Heat transfer in pores and fractures – lessons learned from mechanical engineering

The absence of an instantaneous local thermal equilibrium between rock and fluid has been observed multiple times in geoscientific, and especially geothermal, applications. The alternative, describing heat transfer between phases explicitly following Newton’s law of cooling, has been found essential to describe various processes, such as thermal stresses around wellbores or thermal breakthrough curves. While heat transfer founds growing interest in the geoscientific community, parameterization of the heat transfer coefficient and experimental data is still ambiguous. On the other hand, heat transfer has been studied extensively for decades in mechanical engineering for applications such as heat exchangers, chemical catalytic reactors, and thermal insulation.

In this work, the lessons learned about heat transfer from mechanical engineering are presented and tested for validity and transferability to geoscientific applications. This includes the differentiation of several heat transfer mechanisms, various scale-dependent types of thermal non-equilibrium, and useful equations for the heat transfer coefficient. As will be pointed out, there are several key findings from mechanical engineering applications, that can be applied to geosciences almost directly. There are a few results that would require further verification, and there are substantial conceptual differences in the heat transfer between mechanical engineering and geosciences. This work will provide present key takeaways from mechanical engineering on heat transfer with a direct influence on geothermal projects and will point out future directions of required research in geosciences.