Heat transfer between the fluid in a pipeline and the ambient soil is ofimportance for accurate modelling of flow hydraulic conditions. Thiswork presents a study on the soil heat transfer from a buried natural gaspipeline. An export gas pipeline from Norway to the continent wassubject to detail investigation. The aim was to improve theunderstanding of the heat exchange with the surrounding soil. Thespatio-temporal development of soil temperatures in response to thepresence of the warmer pipe was both measured and modelled. Thethermal and hydraulic properties of the soil were determined throughexperimental methods and physical correlations/predictive modelling.The pipeline and the surrounding soil were instrumented with an arrayof temperature and soil moisture sensors providing the in-situmeasurements. A CFD model of the experimental set-up wasdeveloped, applying the achieved soil thermal properties and localgeology. In the model, measured soil surface and pipe walltemperatures were used as time dependent boundary conditions. Thetransient development of the thermal regime of the soil surrounding thepipeline was compared to the actual temperature measurement values.The model was used to assess the validity of the commonly usedassumption that conduction is the prevailing heat transfer model. Thecontribution of natural convection heat transfer from ground water wasalso assessed. The results show that, given the thermal propertiesdetermined for the soil surrounding the instrumented section of thepipeline, a numerical calculation model using only heat conduction canrepresent the soil temperatures accurately at some distance to the pipe.Close to the pipe wall the predictions are less accurate. The role groundwater plays in natural convection was demonstrated and found to be ofminor significance for the case at hand. The cause of the temperaturediscrepancy close to the pipe wall warrants further investigation.
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