Stanley Reitsma

Experimental investigations of colloidal silica grouting in porous media.

This paper presents the results of an experimental investigation performed to understand the processes influencing the injection of colloidal silica grout into porous media. Based on the combined analysis of grout injection pressures and the visually observed grout distribution patterns, three major processes, gelation, shear, and viscous fingering, have been identified to occur during grout injection. The results demonstrate the dynamic interplay between grout viscosity variations and the resulting flow instabilities.

On Fluid Flow and Heat Transfer in a Pipe With a U-Bend

Vertical ground source heat pumps operate by pumping a heat transfer fluid through a pipe buried in the ground. There is a U-Bend at its deepest point to return the fluid to the surface. Incidentally, the U-Bend does more than packing the extensive length of the heat transferring conduit within a single compact borehole. Large flow structures called Dean’s vortices are generated in the bend and these, along with the resulting turbulence produced, are known to significantly enhance the heat transfer processes, and hence, shorten the required length. This study examines the specific roles of Reynolds and Dean numbers on the flow structure and the resulting heat transfer in a pipe with a U-Bend. Water flowing in a pipe without and with heated wall was simulated using FLUENT. The model was verified based on available data in the literature. The efficacy of the local heat transfer rate along the pipe was cast with respect to the subtle changes in the flow characteristics under varying Reynolds number and Dean number.Copyright

Simulation of Colloidal Silica Grout Injection Using Shear Effects

The colloidal silica grout systems are being investigated for environmental containment barriers and ground improvement. Colloidal silica (CS) grout system behaves as a fluid but reacts after a predetermined time to form a solid, semi-solid or gel. These solid or semi-solid gels offer several orders of magnitude reduction in hydraulic conductivity in the porous media. A numerical model is developed to simulate chemical grouting into porous media by combining a groundwater flow simulation model (MODFLOW) and a 3D multi-species reactive transport model (RT3D). The methods to estimate the grout gel viscosity as a function of gel cure time (gel age), shear rate, and grout concentration are incorporated. The non-uniform gel viscosity is indirectly incorporated into MODFLOW by changing the effective hydraulic conductivity in each cell. The present model is used to analyse the experimental observations on colloidal silica grout injection into a sand column. The model was able to reproduce the observed injection pressures to a large extent. It has been shown that the shear effect needs to be incorporated in the grout gelation model. The model will help in better understanding the physics of grouting, the processes taking place and identifying the parameters.

Ground source heat pumps: should we use single U-bend or coaxial ground exchanger loops?

Ground source heat pumps are becoming more common as traditional energy costs rise. Innovative pipe loop configurations promise increased performance and efficiency. The coaxial ground loop is among these new systems. The working fluid flows through a pipe to the depth of the system and returns to the surface through a larger annulus surrounding the delivery pipe. This study compares the coaxial and the single U-bend. By use of numerical CFD modelling, it was found that the coaxial performs both better than the U-bend but also exhibits a smaller pressure loss over equal lengths. It was found that the residence time of the fluid in the loop affects the heat transfer greatly, but the U-bend was affected more than the coaxial. Thus, coaxial ground loops are essential for efficient design and performance.

Simulation of Natural River Flow by a Three-Dimensional Hydrodynamic Model

A fully calibrated three-dimensional hydrodynamic model, namely Curvilinear Hydrodynamics in 3-Dimensions (CH3D), has been developed to determine changes of flow velocity in a natural river. The objective of this paper is to present the application of the CH3D modeling. A grid scheme was constructed by using SMS software along an example river-the Detroit River from Lake St. Clair to Lake Erie with two natural curved banks as the transversal boundaries. The water depth (vertical ?-) was divided into several layers from water surface to the river bottom. A modification to the program was made by the authors to enable flexible Manning’s roughness by applying the Strickler’s formula. The National Oceanic and Atmospheric Administration (NOAA, USA) bathymetry data were post-processed for water level corrections by using MapInfo software. The data were also extended to areas where there were no NOAA measurements in the Detroit River basin. Modeling results show that computed velocities and velocity measurements at various river cross-sections are in a good agreement typically below 10% error. Comparison between the computational water surface elevations versus that of records in gauge stations along the Detroit River is also in a good agreement.

Effect of heterogeneity scale on chemical grouting in porous media

Performance of chemical grouting as a containment technology is investigated through a numerical modeling study. A new grouting model that couples MODFLOW [1] and RT3D [2] combined new modules for the gelling process is presented. The present study is aimed at understanding the role of heterogeneity on grout curtain performance. The paper addresses two important issues related to heterogeneity and grid resolution: (1) relative influence of small-scale heterogeneity and large-scale heterogeneity, and (2) effect of numerical grid resolution on predicted curtain performance. Monte-Carlo simulations with statistically equivalent heterogeneous hydraulic conductivity ( K ) fields are conducted to assess the uncertainty of the grout performance. Grid resolution adequacy is determined by generation of heterogeneous K -fields at a coarse resolution and completing simulations using grid resolution equal to the K -field resolution and then refining that grid up to five times. Comparison of results at different grid resolution provides estimates of increased error associated with grid coarsening. Using the optimal grid resolution, effect of large-scale and small-scale heterogeneity is explored using simulations that incorporate primary and secondary heterogeneity each with different correlation lengths and variability and comparing to simulations having only large-scale heterogeneity. Grout curtain performance is assessed by simulation of grout injection, determinatin of post-grouted conductivity field, and assessment of overall grout curtain hydraulic conductivity using a flow model.