Convective Heat and Mass Transfer
Convective Heat and Mass Transfer
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DOI：
10.1007/978-1-4419-1564-1_7
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发表时间：
2010
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影响因子：
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通讯作者：
Herbert Oertel
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文献类型：
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作者：
Herbert Oertel
这一章的非对流传热和传质是从普朗特的原章节《流动液体中的传热》开始的。我们将处理由温度和浓度梯度引起的流体密度变化引起的无对流流动。这些会在引力场中产生升力，进而导致对流流动。在图1.6的导论章节中展示了在被加热的圆柱体和板上自由对流流动的例子。图1.5中的瑞利-巴姆纳德对流和扩散对流也是自由对流的例子。当外力（如压力梯度）也作用于流动时，就会发生强制对流流动。例如，在热交换器中使用的加热或冷却管道中会发生强制对流。热交换和质量交换过程存在于海洋中，也存在于化学技术的许多不同过程中，如吸收、吸附、萃取和蒸馏。当水在海洋表面蒸发时，高盐浓度仍然存在，并且出现了具有扩散不稳定性的不稳定密度层。溶剂中物质的膨胀和离心机中物质的分离是进一步的例子。生物质量交换过程的例子是向血液提供氧气和吸收体内的食物。
This chapter onconvective heat and mass transferstarts out from Prandtl’s original chapterHeat Transfer in Flowing Liquids. We will treatfree convection flows, caused by the density changes in the fluid due to temperature and concentration gradients. These cause a lift in the gravitational field, which in turn causes convection flows. Examples of free convection flows at heated cylinders and plates were shown in the introductory chapter in Figure 1.6. The Rayleigh–Bénard convection of Figure 1.5 and diffusion convection are also examples of free convection flows.Forced convection flowsoccur when an external force, such as a pressure gradient, also acts on the flow. Forced convection flows occur, for example, in heated or cooled pipes such as those used in heat exchangers.Heat and mass exchange processesare found in the ocean and in many different processes in chemical technology, such as absorption, adsorption, extraction, and distillation. When water evaporates on the surface of the oceans, a high salt concentration remains, and an unstable density layer with diffusion instabilities occurs. The expansion of substances in solvents and the separation of substances in centrifuges are further examples. Examples of biological mass exchange processes are the supply of oxygen to the blood and absorption of food in the body.