UĞUR AKYOL, TUĞRUL AKYOL, A. DENİZ KARAOĞLAN, BEDRİ YÜKSEL, ASİYE ASLAN

Flow Rate Estimation Modelling in a Transmission Pipeline Using Response Surface Methodology (RSM)

The source of geothermal energy to be used for district heating systems is, in most cases, located some distance from the heating market, although geothermal water may also be found within the market area. A transmission pipeline is therefore needed to transport the geothermal fluid from the geothermal field to the end users. Geothermal fluids can be transported over fairly long distances in thermally insulated pipelines. Transmission pipelines of even 60 km length have been built with acceptable heat loss values, though shorter transmission distances are much more common and clearly more desirable. At flowing conditions, the temperature drop in insulated pipelines is in the range of 0.1 to 1.0°C/km, while in uninsulated lines it is 2 to 5°C/km (in the range of 5 to 15 l/s flow for 15-cm diameter pipe). In addition to a group of parameters, which are almost constant, such as the length, diameter, thickness, thermal insulation properties and material type of the pipeline, whether above ground or buried and so on, temperature drop rate in transmission pipelines is strongly affected by flow rates. At low flow rates, the temperature drop is higher than that of greater flow rates. The temperature drop depending on the flow rate becomes more apparent for relatively long pipelines. In this study, the temperature drops in the transmission pipeline of the Bigadiç geothermal district heating system (GDHS), a buried 18 km long pipeline, is investigated for varying flow rates. Response Surface Methodology (RSM) is then used for modelling and estimating the flow rate depending on the temperature drop in the pipeline. The results show that the flow rates given by the model (with R2, coefficient of determination, of 96.67%) are in a good agreement with those measured by the flowmeter.

Keywords:

District heating system; Flow rate; Response Surface Methodology (RSM); Transmission pipeline,

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