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的入口结构对过渡区管内局部换热和压降的影响。这包括大约200到10,000之间的雷诺数，具体取决于进气口结构的类型。局部换热、压降和间歇系数的测量将在管子入口处附近进行，这些测量将持续到下游足够远的地方，从而实现充分发展的层流或湍流，通常引用的关联式可能是有效的。将测试各种入口配置。将使用现有的数值技术对管道入口附近的流动进行建模，并将结果与实验研究进行比较。将使用未加热透明管中压降和速度分布的独立测量以及流动可视化研究来辅助对流动现象进行建模。对于层流和完全湍流区的管内流体流动过程，可以获得大量的数据和分析模型。然而，对于雷诺数约为200到10,000的过渡流态问题的研究却很少。在实际工程设计中，通常的建议是避免在这种制度下设计和运行；然而，在设计约束下，这并不总是可行的。此外，许多可获得的信息涉及远离入口的充分发展的流动，或涉及高度理想化的入口下游的入口效应。因此，建议的研究将提供管流频谱的基本了解和数据，并可能具有重要的实际设计应用，导致改进设计方法。

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.