Dissipative Losses Research Articles

Ginseng‐Bioinspired 3D Photothermal Evaporator for Efficient Seawater Desalination Using Conjugated Microporous Polymer

AbstractPhotothermal conversion technology presents a promising approach for harnessing solar energy to facilitate seawater desalination. However, salts will accumulate on the surface of the photothermal conversion structure during seawater desalination, which hinders solar energy absorption. Meanwhile, the photothermal conversion structure directly immersing in a large water body results in a large heat dissipation loss. Both factors impair solar energy conversion and water steam generation. To address the issues, inspired by a ginseng plant (with a trunk‐to‐branch water supply system), a 3D cotton‐based photothermal evaporator with tunable water supply is facilely designed herein via simple cloak‐weaving of a porphyrin‐based conjugated microporous polymer (PPCMP) as the photothermal conversion material. The as‐designed 3D cloak‐like photothermal evaporator achieves an equilibrium between the water supply flux and evaporation rate via optimizing PPCMP weaving and the water path. As a result, a high evaporation rate of 2.81 kg m−2 h−1 and photothermal conversion efficiency of 155% are obtained under 1 sun illumination. The findings underline the importance of 3D porous organic polymer‐based fabrics as effective media for harnessing solar energy and highlight their potential for seawater desalination.

Research on the Flow Mechanism of a High-Loading Biomimetic Low-Pressure Turbine Cascade

The biomimetic turbine has an excellent flow drag reduction ability and wide incidence adaptability, so it has the potential to achieve high efficiency within a wide working range of high-performance variable cycle engines. A biomimetic cascade that can broaden the effective working incidence angles was designed based on a high-loading low-pressure turbine cascade, and its flow mechanism and aerodynamic performance were studied using experimental and numerical methods under the incidences angle (i) of 0° to 15° and Reynolds number of 1.0 × 105. A series of counter rotating vortex pairs induced by the biomimetic cascade bring additional dissipation losses, but it accelerates the energy exchange between the boundary layer and mainstream, enhancing the dissipation of the pressure side leg of horseshoe vortex, and thus suppressing the flow separation and passage vortices. The undulating surface of biomimetic cascades can suppress the expansion of secondary flow in a spanwise direction in the end region, especially for large-scale separation under high incidence conditions. When i < 5°, the loss of biomimetic cascades is slightly higher than that of the original cascades, but the increase is only 0.5%; when i > 5°, the losses of biomimetic cascades are significantly reduced, with a maximum reduction of 70% at i = 15°.

Designs of Optomechanical Acceleration Sensors with the Natural Frequency from 5 Hz to 50 kHz

In many applications, such as space navigation, metrology, testing, and geodesy, it is necessary to measure accelerations with frequencies ranging from fractions of a hertz to several kilohertz. For this purpose, optomechanical sensors are used. The natural frequency of such sensors should be approximately ten times greater than the frequency of the measured acceleration. In the case of triaxial acceleration measurements, a planar design with two sensors that measure accelerations in two perpendicular in-plane directions and a third sensor that measures out-of-plane acceleration is effective. The mechanical characteristics of the existing designs of both in-plane and out-of-plane types of sensors were analyzed, and the improved designs were elaborated. Using numerical simulation, the dependencies of the natural frequency level in the range from several hertz to tens of kilohertz on the designs and geometric parameters of opto-mechanical accelerometers were modeled. This allows one to select the accelerometer design and its parameters to measure the acceleration at the assigned frequency. It is shown that the opto-mechanical accelerometers of the proposed designs have reduced dissipation losses and crosstalk.

Numerical study of porous tip treatment in suppressing tip clearance vortices in cavitating flow

Tip clearance cavitation (TCC) is a type of vortex cavitation. It widely exists in axial flow hydraulic machinery and has significant negative influence on the mechanical service life and the operating stability. It is necessary to suppress the tip clearance vortices (TCV) to control the TCC in engineering applications. Based on the analysis of the advantages and disadvantages of the present various suppression strategies, a new coupling method is proposed in this study by combining the damping approach and the diversion approach. Porous medium material is used to realize the coupling effect. A 2 mm span length porous tip is installed on the solid tip surface of a hydrofoil under two gap sizes conditions (representing two types of gap flow pattern), and excellent suppression results of the TCV and TCC are obtained. The characteristics and mechanism of the clearance flow are analyzed by numerical simulation. The numerical accuracy is verified by experimental qualitative observations. The simulation results show that the temporal and spatial stability of the clearance flow field is enhanced, and the leakage velocity and the TCV strength are weakened via the combined action of damping and diversion effects. There is a difference in the damping mechanism between the two gap flow patterns. It is a comprehensive result of viscous dissipation and momentum loss in the jet pattern represented by the small gap size, and primarily, the result of momentum loss in the rolling pattern represented by the large gap size.

Strong field enhancement and ultra-narrow linewidth based on the coupling of anapole/gap modes in silicon nanodimer-ring arrays

All-dielectric metamaterials have recently received significant attention in the field of nanophotonics, due to their negligible dissipative losses and strong polariton response compared with metallic metamaterials. However, simultaneously achieving an ultra-narrow resonance linewidth and a significant field enhancement in the all-dielectric metamaterials is still a great challenge, limiting their further practical application. In this work, a novel nanostructure composed of silicon ring and nanodimer arrays is theoretically proposed and numerically simulated. Through introducing the coupling between the anapole mode originating from the ring arrays and the gap mode deriving from the nanodimer arrays, the as-designed dielectric metamaterial manifests dual-band high-quality resonance characteristics with strong electric field enhancement reaching up to 300 times, an ultra-narrow linewidth as narrow as 0.35 nm, and a large Q-factor of 4223.43 synchronously. Benefiting from the exceptional optical spectral characteristics, the proposed dielectric nanodimer-ring metamaterial can work as a high-available refractive index sensor, whose sensitivity can reach 307.69 nm RIU−1 with its figure of merit attaining 879.11 RIU−1, efficiently distinguishing an index change of less than 0.01. This research opens up a promising path for achieving extremely narrow spectral linewidth and significant enhancement of the electric field, exhibiting immense possibilities in applications such as biochemical sensing, nonlinear optics, and surface enhanced spectroscopy.

Estimating and reducing dissipative losses in thermal spray: A parametrized material flow analysis approach

Thermal spray is a family of surface engineering technologies necessary to meet technical functionalities of components under harsh environmental conditions. Those technologies come at the expense of dissipative losses of coating materials throughout the life cycle of components. Measuring these material losses has so far retained little attention in the field. This research provides a framework to estimate material dissipative losses in surface engineering applications based on specific parameters, mainly deposition efficiencies. We applied material flow analysis to quantify dissipative losses for the main metals used in thermal spray (Cr, Co, Mo, Ni, Si, W, Y and Zr). Results show that the coating process is the most contributing life cycle stage (up to 39% of the losses). Improving the deposition efficiency, recovering the unadhered and stripping the components at their end-of-life are key material efficiency strategies to reduce the material losses (up to 50%).

Efficient and Shape-Sensitive Manipulation of Nanoparticles by Quasi-Bound States in the Continuum Modes in All-Dielectric Metasurfaces.

Current optical tweezering techniques are actively employed in the manipulation of nanoparticles, e.g., biomedical cells. However, there is still huge room for improving the efficiency of manipulating multiple nanoparticles of the same composition but different shapes. In this study, we designed an array of high-index all-dielectric disk antennas, each with an asymmetric open slot for such applications. Compared with the plasmonic counterparts, this all-dielectric metasurface has no dissipation loss and, thus, circumvents the Joule heating problem of plasmonic antennas. Furthermore, the asymmetry-induced excitation of quasi-bound states in continuum (QBIC) mode with a low-power intensity (1 mW/µm2) incidence imposes an optical gradient force of -0.31 pN on 8 nm radius nanospheres, which is four orders of magnitude stronger than that provided by the Fano resonance in plasmonic antenna arrays, and three orders of magnitude stronger than that by the Mie resonance in the same metasurface without any slot, respectively. This asymmetry also leads to the generation of large optical moments. At the QBIC resonance wavelength, a value of 88.3 pN-nm will act on the nanorods to generate a rotational force along the direction within the disk surface but perpendicular to the slot. This will allow only nanospheres but prevent the nanorods from accurately entering into the slots, realizing effective sieving between the nanoparticles of the two shapes.

Multi-dimensional flow simulation analysis and kriging-based optimization study on thermodynamic process mechanism of pulse tube refrigerator with displacer

Pulse tube refrigerators with active displacers have become increasingly popular due to superior phase shift capability and avoidance of dissipation losses. However, mechanisms of thermodynamic processes within refrigerators due to variations in parameters related to critical structures and operations are not yet clear, making it difficult to optimize the comprehensive performance. In this paper, multi-dimensional flow simulation method instead of one-dimensional simulation method with poor computational accuracy is used to analyze the influence of five key parameters on performance of pulse tube refrigerators with active displacers. An intelligent optimization algorithm combined with efficient Kriging surrogate models is developed for single-objective and multi-objective optimization. Results demonstrate that the mean errors of the Kriging models for cooling capacity, total input power and performance coefficient are 1.81%, 3.94% and 3.37%. The single-objective optimization produces a maximum cooling capacity of 7.29 W and performance coefficient of 7.38%. The combined optimal solution delivers 6.65W in cooling capacity and 7.02% in performance coefficient, obtaining improvements of 150.94% and 75.94%. This study reveals the influence mechanism of key parameters on cooling performance of pulse tube refrigerators with displacers and establishes an efficient global optimization method, which is of great significance for the development of advanced refrigeration technology.

Optimization of Exergy Efficiency in a Walking Beam Reheating Furnace Based on Numerical Simulation and Entropy Generation Analysis

An analysis of entropy generation and exergy efficiency can effectively explore the energy-saving potential of reheating furnaces. This paper simulated the combustion, flow, and heat transfer in a walking beam reheating furnace by establishing a half-furnace model. The entropy generation rate distribution of different thermal processes was numerically calculated. The effect of slab residence time and fuel distribution in the furnace was studied to optimize exergy efficiency. The results indicated that combustion and radiative heat transfer are the primary sources of entropy generation. Irreversible losses accounted for 26.39% of the total input exergy, in which the combustion process accounted for 16.43%, and radiative heat transfer accounted for 8.47%. Reducing the residence time by 60 min decreased irreversible exergy loss by about 2.5% but increased heat dissipation and exhaust exergy loss by 5.8%. Energy saving can only be achieved when the heat exchanger’s exergy recovery efficiency exceeds 36% under different fuel supplies. Keeping the total fuel supply unchanged, increasing the fuel mass flow rate in heating-I zone while decreasing it in heating-II zone resulted in a 1.5% decrease in exergy efficiency. This study provides new insights into the energy-saving potential of reheating furnaces.

Effect of Sr-doping toward the optoelectrical ZnO properties

The current study focuses on how Sr doping affects ZnO's structural, optical, optoelectronic, transport, and dielectric properties. Sr-doped ZnO nanoparticles were produced using a simple sol-gel process with a hydrothermal step procedure. Regarding Zn content, the Sr-doping levels were 0, 0.025, 0.050, and 0.075. Based on XRD, SEM imaging, XPS, UV–visible diffuse reflectance (UV–Vis DRS) spectroscopy, FTIR-ATR, and photoluminescence (PL) spectroscopies, the physico-chemical properties were deduced. A study was done on the relationship between Sr-doping degree, optical, electrical, and thermal conductivities, as well as the dielectric characteristics. Surface and bulk contributions to dissipation loss were assessed. In consideration of photon energy contributions and material formulation, the dynamics of transport were studied. The contradictory effects of Sr are discussed according to the literature, and Sr impacts were situated to Ag and B atoms.

Quasi-classical dynamics of a charged particle under conditions of ionization losses in a weak magnetic field

The quasi-classical dynamics of a charged particle in a weak magnetic field in the presence of dissipative losses caused by ionization of the medium is studied. The approximate approach proposed here is a generalization of the Caldirola—Kanai method for quantizing the translational motion of particles in dissipative media. It is shown that a weak curvature of a classical trajectory by the magnetic field is accompanied by an isotropic increase of uncertainty of the particle coordinates to the some maximum value at the moment the localized probability density wave packet stops. The limitation of the increase of coordinate uncertainty is due to irreversible ionization losses.

A self-excited bistable oscillator with a light-powered liquid crystal elastomer

The nonlinearity in the dynamics of a liquid crystal elastomer-based systems plays an important role when designing and controlling a responsive LCE-based smart system. In this work, we proposed an LCE-based bistable oscillator and investigated its self-excited oscillation behavior. The oscillator consists of a lumped mass, connected by two lateral helical springs, and one liquid crystal elastomer fiber spring which is subjected to a steady light illumination. After inserting the dynamic model of the light-powered LCE fiber into that of the oscillator, the nonlinear vibration response is obtained by using a fourth-order Runge-Kutta method. Different from the reported mono-stable limit circle modes, the self-vibration has a snap-through oscillation mode owing to an opto-mechanical coupling where the light energy can overcome the potential well of the mechanical part. Since the light illumination energy compensates the dissipative energy loss in each nonlinear vibration period, the nonlinear vibration of the LCE-based bistable oscillator is sustainable. We discuss the influence of both the linear and nonlinear parameters on the self-excited vibration response of the bistable oscillator. The nonlinear parameters of the lateral spring, such as the stiffness ratio and the length ratio, as well as the linear parameters of the LCE fiber, including the damping ratio, spring stiffness, light intensity, light contraction coefficient, and gravity, are all taken into consideration in our analysis. Our results reveal that the self-excited vibration can be controlled by adequately tuning these linear and/or nonlinear parameters. The investigation may pave a way for promising applications such as intelligent structural design, energy harvesting, sensing, actuating, and bio-mimic/bio-inspired system using the LCE fiber.

Heat transfer characteristics of liquid cooling system for lithium-ion battery pack

To improve the thermal uniformity of power battery packs for electric vehicles, three different cooling water cavities of battery packs are researched in this study: the series one-way flow corrugated flat tube cooling structure (Model 1), the series two-way flow corrugated flat tube cooling structure (Model 2), and the parallel sandwich cooling structure (Model 3). Based on the fluid-solid coupling method, this study analyzes the cooling performance of the three models, including thermal uniformity, heat dissipation, and pressure loss. At a high discharge rate, compared with the series cooling system, the parallel sandwich cooling system makes the average temperature and maximum temperature of the battery pack decrease by 26.2% and 26.9% respectively, and the battery pack temperature difference decreases by 62%, and the coolant pressure loss decreases by 95.8%. The results show that the Model 3 overcomes the temperature accumulation caused by the series flow of coolant and achieves a better level of thermal uniformity while improving the heat dissipation and pressure loss performance. The research provides scholars and industries with a reference for upgrading thermal management and improving the stability of the power battery pack for electric vehicles, which has both theoretical and practical significance.

Synchronously enhancing thermal conductivity and dielectric properties in epoxy composites via incorporation of functionalized boron nitride.

Polymer-like dielectrics with superb thermal conductivity as well as high dielectric properties hold great promise for the modern electronic field. Nevertheless, integrating these properties into a single material simultaneously remains problematic due to their mutually limited physical connotations. In this study, we developed high-quality thermally conductive epoxy composites with excellent dielectric properties. This was achieved by incorporating surface-functionalized microscale hexagonal boron nitride (BN) along with N-[3-(Trimethoxysilyl)propyl]ethylene diamine (DN) and N-[3-(Trimethoxysilyl)propyl]aniline (PN). In the resulting epoxy composite, microscale BN serves as the primary building block for establishing the thermally conductive network, while silica particles act as bridges to regulate heat transfer and reduce interfacial phonon-scattering. The prepared composites were thoroughly examined across various filler contents (ranging from 10 to 80 wt%). Among them, the DNBN/epoxy composite exhibited higher thermal conductivity (in-plane: 47.03 W m-1 K-1) at 60 wt% filler content compared to BN/epoxy (39.40 W m-1 K-1) and PNBN/epoxy (33 W m-1 K-1) composites. These results highlight the usefulness of surface modification of BN in improving compatibility between fillers and epoxy, ultimately reducing composite viscosity. Furthermore, the DNBN/epoxy composite at 60 wt% demonstrated superb dielectric constant (∼6.15) without compromising on dissipation loss (∼0.06). The strategy adopted in this study offers significant insights into designing dielectric thermally conductive composites with superior performance outcomes.

Energetic and exergetic assessment of a ground source heat pump system using low temperature resources in a tropical climate

The energy crisis is a global issue which all nations are involved with it. To this purpose, scientists are developing new energy sources that have less downsides than traditional energy sources. In the current investigation, a ground source cooling system is built in a 234 m2 office building at the gas company bureau in Qom province, Iran, which has a tropical environment. In this climate, which the ground temperature is almost 21 °C, some closed vertical type ground coil with about 170 m depth is constructed for the system, and then some measurements are recorded. The system has been evaluated using the extracteddata and energy and exergy evaluations have been conducted. The outputs show a great sensitivity of the coefficient of performance to the outlet ground coil temperature and the exergy analysis demonstrates that the exergy loss of the ground coil is slightly increased over the workday and the heat pump with exergy dissipation and exergy loss coefficient of 6.4 kW and 0.22 has higher rate of irreversibility compared to other components. Moreover, the average values of Coefficient of Performance (COP) and outlet temperature of ground coil during a workday were obtained as 4.43, 27.43C respectively.

Vortex dynamics characteristics in the tip region based on Wray–Agarwal model

In order to solve the blockage effect and energy dissipation phenomenon caused by cavitation in the low-pressure vortex core region, this paper analyzes the spatial evolution of vorticity intensity and turbulent kinetic energy intensity under different cavitation conditions based on the Wray–Agarwal (WA) model. First, the tip leakage flow characteristics are studied, the evolution of vorticity and vorticity intensity is analyzed, then the distribution of turbulent kinetic energy distribution in the blade tip region is studied, and finally, the vorticity transport characteristics of the tip region are analyzed. It is found that the tip leakage rate is less affected by the vortex cavitation of the tip leakage, and there is a strong interaction between the leakage flow at the tip leading edge and the trailing edge, and the separation vortices and low-speed regions formed in the end-wall region cause blockage of the flow passage. Low pressure causes cavitation to cover most regions of the suction surface, inhibiting the formation and development of the tip leakage vortices. The distribution range of high turbulent kinetic energy region is almost the same as that of high-vorticity region, and there is a positive correlation between the two intensities. Severe cavitation causes the high turbulent kinetic energy region at the outlet of the flow passage to develop in the radial and axial directions of the impeller, which increases the turbulent dissipation and energy loss. The change of vorticity transport intensity caused by cavitation is mainly reflected in the expansion contraction term, and the Coriolis force term plays a dominant role in the vorticity transport process. This paper provides a reference for further improving the performance of mixed-flow pumps.

Raman Microscopy Identification of Secondary Spurious Phases in Molten GdSr2RuCu2O8-δ Superconductor for Photonics and Plasmonic Applications

Plasmonic and Photonics applications of superconducting materials, suggested at first by the necessity to minimize the dissipative losses of conventional metals in the high frequency ranges, are topics of growing interest in Optics. In this perspective, GdSr2RuCu2O8-δ (Gd1212) Rutheno-Cuprate Superconductor presents very promising properties, showing both superconducting and magnetically ordered phases coexisting in the same cell. To investigate its features, the fabrication of macroscopic crystallographically oriented samples is necessary. The use of melt texturing techniques has shown to be among the most effective ways to achieve the best characteristics, although the fabrication of high-quality Gd1212 samples is intrinsically difficult. To reach a better understanding of Gd1212 incongruent melting reaction, a series of bulk samples annealed at temperatures below and above the melting temperature was prepared. Raman Microscopy and Mapping performed on molten and re-solidified samples revealed the presence of different phases, corresponding to those identified in our previous studies. These observations were also confirmed by XRD, TGA-DTA, and SEM+EDS characterisations. Secondary phases formation showed a strong dependence on the temperature of the annealing treatments. Susceptibility and magnetization measurements show both superconducting and magnetic transitions and a contribution of different spurious magnetic phases as suggested by EDS.

Effects of dimethyl ether blending on H2-fueled combustion characteristics and thermal improvement in fuel-lean condition

Micro-combustors play a pivotal role in micro powering system due to the potential for high energy density. However, addressing challenges such as incomplete combustion and high heat dissipation losses are essential for optimizing the working performance. So, the blended DME is proposed to micro-combustion, which acts as a promising oxygenated fuel with significant attention due to its higher reactivity, lower pollutant emissions, and carbon–neutral properties. However, the lack of dynamic models applicable to H2/DME fueled combustion in micro condition, so an optimized mechanism for blended H2/DME combustion is developed and validated. The results demonstrate that a reduced mechanism comprising 29 species and 106 reactions (M29-106*) can be commendably employed in micro H2/DME/air combustion simulation, according to the sensitivity analysis and reaction modification. Besides, investigation is conducted to explore micro-combustion characteristics of H2/DME/Air. The result shows that burning process and heat transfer are notably influenced by DME addition, leading to shifts in flame positions and adjustments in combustion reaction rates. So, DME addition enhances energy efficiency and modifies flame location through fluid field optimization and reduced heat loss. The thermal performance of the combustor is significantly improved with DME blending, resulting in higher radiative power and radiation efficiency. However, the choice of DME blending ratio must be carefully considered, as high blending ratios may compromise flame stability and lead to increased exhaust heat losses under fuel-lean conditions. Specifically, burning with 30 % DME addition achieves a radiative power of 20.24 W and a radiative efficiency of 40.57 % at the same chemical energy Ec = 49.9 W, which is 5.57 W and 11.17 % higher than that of pure H2-fueled combustion, respectively. These findings offer valuable insights for the design and optimization of micro-combustors, where compact and efficient power sources are required.

Topological and high-performance nonreciprocal extraordinary optical transmission from a guided mode to free-space radiation

Extraordinary optical transmission (EOT) is a hallmark of surface plasmons and a precursor to nanoplasmonics and metamaterials. However, to the best of our knowledge, this effect has never been topologically protected in three dimensions, leaving it vulnerable to structural imperfections, nonlocal effects, and backreflections. We report broadband, three-dimensional unidirectional structures that allow for EOT (normalized transmission > 1) through deep-subdiffractional single holes, immune to these deleterious effects. These structures avoid unnecessary propagation losses and achieve maximum transmission through a single hole, limited only by unavoidable dissipative losses. In the limit of vanishing losses, the transmission through a deep-subdiffractional hole can approach unity, significantly surpassing existing devices, and rivaling the performance of negative-index ‘perfect’ lenses. The topological stability of these structures renders them robust against surface roughness, defects, and nonlocality, without the need for elaborate meta-structures or tapering.

Formulation of an Efficiency Model Valid for High Vacuum Flat Plate Collectors

High Vacuum Flat Plate Collectors (HVFPCs) are the only type of flat plate thermal collectors capable of producing thermal energy for middle-temperature applications (up to 200 °C). As the trend in research plans is to develop new Selective Solar Absorbers to extend the range of HVFPC application up to 250 °C, it is necessary to correctly evaluate the collector efficiency up to such temperatures to predict the energy production accurately. We propose an efficiency model for these collectors based on the selective absorber optical properties. The proposed efficiency model explicitly includes the radiative heat exchange with the ambient, which is the main source of thermal losses for evacuated collectors at high temperatures. It also decouples the radiative losses that depend on the optical properties of the absorber adopted from the other thermal losses due to HVFPC architecture. The model has been validated by applying it to MT-Power HVFPC manufactured by TVP-Solar. The dissipative losses other than thermal radiation were found to be mostly conductive with a linear coefficient k = 0.258 W/m2K. The efficiency model has been also used to predict the energy production of HVFPCs equipped with new, optimized Selective Solar Absorbers developed in recent years. Considering the 2019 meteorological data in Cairo and an operating temperature of 250 °C, the annual energy production of an HVFPC equipped with an optimized absorber is estimated to be 638 kWh/m2.