换热器外文翻译资料

1 换热器

简介，分类

及选型

1.1 简介

换热器是一种用于不同温度的两种或两种以上流体间传递内部热量的传热设备。大部分换热器中流体被传热面分隔开，理想情况下他们之间不发生混合。换热器应用于过程、电力、石油、运输、空调、制冷、低温、热量再生、替代燃料等工业。我们日常生活中常见的换热器如汽车散热器、冷凝器、蒸发器、空气预热器以及油冷器。换热器的分类有多种方式。

1.2 换热器的构造

一台换热器由热交换元件，如含传热面的芯或管阵，以及流体分配元件，如封头或贮罐、进出口接管等构成。换热器中通常没有移动部件，但也有例外，比如在旋转式再生器中，管阵被设计成以一定速度旋转；在刮板式换热器中，带刮刀的旋转元件在传热管内不断旋转。传热面与流体直接接触从而使热量以热传导的方式传递。传热面中分隔流体的那部分叫做主接触面或直接接触面，二级传热面如翅片可以附在主接触面上以增加传热面积。图1.1展示了一些类型的换热器。

1.3 换热器的分类

一般而言，工业上的换热器按以下来分类：(1)结构；(2)传热过程；(3)传热面的紧凑程度；(4)流动布局；(5)分程情况；(6)流体的相态；(7)传热机理。在此简要介绍了分类情况，换热器的分类和结构的详情参见文献Shah ^[1,2]、Gupta ^[3]和Graham Walker ^[4]，关于换热器的分类和选型的详细步骤参见Larowski等^[5a,5b]文献。表1.1示出了一些类型的换热器及其构造细节和性能参数。

1.3.1 根据结构分类

根据结构不同，换热器可分为^[1]：

管式换热器，包括套管式、管壳式、盘管式；

板式换热器(PHEs)，包括垫片式、钎焊板式、全焊接板式、螺旋板式、面板盘绕式、板壳式；

延伸表面换热器，包括管翅式、板翅式；

再生器，包括固定管阵式、旋转式。

1.3.1.1 管式换热器

1.3.1.1.1 套管式换热器

套管式换热器由两个同心管构成，通常设计成U形，流动方向为逆流式，可根据需要将多个套管式换热器串联或并联，通常用于传热负荷较小的情况，特别是面积小于300ft²时，也适用于高温高压场合，耐用性好^[5]。由于可以根据需要添加或拆除部件，灵活性强，而且由于它是标准化的所以不需要很多库存来备用，设计维护简单。内管外的环形空间设置纵向或周向的翅片以加强环内流体对内管流体的换热。其设计压力和温度大体与管壳式换热器(STHEs)类似，这种换热器设计方法简单，可用凯恩法或专有的程序来执行。美国科克传热公司(The Koch Heat Transfer Company LP, USA)最早设计了套管式换热器。图1.2-1.4为套管式换热器。

1.3.1.1.1.1 应用 在换热过程中要求温度交叉（即热流体的出口温度低于冷流体的出口温度）的情况下，采用套管式换热器是最有效的且需要的截面和换热面积更小。套管式换热器通常也用于高结垢率的情况下，如流体为浆状，以及较小热负荷的情况，热负荷较大时可采用多管。

当满足下列条件中的一个或多个时，可考虑套管式换热器：

• 换热过程中有温度交叉
• 管侧压力高
• 要求其中一侧压降低
• 需要增加装置来提高换热系数
• 换热器受到热冲击
• 流激振动的影响
• 流动过程存在固体颗粒或浆料

1 Heat Exchangers

Introduction,Classification,

and Selection

1.1 INTRODUCTION

A heat exchanger is a heat transfer device that is used for transfer of internal thermal energy between two or more fluids available at different temperatures. In most heat exchangers, the fluids are separated by a heat transfer surface, and ideally they do not mix. Heat exchangers are used in the process, power, petroleum, transportation, air-conditioning, refrigeration, cryogenic, heat recovery, alternate fuels, and other industries. Common examples of heat exchangers familiar to us in day-to-day use are automobile radiators, condensers, evaporators, air preheaters, and oil coolers. Heat exchangers can be classified into many different ways.

1.2 CONSTRUCTION OF HEAT EXCHANGERS

A heat exchanger consists of heat-exchanging elements such as a core or matrix containing the heat transfer surface, and fluid distribution elements such as headers or tanks, inlet and outlet nozzles or pipes, etc. Usually, there are no moving parts in the heat exchanger; however, there are exceptions, such as a rotary regenerator in which the matrix is driven to rotate at some design speed and a scraped surface heat exchanger in which a rotary element with scraper blades continuously rotates inside the heat transfer tube. The heat transfer surface is in direct contact with fluids through which heat is transferred by conduction. The portion of the surface that separates the fluids is referred to as the primary or direct contact surface. To increase heat transfer area, secondary surfaces known as fins may be attached to the primary surface. Figure 1.1 shows a collection of few types of heat exchangers.

1.3 CLASSIFICATION OF HEAT EXCHANGERS

In general, industrial heat exchangers have been classified according to (1) construction, (2) transfer processes, (3) degrees of surface compactness, (4) flow arrangements, (5) pass arrangements, (6) phase of the process fluids, and (7) heat transfer mechanisms. These classifications are briefly discussed here. For more details on heat exchanger classification and construction, refer to Shah [1,2], Gupta [3], and Graham Walker [4]. For classification and systematic procedure for selection of heat exchangers, refer to Larowski et al. [5a,5b]. Table 1.1 shows some types of heat exchangers, their construction details, and performance parameters.

FIGURE 1.1 Collection of few types of heat exchangers. (Courtesy of ITT STANDARD，Cheektowaga,NY.)

1.3.1 Classification According to Construction

According to constructional details, heat exchangers are classified as [1] follows:

Tubular heat exchangers—double pipe, shell and tube, coiled tube

Plate heat exchangers (PHEs)—gasketed, brazed, welded, spiral, panel coil, lamella

Extended surface heat exchangers—tube-fin, plate-fin

Regenerators—fixed matrix, rotary matrix

1.3.1.1 Tubular Heat Exchanger

1.3.1.1.1 Double-Pipe Exchangers

A double-pipe heat exchanger has two concentric pipes, usually in the form of a U-bend design. Double-pipe heat changers with U-bend design are known as hairpin heat exchangers. The flow arrangement is pure countercurrent. A number of double-pipe heat exchangers can be connected in series or parallel as necessary. Their usual application is for small duties requiring, typically, less than 300 ft² and they are suitable for high pressures and temperatures and thermally long duties [5]. This has the advantage of flexibility since units can be added or removed as required, and the design is easy to service and requires low inventory of spares because of its standardization. Either longitudinal fins or circumferential fins within the annulus on the inner pipe wall are required to enhance the heat transfer from the inner pipe fluid to the annulus fluid. Design pressures and temperatures are broadly similar to shell and tube heat exchangers (STHEs). The design is straightforward and is carried out using the method of Kern [6] or proprietary programs. The Koch Heat Transfer Company LP, USA, is the pioneer in the design of hairpin heat exchangers. Figures 1.2 through

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