Nottingham Heating, Inversion Temperature and Joule Heating

Long-term research has been done on the unstable behaviors and electron emission from microprotrusions, but the whole reason is still not clear. It is difficult to study instabilities experimentally since vacuum breakdown can happen. In this model, we show the factors that lead to thermal instability during field emission. After the Nottingham flux inversion, we see a considerable rise in temperature above a threshold electric field, followed by a thermal runaway. Cathode spots experience unexpected thermal defects and breakdowns, which is a phenomenon known as the Nottingham Inversion Instability. Although the idea of micro protrusions is frequently used in modeling studies, this study concentrates on the thermal effects during field emission from a planar cathode without taking the existence of such protrusions into account. The study reveals how Nottingham’s heating effect changes from heating to cooling. In our study, we have investigated the interaction between Nottingham, Joule heating, and effective work function. The results also imply that faster reaching critical temperature is associated with larger maximum beta values. These discoveries have significance for the design and improvement of high-voltage systems and help to understand vacuum breakdown. The possibility of cathode spot ignition and subsequent vacuum breakdown is predicted by our model, which would make it possible to create a self-consistent model for that.

Heat Absorption and Joule Heating Effects on Transient Free Convective Reactive Micropolar Fluid Flow Past a Vertical Porous Plate

Mathematical model for an unsteady,incompressible,electrically conducting micropolar fluid past a vertical plate through porous medium with constant plate velocity has been investigated in the present study.Heat absorption,Joulian dissipation,and first-order chemical reaction is also considered.Under the assumption of low Reynolds number,the governing transport equations are rendered into non-dimensional form and the transformed first order differential equations are solved by employing an efficient finite element method.Influence of various flow parameters on linear velocity,microrotation velocity,temperature,and concentration are presented graphically.The effects of heat absorption and chemical reaction rate decelerate the flow is particularly near the wall.Skin friction and wall couple stress increases as heat absorption increases but the reverse phenomenon is observed in the case of chemical reaction rate.Wall mass transfer rate increases for chemical reaction and Sherwood number increases for heat absorption.Finite element study is very versatile in simulating unsteady micropolar rheo-materials processing transport phenomena.However,a relatively simple reaction effects restricted to first order.

Peristaltic flow in an asymmetric channel with convective boundary conditions and Joule heating

The peristaltic transport of viscous fluid in an asymmetric channel is concentrated. The channel walls exhibit convective boundary conditions. Both cases of hydrodynamic and magnetohydrodynamic(MHD) fluids are considered. Mathematical analysis has been presented in a wave frame of reference. The resulting problems are non-dimensionalized. Long wavelength and low Reynolds number approximations are employed. Joule heating effect on the thermal equation is retained. Analytic solutions for stream function and temperature are constructed. Numerical integration is carried out for pressure rise per wavelength. Effects of influential flow parameters have been pointed out through graphs.

Numerical analysis on Joule heating of double-loop channel induction furnaces

In order to investigate Joule heating power,a three-dimensional finite element model(FEM) was developed to predict Joule heating power in the channels of double-loop inductor. The simulated results were compared with experimental data from low load trials for a 400 kW inductor. The results,such as power factor and Joule heating power,show reasonable correlation with experimental data,and Joule heating rate reaches the maximum at the corners and the minimum at the centre of the cross-section area. With increasing relative permeability of iron core,length of coils,current frequency and resistivity of metal melt,the power factor and Joule heating power change. It is concluded that current frequency,the resistivity and length of the coil play a critical role in determining the power factor and Joule heating power,whereas relative permeability of the magnetic core shows no significant influence on them.

Effect of Joule heating on the electroosmotic microvortex and dielectrophoretic particle separation controlled by local electric field

Dielectrophoresis(DEP)technology has become important application of microfluidic technology to manipulate particles.By using a local modulating electric field to control the combination of electroosmotic microvortices and DEP,our group proposed a device using a direct current(DC)electric field to achieve continuous particle separation.In this paper,the influence of the Joule heating effect on the continuous separation of particles is analyzed.Results show that the Joule heating effect is caused by the local electric field,and the Joule heating effect caused by adjusting the modulating voltage is more significant than that by driving voltage.Moreover,a non-uniform temperature distribution exists in the channel due to the Joule heating effect,and the temperature is the highest at the midpoint of the modulating electrodes.The channel flux can be enhanced,and the enhancement of both the channel flux and temperature is more obvious for a stronger Joule heating effect.In addition,the ability of the vortices to trap particles is enhanced since a larger DEP force is exerted on the particles with the Joule heating effect;and the ability of the vortex to capture particles is stronger with a stronger Joule heating effect.The separation efficiency can also be increased because perfect separation is achieved at a higher channel flux.Parameter optimization of the separation device,such as the convective heat transfer coefficient of the channel wall,the length of modulating electrode,and the width of the channel,is performed.

Joule heating effect of electroosmosis in a finite-length microchannel made of different materials

This paper presents a numerical analysis of Joule heating effect of electroosmo- sis in a finite-length microchannel made of the glass and polydimethylsiloxane （PDMS） polymer. The Poisson-Boltzmann equation of electric double layer, the Navier-Stokes equation of liquid flow, and the liquid-solid coupled heat transfer equation are solved to investigate temperature behaviors of electroosmosis in a two-dimensional microchannel. The feedback effect of temperature variation on liquid properties （dielectric constant, vis- cosity, and thermal and electric conductivities） is taken into account. Numerical results indicate that there exists a heat developing length near the channel inlet where the flow velocity, temperature, pressure, and electric field rapidly vary and then approach to a steady state after the heat developing length, which may occupy a considerable portion of the microchannel in cases of thick chip and high electric field. The liquid temperature of steady state increases with the increase of the applied electric field, channel width, and chip thickness. The temperature on a PDMS wall is higher than that on a glass wall due to the difference of heat conductivities of materials. Temperature variations are found in the both longitudinal and transverse directions of the microchannel. The increase of the temperature on the wall decreases the charge density of the electric double layer. The longitudinal temperature variation induces a pressure gradient and changes the behavior of the electric field in the microchannel. The inflow liquid temperature does not change the liquid temperature of steady state and the heat developing length.

Direct ink writing of multifunctional gratings with gel-like MXene/norepinephrine ink for dynamic electromagnetic interference shielding and patterned Joule heating

Intelligent electromagnetic interference(EMI)shielding modulators with a wide tuning range and cyclic stability are urgently needed but their fabrication remains challenging.A gel-like MXene/norepinephrine ink is developed and multifunctional MXene gratings with wide EMI shielding effectiveness(SE)tuning range,superior reversibility,and high mechanical flexibility are constructed by direct ink writing approach for dynamic EMI shielding and patterned Joule heating applications.The modulable MXene/norepinephrine grating with a high conductivity of 3510 S·cm-1 can conveniently realize the seamless modulation of the EMI SE by adjusting the angle between the MXene grating filaments and the electric field of the incident electromagnetic waves,offering highly reversible switching between shielding“On”(28.0 dB)and“Off”(0.5 dB)states.Notably,due to the optimized integration of the MXene ink and the rationally designed pattern,a superior specific EMI SE of 95,688.2 dB·cm^(2)·g^(-1) is achieved in the“On”state.Furthermore,the MXene/norepinephrine ink can be used to fabricate many complex patterned gratings with superior stability,instant responsibility,and superb mechanical flexibility,exhibiting a unique patterned Joule heating behavior.Direct writing of multifunctional gratings paves a means for developing intelligent EMI shielding materials,wearable electronic devices,and advanced thermal management materials.

Transient synthesis of carbon-supported high-entropy alloy sulfide nanoparticles via flash Joule heating for efficient electrocatalytic hydrogen evolution

High entropy alloys(HEA)are frequently employed as catalysts in electrocatalytic hydrogen evolution.However,the traditional high entropy alloy synthesis methods are time-consuming,energy-intensive,and environmentally polluting,which limits their application in the hydrogen evolution reaction(HER).This study leveraged the capabilities of flash Joule heating(FJH)to synthesize carbon-supported high-entropy alloy sulfide nanoparticles(CC-S-HEA)on carbon cloth(CC)with good self-standing properties within 300 ms.The carbon thermal shock generated by the Joule heating could pyrolyze the sulfur source into gas,resulting in numerous pore structures and defects on CC,forming an S-doped carbon substrate(CC-S).Then the S atoms were used to stably anchor the metal atoms on CC-S to form high-density uniformly dispersed HEA particles.The electrochemical test results demonstrated that CC-S-HEA prepared at 60 V flash voltage had HER performance comparable to Pt/C.The density functional theory(DFT)calculation indicated that the S atoms on CC-S accelerated the electron transfer between the carbon substrate and HEA particles.Moreover,the unique electronic structure of CC-S-HEA was beneficial to H*adsorption and promoted catalytic kinetics.The simplicity and versatility of FJH synthesis are of great significance for optimizing the synthesis of HEA and improving the quality of HEA products,which provides a broad application prospect for the synthesis of nanocatalysts with efficient HER performance.

General synthesis of transition metal nitride arrays by ultrafast flash Joule heating within 500 ms

Transition metal nitrides(TMNs)are considered as viable alternatives to noble metal catalysts owing to their versatile electronic structure and favorable catalytic performance.However,the conventional synthetic processes for TMNs suffer from high energy consumption and low production yield.In this study,a range of TMNs and their hetero-composite arrays were successfully synthesized via an ultrafast flash Joule heating technology within 0.5 s.As a proof concept,the nitrides and hetero-composites were applied for the electrocatalytic hydrazine oxidation reaction(HzOR),in which the Co_(4)N/Mo_(16)N_(7)arrays shows the best performance with a geometric current density of 100 mA cm^(-2)at 23 mV(vs.reversible hydrogen electrode(RHE)).This work paves a new way for the ultrafast synthesis of TMNs which could meet the ever-increased energy crisis.

Ultra-thin robust CNT@GC film integrating effective electromagnetic shielding and flexible Joule heating

The demand for lightweight,thin electromagnetic interference(EMI)shielding film materials with high shielding effectiveness(SE),excellent mechanical properties,and stability in complex environments is particularly pronounced in the realm of flexible and portable electronic products.Here,we developed an ultra-thin film(CNT@GC)in which the glassy carbon(GC)layer wrapped around and welded carbon nanotubes(CNTs)to form a core-shell network structure,leading to exceptional tensile strength(327.2 MPa)and electrical conductivity(2.87×10^(5) S·m^(−1)).The CNT@GC film achieved EMI SE of 60 dB at a thickness of 2µm after post-acid treatment and high specific SE of 3.49×10^(5) dB·cm^(2)·g^(−1),with comprehensive properties surpassing those of the majority of previous shielding materials.Additionally,the CNT@GC film exhibited Joule heating capability,reaching a surface temperature of 135℃at 3 V with a fast thermal response of about 0.5 s,enabling anti-icing/de-icing functionality.This work presented a methodology for constructing a robust CNT@GC film with high EMI shielding performance and exceptional Joule heating capability,demonstrating immense potential in wearable devices,defense,and aerospace applications.

Tailoring of a robust asymmetric aramid nanofibers/MXene aerogel film for enhanced infrared thermal camouflage and Joule heating performances

The development of infrared(IR)surveillance technology has led to a growing interest in thermal camouflage.However,the trade-off relationship between low IR-emissivity and thermal insulation hinders the advance of thermal camouflage materials.Herein,guided by multi-physics simulation,we show a design of asymmetric aramid nanofibers/MXene(ANF/MXene)aerogel film that realizes high-efficient thermal camouflage applications.The rationale is that the asymmetric structure contains a thermal-insulation three-dimensional(3D)network part to prevent effective heat transfer and a low IR-emissivity(~0.3)dense surface layer to suppress radiative heat emission.It is remarkable that the synergy mechanism in the topology structure contributes to over 40%reduction of target radiation temperature.Impressively,the tailored asymmetric ANF/MXene aerogel film also enables sound mechanical properties such as a Young’s modulus of 44.4 MPa and a tensile strength of 1.3 MPa,superior to most aerogel materials.It also exhibits great Joule heating performances including low driving voltage(4 V),fast thermal response(<10 s),and long-term stability,further enabling its versatile thermal camouflage applications.This work offers an innovative design concept to configure multifunctional structures for next-generation thermal management applications.

Flexible mille-feuille structure electromagnetic interference shielding film with excellent thermal conductivity and Joule heating

The intelligent electronic devices have urgent demands for electromagnetic interference(EMI)shielding films with excellent heat dissipation capability.However,it is challenging to obtain excellent EMI shielding and thermal conductivity performances simultaneously.Herein,inspired by mille-feuille structure,the multifunctional EMI shielding films developed by a layer-by-layer self-assembly and hot-pressing strategy.The ingenious introduction of silver nanoparticles(AgNPs)with large specific surface area and highly conductive into the network formed by TEMPO-oxidized cellulose nanofibrils(TOCNFs)with large aspect ratio to form the TOCNFs/AgNPs.And the graphene nanoplates(GNPs)with high conductivity loss distributed alternately with TOCNFs/AgNPs to construct mille-feuille structure,which had highly efficient conductive network,complete thermally conduction pathway and rich heterogeneous interfaces.Consequently,the designed films presented high electrical conductivity of 8520 S/cm,superb EMI effectiveness(SE)of 98.05 dB,and excellent thermal conductivity of 18.82 W/(m·K).Furthermore,the films possessed outstanding Joule heating performances with low voltages,including high heating temperature(100℃),fast response time(<20 s),and impressive heating stability and reliability.Thus,such high-performance EMI shielding films with fascinating thermal conductivity and Joule heating performances have substantial application in flexible electronics,electromagnetic waves shielding and thermal management.

Highly conductive calcium ion-reinforced MXene/sodium alginate aerogel meshes by direct ink writing for electromagnetic interference shielding and Joule heating

Although MXene sheets possess high electrical conductivity and rich surface chemistry and are well suit-able for fabricating electrically conductive nanocomposites for electromagnetic interference(EMI)shield-ing applications,it remains challenging for MXene nanocomposites to achieve tunable EMI shielding per-formances and customized geometries.Herein,an aqueous MXene/sodium alginate ink is developed to print aerogel meshes with customized geometries using a direct ink writing approach.An ion-enhanced strategy is proposed to reinforce the printed aerogel meshes by multi-level cross-linking.The resultant 3D printed aerogel mesh exhibits an ultrahigh electrical conductivity of 2.85×10^(3)S m^(−1),outstanding mechanical properties,and excellent structural stability in wet environment.More importantly,a wide range of tunable EMI shielding efficiencies from 45 to 100 dB is achieved by the structural design of the 3D printed ion-enhanced MXene/sodium alginate aerogel meshes.As a Joule heater,in addition,the printed aerogel meshes can achieve a wide temperature range of 40-135℃at low driving voltages.This work demonstrates a direct ink writing approach for the fabrication of ion-enhanced MXene/sodium al-ginate aerogel meshes with tunable EMI shielding properties and multi-functionalities for applications in many scenarios.

Graphene/SiC-coated textiles with excellent electromagnetic interference shielding,Joule heating,high-temperature resistance,and pressure-sensing performances

Multifunctional,wearable,and durable textiles integrated with smart electronics have attracted tremendous attention.However,it remains a great challenge to balance new functionalities with high-temperature stability.Herein,textile-based pressure sensors with excellent electromagnetic interference(EMI)shielding,Joule heating,and high-temperature resistance were fabricated by constructing graphene/SiC(G/SiC)heterostructures on carbon cloth via laser chemical vapor deposition(LCVD).The resultant textiles exhibited excellent EMI efficiency of 74.2 dB with a thickness of 0.45 mm,Joule heating performance within a low working voltage(V)range of 1-3 V,and fast response time within 20 s.These properties arose from multiple reflections,interfacial polarization,and high conductivity due to the numerous amounts of nanoscale G/SiC heterostructures.More importantly,G/SiC/carbon fibers(CFs)demonstrated well high-temperature resistance with a heat resistance index(THri)of 380.2 C owing to the protection of a coating layer on the CFs upon oxidation.Meanwhile,the G/SiC/CFs presented good pressure-sensing performance with high sensitivity(S)of 52.93 kPal,fast response time of 85 ms,and a wide pressure range of up to 186 kPa.These features imply the potential of the G/SiC/CFs as efficient EMI shielding,electrical heater,and piezoresistive sensor textiles.

Janus(BNNS/ANF)-(AgNWs/ANF)thermal conductivity composite films with superior electromagnetic interference shielding and Joule heating performances

Highly thermal conductivity materials with excellent electromagnetic interference shielding and Joule heating performances are ideal for thermal management in the next generation of communication industry,artificial intelligence and wearable electronics.In this work,silver nanowires(AgNWs)are prepared using silver nitrate as the silver source and ethylene glycol as the solvent and reducing agent,and boron nitride(BN)is performed to prepare BN nanosheets(BNNS)with the help of isopropyl alcohol and ultrasonication-assisted peeling method,which are compounded with aramid nanofibers(ANF)prepared by chemical dissociation,respectively,and the(BNNS/ANF)-(AgNWs/ANF)thermal conductivity and electromagnetic interference shielding composite films with Janus structures are prepared by the"vacuum-assisted filtration and hot-pressing"method.Janus(BNNS/ANF)-(AgNWs/ANF)composite films exhibit"one side insulating,one side conducting"performance,the surface resistivity of the BNNS/ANF surface is 4.7×10^(13) Ω,while the conductivity of the AgNWs/ANF surface is 5,275 S/cm.And Janus(BNNS/ANF)-(AgNWs/ANF)composite film with thickness of 95 pm has a high in-plane thermal conductivity coefficient of 8.12 W/(m·K)and superior electromagnetic interference shielding effectiveness of 70 dB.The obtained composite film also has excellent tensile strength of 122.9 MPa and tensile modulus and 2.7 GPa.It also has good temperature-voltage response characteristics(high Joule heating temperature at low supply voltage(5 V,215.0℃),fast response time(10 s)),excellent electrical stability and reliability(stable and constant real-time relative resistance under up to 300 cycles and 1,500 s of tensile-bending fatigue work tests).

Study of heat and mass transfer with Joule heating on magnetohydrodynamic(MHD)peristaltic blood flow under the influence of Hall effect

In this article,heat and mass transfer with Joule heating on magnetohydrodynamic(MHD)peristaltic blood under the influence of Hall effect is examined.Mathematical modelling is based on momentum,energy and concentration which are taken into account using ohms law.The governing partial differential equations are further simplified by neglecting the inertial forces and long wavelength approximations.Exact solutions have been presented for velocity,temperature and concentration profile.The influence of all the physical pertinent parameters is taken into account with the help graphs.It is found that Hartmann number and Hall parameter shows opposite behaviour on velocity,temperature and concentration profile.It is worth mentioning that pressure rise also depicts opposite behaviour for Hartmann number and Hall parameter.The present analysis is also presented for Newtonian fluid(α→0)as a special case for our study.It is observed that Hall Effect and magnetic field shows opposite behaviour on velocity and temperature profile.Temperature profile increases due to the increment in Prandtl number and Eckert number.Numerical comparison is also presented between the existing published results by takingα=0;M=0 as a special case of our study.

Effects of thermal boundary conditions on the joule heating of electrolyte in a microchannel

Joule heating effects on a slit microcharmel filled with electrolytes are comprehensively investigated with emphasis on the thermal boundary conditions. An accurate analytical expression is proposed for the electrical field and the temperature distributions due to Joule heating are numerically obtained from the energy balance equation. The results show that a thermal design based on the average electric potential difference between electrodes can cause severe underestimation of Joule heating. In addition, the parame- tric study of thermal boundary conditions gives us an insight into the best cooling scenario for microfluidic devices. Other significant thermal characteristics, including Nusselt number, thermophoretic force, and entropy generation, are discussed as well. This study will provide useful information for the optimization of a bioMEMS device in relation to the thermal aspect.

Effects of viscous dissipation and Joule heating on the Couette and Poiseuille flows of a Jeffrey fluid with slip boundary conditions

In this article,we have presented the exact solutions of the Couette,Poiseuille and generalized Couette flows of an incompressible magnetohydrodynamic Jeffrey fluid between parallel plates through homogeneous porous medium.The effects of slip boundary conditions and heat transfer are considered.Viscous dissipation,radiation and Joule heating are also considered in the energy equation.The governing equations of the Jeffrey fluid flow are modeled in Cartesian coordinate system.Analytical solutions for the velocity and temperature the velocity and temperature profiles are studied and the results are presented through graphs.It Temperature behaves as a decreasing function due to the impact of Hartmann number,non-Newtonian parameter and slip parameter in all noted problems.

Joule heating and viscous dissipation effect on electroosmotic mixed convection flow in a vertical microchannel subjected to asymmetric heat fluxes

The impact of Joule heating due to electric double layer(EDL)and viscous dissipation on electroosmotic mixed convection flow in a vertical microchannel with asymmetric heat fluxes is established in this article.The Poisson-Boltzmann,momentum and energy equations representing the electric potential,velocity profile and temperature distribution in the microchannel are obtained in dimensionless forms.Using the Debye-Hückel linearization,exact solutions are obtained for electric potential,velocity profile and temperature distributions by method of undetermined coefficients in the absence of viscous dissipation and Joule heating while an inbuilt Matlab function called pdepe is employed to solve the coupled nonlinear momentum and energy equations in the presence of Joule heating and viscous dissipation.Results show that the presence of Joule heating and viscous dissipation lead to decrease in velocity profile and temperature distributions throughout the microchannel.

Convective heat and mass transfer analysis on peristaltic flow of Williamson fluid with Hall effects and Joule heating

This paper deals with the peristaltic flow of an incompressible and electrically conducting Williamson fluid in a symmetric planar channel with heat and mass transfer. Hall effects, viscous dissipation and Joule heating are also taken into consideration. Mathematical model is presented by using the long wavelength and low Reynolds number approximations. The differential equations governing the flow are highly nonlinear and thus perturbation solution for small Weissenberg number （0 〈 We 〈 1） is presented. Effects of the heat and mass transfer Biot numbers and Hall parameter on the longitudinal velocity, temperature, concentration and pumping characteristics are studied in detail. Main observations are presented in the concluding section, The streamlines pattern and trapping are also given due attention.