V-shaped Surface Research Articles

Thermal Efficiency of a Solar Air-Heating Collector with a Metal Chip Absorber

It is known that one of the main issues of heat transfer in complex designs of solar air-heating collectors is the problem of determining the coefficient of convective heat transfer in some parts of absorbers. The article studies the processes of heat transfer occurring in a solar air-heating collector with an absorber, which is a system of metal flow chips and a V-shaped surface. A description of the design of a solar air-heating collector with a metal chip absorber is given. The absorber allows us to increase the contact surface between the coolant and the absorber. The experimental procedure and the results are presented. The experiments have shown that within the range of 850 – 950 W / m2 of direct incident solar radiation density, the average heating of coolant is 17.5 °C; within the range of 650 – 750 W / m2, it is 14.1 °C; within the range of 450 – 550 W / m2, it measures 10.1 °C. The maximum coolant heating is 27 °C which is equal to the output collector temperature 60 °C. The average heating of the coolant is 14 °C, which corresponds to the average output temperature of 45 °C. According to the data obtained in the experiment, empirical formulas are concluded. They are presented in the form of the dependence Nu = f (Re), it is aimed at determining the heat transfer coefficient of flow metal chips and V-shaped absorbers of a solar air-heating collector. The dependence of the absorbers heat transfer from metal flow chips and the V-shaped surface of the solar air-heating collector on the Re numbers within the range of 103÷104 is shown. A formula is derived that allows us to compare the effectiveness of absorbers of various types with a flat absorber of a solar air-heating collector

Equivalent modeling and evaluation of molars using point-contact higher kinematic pair based on occlusal dynamic analysis

As a representative part of the oral system and masticatory robot system, the modeling method of the dental model is an important factor influencing the accuracy of the multi-body dynamic model. Taking the right first molars of the masticatory robot as the research object, an equivalent model, point-contact higher kinematic pair composed of v-shaped surface and sphere surface, was proposed. Firstly, the finite element method was used to analyze the occlusal dynamics of the original model in three static contact cases (intrusive contact, centric occlusion, and extrusive contact) and one dynamic chewing case, and the expected bite force was obtained. Secondly, the Hertz contact model was adopted to establish the analytical expression of the bite force of the equivalent model in three static contact cases. The normal vectors and contact stiffness in the expression were designed according to the expected bite force. Finally, the bite force performance of the equivalent model in three static contact cases and one dynamic chewing case was evaluated. The results showed that the equivalent model could achieve the equivalent bite force of 8 expected items in the static contact cases. Meanwhile, the bite force in the early and late stages of the dynamic chewing case coincides well with the original model. In the middle stage, a certain degree of impact is introduced, but it can be weakened by subsequent trajectory planning. The equivalent modeling scheme of the dental model proposed in this paper further improves the accuracy of the dynamic model of the multi-body system. It provides a new idea for the dynamic modeling of other complex human contacts.

Switchable Isotropic/Anisotropic Wettability and Programmable Droplet Transportation on a Shape-Memory Honeycomb.

Programmable droplet transportation is required urgently but is still challenging. In this work, breath figure was employed to fabricate shape-memory poly(lactic acid) (PLLA) honeycombs in which tiny crystals and an amorphous network act as the shape-fixed phase and recovery phase, respectively. Upon uniaxial tension, circle pores from the breath figure were deformed to elliptical pores, producing contact angle differences and anisotropic wetting behaviors in two directions. Both pore geometry and anisotropic wettability can be tailored via the draw ratio. On the PLLA honeycomb surface with a lower draw ratio, the contact angle difference is too small to induce droplet transportation along the desired direction. In the case of a higher draw ratio, however, the movement of water droplets has been controlled absolutely along the tension direction. The transition between them can be achieved reversibly during uniaxial tension and recovery processes based on the shape-memory effect. The enhanced flow control, which can be attributed to the synergism between optimal hydrophobicity and enlarged anisotropic wetting behaviors, endows water droplets with the ability to turn a corner spontaneously on a V-shaped surface including two regions exhibiting different oriented directions.

Heat transfer enhancement and pressure loss in a plate-fin heat exchanger with V-shaped oblique wavy surface

Numerical investigations on the heat transfer and pressure loss of a plate-fin heat exchanger with V-shaped oblique wavy surface have been conducted. The effects of pointing direction of V shape, oblique angle and wave amplitude are systematically studied to find out the geometry with the best thermal-hydraulic performance. It is found that the oblique wavy surface induces two pairs of counter rotating secondary flows which significantly enhance heat transfer irrespective of the pointing direction of the V shape. Meanwhile, the oblique wavy surface with the V shape pointing downstream shows relatively low pressure loss. It is also found that moderate oblique angle and large amplitude are beneficial for heat transfer augmentation, while oblique angle near 75o and small amplitude are beneficial for relieving pressure loss. The optimal geometry which balances heat transfer enhancement and pressure loss is obtained by adopting an acute oblique angle close to 75o with large amplitude, and its Colburn factor j and goodness factor j/f increased by 150% and 16% at Re = 500, respectively, compared with the plain channel.

Experimental and numerical study on liquid pouring from a beverage can

A numerical method of liquid pouring from a beverage can was proposed in the present paper, and a numerical model of the effects of dew condensation on the flow from the can was also developed. An experimental observation showed that the liquid flowed over the can lid and was once obstructed by the rim of the lid. Then, it flowed over the rim and fell off, forming a V-shaped surface. The numerical result agreed with the experimental result. Effects of condensation formed on a can surface were also simulated. In the simulation, the effect of condensation was considered by adjusting a contact angle, defined as an “effective” contact angle. The trajectory of the falling liquid came close to the can body for higher wettability by condensation. With more condensation, the liquid pouring from a can trickled down along the can body. The computation reproduces these experimental observations.

Condensation on Composite V-Shaped Surface with Different Gravity in Nanoscale

The model of water vapor condensation on a composite V-shaped surface with multi wettability gradients was built and the condensation process with different gravity was studied by molecular dynamics to find out whether this model could control the condensation mode and accelerate the condensate drainage from the micro-perspective. With the absence of gravity, the simulation results indicated that the condensation mode could be controlled as a dropwise condensation. What’s more, the movement of condensate nano-droplet also could be controlled, which was helpful for increasing the efficiency of condensate drainage. The temperature of hot wall was largest while it was smallest for cold wall. The temperature of water was in the middle. The result was in accordance with the law of energy conservation. However, the condensation process was different with the effect of gravity. It can be concluded that the condensation process was much quicker with greater gravity, leading to the larger condensation rate. The temperature of cold wall and water were larger than that of hot wall, especially for greater gravity. It was because the part of energy generated by gravity transferred to the thermal energy of water and cold wall, and the other part transferred to the kinetic energy of water. The gravitational potential energy and kinetic energy increased with greater gravity, while the thermal energy increased first and then decreased, corresponding well with the final temperature of condensation process with different gravity. The results will provide a microcosmic mechanism for space experiment and guidance for space system drainage.

Tribological Properties of V-Shaped Surface Texture under Oil Lubrication Condition

In order to study the tribological properties of V-shaped texture under oil lubrication conditions, the loading force and speed are selected as the influencing factors, each factor selected six levels. Experimental study on friction and wear of V-shaped texture with ring arrangement is finished by MMG-10 Multifunctional Friction and Wear Testing Machine, and the data of the experimental results are analyzed by using Matlab. The results show that there is a near linear relationship between the friction coefficient and the loading force and velocity. The relationship between the friction coefficient and the loading force and velocity can be expressed by a functional equation. The loading force has a greater influence on the friction coefficient than the speed. The SEM images of the post-test specimens show that the main weared zone of the V-shaped texture is the tip part. Create a single V-shaped texture model with Solidworks and use CFD to divide the mesh into the Fluent solution. According to the pressure distribution cloud diagram and the turbulence intensity cloud diagram, the stability of the oil film is improved due to the enhanced fluidity of the oil film and the small change in the oil pressure. The tip portion is also the region with a large turbulence intensity value. The improvement of the stability of the oil film is the key to reduce the friction coefficient of the V-shaped texture when the loading force increases.

Research on the Design Method of a Bionic Suspension Workpiece Based on the Wing Structure of an Albatross.

An air suspension platform uses air pressure to realize the suspension function during the suspension process, and it has the disadvantage of large air pressure and a small suspension force. In this study, an air suspension platform was built using bionic design to reduce the required air pressure and increase the suspension force. A suspension structure mapping model was established according to the physiological structure characteristics of albatross wings. A bionic model was established by using the theoretical calculation formula and structural size parameters of the structural design. A 3D printer was used to manufacture the physical prototype of the suspended workpiece. Based on this, a suspension test rig was built. Six sets of contrast experiments were designed. The experimental results of the suspension test bench were compared with the theoretical calculation results. The results show that the buoyancy of the suspended workpiece with a V-shaped surface at a 15-degree attack angle was optimal for the same air pressure as the other workpieces. The surface structure of the suspended workpiece was applied to the air static pressure guide rail. By comparing the experimental data, the air pressure of the original air suspension guide rail was reduced by 37%, and the validity of the theory and design method was verified.

Deep spectral reflectance and illuminant estimation from self-interreflections.

In this work, we propose a convolutional neural network based approach to estimate the spectral reflectance of a surface and spectral power distribution of light from a single RGB image of a V-shaped surface. Interreflections happening in a concave surface lead to gradients of RGB values over its area. These gradients carry a lot of information concerning the physical properties of the surface and the illuminant. Our network is trained with only simulated data constructed using a physics-based interreflection model. Coupling interreflection effects with deep learning helps to retrieve the spectral reflectance under an unknown light and to estimate spectral power distribution of this light as well. In addition, it is more robust to the presence of image noise than classical approaches. Our results show that the proposed approach outperforms state-of-the-art learning-based approaches on simulated data. In addition, it gives better results on real data compared to other interreflection-based approaches.

Direct numerical simulations of premixed and stratified flame propagation in turbulent channel flow

Direct numerical simulations are performed to investigate the transient upstream flame propagation (flashback) through homogeneous and fuel-stratified hydrogen-air mixtures transported in fully-developed turbulent channel flows. Results indicate that, for both cases, the flame maintains steady propagation against the bulk flow direction and the global flame shape and the local flame characteristics are both affected by the occurrence of fuel stratification. Globally, the mean flame shape undergoes an abrupt change when the approaching reactants transition from an homogeneous to a stratified mixing configuration. A V-shaped flame surface, whose leading-edge is located in the near-wall region, characterizes the non-stratified, homogeneous mixture case while a U-shaped flame surface, whose leading-edge propagates upstream at the channel centreline, distinguishes the case with fuel stratification (fuel-lean in the near-wall region and fuel-rich away from the wall). The characteristic thickness, wrinkling and displacement speed of the turbulent flame brush are subject to considerable changes across the channel due to the dependence of the turbulence and mixture properties on the distance from the channel walls. More specifically, the flame transitions from a moderately wrinkled, thin-flamelet combustion regime in the homogeneous mixture case to a strongly wrinkled flame brush more representative of a thickened-flame combustion regime in the near-wall region of the fuel-stratified case. The combustion regime may be related to Karlovitz number and it is shown that a nominal channel-flow Karlovitz number, Kachin, based on the wallnormal variation of canonical turbulence (tη = (ν/e) 1/2) and chemistry (tl = δl/Sl) time scales in fully-developed channel flow, compares well with an effective Karlovitz number, Kachfl, extracted from the present DNS datasets using conditionally sampled values of tη and tl in the immediate vicinity of the flame (0.1 < C < 0.3).

Numerical simulation and experimental study of liquid–liquid flow dispersion in conical spiral pipes

This paper presents the numerical simulation and experimental study of an immiscible liquid–liquid flow dispersion in conical spiral pipes for oil–water separation. Flow patterns of oil–water flow in the pipe are identified. The flow characteristics such as pressure drop, cross sectional phase distribution, and outlet flow rate are obtained. In addition to flow behavior, separation performance of the conical spiral pipes is examined under different operating conditions. The effects of geometric parameters such as conical angle, pipe diameter, pitch height, and outlet split ratio, on oil–water separation are revealed. Moreover, the effects of inlet velocity, inlet oil concentration, and operating temperature on the separation are obtained. In addition, it has shown that surface treatment for the conical spiral pipes has an impact on the oil–water separation. In particular, the V-shaped sawtooth surface microstructure can enhance the oil–water separation, and Graphene-coated surface exhibits good separation capacity under high flow velocity.

In brief

PAGE 582 Researchers in Germany present a red emitting laser with V-shaped surface grooves in the p-confinement layer, which result in low radiation losses. The laser will be suitable for many applications that require laser sources that emit high-power at precisely defined wavelengths, such as interferometry, free-space communication, metrology and light detection. PAGE 558 A collision avoidance scheme for ground vehicles is proposed in work from Korea. The scheme including a modified turn algorithm improves driving performance by minimising sudden curvature changes and side-slips of the vehicle. A non-linear estimator for time-to-collision is also introduced to increase collision avoidance. Surface grooves in a red emitting laser result in low radiation losses to produce high output power. PAGE 584 Work from the US demonstrates that a 3D metamaterial structure with back-to-back, vertically oriented metallic cross dipoles efficiently linearly polarises light. The control over light polarisation in the presented metamaterial surpasses that of traditional 2D polarisers due to a reduction in reflected and transmitted polarisation. A scheme to improve driving performance reduces sudden changes in curvature of ground vehicles. PAGE 580 Researchers in Japan design an all-optical AND logic gate using photonic crystal (PC) quantum dot semiconductor optical amplifiers (QDSOA) for optical equipment, like multiplexers. The proposed gate is compared to traditional QDSOA optical gates and the incorporation of a PC is shown to reduce energy consumption and device volume. Efficient linear polarisation of light with a 3D metamaterial structure. PAGE 595 A method to resolve terrain features to adjust the trajectory of a mobile robot using vibrations from vehicle-terrain interactions is reported in work from Korea. The presented algorithm allows a robot that explores an unfamiliar area to efficiently plan their path across different surfaces with differing features and textures. An all-optical quantum dot semiconductor photonic crystal AND logic gate is presented with low energy consumption. Vehicle-terrain interactions are used to adjust a planned route for efficient terrain exploration.

Effects of extended surface and surface gold plating on condensation characteristics of steam with large amount of CO2

To promote steam condensation with high concentration of non-condensable gas, vapor mixture with 45–95% CO2 is adopted to experimentally investigate the effects of extended surface and surface gold plating on the heat-transfer enhancement. The results show that a gold-plated stainless vertical surface does not exhibit superior performance under the influence of less condensate and slower update frequency of the drops. A V-shaped fluted surface can enhance heat transfer under CO2 concentrations of 85% and 95%, but no further enhancement is shown after the gold-plating treatment on the surface. Although droplets formed at both the inclined surfaces and bottom of the groove, the disturbance of the droplet movement on the gas boundary layer is much weaker due to the lower heat flux. Both experimental results indicate that a proper increase in the fin spacing and height can improve the heat-transfer process on both untreated and gold-plated fluted surfaces.

Design of a novel bandwidth-enhanced double-slot TSA and analysis according to the microwave network theory

In this paper, a novel bandwidth-enhanced ultra-wideband (UWB) tapered slot antenna with Y-shaped corrugated edges, is proposed. In the double-slot structure, the two slots are separated by a V-shaped metal surface with straight edges, which is beneficial to improve the directivity of the antenna. Meanwhile, an exponential Y-shaped corrugated edge is designed. This novel corrugated edge can not only improve the impedance bandwidth, but also enhance the gain of the antenna. Additionally, according to the theory of microwave network, this paper analyzes the reason of bandwidth enhancement realized by double-slot structure. The proposed antenna provides 167% fractional bandwidth from 2.5GHz to 28GHz. The gain of the proposed antenna is more than 10dB from 3.5GHz to 25GHz, and more than 8dB at the whole operating band.

Gain‐improved double‐slot TSA with Y‐shaped corrugated edges

A novel bandwidth-enhanced UWB tapered slot antenna with Y-shaped corrugated edges is proposed. In the double-slot structure, the two slots are separated by a V-shaped metal surface with straight edges, which is beneficial to improve the directivity of the antenna. Meanwhile, an exponential Y-shaped corrugated edge is designed. This novel corrugated edge not only enhances the impedance bandwidth, but also improves the gain by concentrating the energy near the tapered slot. The impedance bandwidth of the double-slot TSA is from 2.5 to 28 GHz. The gain of the antenna is >10 dB from 3.5 to 25 GHz, and >8 dB in the whole operating band.

Controlled droplet transport to target on a high adhesion surface with multi-gradients

We introduce multi-gradients including Laplace pressure gradient, wettable gradient and wettable different gradient on a high adhesion surface via special wedge-pattern and improved anodic oxidation method. As a result of the cooperative effect mentioned above, controlled directional motion of a droplet on a high adhesion surface is realized, even when the surface is turned upside down. The droplet motion can be predicted and the movement distances can be controlled by simply adjusting the wedge angle and droplet volume. More interestingly, when Laplace pressure gradient is introduced on a V-shaped wettable gradient surface, two droplets can move toward one another as designed.

Enhancing the spatial rainfall uniformity of pressurized nozzle simulators

PurposeRainfall simulators are used on experimental hydrology, in areas such as, e.g., urban drainage and soil erosion, with important timesaving when compared to real scale hydrological monitoring. The purpose of this paper is to contribute to increase the quality of rainfall simulation, namely, for its use with scaled physical models.Design/methodology/approachTwo pressurized rainfall simulators are considered. M1 uses three HH-W 1/4 FullJet nozzles under an operating pressure of 166.76 kPa and was tested over a 4.00 m length by 2.00 m width V-shaped surface. M2 was prepared to produce artificial rainfall over an area of 10.00 m length by 10.00 m width. The spatial distribution of rainfall produced from a single nozzle was characterized in order to theoretically find the best positioning for nozzles to cover the full 100 m2 area with the best possible rainfall uniformity.FindingsExperiments with M1 led to an average rainfall intensity of 76.77-82.25 mm h−1 with a 24.88 per cent variation coefficient and a Christiansen Uniformity Coefficient (CUC) of 78.86 per cent. The best result with M2 was an average rainfall intensity of 75.12-76.83 mm h−1 with a 21.23 per cent variation coefficient and a CUC of 83.05 per cent.Practical implicationsThis study contributes to increase the quality of artificial rainfall produced by pressurized rainfall simulators.Originality/valueM2 is the largest rainfall simulator known by the authors worldwide. Its use on rainfall-runoff studies (e.g. urban areas, erosion, pollutant transport) will allow for a better understanding of complex surface hydrology processes.

The influence of substrate and atmosphere on the properties of FeSiB(Cu,Nb) alloy melts

The surface tensions and contact angles of Fe78Si9B13 and Fe73.5Cu1Nb3Si13.5B9 alloy melts were studied as a function of temperature in various atmospheres (vacuum, Ar and N2 gas) and on different substrates (SiC, Al2O3 and BN). It is indicated that Si3N4, NbN, Fe2AlB and B13C2 are generated as new phases at the interface between the melt and substrate, and reactive wetting behaviour exists during the heating process. The surface tensions of two alloy melts on BN substrate both firstly decrease and then increase along with increasing temperature, leading to V-shaped surface tension versus temperature, which results from atomic diffusion effects in the surface layer during the oxidation of BN and formation of C-rich layer. Comparably, the surface tensions on Al2O3 and SiC substrates decrease with increasing temperature throughout the entire temperature range. Among three substrates, BN exhibits the mildest wetting behaviour. The vacuum environment has the strongest protective effect on melt stability among the tested atmospheres. These findings enrich our knowledge about the effects of the substrate and atmosphere on Fe-based alloy melts at a high temperature, and provide theoretical reference for designing jet nozzles in melt-spinning techniques.

Gas–Solid Erosive Wear of Biomimetic Pattern Surface Inspired from Plant

ABSTRACTGas–solid erosive wear is a phenomenon in which serious mechanical damage is caused by the impact of solid particles on a wall. In this study, we investigated the erosive wear characteristics and mechanism of biomimetic groove surfaces in gas–solid erosive wear. Orthogonal experimental results showed that the order of the factors that influenced the erosive wear of the biomimetic groove surface was morphology > space > feature size. The V-shaped groove surface exhibited the best erosive wear resistance over the smooth, square, and U-shaped groove surfaces. The surface microstrain calculated by X-ray diffraction lines was used to study the mechanism of erosive wear resistance enhancement of the biomimetic surface. The microstructure of the eroded surface was analyzed by scanning electron microscopy. The appearance of ribs on the biomimetic groove surface increased the erosive wear of the surface in a distal position with respect to the ribs themselves. This article shows more opportunities for bionic application in improving the anti-erosion performance of moving parts that work under dirt and sand particle environments.

Ultrasmooth Ru(0001) Films as Templates for Ceria Nanoarchitectures

Single crystalline magnetron sputter-deposited Ru(0001) epitaxial thin films on c-plane sapphire were prepared and used as a template for reactive CeO2 growth. Low-energy electron microscopy and diffraction, as well as transmission electron microscopy and atomic force microscopy, experiments were performed to investigate the crystallinity and morphology of the prepared films. Multiple cycles of Ar+ sputtering and high-temperature annealing produces films of exceptional surface quality. High-temperature reactive ceria growth leads to perfectly aligned triangular single-crystalline CeO2(111) islands of extraordinary morphological and structural homogeneity. At the chosen growth conditions, ceria nucleation takes place only at V-shaped surface defects on the otherwise atomically flat Ru terraces, opening up the possibility to influence the nucleation by introducing artificial surface defects using standard etching techniques. Due to their high crystallinity and extraordinary surface quality, these substrates...