Constraining the heat transfer coefficient of rock fractures. (November 2021)

• Record Type: Journal Article
• Authors: Heinze, Thomas
• Is Part Of: Renewable energy. Volume 177(2021)
• Page Start: 433
• Page End: 447
• Publication Date: 2021-11
• Subjects: Heat transfer -- Local thermal non-equilibrium -- Geothermal energy -- Fracture; Renewable energy sources -- Periodicals; Power resources -- Periodicals; Énergies renouvelables -- Périodiques; Ressources énergétiques -- Périodiques; 333.794
• DOI: 10.1016/j.renene.2021.05.089
• Languages: English
• ISSNs: 0960-1481

Abstract

Abstract: Estimating the heat transfer in deep underground geothermal systems is a challenging task. The concept of explicitly describing the heat transfer between phases has been shown superior to the conventional approach but the heat transfer coefficient of fractures is still ambiguous. In this work, a definition of the lower and upper bound of the heat transfer coefficient between rock and flowing fluid in a single rock fracture is derived and validated with almost 250 experiments from other studies. The resulting values range between 8 and 260 W/m 2 °C, with upper bounds roughly a factor 10 larger. Further, as shown in this work, the assumption of local thermal equilibrium can result in lower production temperatures than the assumption of heat transfer between phases depending on reservoir conditions. A dimensionless number is derived to distinct those cases and to determine the lower limit of the outflow temperature in any scenario. The results of this work enable a quantification of the value range of the heat transfer coefficient from laboratory experiments and allow a tabulation of the heat transfer coefficient for all kind of scenarios. The presented results can be used in discrete fracture models for an improved prognosis of production temperatures. Highlights: Lower and upper bound of heat transfer coefficient for rock fractures derived. Model is validated using 246 experiments from three different experimental studies. Resulting value range is 8–260 W/(m 2 °C) for the heat transfer coefficient. Dimensionless number introduced to determine lower bound model.