受限距离影响下竖向顺流火蔓延规律研究

以长45.0 cm、宽5.0 cm、厚2.0 mm的广告画布作为研究对象,开展了受限距离为3.0〜9.0 cm的竖向顺流火蔓延实验,定量分析受限距离对火焰长度、火蔓延速度、点燃时间等参数的影响。结果表明:受限距离3.0〜8.0 cm时,受限侧火焰长度明显大于未受限侧火焰长度;受限距离超过8.0 cm时,两侧火焰长度基本一致。随受限距离增加,火焰长度与火蔓延速度均表现为先增加后减小,最终趋于稳定,而点燃时间则表现为先减小后增加,最终趋于稳定值。建立了材料表面接收热流与点燃时间的关系式,分析了材料表面接收热流随受限距离的变化趋势,阐释了火蔓延速度随受限距离非单调变化的原因。

Peristaltic transport of MHD Williamson fluid in an inclined asymmetric channel through porous medium with heat transfer

The intention of this investigation is to study the effects of heat transfer and inclined magnetic field on the peristaltic flow of Williamson fluid in an asymmetric channel through porous medium. The governing two-dimensional equations are simplified under the assumption of long wavelength approximation. The simplified equations are solved for the stream function, temperature, and axial pressure gradient by using a regular perturbation method. The expression for pressure rise is computed numerically. The profiles of velocity, pressure gradient, temperature, heat transfer coefficient and stream function are sketched and interpreted for various embedded parameters and also the behavior of stream function for various wave forms is discussed through graphs. It is observed that the peristaltic velocity increases from porous medium to non-porous medium, the magnetic effects have increasing effect on the temperature, and the size of the trapped bolus decreases with the increasing of magnetic effects while the trend is reversed with the increasing of Darcy number. Moreover, limiting solutions of our problem are in close agreement with the corresponding results of the Newtonian fluid model.

Study on Heat Dissipater for High-Power Thyristors in Explosion-Proof Shell

A new type water-cooled heat dissipater for multiple high-power thyristors in explosion-proof shell used in coal mine was designed, and then, the numerical computation of the three-dimensional steady-state temperature distributions under different working conditions for cooling core was conducted in order to understand in detail the heat transfer performance. Based on the computation results, the temperature differences and the maximum heat transfer rates were given. These results of the study on the heat dissipater lay a basis for optimising its structure design and guiding its operation.

Dynamic Force Reduction and Heat Transfer Improvement for Horizontal Tubes in Large-Particle Gas-Fluidized Beds

The effects of tube bank configuration on forces and heat transfer were investigated for both two-dimensional and three-dimensional gas fluidized beds. Effective dynamic forces and heat transfer coefficients were measured for several tube bank configurations, and it was found that the average forces are smaller than for a single tube. The heat transfer coefficient can be increased by providing sufficient space for particles to descend around both sides of the tube bank. The results provide useful guidelines for optimizing the configuration of tube banks to achieve high heat transfer coefficients while reducing tube erosion due to dynamic forces.

Condensation Heat Transfer Inside a Tube in a Microgravity Environment

This paper introduces a method for studying condensation heat transfer inside a tube in a microgravity environment. The model assumes laminar flow in the condensate film and an annular flow pattern. The local heat transfer coefficient is then calculated by gravitational acceleration, gi from 0 to 9.8 m/s2.The model was tested indirectly by measuring condensation heat transfer inside a vertical tube in a normal gravity environment through experiments.

Heat Transfer and Hydrodynamics in Annular Chromatography: CFD-Simulation and Experiments

Continuous annular chromatography(CAC) is a separation process for multicomponent liquid mixtures. The performance of the apparatus can be seriously decreased by temperature gradients inside the adsorbent bed. It is shown, that the temperature gradients can be significantly reduced by a pre-heating of the entering liquid in the apparatus itself. Heat transfer and hydrodynamics in the porous media are described by two different modelling approaches. Both are based on a pseudo-homogeneous model for heat transfer with temperature dependent fluid viscosities. The first model considers one-dimensional fluid now and two-dimensional heat transfer. The second, more rigorous one is a three-dimensional model for heat transfer and hydrodynamics. The simulation results obtained with both models are in good agreement with experimental results. The experiments have been performed with glass beads as the stationary phase and water as the liquid phase under different boundary conditions. The temparature profiles inside the packed bed have been measured with thermocouples.

Three－Dimensional Numerical Simulation of Natural Convection Heat Transfer in an Inclined Cylindrical Annulus

A numerical study of natural convection heat transfer in an inclined cylindrical annulus has been conducted. The inner cylinder of the annulus is maintained at uniform heat flux and the outer cylinder at constant temperature. The two end walls are assumed to be insulated. A numerical code has been developed to calculate the steady state three-dimensional natural convection in an inclined cylindrical annulus, and the research emphasis is placed on the influences of inclination angle or and modified Rayleigh number Ra on the natural convection heat transfer in the annulus. Computations were carried out in the ranges of 0°α 90*, 2.5×105 Ra* and Pr=0.7 with fixed aspect ratio of H=28.97 and radius ratio of K= 3.33. The numerical results are compared with the experimental correlations from the literature and the inclination angle effect on heat transfer is found to be insignificant. Detailed results of heat transfer rate, temperature, and velocity fields are presented for the case of or α=45° and discussion is also made concerning the comparison between the numerical and experimental results for the specific case of α=90°.

An Investigation of the Swirling Flow and Heat Transfer in a Duct

This paper presents the results of experiments and numerical simulation of the turbulent swirling flow and heat transfer in a duct.The calculated results are in good agreement with data obtained by measurements.It is found that the swirling flow promotes heat transfer to the wall of the duct;the swirl numbers are dependent upon the vane exit angles of the swirler,distance from the swirler and the duct Reynolds number.But the decay of swirling flow in streamwise direction is related to local Reynolds numbers and is independent of the swirler exit angle.The swirl flow characteristics presented in this paper may be used for engineering purposes.

Numerical Prediction of Turbulent Flow and Heat Transfer with Phase Change in Crystallizer of Inverse Casting

A two-dimensional mathematical model has been undertaken to describe coupled liquid steel’s turbulent flow and heat transfer with solidification in the crystallizer of inverse casting. The solid-liquid phase change phenomena have been modeled by using the continuum formulations and considering the mush zone as porous media. The turbulence flow has been accounted for, using a modified version of the low-Reynolds-number k -ε turbulence model. A well-known numerical procedure, SIMPLE, has been used to solve the control equations. The effects of some main parameters on the solidification behavior have been studied, such as the casting speed, the thickness and the initial temperature of mother sheet the superheat degree of liquid steel.

Natural Convective Heat and Mass Transfer on a Vertical Heated Plate for Water Flow Containing Metal Corrosion Particles

Corrosion products of structural materials when contained in water usually are in two states:soluble state and colloidal particles with diameter about 10^(-3)—10^(-1)μm.Deposits of such corrosion products on tube surfaces under high pressure will jeopardize the operating economy of power plant equipment and even result in accidents. A numerical study is reported in this paper of the natural convective heat and mass transfer on a vertical heated plate subject to the first or mixed kind of boundary conditions for high-pressure water(P=17MPa)containing metal corrosion products with consideration of variable thermophysical properties.

Theoretical Analysis of Hydraulic Jump on ExtremelySmall Size Liquid Jet Impingement

A theoretical study was conducted to characterize hydraulic jump of laminar circular liquid jets. The objective of this research was to determine the jump location in a simple explicit form. The effects of many factors were investigated including nozzle diameter, jet exit pressure, nozzle-to-plate spacing, jet velocity and Reynolds number. It was found that the theoretical data collapsed well over the range of jet Reynolds number 500 Re 1800 with previous data.

Local Heat and Mass Transfer for Gas-Solid Two Phase Flow in CFB

An experimental investigation on the flow characteristics and the local heat and mass transfer between coarse wet particles and hot gas in the circulating fluidized bed (CFB) has been performed. A two-thermocouple contrast method was developed to measure the local gas and solid temperature along the height of the bed. The influences of air superficial velocity, solid rate and initial moisture content on the local heat and mass transfer between gas and solid were examined. The correlations of heat and mass transfer coefficients between gas and coarse wet particles in CFB were obtained.

Hydrodynamic and Heat Transfer Characteristics of Magnetofluidized Beds

To investigate the flow and heat-transfer behaviors of magnetofluidized beds, an experimental facilitywas designed. A constant uniform magnetic field is produced by a Helmholtz electromagnet. The nature of fiuidization and heat-transfer characteristics of a horizontal electrically heated tube immersed in the bed were measured. The bed material is iron shots. Depending upon the intensity of magnetic field (weak, moderate and strong), the bed pressure drop and heat transfer coefficient are classified into three ranges of magnetic fields. The range of variation of maximum magnetic-field intensity is from 0 to about 20690 A/m.

Effect of Eccentricity and Radius Ratio on Fluid Flow and Heat Transfer Inside an Eccentric Semicircular Enclosure

The Problem of laminar natural convective heat transfer inside an eccentric semicircular enclosure of different radius ratio and eccentricity is investigated numerically. At the same time, combined effect of the radius ratio and eccentricity on fluid flow is also observed with isothermal upper and lower surface. Here laminar, steady natural convection heat transfer are predicted for radius ratio R*=1.75, 2.0, 2.25, 2.5. Simulation was carried out for a range of eccentricity, ε=0.0 to 0.6. Governing equations are solved using finite volume method with a body fitted grid with collocated variable arrangement for a range of Grashof number 101-107 based on R0.Results are presented in the form of constant stream function, isothermal lines, local Nusselt number and average Nusselt number at different angular position. Eccentricity has little dominance on heat transfer rate. But significant effect of eccentricity is observed on flow field. Radius ratio has significant effect on natural convection heat transfer as wen as on flow field. At higher eccentricity, bi-cellular now is observed with one crescent-shape vortex at narrower cross section.This crescent shaped vortex is broken down into two cells with the increase of radius ratio that means transition Grashof number for bi-cellular now to tri-cellular flow is decreased with the increase of radius ratio. Eccentricity also has the same effect on flow field. Eccentricity has little effect on heat transfer but with the increase of radius ratio, average heat transfer rate increases.

Heat and Mass Transfer Enforcement of Vibrating Fluidized Bed

This paper briefly introduces the development of vibrating fiuidized bed at home and abroad, elaborates the vibration properties of vibrating fluidized bed, the fluidizing velocity and pressure drop of the bed layer. It also deduces the non-steady state drying dynamic equations of vibrating fluidized bed,analyzes main factors which influence the drying rate and inquires into drying rules of fixed bed and vibrating fluidized bed.

Numerical Simulation of Deflecting Flow in a Symmetric Enlarged Channel

Numerical results of three-dimensional separated flow and heat transfer in a rectangular channel with a sudden expansion are presented in this paper. Numerical simulations of Navier-Stokes and energy equations are carried out using the finite difference method. The results of three-dimensional calculations are compared with the two-dimensional ones, and effects of the aspect ratio of channel upon the flow are shown. The transition from symmetric to asymmetric flow appears at lower Reynolds number as increasing the aspect ratio. The details of local heat transfer characteristics in two different separated flow regions on two downstream walls are clarified. Two-dimensionality of the flow and heat transfer almost disappears for the aspect ratio considered.

Qualitative analysis on adiabatic and dynamic stability of LTS/HTS hybrid conductor with concentric configuration

The I-V characteristic of a superconductor is generally described by power-law,in which the superconductor with a high n transfers quickly from superconducting state to the normal conducting state.With a high transport current,in the low n value area,flux flow voltage becomes lower than in the high n value area,so that the transient characteristics strongly affect its stability.Based on those properties,we propose a new hybrid conductor which is made of low temperature superconductor(LTS) and high temperature superconductor(HTS) with concentric configuration in which the HTS coat is located outside of the LTS core.According to their power-law models,the modified adiabatic and dynamic stability criteria are qualitatively obtained by taking account into not only their critical currents but also n values.As a result,the new hybrid conductors have potential applications with higher engineering current density and improved stability.

All-vacuum fabrication of yellow perovskite light-emitting diodes

Yellow light-emitting diodes(LEDs) are widely utilized in high-quality lighting, light communication,indicator lamps, etc. Owing to their outstanding material properties and device performance, the metal halide perovskites have demonstrated a significant potential for LED applications. However, the performance of the yellow perovskite LEDs(PeLEDs) is inferior to that of their green and red counterparts, with the maximum external quantum efficiency(EQE) limited to ~3.1%. Further, a majority of the yellow PeLEDs are fabricated using the spin-coating methods. The current study reports the development of the yellow CsPbBr_(2)I PeLEDs based on an all-vacuum deposition approach, which has been widely employed in the commercial organic LEDs(OLEDs). By controlling the co-evaporation rate of CsI and PbBr;, the growth kinetics of the perovskite layer are regulated to achieve a small grain size of~31.8 nm. Consequently, an improved radiative recombination rate(8.04 × 10^(-9)cm^(3)/s) is obtained owing to the spatial confinement effect. The PeLEDs based on the optimal perovskite film demonstrate the yellow electroluminescence(574 nm) with a maximum EQE of ~3.7% and luminance of~16,200 cd/m^(2), thus, representing one of the most efficient and bright yellow PeLEDs. Overall, this study provides a useful guideline for realizing the efficient PeLEDs based on the thermal evaporation strategy and highlights the potential of PeLED as an efficient and bright yellow light source.

Natural Convective Heat and Mass Transfer of Water with Corrosion Products at Super-Critical Pressures under Cooling Conditions

A numerical study is reported of laminar natural convective heat and mass transfer on a vertical cooled plate for water containing metal corrosion products at super-critical pressures. The influence of variable properties at super-critical pressures on natural convection has been analyzed. The difference between heat and mass transfer under cooling or heating conditions is also discussed and some correlations for heat and mass transfer under cooling conditions are recommended.

Peristaltic transport of hydromagnetic Jeffrey fluid with temperature-dependent viscosity and thermal conductivity

In this paper, we investigate the effects of variable viscosity and thermal conductivity on peristaltic flow of Jeffrey fluid in an asymmetric channel. The inclined magnetic field, viscous dissipation and Joule heating are also considered. Wave frame and long wave-length approximations are made to formulate the problem. Pressure gradient, pressure drop per wavelength, velocity and temperature profiles are calculated analytically and discussed graphically. Comparison is made with the previous work for reliability.