Robust Newton solver based on variable switch for a finite volume discretization of Richards equation

International audienceWe propose an efficient nonlinear solver for the resolution of the Richards equation. It is based on variable switching and is easily implemented thanks to a fictitious variable allowing to describe both the saturation and the pressure. Numerical experiments show that our method enables to use Newton's method with large time steps, reasonable number of iterations and in regions where the pressure-saturation relationship is given by a graph

Energy performance of diaphragm walls used as heat exchangers

The possibility of equipping diaphragm walls as ground heat exchangers to meet the full or partial heating and cooling demands of overlying or adjacent buildings has been explored in recent years. In this paper, the factors affecting the energy performance of diaphragm walls equipped as heat exchangers are investigated through finite element modelling. The numerical approach employed is first validated using available experimental data and then applied to perform parametric analyses. Parameters considered in the analysis include panel width, the ratio between the wall and excavation depths, heat transfer pipe spacing, concrete cover, heat-carrier fluid velocity, concrete thermal properties and the temperature difference between the air within the excavation and the soil behind the wall. The results indicate that increasing the number of pipes by reducing their spacing is the primary route to increasing energy efficiency in the short term. However, the thermal properties of the wall concrete and the temperature excess within the excavation space are also important, with the latter becoming the most significant in the medium to long term. This confirms the benefits of exploiting the retaining walls installed for railway tunnels and metro stations where additional sources of heat are available

Modelando os efeitos da variabilidade da viscosidade dinâmica relacionada à temperatura na zona afetada por efeitos térmicos em sistemas de bombeamento de água subterrânea por calor

Thermal perturbation in the subsurface produced in an open-loop groundwater heat pump (GWHP) plant is a complex transport phenomenon affected by several factors, including the exploited aquifer’s hydrogeological and thermal characteristics, well construction features, and the temporal dynamics of the plant’s groundwater abstraction and reinjection system. Hydraulic conductivity has a major influence on heat transport because plume propagation, which occurs primarily through advection, tends to degrade following conductive heat transport and convection within moving water. Hydraulic conductivity is, in turn, influenced by water reinjection because the dynamic viscosity of groundwater varies with temperature. This paper reports on a computational analysis conducted using FEFLOW software to quantify how the thermal-affected zone (TAZ) is influenced by the variation in dynamic viscosity due to reinjected groundwater in a well-doublet scheme. The modeling results demonstrate nonnegligible groundwater dynamic-viscosity variation that affects thermal plume propagation in the aquifer. This influence on TAZ calculation was enhanced for aquifers with high intrinsic permeability and/or substantial temperature differences between abstracted and post-heat-pump-reinjected groundwater