205 62 Optimal flow through a humidity induced convection pump A. H. Christensen DTU Physics, Technical University of Denmark ABSTRACT The inspiration for potential new sources of renewable energy can come from a wide variety of phenomena. This project was inspired by the flow of atmospheric gases through emergent plants, like the waterlily. In energy conversion reactions, in e.g. plants, oxygen plays an important role. For plant cells on land this is not a problem as oxygen is readily available in the atmosphere and diffuse easily to the parts of the plants where it is needed. For emergent plants however, this process is not sufficient. These plants have therefore developed some kind of lung-like organs, in which a network of veins works to transport oxygen, which diffuses through a porous surface in the leaves, through the plant to the submerged parts of the stem and the roots. The physical mechanisms that drive the flow are, however, at the moment not completely understood. In particular it is unknown how the flow depends on the different geometric parameters of the system. Should this pump be used in biologically inspired engineering as e.g. a source of renewable energy, it is of interest to find out if there exists an optimal geometric configuration. A simplified structure of such a humidity induced convection pump mimicking the structure of a plant has in this project been studied. The simplified pump consists of a chamber containing a reservoir of water covered by a porous membrane and connected to a venting pipe. Assuming that the relative humidity is higher in the chamber than in the atmosphere, an advective flow will be present through the venting pipe. If one was to place a turbine at the end of the venting pipe, this pump could potentially be used to produce electricity. The flow of gases through the pump due to humidity induced convection is influenced by a number of factors including the partial pressures of the different gas components and the resistances to flow offered by the porous membrane and venting pipe, which in turn depend on their respective geometries and sizes. Using the laws of conservation of particles and the fluid mechanical principles of diffusive and advective flows, a mathematical model for the flow of oxygen through the pump was derived. By analyzing the mathematical model for the simplified humidity induced convection pump it was found that the flow through the venting pipe does depend on the different geometric parameters of the system. Moreover, it was found that the flow through the venting pipe reached a maximum at a specific value for the membrane pore radius, which in turn was found to only depend on the other geometric parameters of the system. Hence if the pump is to be used as a source of renewable energy it would be advantageous for the geometric parameters to satisfy this specific relationship. ENERGY FROM WIND, SUN AND WATER POSTER IDEA BACHELOR LEVEL COURSE / PROJECT
Grøn Dyst 2016
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