外文翻譯---干燥囊括科學(xué)之技巧

1、<p><b>　　附錄一 中文譯文</b></p><p>　　干燥：囊括科學(xué)之技巧</p><p>　　——面對(duì)商業(yè)障礙和復(fù)雜的關(guān)系設(shè)計(jì)干燥器</p><p>　　經(jīng)過半個(gè)世紀(jì)以來(lái)，濕料-泥漿和溶液的干燥仍傭盡科學(xué)之技巧。干燥技術(shù)的發(fā)展受商業(yè)障礙和傳統(tǒng)所阻擋，但影響更大的是在多種干燥物質(zhì)中固-液-氣關(guān)系的復(fù)雜性和它們的一些不同的

2、屬性。</p><p>　　干燥應(yīng)用極廣，例如食物、藥品、集合物、礦物質(zhì)、回收品以及大量的有機(jī)物和無(wú)機(jī)物都需要干燥。由于干燥之后的濕氣各不相同，即使相同的物質(zhì)也很少能表現(xiàn)出一致的干燥特性。</p><p>　　因此干燥器的設(shè)計(jì)不基于干燥理論原理，而是建立在實(shí)驗(yàn)測(cè)試或過去經(jīng)驗(yàn)的數(shù)據(jù)的基礎(chǔ)上。這些數(shù)據(jù)有助于確定干燥系統(tǒng)的尺寸或者估計(jì)已有的大小。使用的方法可以是粗略的估計(jì)，也可以使用公式進(jìn)行細(xì)致

3、的分析。相比與機(jī)械設(shè)計(jì)，干燥器的設(shè)計(jì)是一個(gè)過程性的設(shè)計(jì)，這是至少150個(gè)制造商使用的200多個(gè)干燥參數(shù)所共有的屬性。</p><p>　　在化學(xué)工業(yè)中，連續(xù)、開放或直通的直接干燥器應(yīng)用最廣泛，主要類型有：噴霧式，閃蒸式，流化床式、滾筒式、回轉(zhuǎn)式以及盤式干燥器。即使在每一同種類型中，大小和設(shè)計(jì)大不想同，但基本的干燥原理都大致一樣。水是大部分干燥中的成分，然而在封閉系統(tǒng)中，也可以干燥其它的液體。</p>

4、<p>　　干濕表長(zhǎng)期都用于估計(jì)干燥器進(jìn)展程度，也需要用算術(shù)來(lái)解決。用一個(gè)實(shí)例來(lái)說明如何用公式法得出結(jié)果。為了減輕工作量，我們把公式輸入到計(jì)算機(jī)的程序中，不過最后結(jié)果局限于輸入的數(shù)據(jù)。</p><p>　　圖1包含關(guān)鍵元素——一種典型，小型的直通設(shè)計(jì)的系統(tǒng)。熱空氣或其他氣體直接地與濕物料接觸，濕分被氣體所蒸發(fā)。這實(shí)例選擇在海拔2000英尺的狀態(tài)下，用天然氣作燃料。處理量是每小時(shí)270磅，進(jìn)口含水量是5

5、5%，出口含水量是5%。表1中給的空氣溫度可進(jìn)行簡(jiǎn)化選擇，得出一個(gè)小的溫度范圍就可以。如果知道干燥其內(nèi)部的濕球溫度，就可以通過查表得到氣體的濕度。</p><p>　　圖1：一個(gè)簡(jiǎn)單的直通式直接干燥系統(tǒng)</p><p>　　要知道外部參數(shù)，就需要做一個(gè)更復(fù)雜的測(cè)量，但是這樣能減少不知道或被忽略的影響，提高準(zhǔn)確率。</p><p>　　干燥器內(nèi)外氣體溫差使干燥能夠進(jìn)行

6、，溫差越大，每磅空氣能干燥的水分就越多。這樣就能減少空氣和能量的使用。然而，由于物料的熱穩(wěn)定性，干燥器里面的最高溫度總受限制。</p><p>　　而且，由于高溫的應(yīng)用，這限制將會(huì)擴(kuò)大，并影響建筑材料的溫度-應(yīng)力值關(guān)系。干燥器出口允許的最小輸出量依賴于期望產(chǎn)品的濕含量和其他特性，有時(shí)也與設(shè)備壁的物料垢有關(guān)。</p><p>　　對(duì)于加熱器，入口氣體的濕含量通過實(shí)驗(yàn)和粗略的使用相對(duì)濕度或其他

7、措施來(lái)測(cè)量，然后用飽和濕度與焓之間的關(guān)系式算出結(jié)果。干濕表非常實(shí)用，幾乎能用于每一種情況。假定干球/濕球溫度為60/50F，從表中就可以得到1大氣壓下，每磅干空氣中含水0.0055磅，這與實(shí)際數(shù)據(jù)足夠接近（比海拔2000英尺下實(shí)際高0.0004）?？諝獾撵屎蜐耋w將在下文中計(jì)算。兩量一起計(jì)算能減少錯(cuò)誤，提高效率。</p><p>　　在燃料的燃燒過程中，由于產(chǎn)生水分，夾入到熱空氣中。其含水量可通過表2種經(jīng)驗(yàn)數(shù)據(jù)得出

8、。在表中，通過各個(gè)低溫和高溫不同的值，表示出了溫差線的斜率，是與濕含量成反比。必要的話，可用插值法計(jì)算值。</p><p>　　斜率乘以溫差就能得到濕含量的增量，如：</p><p>　　Mf = Sl (T2 - T1) = 2.30 x 10-5 x (260 - 60)= 0.0046 </p><p>　　總濕含量，磅/磅干空氣</p>&

9、lt;p>　　M2 = M1 + Mf = 0.0055 + 0.0046 = 0.0101 </p><p>　　加熱器出口空氣的含濕量，磅/磅干空氣</p><p>　　注意到濕含量是用每單位重的干空氣的含水量來(lái)表示。同樣也可用于焓和濕體的表示。例如，焓單位是Btu/lb干空氣。這些比率使關(guān)系得到統(tǒng)一，簡(jiǎn)化了計(jì)算。</p><p>　　空氣的焓濕干氣及

10、其濕氣的熱量的總和。特別地，在200F到1000F干空氣的熱量從0.24升到0.25，所以在這我們可以用一個(gè)值0.24來(lái)進(jìn)行計(jì)算個(gè)點(diǎn)的值（C1=C2=C3）。然而，水蒸氣的焓隨溫度的變化變化很大。它的經(jīng)驗(yàn)式是：</p><p>　　Wi = 1061.8 + 0.433 Ti + 0.00004 Ti2 W1 = 1087.9 W2 = 1177.1 W3 = 1123.2 enthalpy of wat

11、er vapor, Btu/lb </p><p>　　空氣的焓的計(jì)算式是：</p><p>　　Hi = Ai Ci Ti + Ai Mi Wi </p><p><b>　　空氣和濕氣的焓，</b></p><p>　　我們定的是1磅干空氣，因此Ai=1.0,代入這三個(gè)點(diǎn)，變成：</p><p&g

12、t;　　H1 = C1 T1 + M1 W1 = 0.24 x 60 + 0.0055 x 1087.9 = 20.4 Btu/lb dry air </p><p>　　H2 = 74.3 H3 = H2 = 74.3 </p><p>　　直接干燥經(jīng)常叫做等熱干燥，也就是干燥器出口處熱量總和與入口處相等，空氣所帶的熱量提供干燥時(shí)必要且隱藏的熱量，而整個(gè)系統(tǒng)中總熱量不發(fā)生變化。大多

13、數(shù)簡(jiǎn)單的干燥裝置近似于等熱干燥。</p><p>　　因?yàn)榧俣ㄊ堑葻岣稍?，?和3點(diǎn)的焓相等，這樣不用的量和物料平衡就能把3點(diǎn)的濕量算出來(lái)?，F(xiàn)通過輸出量就能計(jì)算出3點(diǎn)的M3：</p><p>　　干燥器出口時(shí)的濕含量，磅/磅干空氣</p><p>　　如果出口氣體的濕球溫度已知，就能避免作等熱的假設(shè)，在干濕表總能讀出口端的濕含量。舉例來(lái)說，假設(shè)側(cè)的濕球溫度濕98F，

14、3點(diǎn)的濕含量就是0.0332磅/磅干空氣，從最后的結(jié)果可以看出，熱量效應(yīng)使流速提高約13%。</p><p>　　能引起等熱操作的偏差的因素如下列舉：</p><p><b>　　供給的熱量</b></p><p>　　通過內(nèi)部環(huán)熱傳導(dǎo)物料的熱量</p><p>　　結(jié)晶或者反應(yīng)固體熱量</p><p

15、><b>　　輻射—對(duì)流熱損失</b></p><p><b>　　產(chǎn)品帶走的熱量</b></p><p>　　各方面空氣的流入（如冷卻）</p><p>　　這些因素的計(jì)算方法在“過程干燥練習(xí)”或其它文章中闡述。在實(shí)際中，它們對(duì)等熱干燥的影響是：1、2條為提高，3、4條為可能提高也可能降低，其它都為降低。</

16、p><p>　　盡管產(chǎn)量是最后考慮的，但與流速和裝置費(fèi)用相關(guān)的是干燥速度。實(shí)際上所有的直接干燥器中，僅在供給端含濕量非常低時(shí)，固體流速影響結(jié)果。下式就是將產(chǎn)量轉(zhuǎn)化成干燥速度</p><p><b>　　干燥速率，磅/小時(shí)</b></p><p>　　干空氣的流速，Ai，是用于計(jì)算干燥器出口量，因?yàn)闆]有什么余漏或其它流速，故也可以用于計(jì)算所有三點(diǎn)。干

17、燥器進(jìn)口端和出口端濕量的差值。</p><p>　　干燥器出口氣體流速，磅/分鐘</p><p>　　空氣的質(zhì)量流速必須轉(zhuǎn)換成體積流量，對(duì)于大多數(shù)干燥器，容器的尺寸大小取決于出口端的體積流量。體積流量也決定著部件的大小，例如產(chǎn)品收集器，鼓風(fēng)機(jī)，煙窗，通風(fēng)管，以及任一種節(jié)約熱量的交換機(jī)和吸熱裝置。規(guī)范入口裝置的大小，例如加熱器和入口空氣過濾器，也是依賴于氣流流量。</p>&l

18、t;p>　　氣流流量受操作壓力的影響，操作壓力可以根據(jù)當(dāng)?shù)睾０胃叨扔?jì)算，一般在500到3000英尺，但也有可能高于5000英尺，計(jì)算壓力可參考式9和式10，濕體可以從式10種得出。</p><p>　　Hg = 29.921 - 0.001078 x El + (8) 1.44559 10-8 x El2 = 29.921 - 2.156 + 0.0578 = 27.823 mmHg 壓力, mmH

19、g </p><p>　　Pt = 14.696 Hg/29.921 = 13.67 壓力, psia </p><p>　　濕體，Cu ft/lb 干空氣</p><p>　　Fi = Ai x Vi (11) F1 = 191.6 x 14.21 = 2,723 F2 = 3,798 F3 = 3,296 </p><p>　　空氣

20、流速，cu ft/min(acfm)</p><p>　　對(duì)于一個(gè)合適絕熱的容器，熱損失大約為熱負(fù)荷的0.2%至0.6%，當(dāng)進(jìn)口與出口端之間的溫差非常小或這是該臺(tái)干燥器有大的漏洞或其他特別的散熱裝置時(shí)，采用大的等熱損失可能是背離其道。更好的方法是給每個(gè)可能成為系統(tǒng)的阻擋物價(jià)一個(gè)適當(dāng)?shù)挠嗔俊＠缂訜崞?、鼓風(fēng)機(jī)和產(chǎn)品收集器。干燥器將來(lái)的發(fā)展就應(yīng)當(dāng)按這方向發(fā)展。</p><p>　　計(jì)算氣流流速

21、時(shí)須根據(jù)干燥器的種類進(jìn)行調(diào)整，但流速不能太高以至于能吹動(dòng)太多的物料，也低于是物料流動(dòng)和傳輸?shù)臉O限速度。這些極限都是決定空氣速率的量，范偉偉從輸送干燥機(jī)的低于100ft/min到一些閃蒸干燥器的高于5000ft/min。</p><p>　　熱負(fù)荷，也稱熱量傳遞速率，與加熱器出口與進(jìn)口空氣焓的差值有關(guān)。</p><p>　　Qt = A1 x 60 x (H2 - H1) = 191.6

22、x 60 x (74.3 - 20.4)= 619,634 熱負(fù)荷， Btu/hr </p><p>　　安裝費(fèi)用與體積流量有很大的牽連，另一方面，操作費(fèi)用主要有熱負(fù)荷決定，在大多數(shù)情況下，約為總能量花費(fèi)的85%。</p><p>　　另外一個(gè)值得考慮的問題，干燥器的出口端影響產(chǎn)品的性質(zhì)，而且還有清理問題，其最重要的是飽和的

23、近視程度。像氣體流量與壓力有關(guān)，通過測(cè)量濕球、露點(diǎn)溫度和相對(duì)濕度來(lái)求出。計(jì)算上述任意參數(shù)，都須用到飽和濕度，Ms，但所有這些參數(shù)在一張干濕表中很輕松地找到。</p><p>　　一些干燥界的專家喜歡選擇等熱飽和率作為參數(shù)，這在等焓條件下，與飽和濕度相區(qū)別的空氣濕度。對(duì)于出口端，在干濕表種菜的飽和濕度市0.0452磅/磅干空氣：</p><p>　　等熱飽和率的封閉循環(huán)系統(tǒng)（對(duì)于非水流體）有

24、類似的計(jì)算，除了所有的進(jìn)入干燥器的濕氣肯定被壓縮，在加熱器中，干燥氣體時(shí)循環(huán)的。使用回收系統(tǒng)更復(fù)雜，尤其是帶有在經(jīng)驗(yàn)中經(jīng)常發(fā)生的漏洞。</p><p>　　參考文獻(xiàn) [1]Cook, E. M., Chem. Eng., April, 1996. [2]Cook, E. M., and H. D. DuMont, "Process Drying Practice," McGraw-Hill

25、, NY,1991. [3]Jorgensen, R. (ed.), "Fan Engineering," 8th edn., Buffalo Forge Co., Buffalo, NY, 1983. [4] Mujumdar, A. S. (ed.), "Handbook of Industrial Drying," Marcel Dekker, NY, 19

26、95 [5]Perry, R. H., and D. W. Green, "Perry's Chemical Engineers' Handbook," 7th edn., McGraw-Hill, NY, 1997.</p><p>　　附錄二 外文資料原文</p><p>　　Drying: As Much Art As Science</

27、p><p>　　Designing dryers in the face of commerical barriers and complex relations</p><p>　　By Edward M. Cook, Energy Saving Consultants, Boynton Beach, Fla.</p><p>　　After a half centu

28、ry, the drying of wet solids, slurries and solutions is still as much art as science. Advances in drying technology are held back partly by commercial barriers and traditions, but more by the complexity of solid–liquid–v

29、apor relations in the myriad substances that can be dried and their many different properties.</p><p>　　Materials that need drying cover a wide range of foods, pharmaceuticals , polymers, minerals, wastes, a

30、nd a host of organic and inorganic chemicals. Even similar substances rarely exhibit identical drying characteristics, because reluctance to release moisture varies widely.</p><p>　　Thus dryer designs are ba

31、sed, not on theoretical concepts, but on data from pilot tests or from past experience. This data helps size new drying systems or evaluate existing ones. The determinations may be rough estimates or detailed analyses u

32、sing equations. It is process design, as contrasted with mechanical design, which is mostly proprietary for each of the more than 200 direct dryer variations available from at least 150 manufacturers.</p><p>

33、;　　Continuous, open or once-through direct dryers are the most widely used in the chemical industry. The main types are spray, flash, fluid-bed, rotary, conveyor and tray dryers. Sizes and designs differ greatly, even wi

34、thin each type, but the basic drying principles are common to all. Water is the liquid in the great majority of cases, but other liquids can be handled in closed systems.</p><p>　　Psychrometric charts are a

35、time-honored means of estimating the process conditions of a dryer, and are even resorted to with the equation method. We'll show with an example how equations yield results. Setting the equations into computer progr

36、ams reduces the work involved, but final accuracy is limited by the input data.</p><p>　　Fig. 1 contains the key elements— a typical, minimum system of the once-through design. Hot air or other gas directly

37、contacts the wet material, evaporates the liquid, and carries off the vapor. The example chosen is at 2,000 ft elevation, and natural gas is the heat source. Feed is 270 lb/hr, and the moisture contents are 55% water in

38、the feed and 5% in the product. The air temperatures are given in Table 1 and were chosen to simplify the operation and confine it to a small area. Knowing the we</p><p>　　Fig. 1. A simple once-through direc

39、t drying system</p><p>　　Knowing it at the outlet requires making a more difficult measurement, but it can eliminate the effects of the unknown or ignored nonadiabatic factors, increasing accuracy.</p>

40、<p>　　Air temperature difference between dryer inlet and outlet drives the process. A greater difference allows more water to be evaporated into each pound of air. This minimizes the use of both air and energy. Th

41、e maximum temperature at dryer inlet is limited, however, by the heat sensitivity of the solids.</p><p>　　And, for high-temperature applications, the limit may be the expansion and temperature–strength relat

42、ions of the materials of construction. The minimum allowed at the dryer outlet depends on the desired product moisture and other properties, and sometimes on material build-up on the equipment walls.</p><p>

43、　　The moisture in the supply air to the heater could be found by trial and error using relative humidity or some other measure, with equations for saturated moisture and enthalpy. But a psychrometric chart is far more pr

44、actical and is used in nearly all cases. At dry bulb/wet bulb of 60/50ºF, a chart drawn for one atmosphere gives 0.0055 lb/lb dry air, which is close enough (at 2,000 ft it is actually 0.0004 higher). Enthalpy and h

45、umid volume of the supply air will be calculated later. Doing them </p><p>　　Combustion of fuel contributes moisture to the airflow, and the amount can be found using the empirical data in Table 2. For low a

46、nd high temperatures it lists the slope of the line of temperature difference (burner outlet minus inlet) plotted against the moisture added. When necessary you can interpolate to get intermediate values.</p><

47、p>　　Slope times the temperature difference gives the moisture added. For instance:</p><p>　　Mf = Sl (T2 - T1)</p><p>　　= 2.30 x 10-5 x (260 - 60)</p><p><b>　　= 0.0046</b

48、></p><p>　　combustion moisture, lb/lb dry air</p><p>　　M2 = M1 + Mf</p><p>　　= 0.0055 + 0.0046</p><p><b>　　= 0.0101</b></p><p>　　air moistur

49、e out of the heater, lb/lb dry air</p><p>　　Note that moisture is expressed as a unit weight of dry air. The same convention is used for enthalpy and humid volume. For example, enthalpy is in Btu/lb dry air.

50、 These ratios unify the relationships and simplify the calculations.</p><p>　　Air enthalpy is total heat in the dry air and its moisture, as given in Eq. 4. Specific heat of dry air varies from 0.24 under 20

51、0ºF to 0.25 at 1000ºF, so here we can use a value of 0.24 for all stations (C1 = C2 = C3 = 0.24). Water vapor enthalpy, however, is very temperature sensitive. An empirical polynomial for it is:</p><

52、p>　　Wi = 1061.8 + 0.433 Ti + 0.00004 Ti2</p><p>　　W1 = 1087.9</p><p>　　W2 = 1177.1</p><p>　　W3 = 1123.2</p><p>　　enthalpy of water vapor, Btu/lb</p><p>

53、　　The equation for air enthalpy is:</p><p>　　Hi = Ai Ci Ti + Ai Mi Wi</p><p>　　enthalpy of air and its moisture, Btu/lb dry air</p><p>　　But our basis is one pound of dry air, thus

54、Ai is 1.0, and for the three stations,</p><p>　　Eq. 4 becomes:</p><p>　　H1 = C1 T1 + M1 W1</p><p>　　= 0.24 x 60 + 0.0055 x 1087.9</p><p>　　= 20.4 Btu/lb dry air</p&g

55、t;<p><b>　　H2 = 74.3</b></p><p>　　H3 = H2 = 74.3</p><p>　　Direct drying is often called adiabatic drying, meaning that the total heat at the outlet to the dryer is the same as

56、 at the inlet. The sensible heat in the air supplies the needed latent heat of evaporation, and no change occurs in the total heat in the system. Most simple plant drying applications are close to adiabatic conditions.&l

57、t;/p><p>　　Because adiabatic drying is assumed here, the enthalpies are the same at stations 2 and 3. This allows station 3 moisture to be calculated without a heat material balance.We can now calculate M3 by r

58、earranging Eq. 4 for the outlet,</p><p>　　station 3:</p><p>　　moisture at dryer outlet, lb/lb dry air</p><p>　　We can avoid making the adiabatic assumption if the wet bulb temperatu

59、re in the outlet air is known. Then the outlet moisture can be read on a psychrometric chart. If, for example, the wet bulb measured 98ºF, the moisture at station 3 would be 0.0332 lb/lb dry air, and the final calcu

60、lations would show that heat effects increase the airflows and heat load by about 13%. The conditions that can cause deviation from an adiabatic operation are listed are:</p><p>　　? Heat in

61、the feed;</p><p>　　? Heat added to the material by internal heat</p><p>　　exchanger;</p><p>　　? Solid's heat of crystallization or reaction;</p><p>　　? Radiation–co

62、nvection heat loss;</p><p>　　? Heat in the product; ? Leaks;</p><p>　　? Miscellaneous air inflows (as for cooling).</p><p>　　Calculations that include these items can be found in &q

63、uot;Process Drying Practice" or other texts. Their influence on operations is: items 1 and 2 improve, item 3 can improve or worsen, the others worsen.</p><p>　　Although product rate is the ultimate conc

64、ern, it is the evaporation rate that relates to airflow and equipment costs. In virtually all direct dryers, the solids rate affects the results only when feed moisture is very low. The equation for converting product ra

65、te to evaporation rate is:</p><p>　　evaporation rate, lb/hr</p><p>　　The flow of dry air, Ai, is calculated for the dryer outlet, but is the same for all three stations because there are no leak

66、s or other airflows. The moisture difference is between dryer inlet and outlet.</p><p>　　airflow at dryer outlet, lb/min</p><p>　　The weight flowrate of air must be converted to volumetric flow

67、(acfm). For most dryer types the acfm at the outlet determines the size of the vessel. It also governs the size of downstream elements, such as product collector, blower, stack, their connecting ductwork, and any heat-sa

68、ving exchangers and exhaust-treating equipment. Sizing the upstream equipment, such as heater and inlet air filter, is based on the acfm at those points.</p><p>　　The acfm is affected by the operating pressu

69、re, which can be computed from the plant elevation, which is typically at 500 ft to 3,000 ft, but may be over 5,000 ft. The pressure is found from Eq. 8 and Eq. 9 and the humid volume from Eq. 10.</p><p>　　H

70、g = 29.921 - 0.001078 x El + (8)</p><p>　　1.44559 10-8 x El2</p><p>　　= 29.921 - 2.156 + 0.0578</p><p>　　= 27.823 mmHg</p><p>　　pressure, mmHg</p><p>　　Pt

71、= 14.696 Hg/29.921</p><p>　　= 13.67 pressure, psia</p><p>　　humid volume, cu ft/lb dry air</p><p>　　Fi = Ai x Vi (11)</p><p>　　F1 = 191.6 x 14.21 = 2,723</p><

72、;p>　　F2 = 3,798 F3 = 3,296</p><p>　　airflow rate, cu ft/min (acfm)</p><p>　　Heat loss is generally between 0.2% and 0.6% of the heat load for a properly insulated vessel. Applying a large arb

73、itrary heat loss can be especially distorting when there is a small temperature difference between inlet and outlet or for a dryer with large leaks or other extra heat requirements. A better practice is to add appropriat

74、e safety margins to components that might be system bottlenecks, such as heaters, blowers and product collectors. Future expansion plans can be handled in the same w</p><p>　　The calculated airflow may have

75、to be adjusted, depending on the type of dryer. Airflow cannot be so high as to carry off too much product, nor be dropped below a minimum for fluidizing or conveying the solids. These limits are a function of the air ve

76、locity and they range from a low of under 100 ft/min for conveyor dryers to over 5,000 ft/min for some flash dryers.</p><p>　　The heat load, also called the heat transfer rate, requires the enthalpy differen

77、ce between the heater outlet and inlet.</p><p>　　Qt = A1 x 60 x (H2 - H1)</p><p>　　= 191.6 x 60 x (74.3 - 20.4)</p><p><b>　　= 619,634</b></p><p>　　head load

78、, Btu/hr</p><p>　　Installation cost is largely a function of the volumetric airflow. Operating cost, on the other hand, depends mainly on heat load, and in most cases is about 85% of total energy costs.</

79、p><p>　　Another consideration, most important at the dryer outlet, where it may affect product properties and add to clean-up problems, is the proximity to saturation. Like the acfm, this is a function of press

80、ure. Measures used to identify it are wet bulb and dew point temperatures and relative humidity. Calculating any of these involves iteration to determine saturation moisture, Ms, but all are easy to find using a psychrom

81、etric chart.</p><p>　　A measure preferred by some drying experts is adiabatic saturation ratio, which is the air moisture divided by the saturation moisture at the same enthalpy. Saturation moisture found on

82、 a psychrometric chart for our outlet condition is 0.0452 lb/lb dry air:</p><p>　　adiabatic saturation ratio Closed-cycle systems (as for nonaqueous liquids) have similar calculations, except that all moistu

83、re that enters the dryer must be condensed, and the drying gas is returned (saturated) to the heater. Partial-recycle systems are more complex, especially with the leakage that often occurs in actual experience.</p>

84、;<p>　　BIBLIOGRAPHY</p><p>　　Cook, E. M., Chem. Eng., April, 1996.</p><p>　　Cook, E. M., and H. D. DuMont, "Process Drying Practice," McGraw-Hill, NY, 1991.</p><p>

85、　　Jorgensen, R. (ed.), "Fan Engineering," 8th edn., Buffalo Forge Co., Buffalo, NY, 1983.</p><p>　　Mujumdar, A. S. (ed.), "Handbook of Industrial Drying," Marcel Dekker, NY, 1995</p>