Experimental Study of Proppant Bridging in a Model of a Hydraulic Fracture

Summary In this article, we investigate formation of the local clogging (bridging) of proppant in a channel with gradually narrowing walls. The experimental facility allows us to simulate the process of the proppant transport in a hydraulic fracture by reproduction of the characteristic channel width, velocity of slurry, rheology of fracturing fluids, and typical concentrations of proppant. The goal of the study is to give qualitative description of the dynamics of the congestion of the proppant up to the complete blockage of the flow. In contrast to common practice of imposing bridging criteria by postulating certain threshold value of the width to proppant size ratio, we demonstrate that the bridging process involves several stages: clogging of two to three particles, growth of stable “islands,” connection of the islands by arches, and, finally, the total sandout of the cell by the bridged proppant. The observations of the paper gives better understanding of the bridging process giving the directions for more precise numerical simulations.

Influences of a Highly Reflective Mulching Membrane on Heat Propagation throughout the Soil

Agro-food chain impacts global greenhouse gas emissions by around 30%. To reduce this score without worsening food crops’ yield, new and more sustainable technologies (i.e., mulching membranes, advanced irrigation systems) were implemented. Within this framework, the present study aims to assess the influences on heat propagation throughout the soil of a highly reflective mulching membrane. An experimental facility was implemented in which the surface temperatures of both the soil and the membrane were monitored together with the temperature of the soil (at three depths). Five statistical days were defined by considering the same amount of percentiles of the monitored temperatures (0th, 25th, 50th, 75th, and 100th percentiles). Then, the attenuation and the phase shift of the thermal wave throughout the soil and the cooling potential of the membrane were calculated. Although negligible variations from the uncovered soil were observed in surface temperature, the membrane enables a greater attenuation of the thermal wave throughout the soil. This can be up to 16 °C cooler than the surface, with potential benefits for plant growth. Furthermore, the membrane optical properties permit to offset carbon emissions from agriculture activities by around 0.1 tCO2-eq m−2.

Assessment of Steady and Unsteady Friction Models in the Draining Processes of Hydraulic Installations

The study of draining processes without admitting air has been conducted using only steady friction formulations in the implementation of governing equations. However, this hydraulic event involves transitions from laminar to turbulent flow, and vice versa, because of the changes in water velocity. In this sense, this research improves the current mathematical model considering unsteady friction models. An experimental facility composed by a 4.36 m long methacrylate pipe was configured, and measurements of air pocket pressure oscillations were recorded. The mathematical model was performed using steady and unsteady friction models. Comparisons between measured and computed air pocket pressure patterns indicated that unsteady friction models slightly improve the results compared to steady friction models.

Experimenting with Odour Proficiency Tests Implementation Using Synthetic Bench Loops

Uncertainty in the quantification of odour measurements is a difficult (but needed) task. Critical aspects include panel selection (required by dynamic olfactometry), sampling, and stability of the samples. Proficiency tests (PTs) can help evaluate such contributions; however, the classical approach to PTs, in which laboratories analyse real samples taken from the field, are not as applicable in this field, and are often implemented by only using dry gas cylinders containing stable compounds. Consequently, uncertainties related to the sampling activity cannot be assessed. In particular, high odour levels and the presence of water vapour in emission sources can create significative biases due to sampling techniques used and chemical reactions that can occur before analysis. In this work, we present experimental notes, developed using the experimental facility ‘LOOP’, realised at the RSE research centre in Italy, in order to “help” the definition, in an upgraded protocol for implementing PTs for odour determinations. Using this bench loop is advantageous as it involves the possibility of implementing samples in conditions very similar to reality (i.e., high temperatures, high water content, and the presence of chemical interferents).