Research Initiation: Heat Transfer and Pressure Drop in Tubes in the Transition Region for Various Entry Configurations

该研究项目的目的是研究不同入口结构对过渡区域管内局部传热和压降的影响。这包括从大约200到10,000的雷诺数，这取决于进口配置的类型。局部传热、压降和间歇系数的测量将在管道入口附近进行，这些测量将持续到足够远的下游，从而实现充分发展的层流或湍流，并且通常引用的相关性可能变得有效。各种入口配置将被测试。管道入口附近的流动将使用现有的数值技术进行模拟，并将结果与实验研究进行比较。在不加热的透明管内进行的压降和速度分布的独立测量和流动可视化研究将用于帮助建立流动现象的模型。对于层流和全湍流状态下管内流体的流动过程，已经有了大量的数据和分析模型。然而，对于雷诺数从200到10000的过渡流态的问题，研究的很少。在实际工程设计中，通常建议避免在这种情况下进行设计和操作；然而，在设计约束下，这并不总是可行的。现有的许多信息还涉及远离入口的完全发育的流，或涉及高度理想化入口下游的入口效应。因此，所提出的研究将提供对管道流动谱的基本理解和数据，并且也可能具有重要的实际设计应用，从而改进设计方法。

The objective of the proposed research project is to study the effects of various entry configurations on local heat transfer and pressure drop in tubes in the transition region. This includes Reynolds numbers from about 200 up to 10,000, depending on the type of inlet configuration. Local heat transfer, pressure drop, and intermittency factor measurements will be made near the entrance of a tube, with those measurements continuing far enough downstream that fully- developed laminar or turbulent flow is achieved and the usually cited correlations presumably become valid. Various entrance configurations will be tested. Flow near the entrance of the tube will be modeled using existing numerical techniques, and the results will be compared to the experimental study. Independent measurements of pressure drop and velocity profiles in unheated transparent tubes and flow visualization studies will be used to assist in modeling the flow phenomena. An enormous amount of data and analytical modeling is available for fluid flow processes in tubes in the laminar and fully-turbulent flow regimes. However, very little has been done to examine the problems in the transition flow regime encompassing Reynolds numbers from perhaps 200 to 10,000. In practical engineering design, the usual recommendation is to avoid design and operation in this regime; however, this is not always feasible under design constraints. Much of the information available furthermore deals with the fully- developed flows far from the entrance, or involves entrance effects downstream from highly idealized entrances. The proposed research, therefore, will provide a basic understanding and data in the spectrum of tube flows, and also could have important practical design applications leading to improved design methods.