Heating Mechanism Research Articles

Numerical modelling, parametric analysis and design of UHPFRC beams exposed to fire

A non-linear sequentially-coupled thermal–mechanical finite element (FE) paradigm that reasonably tracks the coupled fire-structure response of ultra-high performance fibre reinforced concrete (UHPFRC) beams subjected to the ISO 834 fire is established and presented. A fire resistance parameter study is conducted on UHPFRC beams via the developed FE paradigm, and then flexural based fire-structural assessment is demonstrated, as an avenue to substantiate the viability of numerical performance-based structural fire design. The parameter study considered two variables, notably heating mechanism and load levels. Comparison of results revealed that the fire-structure response was more severe under the hydrocarbon than the ISO 834 heating mechanism and hydrocarbon fire resistance ratings estimation were found to be 30 minutes lower than those determined using the ISO 834 fire. Predicted failure of the beams under the ISO 834 and hydrocarbon fires was observed at load ratios exceeding 0.6 and 0.4, respectively. By reposing on ACI544’s analytical model for UHPFRC beams in flexure, and numerically acquired heat-transfer response, the time-variant reduced nominal moment capacities of UHPFRC beams were computed. Failure predicted via computed residual moment capacities was somewhat consistent with that reckoned by load ratio parameter study.

Electron dynamics in planar radio frequency magnetron plasmas: II. Heating and energization mechanisms studied via a 2d3v particle-in-cell/Monte Carlo code

The present work investigates electron transport and heating mechanisms using an (r, z) particle-in-cell simulation of a typical rf-driven axisymmetric magnetron discharge with a conducting target. Due to a strong geometric asymmetry and a blocking capacitor, the discharge features a large negative self-bias conducive to sputtering applications. Employing decomposition of the electron transport parallel and perpendicular to the magnetic field lines, it is shown that for the considered magnetic field topology the electron current flows through different channels in the (r, z) plane: a ‘transverse’ one, which involves current flow through the electrons’ magnetic confinement region (EMCR) above the racetrack, and two ‘longitudinal’ ones, where electrons’ guiding centers move along the magnetic field lines. Electrons gain energy from the electric field along these channels following various mechanisms, which are rather distinct from those sustaining dc-powered magnetrons. The longitudinal power absorption involves mirror-effect heating (MEH), nonlinear electron resonance heating, magnetized bounce heating (MBH), and the heating by the ambipolar field at the sheath-presheath interface. The MEH and MBH represent two new mechanisms missing from the previous literature. The MEH is caused by a reversed electric field needed to overcome the mirror force generated in a nonuniform magnetic field to ensure sufficient flux of electrons to the powered electrode, and the MBH is related to a possibility for an electron to undergo multiple reflections from the expanding sheath in the longitudinal channels connected by the arc-like magnetic field. The electron heating in the transverse channel is caused mostly by the essentially collisionless Hall heating in the EMCR above the racetrack, generating a strong azimuthal drift velocity. The latter mechanism results in an efficient electron energization, i.e. energy transfer from the electric field to electrons in the inelastic range. Since the main electron population energized by this mechanism remains confined within the discharge for a long time, its contribution to the ionization processes is dominant.

Multifluid Simulations of Upper-chromospheric Magnetic Reconnection with Helium–Hydrogen Mixture

Our understanding of magnetic reconnection (MR) under chromospheric conditions remains limited. Recent observations have demonstrated the important role of ion–neutral interactions in the dynamics of the chromosphere. Furthermore, the comparison between the spectral profiles and synthetic observations of reconnection events suggests that current MHD approaches appear to be inconsistent with observations. First, collisions and multithermal aspects of the plasma play a role in these regions. Second, hydrogen and helium ionization effects are relevant to the energy balance of the chromosphere. This work investigates the multifluid multispecies (MFMS) effects on MR in conditions representative of the upper chromosphere using the multifluid Ebysus code. We compare an MFMS approach based on a helium–hydrogen mixture with a two-fluid MHD model based on hydrogen only. The simulations of MR are performed in a Lundquist number regime high enough to develop plasmoids and instabilities. We study the evolution of the MR and compare the two approaches including the structure of the current sheet and plasmoids, the decoupling of the particles, the evolution of the heating mechanisms, and the composition. The presence of helium species leads to more efficient heating mechanisms than the two-fluid case. This scenario, which is out of reach of the two-fluid or single-fluid models, can reach transition region temperatures starting from upper-chromospheric thermodynamic conditions, representative of a quiet Sun scenario. The different dynamics between helium and hydrogen species could lead to chemical fractionation and, under certain conditions, enrichment of helium in the strongest outflows. This could be of significance for recent observations of helium enrichment in the solar wind in switchbacks and coronal mass ejections.

A Heating Mechanism via Magnetic Pumping in the Intracluster Medium

Turbulence driven by active galactic nuclei activity, cluster mergers, and galaxy motion constitutes an attractive energy source for heating the intracluster medium (ICM). How this energy dissipates into the ICM plasma remains unclear, given its low collisionality and high magnetization (precluding viscous heating by Coulomb processes). Kunz et al. proposed a viable heating mechanism based on the anisotropy of the plasma pressure under ICM conditions. The present paper builds upon that work and shows that particles can be heated by large-scale turbulent fluctuations via magnetic pumping. We study how the anisotropy evolves under a range of forcing frequencies, what waves and instabilities are generated, and demonstrate that the particle distribution function acquires a high-energy tail. For this, we perform particle-in-cell simulations where we periodically vary the mean magnetic field B (t). When B (t) grows (dwindles), a pressure anisotropy P ⊥ > P ∥(P ⊥ < P ∥) builds up (P ⊥ and P ∥ are, respectively, the pressures perpendicular and parallel to B (t)). These pressure anisotropies excite mirror (P ⊥ > P ∥) and oblique firehose (P ∥ > P ⊥) instabilities, which trap and scatter the particles, limiting the anisotropy, and providing a channel to heat the plasma. The efficiency of this mechanism depends on the frequency of the large-scale turbulent fluctuations and the efficiency of the scattering the instabilities provide in their nonlinear stage. We provide a simplified analytical heating model that captures the phenomenology involved. Our results show that this process can be relevant in dissipating and distributing turbulent energy at kinetic scales in the ICM.

Mechanism and reservoir simulation study of the autothermic pyrolysis in-situ conversion process for oil shale recovery

The autothermic pyrolysis in-situ conversion process (ATS) consumes latent heat of residual organic matter after kerogen pyrolysis by oxidation reaction, and it has the advantages of low development cost and exploitation of deep oil shale resources. However, the heating mechanism and the characteristic of different reaction zones are still unclear. In this study, an ATS numerical simulation model was proposed for the development of oil shale, which considers the pyrolysis of kerogen, high-temperature oxidation, and low-temperature oxidation. Based on the above model, the mechanism of the ATS was analyzed and the effects of preheating temperature, O2 content, and injection rate on recovery factor and energy efficiency were studied. The results showed that the ATS in the formation can be divided into five characteristic zones by evolution of the oil and O2 distribution, and the solid organic matter, including residue zone, autothermic zone, pyrolysis zone, preheating zone, and original zone. Energy efficiency was much higher for the ATS than for the high-temperature nitrogen injection in-situ conversion process (HNICP). There is a threshold value of the preheating temperature, the oil content, and the injection rate during the ATS, which is 400 °C, 0.18, and 1100 m3/day, respectively, in this study.

Modeling of very high frequency large-electrode capacitively coupled plasmas with a fully electromagnetic particle-in-cell code

Phenomena taking place in capacitively coupled plasmas with large electrodes and driven at very high frequencies are studied numerically utilizing a novel energy- and charge-conserving implicit fully electromagnetic particle-in-cell (PIC)/Monte Carlo code ECCOPIC2M. The code is verified with three model problems and is validated with results obtained in an earlier experimental work (Sawada et al 2014 Japan. J. Appl. Phys. 53 03DB01). The code shows a good agreement with the experimental data in four cases with various collisionality and absorbed power. It is demonstrated that under the considered parameters, the discharge produces radially uniform ion energy distribution functions for the ions hitting both electrodes. In contrast, ion fluxes exhibit a strong radial nonuniformity, which, however, can be different at the powered and grounded electrodes at increased pressure. It is found that this nonuniformity stems from the nonuniformity of the ionization source, which is in turn shaped by mechanisms leading to the generation of energetic electrons. The mechanisms are caused by the interaction of electrons with the surface waves of two axial electric field symmetry types with respect to the reactor midplane. The asymmetric modes dominate electron heating in the radial direction and produce energetic electrons via the relatively inefficient Ohmic heating mechanism. In the axial direction, the electron energization occurs mainly through an efficient collisionless mechanism caused by the interaction of electrons in the vicinity of an expanding sheath with the sheath motion, which is affected by the excitation of the surface modes of both types. The generation of energetic electron populations as a result of such mechanisms is shown directly. Although some aspects of the underlying physics were demonstrated in the previous literature with other models, the PIC method is advantageous for the predictive modeling due to a complex interplay between the surface mode excitations and the nonlocal physics of the corresponding type of plasma discharges operated at low pressures, which is hard to reproduce in other models realistically.

ZnO based NOx gas and VOC detection sensor fabrication techniques and materials

Nano- or micro-nano gas sensors have attracted a lot of attention since they have the potential for several applications. Utilizing a coplanar integrated design of the microheater and the inter-digitated electrode, a chemo resistive ethanol gas sensor with a thin layer of zinc oxide (ZnO) as a sensing layer has been examined (IDE). The article's conclusion offers potential future paths and research opportunities for improved sensitivity and selectivity for these sensors. SnO2-based sensors have received a lot of attention in the field of hazardous gas detection because of their extraordinary sensitivity. ZnO thin films are created using a chemical method. Gas sensors must have reduced packaging because they are essential in modern industry for managing environmental concerns. Since the gas sensor must operate at temperatures higher than ambient temperature, using the heater is necessary. The heating mechanism for the detecting layer in the various gas sensors that have recently been developed is either external or incorporates additional layers. The suggested architecture might be helpful in cutting down on the number of layers that must be deposited for the sensor and additional heating circuits. A new architecture with a coplanar microheater and IDEs has been created to analyse the gas response. The ongoing work is built on the coplanar microheater with IDEs produced for the ethanol sensor. Additionally, studies have been conducted to examine how the sensor's sensing capabilities are impacted by the integrated architecture. The sensor detects a layer thickness of 430 nm with a sensing response of 110 the sensing layer is active over the substrate. The study's major goal is to show how an integrated coplanar microheater and IDE architecture may be used with ethanol sensor based on ZnO.

Energy Partition of Thermal and Nonthermal Particles in Magnetic Reconnection

Magnetic reconnection has long been known to be the most important mechanism for quick conversion of magnetic field energy into plasma kinetic energy. In addition, energy dissipation by reconnection has gained attention not only as a plasma heating mechanism, but also as a plasma mechanism for accelerating nonthermal particles. However, the energy partitioning of thermal and nonthermal plasmas during magnetic reconnection is not understood. Here, we studied energy partition as a function of plasma sheet temperature and guide magnetic field. In relativistic reconnection with an antiparallel magnetic field or a weak guide magnetic field, it was found that the nonthermal energy density can occupy more than 90% of the total kinetic plasma energy density, but strengthening the guide magnetic field suppresses the efficiency of the nonthermal particle acceleration. In nonrelativistic reconnection for an antiparallel magnetic field, most dissipated magnetic field energy is converted into thermal plasma heating. For a weak guide magnetic field with a moderate value, however, the nonthermal particle acceleration efficiency was enhanced, but strengthening the guide field beyond the moderate value suppresses the efficiency.

Nonlinear Coupling of Alfvén and Slow Magnetoacoustic Waves in Partially Ionized Solar Plasmas: The Effect of Thermal Misbalance

Solar chromosphere and photosphere, as well as solar atmospheric structures, such as prominences and spicules, are made of partially ionized plasmas. Observations have reported the presence of damped or amplified oscillations in these solar plasmas, which have been interpreted in terms of magnetohydrodynamic (MHD) waves. Slow magnetoacoustic waves could be responsible for these oscillations. The present study investigates the temporal behavior of the field-aligned motions that represent slow magnetoacoustic waves excited in a partially ionized prominence plasma by the ponderomotive force. Starting from single-fluid MHD equations, including radiative losses, a heating mechanism and ambipolar diffusion, and using a regular perturbation method, first- and second-order partial differential equations have been derived. By numerically solving second-order equations describing field-aligned motions, the temporal behavior of the longitudinal velocity perturbations is obtained. The damping or amplification of these perturbations can be explained in terms of heating–cooling misbalance, the damping effect due to ambipolar diffusion and the variation of the first adiabatic exponent with temperature and ionization degree.

Toward the Separation of Different Heating Mechanisms in Magnetic Particle Hyperthermia.

Magnetic particle hyperthermia (MPH) is a promising method for cancer treatment using magnetic nanoparticles (MNPs), which are subjected to an alternating magnetic field for local heating to the therapeutic range of 41-45 °C. In this window, the malignant regions (i.e., cancer cells) undergo a severe thermal shock while healthy tissues sustain this thermal regime with significantly milder side effects. Since the heating efficiency is directly associated with nanoparticle size, MNPs should acquire the appropriate size to maximize heating together with minimum toxicity. Herein, we report on facile synthetic controls to synthesize MNPs by an aqueous precipitation method, whereby tuning the pH values of the solution (9.0-13.5) results in a wide range of average MNP diameters from 16 to 76 nm. With respect to their size, the structural and magnetic properties of the MNPs are evaluated by adjusting the most important parameters, i.e. the MNP surrounding medium (water/agarose), the MNP concentration (1-4 mg mL-1), and the field amplitude (20-50 mT) and frequency (103, 375, 765 kHz). Consequently, the maximum heating efficiency is determined for each MNP size and set of parameters, outlining the optimum MNPs for MPH treatment. In this way, we can address the different heat generation mechanisms (Brownian, Néel, and hysteresis losses) to different sizes and separate Brownian and hysteresis losses for optimized sizes by studying the heat generation as a function of the medium viscosity. Finally, MNPs immobilized into agarose solution are studied under low-field MPH treatment to find the optimum conditions for clinical applications.

NIRwave: A wave-turbulence-driven solar wind model constrained by PSP observations

Aims. We generate a model description of the solar wind based on an explicit wave-turbulence-driven heating mechanism, and constrain our model with observational data. Methods. We included an explicit coronal heating source term in the general 3D magnetohydrodynamic code NIRVANA to simulate the properties of the solar wind. The adapted heating mechanism is based on the interaction and subsequent dissipation of counter-propagating Alfvén waves in the solar corona, accounting for a turbulent heating rate Qp. The solar magnetic field is assumed to be an axisymmetric dipole with a field strength of 1 G. Our model results are validated against observational data taken by the Parker Solar Probe (PSP). Results. Our NIRwave solar wind model reconstructs the bimodal structure of the solar wind with slow and fast wind speeds of 410 km s−1 and 650 km s−1 respectively. The global mass-loss rate of our solar wind model is 2.6 × 10−14 M⊙ yr−1. Despite implementing simplified conditions to represent the solar magnetic field, the solar wind parameters characterising our steady-state solution are in reasonable agreement with previously established results and empirical constraints. The number density from our wind solution is in good agreement with the derived empirical constraints, with larger deviations for the radial velocity and temperature. In a comparison to a polytropic wind model generated with NIRVANA, we find that our NIRwave model is in better agreement with the observational constraints that we derive.

Investigation on the microwave sintering heating process and mechanism of h-BN/ZrO2/SiC composites

To explore the potential of microwave sintering's application in the preparation of h-BN/ZrO2 based side sealing plate, h-BN/ZrO2/SiC composites were sintered using above technology. The effect of feedstock material composition and input microwave power regulation rate on the microwave sintering process was emphatically analyzed. The phase composition, microstructure and related physical properties of sintered composites were examined. The results indicated that ZrB2 was generated in microwave sintered h-BN/ZrO2/SiC. The fracture strength and apparent porosity were 42 MPa and 11%, respectively, when the composite was sintered at 1550 °C for 30 min. Regarding the heating process of sample during microwave sintering, larger input power in the heating stage could increase the heating rate and ensure the sample obtain higher sintering temperature. After reaching the sintering temperature, the highest sintering temperature could be maintained even if the input power was greatly reduced in the holding stage. When the temperature exceeded a critical value, the sintering temperature of the sample would decrease obviously even if the input power greatly increased. The above phenomenon could be attributed to the power redistribution effect of microwave sintering. Based on this effect, the change of SiC content also had a significant impact on the microwave sintering process, which mostly depended on the variations of dielectric loss and electroconductibility of SiC due to the evolution of temperature.

Transient energetic particles as the origin of the mid-infrared north polar hotspot of Jupiter

Since it was detected in 1980, Jupiter's 8-μm CH4 north polar hot spot (8CNPHS), ∼20 K warmer than the surrounding polar stratosphere, has been observed for four decades. Unlike normal auroral ovals (i.e., the bright rings of auroral emissions), it is usually filled with bright emission. The causes of both its shape and longevity are not understood, although several mechanisms have been proposed to explain its existence. In order to investigate the deriving mechanism of the 8CNPHS, we have observed the north polar regions near 3 μm, where line emission from another CH4 band as well as a C2H6 fundamental band occur. Using Gemini North/GNIRS in 2013, 2020, 2021, and 2022, we have detected transient 3-μm CH4 and/or C2H6 bright spots within the 8CNPHS, and occasionally no apparent bright spots. By comparing the emission from CH4 with that from C2H6, we demonstrate that the origin of the 8CNPHS must be due to transient and energetic magnetospheric particles, which can penetrate down to the hydrocarbon layers, heating the homopause (∼1 μbar level) and the stratosphere (∼1 mbar level) and energize the 8CNPHS. Based on our observations and analysis, we propose the following three mechanisms for maintaining and containing the decades long warmth of the 8CNPHS: 1) energetic and transient auroral particle precipitations warming the stratosphere of the 8CNPHS, 2) a longer radiative cooling time in the 8CNPHS stratosphere (∼6 months) compared to less than or equal to one month at the homopause, and 3) recently detected polar stratospheric jets likely associated with polar fronts, which resist the free flow of warm gas in the 8CNPHS to the surrounding polar regions. We show that other heating mechanisms proposed so far in the literature, such as Joule heating, polar haze heated by sunlight, etc., are only the secondary mechanisms that follow atmospheric ionization caused by energetic particle bombardment. Our finding of the magnetospheric-ionospheric-stratospheric coupling in the Jovian polar regions open the possibility of quantitatively refining 3-D global circulation models for the atmospheres of giant planets and exoplanets.

Two-dimensional particle-in-cell simulation of electron heating effect in multiple hollow cathode trenches with curved boundary

A particle-in-cell simulation is suitable for simulating capacitively coupled plasma devices because it calculates the trajectory of particles with arbitrary energy distributions and has the advantage of analyzing sheath dynamics precisely. Implementing the ghost grid method in the Poisson solver makes it possible to simulate a curved structure in the structured grids. The electron transport and heating mechanism are determined according to the two-dimensional (2D) sheath dynamics. The hollow cathode effect on electron transport was analyzed by varying the hole shape and gas pressure. The spatial distributions of electron density and temperature are influenced by the energy relaxation length of electrons, which is affected by the energy distribution function and gas pressure. As a result, a new electron heating mode appears in the 2D structure.

Presence of liquid water during the evolution of exomoons orbiting ejected free-floating planets

AbstractFree-floating planets (FFPs) can result from dynamical scattering processes happening in the first few million years of a planetary system's life. Several models predict the possibility, for these isolated planetary-mass objects, to retain exomoons after their ejection. The tidal heating mechanism and the presence of an atmosphere with a relatively high optical thickness may support the formation and maintenance of oceans of liquid water on the surface of these satellites. In order to study the timescales over which liquid water can be maintained, we perform dynamical simulations of the ejection process and infer the resulting statistics of the population of surviving exomoons around FFPs. The subsequent tidal evolution of the moons’ orbital parameters is a pivotal step to determine when the orbits will circularize, with a consequential decay of the tidal heating. We find that close-in ($a \lesssim 25$RJ) Earth-mass moons with carbon dioxide-dominated atmospheres could retain liquid water on their surfaces for long timescales, depending on the mass of the atmospheric envelope and the surface pressure assumed. Massive atmospheres are needed to trap the heat produced by tidal friction that makes these moons habitable. For Earth-like pressure conditions (p0= 1 bar), satellites could sustain liquid water on their surfaces up to 52 Myr. For higher surface pressures (10 and 100 bar), moons could be habitable up to 276 Myr and 1.6 Gyr, respectively. Close-in satellites experience habitable conditions for long timescales, and during the ejection of the FFP remain bound with the escaping planet, being less affected by the close encounter.

Characterization of the tensile behavior of continuous carbon fiber reinforced polyamide 6 under self‐resistance electrical heating

AbstractThe stamping molding with self‐resistance electric (SRE) heating is advantageous for the mass production of carbon fiber reinforced thermoplastic (CFRT) because of its short production cycle and energy efficiency. The mechanism of SRE heating is different from traditional oven heating. The impact on CFRT laminates under loading is ambiguous. In this article, the tensile testing systems with SRE heating and traditional heating were designed. The temperature distribution, mechanical response, strain, and failure mode of carbon fiber reinforced polyamide 6 (CFR‐PA6) laminates under SRE heating are studied and contrasted with traditional heating. Specifically, to measure the full‐field strain distribution, digital‐image correlation (DIC) technique and high‐speed camera were introduced. It is found that the electric resistance fluctuates in tensile test with SRE heating and shown temperature sensitivity. Temperature distribution of the specimen under SRE heating is relatively uniform. Besides, the mechanical properties (i.e., tensile strength and elastic modulus) of CFR‐PA6 seem to be insensitive to heating mode. DIC results show that deconsolidation phenomenon makes the specimen fracture randomly. Inversely, heating method has an obvious influence on failure modes. To be specific, there are more shearing damage in traditional heating during high temperature. High current under SRE heating causes corrosion on fiber surface and destroy the fiber‐resin matrix interface.

Energizing gamma ray bursts via Z^{prime } mediated neutrino heating

The pair annihilation of neutrinos (nu {overline{nu }}rightarrow e^+e^-) can energize violent stellar explosions such as gamma ray bursts (GRBs). The energy in this neutrino heating mechanism can be further enhanced by modifying the background spacetime over that of Newtonian spacetime. However, one cannot attain the maximum GRB energy (sim 10^{52}~text {erg}) in either the Newtonian background or Schwarzschild and Hartle–Thorne background. On the other hand, using modified gravity theories or the Quintessence field as background geometries, the maximum GRB energy can be reached. In this paper, we consider extending the standard model by an extra U(1)_{{mathrm{B-L}}} gauge group and augmenting the energy deposition by neutrino pair annihilation process including contributions mediated by the Z^{prime } gauge boson belonging to this model. From the observed energy of GRB, we obtain constraints on U(1)_{{mathrm{B-L}}} gauge coupling in different background spacetimes. We find that the bounds on gauge coupling in modified gravity theories and quintessence background are stronger than those coming from the neutrino-electron scattering experiments in the limit of small gauge boson masses. Future GRB observations with better accuracy can further strengthen these bounds.

Comparative Study of Sensory and Physicochemical Characteristics of Green-Tea-Fortified Cupcakes upon Air Frying and Oven Baking.

The air fryer and the oven are common cooking methods in our daily lives. However, previous investigations of the air fryer were limited to its comparison with deep-fat frying. This study compared the differences between air frying and household oven baking (without a fan or other forced airflow inside) on food quality and physicochemical properties using a cupcake model. Results showed that the oven-baked cupcakes were softer in texture (87.15%), greener in color (6.07%), and lower in weight loss (7.78%) and toxic advanced glycation end products (AGEs, 21.40%) when the heating temperature and duration were the same as oven baking. To improve the sensory characteristics and health value, the cupcakes were fortified with green tea. The differences in texture, color, and level of toxicants between the two cooking methods were diminished after the addition of green tea. Moreover, the chemical profiles of green tea catechins in the green-tea-fortified cupcakes remained similar upon thermal cooking, except that the air-fried cupcakes were lower in gallic acid (GA) but higher in (-)-gallocatechin (GC). Collectively, based on the differences in heating mechanisms, our data indicated that oven baking is a better cooking method suitable to prepare cupcakes than air frying from the perspectives of sensory characteristics and food safety, while green tea additives effectively counter the drawbacks of the air fryer.

Pyrolysis of banana peel with microwave and furnace as the heating sources: The distinct impacts on evolution of the pyrolytic products

Microwave pyrolysis features with different heating mechanisms and heat transfer directions from traditional pyrolysis with furnace heating, which might impact evolution of volatiles and nature of biochar in varied ways. This was investigated in this study by pyrolysis of wet and dried banana peel with microwave heating and furnace heating at 400 and 600 °C in a fixed-bed reactor. The results showed that microwave pyrolysis could drastically promote gasification of volatiles to form significantly more gases like H2 via dehydrogenation and CO via cracking and decarbonylation. This was especially evident in the pyrolysis of wet banana peel with abundant water as the heat transfer medium. The dominance of cracking/gasification of volatiles in microwave pyrolysis was due to the rapid heating and the minimized heat transfer limitation, which suppressed the secondary condensation and thus diminished the formation of bio-oil and biochar. Microwave pyrolysis also favored the cracking of the cellulose/hemicellulose-derived aliphatic organics via cracking but promoted the formation of phenolics via cracking of lignin in banana peel. Moreover, the excessive cracking reactions in the microwave pyrolysis led to the biochar of more excellent thermal stability, lower abundance of oxygen-containing functionalities like CO and more rugged morphology than that with furnace heating source.

Surface temperature characterization of dielectric barrier discharge plasma actuator in quiescent air

Dielectric barrier discharge plasma actuators (DBDPAs) have been investigated for active flow control. The discharge induces ionic wind, which can be utilized for flow control; however, it simultaneously heats the flow and the dielectric surface. The thermal characteristics of the DBDPA must be clarified for applications in thermo-fluid engineering, such as forced convective cooling. In this study, we constructed a similarity law for the time variation of the surface temperature, assuming that the induced flow was heated by the discharge and that the dielectric was heated by the airflow. The similarity law was derived from the one-dimensional heat conduction equation in the dielectric, and the spatially averaged normalized temperature was then formulated as a function of the Biot and Fourier numbers. To experimentally validate the similarity law, the surface temperature, thrust, and power consumption were measured. The induced flow temperature and heat transfer coefficient were estimated based on the thrust and power consumption. The measured results verified that the similarity law was valid, regardless of the dielectric material, thickness, or applied voltage. This result supports the hypothesis regarding the heating mechanism in which the airflow is heated by Joule heating and the dielectric is heated by forced convection.