bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave absorption enhancement via graphene sheet-guided preparation of flake-like titanium carbide
Authors: Wang Shasha , Li Jianjun , Sun Xianxian , Yang Minglong , Yang Shuang , Yin Weilong , Li Yibin
Published: December 2021

With the development of electromagnetic technology, there is an urgent need for further research on highly efficient and lightweight microwave absorption materials. Transition metal carbides have drawn tremendous attention due to their strong microwave dissipation ability and perfect stability in extreme environments. However, owing to carburization under high temperatures, synthesizing metal carbides with specified morphology is still a challenge. Here, titanium carbide (TiC) with a flake-like structure was prepared through a carbothermic reduction method guided by two-dimensional graphene sheets. The prepared flake-like TiC sheets show excellent microwave absorption properties in 1–40 GHz compared with TiC spherical particles. A minimum reflection loss (RL) of −57.0 dB at 11.8 and 3.2 GHz effective absorption bandwidth (RL < −10 dB) was achieved. Meanwhile, an optimal RL of −57 dB is also achieved at 35.8 GHz together with an even broader absorption bandwidth from 34.2 to 40 GHz (5.8 GHz in total). This excellent microwave absorption performance is attributed to the flake-like morphology, which dramatically enhances the multiple polarization loss. The method of utilizing graphene sheets as a guide to fabricate flake-like TiC not only illuminates a new strategy for fabricating transition metal carbides with specified morphology but also provides an attractive candidate for microwave absorption applications.
Hydrodynamic analysis of fish schools arranged in the vertical plane
Authors: Li Xiaohu , Gu Jiayang , Su Zhen , Yao Zhenqiu
Published: December 2021

Schools of fish can provide individuals with hydrodynamic advantages, thereby improving the swimming efficiency. Fish schools in nature are mostly spatial configurations, not just limited to the horizontal plane. Through three-dimensional numerical simulations, this paper discusses the hydrodynamic characteristics and flow field structure of fish schools in various vertical patterns. The results show that a school of fish arranged vertically can improve the thrust and swimming efficiency of individuals as well as those arranged horizontally. There are two ways to significantly enhance hydrodynamic advantages. One is to maximize the channeling effect in multiple planes. In a vertical circular pattern, the fish school forms multiple coupled channels, which hinder the free expansion of flow in both vertical and horizontal planes, thereby obtaining higher energy-saving benefits. The other is the combined exploitation of the channeling effect and wake energy, which is illustrated in the vertical rectangular pattern. The following fish can use the channeling effect to increase the thrust due to the presence of parallel companion. Meanwhile, the high speed region of the following fish can merge with the jet flows of the preceding fish, thereby capturing the wake energy and further improving swimming efficiency.
Dynamics of an acoustically driven cavitation bubble cluster in the vicinity of a solid surface
Authors: Ezzatneshan Eslam , Vaseghnia Hamed
Published: December 2021

The dynamics of a cavitation bubble cluster under the influence of an acoustic field is a complex multiphase system that can be observed in acoustic cavitation. In the present study, a three-dimensional computational technique based on the multiphase lattice Boltzmann method (LBM) with multiple relaxation time (MRT) is adopted to investigate the acoustically driven cavitation bubble cluster dynamics near a solid wall at different wetting conditions. Herein, the Peng–Robinson–Stryjek–Vera equation of state with an acentric factor is incorporated in the LBM to accurately impose the physical properties of actual fluids. The validity and capability of the adopted MRT-LBM are confirmed by the excellent agreement of the present results compared to the computed data based on the Rayleigh–Plesset equation for a heterogeneous cavitation phenomenon. The obtained results for the acoustically driven cavitation bubble cluster dynamics demonstrate that the shielding effect of top bubbles prevents the pressure pulse from reaching the lower bubbles. Therefore, the cluster core and the bubbles near the solid surface are more affected by the destruction of the upper layer bubbles than the acoustic field. Also, it is found that the wettability of the solid wall significantly affects the irradiated impulsive pressure waves around the cluster. To justify this result from the physical point of view, the magnitude of the primary and secondary Bjerknes forces is measured and, accordingly, the growth and collapse of bubbles in the cluster under the influence of the acoustic field are discussed in detail.
Comparison of the phase transitions of high-pressure phases of ammonium fluoride and ice at ambient pressure
Authors: Sharif Zainab , Salzmann Christoph G.
Published: December 2021

The phase diagrams of water and ammonium fluoride (NH4F) display some interesting parallels. Several crystalline NH4F phases have isostructural ice counterparts and one of the famous anomalies of water, the fact that the liquid is denser than ice Ih, is also found for NH4F. Here, we investigate the phase transitions of the pressure-quenched high-pressure phases of NH4F upon heating at ambient pressure with x-ray diffraction and calorimetry, and we compare the results with the corresponding ices. NH4F II transforms to NH4F Isd, which is a stacking-disordered variant of the stable hexagonal NH4F Ih polymorph. Heating NH4F III gives a complex mixture of NH4F II and NH4F Isd, while some NH4F III remains initially. Complete conversion to NH4F Isd is achieved above ∼220 K. The NH4F II obtained from NH4F III persists to much higher temperatures compared to the corresponding pressure-quenched NH4F II. Quantification of the stacking disorder in NH4F Isd reveals a more sluggish conversion to NH4F Ih for NH4F Isd from NH4F III. In general, the presence of stress and strain in the samples appears to have pronounced effects on the phase transition temperatures. NH4F shows a complete lack of amorphous forms at low temperatures either upon low-temperature compression of NH4F Ih or heating NH4F III at ambient pressure. The amorphous forms of ice are often used to explain the anomalies of water. It will, therefore, be interesting to explore if liquid NH4F displays more water-like anomalies despite the apparent lack of amorphous forms at low temperatures.
Variation in a worldwide collection of fennel (
Authors: Hosseini Elaheh , Majidi Mohammad Mahdi , Ehtemam Mohammad Hossein , Ghanadian Mustafa
Published: December 2021

Fennel (Foeniculum vulgare Mill.) is an old medicinal plant and has been commonly used as a traditional food and medicine. This study aimed to evaluate genetic variation for agro-morphological traits and essential oil content and components in a worldwide collection of bitter fennel (F. vulgare var. vulgare). We examined production stability of different accessions, and identified associations between traits in order to find the best criteria for use in future breeding programs. The study evaluated 33 bitter fennel accessions from 11 countries in the field for morphological characters across 4 years (2015–18), and for important phytochemical characters in 2 years (2015 and 2016). Comparisons across years revealed varied responses from fennel genotypes. Highest mean production was observed in the third year, and highest essential oil content in the second year. Based on gas chromatography–mass spectrometry analysis, trans-anethole (59.86–78.82% of total oil content), estragole (3.61–24.39%), fenchone (9.58–18.26%) and limonene (0.52–3.66%) were detected as major essential oil components in the studied germplasm. Based on principal component and cluster analysis, genotypes were grouped into different clusters. Classification of genotypes was mainly in agreement with available information regarding their origins. The results support available information on the history of human establishments and the introduction of fennel from Mediterranean gene pools to other regions in ancient times. The negative correlation between some essential oil components indicates that some components are isomers and this could limit the simultaneous selection of components. Superior genotypes were identified in the studied germplasm, which can be used for future breeding programs with specific purposes.
Trophic interactions between native and exotic cichlids in a shallow tropical estuary (Lake Vembanad, India)
Authors: Roshni Kuttanelloor , Renjithkumar Chelapurath Radhakrishnan , Sreekanth Giri Bhavan , Raghavan Rajeev , Ranjeet Kutty , Harikrishnan Mahadevan , Kurup Balakrishnan Madhusoodana
Published: December 2021

Feeding ecology and seasonal diet variation between a non-native (Oreochromis mossambicus) and two native cichlids (Etroplus suratensis and Pseudetroplus maculatus) in a tropical estuary was studied. E. suratensis and O. mossambicus fed predominately on blue green algae, whereas P. maculatus preferred aquatic insects. Trophic niche breadth analysis showed that P. maculatus had a broader diet spectrum than did E. suratensis and O. mossambicus. Feeding strategy analysis through dominant prey items showed that E. suratensis and O. mossambicus preferred blue green algae, whereas P. maculatus relied mostly on animal diet (mainly insects), highlighting food segregation shown by this species compared with the other two large-growing cichlids. The highest diet overlap index value was recorded between E. suratensis and O. mossambicus (0.83), compared with P. maculatus and O. mossambicus (0.69), and E. suratensis and P. maculatus (0.64). Intensity of trophic interdependence among the three cichlids showed that the two, large growing species share available food resources, whereas the smaller species considerably alters its food preference.
The geometry of decision-making in individuals and collectives
Authors: Sridhar Vivek H. , Li Liang , Gorbonos Dan , Nagy Máté , Schell Bianca R. , Sorochkin Timothy , Gov Nir S. , Couzin Iain D.
Published: December 2021

Significance

Almost all animals must make decisions on the move. Here, employing an approach that integrates theory and high-throughput experiments (using state-of-the-art virtual reality), we reveal that there exist fundamental geometrical principles that result from the inherent interplay between movement and organisms’ internal representation of space. Specifically, we find that animals spontaneously reduce the world into a series of sequential binary decisions, a response that facilitates effective decision-making and is robust both to the number of options available and to context, such as whether options are static (e.g., refuges) or mobile (e.g., other animals). We present evidence that these same principles, hitherto overlooked, apply across scales of biological organization, from individual to collective decision-making.
Evolution of variable lymphocyte receptor B antibody loci in jawless vertebrates
Authors: Das Sabyasachi , Rast Jonathan P. , Li Jianxu , Kadota Mitsutaka , Donald John A. , Kuraku Shigehiro , Hirano Masayuki , Cooper Max D.
Published: December 2021

Significance

Jawless vertebrates, lampreys and hagfish, use three types of variable leucine-rich repeat proteins as antigen receptors: VLRB on B-like cells and VLRA or VLRC on T-like lymphocytes. In their incomplete germline status, theVLRBgenes in different lamprey species uniquely possess long noncoding intervening regions, which contain different sets of transposable elements and potential donor cassettes. Phylogenetic analysis of the germlineVLRgenes reveals ongoing evolution over the last 250 million y. Comparative assessment of genomic sequences in two lamprey species yields a detailed map of theirVLRBloci. The use of this map, together with an analysis of cassette usage in a large repertoire of expressedVLRBs, supports a fragmented Lego-like model ofVLRBassembly.
Constraining the number of horizons with energy conditions
Authors: Yang Run-Qiu , Cai Rong-Gen , Li Li
Published: December 2021

We show that the number of horizons of static black holes can be strongly constrained by energy conditions of matter fields. After a careful clarification on the ‘interior’ of a black hole, we prove that if the interior of a static black hole satisfies strong energy condition or null energy condition, there is at most one non-degenerated inner Killing horizon behind the non-degenerated event horizon. Our result offers some universal restrictions on the number of horizons. Interestingly and importantly, it also suggests that matter not only promotes the formation of event horizon but also prevents the appearance of multiple horizons inside black holes. Furthermore, using the geometrical construction, we obtain a radially conserved quantity which is valid for general static spacetimes.
Spin wave propagation and nonreciprocity in metallic magnonic quasi-crystals
Authors: Manago Takashi , Fujii Kanta , Kasahara Kenji , Nakayama Kazuyuki
Published: December 2021

The characteristics of spin waves (SWs) propagating in Fibonacci magnonic quasi-crystals (MQCs) were investigated in micromagnetic simulations. The SWs feel 1/3 of the characteristic Fibonacci sequence length as a period, and mini band gaps reflected by MQCs are formed. The effect of the MQC on the SW’s propagation becomes prominent above the first band gap frequency. The properties of SWs in MQCs generally depend on the propagation direction, because SWs feel different structures depending on the direction. Therefore, the nonreciprocity (NR) characteristics becomes complex. The NR characteristics change at every band gap frequency and hence across the frequency regions defined by them. In particular, some frequency regions have almost no NR, while others have enhanced NR and some have even negative NR. These characteristics seem to provide a new way to control NR.
Influence of different O2/H2O ratios on He atmospheric pressure plasma jet impinging on a dielectric surface
Authors: Liu Jie , Wang Lijun , Lin Xin , Zhang Runming
Published: December 2021

A two-dimensional (2D) axisymmetric fluid model is built to investigate the effect of different O2 and H2O admixture on the plasma dynamics and the distribution of reactive species in He atmospheric pressure plasma jet (APPJ). The increase of O2:H2O ratio slows down both the intensity and the propagation speed of the ionization wave. Due to the decrease of both H2O ionization rate and H2O Penning ionization as well as the stronger electronegativity of O2, the increase of O2:H2O ratio results in a significant reduction of electron density in the APPJ, which restricts the occurrence of electron collision ionization reactions and inhibits the propagation of plasma. The excitation energy loss of O2 is not the reason for the weakening of the plasma ionization wave. The densities of O2
+, O− and O2
− increase with the rise of O2 admixture while H2O+ decreases due to the decrease of electron density and H2O concentration. OH− density is affected by both the increase of O− and the decrease of H2O so it shows a peak in the case of O2:H2O = 7:3. O is mainly produced by the excitation reactions and the electron recombination reaction (e + O2
+ → 2O), which is directly related to the O2 concentration. OH is mainly produced by e + H2O → e + H + OH so the OH density decreases due to the decrease of electron density and H2O concentration with the increase of O2:H2O ratio. On the dielectric surface, when the propagation of the streamer extinguishes, O flux shows an upward trend while the OH flux decreases, and the propagation distance of O and OH decreases with the increase of O2:H2O ratio.
Influence of B/N co-doping on electrical and photoluminescence properties of CVD grown homoepitaxial diamond films
Authors: Kunuku Srinivasu , Ficek Mateusz , Wieloszynska Aleksandra , Tamulewicz-Szwajkowska Magdalena , Gajewski Krzysztof , Sawczak Miroslaw , Lewkowicz Aneta , Ryl Jacek , Gotszalk Tedor , Bogdanowicz Robert
Published: December 2021

Boron doped diamond (BDD) has great potential in electrical, and electrochemical sensing applications. The growth parameters, substrates, and synthesis method play a vital role in the preparation of semiconducting BDD to metallic BDD. Doping of other elements along with boron (B) into diamond demonstrated improved efficacy of B doping and exceptional properties. In the present study, B and nitrogen (N) co-doped diamond has been synthesized on single crystalline diamond (SCD) IIa and SCD Ib substrates in a microwave plasma-assisted chemical vapor deposition process. The B/N co-doping into CVD diamond has been conducted at constant N flow of N/C ∼ 0.02 with three different B/C doping concentrations of B/C ∼ 2500 ppm, 5000 ppm, 7500 ppm. Atomic force microscopy topography depicted the flat and smooth surface with low surface roughness for low B doping, whereas surface features like hillock structures and un-epitaxial diamond crystals with high surface roughness were observed for high B doping concentrations. KPFM measurements revealed that the work function (4.74–4.94 eV) has not varied significantly for CVD diamond synthesized with different B/C concentrations. Raman spectroscopy measurements described the growth of high-quality diamond and photoluminescence studies revealed the formation of high-density nitrogen-vacancy centers in CVD diamond layers. X-ray photoelectron spectroscopy results confirmed the successful B doping and the increase in N doping with B doping concentration. The room temperature electrical resistance measurements of CVD diamond layers (B/C ∼ 7500 ppm) have shown the low resistance value ∼9.29 Ω for CVD diamond/SCD IIa, and the resistance value ∼16.55 Ω for CVD diamond/SCD Ib samples.
Visualizing rheological mechanism of magnetorheological fluids
Authors: Shen Yurui , Hua Dezheng , Liu Xinhua , Li Weihua , Krolczyk Grzegorz , Li Zhixiong
Published: December 2021

In order to study the rheological properties of aqueous magnetorheological fluids (MRFs) from microscopic point of view, an experimental observation method based on fluorescence confocal laser scanning microscope is proposed to clearly shown the chain shape of magnetic particles. Firstly, the mathematical model of the magnetic particles is established in a magnetic field using the magnetic dipole theory, and the MRFs with different volume fraction and different magnetic fields are investigated. Furthermore, an aqueous MRFs experiment is prepared, in which the magnetic particles are combined with Alexa 488 fluorescent probe. On this basis, an observation method is innovatively developed using two-dimensional and three-dimensional image analysis by the fluorescence confocal microscope. The rheological mechanism of the aqueous MRFs is investigated using four different types of MRFs in an external magnetic field. The analysis results demonstrate that the simulation and experimental rheological properties of the MRFs are consistent with the magnetic dipole theory. Moreover, the proposed method is able to real-time observe the rheological process of the MRFs with a very high resolution, which ensures the correctness of the analysis result of the rheological mechanism.
A design method for metamaterials: 3D transversely isotropic lattice structures with tunable auxeticity
Authors: Peng Xiang-Long , Bargmann Swantje
Published: December 2021

A method for designing 3D transversely isotropic auxetic lattice structures is proposed. Based on it, two new auxetic structures have been designed. Systematically, their effective elastic properties are investigated computationally and analytically in all loading directions. The effective Young’s moduli and Poisson’s ratios within the transverse plane and those along the longitudinal direction are widely tunable by tailoring the structural geometry. Both structures exhibit transverse and longitudinal auxeticities concurrently as well as separately. The proposed auxetic structures expand the existing auxetic material space in terms of elastic anisotropy.
All polarization-maintaining Er:fiber-based optical frequency comb for frequency comparison of optical clocks
Authors: Zhang Pan , Zhang Yan-Yan , Li Ming-Kun , Rao Bing-Jie , Yan Lu-Lu , Chen Fa-Xi , Zhang Xiao-Fei , Chen Qun-Feng , Jiang Hai-Feng , Zhang Shou-Gang
Published: December 2021

We demonstrate an optical frequency comb (OFC) based on a turnkey mode-locked laser with a figure-9-shape structure and polarization-maintaining fibers, for the comparison of frequency among optical clocks with wavelengths of 698 nm, 729 nm, 1068 nm, and 1156 nm. We adopt a multi-branch approach in order to produce high power OFC signals at these specific wavelengths, enabling the signal-to-noise ratio of the beatnotes between the OFC and the clock lasers to exceed 30 dB at a resolution bandwidth of 300 kHz. This approach makes the supercontinuum spectra much easier to be generated than a single branch OFC. However, more out-of-loop fibers degrade the long-term frequency instability due to thermal drift. To minimize the thermal drift effect, we set the fiber lengths of different branches to be similar, and we stabilize the temperature as well. The out-of-loop frequency instability of the OFC due to the incoherence of the multi-branch is about 5.5 × 10−19 for 4000 s, while the in-loop frequency instability of f
ceo and that of f
beat are 7.5 × 10−18 for 1 s and 8.5 × 10−18 for 1 s, respectively. The turnkey OFC meets the requirement for the comparison of frequency between the best optical clocks.
Measuring Loschmidt echo via Floquet engineering in superconducting circuits
Authors: Zhao Shou-Kuan , Ge Zi-Yong , Xiang Zhong-Cheng , Xue Guang-Ming , Yan Hai-Sheng , Wang Zi-Ting , Wang Zhan , Xu Hui-Kai , Su Fei-Fan , Yang Zhao-Hua , Zhang He , Zhang Yu-Ran , Guo Xue-Yi , Xu Kai , Tian Ye , Yu Hai-Feng , Zheng Dong-Ning , Fan Heng , Zhao Shi-Ping
Published: December 2021

The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearest-neighbor (NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.
Quantum key distribution transmitter chip based on hybrid-integration of silica and lithium niobates
Authors: Li Xiao , Wang Liang-Liang , Zhang Jia-shun , Chen Wei , Wang Yue , Wu Dan , An Jun-Ming
Published: December 2021

A quantum key distribution transmitter chip based on hybrid-integration of silica planar light-wave circuit (PLC) and lithium niobates (LN) modulator PLC is presented. The silica part consists of a tunable directional coupler and 400-ps delay line, and the LN part is made up of a Y-branch, with electro-optic modulators on both arms. The two parts are facet-coupled to form an asymmetric Mach–Zehnder interferometer. We successfully encode and decode four BB84 states at 156.25-MHz repetition rate. Fast phase-encoding of 0 or π is achieved, with interference fringe visibilities 78.53% and 82.68% for states |+〉 and |–〉, respectively. With the aid of an extra off-chip LN intensity modulator, two time-bin states are prepared and the extinction ratios are 18.65 dB and 15.46 dB for states |0〉 and |1〉, respectively.
Stochastic forcing of the 2D boundary layer by DBD plasma actuator
Authors: Moralev Ivan , Popov Ilya , Selivonin Igor , Ustinov Maxim
Published: December 2021

The paper describes the results of the parametric study of the broadband velocity pulsations, induced by DBD plasma actuator in 2D subsonic boundary layer. The presented data include the analysis of the disturbance growth at various pressure gradients. It is assumed that the broadband pulsations are composed of the elementary disturbances, induced by an individual microdischarges, wandering along the electrode edge. These disturbances have a streak-like structure in a near field, and evolve into a fan of packets of Tollmien-Schliechting waves as one moves downstream. The streamwise length, needed for transition to modal behavior, depends on the stability properties of the boundary layer.
Measurements of electron number density and temperature in a supersonic plasma jet by optical emission spectroscopy
Authors: Pashchina A S
Published: December 2021

The results of experimental studies of the shock-wave region of the supersonic plasma jet flow formed by a pulsed capillary discharge with a polymeric wall are presented. Using optical emission spectroscopy of high spatial resolution, a detailed picture of the evolution of the radial profiles of the electron number density and temperature along the initial section of an underexpanded plasma jet, starting from the capillary outlet and ending with the flow stagnation zone, has been obtained. It was found that the profiles of the electron number density and temperature reflect all the features of the shock-wave flow region, tracing the influence of intercepting, central and reflected shock waves.
Influence of the position and energy of local rapid heating of the supersonic gas flow on the position of the separation point on the surface of airfoil
Authors: Saveliev A S
Published: December 2021

Using numerical simulation, the study of the process of rapid local energy release in supersonic flow in a two-dimensional unsteady case and the process of separation point shift by a gas-dynamic perturbation caused by the energy input into the flow were carried out. The flow around the airfoil was modeled as laminar, and local heat release as a instantaneous isochoric process without changing the gas density. The value of energy input and the place of gas heating on the surface of the airfoil were varied. The cases of initiation of energy input at a certain distance before and after the initial position of the separation point, as well as immediately before the separation point, were considered. During obtained flow patterns processing, the displacement of the separation point position downstream, the time of this displacement, the position and size of the separation region with reattachment and the lifetime of this flow zone were determined. The obtained data can help to choose a strategy for initiating energy input in a repetitively pulsed regime, as well as in a regime of a variable position of energy release on the surface of a body, streamlined by compressible gas flow.
Chemical method for reducing the concentration of electrons in the plasma behind a strong shock wave
Authors: Baryshnikov A S , Bezverhny N O
Published: December 2021

In this paper it is shown theoretically using computational methods that the addition of phosphorus-containing substances during the shock wave leads to a decrease in the concentration of electrons at temperatures in the front of shock wave 300 K and behind it of 6000 – 13000° K. Shock wave Mack number is high up to 14. The density is about of 0.35 – 0.7 kg/m3.
Role of pressure waves in the heating of the end-gas in HCCI engine with activation by pulsed corona discharge
Authors: Dobrovolskaya A S , Filimonova E A , Bityurin V A , Bocharov A N
Published: December 2021

In this paper we present numerical research of pressure waves influence on the end-gas in HCCI engine with discharge activation. It is shown that there is certain promotion of exothermic chemical reactions by pressure waves. That leads to the slight heating of the end-gas, but mainly the end-gas is heated due to the compression in the process of combustion wave propagation.
Fractional diffusant model of a multicomponent inhomogeneous gas mixture as a basis for the diffusant approximation
Authors: Burakhanov B M
Published: December 2021

It can be shown that for a correct description of the motion of an inhomogeneous multicomponent mixture of gases, such concepts as a multi-velocity continuum and interpenetrating motion are not enough. This is the basis for the introduction of the concept of “poly-velocity motion”. The reason for the need to use this concept is that to describe the motion of each component of an inhomogeneous mixture, it is necessary to use not one, but two velocity fields. The use of two velocity fields to describe the motion of a mixture component is the basis for constructing a fractional model of the mixture component, in which each component is divided into two fractions. This model serves as the basis for constructing the proposed fractional diffusant model of a multicomponent inhomogeneous gas mixture.
The phenomenon of relay race molecular transfer of the amount of motion and its relationship with the diffusion phenomenon
Authors: Burakhanov B M
Published: December 2021

The very fact of molecular transfer of the amount of motion, including in an ideal gas in an equilibrium state, has long been well known. However, this fact is still not realized as a physical phenomenon of transfer, equivalent to such transfer phenomena as diffusion, thermal conductivity and viscosity. The key concept used in this paper when describing the phenomenon of relay race molecular transfer of the amount of motion is the concept - “molecular relay race type of motion”. A molecular relay race model of an ideal gas in an equilibrium state is proposed, as well as a molecular relay race model of a mixture of two ideal gases at constant temperature and pressure. It is shown that the value of the velocity modulus of diffusion flows is one of the physical characteristics of the mixture as a whole. It is also shown that the total density of the substance carried by the diffusion flows is many orders of magnitude less than the total density of the inhomogeneous multicomponent mixture.
Study of the factors that determine the transfer of water and organic compounds into the gas phase from aqueous solutions in a discharge with a liquid cathode
Authors: Chistolinov A V , Khromov M A , Yakushin R V , Gadzhiev M Kh , Tyuftyaev A S
Published: December 2021

A study was performed to investigate the transfer of organic compounds and water from an aqueous solution to the gas phase under the action of a direct current discharge, in which an aqueous solution that contains organic compounds plays the role of a cathode. The effect of the area of the free surface of a liquid in various reactors, as well as the effect of the stirring mode of a solution near the surface of a liquid on the rate of transfer of water and organic compounds under the action of a discharge of this type, have been investigated. It is shown that a change in the area of the free surface of a liquid has no significant effect on the rate of transfer of water and organic compounds from solution to the gas phase under the action of a direct current discharge with a liquid cathode. It is shown that the stirring mode and the temperature of the solution, on the contrary, have a very significant effect on the rate of nonequilibrium transfer of both water and organic compounds from solution to the gas phase under the action of a discharge with a liquid cathode.
Flow control in cavity by means of sDBD actuator
Authors: Kazanskii P N , Moralev I A , Selivonin I V
Published: December 2021

This paper presents results of controlling the hydrodynamic cavity pulsations by plasma sDBD actuators. The study was held at flow velocity 36 m/s. The discharge was organized near the upstream edge of cavity. The discharge pulse energy was 0.03 J, Excitation of resonant modes, whose frequency coincides with the modulation frequency of the discharge, is obtained. Also, in the case of the detuned discharge operation, locking of the cavity to the discharge modulation frequency occurs.
Influence of the surface DBD parameters on the streaks development in the boundary layer
Authors: Yarantsev D , Selivonin I , Moralev I
Published: December 2021

The effect of the filamentary barrier discharge parameters on the boundary layer streaks generation and instability was studied. The streaks are formed near the constricted discharge channels due to vortices formation driven by spanwise Coulomb volume force. The secondary instability of the streaky structures can lead to the laminar-turbulent transition of the boundary layer. This work demonstrates that supply voltage parametrs affect the period of the constricted channels and thus the streaks transversal period within the boundary layer. For the various streaks periods, different modes of streak instability are shown to dominate.
Variations of nanoparticle layer properties during nucleate pool boiling
Authors: Okawa Tomio , Nakano Koki , Umehara Yutaro
Published: December 2021

The nanoparticle layer detachment during nucleate pool boiling and its influences on heat transfer surface properties were explored experimentally. The material of the heat transfer surface was copper and the nanoparticle layer was formed on the heat transfer surface by nucleate boiling in the water-based TiO2 nanofluid. It was found that the detachment of the nanoparticle layer during nucleate boiling in pure water is significant. In the present experiment, more than half of nanoparticles deposited on the heated surface were detached before the CHF condition was reached. The thickness and roughness decreased accordingly. However, the wettability and wickability that are the influential parameters on the CHF value were maintained even after the occurrence of nanoparticle layer detachment and deteriorated only after the CHF condition was reached. It is therefore considered that the onset of CHF brings qualitative change to the capillary suction performance of the layer of nanoparticles. In exploring the effect of the nanoparticle layer properties on the nucleate boiling heat transfer, sufficient attention should be paid to the variation of the nanoparticle layer properties during nucleate boiling.
Heat transfer and exergy analysis of flow boiling evaporation in u-bend channel
Authors: Jatau T , Bello-Ochende T
Published: December 2021

This study presents, a numerical method used to evaluate the exergy analysis of flow boiling evaporation of R134a in a U-bend channel using entropy generation criterion which is concerned with the degradation of exergy during the process due to irreversibilies (entropy generation) contributed by heat transfer and pressure drop. The simulations were conducted with the heat flux of 15 kW/m2, mass fluxes of 200-600 kg/m2s of R134a at the saturation temperature of 15 °C. Three(3) different geometries sizes of U-bend channel’s diameter 6, 8 and 10 mm with the bend radius of 10.2 mm were utilized. The Volume of Fluid (VOF) multiphase flow formulation was used in Ansys Fluent. The results show that the entropy generation increases with increase in mass fluxes due to irreversibilies contributed by the heat transfer coefficient and pressure drop as mass fluxes increase. Based on the size of the U-bend channel, the entropy generation was found to increase as the diameter of the channel increases. The numerical results were compared with the data in the open literature and there was a good agreement.
Pool boiling performance of laser-textured surfaces with time-dependent wettability
Authors: Zupančič Matevž , Gregorčič Peter , Golobič Iztok
Published: December 2021

In last years, the direct laser texturing proved as environmentally friendly, scalable, flexible and efficient approach for surface functionalisation by creating appropriate surface features for enhanced boiling performance. When metal surface is laser-processed in open (oxygen-containing) atmosphere, it oxidizes and becomes (super)hydrophilic. However, it is well known that the wettability transition towards (super)hydrophobic state occur, if such a surface is exposed to the presence of hydrophobic contaminants. When water is used as a working fluid, this wettability transition can have a significant effect on nucleate boiling performance, which is investigated in this work.
Pool boiling of nanofluids on biphilic surfaces
Authors: Pontes P , Freitas E , Fernandes D , Teixeira A , Ferreira R , Bellmann S , Cautela R , Moita A. S. , Bahadur V , Miranda J , Lima R , Ribeiro APC. , Moreira ALN
Published: December 2021

This study addresses the combination of customized surface modification with the use of nanofluids, to infer on its potential to enhance pool boiling heat transfer. Hydrophilic surfaces patterned with superhydrophobic regions are prepared and used to act as surface interfaces with nanofluids (water with gold, silver and alumina nanoparticles) and infer on the effect of the nature and concentration of the nanoparticles in bubble dynamics and consequently in heat transfer processes. The main qualitative and quantitative analysis was based on extensive post-processing of synchronized high-speed and thermographic images. The results show an evident benefice of using biphilic patterns, but with well-stablished distances between the superhydrophobic regions. Such patterns allow a controlled bubble coalescence, which promotes fluid convection at the hydrophilic surface between the superhydrophobic regions, which clearly contributes to cool down the surface. The effect of the nanofluids, for the low concentrations used here, was observed to play a minor role.
Numerical simulation of dropwise condensation over hydrophobic surfaces using vapor-diffusion model
Authors: Suzzi N , Croce G
Published: December 2021

Dropwise condensation of humid air over hydrophilic and hydrophobic surfaces is numerically investigated using a phenomenological, Lagrangian model. Mass flux through droplets free surface is predicted via a vapor-diffusion model. Validation with literature experimental data is successfully conducted at different air humidities and air velocities. The accuracy of the implemented condensation model is compared with a standard analogy between convective heat and mass transfer, showing that the latter is not able to predict heat transfer performances in the investigated air velocity range.
Thermal performance deterrence caused by PCM inclusion in firefighting garments: The other side of the story
Authors: Fonseca A , Neves S F , Campos J B L M
Published: December 2021

Firefighters usually encounter high heat flux exposures, which can cause severe burns. The addition of a phase change material (PCM) layer into a firefighting garment assembly has proven to be beneficial as it lowers the garments temperature during the fire exposure. However, after the fire exposure, accumulated heat in the PCM garment is discharged towards skin and environment which can have a negative influence on thermal performance. In this study, a one dimensional numerical approach was used to study the effect of environment parameters (ambient convective heat flux) as well as PCM parameters (latent heat, melting temperature) on the thermal performance of the firefighting garment, after the fire exposure. It was concluded that the amount and phase change temperature at which latent heat is discharged had a significant effect on thermal performance, depending on the heat exposure scenario. For high – intensity exposures, skin damage is promoted by an increase in both properties whilst for low intensity exposures, a decrease in melting temperature would promote greater skin damage. The results outlined in this paper could aid in the manufacture of PCM firefighting garments, as skin damage due to PCM resolidification might be an important parameter to take into account when maximizing thermal performance.
Fire behaviour of a Carbon/Nomex honeycomb sandwich composite used in aircraft interior
Authors: Papadogianni V , Romeos A , Perrakis K , Panidis T
Published: December 2021

Fire behaviour of a carbon/Nomex honeycomb composite, used as ceiling panel in aircraft interiors, was investigated in Cone Calorimeter at different incident heat fluxes, ranging from 20 to 70 kW/m2. The material exhibited good fire performance with relatively low amount of heat release and long ignition times. Combustion of the material at 40 kW/m2 proceeded in one stage, while at higher heat fluxes two stages were observed. The burning mechanisms and char formation during thermal decomposition at different heat fluxes was also examined. The long tail after flame-out in heat release curves and the significant increase of CO production and mass loss were analysed with respect to char residue.
Comparison of finite volume and one dimensional network methodologies for thermal management of lighting applications
Authors: Joshi P S
Published: December 2021

Signify is focused on building a state-of-the-art, innovative and sustainable solutions for industries, homes, buildings, and communities. In the last decade or so there has been a considerable shift from using traditional incandescent luminaires to highly efficient, cheaper, and robust LED (Light Emitting Diode) based lighting fixtures. LEDs are semiconductor devices and thus their life depends largely on operating temperatures. Thermal management of the lighting fixture, therefore, becomes crucial for the overall performance. Heat sinks are designed for given operating conditions for better thermal management. With the improved LED efficiencies there are two alternatives that the product designer can opt for namely, to increase the lumen output for the present fixture or to reduce the overall heat sink size. To assist the product designer in this aspect, the present paper reports the thermal management of lighting luminaries using two different modelling techniques such as Finite Volume Method (FVM) and One Dimensional (1D) resistive network analysis. These two modelling techniques are employed to predict the temperature profiles on the luminaire and then compared them with the actual test results. The processing time, accuracy, and method of implementation for both these techniques are then discussed.
Experimental study of a natural convection flow in a cubic enclosure with a partially heated inner block
Authors: Weppe Alexandre , Moreau Florian , Saury Didier
Published: December 2021

In many industrial contexts, buoyancy driven flows are the only cooling strategy in case of breakdown of the forced convection cooling system. In order to study those flows in a simplified configuration, a buoyancy-driven flow is generated inside a cubic enclosure by a partially heated block (Ra = 1.4 × 109). The flow is studied experimentally in the vertical median plane, in the part of the enclosure where the flow is generated i.e. close to the heated side of the block. Velocity fields, mean profiles and RMS statistics are analyzed. The results show the presence of boundary layer flows with a central zone nearly at rest and stratified. RMS velocities are intensified with elevation.
Thermal conditions for the formation of self-assembled cluster of droplets over the water surface
Authors: Fedorets Alexander A , Dombrovsky Leonid A , Shcherbakov Dmitry V , Frenkel Mark , Bormashenko Edward , Nosonovsky Michael
Published: December 2021

The effect of temperature profile of the water layer surface on the formation and structure of a levitating droplet cluster is studied in the paper. The laboratory experiments indicate that a local temperature maximum of water is a necessary condition for the formation of a cluster. A quantitative criterium of transformation of a monolayer of randomly positioned microdroplets to a self-assembled cluster of relatively large droplets is obtained.
Development of measurement setup for thermal conductivity at high temperatures using the parallel hot-wire
Authors: Nonneman Jasper , Couvreur Kenny , Vancoillie Andrey , Paepe Michel De
Published: December 2021

An experimental setup is built to determine the thermal conductivity of a mixture of KNO3 and NaNO3 with a ratio of 54-46m% which is used in high temperature thermal storage systems. The measurement principle is based on the transient parallel hot-wire method which is described in the standards NBN B 62-202 and ISO 8892-2. The setup is designed to measure the thermal conductivity around the melting temperature (<300°C). Measurements within the liquid region show faulty results caused by natural convection within the sample. The measured thermal conductivity within the solid region is 0.5466-0.5529W/mK close to the melting point and 0.7174W/mK at room temperature, which shows a decreasing thermal conductivity with increasing temperature in the solid region.
A comparison of postprocessing methods for hot film sensors for the heat transfer analysis of impinging jet flows
Authors: Murphy Paula , Persoons Tim , O’Shaughnessy Seamus , Murray Darina
Published: December 2021

The aim of this investigation is to optimise the data post-processing techniques associated with hot film sensors when intended to be used as a means of accurate, high-resolution heat flux measurement. More specifically, this project focuses on the performance of hot film sensors operated in a constant temperature anemometer bridge, used in conjunction with impinging jet air flows. The characteristic heat transfer behaviour in this impinging jet flow provides the reference against which the heat flux data attained using the hot film sensor is compared. As part of this investigation, three hot film calibration methods are examined for a range of sensor overheat values: (A) a wall shear correction method, (B) a physical quasi 1-D conduction model and (C) a physical quasi 2-D fin conduction model. The results show that the method C, when used in conjunction with a 5 K sensor overheat, best replicated that of the reference heat flux sensor for the jet configurations investigated.
Research on xylitol crystallization by shearing and seeding for its use as a phase change material
Authors: Delgado Mónica , Navarro Miguel , Lázaro Ana , Boyer Séverine A E , Peuvrel-Disdier Edith
Published: December 2021

As thermal energy storage is becoming more important, new materials are being studied. Sugar-alcohols (SA) are very promising as phase change materials (PCM) because they are non-toxic, affordable and their latent heat is high. However, undercooling and low crystallization rates are some of the problems present in these materials. The SA studied in this work is xylitol, and using a microscope connected to a transparent counter-rotating shear cell, the effect of secondary nucleation is studied, as well as the crystallization rate of xylitol and how undercooling affects it. From the results, it is deduced that a proper seed preparation and handling is needed. The crystal structure is also studied, using XRPD diffractograms and differential scanning calorimetry.