换热器系统性选择的步.doc

换热器系统性选择的步

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个人收集整理 勿做商业用途
换热器系统性选择的步骤
该篇论文写给负责准备热交换数据表的工程师,数据表内的所有参数按照投标该设备的买主要求列明.首先，工程师必须决定最适合他的产品的设备类型；论文第一部分给出关于这方面选择的指引.最后，工程师准备他的设计之前，必须提交由专家要求的所有数据。至于专利设备，该数据将局限于具体步骤中。对于一般设备而言，尤其是管壳式换热器，工程师还需提交一些设备的具体细节.论文第二部分给出准备管壳式换热器数据表的指引。

第一章 引言
总体来说，这篇关于换热器的选择论述只限定于制造工业中的换热器，制造工业中不同种类的换热器被用于大量不同的服务当中。热交换就是一种或多种液体之间热量的交换，这个工程中还可能包含一种或多种液体的冷凝或蒸发。这些液体本身可以是单一化合物或混合物.不同的任务温度以及压强可能相差很多。液体可以是纯净的，或污浊的，或大比例的,或具腐蚀性的.经济条件下所允许的温差。这些因素在换热器的选择上都起一定作用。
该论文假设生产过程中所有条件都进行了正确优化，并且热负荷，压强温度均被详细说明；这些液体的物理特性都是已知或可计算.如发生相位变化，那么假定一个放热曲线存在。在这种情况下，由工程师决定最合适的的热交换器类型。
我们熟悉的管壳式换热器是最常见的因为它用途广泛。然而，它不一定总是最便宜的。由于在所有的换热器型号中，管壳式换热器的结构类型最多，因此它的选择过程也是最复杂的,介于这点，关于管壳式换热器的具体论述将拖都最后。
第二章 第一部分 换热器类型的选择
下面说明一些在制造业中常见的换热器。

2。1气冷式换热器（ACHE）

冷却过程通常用气冷或水冷或两种的组合。气冷一般来说是最经济的而水冷则很贵或供应不足，或可能法律不允许有热损失在水里。
气冷式换热器在需冷却液体通过的翅片管上吸气或吹气。气冷式换热器比水冷系统受昼夜之间或冬夏之间温度波动的影响更大。极端温度可以通过在热天使用装有小型后续水冷装置的气冷式换热器来解决，或在冷天使用蛇形蒸汽管或使排出的热空气循环进入来解决.
气冷式换热器比简单的直流水冷水冷器占地要大（如果需要使用冷却塔则不然），但安装时可以高于指标,通常高于管长.扇片发出的噪音如果在设计时如没有考虑到，则对于操作者以及周围居民来说都是很令人讨厌的。
气冷式换热器可以为高压和高温设计，尽管为了寻求效率的生产环境，温度很少超过周围温度200-300℉。
设计通常由能优化如下标准的专家实施:
a) 资本及运营标准,
b) 诱导及推动通风风扇（诱导风扇=较好的送风及冰霜防护；推动风扇=节能及维护简单），
c) 翅片类型及间距,
d) 管道行数，
e) 风扇噪音，型号及设计。
2.2 板式换热器（PHE）
板式换热器在食品加工工业应用了很多年,现在越来越多的用于加工工业（图一）。他现在在某些应用方面正在逐渐代替管壳式换热器的地位，因为就他的成本,占地以及重量而言它有更好的传热比率。板式换热器占有更好的成本比率是因为它使用大量的进口材料.在国外重量和占地都要花费更多.
板式换热器在结构上由一些夹紧的波形板组成.换热流体由入口进入在各种板片之间形成薄矩形通道流动，通过半片进行换热。（图2）板的边缘经常用垫圈密封以防止泄露。板式换热器板片为独立元件,可按要求随意增减流程，形式多样;可适用于各种不同的、工艺的要求。

2.5 Plate fin heat exchangers (PFHE） 2。5 版翅式换热器
Usually made in aluminum alloy (US designation 3003）， the PFHE has found extensive application in low temperature processing such as the cold section of air separation plants, hydrogen separation plants and natural gas liquefaction plants. 板翅式换热器通常由铝合金制成，在低温加工方面应用广泛，如低温空分工厂,氢分离工厂，液化天然气工厂等。There are also increasing applications at higher temperatures， e。g。， on plants handling LPG, ethylene， enriched uranium or xylenes.现在也越来越多的应用于高温工厂如，石油气处理工厂，乙烯处理工厂,浓缩铀或二甲苯工厂。
Normally， secondary surface is less efficient than primary surface because of fin inefficiency， so it does not pay to add secondary surface to both sides-it is cheaper to increase the primary surface instead。通常来说，由于翅片的低效，副表面比基表面效率低，因此在两边添加副表面是免费的,相反的，添加基表面很 。The exceptions are （a） where primary surface is expensive because it must be thick to retain the pressure, (b) space is at a premium， (c) the heat fluxes are very low (i.e。 high fin efficiency)但有如下例外，a) 由于要保证厚度来维持压强，因而基表面会很贵，b） 地价很贵,c) 热负荷很低（也就是高肋片效率）。The cryogenic application fits the last category and in addition the secondary finned surface confers additional strength to the assembly.制冷工艺符合最后一项，并且加装肋片的副表面给组装添加了额外的强度。The PFHE offers significant advantages wherever there are clean fluids with thermally long duties。板翅式换热器在处理长热的纯净流体时有很大优势。个人收集整理，勿做商业用途文档为个人收集整理，来源于网络
Layers of corrugated fins are dip—brazed between flat plates， sandwich fashion (Figs。 8 and 9).多层波浪式肋片使用铜浸焊式焊接在平板间,“三明治"式（图8和9)。Fluids in adjacent channels exchange heat through the finned surface and plates.相邻管道内的流体通过装有肋片的表秒和平板交换热量。Fin types can be varied to suit specific heat transfer and pressure drop requirements。具体不同的热传导和降压任务使用不同类型的肋片。Because the finned surface does not have to withstand a pressure differential, it can be very thin yet still be effective in heat transfer.由于装有肋片的表面不需要承受一定的压力差，所以就算它的外皮很薄它一样能有效的传热.Consequently the PFHE packs a very high surface area per unit weight and volume, and is cheap per unit heat load。因此板翅式换热器每单位重量及体积都包裹着大面积的外表面，而且每单位的热负荷也很便宜。个人收集整理，勿做商业用途本文为互联网收集，请勿用作商业用途
The method of construction prevents mechanical cleaning so restricts the PFHE to clean， solid free fluids， or to deposits which can be removed by solvent cleaning, back—flushing， or by warming up。板翅式换热器的结构使得它不能用机械式清理，因此该换热器只能换热清洁流体,或换热溶解式清理，反向冲洗或加热可以清理掉其沉淀的流体.
Most common applications for PFHEs are therefore in cryogenic services where their only competitor is the coiled-tube heat exchanger (q.v。）。由于板翅式换热器的这点特性,它大多数应用于制冷业因为该行业只有coiled-tube heat exchanger可以和它媲美。
The PFHE can handle up to eight multiple streams and any of these may enter or exit part way along the exchanger.板翅式换热器可以装下最多16条流道，而且每条流道的液体都可以从换热器的一条通道流进或流出。All streams flow over finned surfaces although the fin design may be specific to the process stream。每条流道的流体都会从装有肋片的表面流过尽管肋片是为用于加工的那条流道设计的。The design may be made truly counter—currrent and can achieve very tight temperature approaches， as low as 1°F.这种设计也许的确于传统工艺相背并且可以实现有极端温度要求的加工方法，可以低到1华氏度。 Because of its short fin length, the PFHE is very suitable for heating or cooling viscous (but clean) fluids。由于它的肋片长度很短，因此它很适合加热或冷却粘性液体（但是纯净）。Uniform flow distribution between the many parallel channels is very important where tight temperature approaches are required, so considerable care is necessary in the design of the inlet and outlet distribution channels.当需要用有极端温度要求的加工方法时，众多平行的管道之间的等流分配就显得很重要，所以在设计中,需要注意入口和出口分配管道。本文为互联网收集,请勿用作商业用途个人收集整理，勿做商业用途
Corrosion resistance is limited by the range of materials which can be formed and brazed successfully。 PFHEs are usually made in aluminium alloy which can be brazed at relatively low temperatures for sizes up to 6 m x 1。2 m x 1.2 m。板翅式换热器的抗腐蚀能力由可以成功铸造并焊接的材料选择决定。板翅式换热器一般由铝合金制成， 铝合金可以在相对低的温度下焊接,最大体积为6m＊1。2m＊1。2m. Other materials， such as stainless
steels, nickel, copper, Inconel， titanium or alloys of them， can also be used, but brazing is always done with copper or nickel with which fluids must also be compatible；还有其他材料可供选择,例如不锈钢，镍，铜，因康镍合金，钛或是它们的合金，但是焊接通常使用可以适应流体的铜焊或镍焊；sizes are restricted by the dimensions of the furnace required to achieve the higher brazing temperatures.大小是由熔炉的规模决定,还得适应较高的焊接温度。
Design pressure is limited by size but rises to about 1100 lbf/in2 for the smaller units。 But if frequent pressure cycling is likely， the possibility of fatigue must be considered with materials， such as aluminium， which have no endurance limit stress。计划压力由尺寸决定但对于较小型的来说可以达到1100 磅力每平方英寸. 但如果经常有循环压强变化，那么材料和它的可承受能力都必须予以考虑，例如没有压力承受极限的铝。For example， ‘switching' PFHEs in alloy 3003 are limited to 150 lbf/in2.举个例子，开关由3003型合金制成板翅式换热器的承受限度是150 磅力每平方英寸.
Maximum design temperatures are limited to about 150°F for aluminium alloys which can lose mechanical strength and become susceptible to corrosion at higher temperatures.铝合金的最高计划温度为150华氏度,在高温下，铝合金会失去机械强度并且变的易受腐蚀。For these reasons PFHEs for service temperatures around or above ambient are generally made from copper bearing alloys， and for these materials the maximum design temperature is limited by the brazing itself.介于以上原因应用于环境温度或高于环境温度下的板翅式换热器一般由含铜合金制成，而且对于这种材料来说,最高计划温度由该焊接材料本身限定.
There are no restrictions on minimum service temperatures for the low temperature range of aluminium alloys.铝合金没有最低的适用温度因为它适用的低温范围很广。Thermal stresses can be high in cryogenic service especially at start—up, shut-down or during upsets， consequently a maximum process fluid bulk temperature differential is often set.在制冷应用上热应力很高,尤其是在启动，关闭或during upsets， 因此经常要设定加工流体的最大整体温度差值。
Surface areas in excess of 100 OOO ft2 are possible.表面区域可以超过100 000ft^2.
Design of PFHEs is highly specialized and must be left to the vendor。板翅式换热器的设计精密，而且必须由卖主要求。It is worthwhile to obtain the vendor’s opinion at the outset as to whether or not the application would suit a PFHE.在一开始,我们需要获得卖主的想法，因为这对于决定是否该使用板翅式换热器很重要。
Mechanical design codes can be applied to PFHEs,
and the finished units are generally works tested hydraulically to full test pressure on each stream independently.机械设计规范适用于板翅式换热器，并且成品的每根流道都要单独做水压测试和完整压力测试。
Reference （3） discusses low temperature applications in general。参考书目（3）整体介绍了低温中的应用。
2.6 coiled-tube heat exchanger（CTHE)2。6 螺旋管换热器 (CTHE）
The coiled tube heat exchanger, also known as a Hampson heat exchanger competes with the plate fin heat exchanger in the cryogenic field， and can also be used for wider services。螺旋管换热器,也叫做汉普森换热器，在制冷业可以与板翅式换热器相媲美，也适用于更广泛的应用。It can be constructed in a wider range of materials than the PFHE （Fig. 10）制造螺旋管换热器的材料范围比板翅式换热器要广。
Small bore ductile tubes are wound in layers around a central mandrel or core。 螺旋管换热器由多层小口径软管围绕一个轴或核构成。Each successive layer is wound the opposite hand to its predecessor from which it is separated by spacing strips.每层相邻的软管有间隔条隔开，与前一层软管向相反方向缠绕。Tubes in individual， or groups of， layers may be brought together into one or more tube plates through which different fluids may be passed counter—current to the single shellside fluid。单层或多层中的软管可以靠拢在一个或多个管板上，流体可以在这些管板上可以与壳程的单一液体逆向流动。Plain
or finned tubes can be used and overall surface areas
can run up to 200000 ft2。平管或肋片管均可安在螺旋管换热器上，并且整体最大基表面可以达到200 000平方英尺。 Materials are usually aluminium alloys for cryogenics or stainless steels for higher temperatures which can be as high as 1350°F。用于制冷业的螺旋管换热器的制成材料通常为铝合金，用于高温中的制成材料通常为不锈钢，最高温度可达1350华氏度。
Because the small passages on both sides of the exchangers do not permit mechanical cleaning these exchangers are used for clean， solid free， fluids only or for fluids whose deposits can be removed by back-flushing or by periodic washes with solvent。由于该换热器的两端口径较小，所以一般的机械清理不能用于该换热器，该种换热器只能换热清洁流体,或换热反向冲洗或加热可以清理掉其沉淀的流体.The exchanger is very compact but slightly less so than a plate fin heat exchanger； however, several of the PFHE disadvantages are overcome by the CTHE.该种换热器很紧凑但要比板翅式换热器稍松一些；因此盘管式换热器可以袮补板翅式换热器的缺点。Differential thermal expansion is less of a problem, dip brazing is not required and design pressures and temperatures can be greater than in PFHEs。该种换热器可以承受热膨胀差，因此不需要使用铜浸焊,设计压力和设计温度比板翅式换热器要高。Close temperature approaches are also possible when the CTHE is operated in counter-flow当该种换热器在处理逆流中时换热温差可以很小.The CTHE is also useful for heat exchange to viscous fluids because of its low LID ratio, a function of the tube’s continuous helix. 螺旋管换热器在处理粘性流体时也很管用,因为，由于它是连续环绕的,所以它的升阻比很小。个人收集整理，勿做商业用途本文为互联网收集，请勿用作商业用途
The design of a CTHE can be exactly matched to process requirements。 螺旋管换热器的设计可以适用多种加工要求。The spacer thickness on the shellside can be adjusted to take up all the allowable shell- side pressure drop and tube bores and lengths can be adjusted to absorb all the allowable tubeside pressure drop.调整壳侧的间隔厚度适应所有可承受范围内的压力落差,调整管口径和长度可以吸收所有可承受范围内的管侧压力落差。 Even distribution into the shell can be achieved
by use of a thin metal shroud.通过使用薄金属罩甚至可以实现向壳内分配液体。The parallel paths on the shellside are all the same length as they are on the tubeside, which also ensures even distribution.壳程的平行流道与管程的长度完全一致这种结构甚至可以保证流速。 Hence maximum effect temperature driving force occurs throughout the length of the exchanger.因此温度推动力的最大影响可以发生在换热器整个管道内.
The CTHE is not cheap because of the material costs, high labour input in winding the tubes, and because the central mandrel is useless for heat transfer but increases the shell diameter。由于材料成本很高,转动管需要大量人力，中心轴承对于传热没有任何用处还增加了外壳直径，因此螺旋管换热器很贵。In practice shell diameters tend to be standardized。在实际应用中外壳直径通常是标准化的。
2.7 Double pipe heat exchangers (DP） 2。7 套管式换热器(DP）
Double pipe heat exchangers are suitable for high pressures and temperatures， and for thermally long duties。 Simple in construction， their usual application is for small duties requiring, typically, less than 300 ft2 surface.套管式换热器适用于高温高压以及长热环境。该种换热器结构简单，通常只应用于小型任务，最典型的是表面小于300平方英尺的。They are not very compact.它们的结构并不是很紧凑.
As implied by their name， one pipe is mounted concentrically inside another， and heat exchange is pure counter—flow。就该种类换热器的名字一样，一个管子套在另一个管子的中心里，而且是逆流换热.The units can be designed to be taken apart for cleaning， but more often they are simply all—welded jacketed pipes， the annulus of which cannot be mechanically cleaned。它的所有组件可以拆开清洗,但一般来说，它通常是全焊式套管，并且不能使用机械式清理.Units can be connected in serpentine fashion but their cost rapidly escalates until a small shell and tube heat exchanger becomes relatively cheaper。组件可以使用U型连接,但是该种换热器的价格上升很快，直到换一个板壳式换热器会相对更便宜.文档为个人收集整理，来源于网络本文为互联网收集,请勿用作商业用途
Design can easily be done by hand using,设计可以由手工轻松完成。Reference （6）， recently published， covers the annulus heat transfer coefficient more thoroughly than the others。最近刚出版的参考书目6,比其他书目更全面的概括了环形套筒的热传递系数。Alternatively simple design programs can be written or purchased.可以写出或买到相对简单的设计程式。
Proprietary designs using double pipes with longitudinal fins within the annulus, are used where additional surface is required relative to the inner pipfor example， where steam is employed in the inner pipe to heat viscous oil in the annulus prior to entering a pump.一些套管的专利设计在套管中加入纵向肋片,用于内管需添加额外表面的场合，举例来说,使用该种设计的套管内管加入蒸气来加热粘性油要优于使用泵。Design is usually left to the vendor but is reasonably straightforward provided the fin efficiency is allowed for.设计一般由供应商决定，但会直接给出最大肋片效率。文档为个人收集整理，来源于网络个人收集整理，勿做商业用途
Design pressures and temperatures depend on the method of construction but are broadly similar to S and T heat exchangers.设计温度与设计压力取决于制造方法，但大体上与管壳式换热器一致。
2。8 Graphite heat exchangers （GHE） 2。8 石墨换热器（GHE）
Carbon， in the form of impervious graphite, has a high thermal conductivity relative to most other heat exchanger materials。不渗透性石墨形式的碳，较其他换热器材料来说热传递性更高。Graphite also has a high resistance to corrosion， being attacked by only a few chemicals， typically strong oxidizing agents such as aqua regia or chromic acid.石墨对于少量化学物质的腐蚀抵抗性很强,尤其是强氧化剂像王水或铬酸.Provided stresses are kept compressive, graphite can be used successfully as a heat exchanger material， of special use when dealing with highly corrosive fluids。石墨压应力很强，可以充当很好的换热器材料,还可以做处理强腐蚀性流体的特殊材料。In some services， typically hydrogen chloride absorbers or sulphuric acid dilution coolers, there are few other suitable and economical materials.在一些应用当中,很少有材料比石墨更适合更经济，尤其是充当氢氯吸收剂或硫酸稀释冷却剂时。个人收集整理，勿做商业用途文档为个人收集整理，来源于网络
Graphite is usually made from finely ground coke bound with plastic hydrocarbons.石墨通常由完好的地下焦炭混合可塑碳水化合物形成.This material is
pressure-moulded to the desired form and then pyrolysed， first to decompose and drive off the binding materials and then to polymerize the carbon to the hexagonal crystal lattice form of graphite at about 5000°F。该材料先由模具压成想用的形状之后进行热解，首先将其分解并去除杂质，之后在5000华氏度高温下将碳聚合成六方晶系石墨，The resulting graphite is impregnated with resins to make it impervious。在用树脂将其充满使其具有不透性.
Graphite is immune to thermal shock and can be used in liquid service up to 400°F or up to 1500°F in some gas ser