1、2009-2-8,第五章 傳熱過(guò)程計(jì)算和換熱器（Chapter 5 Calculations of heat transfer and heat exchangers）,5.3 間壁式換熱器 5.3.1列管式換熱器（管殼式換熱器） 5.3.2其它類型的換熱器 5.3.3傳熱過(guò)程的強(qiáng)化,5.3 間壁式換熱器,間壁式換熱器是一種傳統(tǒng)的、應(yīng)用最廣泛的熱交換設(shè)備。由于它結(jié)構(gòu)堅(jiān)固，且能選用多種材料制造，故適應(yīng)性極強(qiáng)，尤其在高溫、高壓和大型裝置中得到普遍應(yīng)用。,2009-2-8,5.3.1列管式換熱器（管殼式換熱器）,一、構(gòu)造,2009-2-8,5.3.1列管式換熱器（管殼式換熱器）,一、構(gòu)造,2009-

2、2-8,5.3.1列管式換熱器（管殼式換熱器）,思考： 如何判斷壁溫tw、Tw接近哪一個(gè)溫度？T、t or t0？,溫差在50以上時(shí)，要考慮溫度補(bǔ)償問(wèn)題,溫度補(bǔ)償問(wèn)題：,換熱器兩端管板和殼體是連為一體的。 其特點(diǎn)是結(jié)構(gòu)簡(jiǎn)單、制造成本低，適用于殼體和管束溫差小、管外物料比較清潔、不易結(jié)垢的場(chǎng)合。 當(dāng)殼體和管子之間的溫差較大(6070 )且殼體承受壓力不太高時(shí)，可采用補(bǔ)償圈（又稱膨脹節(jié)）。,補(bǔ)償圈補(bǔ)償-固定管板式換熱器,2009-2-8,溫度補(bǔ)償問(wèn)題：,浮頭補(bǔ)償-浮頭式換熱器 U型管補(bǔ)償-U型管式換熱器,一端管板用法蘭與殼體連接固定，另一端在殼體中自由伸縮，整個(gè)管束可以由殼體中拆卸出來(lái)。 適用于殼

3、體與管束間溫差大且需經(jīng)常進(jìn)行管內(nèi)外清洗的場(chǎng)合。,用于殼體與管子間溫差大的場(chǎng)合，但管內(nèi)清洗比較困難。,5.3.1列管式換熱器（管殼式換熱器）,二、選用、設(shè)計(jì)原則,設(shè)計(jì)方法及步驟：,5.3.1列管式換熱器（管殼式換熱器）,Example 5.6 A heat exchanger is to be mounted at the top of a fractionating column about 15 m high to condense 4 kg/s of n-pentane at 205 kN/m2; corresponding to a condensing temperature of 3

4、33 K. Give an outline of the calculations you would make to obtain an approximate idea of the size and construction of the exchanger required. For purposes of standardisation, the company will use 19 mm outside diameter tubes of 1.65 mm wall thickness and these may be 2.5, 3.6, or 5 m in length. The

5、 film coefficient for condensing pentane on the outside of a horizontal tube bundle may be taken as 1.1 kW/m2 K. The condensation is effected by pumping water through the tubes; the inlet water temperature being 288 K. The latent heat of condensation of pentane is 335 kJ/kg. For these 19 mm tubes, a

6、 water velocity of 1 m/s corresponds to a flowrate of 200 g/s of water.,Solution The calculations follow the sequences in that heat load, temperature driving force, and overall coefficient are obtained and hence the area evaluated. It then remains to consider the geometry of the unit bearing in mind

7、 the need to maintain a reasonable cooling water velocity. In general, the n-pentane will be passed through the shell and cooling water through the tubes. Heat Load Q=(4.0335)=1340 kW assuming there is no sub-cooling of the condensate. the outlet temperature of the cooling water will be taken as 310

8、K, and for a flow of m kg/s: 1340=m 4.18(310-288) or m=14.57 kg/s,Temperature driving force t1=(333-288)=45 K, t2=(333-310)=23 K and: tm=(45-23)/ln(45/23)=32.8 K Overall coefficient Inside: For forced convection to water in tubes, equation (4-73) may be used:,Wall: For steel, =45 W/m2 K and b=0.0016

9、3 Outside: K=825.9 W/m2 K,Area Q=KAtm and hence:A=1340/(0.8259 32.8)=49.5 m2 Outer area of 0.019 m diameter tube = (3.142 0.019 1)=0.0597 m2 /m and hence total length of tubing required = (49.5/0.0597) = 830.8 m. Thus with 2.5, 3.6, and 5.0 m tube, the number of tubes will be 332, 231 or 166. The to

10、tal cooling water flow rate = 14.57 kg/s and for u=1 m/s, the flow through 1 tube is 0.20 kg/s hence: the number of tubes / pass = (14.57 / 0.20)=73 Clearly 3 passes are usually to be avoided, and hence 2 or 4 are suitable, that is 146 or 292 tubes, 5.0 or 2.5 m long.,The former is closer to a stand

11、ard shell size and 166 19 mm tubes on 25.4 mm square pitch with two tube side passes can be fitted within a 438 i.d. shell. In this event, the water velocity would be slightly less than 1 m/s (in fact (1 146/166)=0.88 m/s), though this would not affect the overall coefficient to any significant exte

12、nt. The proposed unit is 166 19 mm o. d. tubes on 25.4 mm square pitch 5.0 m long with a 438 mm i.d. shell. In making such calculations it is good practice to add an overload factor to the heat load, say 10%, to allow for errors in predicting film coefficients, although this is often taken into acco

13、unt in allowing for extra tubes within the shell. In this particular example, the fact that the unit is to be installed 15 m above ground level is of significance in limiting the pressure drop and it may be that in an actual situation space limitations would immediately specify the tube length.,強(qiáng)化管式換熱器： 翅片管式-橫向傳熱面積大，傳熱效率高，總傳熱系數(shù)為光管的四至八倍。,5.3.2其它類型的換熱器,2009-2-8,2009-2-8,板式換熱器,5.3.2其它類型的換熱器,板式換熱器是由一組波紋金屬板組成,板上有孔,供傳熱的兩種流體通過(guò).金屬板片安裝在一個(gè)側(cè)面有固定板和活動(dòng)壓緊板的框架內(nèi),并用夾緊螺栓夾緊. 板式換熱器作為一種新型、高效、節(jié)能的換熱設(shè)備已越來(lái)越在眾多領(lǐng)域廣泛應(yīng)用,并且有逐步取代其它類型之趨勢(shì).,2009-2-8,螺旋板換熱器：,傳熱效率高傳熱效率為列管式換熱器的13倍 阻力小以較低的壓力損失，處理大容量蒸氣或氣體；有自清