Search Results (94)

This present investigative work proceeds with the statistical study of the heat transfer coefficient (CTC) in the different flow transitions that are formed in a horizontal pipe with variation in the angles of inclination in a collector/evaporator component of a heat pump of solar assisted direct expansion (DX-SAHP) by using R600a refrigerant as working fluid in Quito - Ecuador. The dimensions of the collector/evaporator are 3.8 and 1000 mm inside diameter and length, respectively. To determine the results obtained, five practical tests are carried out with inclination angles of 10, 20, 30, 40 and 45°, with speeds or mass flows that vary between 203.24 and 222.28 kg·m⁻²·s⁻¹, the heat fluxes reached values between 200.58 and 507.23 W·m⁻². The correlations proposed by Kattan, Kundu, and Mohseni, and the experimental data were considered for the analysis of the effects of heat transfer on flow patterns. The results obtained from the investigation show that the maximum CTC is 6163.83 W·m⁻²·K⁻¹ with an inclination angle of 45°. Statistical analysis was performed considering the direction of Pearson presented results that for the angle of inclination of 10° a greater inverse direction of −0.316 is obtained. Full article

Integrating photovoltaic (PV) systems with green roofs presents a synergistic approach to urban sustainability. Many existing flat-roof PV installations, often east–west oriented with limited elevation, present integration challenges for green roofs and are therefore understudied. This study addresses this by investigating the microclimatic effects of retrofitting an extensive green roof beneath such an existing PV array. Over a two-year period, continuous measurements of sub-panel air temperature, relative humidity, and module surface temperature were conducted. Results show that the green roof reduced average midday sub-panel air temperatures by 1.7–2.2 °C, with peak reductions up to 8 °C during summer, while nighttime temperatures were higher above the green roof. Relative humidity increased by up to 8.1 percentage points and module surface temperatures beneath the green roof were lowered by 0.4–1.5 °C, though with greater variability. Computational fluid dynamics simulations confirmed that evaporative cooling was spatially confined beneath the panels and highlighted the influence of structural features on airflow and convective cooling. Despite limited vegetation beneath the panels, the green roof retained moisture longer than the gravel roof, resulting in particularly strong cooling effects in the days following rainfall. The study highlights the retrofitting potential for improving rooftop climates, while showing key design recommendations for enhanced system performance. Full article

The building sector accounts for nearly 40% of global primary energy consumption, with heating, ventilation, and air conditioning (HVAC) systems contributing significantly to energy use and greenhouse gas emissions. Conventional HVAC systems face challenges in addressing humidity control and efficiency, particularly in cold and dry climates. This research demonstrates the development and transient simulation of a novel solar-assisted desiccant wheel-based system for heating and humidification (SDHH) in Taxila, Pakistan. The proposed system includes a desiccant wheel, heat wheel, water-to-air heat exchanger, and a direct evaporative cooler. An array of flat plate collectors supply hot water to the heat exchanger. TRNSYS simulations investigated the performance of SDHH by evaluating heating capacity, humidification, and indoor temperature and humidity values in winter. Results show that the SDHH system maintained the required temperature in the zone and improved the zone humidity level. The desiccant wheel increased the absolute humidity of product air by 0.003 kg/kg. The average indoor temperature was 21 °C, and the average absolute humidity was around 0.008 kg/kg. These results justify using the proposed system in dry and cold climate conditions. Full article

Chip-level cooling has become a thermal bottleneck in next-generation data centers. Although previous studies have optimized evaporator wick structures, they are limited to a single condensation path and ignore the combined effects of the loop heat pipe (LHP) orientation on the capillary wick (CW) replenishment and reflux subcooling. To bridge this gap, this study successfully designed an innovative flat-plate evaporator water-cooled LHP with a parallel condensation pipeline. Experiments were conducted with a 20 °C coolant and at a 4 L/min flow rate across nine orientations. The heat transfer characteristics of LHPs with parallel and series condensation pipelines were compared. The analysis focused on the relationship between the working fluid (WF) replenishment of the CW and the WF reflux temperature in the compensating chamber (CC). The experimental results demonstrated that the parallel condensation LHP could sustainably dissipate 750 W without thermal runaway. At this power, the minimum junction temperature of 82.34 °C was measured at orientation 2 (+60°). For low power and at the nine orientations, the series LHP generally had lower temperatures. However, when the power exceeded 600 W, the parallel LHP showed lower temperatures at orientations 1 (+90°), 2 (+60°), and 3 (+30°). At orientation 9, the parallel LHP had lower temperatures when the power surpassed 200 W. Theoretical analysis indicated that the orientation changes affected the heat transfer via the WF reflux temperature, reflux resistance, and CW replenishment rate. Furthermore, the LHP system we developed in this study is capable of fully satisfying the cooling requirements of data center server chips. Full article

The kinetics of liquid transport in textiles are determined by the thermodynamic boundary conditions and the substrate’s structure. The knitting process offers a wide range of possibilities for modifying the fabric structure, making it ideal for high-performance garments and technical applications. Given the highly complex nature of textiles’ interaction with liquids, this paper investigates how fabric structure affects combined wicking and drying behaviour. This facilitates comprehension of the underlying transport processes on the yarn and fabric scale, which is important for understanding the behaviour of the material as a whole. The presented experiment combines analysis of wicking through radial liquid spread using imaging techniques and analysis of the drying process through gravimetric measurement of evaporation. Eight samples of single jersey knitted fabrics were produced using polyester yarns of different texturization and fibre diameters on flat and circular knitting machines. The fabrics demonstrate significantly different wicking behaviours depending on their structure. The fabric’s drying time and rate are directly linked to the macroscopic spread of the liquid. Large inter-yarn pores hinder liquid spread. For the lowest liquid saturations, the yarn structure plays a critical role. Using fine, dense yarns can hinder convective drying within the yarn. Textured yarns tend to exhibit higher specific drying rates. The results offer a comprehensive insight into the interplay between the fabric’s structure and its wicking and drying behaviour, which is crucial for the development of functional fabrics in the knitting process. Full article

Sadi Carnot’s seminal work laid the foundation for exploring the effects of thermodynamics across diverse domains of physics, stretching from quantum to cosmological scales. Here, we build on the principles of the original Carnot heat engine, and apply it in the context of a particular toy model black brane. This theoretical construct of an effectively two-dimensional, stable, and stationary gravitational object in four-dimensional spacetime derives from a hypothetical flat planet collapsed under the influence of gravity. By constructing a thermodynamic cycle involving three such black branes, we explore the possibility of energy extraction or mining, driven by the temperature gradients and gravitational potential differences characteristic of curved spacetime. Analytic solutions obtainable within this toy model illuminate key aspects of black hole thermodynamics in general, particularly for spacetimes that are not asymptotically flat. Central to these findings is the relation between gravitationally induced temperature ratios and entropy changes, which collectively offer a novel perspective on obtainable energy transfer processes around gravitational structures. This analysis highlights potential implications for understanding energy dynamics in gravitational systems in general, including for black hole evaporation and experimentally implemented black hole analogues. The presented findings not only emphasise the universality of the thermodynamic principles first uncovered by Carnot, but also suggest future research directions in gravitational thermodynamics. Full article

Triassic strata of the Yangtze Platform at Guanling contain a dolomitized interior, undolomitized margin, and partially dolomitized slope to basin margin. Dolomitized microbial laminate caps of peritidal cycles and massive dolomite with associated evaporite nodules and solution collapse breccias are consistent with penecontemporaneous tidal flat and evaporative dolomitization in the platform interior. The preferential dolomitization of the slope and basin margin (up to 7 km basinward of the margin), dolomitization along fractures, and selective dolomitization of the matrix in slope breccia that diminishes toward the margin are interpreted to have resulted from the incursion of basin-derived fluids during burial. Integrated analysis of fluid-inclusion microthermometry, oxygen, carbon, and strontium isotopes, trace element geochemistry, U-Pb age dates of carbonate phases, and burial history support the recrystallization of interior dolomite and slope to basin-margin dolomitization by brines at high temperatures during burial. The Yangtze Platform at Guanling provides an excellent example of widespread stratiform dolomitization resulting from the superposition of multiple mechanisms, including penecontemporaneous dolomitization by evaporative seawater brines, high-temperature dolomitization of the slope and basin margin by basinal brines, and high-temperature recrystallization of dolomite by brines during burial. This study provides an example that suggests that widespread stratiform dolomite may result from superposed Earth surface and high-temperature burial dolomitization processes and provides a valuable analog for other carbonate platforms in which the margin remains undolomitized while the interior and basin margin are dolomitized. Similar mechanisms likely contributed to the widespread dolomitization of platforms across the Nanpanjiang and Sichuan basins. Full article

Unveiling the heat transfer behavior of solar collectors in concentrating solar thermochemical energy storage is crucial for harnessing full-spectrum solar light. In this study, a glass Flat Tube-Shaped Heat Pipe (FT-SHP) was developed, and a visualization experimental platform was established to investigate its internal operation mechanisms and heat transfer characteristics. The results revealed that the liquid filling ratio (FR) significantly affects the heat transfer performance, with an optimal value identified as 25%. As the heat flow temperature in the evaporation section increased, both the Bubble Growing Frequency (BGF) and Droplet Condensation Reflux Period (DCRP) decreased, leading to a reduction in thermal resistance. Conversely, an increase in the cooling flow rate resulted in opposite trends in BGF and DCRP within the tube, while both the Reynolds (Re) number and thermal resistance decreased. As such, an empirical correlation between thermal resistance and Re number was derived, demonstrating a nonlinear relationship between thermal resistance, BGF, and DCRP. These findings provide important insights for the design of heat pipes, with the potential to enhance the efficiency and reliability of solar collectors. Full article

Self-assembly of amphiphilic molecules is an important phenomenon attracting a broad range of research. In this work, we study the self-assembly of KTOF₄ sphere–rod amphiphilic molecules in mixed water–dioxane solvents. The molecules are of a T-shaped geometry, comprised of a hydrophilic spherical Keggin-type cluster attached by a flexible bridge to the center of a hydrophobic rod-like oligodialkylfluorene (OF), which consists of four OF units. Transmission electron microscopy (TEM) uncovers self-assembled spherical structures of KTOF₄ in dilute solutions. These spheres are filled with smectic-like layers of KTOF₄ separated by layers of the solution. There are two types of layer packings: (i) concentric spheres and (ii) flat layers. The concentric spheres form when the dioxane volume fraction in the solution is 35–50 vol%. The flat layers are formed when the dioxane volume fraction is either below (20 and 30 vol%.) or above (55 and 60 vol%.) the indicated range. The layered structures show no in-plane orientational order and thus resemble thermotropic smectic A liquid crystals and their lyotropic analogs. The layered packings reveal edge and screw dislocations. Evaporation of the solvent produces a bulk birefringent liquid crystal phase with textures resembling the ones of uniaxial nematic liquid crystals. These findings demonstrate that sphere–rod molecules produce a variety of self-assembled structures that are controlled by the solvent properties. Full article

The ridge–furrow plastic mulching technique has been widely applied due to its benefits of increasing temperature, conserving moisture, reducing evaporation, and boosting yields. Hydrus-2D is a computer model designed to simulate the two-dimensional movement of water in soil characterized by a low cost and high flexibility compared to field experiments. This study, based on field experiment data from Jianping County, Liaoning Province, China, during 2017–2018, developed Hydrus-2D models for two distinct field management practices: non-mulched flat cultivation (NM-FC) and mulched ridge tillage (M-RT). Furthermore, it simulated the dynamic changes in farmland water variations during the summer maize growth period (2021–2100) under climate change scenarios, specifically medium and high emission pathways (SSP2-4.5 and SSP5-8.5), based on the FGOALS-g3 model, which exhibits the highest similarity to the climate pattern of Jianping County in the Coupled Model Intercomparison Project Phase 6 (CMIP6) global climate models and the Shared Socioeconomic Pathways (SSPs). The results showed that in the future FGOALS-g3 model, net radiation exhibited a significant upward trend under the SSP2-4.5 scenario (Z = 2.38), while the average air temperature showed a highly significant increase under both SSP2-4.5 and SSP5-8.5 scenarios, with Z-values of 6.48 and 8.90, respectively. The Hydrus-2D model demonstrated high simulation accuracy in both NM-FC and M-RT treatments (R² ranging from 0.86 to 0.96, with RMSE not exceeding 0.011), accurately simulating the dynamic changes in soil water content (SWC) under future climate change. Compared to NM-FC, M-RT reduced evaporation, increased transpiration, and effectively decreased the leakage caused by increased future precipitation, resulting in a 0.04 and 0.01 cm³/cm³ increase in surface and deep soil SWC, respectively, during the summer maize growing season, significantly improving water use efficiency. Moreover, M-RT treatment reduced the impact coefficients of climate change on various water balance parameters, stabilizing changes in these parameters and SWC under future climate conditions. This study demonstrates the significant advantages of M-RT in coping with climate change, providing key scientific evidence for future agricultural water resource management. These findings offer valuable insights for policymakers and farmers, particularly in developing adaptive land management and irrigation strategies, helping to improve water use efficiency and promote sustainable agricultural practices. Full article

The Lower Cambrian Changping Formation in the Western Hills of Beijing hosts tidal flat and lagoonal carbonates comprising dolomites, limestones, and dolomitic limestones, reflecting the processes of dolomite cementation and dolomitization within a sedimentary framework. Based on petrographic textures, two types of dolomites were identified: microcrystalline dolomite and fine-mesocrystalline dolomite. Integrating petrological and geochemical data unveils two diagenetic stages. The initial dolomite formation, attributed to hypersaline fluids, occurred in a supratidal-sabkha setting during the early Cambrian. The dolomitization at the top of the Changping Formation, driven by evaporatively concentrated brines from the overlying Mantou Formation, altered peritidal carbonates. This study evaluates the original sedimentary environment and dolomitization within a sequence stratigraphic context, revealing a correlation between dolomitization episodes and the stratigraphic framework in the study area. Factors influencing this framework profoundly impact depositional environments and material composition, leading to micromorphological differences in dolomites. Sabkha dolomite formation, associated with evaporative pumping, predominates near the base of transgressive systems tracts. Seepage reflux dolomite, often linked with evaporative pumping dolomite, constitutes a vertical cycle in the sequence framework. The sequence from bottom to top is sabkha microcrystalline dolomite, limestone and dolomitic limestone, seepage reflux saccharoidal dolostone, and sabkha dolomite. Full article

The Laizhou Bay area in China harbors a significant amount of Quaternary brine resources, which have been gradually depleted due to intensive long-term exploitation. It is widely accepted that underground Quaternary brine in Laizhou Bay originates from seawater. However, there are disputes regarding the specific form of seawater concentration and the geological processes leading to brine formation. Revealing the genesis of shallow brine in different geological environments is of great scientific significance for resource production and environmental protection. This study analyzed the hydrodynamic conditions of underground brine and adjacent strata based on grain size data, and the possible formation mechanisms of brine layers at different depths were discussed. The mineralization of underground brine is a complex process controlled by various factors, such as specific meteorological and paleogeographic environments, topography, and hydrogeological conditions. On the southern coast of Laizhou Bay, there are three ways in which underground brine layers are formed: residual evaporation from lagoons during the initial regression stage, the hypersaline zone in estuarine lagoons during high-sea-level periods, and brine formation from seawater evaporation on intertidal flats. Turbulent sea–land interactions and the development of river deltas are also necessary conditions for brine mineralization, as they are favorable for replenishing, transporting, and storing underground brine layers. Full article

At present, research on aerial spraying operations with UAVs mainly focuses on the deposition outcomes of droplets, with insufficient depth in the exploration of the movement process of droplet deposition. The movement characteristics of droplet deposition as the most fundamental factors affecting the effectiveness of pesticide application by UAVs are of great significance for improving droplet deposition. This study takes flat spray nozzles as the research object, uses the Particle Image Velocimetry (PIV) technique to obtain movement data of water droplet deposition under the influence of rotor flow fields, and investigates the variation characteristics of droplet deposition speed under different influencing factors. The results show that the deposition speed and the distribution area of high-speed (>12 m/s) particles increase with the increase of rotor speed, spraying pressure, and nozzle size. When the rotor speed increases from 0 r/min to 1800 r/min, the average increase in maximum droplet deposition speed for nozzle models LU120-02, LU120-03 and LU120-04 is 33.26%, 19.02%, and 7.62%, respectively. The rotor flow field significantly increases the number of high-speed droplets, making the dispersed droplet velocity distribution more concentrated. When the rotor speed is 0, 1000, 1500, and 1800 r/min, the average decay rates of droplet deposition speed are 36.72%, 20.00%, 15.47%, and 13.21%, respectively, indicating that the rotor flow field helps to reduce the decrease in droplet deposition speed, enabling droplets to deposit on the target area at a higher speed, reducing drift risk and evaporation loss. This study’s results are beneficial for revealing the mechanism of droplet deposition movement in aerial spraying by plant protection UAVs, improving the understanding of droplet movement, and providing data support and guidance for precise spraying operations. Full article

Arable land loss has become a critical issue in China because of rapid urbanization, industrial expansion, and unsustainable agricultural practices. While previous studies have explored the factors contributing to this loss, they often fall short in addressing the challenges of spatial heterogeneity and large-scale dataset analysis. This research introduces an innovative approach to geographically weighted regression (GWR) for assessing arable land loss in China, effectively addressing these challenges. Focusing on Chongqing, Guizhou, and Yunnan Provinces over the past two decades, it examines spatial autocorrelation with R-squared values exceeding 0.6 and residuals. Eight factors, including environmental elements (rain, evaporation, slope, digital elevation model) and human activities (distance to city, distance to roads, population, GDP), were analyzed. By visualizing and analyzing R² spatial patterns, the results reveal a clear spatial agglomeration distribution, primarily in urban areas with industries, highly urbanized cities, and flat terrains near rivers, influenced by GDP, population, rain, and slope. The novelty of this study is that it significantly enhances GWR computational capabilities for handling extensive datasets by utilizing Compute Unified Device Architecture (CUDA) on a high-performance GPU cloud server. Simultaneously, it conducts comprehensive analyses of the GWR model’s local results through visualization and spatial autocorrelation tools, enhancing the interpretability of the GWR model. Through spatial clustering analysis of local results, this study enables targeted exploration of factors influencing arable land changes in various temporal and spatial dimensions while also evaluating the reliability of the model results. Full article

Pin-fin and flat-tube heat exchangers (PFFTHXs) offer a promising alternative to traditional louvered-fin and flat-tube heat exchangers (LFFTHXs), especially when used as evaporators. The streamlined structure of pin fins helps to effectively remove condensate and defrost water. In this study, we conducted a numerical analysis of 60 different pin-fin configurations across three pin diameters to enhance heat transfer in PFFTHXs. Our investigation focused on how pin pitch affects both airflow and heat transfer efficiency. The results show that a closer pin pitch increases both the heat transfer rate per unit area and the pressure drop for a given airflow velocity. We evaluated the overall performance of these configurations using the heat transfer rate per unit frontal area obtained at equivalent fan power levels. The analysis identified optimal configurations for each pin diameter, with the 0.2 mm diameter configuration demonstrating the highest heat transfer efficiency—this was on par with louvered fins but used fewer resources. This makes it an ideal choice for evaporative applications in PFFTHXs. Full article