•Proposed a thermal contact resistance prediction model.•Radiation effect whether to be considered is analyzed.•The prediction model is experimentally validated.
The precise prediction or test of ...thermal contact resistance is a key issue on increasing or decreasing thermal energy transmission efficiency between two solids. This paper raises a thermal contact resistance prediction model based on measuring actual surface topography under different loading pressures and different heating temperatures. The actual topography of contact surfaces is measured by a 3-D optical microscope named Bruker Contour GT-K. The contact surfaces are reconstructed with language Python according to the data of surface topography from the microscope and the numerical contact model is generated. Then the thermal contact resistance simulation is implemented with software ABAQUS. Based on the elastic-plastic constitutive equations and steady state heat conduction theory, finite element analysis of mechanical and heat transfer performance of the contact model is performed with ABAQUS in the light of sequential coupling method. The studied material pairs are Ti-6Al-4V—Ti-6Al-4V with three kinds of different interstitial material e.g., vacuum, air and conductive silicone grease. The effect of radiation on thermal contact resistance under air and vacuum atmosphere is further studied and analyzed. Besides, the solid thermal conductivity on thermal contact resistance is investigated. To verify the accuracy of the method, the simulated results from ABAQUS are compared with the experimental results of air gap with the same boundary conditions. The maximum deviation between simulation results and experimental results is 9.57% while 75% of the deviations are within 5%. A correlation of thermal contact conductance with the average contact surface temperature and loading pressure is proposed. The results show that this method has high precision to predict thermal contact resistance in the engineering application.
To obtain higher thermal efficiency, advanced gas turbines operate at a turbine inlet temperature (TIT) up to 2000K, which causes an extremely high thermal load on the first stage vane endwall. ...Therefore, it is critical to understand the complex thermal environment near the endwall and develop efficient cooling schemes. In this study, adiabatic cooling effectiveness measurements on an annular cascade endwall with purge flow were conducted using a high-resolution infrared thermography technique. Effects of profiles and locations of an upstream slot on endwall film cooling behaviors were investigated at three coolant-to-mainstream mass flow ratios and an engine-like density ratio. Using numerical simulation, the flow details were illustrated to support the measured cooling effectiveness. Results indicate that moving the slot to a further upstream location will reduce film cooling effectiveness on the endwall. However, a further upstream slot can improve the uniformity of the film cooling effectiveness distribution. Compared with the normal slot, the convergent slot accelerates the coolant ejection to a higher momentum and thus inhibits the influence of secondary flows on endwall film cooling. Therefore, the convergent slot significantly improves both the coolant coverage and local film cooling effectiveness for all mass flow ratios and slot locations investigated. Quantitatively, an enhancement of approximately 25% in laterally averaged cooling effectiveness can be achieved by the convergent slot.
•Measurements of adiabatic cooling effectiveness on an annular cascade endwall were conducted.•Effects of profiles and locations of the slot on endwall film cooling effectiveness were investigated.•The relationship between endwall secondary flows and film cooling behaviors was discussed.•The numerical results were used to reveal the flow details and film cooling mechanism.
Cool materials, with their high reflectivity, can significantly reduce the heat absorbed by buildings in summer and thus reduce energy consumption. The amount of solar radiation received by building ...surfaces varies with their orientation, so the effectiveness of cool materials on different building surfaces may vary. This study investigated the effects of using cool materials on scaled-down building models and full-scale real buildings through a combination of experiments and simulations, considering factors including building surfaces of different orientations, material properties, and weather conditions. Both experimental measurements and simulation studies showed that applying cool materials on roofs has the best cooling effect, reducing indoor temperatures by 0.93 °C in full-scale models. The south and west façades also showed good cooling effects when using cool materials. The north façade has the least cooling effect when using cool materials. Compared to exposed cement boards and regular materials, cool materials showed significantly better cooling effects, similar to those of 2 cm thick XPS insulation boards. Overall, buildings with poorer thermal insulation performance benefit more from the cooling effect of cool materials in summer. Additionally, the cooling effect of cool materials is ineffective on cloudy and rainy days. We found that the cooling effect of cool materials was significantly reduced when the solar radiation was less than 400 W/m2. The findings of this study provide guidance for the use of cool materials in energy retrofitting of existing buildings and the construction of low-carbon cities.
•The combined experimental and simulation approach was employed.•The thermal insulation properties of four building surface materials were compared.•The cooling effect of using cool materials on different oriented building surfaces was analyzed.•Using cool materials on roofs can lower indoor temperatures by 0.93 °C for real buildings.•The effect of cool materials is significantly reduced when solar radiation is less than 400 W/m2.
In this paper, we analyze the reset transition in bipolar TiN/Ti/HfO2 (10 nm)/Al2O3(2 nm)/W ReRAM devices using a tool that allows studying the temporal behaviour of these devices. This tool, the ...Dynamic Route Map (DRM), provides information about the temporal evolution of the state variable that governs the behaviour of the device, thus allowing an increased insight into resistive switching processes. Here, we show that this DRM is a powerful tool, that may help explaining some non intuitive behaviours of memristors, like the difference in the reset voltage when the inputs are from different frequency or shape. Using this tool, this fact can be explained as a different trajectory on a unique surface defining the device. As a first step, we have used two different models, one based on a physical description, and another one based on the mathematical definition of memristor as a non linear relation between charge and flux. We check that similar DRM can be obtained from both models. Additionally, several series of set-reset transitions have been measured using voltage ramps of different slopes. From the measured transitions, the corresponding resistance has been extracted and, assuming conductive filaments (CF) as the switching mechanism, the corresponding CF radius has been calculated. Using these data, we show that explanations from the model are also supported when using experimental data, thus proving the validity of the approach.
Superabrasives like synthetic diamonds are indispensable in today’s construction industry, particularly for core drilling applications in reinforced concrete. The increase of the cutting efficiency ...of such core bits strongly depends on the material removal behavior of single diamond grains placed in a diamond segment acting as cutting elements. Therefore, this paper presents a newly developed experimental setup for a 3-mm single diamond grain scratch test, as well as the application of a Smoothed Particle Hydrodynamics (SPH) method to model single diamond grains scratching a rebar base material at operational parameters. Diamonds in two main different crystallographic and geometric orientations are tested and investigated with respect to their forces and temperatures at the cutting edge. Furthermore, the chip formation and different material removal mechanisms are analyzed for each orientation and compared with the model output. Validation tests and sensitivity analyses are performed in 3D and high resolution, thanks to the runtime acceleration of SPH through parallel computing on the graphics card. The results indicate: 1) A significantly different material removal behavior as a result of changing the diamond orientation; 2) The capability and high efficiency of SPH for modeling single grain scratch tests.
•Effects of initial surface treatment on shot peening residual stresses are studied.•Surface hardness variation plays a significant role on peening residual stress field.•Initial tensile stresses ...increase the depth of compressive layer in thin samples.•The present model is able to predict tensile residual stresses beneath the surface.•The analytical results are in good agreement with the experimental measurements.
Shot peening is the most common surface treatment employed to enhance the fatigue performance of structural metallic materials and often carried out after other surface treatments. This paper mainly focuses on the effects of initial conditions of surface such as initial stress filed and hardness profile on shot peening residual stress field. The residual stress distribution induced by shot peening is obtained using Hertzian contact theory and elastic–plastic evaluation after yielding occurred during impingement and rebound of shots. Elastic plastic calculations are performed using different hardening models considering Bauschinger effect. The present model is able to predict redistribution of residual stresses in shot peening process by considering the initial conditions of target surface. Initial stress distribution and yield stress variation produced by previous surface treatments are taken into account by measuring residual stresses and hardness profile at near surface layers. An analytical parametric study is performed to evaluate the influence of initial conditions induced by surface pretreatments on shot peening residual stress field. The results of analytical model are validated by experimental data obtained in the literature as well as by our own measurements. The analytical results generally agree with the experimental measurements.
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The development of metasurfaces has unlocked various use cases in wireless communication networks to improve performance by manipulating the propagation environment. Intelligent omni-surface (IOS), ...an innovative technique in this category, is proposed for coverage extension. In contrast to the widely studied reflective metasurfaces, i.e., intelligent reflecting surfaces (IRSs), which can only serve receivers located on the same side of the transmitter, the IOS can achieve full-dimensional wireless communications by enabling the simultaneous reflection and refraction of the surface, and thus users on both sides can be served. In this paper, we provide a comprehensive overview of the state-of-the-art in IOS from the perspective of wireless communications, with the emphasis on their design principles, channel modeling, beamforming design, experimental implementation and measurements, as well as possible applications in future cellular networks. We first describe the basic concepts of metasurfaces, and introduce the corresponding design principles for different types of metasurfaces. Moreover, we elaborate on the reflective-refractive model for each IOS element and the channel model for IOS-aided wireless communication systems. Furthermore, we show how to achieve full-dimensional wireless communications with the IOS for three different scenarios. In particular, we present the implementation of an IOS-aided wireless communication prototype and report its experimental measurement results. Finally, we outline some potential future directions and challenges in this area.
•The pressure drop in three horizontal pipes of 12.70, 19.05 and 25.40mm is studied.•The pressure drop increases with higher volumetric qualities for the cases of constant water flow rate but ...decreases for higher volumetric qualities of constant total flow rate due to the change in flow pattern•The drift-flux model and homogenous model are the most suitable models for pressure drop prediction.
The pressure drop has a significant importance in multiphase flow systems. In this paper, the effect of the volumetric quality and mixture velocity on pressure drop of gas-liquid flow in horizontal pipes of different diameters are investigated experimentally and numerically. The experimental facility was designed and built to measure the pressure drop in three pipes of 12.70, 19.05 and 25.40mm. The water and air flow rates can be adjusted to control the mixture velocity and void fraction. The measurements are performed under constant water flow rate (CWF) by adding air to the water and constant total flow rate (CTF) in which the flow rates for both phases are changed to give same CTF. The drift-flux model is also used to predict the pressure drop for same cases. The present data is also compared with a number of empirical models from the literature. The results show that: i) the pressure drop increases with higher volumetric qualities for the cases of constant water flow rate but decreases for higher volumetric qualities of constant total flow rate due to the change in flow pattern. ii) The drift-flux model and homogenous model are the most suitable models for pressure drop prediction.
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