As an emerging automated construction technology, 3D concrete printing opens the opportunity for the construction of hard rock tunnel linings. However, very limited studies were carried out in this ...regard, especially the adhesion between freshly printed cementitious materials and the excavated rock wall deserves further attention. In this study, the adhesive performance of the fresh cementitious material at two representative surface inclinations, including the overhead position (inclination of 180°) and the side position (inclination of 90°), was explored by a tack test and a shear test. This was further studied by two series of 3D concrete printing tests including horizontal printing at the underside of a supported slab and vertical printing against an upright slab. Results demonstrated the adhesion at the overhead position was limited by both the shear resistance of the fresh cementitious material and the property of the material-to-substrate interface, while the adhesion at the side position was mainly constrained by the shear resistance of the fresh cementitious material. Moreover, the stress state analysis of the printed layers at the overhead position and the side position indicated that the tack test and shear test gave a good prediction about the printing capacity of the fresh cementitious material for hard rock tunnel linings.
•3D concrete printing is used for the construction of hard rock tunnel linings.•The adhesive performance of the fresh cementitious material for different surface inclinations is explored.•The stress states of the printed layers at the overhead position and the side position are analyzed.
Hydrogen production rate increases as current density increases in a water electrolysis. At a certain high current density, the cell potential abruptly increases due to the hydrogen film formed at ...the cathode, which is known as the critical current density (CCD). Hence, it is imperative to increase the CCD for effective hydrogen production. However, the investigations regarding hydrodynamic parameters, which affect the CCD have hardly been performed. This work investigated the influence of the hydrodynamic parameters such as mass flux, inclination of cathode channel and inlet void fraction on the CCD in water electrolysis. The increase in the mass flux increased the CCD regardless of the channel inclination and the inlet void fraction due to the enhanced hydrogen bubble elimination near the surface, which retards hydrogen film formation. The influence of the inlet void fraction showed different trend according to the channel inclination. Monotonically decreasing trend was measured in the vertical channel due to reduced flow rate near the surface as the void fraction increased. Meanwhile, a peak was measured in the inclined channels. The inlet voids at bubbly flow regime dispersed the hydrogen bubbles from the cathode, while those at the slug flow regime aided and enhanced the hydrogen film formation at the cathode. It is concluded that the inlet void fraction either enhances or impairs the CCD depending on the flow regime. The authors expect that this work would shed light on the roles of hydrodynamic parameters for efficient hydrogen production.
•The influences of mass flux, inclination and inlet void fraction on CCD were investigated.•Hydrodynamic aspects of hydrogen production and two-phase flow regime were compared.•CCD increased with mass flux and decreased as channel inclination became horizontal.•Increased inlet void decreases the CCD at vertical channel reducing flow rate near the wall.•Inlet void either enhances or impairs CCD depending on flow regimes at inclined channel.
The majority of cutting force models applied for the ball end milling process includes only the influence of cutting parameters (e.g. feedrate, depth of cut, cutting speed) and estimates forces on ...the basis of coefficients calibrated during slot milling. Furthermore, the radial run out phenomenon is predominantly not considered in these models. However this approach can induce excessive force estimation errors, especially during finishing ball end milling of sculptured surfaces. In addition, most of cutting force models is formulated for the ball end milling process with axial depths of cut exceeding 0.5mm and thus, they are not oriented directly to the finishing processes. Therefore, this paper proposes an accurate cutting force model applied for the finishing ball end milling, which includes also the influence of surface inclination and cutter's run out. As part of this work the new method of specific force coefficients calibration has been also developed. This approach is based on the calibration during ball end milling with various surface inclinations and the application of instantaneous force signals as an input data. Furthermore, the analysis of specific force coefficients in function of feed per tooth, cutting speed and surface inclination angle was also presented. In order to determine geometrical elements of cut precisely, the radial run out was considered in equations applied for the calculation of sectional area of cut and active length of cutting edge. Research revealed that cutter's run out and surface inclination angle have significant influence on the cutting forces, both in the quantitative and qualitative aspect. The formulated model enables cutting force estimation in the wide range of cutting parameters, assuring relative error's values below 16%. Furthermore, the consideration of cutter's radial run out phenomenon in the developed model enables the reduction of model's relative error by the 7% in relation to the model excluding radial run out.
•Cutting force model applied for the finishing ball end milling is proposed.•Run out is included also in expression of active length of cutting edge.•Surface inclination has quantitative and qualitative influence on cutting forces.•Small run out's value (3μm) can cause influential cutting force variations (~30%).•Proposed force model enables the obtainment of global estimation errors below 16%.
Condensation of water vapor on a surface plays an important role in thermal based water purification methods. Appropriate texturing of such surfaces facilitates dropwise condensation with better heat ...transfer coefficient and water collection. In this context, we explore texturing patterns via laser ablation to achieve lower aspect ratio (10 μm depth to 100 μm width) and via wire electric discharge machining process for higher aspect ratio (300 μm depth to 100 μm width). The transition from Cassie-Baxter to Wenzel is seen experimentally as well as through the simulations for lower aspect ratio, whereas the transition does not occur for higher aspect ratio. Simulations are also carried out for the sessile as well as pendant drop, which is more relevant to thermal based water purification. However, in the experiments the drop is always in the pendant mode. The condensing surface inclination plays a very significant role in the water collection. In order to have more water production underneath the copper plate, the optimum angle of inclination found is 35°.
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•Hydrophobic surface using physical texturing by laser and EDM micromachining•Simulations for transition from Cassie Baxter to Wenzel state•Water production using physically textured and plain surface in desalination system•Time required for first drop to slide off on textured and plain surface•Effect of inclination angle on drop sliding on textured and plain surface
•Performed experiments of pool boiling of PF-dielectric liquid on dimpled Cu surfaces.•Investigated and correlated effects of inclination angle and liquid subcooling on nucleate boiling and critical ...heat flux.•Dimpled Cu surfaces enhance both nucleate boiling and the critical heat flux.•Critical heat flux increases linearly with liquid subcooling.
This paper investigated natural convection and nucleate boiling of PF-5060 dielectric liquid on 10×10mm uniformly heated copper (Cu) surfaces with different diameter dimples, for potential application to immersion cooling of high power computer chips. The circular dimples, 300, 400, and 500μm in diameter and 200μm deep, have a triangular lattice with a pitch-to-diameter ratio of 2.0. The total number of dimples on the 10×10mm surfaces increases with decreasing the dimple diameter. In addition to the dimple diameter, the performed experiments quantified the effects of the surface inclination angle and the liquid subcooling on the nucleate boiling heat transfer coefficient, hNB, and the critical heat flux (CHF). The inclination angle varied from 0° (upward facing) to 180° (downward facing) in increments of 30°, and the liquid subcooling includes 0K (saturation), 10K, 20K and 30K. In the upward facing orientation, the Cu surface with 400μm dimples gives the highest hMNB (∼1.06W/cm2K) and CHF (∼19.3W/cm2). The values for the surface with 500μm dimples are ∼1.0W/cm2K and ∼18.7W/cm2, respectively, and ∼0.7W/cm2K and ∼18W/cm2 on the surface with 300μm dimples. The CHF and hMNB on all dimpled Cu surfaces decrease with increased inclination angle to the lowest values in the downward facing orientation. These values are ∼36% and ∼33% of those in the upward facing orientation, respectively. In addition, the CHF in the upward facing orientation, increases linearly with increased liquid subcooling at a rate of 1.8%/K.
In this work, the combined impacts of magnetohydrodynamics and fin surface inclination on thermal performance of convective-radiative porous fin with temperature-invariant thermal conductivity is ...numerically study using finite difference method. Parametric studies reveal that as the inclination of fin, convective, radiative, magnetic and porous parameters increase, the adimensional fin temperature decreases which leads to an increase in the heat transfer rate through the fin and the thermal efficiency of the porous fin. It is established thatthe porous fin is more efficient and effective for low values of convective, inclination angle, radiative, magnetic and porous parameters. The thermal performance ratio of the fin increases with the porosity parameter.
•A boiling-meter is designed and implemented in a new experimental set up.•This new device allows an original investigation of the heat transfer in natural and pool boiling regimes.•Time evolution of ...temperature and heat transfer characteristics of the boiling wall are provided for the first time.•Averaged heat transfer curves are carried out versus the orientation of the wall to the gravity.•The onset of nucleate boiling as well as the onset of natural convection is found to vary with the tilt angle of the wall.•An interpretation of the Onset of Nucleate Boiling (ONB) is provided based of the obtained original results.
The works carried out in this study aimed to get a better understanding of the heat transfer in natural convection and nucleate boiling as well as the transition between these two regimes. An experimental test set up was built to generate the liquid boiling on the wall using a boiling-meter. This sensor was developed in order to investigate the heat transfer and its dependence with time in well controlled conditions. Temperature, pressure and heat flux required for the measurements were implemented. Experiments were focused on determining the characteristic curves of heat transfer in the natural convection regime and the nucleate boiling regime. The influence of the orientation of the wall relative to the gravity on the heat transfer is investigated. Characteristic heat transfer curves were obtained in several operating conditions and wall orientation with regard to gravity.
At the transition regime between natural convection and nucleate boiling regimes, it was highlighted a competition between these two regimes. It was found, that the transferred heat flux differs depending on the orientation of the wall and the degree of liquid superheat in the nucleate boiling regime. In the natural convection regime, the measured heat fluxes exhibited a slight variation with the tilt angle of the wall. While in the nucleate boiling regime, strong variations were observed on the onset of nucleate boiling as well as for the heat flux. At very low heat flux, the heat transfer increases with the tilt angle while it decreases for moderate heat flux. The onset of nucleate boiling (ONB) and the onset of dominant natural convection (ONC) were found to decrease as a function of the tilt angle of the wall with different variation laws. The wall superheats values for the ONB and ONC are getting closer when the tilt angle tends to 180°.
The present study aims to investigate the effect of incline and decline walking on ground and joint reaction forces (JRF) of lower extremity and plantar fascia strain (PFS) under certain surface ...inclination angles.
Twenty-three male subjects walked on a customized platform with four different surface inclinations (i.e., 0, 5, 7.5 and 10°) with inclined and declined directions. The motion of the ten reflective markers was captured using Qualysis motion capture system (Qualysis, Gothenburg, Sweden) and exported to a visual three-dimensional (3D) software (C-motion, Germantown, USA) in order to analyze the GRF, JRF and PFS.
The results found that the peak vertical GRF is almost consistent for 0 and 5° inclination slope but started to decrease at 7.5° onwards during decline walking. The most affected JRF was found on knee at medial-lateral direction even as low as 5 to 10° inclination for both walking conditions. Furthermore, the findings also show that the JRF of lower extremity was more affected during declined walking compared to inclined walking based on the number of significant differences observed in each inclination angle. The PFS was found increased with the increase of surface inclination.
The findings could provide a new insight on the relationship of joint reaction forces and strain parameter in response to the incline and decline walking. It would benefit in providing a better precaution that should be considered during hiking activity, especially in medial-lateral direction in order to prevent injury or fall risk.
Surface exploration in virtual reality has a large potential to enrich the user's experience. It could for example be used to train and simulate medical palpation. During palpation, users tap, ...indent, and rub the surface of a sample to estimate the underlying properties. However, up to now there is no good approach to render such intricate interaction realistically. This paper introduces 6 degrees of freedom (DoF) encountered-type haptic display technology for simulating surface exploration tasks. Among the different phases of exploration, this article focuses on the 'in-contact sliding' phase. Two novel control approaches to render sliding over a virtual surface are elaborated. A first rendering method generates lateral frictional forces as the finger slides over the surface. A second method adjusts the inclination of the end-effector to render tissue properties. With both methods a stiff nodule embedded in a soft tissue was prepared. User experiments were carried out to find proper parameter and intensity ranges and to confirm the feasibility of the new rendering schemes. Participants indicated that both rendering schemes felt realistic. Compared to earlier work, where only the vertical stiffness was altered, lower thresholds to detect and localise embedded virtual nodules were found. Users also made fewer errors in detecting nodule edges. Furthermore, the method that used end-effector inclination allowed faster discovery of the nodule's edges. It is expected that approaches that combine both rendering methods could provide an even more realistic feel.
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