Principia and Design of Heat Exchanger Device 热交换器原理与设计

Transcription

1 Principia and Design of Heat Exchanger Device 热交换器原理与设计 School of Energy and Power Engineering, SDU Presented: 杜文静 Telephone:

2 1. Spiral heat exchanger 螺旋板式热交换器

3 basic structure and principle 基本构造和原理 Advantage: high heat transfer coefficient, small temperature difference, compact, easy manufacture and installation Low pressure drop, so the high design velocity can be adopt, water m/s, gas 0m/s Heat transfer coefficient could be 50~100% higher than shell-and-tube Long flow path, which is of benefit to low temperature energy recovering. Disadvantage: maximum size is limited. Maximum pressure (0.6~.5Mpa). field repair is difficult due to construction features Structure spiral plates, separate plat, cover, mandrel Classification Removable, irremovable

4 The spiral heat exchanger is made in three main types which are different in the connections and flow arrangements. I 型 :both fluids in spiral counterflow 两流体均匀螺旋流动 The media flow countercurrent through the channels via the connection in the center and at the periphery. one stream enters at the center of the unit and flows from inside outward. The other stream enters at the periphery and flows towards the center. Thus, the true counterflow is achieved this type is used to exchange heat between media without phase changes such as liquid-liquid, gas-liquid, or gas-gas. Small flow, welded, II 型 :As same as the type 1, but can be disassembled 流动方式同 I 型相同 交错焊接, 密封垫圈, 可拆卸

5 III 型 :one fluid in spiral flow, the other in crossflow across the spiral 一侧螺旋流 ( 从周边进, 从另一周边流出 ), 一侧轴向流动 One channel is completely seal-welded, while the other is open along both sheet metal edges. Therefore, this type has one medium in spiral flow and the other in corssflow This type is mainly used as a surface condenser in evaporating plants. It is also highly effective as a vaporizer. 流量大 标准 JB/T 螺旋板式换热器型号表示方法 : X X X X/X - X - X /X - X/X - X B/K L C/S 工作压力换热面积板宽 / 直径通道间距 D/G B 不可拆,K 可拆, L 螺旋板式换热器, C 碳钢,S 不锈钢 D 堵死型,G 贯通型

6 .Design calculation 设计计算 1) heat transfer coefficient 换热系数计算 a)turbulent flow 湍流 (Re>6000) Nu Re Pr n d ( D d e equivalent diameter 当量直径,m, de=h e b/(h e +b) H e the plate height 螺旋板有效宽度 D m average diameter of flow path (D+d)/ b gap of the flow path 通道间距 b) laminar flow 层流 (Re<000) 0. e m ) 8 Mc p.4 M: mass flow rate l t :length of the spiral channel lt c)transition flow 过渡流至湍流 Re>1000) Nu (0.0315Re lt b 1.3 )Pr 0.5 ( ) w 0.17

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8 plate-and-frame heat exchanger 板式热交换器

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10 Components: gasket plate, spiral plate, lamella basic structure and principle advantage: high turbulence at low Re number, high heat transfer coefficient, low fouling factor, compact, easy cleaning, inspection and maintenance, flexible, heat transfer between multi-fluids disadvantage: cannot accommodate very high pressure, temperature or pressure and temperature differences, No corrosive fluid for gasket plate Structure:metal plant, gasket, frame Classification:gasket, welded, brazed Or gasket plate, spiral plate, lamella( 薄片 ) Gasketed plate: a gasket plate heat exchanger consists of a series of thin plates with corrugations or wavy surface that separates the fluids

11 Standard 标准 GB 板式热交换器 型号表示方法 : X X X - X - X - X - X B/BL/BZ 板片波纹形式代号 设计压力 垫片材料号 B 板式换热器 单板换热面积 换热器换热面积 框架结构形式号 BL 板式冷凝器 BZ 板式蒸发器 流程组合 :channels in either series or parallel passage 流体可以串列 并联和混联 Single pass or multi-pass 流程可以受单流程和多流程

12 .design calculation 设计计算 1) heat transfer coefficient 换热系数计算 Mean temperature difference 平均温差 t t 查图 c Heat transfer coefficient 传热系数 : 1 K o 1 i w i w o 1 o n m Convention heat transfer coefficient 对流换热系数 : Nu C Re Pr ( ) Equivalent diameter 当量直径 de=4a/u=4lb/l=b L 板有效宽度, b 板间距 ) pressure drop 压力损失计算 Eu=bRe d Eu=P/w 欧拉数 m 流程数 Equivalent diameter 当量直径 :de=4a/u=4lb/((l+b) w Z

13 3 plate-fin heat exchanger(extended surface heat exchanger) 板翅式热交换器

14 basic structure and principle Each channel is defined by two parallel plates separated by fins advantage: high heat transfer coefficient, Compact, high surface area densities, flexible(gas-gas, gas-liquid, liquid-liquid, phase change) disadvantage: manufacturing complexity, Corrosion, Not easy cleaning and inspecting structure: plate, corrugated plate, sealing bar classification:plain fin, plain- perforated fin serrated fin (lanced),interrupted,multientry) herringbone or wavy fin arrangements:counterflow, parallel flow, cross flow, mixed flow

15 . 设计计算 design calculation 1) fin efficiency 翅片效率 a) fin efficiency 翅片效率 Book, picture 3.36 Q Q F t w t ) heat transferred through the area of plate ( 1 1 f F( t m t ) heat transferred through the area of fins f t w wall temperature t m mean temperature of fin, it is a unknown parameter using t w instead of t m fin efficiency will be introduced Q F ( t t f w f ) Thus f F ( t F ( t m w t t f f ) ) t t m w t t f f

16 Defined: actual heat transfer rate / maximum heat transfer rate through fins 翅片的实际传热量和最大传热量之比 f is a measure of thermal performance of a fin tanh( mb) f mb m, f b characteristic size, thicknesses of fin, see p149 Influence factors of fin efficient 1)characteristic size 翅片定性尺寸 b 小, f 大 )thickness 翅片 厚, f 大 3)convection heat transfer coefficient 翅片和流体的对流换热系数 小, f 大 4)thermal conductivity of fin 翅片的导热系数 大, f 大

17 b) overall fin efficiency 翅片壁面总效率 ) ( ) )( ( ) ( ) ( f w f w f f w f f w t t F t t F F t t F t t F Q F F F f 1 0

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25 )heat transfer coefficient 换热系数计算 Single phase 无相变时的对流换热系数 j c G p 3 Pr j heat transfer factor, G mass flow rate serrated fin(re=300~7500)( 锯齿翅片 ) lnj= x10 - (ln(re) (lnRe) lnRe plain-perforated fin (Re=400~10000) ( 多孔翅片 ) lnj= x10 - (ln(re) (lnRe) lnRe Plain fin(re=400~10000) ( 平直翅片 ) lnj= (lnre) lnRe+3.11 Multiphase (see paper 154)

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28 3)pressure drop calcualtion Inlet, outlet, center a)inlet section ) (1 G K G P c G mass flow, ratio of areas, K c factor, check reference b)outlet section ) (1 G K G P e K e factor c)center section m d e fl G P f friction factor, L length, d e equivalent diameter, m density of flow Total pressure drop P P=P 1 +P +P 3

29 4)plate-fin heat exchanger design procedures 翅片式热交换器的设计步骤 a)flow type (counterflow, parallel flow cross flow etc) 确定流动形式 b)fin type and sizes 翅片形式和几何参数 c)length, cross area 宽度, 截面积等 d)characteristics of fluids 物性参数 e)select velocity and number of passes 选定流速, 决定通道数 f)calculate convection heat transfer coefficient 计算流体换热系数 g)calculate fin efficiency 计算翅片效率 h)calculate heat transfer coefficient K 计算传热系数 i)calculate mean temperature 对流平均温差 j)calculate heat transfer area 传热面积 k)calculated length and used length 翅片单元的理论长度和实际长度 l)calculate pressure drop 压力损失计算