Dissipation Coefficient Research Articles

Photothermal insulation polydimethylsiloxane coating based on phase change materials for anticorrosion applications

Phase change materials have potential to enhance the heat preservation properties of coatings. Herein, an assumption was proposed that the phase change material can store the heat generated by photothermal materials and release it near the phase transition temperature. A photothermal heat-preserving polydimethylsiloxane coating was prepared based on PEG@CuS phase change nanofillers, which was proven to have thermodynamic stability through molecular dynamics simulations. This composition exhibited thermodynamic stability, as evidenced by molecular dynamics simulations. In the composite coatings, CuS nanofillers generate heat through solar energy, while PEG stores heat via the phase change process. Due to the phase change process of nanofillers and the low heat dissipation coefficient of composite coating, the composite coatings demonstrate excellent heat preservation property as verified by finite element calculations. Furthermore, we investigated the water permeation processes and corrosion resistance of the coating using distribution of relaxation time analysis and finite element calculations. The results indicate that the composite coatings process a diffusion coefficient of approximately 1.99 × 10-15 m·s−1, providing water resistance for up 20 days. This strategy presents an innovative approach to extend the functionality of coatings in heat management function.

Anisotropic characteristics of layered backfill: Mechanical properties and energy dissipation

Layered backfill is commonly used in mining operations, and its mechanical behavior is strongly influenced by delamination parameters. In this study, 13 specimens with different numbers of delamination and delamination angle were prepared to investigate the anisotropic mechanical behavior, energy dissipation characteristics and crack development of backfill. P-wave velocity, uniaxial compression, scanning electron microscope (SEM), and acoustic emission (AE) experiments were conducted. The results indicate that: (1) The P-wave velocity has linear and elliptical relationships with the number of delamination surface and delamination angle, respectively; the strength, delamination parameters and P-wave velocity show a high degree of coincidence in terms of their function relationship, which can realize the rapid prediction of strength. (2) The microstructure of the delaminated surface is looser than that of the matrix, leading to a decrease in strength and an increase at the pore-fissure compaction stage. The number and angle of delamination increase linearly with the anisotropy coefficient. (3) The energy evolution in angle-cut backfill can be divided into four stages, with a decrease in the proportion of elastic energy at the initiation stress and peak stress with increasing number of delamination planes and delamination angle. (4) Crack development increases with the number of delamination surface and delamination angle, resulting in a decrease in energy dissipation coefficient and peak AE energy. These findings provide valuable insights for the design of filling materials and processes in mining operations.

An Experimental Study on the Heat and Mass Transfer Characteristics of an Evaporative Cooler

To study the heat and mass transfer characteristics of an evaporative cooler for cooling high-temperature working fluids, an experimental device of the evaporative cooler was built, and a corresponding test system was constructed. Then, the experimental study was carried out based on an orthogonal experimental design, and the law and extent of the influence of water flow in the tube, the spray water flow rate, the inlet water temperature in the tube, and the air flow rate on the heat dissipation, cooling efficiency, and heat and mass transfer coefficients were obtained. The correlation equations of the heat and mass transfer coefficients were obtained by fitting the orthogonal experimental data, and the validity of the correlation equations was confirmed by the verification experiment.

Experimental investigation and modeling on the supersaturated total dissolved gas (TDG) dissipation in aeration.

Supersaturated total dissolved gas (TDG) generation in rivers poses great harm to aquatic organisms. In this paper, 30 groups of supersaturated TDG dissipation experiments with aeration were carried out. These results showed that aeration actively promoted the dissipation of supersaturated TDG. The aeration rate decreased by 34.94% from 1.0 m3/h to 5.0 m3/h, the reduced proportion of aeration aperture was 35.51% from 215 mm to 260 mm, whereas the aeration depth increased by 16.93% from 0.4 m to 1.2 m for the TDG dissipation time required, resulting in corresponding the variation of TDG dissipation coefficients were 86.26%, 23.74% and -5.39%, respectively. In general, the effect on TDG dissipation is that the aeration rate is the largest, followed by the aeration aperture, and the aeration depth is the smallest. A quantitative relationship was established between TDG dissipation coefficient and aeration conditions, and followed a power function, while the aeration depth inhibited its dissipation. Moreover, what matters was that a numerical model was presented for predicting the TDG dissipation in Eulerian-Eulerian. When the parameter was β = 10.52, the error between the original experimental data and the simulated of a multiphase TDG dissipation model was 0.2%. The study provides essential scientific data for mitigating the harms of supersaturated TDG.

Oscillatory and regularized shock waves for a dissipative Peregrine–Boussinesq system

Abstract We consider a dissipative, dispersive system of the Boussinesq type, which describes wave phenomena in scenarios where dissipation plays a significant role. Examples include undular bores in rivers or oceans, where turbulence-induced dissipation significantly influences their behavior. In this study, we demonstrate that the proposed system admits traveling wave solutions known as diffusive-dispersive shock waves. These solutions can be categorized as oscillatory and regularized shock waves, depending on the interplay between dispersion and dissipation effects. By comparing numerically computed solutions with laboratory data, we observe that the proposed model accurately captures the behavior of undular bores over a broad range of phase speeds. Traditionally, undular bores have been approximated using the original Peregrine system, which, even though it doesn’t possess these as traveling wave solutions, tends to offer accurate approximations within suitable time scales. To shed light on this phenomenon, we demonstrate that the discrepancy between the solutions of the dissipative Peregrine system and the non-dissipative counterpart is proportional to the product of the dissipation coefficient and the observation time.

Hyperbolic field theory as a Lorentz covariant description for the dissipation

Based on the extension of the space of solutions for the D’Alambertian operator on the hyperbolic complex plane, we construct a formalism for the dissipative dynamics of two charged scalar fields, with explicit internal and background Lorentz symmetries, as opposed to the well-established scheme based on damping oscillators physics, which breaks down explicitly such a symmetry. The hyperbolic extension implies that the usual U(1) symmetry for charged scalar fields is extended with the incorporation of a non-compact SO(1,1) symmetry that will allow to describe the damping effects. As response properties of the interaction, the dissipation coefficients in time and in space are determined in the frequency-momentum space; the regimes with and without gapped energy–momentum states emerge; additionally the partition function and an entangled state generated by the dissipation are constructed. The pair of charged fields can be identified with field theories on asymptotic boundaries of gravitational backgrounds, and the possible holographic scenarios are discussed.

Revealing the hot deformation behavior of AZ42 Mg alloy by using 3D hot processing map based on a novel NGO-ANN model

The hot deformation behavior of AZ42 alloy was observed using thermal compression tests at a temperature scope of 250–400 °C and strain rate scope of 0.001–1 s−1. True stress-strain curves exhibited a combination of work hardening and dynamic softening features. A Northern Goshawk algorithm (NGO)-optimized artificial neural network (ANN) model was proposed. The established NGO-ANN model demonstrated impressive prediction accuracy, achieving a high determination coefficient of 0.991, a mean absolute percentage error of 3.51 %, and a root mean square error of 2.73. Subsequently, three-dimensional (3D) hot processing map based on the dynamic material model (DMM) theory was created. There were three different regions within the processing maps: the flow instability region (region A: 250–260 °C, 0.02–1 s−1, and region B: 300–400 °C, 0.01–0.1 s−1), high-power dissipation coefficient region (region C: 350–400 °C, 0.001–0.02 s−1, and region D: 300–350 °C, 0.5–1 s−1), and low power dissipation efficiency safety region (region E: the rest ones). Microstructural analysis revealed significant local plastic flow features in the flow instability region and a combination of coarse initial deformation grains and fine dynamic recrystallization (DRX) grains in the low power dissipation efficiency safety region. Fine and uniform grains were observed in the high-power dissipation efficiency region with DRX degree VDRX as high as 85.6 %, resulting in the best mechanical properties. Based on the established 3D hot processing map, the optimal process domains were determined.

A small-eddy-dissipation mechanism for turbulence modeling and application to wall-bounded flows

A small-eddy-dissipation (SED) mechanism is proposed in the present study for the development of turbulence models. According to the SED mechanism, a turbulence model introduces artificial dissipation to filter out small eddies so that a lower resolution mesh can be used in the simulation. In addition, the artificial dissipation should be applied outside the energy-containing range so that the large-scale motions are not affected. A small-eddy-dissipation mixing length (SED-ML) model is developed based on the SED mechanism to calculate wall-bounded flows. A local Reynolds number ys+=|det(∇u)|1/3/s is introduced in the SED-ML model to distinguish laminar flows from turbulent flows. Therefore, in addition to fully turbulent flows, the SED-ML model can also be used to calculate weakly turbulent or laminar flows. To demonstrate the performance of the SED-ML model, turbulent channel flows with the Reynolds numbers Reτ up to 4200 are simulated. The numerical results are extensively compared with the large eddy simulation (LES) results using the classical subgrid-scale models. The numerical results show that the SED-ML model predicts the statistical results with a good accuracy, while requiring a lower mesh resolution than the classical LES models. The accuracy of the calculated statistical results can be further improved by the parameter extension. The friction coefficient f for channel flows can be extended directly from the reference solution according to the relation ∂f/∂ϕ/f=−9, where ϕ is a dissipative strength coefficient. The energy and dissipation spectra confirm that the SED-ML model introduces significant dissipation at high wavenumbers. This feature is beneficial in maintaining the high accuracy of the simulation results and reducing the computational cost. The numerical study also shows that a sharp filtering of the turbulent kinetic energy in the wavenumber space is essential for the development of the turbulence model with high performance.

Theoretical and observational prescription of warm-inflation in FLRW universe with torsion

The paper deals with Warm Inflationary scenario in FLRW with torsion both from theoretical and observational point of view. In the background of flat FLRW model the Hubble parameter is found to be proportional to the torsion function and warm inflation is examined both in weak and strong dissipation regimes for the power law choice of potential using slow-roll approximation with quasi-stable criteria for radiation. The slow-roll parameters, no.of e-folds, scalar spectral index, and tensor-to-scalar ratio are determined in the present model for mainly three choices of the dissipation coefficient Gamma using the Planck data set. Finally, we focus on single-field chaotic quartic potential with the above choices of the dissipation coefficient to confront the warm inflation observational predictions directly with the latest observational data set.

Interaction between regular waves and floating breakwater with protruding plates: Laboratory experiments and SPH simulations

Overseas construction often adopts floating breakwaters as working platforms or wave attenuation. Laboratory and numerical investigations of the hydrodynamics during the interaction between regular waves and floating breakwater with protruding plates were conducted. By coupling DualSPHysics and MoorDyn, the motion of the floating structure under the mooring system is realized. The accuracy of the coupling model is verified by comparing the free surface elevation and floating motion. The effects of protruding types and plate length on the performance of the floating breakwater are analyzed. The results show that the reflection and dissipation coefficients increase with the increase of plate length. Under medium-long period waves, the wave attenuation of floating breakwater with protruding plates is weak. Horizontal protruding plates are more capable of restraining sway than vertical plates. Under the large draft, the horizontal protruding plates are more effective in suppressing the roll.

Numerical and Theoretical Analyses of Friction-Oval Section Mild Steel Rod Composite Dampers

In order to improve the seismic and energy dissipation capacity of the whole structure, a friction-oval section mild steel rod composite damper (FOSRCD) was proposed, and its working principle was clarified. The finite element analysis of FOSRCD was carried out, and the effects of friction, frequency and displacement on the damper performance were studied. Considering the structural characteristics of FOSRCD and the mechanical models of friction dampers and mild steel rod dampers, the restoring force model of the composite dampers was proposed and compared with the numerical simulation results. The results showed that the FOSRCDs had good performance and could provide stable energy dissipation capacities in both directions, with the energy dissipation coefficient exceeding 2.3 and the equivalent damping ratio exceeding 0.37. The theoretical analysis results were in good agreement with the numerical simulation results, which verified the theoretical restoring force model; the FOSRCDs make full use of the friction energy dissipation and the shear and bending energy dissipations of the mild steel rod. It enables the two dampers to work together to achieve the purpose of multi-stage energy dissipation. FOSRCD’s structure allows it to dissipate energy in both the X- and Y-directions. The composite dampers have a variety of restoring force models and can be utilized in a wide range of practical applications.

Experiment study on seismic performance and size effect in BFRP-RC squat shear walls with different horizontal reinforcement ratios

Focusing on the combined effects of the horizontal reinforcement ratio and the structural size on the seismic performance of BFRP reinforced concrete (BFRP-RC) shear walls, the present study experimented on six shear walls with different structural sizes up to 1800 mm × 1800 mm × 240 mm (length × height × thickness) having various horizontal reinforcement ratios of 0.25% and 0.50%. From the experiment, it is concluded that: (1) the failure modes of the specimens with horizontal reinforcement ratios of 0.25% and 0.50% are mainly shear failure and compressive-shear failure, respectively. (2) When the length of the specimen increases from 600 mm to 1800 mm, the nominal cracking, elastic and shear strength of shear walls with the horizontal reinforcement ratio of 0.25% (resp. 0.50%) decreases by 66% (resp. 59%), 30% (resp. 29%) and 28% (resp. 24%), respectively. The results demonstrate that the size effect on the BFRP-RC shear wall is significant. Meanwhile, the ductility coefficients decreased by 19% (resp. 22%), and energy dissipation coefficients decreased by 39% (resp. 18%). (3) When the horizontal reinforcement ratio increases from 0.25% to 0.50%, the nominal shear strength of specimens with lengths of 600 mm, 1200 mm and 1800 mm increases by 14%, 15% and 19%. It is worth noting that the size effect is significantly suppressed with the increase of horizontal reinforcement ratios. Besides, the good consistency found between the experiments and the size effect law proposed by Jin et al. allows the validation of the accuracy and rationality of the size effect law.

Determination of Formulae for the Hydrodynamic Performance of a Fixed Box-Type Free Surface Breakwater in the Intermediate Water

A two-dimensional viscous numerical wave tank coded mass source function in a computational fluid dynamics (CFD) software Flow-3D 11.2 is built and validated. The effect of the core influencing factors (draft, breakwater width, wave period, and wave height) on the hydrodynamic performance of a fixed box-type free surface breakwater (abbreviated to F-BW in the following texts) are highlighted in the intermediate waters. The results show that four influence factors, except wave period, impede wave transmission; the draft and breakwater width boost wave reflection, and the wave period and wave height are opposite; the draft impedes wave energy dissipation, and the wave height is opposite; the draft and wave height boost the horizontal extreme wave force; four influence factors, except the draft, boost the vertical extreme wave force. Finally, new formulas are provided to determine the transmission, reflection, and dissipation coefficients and extreme wave forces of the F-BW by applying multiple linear regression. The new formulas are verified by comparing with existing literature observation datasets. The results show that it is in good agreement with previous datasets.

Heat Transfer Performance of Water-cooled Heat Sink for I&C System Controller Chip in Nuclear Power Plant

To improve the heat dissipation reliability of the nuclear power control system chip, the structure of its water-cooled heat sink is compared and analyzed. Three schemes of water-cooled heat sinks are proposed, and CFD analyzes the heat dissipation performance of the heat sink. The simulation data of the heat transfer coefficient, pressure loss, and heat sink comprehensive coefficient are compared. The results show that the average temperature of the bottom surface of the three heat sinks tends to be flat with the flow velocity increase, and the heat dissipation coefficient Nu is also the same. The S-type heat sink has a higher heat transfer coefficient and lower average bottom temperature. The pressure loss of the S-type heat sink is much higher than that of the other two schemes with the increased flow rate, and the system resistance is large. By calculating the comprehensive coefficient of the heat dissipation process of the three heat sinks and considering the heat dissipation capacity and other factors, it is considered that the circular fin heat sink can be the optimal solution.

Contribution to the Characterization of Vibration Isolators Based on Metal Mesh

The prediction of the behavior of vibration isolators is essential for effective and efficient design of these devices, as well as for accurately characterizing the isolator behavior. In this work, an experimental study was performed to characterize the behavior of metal-mesh isolators. Although these elements’ performance is of great interest because of their usage in several applications, their characterization is complex due to their nonlinear nature, among other factors. This study’s aim was to obtain the quasi-static behavior of these isolators, although dynamic tests are required for their complete characterization. These quasi-static tests allowed for the highlighting of some characteristics in a simpler and faster manner and also provided a starting point for designing future dynamic tests. The quasi-static tests performed resulted in the calculation of the hysteresis cycle under different operating conditions and manufacturing parameters. The study of different insulator characteristics, such as the energy dissipation coefficient and stiffness, led to interesting conclusions about the isolator performance. From the results, it was observed that the relative density affected most the nonlinear behavior of the insulator. Moreover, to correctly characterize their behavior, not only the Coulomb’s damping but also the viscous damping had to be considered.

Molecular Modeling of Supercritical Processes and the Lattice—Gas Model

The existing possibilities for modeling the kinetics of supercritical processes at the molecular level are considered from the point of view that the Second Law of thermodynamics must be fulfilled. The only approach that ensures the fulfillment of the Second Law of thermodynamics is the molecular theory based on the discrete–continuous lattice gas model. Expressions for the rates of the elementary stage on its basis give a self-consistent description of the equilibrium states of the mixtures under consideration. The common usage today of ideal kinetic models in SC processes in modeling industrial chemistry contradicts the non-ideal equation of states. The used molecular theory is the theory of absolute reaction rates for non-ideal reaction systems, which takes into account intermolecular interactions that change the effective activation energies of elementary stages. This allows the theory to describe the rates of elementary stages of chemical transformations and molecular transport at arbitrary temperatures and reagent densities in different phases. The application of this theory in a wide range of state parameters (pressure and temperature) is considered when calculating the rates of elementary bimolecular reactions and dissipative coefficients under supercritical conditions. Generalized dependencies are calculated within the framework of the law of the corresponding states for the coefficients of compressibility, shear viscosity, and thermal conductivity of pure substances, and for the coefficients of compressibility, self- and mutual diffusion, and shear viscosity of binary mixtures. The effect of density and temperature on the rates of elementary stages under supercritical conditions has been demonstrated for a reaction’s effective energies of activation, diffusion and share viscosity coefficients, and equilibrium constants of adsorption. Differences between models with effective parameters and the prospects for developing them by allowing for differences in size and contributions from the vibrational motions of components are described.

Sill Role Effect on the Flow Characteristics (Experimental and Regression Model Analytical)

This study investigates the effects of gate openings and different sill widths on the sluice gate’s energy dissipation and discharge coefficient (Cd). The physical model of the sills includes rectangular sills of different dimensions. The results show that the gate opening size is inversely related to the Cd for a gate without a sill. In addition, increasing the gate opening size for a given discharge decreases the relative energy dissipation, and increasing the Froude number increases the relative energy dissipation. The results also show that the Cd and relative energy dissipation decrease when the width of the sill is decreased, thus increasing the total area of the flux flowing through the sluice gate and vice versa. According to the experimental results, the relative energy dissipation and the Cd of the sluice gate are larger for all sill widths than without the sill. Finally, non-linear polynomial relationships are presented based on dimensionless parameters for predicting the relative energy dissipation and outflow coefficient.

Experimental and Numerical Study of the Nonlinear Evolution of Regular Waves over a Permeable Submerged Breakwater

The permeable submerged breakwater has gained popularity in recent days due to its merits of reducing incident wave energy without negatively impacting the aesthetics of the ocean view and allowing for water exchange. However, the effect of porosity on wave nonlinearity and turbulence motion close to the water/structure interface is not well resolved in the literature. This paper presents an experimental and numerical study of regular wave propagation over a permeable submerged breakwater with a wide top width. The laboratory experiments were conducted in a wave flume and included 45 test cases. The numerical simulations were performed utilizing validated olaFoam. The results show that the nonlinearity of the waves on the permeable submerged breakwater is weak, which can effectively suppress and reduce the second harmonic waves. A large amount of turbulent kinetic energy exists at the interface between the permeable submerged breakwater and the water body, which helps to dissipate wave energy. For the wider permeable submerged breakwater in this paper, the wave dissipation capacity is greatest when the porosity is between 0.2 and 0.3, and as the length of the breakwater increases, the energy transmission coefficient decreases, and the energy dissipation coefficient increases. Better wave attenuation is achieved when the permeable submerged breakwater has a certain porosity and a large width.

An experimental study on heat power stored by thermal dissipation in electronic components using thermosyphon integrated hybrid nanocomposite phase change material

This study investigates the heat power stored by the thermal dissipation of electronic components using a thermosyphon integrated hybrid nanocomposite phase change material storage system. The study examines various thermal performances including the percentage of thermal dissipation, thermal resistance and heat transfer coefficient using benzene, deionized water, methanol and methyl acetate as heat transfer fluids, with an intended heat input of 50 – 120 W. The 0.5 wt% copper-titania hybrid nanocomposite particles are dispersed with phase change material (methyl cinnamate) and chosen as hybrid nanocomposite phase change material. The assessment of charging and retrieving characteristics of stored hybrid nanocomposite phase change material has been done by the impact of heat transfer fluids flowing through the copper tube at the different heat inputs. The result findings show that methyl acetate has the maximum percentage of thermal dissipation, low thermal resistance and high heat transfer coefficient of about 99.2 %, 0.311 K/W and 242.36 W/(m2.K) respectively at 120 W. The obtained results are attributed to the low boiling point and enthalpy of vapourization of methyl acetate. The highest heat power stored by hybrid nanocomposite phase change material is discovered as 6.5 W during melting by the impact of vapourized methyl acetate at maximum heat input owing to the higher mass flow rate and lesser time to attain steady state temperature of hybrid nanocomposite phase change material. Also, the developed system promotes thermal management in electronic components along with a minimum power saving of about 5–6 %.

Analysis of submerged breakwater models using ripple tank

A breakwater is an infrastructure that functions to dampen wave energy. To secure the area directly adjacent to the coast, an effective breakwater model is needed based on the analysis of the dissipation coefficient value ( ). This study aims to determine a good breaker model based on the value using a ripple tank. The data analyzed were wave heights before and after passing through the breakwaters of the three concrete models whose arrangement was varied. The results showed that the breaker model that is effective in reducing wave energy is the Grooved cube model with holes arranged horizontally based on the resulting small reflection coefficient ( ) and transmission coefficient ( ) values and large values