Carbonisation of bagasse in a fixed bed reactor: influence of process variables on char yield and characteristics

Carbonisation experiments on samples of sugar cane bagasse were conducted in a static fixed bed reactor to determine the effect of process variables such as temperature, heating rate, inert sweep gas flow rate and particle size on the yield and composition of solid product char. Experiments were performed to the final temperatures of 250–700°C with heating rates from 5 to 30°C/min with nitrogen sweep gas flow rate of 350 cc/min. Additional tests were aimed at studying the effect of different flow rates of nitrogen sweep gas from 0 to 700 cc/min during carbonization and different particle size fractions of bagasse. The results showed that as the carbonisation temperature was increased, the yield of char decreased. The reduction in yield was rapid up to a final temperature of 500°C and was slower thereafter. The yield of char was relatively insensitive to the changes in heating rate and particle size. Increasing the sweep gas flow rate to 350 cc/min reduced the yield of char. It appears the presence of inert sweep gas reduced secondary reactions which promoted char formation. The proximate analysis of the char suggests that fixed carbon and ash content increased with temperature. The char obtained at temperatures higher than 500°C have high carbon content and is suitable as renewable fuel and for other applications. The carbonization of bagasse has the potential to produce environmental friendly fuels and can assist in reducing deforestation for the production of charcoal.     

Effective heating for tumors with thermally significant blood vessels during hyperthermia treatment

Significant cooling effect by blood vessels, particularly in treated tumor region, during hyperthermia treatment has been recognized by researchers. The present study investigated a heating strategy, using a preheating zone and adaptive optimization, to effectively reduce the cooling effect as thermally significant blood vessels flowed through treated region during hyperthermia treatment. The preheating zone is located in a vessel's entrance region adjacent to treated tumor and the heating strategy attempted to elevate blood temperature before blood flowing into the treated region. We numerically calculated blood and tissue temperatures using 3-D models and the goal of treatment was to reach a uniform therapeutic temperature in the tumor region using the proposed heating strategy. Results showed first, for large blood vessels, the heating strategy effectively elevated blood temperature at the entrance of treated tumor and reduced total tumor power deposition. Consequently, it helped to reach the ideal treated temperature on tumor more effectively, and avoided extreme power deposition due to the cooling effect of blood vessels entering the treated region. For small blood vessels, the preheating zone could further improve the treatment result. Secondly, heating flowing blood with adaptive optimization results in a unique phenomenon along blood flow paths. That is a strong convective nature of blood flow, which creates high thermal gradients in the treated region. Thus, it plays a different and significant role in adaptive optimization process as compared to thermal diffusion of solid tissues.     

Basic natural convection in a vertical porous layer differentially heated from its sidewalls subject to lack of local thermal equilibrium

A vertical porous layer subject to lack of local thermal equilibrium and differentially heated from its sidewalls experiences extremely different conditions when it is heated via a constant heat flux, rather than via a hot temperature imposed on the sidewall. For a start the steady state basic temperatures of the fluid and solid differ, as distinct from the corresponding case of imposed temperature on the sidewall when both fluid and solid temperatures are identical and linear at steady state and the lack of local thermal equilibrium (LaLotheq) can manifest itself at transients or when the basic temperature profiles stated above become unstable. In addition, in the case of heating via a constant heat flux the steady state basic temperatures of the fluid and solid are not only distinct but also nonlinear. The analytical derivation of these nonlinear solutions for the basic natural convection in a vertical porous layer differentially heated from its sidewalls, subject to lack of local thermal equilibrium and heating via a constant heat flux is presented and the results analyzed over a wide range of parameter space. In general it is shown that the lack of local thermal equilibrium destroys the symmetry of the problem via deviatoric terms in the solutions.     

Mathematical modelling of the transient response of pipeline

Steam pipelines applied in power units operate at high pressures and temperatures. In addition, to stress from the pipeline pressure also arise high thermal stresses in transient states such as start-up, shutdown or a load change of the power unit. Time-varying stresses are often the cause of the occurrence of fatigue cracks since the plastic deformations appear at the stress concentration regions. To determine the transient temperature of the steam along the steam flow path and axisymmetric temperature distribution in the pipeline wall, a numerical model of pipeline heating was proposed. To determine the transient temperature of the steam and pipeline wall the finite volume method (FVM) was used Writing the energy conservation equations for control areas around all the nodes gives a system of ordinary differential equations with respect to time. The system of ordinary differential equations of the first order was solved by the Runge-Kutta method of the fourth order to give the time-temperature changes at the nodes lying in the area of the wall and steam. The steam pressure distribution along pipeline was determined from the solution of the momentum conservation equation. Based on the calculated temperature distribution, thermal stresses were determined. The friction factor was calculated using the correlations of Churchill and Haaland, which were proposed for pipes with a rough inner surface. To assess the accuracy of the proposed model, numerical calculations were also performed for the thin-walled pipe, and the results were compared to the exact analytical solution. Comparison of the results shows that the accuracy of the proposed model of pipeline heating is very satisfactory. The paper presents examples of the determination of the transient temperature of the steam and the wall.     

用传热法测量燃煤锅炉气力输送中煤流量的研究

将一电加热的传感探头置于气固两相流中,不同流速、浓度及颗粒直径的流动介质将与探头产生不同的传热效果,在确定的输送风量（风速）条件下,根据探头的电加热功率和测取探头的表面温度来测取气固两相流中的固相流量。在模拟稀相气力输送的试验台上,对窄筛分石英砂做了大量不同条件下的输送实验及测量。研究结果表明,本文首次提出的传热法为稀相气力输送中固相流量的测量提供了一种简单、可靠的新方法。     

Heating/melting of a fused silica particle by convection and radiation

The effect of internal absorption and emission of radiation on the heating/melting process of small fused silica particles is analyzed. The particle is considered to be semitransparent to radiation, and the radiative transfer theory is used to predict the local volumetric absorption/emission rate. The transient energy equation with conduction and radiation accounted for is solved to predict the temperature distribution in the particle and the solid–liquid interface position after the melting has started. The radiative transfer calculations are carried out on the spectral basis using published spectral optical property data for fused silica. Results of parametric calculations for different diameter particles, surroundings temperatures and external flow conditions are reported and discussed.     

New approach to a problem of heat transfer with chemical reaction in a cylinder of finite dimensions

The three-dimension heat transfer problem of non-isothermal decomposition for a solid cylindrical particle was studied. The non-stationary thermo-chemical process with high activation energy in the particle was described by the system of two non-linear integro-differential equations over the temperature and material density. The solution of these equations was obtained by the semi-analytical method. The influence of chemical reaction parameters on the temperature field inside the cylinder was established. The numerical simulation was carried out for a solid particle heated with linearly increasing temperature from 30 to 700 °C. Special attention was paid to the spatial and time dependent distributions of the temperature field for different heating rates. This approach can be applied for kinetic parameter estimation of thermogravimetric measurements.     

A comparison of extended Kalman filter,particle filter,and least squares localization methods for a high heat flux concentrated source

State estimation procedures using the extended Kalman filter, particle filter, and least squares are investigated for a transient heat transfer problem in which a high heat flux concentrated source is applied on one side of a thin plate and ultrasonic pulse time of flight is measured between spatially separated transducers on the opposite side of the plate. This work is an integral part of an effort to develop a system capable of locating the boundary layer transition region on a hypersonic vehicle aeroshell. Results from thermal conduction experiments involving one-way ultrasonic pulse time of flight measurements are presented. Comparisons of heating source localization measurement models are conducted where ultrasonic pulse time of flight readings provide the measurement update to the extended Kalman filter, particle filter, and least squares. Two different measurement models are compared: (1) directly using the one-way ultrasonic pulse time of flight as the measurement vector and (2) indirectly obtaining distance from the one-way ultrasonic pulse time of flight and then using these obtained distances as the measurement vector. For the direct model, the Jacobian required by the extended Kalman filter and least squares is obtained numerically using finite differences and a finite element forward conduction solution. For the indirect model, the derivatives with respect to the state variables are obtained in closed form. Heating source localization results and convergence behavior are compared for the three inverse methods and the two measurement models. The extended Kalman filter, least squares, and particle filter methods using the one-way ultrasonic pulse time of flight measurement model (direct model) produced similar results when considering accuracy of converged solution, ability to converge to the correct solution, and smoothness of convergence behavior. The results provide quantified justification for moving forward with development of an extended Kalman filter-based localization solution.     

陶瓷过滤器脉冲清灰系统的性能测定与分析

在由3根滤管组成的高温陶瓷过滤器实验装置上,测定了不同过滤气体温度下滤管脉冲反吹系统的循环性能．比较不同直径的喷嘴在不同脉冲宽度和反吹温度下的气体耗量,利用加尘实验得出各操作参数对过滤循环稳定性和清灰性能的影响规律．实验结果表明,喷嘴每次反吹的气体消耗量与脉冲宽度近似呈线性关系；适当增大喷嘴直径能提高清灰效果,延长反吹周期,但气体消耗量也随之增加．利用已建立的脉冲反吹系统动态模型,对脉冲反吹系统进行了模拟计算,得出了脉冲反吹系统的储气罐容积、管线直径对反吹气体流量和气体消耗量的影响规律．这些结果可用于高温陶瓷过滤器的工程设计和脉冲反吹系统的优化．     

Assessment of a novel numerical model for combustion and in-flight heating of particles in an industrial furnace

The key factors for efficient in-flight particle heating in a combusting flow were investigated within this paper for the development of a novel boiler slag bead production furnace. A natural gas fired industrial burner with a thermal input of 1.2?MW was thus evaluated using Computational Fluid Dynamics (CFD). The steady laminar flamelet model (SFM) and a detailed chemical reaction mechanism, considering 25 reversible chemical reactions and 17 species were used to account for the steady-state gas phase combustion. Measurements of gas temperature and flow velocity within the furnace were found to be in good accordance with the numerical results. In the second step, sintered bauxite beads were injected into the furnace as an experimental material and heated up in flight. The particle heating characteristics were investigated using the Discrete Phase Model (DPM). The computational results of the particle laden flow raised the issue that convective heat transfer is a key factor for efficient particle heating. At the burner chamber outlet, the temperature of a particle which had been injected into the burner flame was 178?K higher compared to a particle, which trajectory led through zones with lower gas temperatures.     

基于神经网络的传热法测量气固两相流中固体流量的研究

利用人工神经网络优良的非线性映射能力,设计了一个3层前馈式神经网络用于传热法预测气固两相流中的固相流量,预测结果和实验结果吻合较好,为稀相气固两相流中固相流量的测量提供了一种简单、可靠的新方法。     

Numerical Modeling of a Moving Particle in a Continuous Flow Subjected to Microwave Heating

Microwave heating of a food particle and carrier liquid as they flow continuously in a circular pipe is investigated numerically. The three-dimensional transient fluid flow as well as electromagnetic and temperature fields are described by a model that includes coupled Maxwell's, continuity, Navier-Stokes, and energy equations. The electromagnetic power and temperature distributions in both the liquid and the particle are taken into account. The hydrodynamic interaction between the solid particle and the carrier fluid is simulated by the force-coupling method (FCM). This article explores the effects of dielectric properties and the inlet position of the particle on microwave energy and temperature distributions inside the particle. The effect of the particle on power absorption in the carrier liquid is studied as well. The results show that electromagnetic power absorption by the particle is greatly influenced by the ratio of dielectric properties of the particle and the liquid as well as the distance between the particle and the location in the applicator where the electromagnetic power takes on its maximum value.     

Weld Pool Shape Identification by Using Bezier Surfaces

This paper deals with the heat transfer analysis in a welding process: A method is developed to determine the shape of the three-dimensional (3-D) phase change front and to estimate the temperature field within the solid part of the work piece. The problem is formulated and solved as an inverse phase-change problem by using an optimization method. The direct problem is solved in the torch frame and so formulated as an Eulerian approach. The interface between the weld pool and the solid region is parameterized by Bezier surfaces. The most important feature of the presented approach is that the liquid–solid interface as well as the temperature distribution within the solid region can be obtained from additional temperature data available in the solid region, without considering heat transfer and fluid flow in a molten zone. The estimate of these thermal characteristics then allows a thermomechanical calculation of the welded joint (calculation of the deformations and residual stresses). The validity of the numerical solution of the inverse problem is checked by comparing the results with the direct solution of the problem.     

Melting and resolidification of a subcooled metal powder particle subjected to nanosecond laser heating

Melting and resolidification of a subcooled spherical metal powder particle subjected to nanosecond laser heating are investigated analytically. The problem is divided into three stages: preheating, melting and resolidification, and thermalization. The temperature distributions in the liquid and solid regions and the location of the solid–liquid interface are obtained using an integral approximate method. The effects of the laser intensity and pulse width, initial subcooling, and particle radius on the melting and resolidification of powder particles were investigated. The Selective Laser Sintering (SLS) process for a pulsed laser can be simulated by repeating the three stages but varying the initial conditions.     

Pipeline transport of biomass: Experimental development of wheat straw slurry pressure loss gradients

Pipeline transport in the form of a slurry can reduce the cost of transportation of biomass material to a biorefinery, as compared to trucks. This research experimentally studies the hydraulics of slurries of wheat straw with water for pipeline transport. Slurries with a range of particle sizes and saturated solid mass fractions are examined in a laboratory-scale 50 mm diameter carbon steel pipeline system. Slurries with particles approximately 3 mm long can flow with saturated solid mass fractions of up to 30%. Pressure loss gradients results suggest the influence of drag reducing fibre suspensions. This phenomenon enables slurry pressure losses to be below that of the carrier fluid alone (water) and be achieved with sufficiently long particle sizes, low saturated solid mass fractions and high velocities. Our results suggest that to reduce pressure losses per unit biomass material, slurries should have short particle sizes, to allow high saturated solid mass fractions to be pumped at low velocities. With the pipeline system and slurries examined in this study, slurries with particles approximately 3 mm long and saturated solid mass fractions of 20–30% pumped at 1.5 m s⁻¹ experience the lowest pressure losses. This result helps in the design and optimal operation of biomass slurry pipeline systems.     

Numerical simulation of the quenching process in liquid jet impingement

Direct numerical simulation is performed for quenching of a hot plate in liquid jet impingement. The flow and thermal characteristics associated with the quenching process, which includes film boiling in the fluid region as well as transient conduction in the solid region, are investigated by solving the conservation equations of mass, momentum and energy in the liquid, gas and solid phases. The liquid–vapor and liquid–air interfaces are tracked by the sharp-interface level-set method modified to treat the effect of phase change. The computations demonstrate that the boiling curve of wall heat flux versus temperature does not depend on the transient or steady-state heating conditions. The effects of initial solid temperature and solid properties on the quenching characteristics are quantified.     

An Estimate of the Temperature of Semitransparent Oxide Particles in Thermal Spraying

A considerable temperature difference in semitransparent oxide particles due to intensive heating in plasma spraying makes it difficult to interpret the optical measurements of their temperature. The problem of determining the bulk temperature of such particles from the experimental data on the color temperature is analyzed by using a recently proposed approximate model for the radiation transfer inside a nonisothermal refracting spherical particle. The same approximation is also employed for developing an improved model of particle heating, taking into account the radiation-conduction interaction inside the particle. Calculations for Al 2 O 3 and ZrO 2 particles in a typical plasma jet show that the color temperature of oxide particles may be less than or greater than their bulk temperature, depending on the spectral absorption coefficient of particle substance. This temperature difference during the melting of particles may reach the value of 200-300 K. A procedure for in situ evaluation of the absorption coefficient by comparison of color and brightness temperatures of molten particles is proposed.     

燃烧器区域速度场对受热面结渣影响的试验研究

应用三维凿子动态分析仪（PDA）对某六角切向燃烧锅炉的冷态模型进行试验研究,通过对燃烧器出口区域气固两相速度场的测量和分析,发现六角切圆燃烧锅炉炉内主旋转气流旋转较弱,在燃烧器上部区域衰减很快,各角射流刚性差异较大,并从流场结构上分析了高温受热面结渣的原因。     

Unsteady CFD simulation on ash particle deposition and removal characteristics in tube banks: Focusing on particle diameter,flow velocity,and temperature

This study establishes a numerical deposition and removal model coupled with unsteady gas–solid turbulent flow to predict transport, impaction, sticking, and removal (or rebounding) characteristics of ash particles with high alkali metals based on Ansys Fluent software extended by user–defined functions. Dynamic mesh analytical strategy is employed to adjust the grid on the interface of flue gas and deposition layer to illustrate ash deposit growth characteristics. In this study, the effects of particle size, flow velocity, and inlet gas temperature on formation and distribution of ash deposits are studied. The results indicate that ash deposit distribution has significant particle size dependence. Larger particles tend to deposit on the windward side of first–row tubes, and account for the greatest share of total deposited mass. Smaller particles may deposit on the leeward side of the tube surfaces. Variation in impaction rates with time are influenced by the thermophoretic force and enlarged deposition area. With the increase in flow velocity, total deposited mass increases gradually. The influence of flow temperature on impacting rates is mainly embodied in the effect of flow temperature on thermophoretic force. However, the increase in inlet gas temperature has little effect on the sticking efficiency and ash deposit distribution. Nevertheless, the total deposited mass shows an increasing trend with inlet flue gas temperature.     

On the calculation of the temperature distribution in a packed bed for solar energy applications

Calculations utilizing the exact solutions for the temperature distributions of the solid in and the fluid flowing through a packed bed with arbitrary initial bed temperature and arbitrary inlet fluid temperature have been carried out. The computational method allows a reversal of the direction of the flow at arbitrary times. The influence of the nondimensional frequency of a periodic flow reversal on the bed and fluid temperatures at the steady periodic state are presented.