Heat diffusion optimization in high performance perovskite solar cells integrated with zeolite

Heat accumulation inside perovskite solar cells causes the decomposition of the perovskite layer and hole transport materials(HTMs)under working conditions,yielding a decrease in long-term stability.Here,we present a zeolite-assisted heat conduction strategy by introducing economic zeolite crystals(e.g.,NaX,NaY,and ZSM-5)as a cooling filter to induce heat diffusion.The fitted thermal diffusion kinetic equation from real-time infrared thermal imaging technology reveals the zeolite skeleton assisted thermal co nduction mechanism of internal lattice vibration.Additionally,the nearly twofold improved conductivity of the modified HTM film is benefited from Na^(+)hopping on the supercages of the zeolite,therefore,the best-performed device with a rapid heat diffusion and defect inhibition obtains a remarkable power conversion efficiency of 23.42%.Both of NaX modified sprio-OMeTAD and PTAA based devices exhibit excellent operational stability after heating 1000 h at 85℃under N_(2)condition.This work demonstrates the potential application of economical porous zeolite materials in improving the thermal stability of PSCs.

Analysis of Heat Transfer Phenomenon in Magnetohydrodynamic Casson Fluid Flow Through Cattaneo–Christov Heat Diffusion Theory

Heat transport phenomenon of two-dimensional magnetohydrodynamie Casson fluid flow by employing Cattaneo-Christov heat diffusion theory is described in this work. The term of heat absorption/generation is incorporated in the mathematical modeling of present flow problem. The governing mathematical expressions are solved for velocity and temperature profiles using RKF 45 method along with shooting technique. The importance of arising nonlinear quantities namely velocity, temperature, skin-friction and temperature gradient are elaborated via plots. It is explored that the Casson parameter retarded the liquid velocity while it enhances the fluid temperature. Fhrther, we noted that temperature and thickness of temperature boundary layer are weaker in case of Cattaneo-Christov heat diffusion model when matched with the profiles obtained for Fourier＇s theory of heat flux.

Connection between heat diffusion and heat conduction in one-dimensional systems

Heat and energy are conceptually different, but often are assumed to be the same without justification. An effective method for investigating diffusion properties in equilibrium systems is discussed. With this method, we demonstrate that for one-dimensional systems, using the indices of particles as the space variable, which has been accepted as a convention, may lead to misleading conclusions. We then show that though in one-dimensional systems there is no general connection between energy diffusion and heat conduction, however, a general connection between heat diffusion and heat conduction may exist. Relaxation behavior of local energy current fluctuations and that of local heat current fluctuations are also studied. We find that they are significantly different,though the global energy current equals the globe heat current.

Diffusion Mechanism of Energy Flow in Multi-heat-source Synthesis of SiC

Through the experiments and the numerical simulation of temperature field in multi-heatsource synthesis Si C furnace, in order to research the feature point in multi-heat-source synthesis furnace, the variation law of heat fl ux was studied and the multi-directional energy fl ow diffusion mechanism was revealed. The results show that, due to the shielding action between the heat-source and the superposition effect of thermal fields, the insulating effect is best in multi-heat-source synthesis furnace. The heat emission effect is good outside the common area between heat-sources, but the heat storage is poor. Compared with the synthesis furnace that heat source is parallelly arranged, the furnace of stereoscopic arrangement has a more obvious heat stacking effect and better heat preservation effect, but the air permeability of heat source connecting regions is worse. In the case with the same ingredients, the resistance to thermal diffusion and mass diffusion is higher in heat source connecting regions.

Modeling vertical heat transport in the wave affected surface layer of the ocean

In considering the vertical heat boundary approximation for the free surface applied. However, due to the existence of the transport problems in the upper ocean, the flat upper and the horizontal homogenous hypothesis are usually wave motion, the application of this approximation may result in some errors to the solar irradiation since it decays quickly in respect to the actual thickness of the water layer below the surface; on the other hand, due to the fluctuation of the water layer depth, it is improper to neglect the effects of the horizontal advection and turbulent diffusion since they also contribute to the vertical heat transport. A new model is constructed in this study to reflect these effects. The corresponding numerical simulations show that the wave motion may remarkably accelerate the vertical heat transferring process and the variation of the temperature in the wave affected layer appears in an oscillating manner.

Study of Heat Transport Across a Quasi-Stochastic Magnetic Field in Magnetic Confined Plasma Physics

Heat diffusion across a non-local quasi-stochastic magnetic field in tokamak plasma is numerically studied. The perturbed magnetic field is found to be a key factor in influencing effective radial heat conductivity whether the magnetic field is stochastic or not. Being different from previous work, a non-local perturbed magnetic field is used. Analytical results and numerical simulation results are compared between the conditions with a full and a quasi-perturbed stochastic field. The analytical results are found to be still consistent with numerical simulation results when the perturbed field is quasi-stochastic.

Analysis of diffusive coefficient of electron heat pulse based on singular value decomposition in HT-7 tokamak

In this paper, singular value decomposition （SVD） as a filter-noise method is applied to electron cyclotron emission （ECE） diagnostic signals. The decomposed vectors contain the information about sawtooth such as the temporal vectors that show the sawtooth period and the spatial vectors that indicate the inverse radius. The propagation of electron heat pulse is investigated from electron cyclotron emission signals by using the perturbation method in HT-7 tokamak. The heat diffusivities are obtained at different densities in ohmic plasmas. The special result is that the heat diffusivity becomes larger as the heat pulse propagates outwards from the outside of the inverse radius.

The Study of Heat Pulse Propagation on HT-7 Tokamak

The propagation of heat pulses originating from sawtooth activity has been studied on the HT-7 tokamak. Two theoretical models are used for determining electron heat diffusivity from the experimental data measured by a diagnostic system of soft x-ray diode-array. The results show that one model called 'dipole model' is more suitable for HT-7 tokamak. In order to improve the signal-to-noise (S/N) ratio of the original signals, over a few tens of sawteeth are averaged to generate nice waveforms. The space-time evolution is found to be diffusive in character, which is consistent with the theoretical model. The electron heat diffusivity determined from heat pulse propagation is larger than that determined from background plasma power balance. The variation of Xe in different discharge phases has been also discussed.

Positive and negative turbulent heat diffusivity observed on a 325-m meteorological tower in Beijing

Turbulent diffusion efficiently transports momentum,heat,and matter and affects their transfers between the atmosphere and the surface.As a key parameter in describing turbulent diffusion,the turbulent heat diffusivity KH has rarely been studied in the context of frequent urban pollution in recent years.In this study,KH under urban pollution conditions was directly calculated based on K-theory.The authors found an obvious diurnal variation in K_(H),with variations also in the vertical distributions between each case and over time.Interestingly,the height corresponding to the high occurrence frequency of negative K_(H) rises gradually after sunrise,peaks at noon,falls near sunset,and concentrates around 140 m during most of the night.The KH magnitude and fluctuation are smaller in the pollutant accumulation stage(CS)at all levels than in the pollutant transport stage and pollutant removal stage.Turbulent diffusion may greatly affect PM_(2.5) concentrations at the CS because of the negative correlation between PM_(2.5) concentrations and the absolute value of KH at the CS accompanied by weak wind speeds.The applicability of K-theory is not very good during either day or at night.These problems are inherent in K-theory when characterizing complex systems,such as turbulent diffusion,and require new frameworks or parameterization schemes.These findings may provide valuable insight for establishing a new turbulence diffusion parameterization scheme for KH and promote the study of turbulent diffusion,air quality forecasting,and weather and climate modeling.

Behaviors of Electron Heat Transportation in HT-7 Sawtoothing Plasma

It is found that in HT-7 ohmic plasma, main energy loss comes from electron heat conduction, hence quantitative data of electron heat diffusivity is a very important issue for investigation of electron heat transportation behavior in different target plasmas so as to get high performance plasma. A time-to-peak method of the heat pulse propagation originating from the sawtooth activity on the soft x-ray intensity signal has been adopted to experimentally determine electron heat diffusivity XeHP on the HT-7 tokamak. Aiming to improve the signal-to-noise (S/N) ratio of the original signal to get a stable and reasonable electron heat diffusivity XeHD value, some data processing methods, including average of tens of sawteeth, is discussed. The electron heat diffusivity XeHP is larger than XePB which is determined from the balance of background plasma power. Based on variation of the measured electron heat diffusivity XeHP, performances of different high confinement plasmas are analyzed.

陶瓷增强高锰钢复合材料的组织与结合机理

在不同的热处理工艺下,生产出高锰钢复合材料。通过扫描电镜对高锰钢、陶瓷复合材料的结合情况、基体的显微组织进行了研究,并探讨了高锰钢、陶瓷的结合机理。结果表明:新热处理工艺下,复合材料基体组织细化;陶瓷与基体结合较好,为扩散结合。

Characteristics of the stem sap flux of Populus euphratica in the lower reaches of the Heihe River Basin, Northwest China

Populus euphratica trees are the sole natural perennial riparian woodlands native to the river oases in the lower reaches of Heihe River Basin in northwestern China.This study investigated characteristics of the stem sap flux of Populus euphratica and its rela-tionship to environmental factors using the thermal dissipation probe(TDP) method.The results showed that(1) daily variation of sap flow of P.euphratica on clear days exhibited an obvious unimodal curve;sap flow rates in June,July,August,and September were 13.39,12.07,12.69,and 5.10 L/d,respectively;(2) the average transpiration of the Populus euphratica from June through September amounted to 1,309.84 L;(3) stem sap flow can be affected by a number of environmental factors that,in terms of the influential degree,can be arranged in the descending order of air temperature,soil moisture,relative humidity,total solar radiation,soil temperature,and wind velocity.

The Hydrodynamic Limit of Nonlinear Fokker-Planck Equation

The non-linear Fokker-Planck equation arises in describing the evolution of stochastic system, which is a variant of the Boltzmann equation modeling the evolution of the random system with Brownian motion, where the collision term is replaced by a drift-diffusion operator. This model conserves mass, momentum and energy;the dissipation is much weaker than that in a simplified model we considered before which conserved only mass, thus more difficult to analyze. The macro-micro decomposition of the solution around the local Maxwellian introduced by T.-P. Liu, T. Yang and S.-H. Yu for Boltzmann equation is used, to reformulate the model into a fluid-type system incorporate viscosity and heat diffusion terms, coupled with an equation of the microscopic part. The viscosity and heat diffusion terms can give dissipative mechanism for the analysis of the model.

A Thermal Analogue of the Zel’Dovich Effect

We analyze in this work anisotropic heat conduction induced by a harmonically oscillating laser source incident on rotating conductors, exploiting an analogy with an effect discovered long ago, called the Zel’dovich effect. We re-covered the main results of a recently published paper that predicts the translational Doppler frequency shift of a thermal wave induced on a sample moving with uniform rectilinear motion. We extend then this framework to take into account the frequency shift of a thermal field propagating on a rotating platform. We show that it coincides with the rotational frequency shift which has been recently observed on surface acoustic waves and hydrodynamic surface waves, called rotational superradiance. Finally, we use an analogy with the Tolman effect to deduce a simple estimate of the average temperature gradient induced by rotation, showing the existence of a new cooling effect associated with heat torque transfer.

Observation and Study of Land Surface Parameters over Gobi in Typical Arid Region

According to the need of popular land surface process models, characteristics and rules of some key land surface process and soil parameters over Gobi in typical arid region of Northwest China are analyzed by using the data observed during the intensive observation period of the Dunhuang Land–Surface Process Field Experiment (DLSPFE) (May–June 2000). Using the relative reflection as weighting factor, the weighted mean of the surface albedo over Dunhuang Gobi in typical arid region is calculated and its values are 0.255 ± 0.021. After canceling the interference of the buildings, the mean values of the roughness length averaged with logarithm is 0.0019 ± 0.00071 m. After removing the influence of the oasis, the soil wetness factor computed with data under condition of no precipitation is 0.0045. After removing the influence of the precipitation , the mean values of the soil heat capacity over Dunhuang Gobi in typical arid region is 1.12 × 106 J m−3K−1, a bit smaller than the values observed in HEIFE. But the soil heat diffusivity and conductivity are about one of those observed in HEIFE. The soil water content over Dunhuang Gobi in typical synoptic condition is very little and does not exceed 1% basically.

在托卡马克离子回旋频段波加热中高能离子轨道损失特性

本文研究了在托卡马克ICRH少数离子基波加热中,高能离子的轨道损失特性。给出了离子扩散轨道损失的约束时间,并揭示,由于射频波的作用,捕获离子的扩散轨道损失大为增加,随着离子吸收波功率的增加,此损失呈饱和趋势。

Molecular Dynamics Simulation of Heat Propagation in Liquid Argon

A two dimensional molecular dynamics simulation has been performed to investigate the propagation behavior of initial thermal perturbations in liquid argon. The model includes 3 000 (150×20) rigid particles. The 12 6 Lennard Jones potential was used to describe the interactions among argon particles. Periodic boundary conditions were employed at the upper and bottom sides, and rigid boundary was used at right side. The thermal perturbations were generated by increasing the kinetic energy of the first five particle layers on the left side. Simulation results demonstrated that heat was transported by diffusion, and even at early time of fast transient heat transfer process, no wave phenomena such as wave front and wave reflection were observed. For a fast and large thermal perturbation propagation, wave like temperature profiles could be seen, which were always associated with the pressure waves rather than the heat waves in the sense of C V model.

Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment

Cementites decomposition of a pearlitic ductile cast iron during graphitization annealing heat treatment was investigated.Fractographies and microstructures of heat treated samples were observed using a scanning electron microscope and mechanical properties were measured by a universal tensile test machine.The results indicated that during isothermal annealing at 750°C,the tensile strength of pearlitic ductile cast iron was increased to a peak value at 0.5h,and decreased gradually thereafter but the elongation was enhanced with the increase of annealing time.Moreover,the diffusion coefficient of carbon atoms could be approximately calculated as 0.56μm2/s that could be regarded as the shortrange diffusion.As the holding time was short（0.5h）,diffusion of carbon atoms was incomplete and mainly occurred around the graphites where the morphology of cementites changed from fragmentized shape to granular shape.In addition,the ductile cast iron with tensile strength of 740MPa and elongation of 7% could be achieved after graphitization annealing heat treatment for 0.5h.Two principal factors should be taken into account.First,the decomposition of a small amount of cementites was beneficial for increasing the ductility up to elongation of 7%.Second,the diffusion of carbon atoms from cementites to graphites could improve the binding force between graphites and matrix,enhancing the tensile strength to 740 MPa.

In-situ TEM study of the dynamic behavior of the graphene-metal interface evolution under Joule heating

The dynamic behavior of the interface between few layer graphene(FLG) and tungsten metal tips under Joule heating has been studied by in-situ transmission electron microscopy(TEM) method. High-resolution and real-time observations show the tungsten tip ‘swallow' carbon atoms of the FLG and ‘spit' graphite shells at its surface. The tip was carbonized to tungsten carbide(WC, W_2 C and WC_x) after this process. A carbon diffusion mechanism has been proposed based on the diffusion of carbon atoms through the tungsten tip and separation from the surface of the tip. After Joule heating, the initial FLG-metal mechanical contact was transformed to FLG-WCx-W contact, which results in significant improvement on electrical conductivity at the interface.

A critical transition rule for broadening exponent of fluctuation and its effect on dissipation in chemical reaction-heat conduction coupling systems

A stochastic model of chemical reaction-heat conduction-diffusion for a one-dimensional gaseous system under Dirichlet or zero-fluxes boundary conditions is proposed in this paper. Based on this model,we extend the theory of the broadening exponent of critical fluctuations to cover the chemical reaction-heat conduction coupling systems as an asymptotic property of the corresponding Markovian master equation (ME),and establish a valid stochastic thermodynamics for such systems. As an illustration,the non-isothermal and inhomogeneous Schl-gl model is explicitly studied. Through an order analysis of the contributions from both the drift and diffusion to the evolution of the probability distribution in the corresponding Fokker-Planck equation(FPE) in the approach to bifurcation,we have identified the critical transition rule for the broadening exponent of the fluctuations due to the coupling between chemical reaction and heat conduction. It turns out that the dissipation induced by the critical fluctuations reaches a deterministic level,leading to a thermodynamic effect on the nonequilibrium physico-chemical processes.