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Pumping capacity

About the pump efficiency

For the calculations of the flow for the WEBAP I pilot measured and modeled wave data was used. For some periods overlapping data was available that could be used for calibration of the calculated data. For the entire measurement period the mean of the flow was then determined. In a few cases, a more detailed analysis has been made which also takes into account the module vertical acceleration. These calculations yielded a slightly greater flow. The method and more results of the analysis and a comparison are provided in the final report. The figure below summarizes the results of the analyses. From the diagram, it becomes clear that both - as expected - there is a minimum level of wave height that provides a flow and partly because there is a fairly clear correlation between flow and wave height. There also appears to be a maximum mean flow.

Figure. Calculated average flows in the WEBAP I pilot as a function of significant wave height Hs.

Observations at the rough sea suggest that the demonstration unit WEBAP I worked as intended but that it “rides” the waves, which is significantly reducing its efficiency. This is caused by the limitation if pilot unit dimensions that are compared to the wave lengths much smaller. For the calculations of the electrical pump WEBAP II direct flow measurements from the pilot and the assumption that the flow is evenly distributed over the tube diameter due to the technical design of the pump was used. Calculated flows were also compared with theoretical calculations from the manufacturer. WEBAP II most operated at 80% of its capacity for most of the time. This corresponded to a power consumption of the aggregate of 10-11 kWh. The measured flow rates ranged from 0.2 to 0.4 m/s, which gives an estimated rate of 1-2 m3/s, these measurements were made at a temperature in surface waters of 17 degrees. At lower altitudes (intake positioned deeper) and thus lower temperature differences between surface and deep water, the pump efficiency increased. Calculations of the expected capacity of a full-scale WEBAP plant were not possible but it can med assumed that an installation with dimensions that correspond at least to typical wave characteristics would avoid the problem of “wave riding” and thus increase the pumping capacity per meter wave crest.

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