The CFD Simulation Of Flow And Heat Transfer Of Single Tube In Heat Exchanger

Heat exchangers are common equipments used in many industrial sectors such aschemical industry, petroleum, power and play an important role in manufacturingprocess. In order to meet the need of industrial heat transfer and energy conversation,it is an inevitable direction to development and design of a new type of heatexchanger to improve the efficiency. Falling film heat exchanger has been widelyapplied for its better heat transfer efficiency, smaller heat transfer volume and lessrefrigerant injection. In this study, the falling film heat transfer exchanger, which isused as a physical model, is abstracted and simplified to get the numerical model. Themethod of flow channel in single tube is applied to study the flow characteristics ofliquid film and heat transfer performance. CFD simulation can provide theoreticalbasis for structure improvement of heat exchanges.A typical characteristic of falling film heat exchanger is the continuous liquidfilm outside single tube. The method of CFD simulation is applied and differentnumerical models are created to study fluid flow and heat transfer performance of thefilm. Because the flow is the basis for heat transfer, heat transfer is the purpose of theflow, so it is difficulty to study heat transfer without detailed understanding about theflow characteristics.2D simulation as the basis for3D simulation can greatly savecomputer storage, shorten computing time and speed up convergence.The objective of3D fluid flowing attempt to investigate the influence ofproperties of refrigerants, feeding height and other factors on the coverage area andthe liquid holdup and try to get the greater area of continuous flow film. Finally, it isto get the ideal equipment with high heat transfer coefficient, small volume and lowmanufacture cost.At the process of3D heat transfer simulations in the study, the heat transfercoefficient is selected as an evaluation index with the ideal condition that single tubeis completely covered by continuous liquid film. In this section, it includes the effectof different heat transfer wall specifications, different models and different spayquantity on heat transfer coefficient and for further main parameters can bedistinguished from minor parameters. Then this work provides appropriate ofparameter reference for design and improvement of heat exchanger equipment. To enhance or improve the heat transfer performance of the heat exchanger, heattransfer enhancement can not only use falling film type, but also can change surfacestructures of single tube, which lead to surface disturbance and produce locallysecondary flow that reduce the thickness of the boundary layer or promote theseparation of boundary layer at flow direction. In this study, the characteristics of theheat transfer coefficients and friction factors of the three enhanced tube such as spiralripple tube, spiral fluted tube and corrugated tube were investigated. The change ofsurface structure not only increases friction factor, but also increases energyconsumption. Therefore comprehensive coefficient of performance parameters isintroduced to judge the performance of single tube. The greater of comprehensivecoefficient of performance parameters, the better heat transfer performance.Though numerical simulation has some limitations because the method of singletube in heat exchange is applied, but its results can still provide some theoretical basisfor the design of heat exchanger. In the future, numerical simulation which is based onthe whole of heat exchanger structure should be used to make it more close to theneed of practical equipment.