Processes

This paper presents a comparative analysis of direct expansion solar-assisted heat pumps (DX-SAHP) with and without photovoltaic cells (PVT-DX-SAHP). Two sets of experiments were conducted to validate the mathematical model: one with PVT-DX-SAHP and another with DX-SAHP. The mathematical model used in this study is based on physical equations using energy, mass, and entropy balance. The heat exchangers were modeled using the moving boundaries technique. The compressor and photovoltaic cells were modeled using a black box model with equations for the efficiencies of these components. The low-global-warming-potential (GWP) refrigerant R290 (propane) was used in this study. Two independent sets of experimental data were used to validate the model, with a mean absolute deviation of 4.8%. The results indicated that PVT-DX-SAHP had a higher season performance factor (SPF) and a lower total equivalent warming impact (TEWI) compared to DX-SAHP, with an average SPF increase of 81% and a TEWI reduction of 30%. The findings also showed that PVT-DX-SAHP had a 24% higher longer payback period than DX-SAHP.

The tight sandstone reservoirs of the Tarim Basin in China are characterized by vertically stacked multi-sweet spots. However, the strong vertical heterogeneity and discontinuity limit the effectiveness of hydraulic fracturing for multilayered co-production. To investigate the mechanisms governing the vertical cross-layer propagation of hydraulic fractures in the multilayered sandstone reservoir, outcrop rocks of fine sandstone and siltstone from the area were collected. Subsequently, these rocks were cemented to fabricate multilayered experimental samples with lithological transition zones. Hydraulic fracturing experiments were performed to systematically study fracture propagation behavior, with particular focus on the influence of interlayered lithology, vertical stress differences, fracturing fluid injection rate, and fluid viscosity on vertical fracture growth. Experimental results demonstrate that hydraulic fracturing in multilayered sandstone can form both passivated and cross-layer fracture networks while also activating lateral propagation along lithological transition zones. When hydraulic fractures extend from high-brittleness layers to low-brittleness layers, their vertical propagation is limited, promoting shear activation along lithological transition interfaces. As the vertical stress difference increases, the vertical propagation range of hydraulic fractures expands progressively, with fracture morphology evolving from a passivated type to a single-wing cross-layer pattern and further developing into a bi-wing cross-layer geometry. Increasing the injection rate and viscosity of the fracturing fluid enhances cross-layer fracture propagation while suppressing the activation of lithological transition zones. The insights derived from this study can provide a theoretical foundation and engineering guidance for the design and implementation of hydraulic fracturing in multilayered tight sandstone reservoirs in the Tarim Basin.

Thermal conductivity is a crucial parameter for heat transfer in asphalt pavements, especially in cold regions where electrically heated snow-melting systems are used. Steel slag, an industrial by-product with high thermal conductivity, holds significant potential to enhance the thermal performance of asphalt mixtures. However, its thermal behavior is influenced by various factors. This study established a thermal conductivity database consisting of 200 samples from published experimental studies, incorporating data collection, graphical digitization, and physically constrained expansion. Mixture composition, volumetric structure, and steel slag properties were used as input variables, with thermal conductivity as the output. Five machine learning models including k-nearest neighbors regression, decision tree, random forest, support vector regression, and gradient boosting were developed. Among them, random forest and gradient boosting showed the highest accuracy and robustness. Feature importance analysis revealed that steel slag content is the primary factor affecting thermal conductivity, while material properties and gradation parameters play secondary roles. This data-driven framework facilitates the efficient prediction and design of thermal conductivity in steel slag asphalt mixtures, supporting the engineering application of functional asphalt pavements.