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Modeling of heat transport in an aquifer during accumulation and extraction of thermal energy

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Category: Mining

Last Updated on 19 February 2013

Published on 16 November 2012

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Authors:

D.V. Rudakov, Dr. Sci. (Tech.), Senior Research Fellow, State Higher Educational Institution “National Mining University”, Professor of the Department of Hydrogeology and Engineering Geology, Dnipropetrovsk, Ukraine

I.A. Sadovenko, Dr. Sci. (Tech.), Professor, State Higher Educational Institution “National Mining University”, Head of the Department of Hydrogeology and Engineering Geology, Dnipropetrovsk, Ukraine

A.V. Inkin, Cand. Sci. (Tech.), Associate Professor, State Higher Educational Institution “National Mining University”, Senior Lecturer of the Department of Hydrogeology and Engineering Geology, Dnipropetrovsk, Ukraine

Z.N. Yakubovskaya, Cand. Sci. (Tech.), State Higher Educational Institution “Ukrainian State University of Chemical Engineering”, Senior Lecturer of the Physics Department, Dnipropetrovsk, Ukraine

Abstract:

Seasonal variations of consumption and limited sources of supplying natural fuels in Ukraine result in the necessity of searching for unconventional methods to extract and store thermal energy. Under the formed mining, geological, and climate conditions of the country the power loads can be smoothed through creating the systems of underground accumulation of coolants. These systems will provide heating, hot water supply and climate conditioning of engineering buildings owing to keeping summer heat and winter cold in aquifers. The efficiency of this geotechnology has to be justified by numerical modeling ground water flow and heat transport in a layer used as a coolant collector.

Calculating implementation of the mathematical model was made in the program ModFlow 2009 (Schlumberger W.S.). A model was validated based on an analytical solution of the radial heat transport problem. Maximal deviation between the temperature profiles obtained by two methods does not exceed 2 °C, which is less than 10% of the temperature difference, and characteristic only for the zone of warm and cold water contact in a stripe of 15–20 m width. The deviation between numerical and analytical solutions does not increase in time. The estimate model accuracy can be considered acceptable to the decision of practical tasks.

As a result of numerical analysis of heat balance it was established that more than 98% of heat stored through a well remain in the aquifer by the time to stop pumping; this corresponds to the actual range of heat conductance in the confining layers. It was shown that total heat loss through the aquifer roof and bed during the pumping period varies insignificantly for the given data range. The differences in heat loss are more significant during a next period, after a pause and subsequent pumping. Thus, as a result of pumping and extracting the equivalent water volume with the same discharge during the same period it is achievable to extract from 62 to 74% of initial thermal energy through a well; this depends on heat conductance of the confining layers.

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