-contained) type.(該設(shè)備可能使單獨(dú)的或單一(也稱為自足)類型。)14. Floor Heating: Achieving Thermal Comfort in Artificial Environments(地板采暖:實(shí)現(xiàn)人工環(huán)境的熱舒適性)We have touched on improvements in building standards but no amount of insulation can change the laws of physics-heat still rises
31、. (我們已經(jīng)提及了改善建筑標(biāo)準(zhǔn),但是沒有任何絕熱的量可以改變熱損失的不斷上升。)Efficient insulation will, however, serve to trap heat above head level in an area where it can make no contribution to human comfort. (然而,高效保溫服務(wù)于保留熱量在一個(gè)區(qū)域的熱水平內(nèi),它可以對人們舒適度不做任何貢獻(xiàn)。) Solving this problem involves a close study of the three types of heat available
32、 to us.(解決這個(gè)問題,涉及到關(guān)于熱量供應(yīng)的三個(gè)類型的一個(gè)已經(jīng)完成的研究。) Radiant heat provides the most pleasurable sensation of comfort.(熱輻射,提高了舒適的愉悅感。) It contributes to the exhilaration of a walk in the spring sunshine even through the ambient air temperature may be only a few degrees above freezing. (它有助于使走在春天的陽光里很高興,即使周圍的空氣溫
33、度只有零上幾攝氏度。) We humans also respond well to conducted heat-thecat-like pleasure that comes from the warmth of a hot water bottle or just cuddling up to another person.(我們?nèi)祟悓τ谙褙堃粯訉?dǎo)熱會(huì)有良好的回應(yīng),很高興熱量來自暖水袋或者只是蜷縮著身子躺在另外一個(gè)人的身邊。) Lastly, there is convected heat caused by the effects of the radiation and conduc
34、tion warming the air and causing it to rise.(最后,對流換熱所導(dǎo)致的輻射影響和傳導(dǎo)變暖的空氣,使其上升。)By using all three types of heat in association we can achieve very high levels of thermal comfort.(通過協(xié)會(huì)所使用的三種類型的熱,我們可以達(dá)到非常高水平的熱舒適性能。) The normal criterion for heating design is to achieve a specified air temperature against the given heat loss of the building at a specified outside ambient te
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