Geometric Factors Research Articles

Exploring the thermoluminescence characteristics of smartphone screen safety glasses for retrospective dosimetry applications

In clinical settings, standard dosimeters might miss radiation mishaps. Retrospective dosimeters could help to track personnel (such as patients and other staff who don't wear dosimeters) exceeding safe limits and assess long-term exposure trends. This study has investigated key thermoluminescence (TL) dosimetric characteristics, including the glow curve structure, dose-response, energy dependence, sensitivity and fading of various safety glasses that are used as screen protectors of smartphones subjected to photon irradiation. Among the studied glasses, the HD Anti-Peep safety glass for iPhone has been found to exhibit a linear dose-response with a regression coefficient of 99% within the dose range of 2–10 Gy. Moreover, all the safety glasses showed independence with respect to photon energy of 6 MV and 10 MV. The TL glow curves of the samples showed a broad glow peak between 125 °C and 325 °C at 10 Gy. The TL kinetic parameters of the safety glasses were also studied by analyzing the glow curves using the peak shape and initial rise method. The geometric factor (μg) is found to be within the range of 0.43–0.53, which indicates the suitability of applying Chen's general-order formula to calculate the kinetic parameters such as activation energy, frequency factor and trap lifetime. The activation energy (E) and frequency factor (s) are found in the range of 0.31–0.54 eV and 4.55 × 103 to 2.12 × 106 s−1 respectively obtained via the peak shape method. The relatively long trap lifetime and observed thermoluminescence features indicate that the HD Anti-Peep safety glass offers a better option to estimate dose retrospectively to ensure the safety of human health.

Influences of grain orientation on high-cycle fatigue performance of laser powder bed fused Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy at room temperature and 500℃

The fatigue performance of titanium (Ti) alloys fabricated by laser powder bed fusion (LPBF) is a crucial factor influencing the structural safety in service. The high-cycle fatigue (HCF) of LPBF Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy at the room temperature and 500 °C was tested. Compared with the room-temperature samples, the fatigue strength of fatigue samples tested at 500 °C is reduced by about 55.8 % after 106 fatigue cycles. Crack initiation on the surface is mainly related to fatigue after fewer cycles under high stress, while interior cracks initiate after a longer fatigue life under low stress. Electron back scattering diffraction (EBSD) was adopted to characterize the orientations of grains on the crack propagation paths and the activated slip systems. All prismatic oriented grains were found to activate prismatic slip systems, the activation of which achieves symmetric slips surrounding crack tips, forms ductile striations, and increases energy absorption during crack propagation. These characteristics are conducive to improved fatigue performance. About half of the basal oriented grains activate prismatic slip systems. These activated prismatic slip systems not only have a high Schmid factor (SF) but also need to have a high geometrical compatibility factor with slip systems activated by adjacent grains. The residual β phase and α phase are aligned according to the Burgers orientation relationship (BOR), so the β phase does not alter the direction of crack propagation. The results were used to predict the fatigue crack propagation paths in LPBF Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy during loading along building and transverse directions were predicted. This, to some extent, provides a basis for comparing fatigue performance of LPBF Ti alloys in different directions.

A Fully-correlated Anisotropic Micrograin BSDF Model

We introduce an improved version of the micrograin BSDF model [Lucas et al. 2023] for the rendering of anisotropic porous layers. Our approach leverages the properties of micrograins to take into account the correlation between their height and normal, as well as the correlation between the light and view directions. This allows us to derive an exact analytical expression for the Geometrical Attenuation Factor (GAF), summarizing shadowing and masking inside the porous layer. This fully-correlated GAF is then used to define appropriate mixing weights to blend the BSDFs of the porous and base layers. Furthermore, by generalizing the micrograins shape to anisotropy, combined with their fully-correlated GAF, our improved BSDF model produces effects specific to porous layers such as retro-reflection visible on dust layers at grazing angles or height and color correlation that can be found on rusty materials. Finally, we demonstrate very close matches between our BSDF model and light transport simulations realized with explicit instances of micrograins, thus validating our model.

Tribological Behaviour of Cross-Shaped Dimples on Sliding Surfaces Under Hydrodynamic Lubrication

Abstract This study reports on the tribological behaviour of sliding surfaces having cross-shaped micro-dimples on a surface. One wall is smooth and moving at a constant speed against the other fixed wall with dimples. The laser machine helps to create the desired dimples on the surface of the fixed wall. For the purpose of generating hydrodynamic pressure and tribological behaviour, the effects of cross-shaped dimples and oriented cross-shaped dimples have been compared with circular-shaped dimples. Additionally, the impact of sliding speed, dimple area density and depth on tribological behaviour was examined. The findings show that compared with a circular-shaped dimple, an unconventional cross-shaped and orientated cross-shaped dimple generates a higher net hydrodynamic pressure in the fluid domain and offers superior stability between the sliding surfaces. It has been demonstrated that geometrical factors like dimple depth and area density as well as operational factors like sliding speed have a substantial impact on the hydrodynamic average pressure and tribological behaviour of sliding surfaces. The experimental findings indicate that, for the same geometric and operating parameters, cross- and orientated cross-shaped dimples have a 20%–25% lower friction coefficient between the sliding surfaces than circular dimples. The results of the experiment support those of the analysis and CFD.

Transport properties through alternating borophene and graphene superlattices

The electronic transport properties of two junctions (BGB, GBG) made of borophene (B) and graphene (G) are investigated. Using the transfer matrix method with Chebyshev polynomials, we have studied single and multiple barriers in a superlattice configuration. We showed that a single barrier exhibits remarkable tilted transport properties, with perfect transmission observed for both junctions under normal incidence. We found that robust superlattice transmission is maintained for multiple barriers, particularly in the BGB junction. It turns out that by varying the incident energy, many gaps appear in the transmission probability. The number, width, and position of these transmission gaps can be manipulated by adjusting the number of cells, incident angle, and barrier characteristics. For diffuse transport, we observed considerable variations in transmission probability, conductance and the Fano factor, highlighting the sensitivity of these junctions to the physical parameters. We showed different behaviors between BGB and GBG junctions, particularly with respect to the response of conductance and Fano factor when barrier height varies. For ballistic transport, we have seen that the minimum scaled conductance is related to the maximum Fano factor, demonstrating their control under specific conditions of the physical parameters. Analysis of the length ratio (geometric factor) revealed some remarkable patterns, where scaled conductance and the Fano factor converged to certain values as the ratio approached infinity.

STATIC BENDING RESPONSE OF COMPOSITE PLATES RESTING ON VARIABLE ELASTIC FOUNDATIONS

This article introduces a finite element approach for examining the static bending behavior of composite plates. The method considers the variable mechanical characteristics of plates and utilizes an elastic foundation with varying stiffness values. The plate's calculation expressions and equilibrium equations are derived using the new style shear deformation theory. The article uses a mesh composed of four-node rectangular components to solve the equilibrium equation. Each node in the mesh has six degrees of freedom. The solution's dependability and convergence are confirmed by comparing it with previously published findings. Based on this premise, the study presents numerical findings that examine how various geometric factors, materials, boundary conditions, and elastic foundations affect the static bending behavior of composite panels. This research is a great resource for engineers, providing excellent guidance for the design, production, and utilization of these structures in real-world applications.

Constitutive model of die-cast light-alloy thin-walled parts considering geometric imperfection

Replacing steel with aluminum and shifting from forging to casting have become important means of automotive lightweight. Large integrated die-cast parts are gaining popularity among original equipment manufacturers. Engineers often ignore the influence of geometric imperfection on mechanical properties when simulating strength of thin-walled parts, therefore causing a bias. To investigate the relation between geometric imperfections and mechanical properties of die-cast light alloy, quasi-static tensile tests are conducted on the specimens of JDA1b aluminum alloy and JDM1 magnesium alloy. The specimens exhibit varying geometric imperfection factors (from 0 to 90 %) achieved by introducing circular holes with different diameters. The results show that the strength and elongation of JDA1b and JDM1 alloys decrease significantly as the geometric defect factor increases. Even small holes can significantly affect tensile strength. A constitutive model that incorporates the stress limit value and geometric imperfection factors is proposed, which has higher accuracy than the J–C model. Experiments and simulations on a die-cast thin-walled part validated the idea and proposed constitutive model. These findings provide essential insights into the influence of structural holes on the mechanical properties of die-cast light-alloy materials. The proposed constitutive model offers high-precision computational support for simulating the mechanical performance of parts.

Adiabatic driving, geometric phases, and the geometric tensor for classical states

We use the Hilbert space formulation of classical mechanics, known as the Koopman–von Neumann formalism, to study adiabatic driving, geometric phases, and the geometric tensor for classical states. In close relation to what happens to a quantum state, a classical Koopman–von Neumann eigenstate will acquire a geometric phase factor expiΦ after a closed variation of the parameters λ in its associated Hamiltonian. The explicit form of Φ is then derived for integrable systems, and its relation with the Hannay angle is shown. Additionally, we use quantum formulas to write an adiabatic gauge potential that generates adiabatic unitary flow between classical eigenstates, and we explicitly show the relationship between the potential and the classical geometric phase. We also define a classical analog of the geometric tensor, thus defining a Fubini–Study metric for classical states, and we use the singularities of the tensor to link the transition from Arnold–Liouville integrability to chaos with some of the mathematical formalism of quantum phase transitions. While the formulas and definitions we use originate in quantum mechanics, all the results found are purely classical, no classical or semiclassical limit is ever taken.

A novel magnet system—which enables uniformity of radial flux density by means of a parabolic yoke—applied in the Planck-Balance

Abstract A uniform magnetic flux density that is effective in the movement range of the coil is essential for accurate Kibble balance experiments. By utilizing Hopkinson’s law and Kirchhoff’s circuit laws, basic formulas have been derived, providing a method to calculate the magnetic flux density distribution in the airgap of a cylindrical magnet system. A parabolic outer contour of the inner yoke has been found to be a suitable solution to achieve uniformity. Experiments show, that this approach results in a relative change of magnetic flux density in the order of 3 ⋅ 10 − 4 per 8 mm movement range, using a magnet system with a mass of only 2.3 kg. Therefore, the system will be integrated into the upgraded version of PTB’s Planck-Balance—a compact variant of a Kibble balance—aiming for sub 1 ⋅ 10 − 6 accuracy level determination of the geometric factor. The solution described provides a comparatively easy means to design a cylindrical magnet system, using only one permanent magnet disc, without the use of complex simulation software.

Quantitative Analysis of Primary Compressive Trabeculae Distribution in the Proximal Femur of the Elderly.

As osteoporosis progresses, the primary compressive trabeculae (PCT) in the proximal femur remains preserved and is deemed the principal load-bearing structure that links the femoral head with the femoral neck. This study aims to elucidate the distribution patterns of PCT within the proximal femur in the elderly population, and to assess its implications for the development and optimization of internal fixation devices used in hip fracture surgeries. This is a retrospective cohort study conducted from March 2022 to April 2023. A total of 125 patients who underwent bilateral hip joint CT scans in our hospital were enrolled. CT data of the unaffected side of the hip were analyzed. Key parameters regarding the PCT distribution in the proximal femur were measured, including the femoral head's radius (R), the neck-shaft angle (NSA), the angle between the PCT-axis and the head-neck axis (α), the distance from the femoral head center to the PCT-axis (δ), and the lengths of the PCT's bottom and top boundaries (L-bottom and L-top respectively). The impact of gender differences on PCT distribution patterns was also investigated. Student's t-test or Mann-Whitney U test were used to compare continuous variables between genders. The relationship between various variables was investigated through Pearson's correlation analysis. PCT was the most prominent bone structure within the femoral head. The average NSA, α, and δ were 126.85 ± 5.85°, 37.33 ± 4.23°, and 0.39 ± 1.22 mm, respectively, showing no significant gender differences (p > 0.05). Pearson's correlation analysis revealed strong correlations between α and NSA (r = -0.689, p < 0.001), and R and L-top (r = 0.623, p < 0.001), with mild correlations observed between δ and NSA (r = -0.487, p < 0.001), and R and L-bottom (r = 0.427, p < 0.001). Importantly, our study establishes a method to accurately localize PCT distribution in true anteroposterior (AP) radiographs of the hip joint, facilitating precise screw placement in proximal femur fixation procedures. Our study provided unprecedented insights into the distribution patterns of PCT in the proximal femur of the elderly population. The distribution of PCT in the proximal femur is predominantly influenced by anatomical and geometric factors, such as NSA and femoral head size, rather than demographic factors like gender. These insights have crucial implications for the design of internal fixation devices and surgical planning, offering objective guidance for the placement of screws in hip fracture treatments.

The roles of symmetry and elongation in developing reference frames.

Previous studies showed that elongation and symmetry (two ubiquitous aspects of natural stimuli) are important attributes in object perception and recognition, which in turn suggests that these geometrical factors may contribute to the selection of perceptual reference-frames. However, whether and how these attributes guide the selection of reference-frames is still poorly understood. The goal of this study was to examine systematically the roles of elongation and symmetry, as well as their combination, in the selection of reference axis and how these axes are developed for unfamiliar objects. We designed our experiments to eliminate two potential confounding factors: (i) extraneous environmental cues, such as edges of the screen, etc. (by using VR) and (ii) pre-learned cues for familiar objects and shapes (by using reinforcement learning of novel shapes). We used algorithmically generated textures with different orientations having specified levels of symmetry and elongation as the stimuli. In each trial, we presented only one stimulus and asked observers to report if the stimulus was in its original form or a flipped (mirror-image) one. Feedback was provided at the end of each trial. Based on previous studies on mental rotation, we hypothesized that the selection of a reference-frame defined by symmetry and/or elongation would be revealed by a linear relationship between reaction-times and the angular-deviation from either the most symmetrical or the most elongated orientation. Our results are consistent with this hypothesis. We found that subjects performed mental rotation to transform images to their reference axes and used the most symmetrical or elongated orientation as the reference axis when only one factor was presented, and they used a "winner-take-all" strategy when both factors were presented, with elongation being more dominant than symmetry. We discuss theoretical implications of these findings, in particular in the context of "canonical sensorimotor theory."

Investigation of structural and TL kinetic parameters of smartphone screen protector glasses for applications in retrospective dosimetry

The study evaluated the structural and thermoluminescence (TL) kinetic parameters of smartphone screen protector glasses in order to use them for post-accident dose reconstruction from unplanned nuclear events. The fact that most individuals use mobile phones in working environments including nuclear power plant sites, served as the impetus for the study. The TL glow curves indicate the physical properties of the defects involved in the luminescence process; therefore, they have been analyzed to study the TL kinetic parameters by employing peak shape, initial rise and glow curve deconvolution method within the dose ranges from 2 to 50 Gy. The geometric factor (μg) ranges between 0.46 and 0.56, suggesting that Chen's general-order method can be used to compute the kinetic parameters, including activation energy (E), frequency factor (s) and trap lifetime (τ). The examined trapping parameters (E = 0.33–0.57 eV, s = 5.22E+03–8.65E+06 s−1 for peak shape and E = 0.36–0.96 eV, s = 2.90E+04–1.88E+11 s−1 for initial rise methods) suggest promise for TL dosimetry applications. Additionally, the observed lifetime (τ = 4.88E+5 s) implies the feasibility of dose reconstruction even several days after an accident, making it suitable for retrospective dosimetry. Micro-Raman spectroscopy revealed a clear correlation between increasing gamma radiation dose and microstructural damage. The analysis of intensity ratio (ID/ISi) for other components to silica, along with the area of deconvoluted micro-Raman spectra in high-frequency regions, indicated dose-dependent structural modifications and internal defect annealing. Further confirmation of structural alterations within the studied dose range was obtained through the analysis of crystallite size (Lc), dislocation density (δ), lattice strain (ɛ) and FWHM (Full Width at Half Maximum) from XRD (X-ray diffraction) patterns. These findings collectively suggest the potential of smartphone screen protector glass as a viable material for emergency dosimetry applications.

The hemodynamic and geometric characteristics of carotid artery atherosclerotic plaque formation.

Ischemic stroke, which has a high incidence, disability, and mortality rate, is mainly caused by carotid atherosclerotic plaque. The difference in the geometric structures of the carotid arteries inevitably leads to the variability in the local hemodynamics, which plays a key role in the formation of carotid atherosclerosis. At present, the combined mechanisms of hemodynamic and geometric in the formation of carotid atherosclerotic plaque are not clear. Thus, this study characterized the geometric and hemodynamic characteristics of carotid atherosclerotic plaque formation using four-dimensional (4D) flow magnetic resonance imaging (MRI). Ultimately, 122 carotid arteries from 61 patients were examined in this study. According to the presence of plaques at the bifurcation of the carotid artery on cervical vascular ultrasound (US), carotid arteries were placed into a plaque group (N=69) and nonplaque group (N=53). The ratio of the maximum internal carotid artery (ICA) inner diameter to the maximum common carotid artery (CCA) inner diameter (ICA-CCA diameter ratio), bifurcation angle, and tortuosity were measured using neck three-dimensional time-of-flight magnetic resonance angiography (3D TOF-MRA). Meanwhile, 4D flow MRI was used to obtain the following hemodynamic parameters of the carotid arteries: volume flow rate, velocity, wall shear stress (WSS), and pressure gradient (PG). Independent sample t-tests were used to compare carotid artery geometry and hemodynamic changes between the plaque group and nonplaque group. The ICA-CCA diameter ratio between the plaque group and the nonplaque group was not significantly different (P=0.124), while there were significant differences in the bifurcation angle (P=0.005) and tortuosity (P=0.032). The bifurcation angle of the plaque group was greater than that of the nonplaque group (60.70°±20.75° vs. 49.32°±22.90°), and the tortuosity was smaller than that of the nonplaque group (1.07±0.04 vs. 1.09±0.05). There were no significant differences between the two groups in terms of volume flow rate (P=0.351) and the maximum value of velocity (velocitymax) (P=0.388), but the axial, circumferential, and 3D WSS values were all significantly different, including their mean values (all P values <0.001) and the maximum value of 3D WSS (P<0.001), with the mean axial, circumferential, 3D WSS values, along with the maximum 3D WSS value, being lower in the plaque group. The two groups also differed significantly in terms of maximum PG value (P=0.030) and mean PG value (P=0.026), with these values being greater in the nonplaque group than in the plaque group. A large bifurcation angle and a low tortuosity of the carotid artery are geometric risk factors for plaque formation in this area. Low WSS and low PG values are associated with carotid atherosclerotic plaque formation.

Optimizing a dew point evaporative cooler in data center applications

Abstract The escalating energy consumption of data centers has led to a pressing need for energy-efficient cooling solutions. This paper presents a countercurrent dew point evaporative cooler (DPEC) for data center refrigeration. We developed and experimentally validated a numerical model for DPEC, then formulated regression models using the response surface method. These models link eight key design factors, including geometrical and operational factors, to three performance indices: cooling capacity per unit volume, coefficient of performance, and outlet primary air temperature. We assessed the extent of factor influence on these indices. By using these regression models as objective functions, we used the genetic algorithm for design optimization under two climatic conditions, resulting in various optimal parameter combinations. Our findings highlight the strong predictive accuracy of these models. In comparison to the original design, the optimal design achieved an improvement of 104.8%, an increase of 23.9%, and a reduction of 13.8% in the three indices.

Effect of Corrosion and Post-Weld Treatment on the Fatigue Behavior of Multipass Robot GMAW Welds of S700MC Steel

High-strength steel is a candidate material for offshore structures, which are currently being constructed with regular-strength steel. These structures are constantly exposed to harsh environmental conditions and experience cyclic loadings, which can lead to premature failure due to the synergistic effects of corrosion and fatigue. In this regard, the current study aims to investigate the effects of corrosion and High-Frequency Mechanical Impact (HFMI) treatment on the fatigue behavior of welded joints made of S700MC steel. Multipass butt-welded joints were fabricated via the Robot GMAW method at an optimally selected heat input of 0.7405 kJ/mm. The microstructure of the weldments was studied using light optical microscopy. Tensile and Vickers microhardness tests were performed to evaluate the mechanical properties of the welded joints. To simulate marine environment corrosion in the laboratory, the as-welded samples were exposed to salt fog spray for 720 h. Subsequently, specimens were subjected to cyclic loading to evaluate their fatigue strength, while SEM and stereomicroscopy were used to analyze the fractured surfaces, providing a comprehensive understanding of the fracture mode. The findings suggest that although corrosion led to increased surface roughness and the formation of corrosion pits, its influence on the fatigue behavior of the weldments might be less significant compared to other geometrical factors, at least for the exposure time employed in the study.

Investigation of geometric and material effects on the fatigue performance of composite and steel adhesive joints

This study experimentally investigates the combined effect of several parameters on the fatigue behaviour of adhesive bonded single lap joints, including: substrate material (steel, glass fibre reinforced polymer (GFRP) and carbon fibre reinforced polymer (CFRP)); adhesive material (epoxy and methacrylate); as well as joint geometry (overlap length and adhesive thickness).Results showed that despite the lower bulk strength of the ductile methacrylate adhesive, in terms of the ratio of fatigue load to ultimate failure load, joints bonded by this adhesive had a higher fatigue performance when compared to joints bonded by the epoxy one, with differences in fatigue life of up to 20 times for the same load ratio. In a similar substrate configuration, flexible GFRP substrates reduced the fatigue life of the joints bonded by the methacrylate adhesive more than 10 times when compared to steel joints for the same load. However, in a dissimilar configuration, an increase in fatigue life was observed which, based on a finite element analysis, was attributed to the ductility of the adhesive and its effects on the stress field. In CFRP joints bonded by the epoxy adhesive, a deterioration in fatigue performance was observed due to the occurrence of interfacial failure.Regarding the geometrical factors, increasing overlap length led to a decrease of the fatigue life for the same nominal shear stress. Similar trend was obtained for adhesive thickness. A parametric analysis revealed that overlap length is the parameter that affects more the fatigue performance of the joints.

Melt pool control-assisted additive manufacturing of thin-walled parts

Thin-walled aerospace components manufactured by laser directed energy deposition are susceptible to thermal accumulation effects owing to their deposition path and efficiency, further leading to the edge collapse. The melt pool width, as the carrier of thermal input, is an important geometric factor reflecting the state of the melt pool. Therefore, an in-situ melt pool control technique was proposed. The melt pool width as the control target was monitored using a coaxial camera, and the laser power was adjusted in real time based on the proportional-integral-derivative algorithm. A thermal accumulation model in conventional mode and a thermal suppression model in control mode were derived. The surface roughness, porosity, microstructure, and tensile properties of AISI 316 L stainless steel were compared between two modes. The results demonstrated that the roughness and porosity of thin-walled parts were respectively reduced by 45.3% and 82.7% after control. The periodic evolution of interlayer columnar and equiaxed crystals, and the increase in deformation twins contributed to a simultaneous increase in tensile strength and toughness, with a maximum increase of 35.7% in elongation.

Micromechanical analysis for effective elastic moduli and thermal expansion coefficient of composite materials containing ellipsoidal fillers oriented randomly

In this study, we examine to derive the solutions of effective elastic moduli and thermal expansion coefficient for composite materials containing ellipsoidal fillers oriented randomly in the material using homogenization theories, which are the self-consistent method and the Mori–Tanaka method. This analysis is carried out by micromechanics combining Eshelby’s equivalent inclusion method for each theory. The solutions for effective elastic moduli and thermal expansion coefficient obtained on each theory are expressed by common coefficients composed of both the physical properties of the constituents of the composite material and geometrical factors depending upon the shape of the fillers. Moreover, these solutions enable us to calculate effective elastic moduli and thermal expansion coefficient for composite materials that contain randomly oriented fillers of various shapes and physical properties. By taking the limit of eliminating the existence of the matrix for these solutions, we can derive effective physical properties of polycrystalline materials. Using the obtained solutions, we investigate the effects of the shape of the fillers on the effective elastic moduli and thermal expansion coefficient. As a result, we confirm that these effective properties fall within the lower and upper bounds, and find that a characteristic result appears when the shape of the fillers is flake or oblate. Through comparisons between the analytical and experimental results, we confirm the practical usability of the solutions obtained in this analysis. Furthermore, we determine originally the shape factor for the filler and can show that this factor has the potential to provide guidelines for the optimal design of filler shape to improve the effective elastic properties of materials.

Convective heat transfer coefficients models for biomass cylindrical particles from low to high aspect ratio

This study investigates the heat transfer of co-firing biomass in coal-fired power station boilers, with a focus on practical application for realistic particle shapes. At present, there are no heat transfer or Nusselt number (Nu) correlations available for biomass particles of cylindrical shape such as straw particles. In this study, a direct numerical simulation (DNS) of the heat transfer between cylindrical particles in a heated flow are performed with OpenFOAM-using a body-fitted mesh. The impact of the Reynolds number Re, aspect ratio AR, and angle of incidence θ in the range of (10 ≤ Re ≤ 2000, 1 ≤ AR ≤ 18, 0° ≤ θ ≤ 90°) on the Nusselt number are determined using a systematical analysis of the thermal flow characteristics for different particle temperature fields. The results show that the aerodynamics and geometrical factors of the cylindrical shape play a dominant role in the heat transfer. A model for the Nusselt number is proposed based on a curve fit of the simulation results, which has a root mean square error (RMSE) of 2.2 × 10-2 and an average relative error of 1.15 %. The independence test of the model has an average error of 5.1 %, indicating a high prediction accuracy. Compared to experimental and simulated data from the literature, the model demonstrates reasonable accuracy within its range of applicability, with a relative error of only 5.05 %. This study provides insights into the heat transfer of biomass particles with cylindrical shape and presents a new mathematical model for the Nusselt number, which can be used to improve the accuracy of the heat transfer prediction using point particle models.

Investigation of the effect of geometric configurations on natural convection heat transfer in external flow

AbstractThe complexities of natural convection heat transfer are investigated through experimentation, focusing on the influence of geometric configurations such as spheres, cylinders, and cubes in external flows. The study aims to understand how different geometries affect heat transfer coefficients, providing insights for architectural and engineering applications. Experimental results revealed significant variations in heat transfer efficiency among geometric models, with cubic configurations exhibiting the lowest heat transfer rates compared with spherical and cylindrical counterparts. This underscores the critical impact of geometric configuration on thermal performance and heat dissipation characteristics. The findings highlight the necessity of considering geometric factors in design processes to optimize thermal management strategies. The study contributes to a deeper understanding of convective heat transfer mechanisms, emphasizing the importance of precise geometric modeling in enhancing energy efficiency and sustainability in built environments