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Spray cooling has been considered one of the most promising thermal control methods of high-heat flux devices. Most of the spray cooling research focuses on electronic components as the main application object to achieve higher heat dissipation heat flow in ambient temperature regions for small areas. Water is the most common cooling medium. This paper investigates the application of spray cooling thermal control over large areas. In this study, the heat-transfer characteristics of liquid nitrogen (LN2) for large areas was investigated by conducting experiments. The test surface is 500 mm × 500 mm, which was cooled by a nine-nozzle array. The spray nozzles used in the experiment were conical nozzles with an orifice diameter of 1.6 mm, a spray angle of 120°, and a spray height of 42 mm. Liquid nitrogen was forcefully ejected from nozzles by the high pressure of a liquid storage tank to cool the test surface. According to the cooled surfaces, spray directions, and spray pressures, three groups of experiments were conducted. The results showed that the smooth flat surface has the best heat-transfer performance in three kinds of surface structures, which are macro surface, porous surface, and smooth flat surface. The heat-transfer coefficient varied by ±20% with different spray directions, and the surface heat-transfer coefficient increased linearly with increasing spray pressure. Most of the spray cooling research focuses on heat dissipation in the ambient temperature region for equipment over small areas. The results can benefit thermal control application in various fields. The research in this paper can provide a reference for the application of large-area spray cooling, and the application areas mainly include metal manufacturing processing cooling, aircraft skin infrared radiation characteristics modulation, and laser weapon equipment cooling.

Grooved grinding wheels play an important role in reducing grinding thermal damage. Aluminum oxide grinding wheels of approximately 1 mm slot width and 35% groove ratio were successfully fabricated using a novel reciprocating ultrafast laser scanning mode to improve the grinding stability. Grinding experiments with grooved and non-grooved wheels were conducted on 42CrMo. The cutting mechanisms of grooved structures were analyzed with the established cutting kinematics of the abrasives in the groove edges and the grinding force components model. The decreased grinding forces were observed and analyzed with abrasive cutting mechanisms, indicating that grooved structures can increase the undeformed chip thickness of grains at the slot edges and decrease the specific grinding energy by reducing the specific plowing and sliding energy. The grooved grinding wheels exhibited high performance in inhibiting grinding heat and workpiece burns. The burned workpiece ground with non-grooved wheels experienced a phase transformation and had a high tensile residual stress state on the ground surface and subsurface, while compressive residual stresses were detected on the unburned workpiece surface ground with grooved wheels. Grooved grinding wheels can improve the grinding quality of workpieces due to the lower grinding temperature and residual stress.

The research object of this paper is the across medium (air and water) Autonomous Underwater Vehicles (AUVs) fairing. When the AUVs are flying in the air, for the purpose of protecting the detection equipment and reducing the air resistance, an ogive fairing is installed at the head of the aircraft. When the AUVs enter the water at a certain angle and speed after arriving at the destination, it is hoped that the fairing will be broken as much as possible, so that it does not affect the normal use of the detection equipment. Therefore, the influence of the dimension parameters of the fairing on the aerodynamic resistance is studied, and the influence of the groove and groove depth on the damage of the fairing after impact is also researched.

In this study, we reported experimental results of a water droplet falling on trapezoidal grooved surfaces of heated silicon wafers with the groove width varied from 20 μm to 640 μm and the depth from 20 μm to 40 μm. Based on the observation of droplet dynamics captured by high-speed camera, we found that on the denser grooved surface, the maximum spreading diameter of the droplet perpendicular to the groove direction was smaller than that on the sparser grooved surface with the same groove depth. The residence time of the droplet on the denser grooved surface was shorter than that on the sparser grooved surface. The Leidenfrost point increased 50 °C with the groove width varied from 20 μm to 640 μm and decreased 10 °C when the depth was changed from 20 μm to 40 μm, which were higher than that on the smooth surface. Due to the deformation of the droplet during the droplet dynamics, it was difficult to calculate the heat transfer by measuring the droplet volume reduction rate. Based on the convective heat transfer from the grooved surface to the droplet, a Leidenfrost point model was developed. The results calculated by the model are in agreement with the experimental data.

Hydrodynamic herringbone-grooved journal bearings (HGJBs) are analyzed by solving Navier–Stokes and energy equations. It is well known that the load capacity of hydrodynamic bearings may be affected by high temperatures and low oil viscosity. Therefore, the main objective of this study is to understand the pressure distribution of hydrodynamic HGJBs under different oil viscosity and eccentricity ratios. In this paper, 3 different configurations are studied, namely, a HGJB, a combined HGJB and thrust bearing, and a combined HGJB and grooved thrust bearing. The bearing characteristics, such as load capacity and attitude angle that vary with different eccentricity ratios, are also discussed. The results show that the load capacity of the bearing decreases with increasing temperature. The pressure difference also increases as the eccentricity ratio increases. The high-pressure region is concentrated at the tip of the groove for the HGJB. In addition, the combined HGJB and grooved thrust bearing can be used to stabilize the journal because of the low attitude angle. These findings may help and facilitate the design of hydrodynamic bearings suitable for working in warm and hot environments in the future.

Discussions of contacts between Britain and Ireland usually focus on monuments and on portable artefacts such as Grooved Ware, Beakers, and metalwork. New research on insular rock art suggests that it originated in the Middle to Late Neolithic period and continued to be used and re-used into the Early Bronze Age. This paper considers its relationship with decorated passage graves and other structures. It argues that the distribution of rock art sheds further light on connections between these islands. Estuaries, bays, and landing places were important, but the siting of pecked motifs indicates other links along three overland routes between the North Sea and the Irish Sea. Certain practices were shared between megalithic tombs and recently excavated rock carvings. It is possible that they expressed similar beliefs at a time when long distance travel was important.

Heat transfer in pool boiling is known as a complex and critical process in thermal systems. Considering the escalating need for higher efficiencies, using nanofluids as an efficient fluid in addition to modifications to surface geometry- particularly grooved surfaces- has been identified as an effective strategy for enhancing the heat transfer coefficient. This research seeks to explore the experimental effects of a hybrid graphene oxide-iron oxide/water nanofluid combined with grooved surfaces on the convective heat transfer coefficient during pool boiling. Tests were performed using a hybrid nanofluid with a 0.05% volumetric concentration on surfaces featuring diverse groove configurations. The findings demonstrated that the use of hybrid graphene oxide-iron oxide/water nanofluid alongside grooved surfaces substantially enhances the heat transfer coefficient. This enhancement stems from the synergistic influence of nanoparticles and surface geometry on the boiling process, coupled with increased turbulence in the liquid boundary layer. Among the tested configurations, the circular surface in the hybrid nanofluid exhibited the highest heat transfer coefficient improvement. Compared to a smooth surface with deionized water, the heat transfer coefficient increased by 67%. This study offers promising insights for advancing heat transfer technologies and designing advanced cooling systems. It also introduces the use of hybrid nanofluids along with engineered surfaces as a new approach to optimizing thermal processes.

The Archimedes Spiral Wind Turbine (ASWT) is a promising candidate for urban wind energy applications due to its helical blade geometry, which enables stable rotation and efficient energy captured at low wind speeds. However, its aerodynamic performance remains limited and can benefit from targeted surface enhancements. This study proposes a novel blade surface design in which semi-cylindrical grooves or bumps are geometrically integrated into the suction or pressure sides of the ASWT blades to improve aerodynamic efficiency. Twelve ASWT configurations were systematically developed using parametric modeling in SolidWorks 2020 and evaluated through computational fluid dynamics (CFD) simulations in ANSYS CFX R2. Among the tested designs, the model featuring longitudinal grooves on the pressure side with 12 groove lines (FWPG-12) demonstrated the highest aerodynamic improvement, achieving an 8.3% increase in power coefficient ( ) at a wind speed of 10 m/s. These improvements are attributed to improved flow attachment and delayed boundary layer separation. In contrast, blades featuring surface bumps showed no aerodynamic advantage and generally led to performance deterioration. The findings underscore the aerodynamic benefits of bioinspired surface modifications and highlight their potential for advancing ASWT performance in urban renewable energy systems.

Mechanical systems are expected to operate under various load conditions, and it is necessary to use a lubrication system to achieve reliability and stable performance. Journal bearings, which are used to achieve such stable lubrication, are representative of hydrodynamic lubrication bearings. In this study, groove-shaped structures and rubber were applied to the ends of the bearings to ensure stable lubrication performance under conditions where, for various reasons, shock loads are applied in addition to static loads under misaligned conditions. The groove structure and rubber contribute to stable lubrication performance by preventing contact between the shaft and bearing as well as absorbing shock loads through elastic deformation of the groove’s end due to oil film pressure. This novel design, which utilizes groove-type flexible structures and rubber, led to journal bearings that exhibited improved lubrication performance under various shock load conditions. When a shock load is applied to a mechanical system, the design proposed in this study contributes to improving the reliability of the mechanical system by enhancing its lubrication performance.

To analyze the metering process and regulation, and to optimize the metering parameters of the spiral outer grooved wheel seed metering device, this research simulated the seed metering using EDEM software. Following the Box-Behnken testing design principle, a regression model was established to relate all factors to the performance index. The independent variables included groove rotation speed, lead angle, and groove number, while the coefficient of variation served as the response variable. The motion processes of seed-filling, seed-cleaning, and seed-protection were examined through EDEM simulations. The results indicated that groove rotation speed and lead angle significantly influenced metering performance, particularly when the lead angle ranged from 0° to 10° and the groove number was between 10 and 14. The factors affecting comprehensive performance, ranked from most to least significant, were groove rotation speed, lead angle, and groove number. However, when the lead angle was adjusted to 5° to 15° and the groove number to 12 to 16, both groove rotation speed and groove number emerged as highly significant factors affecting metering performance, with the order of influence being groove number, groove rotation speed, and lead angle. By solving the regression model for a low coefficient of variation, the optimal working parameters were determined to be a groove rotation speed of 43.15 r/min, a lead angle of 9.81°, and a groove number of 16. Verification tests revealed a coefficient of variation of 7.20%, and when compared to the simulation results, the relative error was 4.97%. This demonstrates the reliability of optimizing the parameters of the spiral outer grooved wheel seed metering device through theoretical analysis and the discrete element method.