Constant Geometrical Parameters Research Articles

Heat transfer analysis and melting behavior of nano composite phase change materials (NCPCMs) in a reverse flow solar air heater

This paper presents a CFD investigation on heat transfer analysis and melting behavior of Nanocomposite Phase Change Materials (NCPCMs) in a Reverse Flow Solar Air Heater (RFSAH). Semicircular tubes filled with PCM are embedded on the top surface of the absorber plate. The study was conducted with three different nanoparticles (CuO, Al2O3, Fe3O4) based NCPCMs at three concentrations of 0.1, 0.2, and 0.3 % by weight. The constant geometrical parameters such as pitch ratio (P/e = 6), height ratio (e/Dh=0.1571), and Reynolds number (Re = 5000) is considered for this study. A 2-D transient numerical analysis using the RNG k-ε turbulence model is performed for the melting behavior of NCPCMs inside the semicylindrical tubes. The incorporation of nanoparticles into the base PCM enhances thermal conductivity but reduces the latent heat of NCPCMs. Thus, it is observed that NCPCMs have a faster melting rate. The CuO based NCPCM shows a more quick and uniform phase transition compared to the Fe3O4, and Al2O3 based NCPCMs and reached their peak value at a higher mass fraction of 0.3. Furthermore, the heat transfer and melting fraction improves with increasing in mass fraction of nanoparticles. The phase transition process of CuO based NCPCM is approximately 1.9 times, and 1.01 times, 1.03 times faster as compared to the base PCM, and Fe3O4, Al2O3 based NCPCMs respectively.

Effect of stirring speed on low acyl gellan gum fluid gels’ rheology, particle morphology and physical ageing

Fluid gels are jammed suspensions of gelled particles widely used across several industries to functionalise materials. They can be obtained for example by applying shear to a gelling hydrocolloid during its sol-gel transition. In the present study, the impact of flow rate, modulated by applying different processing stirring speeds under constant geometrical parameters, on the rheology, particle morphology and physical ageing of low acyl gellan gum fluid gels was investigated. Fluid gel particle elongation was observed in samples processed at higher stirring speeds whereas, no decrease in particle size was measured. The increase in aspect ratio is attributed due to the flow rate experienced by the particles through the geometry used to manufacture the samples. Fluid gels processed at higher stirring speeds generally showed lower low-shear viscosity, elastic modulus and higher yielding properties and interconnectivity. This might be due to the elongation of the fluid gel particles which would decrease particle voluminosity but increase the likelihood of mechanical entanglement, increasing their viscous dissipation. In addition, samples manufactured at higher stirring speeds exhibited a G′ increase with the number of shear cycles performed whereas, samples processed at lower stirring speeds showed a G′ decrease with the number of shear cycles performed. This behaviour might be caused by the balance between two counteracting mechanisms: abrasion (decrease in G′) and compaction (increase in G′). In addition, the higher the stirring speed the higher the ageing exponent. This might be due to the larger surface area of elongated particles which might ease interparticle link formation. Furthermore, the impact of the gravitational field on the physical ageing of low acyl gellan gum fluid gels was investigated by entrapping silica microparticles within the fluid gel particles, allowing tuning the density difference between the continuous and dispersed fluid gel phases. Finally, this study helps providing a better understanding on how processing stirring speed could be used to tune fluid gels’ properties for specific industrial applications.

Mechanics of re-entrant anti-trichiral honeycombs with nature-inspired gradient distributions

This study focuses on the nature-inspired gradient-based approach to re-designing re-entrant anti-trichiral (REAT) honeycombs through extensive experimental quasi-static compression. Novel perspectives on REAT honeycomb are offered through the introduction of gradient distributions on two critical geometrical parameters, the cylindrical diameter (chiral) and height of the unit cell, rather than the traditional thickness-based gradient approach. Chiral-based gradient approach demonstrated clear advantages in elastic stiffness, specific energy absorption (SEA) and densification strain over uniform REAT structures of constant geometrical parameters. These advantages are exhibited in their extended and constantly increasing quasi-plateau stage, consistent specific energy absorption (SEA) especially during early stages of compression, and most importantly, the ability to maintain a relatively constant energy absorption efficiency that is 25% more than that of the Base uniform REAT structure. Height gradient-based REAT structures, on the other hand, were able to leverage on associations between the negative Poisson's ratio (NPR) effect and height of unit cell to demonstrate notable deformation patterns across various portions of the structure. The present work reveals the performance enhancements through alternative gradient-based approaches over thickness-based gradient approaches and highlighted the differences in NPR between layers as the main driver of compressive collapse apart from the commonly concluded difference in relative density.

The investigation on dynamic damage evolution and energy absorption of FML pin joints with different ply stacking sequences

With fiber reinforced composites widely applied in aerospace, the crashworthiness aspects for aircraft have been an important part of the design. Fiber metal laminate (FML) is a kind of hybrid composite fabricated by fiber reinforced plastic composites and metal layers, showing a potential application on energy absorption. In this work, the damage evolution and energy absorption of FML pin joints are investigated comprehensively. The configurations of FML pin joints with constant geometric parameters are designed to avoid net-tension damage failure in the experiments. The damage evolution processes of specimens are captured by a high-speed camera, and the surface strain is calculated by Digital Image Correlation (DIC) method. Abaqus/Explicit solver is adopted to simulate the mechanical responses of FML pin joint considering ductile damage of metal, damage evolution of composites, and delamination of the interface. The results indicate that the initial dynamic ultimate bearing strength of FML incorporate notable contribution from inertia effects. The average bearing strength associated with energy absorption efficiency is related to the ply stacking sequence of composites. The fiber direction of laminates should be perpendicular to the movement direction of pin as much as possible under the premise that the initial ultimate bearing strength satisfies the design requirement. The results obtained in this work provide comprehensive design guidance for the improvement of crashworthiness in the composite fuselage.

In English

An influence of the adsorbed molecules layer on the optical characteristics of the spherical metallic nanoparticles has been studied in the work. In order to do this one considers the additional term which takes into account the scattering of electrons at the interface between metal and adsorbate. The analytical expressions for the frequency dependences for the parameter of coherence loss due to the scattering at the interface “metal – adsorbed layer” have been obtained. It has been found that the presence of the adsorbed molecules results in the electron scattering anisotropy, and, hence, in the anisotropy of the optic response of such systems. The result of the indicated anisotropy is the appearance of the additional maximum in the infrared part of the spectrum in the frequency dependences for the optical characteristics. An evolution of the frequency dependences for the components of the polarizability tensor and the absorption cross-section and scattering cross-section for the two-layer spherical nanoparticles of the type “metal – adsorbate” under the variation of their geometrical parameters has been analyzed. It has been shown that the weak maximum of the real, imaginary parts and the module of the transverse component of the polarizability tensor and the absorption and scattering cross-sections in the infrared part of the spectrum appears due to inducing of the local density of the states by adsorbate. The reason of the shift of the maxima of the absorption cross-section and scattering cross-section for the nanoparticles of the constant sizes with the cores of different metals has been found. It has been demonstrated the existence of the small-scale oscillations at the frequency dependences for the components of the polarizability tensor and at the absorption and scattering cross-sections, caused by an oscillating contribution of the surface electron scattering. The dependence of the location and the value of the maximum of the absorption cross-section for the particle “metal – adsorbate” with the constant geometrical parameters and content on the dielectric permittivity of the medium, in which the nanoparticle is situated, has been proved.

Numerical Investigation of the Scale Effects of Rock Bridges

Due to the challenge of measuring rock bridges in the field and the negligence of progressive damage and changes in stresses within a rock mass when defining rock bridges, it is questionable to evaluate mechanical properties of rock bridges using only geometric parameters. A demonstration is the scale effects of rock bridges, because the same geometric parameter may refer to different sizes and numbers of rock bridges, leading to erroneous equivalent rock mass responses. In this context, in-plane rock bridges in rock slope engineering were equivalent to rock bridges subjected to direct shear by conducting numerical simulations employing the Universal Distinct Element Code (UDEC) and described by constant geometric parameters, i.e., joint persistence, while the sizes and numbers of rock bridges were variant. In this way, the scale effects of rock bridges were investigated from the perspective of load–displacement curves, stress and displacement fields, crack propagations and AE characterizations. The results revealed that the mechanical properties of rock bridges deteriorated with decreasing scales. More specifically, the shear resistance and the area and value of stress concentration decreased with decreasing scale. Furthermore, an uneven distribution of displacement fields in an arc manner moving and degrading away from the load was observed, indicating the sequential failure of multiple rock bridges. It was also found that the propagation of tensile wing cracks was insensitive to scale, while the asperity of macro shear fracture mainly formed by secondary cracks decreased with decreasing scale. In addition, increasing the dispersion of rock bridges would overlap the failure precursors identified by intense AE activities. Based on the abovementioned results, the scale effects of rock bridges were characterized using existing rock bridge potential (RBP) index and degree of persistence (DoP) index. Interestingly, a scale threshold to possibly identify a rock bridge was found.

The Development of Top-Hat Flow Field in a Circular Symmetrical Subsonic Nozzle

In this work, the numerical analysis and experimental measurements were made to investigate the development of top-hat flow field at atmospheric pressure in a circular symmetrical subsonic nozzle. Measurements were carried out over a range of inlet velocities (about 0.07-7 m/s) based on a nozzle with constant geometric parameters, which also provided verification for the numerical simulation. The objective of this study was to determine the change of top-hat flow field from the well-known pipe velocity profile to the saddle-back distribution as well as the key behaviours for the process. Results revealed a close coupling relationship between the process and the pressure gradient inside nozzle. It was concluded that the local flow direction of fluid near the edge of cross section was changed by static pressure gradient and overlapped with the mainstream. The increase in kinetic energy of each gas particle on the cross section was different contributed to the formation of top-hat flow field. The saddle-back distribution seems to occur after the appearance of the critical position. In addition, the influence of inlet velocity on the location of critical position as well as the degree of saddle-back distribution was also concerned.

Geometric optimization model for the solar cavity receiver with helical pipe at different solar radiation

In consideration of geometric parameters, several researches have already optimized the thermal efficiency of the cylindrical cavity receiver. However, most of the optimal results have been achieved at a fixed solar radiation. At different direct normal irradiance (DNI), any single optimal result may not be suitable enough for different regions over the world. This study constructed a 3-D numerical model of cylindrical cavity receiver with DNI variation. In the model of a cylindrical cavity receiver containing a helical pipe, the heat losses of the cavity and heat transfer of working medium were also taken into account. The simulation results show that for a particular DNI in the range of 400 W/m2 to 800 W/m2, there exists a best design for achieving a highest thermal efficiency of the cavity receiver. Besides, for a receiver in constant geometric parameters, the total heat losses increases dramatically with the DNI increasing in that range, as well as the temperature of the working medium. The thermal efficiency presented a different variation tendency with the heat losses, which is 2.45% as a minimum decline. In summary, this paper proposed an optimization method in the form of a bunch of fitting curves which could be applied to receiver design in different DNI regions, with comparatively appropriate thermal performances.

Bearing strength and progressive failure analysis of the punched hole of CFRP under tensile loading

Mechanical joints in composite structures are broadly used in many applications due to their accessibility for disassembly during maintenance. The capability of mechanical joints (bolted joints, pin joints, rivet joints, etc.) depends on the hole quality because the load transmitted via fastener gives rise to stress concentration around the hole-fastener boundary. This experimental study investigates the pattern on the effect of hole preparation techniques, namely, drilling and punching, on carbon-fiber-reinforced polymer with constant geometric parameters to the bearing strength and progressive failure analysis of the hole under tensile loading. A bearing test is conducted according to ASTM D5961 Procedure-A double shear with single-pin fastener using a modified fixture. The progressive failure modes resulting from the experiment are quantified and compared to those in literature. Results reveal clear differences in the bearing-response profiles plotted in the load–displacement graph between the drilling and punching techniques.

Spatial Rack Drives Pitch Configurations: Essence and Content

Abstract The practical realization of all types of mechanical motions converters is preceded by solving the task of their kinematic synthesis. In this way, the determination of the optimal values of the constant geometrical parameters of the chosen structure of the created mechanical system is achieved. The searched result is a guarantee of the preliminary defined kinematic characteristics of the synthesized transmission and in the first place, to guarantee the law of motions transformation. The kinematic synthesis of mechanical transmissions is based on adequate mathematical modelling of the process of motions transformation and on the object, realizing this transformation. Basic primitives of the mathematical models for synthesis upon a pitch contact point are geometric and kinematic pitch configurations. Their dimensions and mutual position in space are the input parameters for the processes of design and elaboration of the synthesized mechanical device. The study presented here is a brief review of the theory of pitch configurations. It is an independent scientific branch of the spatial gearing theory (theory of hyperboloid gears). On this basis, the essence and content of the corresponding primitives, applicable to the synthesis of spatial rack drives, are defined.

Kinematic Calibration and Forecast Error Compensation of a 2-DOF Planar Parallel Manipulator

Due to large workspace, heavy-duty and over-constrained mechanism, a small deformation is caused and the precision of the 2-DOF planar parallel manipulator is affected. The kinematic calibration cannot compensate the end-effector errors caused by the small deformation. This paper presents a method combined step kinematic calibration and linear forecast real-time error compensation in order to enhance the precision of a two degree-of-freedom (DOF) planar parallel manipulator of a hybrid machine tool. In the step kinematic calibration phase of the method, the end-effector errors caused by the errors of major constant geometrical parameters is compensated. The step kinematic calibration is based on the minimal linear combinations (MLCs) of the error parameters. All simple and feasible measurements in practice are given, and identification analysis of the set of the MLCs for each measurement is carried out. According to identification analysis results, both measurement costs and observability are considered, and a step calibration including step measurement, step identification and step error compensation is determined. The linear forecast real-time error compensation is used to compensate the end-effector errors caused by other parameters after the step kinematic calibration. Taking the advantages of the step kinematic calibration and the linear forecast real-time error compensation, a method for improving the precision of the 2-DOF planar parallel manipulator is developed. Experiment results show that the proposed method is robust and effective, so that the position errors are kept to the same order of the measurement noise. The presented method is attractive for the 2-DOF planar parallel manipulator and can be also applied to other parallel manipulators with fewer than six DOFs.

Porosity and Permeability Effects on Centerline Temperature Distributions, Peak Flame Temperature, Flame Structure, and Preheating Mechanism for Combustion in Porous Media

The applicability and usefulness of combustion in porous media is of much interest due to its competitive combustion efficiency and lower pollutants formation. In the previous works, the focus has been on the effects of combustion and heat transfer parameters such as excess air ratio, thermal power, solid conductivity, convective heat transfer coefficient, and radiation properties on centerline temperature and pollutant formations. A premixed combustion scheme and a fixed porous medium with constant geometrical parameters have been used in these works; therefore, the effects of porous material parameters have been less considered. In this research, the effects of geometrical parameters of porous medium, namely porosity and permeability, on centerline temperature distributions, peak flame temperature, flame structure, and gas mixture preheating have been investigated by numerical methods. To this, a two-dimensional axis-symmetric physical model of porous burner is considered. As the most typical porous burners, a two stage one which has preheating porous zone (PPZ) and combustion porous zone (CPZ) is studied. The continuity, momentum, energy, turbulence, and species transport equations are solved employing a one-step chemical reaction mechanism with an eddy-dissipation model for rate of reactions. The turbulence is modeled with two transport equations which are not considered in similar works. The combustion regime is assumed to be diffusion and combustion parameters are fixed in all cases. Porosity effects on the structure and temperature characteristic of the flame are probed in a wide range for PPZ and CPZ. Critical permeability is defined and permeability effects on flame characters in both of the preheating and combustion regions are studied thoroughly.

Influence of Spiral Angle on Heat Transfer during Condensation inside Spiralled Micro-Fin Tubes

This paper reports the influence of the spiral angle on the heat transfer performance during condensation inside spiraled micro-fin tubes having constant geometric parameters such as fin height, pitch, shape (apex angle), and fin number, as various papers previously published in this field had not clearly established this influence. Tests were conducted for condensation of R-22, R-134a, and R-407C inside a smooth tube (9.52 mm outer diameter) and three micro-fin tubes with approximately the same diameter and spiral angles of 10°, 18°, and 37°, respectively. Experimental results indicated a heat transfer augmentation with spiral angle increase. A new semi-empirical predictive correlation was developed for the practical design of spiraled micro-fin tubes. The proposed new correlation predicted the majority of experimental results of the present study within a deviation zone of ±20 percent.

Design and Analysis of Crosshead Annular Die for Braided Medical Tubing Extrusion

A theoretical method is proposed for optimum design of a crosshead annular die used for medical tubing. According to this method, the geometric variables are determined to minimize the change in gapwisely-averaged flow velocities due to the variation in flow patterns inside the transitional region of the flow channel of the die, namely the gum space. To achieve this, a numerical approach to flow analysis is put forward based upon the simplified motion and energy equations as well as the approximation of the flow channel using a series of varying annular slits, each having constant geometric parameters. Accordingly, the numerical schemes for flow analysis and design optimization are established, and the computer program is developed using Microsoft Visual C ++ 6.0. For an optimum die design, the heat adhesion between the cold-fed inner tube and the hot melt during the over-extrusion is evaluated based upon the temperature rise and pressure profile of the melt in the die land. Based upon the optimum die design obtained from the method, the flow is well balanced with enhancement of extrusion quality. Also, it is found that the optimum die designs are less sensitive to extrusion conditions within a certain range.

Design and Analysis of Crosshead Annular Die for Braided Medical Tubing Extrusion

A theoretical method is proposed for optimum design of a crosshead annular die used for medical tubing. According to this method, the geometric variables are determined to minimize the change in gapwisely-averaged flow velocities due to the variation in flow patterns inside the transitional region of the flow channel of the die, namely the gum space. To achieve this, a numerical approach to flow analysis is put forward based upon the simplified motion and energy equations as well as the approximation of the flow channel using a series of varying annular slits, each having constant geometric parameters. Accordingly, the numerical schemes for flow analysis and design optimization are established, and the computer program is developed using Microsoft Visual C++ 6.0. For an optimum die design, the heat adhesion between the cold-fed inner tube and the hot melt during the over-extrusion is evaluated based upon the temperature rise and pressure profile of the melt in the die land. Based upon the optimum die design obtained from the method, the flow is well balanced with enhancement of extrusion quality. Also, it is found that the optimum die designs are less sensitive to extrusion conditions within a certain range.

Energy dependence in proton inelastic scattering

Differential elastic and inelastic scattering of protons from 92Mo was investigated under conditions chosen to emphasize the energy dependence of the cross sections in the region from 25–45 MeV. Elastic scattering data are described in terms of an optical-model potential with energy-dependent potential-well depths and constant geometrical parameters. Inelastic scattering cross sections are calculated in distorted-wave Born approximation with form factors given by the vibrational model for five low-lying eigenstates. Apart from a possible anomaly at the lowest energy studied, no evidence was obtained for an explicit dependence of deformation length on incident proton energy. The sensitivity of the deformation lengths to the details of the analysis is discussed.

Elastic and inelastic scattering of alpha particles onNi58andNi60in a broad range of energy and angle

The differential cross sections for ..cap alpha.. particles elastically and inelastically scattered from /sup 5/8Ni (at 29, 34, 38, and 58 MeV) and elastically scattered from /sup 6/0Ni (at 29 and 34 MeV), are measured together with excitation functions in the 25--38 MeV region at 178.5/sup 0/ lab. These data together with the data of 26.5, 32.3, 104, and 139 MEV for /sup 5/8Ni and 32.3 and 104 MeV for /sup 6/0Ni from other sources were analyzed using an optical model with volume and surface absorptions and the Saxon-Woods square form factors. The analysis yielded energy dependent depths of both real and imaginary parts of the potential and constant geometric parameters. The analytical expressions for depths of the real and both absorption potentials are obtained. The coupled channel calculations using the above optical potential were performed for the first excited state of /sup 5/8Ni. Both elastic scattering data and coupling with the first excited state of /sup 5/8Ni are well reproduced using the above potential in the wide scattering energy range.