Can Borehole Heat Exchangers Trigger Cross-Contamination between Aquifers?

Borehole heat exchangers (BHEs) commonly reach depths of several tens of meters and cross different aquifers. Concerns have been raised about the possibility of boreholes to act as preferential pathways for contaminant transport among aquifers (cross-contamination). This article employs numerical modelling of contaminant transport in the subsurface to address these concerns. A common hydrogeological setup is simulated, composed of three layers: A shallow contaminated and a deep uncontaminated aquifer separated by an aquitard, all crossed by a permeable borehole. The hydraulic conductivity of the borehole and, to a lesser extent, the vertical hydraulic gradient between the aquifers are the key factors of cross-contamination. Results of the numerical simulations highlight that, despite the severe conditions hypothesized in our modelling study, the cross-contamination due to the borehole is negligible when filled with a slightly permeable material such as a geothermal grout properly mixed and injected. A good agreement was found with analytical formulas used for estimating the flow rate leaking through the borehole and for studying the propagation of leaked contaminant into the deep aquifer.

Hybrid contact lenses for the correction of primary and induced ametropias

The review presents the data on the use of hybrid contact lenses (HCL), a modern method of contact correction of ametropias of diverse origins. A HCL has a central rigid optical zone made of highly gas-permeable material and a flexible peripheral part made of hydrophilic material. These lenses combine the optical effect of gas-permeable corneal lens with the comfort and stable fitting of soft contact lenses. Compared with the corneal (RGP) lenses, HCLs are more comfortable, often are better centrated and more stably fit on the eye. HCLs are successfully used in various refractive disorders: ametropias (with regular cornea), irregular astigmatism, presbyopia, including that combined with astigmatism. This type of lens is a good option of contact correction for patients who have high requirements to the quality of vision.

Experience in application of hybrid contact lenses for astigmatism correction

The review covers the issue of hybrid contact lenses application as one of the modern contact correction methods in patients with ametropias of various genesis. Hybrid contact lenses consist of a rigid central optical part made of highly gas-permeable material and a flexible peripheral part made of hydrophilic material. These lenses combine the optical correction qualities of gas-permeable corneal lenses with the comfort and stable fit usually provided by soft contact lenses. Compared to gas-permeable corneal lenses, hybrid lenses are more comfortable; often have better centration and more stable fit on the eye. Hybrid contact lenses successfully correct both types of astigmatism: regular and irregular. This type of lenses is a good alternative method of contact correction for patients who place heavy demands in terms of the quality of vision.

Permeable ceramics filled with the threefraction electrofused corundum and the porcelain bond

By means of the raw material grading the porous permeable material was prepared with the electrofused corundum with the porcelain PFL-1 bond. The samples with improved properties were obtained when introducing in the mass of 5 weigh percent of porcelain bond (above 100 % of the fller) after the burning at 1450 оC. Their ultimate strength at bending was 14,6 MPa, the open porosity was 44 % and the gas permeability factor was 0,85 micron2. Ref. 10. Tab. 3.

The Assembly Loads and Some Strengthening Methods of the Products from Porous Material with Coiled Wire

The product from porous permeable material based on a wire coil consists of a round, porous, thin-walled tube. The impact of assembly loads of the porous tube has been examined to determine the maximum values of the compressive force and axial elastic strain during the assembly. To improve mechanical properties of the product additional reinforcement has been proposed: larger diameter wire, woven wire cloth or spring.