Graduate Thesis Or Dissertation
 

Flow measurement and characterization in shallow geothermal systems used for downhole heat exchanger applications

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/mp48sh81s

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  • This thesis reports on an investigation of flow patterns in shallow geothermal wells in Klamath Falls, Oregon, Although wells have been extensively used in the area, the exact nature of the flows in the wells has not been characterized. Flow characterization is a principal object of this study. Horizontal crossflows of geothermal fluid may occur at upper and/or lower levels in the well where perforations in the well casing are situated. In addition, natural convection may induce vertical flows within the well casing which would be influenced by the presence or absence of a heat exchanger. Preliminary vertical flow measurements were made with a type of turbinemeter called a "spinner" which was calibrated in a vertical pipe. This type of instrument had limitations in regard to the overall objectives of the study in that (i) the spinner partially blocked flow in the well, possibly altering flow patterns and rates, and (ii) the spinner could not detect or measure horizontal flows. In order to obtain a more satisfactory flow-measuring method, a literature search on flow measurement in confined spaces was undertaken. As a result of the search, a hot-film anemometer was selected to make the detailed flow measurements. The hot-film anemometer was a two-sensor probe that was calibrated in a special calibration system. The high-temperature water in the system was pressurized so that local boiling would not occur at the heated hot-film surface. A number of difficulties occurred with the probe during calibration, possibly due to the severe environment. Measurements of vertical and horizontal flows were attempted on a single cased well with no downhole heat exchanger. A steel cage was built to provide protection for the probe when in the well. Vertical flow measurements showed agreement with past analytical work and also confirmed the effect of spinner flow blockages. Turbulence in the lower perforation region was detected with the vertical flow Measuring channel. Turbulence in the tower perforation region was again detected with the horizontal flow measuring channel. There was difficulty in separating horizontal and vertical flow components. No evidence of high horizontal velocities was found.
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