建筑工程及給排水專業(yè)中英文對(duì)照翻譯

1、<p>　　Laminar and Turbulent Flow</p><p>　　Observation shows that two entirely different types of fluid flow exist. This was demon- strated by Osborne Reynolds in 1883 through an experiment in which wate

2、r was discharged from a tank through a glass tube. The rate of flow could be controlled by a valve at the outlet, and a fine filament of dye injected at the entrance to the tube. At low velocities, it was found that the

3、dye filament remained intact throughout the length of the tube, showing that the particles of water moved in parallel li</p><p>　　As the velocity in the tube was increased by opening the outlet valve, a poin

4、t was eventually reached at which the dye filament at first began to oscillate and then broke up so that the colour was diffused over the whole cross-section, showing that the particles of fluid no longer moved in an ord

5、erly manner but occupied different relative position in successive cross-sections. This type of flow is known as turbulent and is characterized by continuous small fluctuations in the magnitude and direc</p><p

6、>　　When the motion of a fluid particle in a stream is disturbed, its inertia will tend to carry it on in the new direction, but the viscous forces due to the surrounding fluid will tend to make it conform to the motio

7、n of the rest of the stream. In viscous flow, the viscous shear stresses are sufficient to eliminate the effects of any deviation, but in turbulent flow they are inadequate. The criterion which determines whether flow wi

8、ll be viscous of turbulent is therefore the ratio of the inertial </p><p><b>　　The ratio</b></p><p>　　Thus, the criterion which determines whether flow is viscous or turbulent is the

9、 quantity ρvl/μ, known as the Reynolds number. It is a ratio of forces and, therefore, a pure number and may also be written as ul/v where is the kinematic viscosity (v=μ/ρ).</p><p>　　Experiments carried out

10、 with a number of different fluids in straight pipes of different diameters have established that if the Reynolds number is calculated by making 1 equal to the pipe diameter and using the mean velocity v, then, below a c

11、ritical value of ρvd/μ = 2000, flow will normally be laminar (viscous), any tendency to turbulence being damped out by viscous friction. This value of the Reynolds number applies only to flow in pipes, but critical value

12、s of the Reynolds number can be estab</p><p>　　In pipes, at values of the Reynolds number > 2000, flow will not necessarily be turbulent. Laminar flow has been maintained up to Re = 50,000, but conditions

13、 are unstable and any disturbance will cause reversion to normal turbulent flow. In straight pipes of constant diameter, flow can be assumed to be turbulent if the Reynolds number exceeds 4000.</p><p>　　Pipe

14、 Networks</p><p>　　An extension of compound pipes in parallel is a case frequently encountered in municipal distribution system, in which the pipes are interconnected so that the flow to a given outlet may c

15、ome by several different paths. Indeed, it is frequently impossible to tell by inspection which way the flow travels. Nevertheless, the flow in any networks, however complicated, must satisfy the basic relations of conti

16、nuity and energy as follows:</p><p>　　1. The flow into any junction must equal the flow out of it.</p><p>　　2. The flow in each pipe must satisfy the pipe-friction laws for flow in a single pipe

17、.</p><p>　　3. The algebraic sum of the head losses around any closed circuit must be zero.</p><p>　　Pipe networks are generally too complicated to solve analytically, as was possible in the simp

18、ler cases of parallel pipes. A practical procedure is the method of successive approximations, introduced by Cross. It consists of the following elements, in order:</p><p>　　1. By careful inspection assume t

19、he most reasonable distribution of flows that satisfies condition 1.</p><p>　　2. Write condition 2 for each pipe in the form</p><p>　　hL = KQn (7.5)</p><p

20、>　　where K is a constant for each pipe. For example, the standard pipe-friction equation would yield K = 1/C2 and n = 2 for constant f. Minor losses within any circuit may be included, but minor losses at the junction

21、 points are neglected.</p><p>　　3. To investigate condition 3, compute the algebraic sum of the head losses around each elementary circuit. ∑hL = ∑KQn. Consider losses from clockwise flows as positive, count

22、erclockwise negative. Only by good luck will these add to zero on the first trial.</p><p>　　4. Adjust the flow in each circuit by a correction, ΔQ, to balance the head in that circuit and give ∑KQn = 0. The

23、heart of this method lies in the determination of ΔQ. For any pipe we may write</p><p>　　Q = Q0 ＋ΔQ</p><p>　　where Q is the correct discharge and Q0 is the assumed discharge. Then, for a circuit

24、</p><p><b>　　(7.6)</b></p><p>　　It must be emphasized again that the numerator of Eq. (7.6) is to be summed algebraically, with due account of sign, while the denominator is summed a

25、rithmetically. The negative sign in Eq. (7.6) indicates that when there is an excess of head loss around a loop in the clockwise direction, the ΔQ must be subtracted from clockwise Q0’s and added to counterclockwise ones

26、. The reverse is true if there is a deficiency of head loss around a loop in the clockwise direction.</p><p>　　5. After each circuit is given a first correction, the losses will still not balance because of

27、the interaction of one circuit upon another (pipes which are common to two circuits receive two independent corrections, one for each circuit). The procedure is repeated, arriving at a second correction, and so on, until

28、 the corrections become negligible.</p><p>　　Either form of Eq. (7.6) may be used to find ΔQ. As values of K appear in both numerator and denominator of the first form, values proportional to the actual K ma

29、y be used to find the distribution. The second form will be found most convenient for use with pipe-friction diagrams for water pipes.</p><p>　　An attractive feature of the approximation method is that error

30、s in computation have the same effect as errors in judgment and will eventually be corrected by the process.</p><p>　　The pipe-networks problem lends itself well to solution by use of a digital computer. Pro

31、gramming takes time and care, but once set up, there is great flexibility and many man-hours of labor can be saved.</p><p>　　The Future of Plastic Pipe at Higher Pressures</p><p>　　Participants

32、in an AGA meeting panel on plastic pipe discussed the possibility of using polyethylene gas pipe at higher pressures. Topics included the design equation, including work being done by ISO on an updated version, and the e

33、valuation of rapid crack propagation in a PE pipe resin. This is of critical importance because as pipe is used at higher pressure and in larger diameters, the possibility of RCP increases.</p><p>　　Several

34、years ago, AGA’s Plastic Pipe Design Equation Task Group reviewed the design equation to determine if higher operating pressures could be used in plastic piping systems. Members felt the performance of our pipe resins wa

35、s not truly reflected by the design equation. It was generally accepted that the long-term properties of modern resins far surpassed those of older resins. Major considerations were new equations being developed and sele

36、ction of an appropriate design factor.</p><p>　　Improved pipe performance</p><p>　　Many utilities monitored the performance of plastic pipe resins. Here are some of the long-term tests used and

37、the kinds of performance change they have shown for typical gas pipe resins.</p><p>　　Elevated temperature burst test</p><p>　　They used tests like the Elevated Temperature Burst Test, in which

38、the long-term performance of the pipe is checked by measuring the time required for formation of brittle cracks in the pipe wall under high temperatures and pressures (often 80 degrees C and around 4 to 5-MPa hoop stress

39、). At Consumers Gas we expected early resins to last at least 170 hrs. at 80 degrees C and a hoop stress of 3 MPa. Extrapolation showed that resins passing these limits should have a life expectancy of more than 5</p&

40、gt;<p>　　At the same temperature, today’s resins last thousands of hours at hoop stresses of 4.6 MPa. Tests performed on pipe made from new resins have been terminated with no failure at times exceeding 5,700 hrs.

41、 These results were performed on samples that were squeezed off before testing. Such stresses were never applied in early testing. When extrapolated to operating conditions, this difference in test performance is equival

42、ent to an increase in lifetime of hundreds (and in some cases even thousands</p><p>　　Environmental stress crack resistance test</p><p>　　Some companies also used the Environmental Stress Crack

43、Resistance test which measured brittle crack formation in pipes but which used stress cracking agents to shorten test times.</p><p>　　This test has also shown dramatic improvement in resistance brittle failu

44、re. For example, at my company a test time of more than 20 hrs. at 50 degrees C was required on our early resins. Today’s resins last well above 1,000 hrs. with no failure.</p><p>　　Notch tests</p>&l

45、t;p>　　Notch tests, which are quickly run, measure brittle crack formation in notched pipe or molded coupon samples. This is important for the newer resins since some other tests to failure can take very long times. No

46、tch test results show that while early resins lasted for test times ranging between 1,000 to 10,000 min., current resins usually last for longer than 200,000 min.</p><p>　　All of our tests demonstrated the s

47、ame thing. Newer resins are much more resistant to the growth of brittle crack than their predecessors. Since brittle failure is considered to be the ultimate failure mechanism in polyethylene pipes, we know that new mat

48、erials will last much longer than the old. This is especially reassuring to the gas industry since many of these older resins have performed very well in the field for the past 25 yrs. with minimal detectable change in p

49、roperties.</p><p>　　While the tests showed greatly improved performance, the equation used to establish the pressure rating of the pipe is still identical to the original except for a change in 1978 to a sin

50、gle design factor for all class locations.</p><p>　　To many it seemed that the methods used to pressure rate our pipe were now unduly conservative and that a new design equation was needed. At this time we b

51、ecame aware of a new equation being balloted at ISO. The methodology being used seemed to be a more technically correct method of analyzing the data and offered a number of advantages.</p><p>　　Thermal Expan

52、sion of Piping and Its Compensation</p><p>　　A very relevant consideration requiring careful attention is the fact that with temperature of a length of pipe raised or lowered, there is a corresponding increa

53、se or decrease in its length and cross-sectional area because of the inherent coefficient of thermal expansion for the particular pipe material. The coefficient of expansion for carbon steel is 0.012 mm/m?C and for coppe

54、r 0.0168mm/m?C. Respective module of elasticity are for steel E = 207×1.06kN/m2 and for copper E = 103×106 kN/m2. As a</p><p>　　It is therefore essential that design of any piping layout makes adeq

55、uate com- pensatory provision for such thermal influence by relieving the system of linear stresses which would be directly related to length of pipework between fixed points and the range of operational temperatures.<

56、;/p><p>　　Compensation for forces due to thermal expansion. The ideal pipework as far as expansion is concerned, is one where maximum free movement with the minimum of restraint is possible. Hence the simplest

57、and most economical way to ensure com- pensation and relief of forces is to take advantage of changes in direction, or where this is not part of the layout and long straight runs are involved it may be feasible to introd

58、uce deliberate dog-leg offset changes in direction at suitable intervals.</p><p>　　As an alternative, at calculated intervals in a straight pipe run specially designed expansion loops or “U” bends should be

59、inserted. Depending upon design and space availability, expansion bends within a straight pipe run can feature the so called double offset “U” band or the horseshoe type or “l(fā)yre” loop. The last named are seldom used for

60、 large heating networks; they can be supplied in manufacturers’ standard units but require elaborate constructional works for underground installation. </p><p>　　Anchored thermal movement in underground pipi

61、ng would normally be absorbed by three basic types of expansion bends and these include the “U” bend, the “L” bend and the “Z” bend. In cases of 90 changes indirection the “L” and “Z” bends are used. Principles involved

62、in the design of provision for expansion between anchor points are virtually the same for all three types of compensator. The offset “U” bend is usually made up from four 90° elbows and straight pipes; it permits go

63、od thermal displacem</p><p>　　All thermal compensators are installed to accommodate an equal amount of expansion or contraction; therefore to obtain full advantage of the length of thermal movement it is nec

64、essary to extend the unit during installation thus opening up the loop by an extent roughly equal the half the overall calculated thermal movement. This is done by “cold-pull” or other mechanical means. The total amount

65、of extension between two fixed points has to be calculated on basis of ambient temperature prevailing a</p><p>　　There are numerous specialist publication dealing with design and stressing calculations for p

66、iping and especially for proprietary piping and expansion units; comprehensive experience back design data as well as charts and graphs may be obtained in manufacturers’ publications, offering solutions for every kind of

67、 pipe stressing problem.</p><p>　　As an alternative to above mentioned methods of compensation for thermal expansion and useable in places where space is restricted, is the more expensive bellows or telescop

68、ic type mechanical compensator. There are many proprietary types and models on the market and the following types of compensators are generally used.</p><p>　　The bellows type expansion unit in form of an ax

69、ial compensator provides for expansion movement in a pipe along its axis; motion in this bellows is due to tension or compression only. There are also articulated bellows units restrained which combine angular and latera

70、l movement; they consist of double compensator units restrained by straps pinned over the center of each bellowsor double tied thus being restrained over its length. Such compensators are suitable for accommodating very

71、pipeline exp</p><p><b>　　層流與紊流</b></p><p>　　有兩種完全不同的流體流動(dòng)形式存在，這一點(diǎn)在1883年就由Osborne Reynolds 用試驗(yàn)演示證明。在試驗(yàn)里，水通過玻璃管從水箱里放出。流量由出口處的閥門來控制，一股很細(xì)的染色流束由入口注入玻璃管內(nèi)。在較低的流速時(shí)，可以看到染色流束在玻璃管中保持著一條完整的遷流。這表明

72、流體粒子以平行的層狀流動(dòng)。這種粘性流體的流動(dòng)就是我們所知的層流，流體各層的質(zhì)點(diǎn)以有序的方式移動(dòng)，并在連續(xù)的截面上保持著相同的相對(duì)位置。</p><p>　　打開出口閥門，管子里的速度就提高。隨著速度提高，最后會(huì)達(dá)到這樣的程度，即染色流束起初開始擺動(dòng)然后破碎，這樣顏色就擴(kuò)散在整個(gè)截面上，這表明流體粒子已不再有次序流動(dòng)卻在連續(xù)的截面上占有相對(duì)不同的位置。這種流體的流動(dòng)形式就是紊流，它的特點(diǎn)就是不斷產(chǎn)生無數(shù)大小不等的渦

73、團(tuán)，質(zhì)點(diǎn)摻混使得空間各點(diǎn)的速度隨時(shí)間無規(guī)則地變化。與之相關(guān)聯(lián)，壓強(qiáng)也隨之無規(guī)則地變化。</p><p>　　當(dāng)一條流束中的某個(gè)流體粒子的運(yùn)動(dòng)被擾亂，則它的慣性會(huì)使它移向新的方向，但周圍流體的粘滯力會(huì)使它與其余流束的運(yùn)動(dòng)保持一致。在粘性流體中，粘性切應(yīng)力足以抵消任何偏差的影響，但在紊流中是不夠的。因此，確定流動(dòng)是粘滯性的還是紊流性的標(biāo)準(zhǔn)就是作用在粒子上的慣性力和粘性力之比：</p><p>

74、　　這樣，用來判斷流動(dòng)是粘滯性的還是紊流性的標(biāo)準(zhǔn)就是ρvl/μ，也就是雷諾數(shù)。這是力之間的比，因此理論上也可以寫成ul/v（v=μ/ρ，流體的運(yùn)動(dòng)粘滯系數(shù)）。</p><p>　　在不同管徑的直管里用許多不同流體所進(jìn)行的試驗(yàn)已經(jīng)證實(shí)，如雷諾數(shù)是通過使L等于管徑并且使用平均速度v來計(jì)算，那么在低于臨界值ρvd/μ = 2000的條件下流動(dòng)一般是層流（粘滯流動(dòng)），任何紊流的傾向都會(huì)由于粘滯摩擦而受到抑制。這個(gè)雷諾數(shù)的

75、值僅適用于管道中的流體，但雷諾數(shù)的臨界值可以用來確定其他形式的流動(dòng)，例如選擇合適的弦桿翼剖面來代替管道直徑。對(duì)于已知直徑的管道中的流體而言，會(huì)有一個(gè)臨界流速vc，以及對(duì)應(yīng)的雷諾數(shù)，如果低于這個(gè)數(shù)，則表明流體是粘滯流動(dòng)。</p><p>　　在管道中，雷諾數(shù)值大于2000的情況下，流體不一定就變?yōu)槲闪鳌恿骺梢跃S持到Re = 50,000,但是條件并不穩(wěn)定，任何干擾都會(huì)使其它又變?yōu)橐话愕奈闪鳌Ｔ谥睆揭欢ǖ闹惫苤?，?/p>

76、果雷諾數(shù)超過4000那么流體就有可能變?yōu)槲闪鳌?lt;/p><p><b>　　管網(wǎng)</b></p><p>　　平行復(fù)合管道的延伸是市政分配系統(tǒng)中常見的一種情況，在這種情況下管道相互連接，使得通向某一出口的流體可以來自不同的路徑。的確，通過觀察往往很難說清楚流體將流經(jīng)哪一個(gè)管路。但是，不管管網(wǎng)有多復(fù)雜，其中的流體都必須確保連續(xù)性與能量的基礎(chǔ)關(guān)系。如下所述：</p&

77、gt;<p>　　流入接合處的流體必須與流出的等量；</p><p>　　在每根管中的流體都必須滿足流體在單管中的管道摩擦定律；</p><p>　　在任何閉合回路中，水頭損失的代數(shù)和必須為0。</p><p>　　管網(wǎng)一般來講由于太過復(fù)雜而難以分析解決，但在簡單一些的情況下是可以</p><p>　　的，例如平行管。Cross

78、 介紹了一種實(shí)用的程序，采用的是連續(xù)性近似法。它由以下的原理組成，包括：</p><p>　　通過仔細(xì)的觀察采取最合理的流體分配方案以滿足條件1；</p><p>　　對(duì)每根管道以方程hL = KQn來判斷是否滿足條件2，式中K是每根管的特性</p><p>　　常數(shù)。例如，標(biāo)準(zhǔn)管道摩擦方程中的K = 1/C2以及n = 2。任何環(huán)路中較小的沿程水頭損失可能是包括的

79、，但局部水頭損失可以忽略不計(jì)。</p><p>　　為了研究條件3，計(jì)算每個(gè)基本環(huán)路中水頭損失的代數(shù)和?！苃L = ∑KQn。假</p><p>　　設(shè)順時(shí)針方向流動(dòng)的損失為正，逆時(shí)針的則為負(fù)，那么在第一次試驗(yàn)中，它們的和只有在非常幸運(yùn)的情況下才會(huì)為零。</p><p>　　通過一個(gè)修正值ΔQ來調(diào)整每條環(huán)路中的流體，使該管路中的水頭平衡，并</p>&

80、lt;p>　　給出∑KQn = 0。這個(gè)方法的核心取決于ΔQ的確定。對(duì)于任何管道我們有：</p><p>　　Q = Q0 ＋ΔQ</p><p>　　式中Q是準(zhǔn)確的流量而Q0是假定的流量。那么，對(duì)于一個(gè)環(huán)路而言：</p><p><b>　　(7.6)</b></p><p>　　必須再次強(qiáng)調(diào)的是方程(7.6)的

81、分子和分母都是采用了適當(dāng)?shù)挠?jì)算符號(hào)確定的。方程(7.6)中的負(fù)號(hào)表明，當(dāng)順時(shí)針方向的環(huán)路上有過量的水頭損失時(shí)，ΔQ必須從順時(shí)針方向的Q0中減去，并增加到逆時(shí)針方向上去。如果順時(shí)針方向的環(huán)路上水頭損失不足時(shí)，情況正好相反。</p><p>　　5．在每條環(huán)路都給予了一個(gè)最初的修正值后，由于環(huán)路之間的相互影響，損失仍不平衡（一些兩條環(huán)路共有的管道就有兩個(gè)單獨(dú)的修正值，每個(gè)值對(duì)應(yīng)一條環(huán)路）。重復(fù)這樣的程序，獲得第二個(gè)修

82、正值，乃至第三、第四個(gè)等等，直到修正值可以忽略不計(jì)。</p><p>　　方程(7.6)的兩種形式都可以用來找出ΔQ。由于K值同時(shí)出現(xiàn)在第一種形式的分子和分母上，相應(yīng)實(shí)際的K值就可以用來確定分配量。結(jié)合水管的管道摩擦力圖表，第二種方程形式使用起來最簡便。</p><p>　　近似法最吸引人的一個(gè)特點(diǎn)就是計(jì)算上的誤差與判斷誤差有相同的效果，而最終它們會(huì)在過程中被加以改正。</p>

83、<p>　　管網(wǎng)問題非常適合于采用計(jì)算機(jī)來解決。編制程序需花費(fèi)大量的時(shí)間和精力，但是一旦完成，就有很大的機(jī)動(dòng)靈活性，許多耗人費(fèi)時(shí)的勞動(dòng)就可省去。</p><p>　　更高壓力下塑料管道的前景</p><p>　　美國煤氣協(xié)會(huì)AGA的一個(gè)針對(duì)塑料管道的專案小組的成員討論了在較高壓力下使用聚乙烯輸氣管的的可能性。討論的主題包括有設(shè)計(jì)方程（其中包括國際科學(xué)組織ISO在更新版本上完成

84、的工作），以及對(duì)PE管樹脂上裂縫快速擴(kuò)展的評(píng)估。這一點(diǎn)非常重要，因?yàn)楫?dāng)管道在較高壓力下使用、而管徑更大的情況下，鋼筋混凝土管的可能性增加了。</p><p>　　若干年以前，AGA的塑料管道設(shè)計(jì)任務(wù)小組檢查了設(shè)計(jì)方程，以確定是否能在塑料管道系統(tǒng)中使用更高的工作壓力。小組成員認(rèn)為管道樹脂的性能并沒有通過設(shè)計(jì)方程反映出來。一般認(rèn)為新的樹脂塑管在耐用性上遠(yuǎn)遠(yuǎn)勝過過去的樹脂塑管，因此主要考慮的問題是新方程的發(fā)展以及合適的

85、設(shè)計(jì)要素的選擇。</p><p><b>　　改良的管道性能</b></p><p>　　許多設(shè)備用來監(jiān)測(cè)塑料管道樹脂的性能。在這里講述一下一些針對(duì)典型的輸氣管道樹脂進(jìn)行過的耐久性測(cè)試，以及幾種性能上的變化。</p><p><b>　　溫升爆裂測(cè)試</b></p><p>　　他們使用像溫升爆裂測(cè)

86、試之類的測(cè)試。在這一測(cè)試中管系的耐久性能通過高溫和高壓下管壁形成脆裂所需的時(shí)間來校核（通常是80攝氏度和4-5MPa的環(huán)壓下）。在供應(yīng)燃?xì)鈺r(shí)我們希望老的樹脂塑管在80攝氏度、3MPa的環(huán)壓下至少可以堅(jiān)持使用170個(gè)小時(shí)。推斷表明通過了這些極限的樹脂預(yù)期其壽命應(yīng)該能超過50年。裝運(yùn)時(shí)對(duì)這些樹脂塑管質(zhì)量檢測(cè)，有時(shí)會(huì)由于沒有達(dá)到這一標(biāo)準(zhǔn)而對(duì)該產(chǎn)品拒絕使用。</p><p>　　在相同溫度條件下，今天的樹脂塑管在4.6M

87、Pa環(huán)壓下可持續(xù)使用數(shù)千小時(shí)。測(cè)試表明用新樹脂制造的管道可使用超過5700小時(shí)而沒有任何損壞。這些結(jié)果是在臨測(cè)試前檢出的（樹脂）抽樣得出的。這種壓力從未在早期的測(cè)試中使用過。根據(jù)工作條件推斷，測(cè)試性能上的區(qū)別與數(shù)百年的壽命增長是相等的（某些情況下甚至是數(shù)千年）。</p><p><b>　　環(huán)壓下的防裂測(cè)試</b></p><p>　　也有些公司進(jìn)行了環(huán)壓下的防裂測(cè)試

88、，用來測(cè)量管道中脆裂的形成，并加大了壓力來減短測(cè)試的時(shí)間。</p><p>　　這個(gè)試驗(yàn)表明了在防止脆裂上的驚人的改進(jìn)。例如，在我的公司里對(duì)于我們的早期樹脂塑管進(jìn)行試驗(yàn)需要20小時(shí)以上的時(shí)間和50攝氏度的溫度。而現(xiàn)在的樹脂塑管能夠良好地持續(xù)1000小時(shí)以上而沒有損壞。</p><p><b>　　槽口測(cè)試</b></p><p>　　可以快速進(jìn)

89、行的槽口測(cè)試，用來測(cè)量帶有槽口的管道或?qū)ｉT澆鑄的試驗(yàn)管中脆裂的形成。這對(duì)新的樹脂塑管非常重要，因?yàn)槠渌脑囼?yàn)需要很長的時(shí)間才能使管道發(fā)生損壞。槽口測(cè)試的結(jié)果說明早期的樹脂塑管持續(xù)的試驗(yàn)時(shí)間在1000到10000分鐘之間，而現(xiàn)在的樹脂塑管則通常可持續(xù)超過200000分鐘。</p><p>　　我們所有的試驗(yàn)證實(shí)了相同的結(jié)果。更新的樹脂塑管比起它們的前輩，對(duì)脆裂的防止有著更好的效果。由于認(rèn)為脆裂是聚乙烯管道中結(jié)構(gòu)的最

90、終損壞，因此我們知道新的材料比起舊的來能夠持續(xù)使用更久。這對(duì)于燃?xì)夤I(yè)特別可靠，因?yàn)樵S多這些舊的樹脂塑管在過去的25年時(shí)間里表現(xiàn)得非常好，而它們的性能只在最小范圍內(nèi)進(jìn)行了些改變。</p><p>　　測(cè)試表明了管道性能很大的改進(jìn)，過去用來建立管道壓力等級(jí)的方程式仍然與原有的相同，除了1978年對(duì)于一個(gè)針對(duì)所有等級(jí)的設(shè)計(jì)因素的改變。</p><p>　　從許多方面來看，如今將管道按壓力進(jìn)行分

91、級(jí)是非常保守的，因此也就需要一個(gè)新的設(shè)計(jì)方程式?，F(xiàn)在我們知道，國際科學(xué)組織正在選舉一個(gè)新的方程式。方程所采用的是通過分析相關(guān)數(shù)據(jù)資料，從技術(shù)上而言更為準(zhǔn)確的方法，能夠給出許多的優(yōu)勢(shì)。</p><p><b>　　管道熱膨脹及其補(bǔ)償</b></p><p>　　一個(gè)極其值得注意的事實(shí)是，管子的長度與截面積隨著溫度的升降而增減，這是因?yàn)楣懿谋旧砭哂袩崤蛎浵禂?shù)。碳鋼的膨脹系

92、數(shù)為0.012mm/m?C，銅為0.0168mm/m?C。它們的彈性模數(shù)分別是：鋼為E＝207×106kN/m2，銅為E＝103×106kN/m2。例如：假設(shè)輸水管的基本溫度為0?C，任何直徑的鋼管和銅管在加熱到120?C時(shí)，各自長度每米線性膨脹量分別為1.4mm和2.016mm。而鋼管的單位軸向力要比鋼管大39％。管子直徑的變化與軸向伸長相比無實(shí)際意義，但由于膨脹或收縮而產(chǎn)生的軸向力是可觀的，且能使施加約束力的附件

93、斷裂，這種力的大小與管子的尺寸有關(guān)。例如：有兩條長度相等而直徑不等的直管，在兩端固定位，加溫升到100?C，對(duì)固定點(diǎn)作用的軸向力的總量近似地與各自直徑成比例。</p><p>　　重要的是，在管道布線的設(shè)計(jì)，要以降低軸線應(yīng)力的方法為這種熱的作用提供充分的補(bǔ)償措施，這種應(yīng)力是與固定點(diǎn)之間的管長度與工作溫度范圍直接相關(guān)的。</p><p>　　熱膨脹力的補(bǔ)償，就膨脹問題而言，理想的管網(wǎng)應(yīng)可能有

94、最大限度的自由移動(dòng)并且伴隨有約束力的最小限度。所以，保障補(bǔ)償和卸掉力的最簡單和最經(jīng)濟(jì)的方法，就是利用管線方向的改變。如果有些地方直行的管道很長，且無方向改變的布線，則在適當(dāng)間距內(nèi)采用預(yù)先準(zhǔn)備好的折線形變向補(bǔ)償，這也是可行的。</p><p>　　另一種做法是，在直行管線上的計(jì)算間距內(nèi)安裝上特別設(shè)計(jì)的膨脹環(huán)管或“U”型彎。根據(jù)設(shè)計(jì)和可利用空間，在直管段上加膨脹彎頭，它具有所謂雙補(bǔ)償“U”型彎頭或是馬蹄型或“豎琴”環(huán)

95、的特點(diǎn)。最后幾種名稱的補(bǔ)償器很少用于大型供熱管網(wǎng)，它們可作為制造廠標(biāo)準(zhǔn)部件供應(yīng)，在地下安裝時(shí)需要完善的結(jié)構(gòu)工程。</p><p>　　地下管道的固定的熱位移量在正常的情況下可以被三種形式的膨脹彎所吸收，這就是：“U”型彎、“L”型彎和“Z”型彎。在管子90? 轉(zhuǎn)向的情況下常用“L”和“Z”型彎。有關(guān)設(shè)計(jì)固定點(diǎn)之間熱膨脹預(yù)防措施的原則，實(shí)際上對(duì)這三種補(bǔ)償器都是一樣的。“U”型彎補(bǔ)償器通常是由4個(gè)90? 的彎頭和直管

96、構(gòu)成的，它容許有良好的熱位移，且固定的荷載比其他形狀的環(huán)管要小。這種形狀的膨脹彎對(duì)于預(yù)制的管中管系統(tǒng)來說是一個(gè)標(biāo)準(zhǔn)化模式。</p><p>　　所有熱補(bǔ)償器的安裝都是為了調(diào)節(jié)等量的膨脹和收縮。因此，為了獲得補(bǔ)償器位移長度的充分利用，必須在安裝時(shí)將補(bǔ)償器環(huán)張開，使伸開量大約等于總計(jì)算熱位移置的一半。這一工藝可以用“冷拉”或是其他機(jī)械手?jǐn)嗤瓿?。兩個(gè)固定點(diǎn)之間總伸長量的計(jì)算要以常年周圍溫度和設(shè)計(jì)運(yùn)行溫度為基礎(chǔ)進(jìn)行，使得

97、在較低和較高溫度時(shí)的應(yīng)力和反力可控制在允許的極限以內(nèi)。預(yù)加應(yīng)力不影響管道的疲勞壽命，因此，在計(jì)算管網(wǎng)應(yīng)力時(shí)不起重要作用。</p><p>　　有大量闡述管道設(shè)計(jì)和應(yīng)力計(jì)算的專門出版物，一些是特別針對(duì)有專利的配管和膨脹節(jié)。以綜合經(jīng)驗(yàn)為背景的設(shè)計(jì)數(shù)據(jù)以及各種圖表，都可以從生產(chǎn)廠家的出版物上獲得，提供各類管子應(yīng)力問題的解決方法。</p><p>　　取代上述熱膨脹補(bǔ)償方法并可用于空間有限地方的補(bǔ)

98、償器是更加昂貴的波紋管或套管式機(jī)械型補(bǔ)償器。市場上有許多種有專利的型號(hào)和樣品，下列幾種型號(hào)較為常用：以軸向補(bǔ)償器為形式的波紋管型膨脹節(jié)，為管子沿著軸線方向膨脹移動(dòng)提供了保證，波紋管內(nèi)在的移動(dòng)僅僅是由拉伸和壓縮產(chǎn)生的。還有一種鉸接式波紋管補(bǔ)償器，它可以把角運(yùn)動(dòng)和橫向運(yùn)動(dòng)組合起來。鉸接式補(bǔ)償器是由兩個(gè)補(bǔ)償單元組成的，由越過每個(gè)波紋管的中線銷住的定位夾板約束，或者是同樣沿長度方向受約束的拉緊的一對(duì)波紋管。這樣的補(bǔ)償器適用于接納很大的管道膨脹量