Thermal regeneration of diesel particulate in metallic fibrous filter

Experiments were performed to study the aerodynamic thermal regeneration of a metallic fibrous particulate filter, which was used to reduce particulate emissions from diesel vehicles. Heated air diluted with nitrogen was used to initiate the regeneration process. Temperatures at 11 locations inside the filter were measured with embedded thermocouples which were equally spaced in the axial direction. Based on the temperature data, the instantaneous heat release of the filter was derived and analyzed. The peak regeneration temperature was found to occur at the region near the filter exit, and fibers in this region could melt when the temperature was sufficiently high. The normal regeneration temperature was around 800°C to 1000°C but local temperature could be as high as 1300°C. Thermal regeneration of the filter was found to depend on several factors, including, oxygen concentration in the heated air, initial particulate loading, packing density, thickness of the filtering element, and flow rate of the heated air. It was found that for regeneration to occur, the temperature of the heated air should exceed 500°C, the filtering element should have a minimum thickness of 50mm and a minimum initial particulate loading of 2 gram. Regeneration, and hence, heat release, was found to start earlier at higher oxygen concentration in the heated air, higher heated air flow rate, lower packing density and higher initial particulate loading. Regeneration temperature was higher at higher oxygen concentration in the heated air, lower heated air flow-rate, higher packing density and higher initial particulate loading. The results had also been compared with those of Kim et al. [12] and Park et al. [13] obtained on ceramic filter and those simulated by Garner and Dent [7].     

Modeling,numerical simulation and experimental verification of the unsteady cooling of a solid body in quiescent ambient air

The scope of the present article is two-fold. Firstly, to conduct an experiment to provide the temperature-time history of the cooling of a hot ball bearing in quiescent ambient air. Secondly, to predict the temporal variation of the bearing under the hypothesis of natural convection, radiation or natural convection coexists with radiation for a non-vanishing total hemispherical emissivity of the surface of the bearing. Numerical solutions of the three governing nonlinear lumped heat equations were carried out with a Runge-Kutta-Fehlberg (RKF45) algorithm accounting for automatic step size control. The experimental data was obtained with chrome steel ball bearings of diameter 0.953 cm (7/16 in) heated in an electric oven to a pre-set temperature. The heated bearing was exposed later to ambient air at atmospheric temperature and pressure.     

Turbulent mixed convection flow over a backward-facing step––the effect of the step heights

Effect of the backward-facing step heights on turbulent mixed convection flow along a vertical flat plate is examined experimentally. The step geometry consists of an adiabatic backward-facing step, an upstream wall and a downstream wall. Both the upstream and downstream walls are heated to a uniform and constant temperature. Laser–Doppler velocimeter and cold wire anemometer were used, respectively, to measure simultaneously the time-mean velocity and temperature distributions and their turbulent fluctuations. The experiment was carried out for step heights of 0, 11, and 22 mm, at a free stream air velocity, u_∞, of 0.41 m/s, and a temperature difference, ΔT, of 30 °C between the heated walls and the free stream air. The present results reveal that the turbulence intensity of the streamwise and transverse velocity fluctuations and the intensity of temperature fluctuations downstream of the step increase as the step height increases. Also, it was found that both the reattachment length and the heat transfer rate from the downstream heated wall increase with increasing step height.     

Natural convection heat transfer from a long heated vertical cylinder to an adjacent air gap of concentric and eccentric conditions

In this work, the natural convection heat transfer from a long vertical electrically heated cylinder to an adjacent air gap is experimentally studied. The aspect and diameter ratios of the cylinder are 55.56 and 6.33, respectively. The experimental measurements were obtained for a concentric condition and six eccentricities from 0.1 to 0.92 at five different heat fluxes. The surface temperature of the heated rod is measured at different heights, and the Nusselt number is calculated at the temperature measurement locations. A correlation is suggested to determine the Nusselt number based on the variation of the eccentric ratio values. The experimental results show a good agreement with other studies.     

An experimental study of fluid flow and heat transfer in decaying swirl through a heated annulus

The mean and turbulent structures of turbulent swirling flow in a heated annulus have been measured. Both forced and free vortex swirling flows were generated, and the outer wall of the test section was heated uniformly. The maximum swirl number was 1.39, Reynolds numbers were up to 200000, and heat input was 10.5 kW. Mean and turbulent velocity components, air and wall temperatures, and wall static pressures were all measured. Hot-film techniques were developed to measure turbulence. From these parameters, the flow and temperature fields, pressure distribution, and heat transfer coefficients were determined. The mechanisms of heat transfer were identified.     

Turbulence measurements from a plane air jet with buoyancy induced curvature

An experimental investigation of the turbulence structure of a heated plane air jet discharged at various angles into quiescent surroundings is described. Hot-wire anemometry was used to obtain the profiles of mean and turbulent velocities and temperature normal and tangential to the curved path of the flow. Measurements in the buoyancy induced curved region of the jet show the relative influence of the stability induced by both buoyancy and jet curvature on the turbulence structure.     

Experimental estimation of evaporation rates of water droplets in high-temperature gases

Evaporation rates of water droplets in high-temperature gases were experimentally determined using high-speed video recording cameras and low-inertia thermocouples (for heated air flow as an example). The experiments were carried out for droplets of initial size (radius) 1–3 mm at an air temperature of 500–1000 K. Dependences of the evaporation rate of water droplets on time and gas temperature were obtained for various initial droplet sizes.     

On the effects of fluid temperature on hot wire characteristics

Subject of this paper is the effect of air temperature on the characteristics of a hot wire. Hot wires of four different lengths have been calibrated over a range of air temperatures from 20 °C to 60 °C. Finite wire length corrections that account for the effects of heat conduction at the ends have been applied to obtain the heat transfer characteristics of an infinitely long heated wire. The reduced data show that the dependence of the heat transfer from an infinitely long heated wire on fluid temperature is such that the Nusselt number vs. Reynolds number relationship, when these are evaluated with property values at the “film temperature”, do not collapse to a single curve. The reduced data show that a linear variation of the heat transfer with a temperature difference corresponds more closely to the experimental observations. Dedicated to Prof. Dr.-Ing. M. Fiebig's 60th birthday     

Free convection enhancement between inclined wall and air in presence of expired jets at temperature difference of 40 K

This paper aims to determine the heat transfer enhancement in natural convection between a downward-facing inclined wall, heated by Joule effect, and air in the presence of small air pulsating expired jets, in conditions of medium temperature difference between wall and air, namely 40 K. Experimental measurements have been taken both with and without pulsating expired jets. The wall is kept in condition of uniform temperature. The expired jets blow out perpendicularly from the wall surface. An infrared thermo-camera was used to check the wall temperature uniformity. Hot-wire anemometer and visualization with smoke were used to find information on the air velocity field.The wall inclination angle which maximizes the convective heat exchange near the leading edge has been investigated too.     

Experimental investigation of free convection above a heated horizontal wire

Results are presented of an experimental investigation of the convective plume above a fine horizontal wire, heated by a constant current in air and in water. The temperature distribution in the plume was investigated using the IAB-451 shadow instrument in the diffraction interferometry method. The experimental results are in good agreement with laminar convection theories above a linear heat source. In the air, a comparison was made with the experimental results of other authors.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhicheskoi Fiziki, Vol. 11, No. 2, pp. 169–173, March–April, 1970.The author wishes to express his indebtedness to V. D. Zimin and N. V. Eyzhanov for their assistance with numerical solutions of Eqs. (1.3).     

Mathematical simulation of ignition of a coal-dust suspension in air by a low-temperature plasma jet

The process of aerosuspension ignition of a suspension in air in a pulverized-coal burner with a preswitched muffle by a central axisymmetric air stream heated in an electric-arc plasmatron to a temperature of about ≈5000K is numerically simulated. This process is the basis of a new fuel-oil-free method of ignition of the boilers of thermal power stations. The method is rather promising from the viewpoint of both economy and ecology. The goal of numerical simulation is to study the process of ignition of coal particles in the flow and to identify the conditions necessary for the transition to self-sustained burning of a coal-dust mixture. The results obtained revealed the significant role of radiative heat transfer in initializing the burning process of solid fuel particles. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 39, No. 3, pp. 134–140, May–June, 1998.     

Numerical study of evaporation-condensation in a vertical diffusion gap

The present work deals with mass transfer between a vertical falling film over a heated plate and a condensing film over a parallel cooled plate in a diffusion gap. This is typically the case of the distillation process in a diffusion still. The governing equations for mass, momentum, and energy are considered for the evaporating film, the diffusion gap, and the condensing film, together with the boundary and interfacial conditions. The local similar technique is used to solve the problem numerically and to get the velocity and temperature distributions in the gap. A comprehensive analysis of the effect of evaporating temperature, condensing temperature, and diffusion gap width over the diffusion mass flow rate and evaporation heat transfer coefficient are carried out. Performance charts of air and helium diffusion gaps are given. Additionally, the analytical results are experimentally validated.     

Optimum separation of asymmetrically heated sub-channels forming a bundle: influence of simultaneous flow and temperature

This paper focuses on laminar heat and fluid flow in an array of sub-channels placed in an uniform stream, which is characterized by a fixed pressure difference and a developing velocity and temperature. The dominant feature of the study deals with the optimal selection of the plate-to-plate separation between subchannels placed in a specified volume that renders maximum heat transmission from the heated plates to the moving fluid. Asymmetric heating from one plate in a typical sub-channel to either air or water is produced by uniform temperature in one case and uniform heat flux in the other case. Upon relaxing the vital condition of developing velocity, the numerical computations for the optimal separation and the maximum heat transmission incurred in little error for both cooling fluids.     

Modeling of convective structures in a thin layer of silicone oil in air flow under heating

Numerical simulation was performed to study convective structures in a thin silicone oil layer heated from below, whose free surface is exposed to air flow generating drift flow. The basic equations are transformation to a form suitable for spectral methods. The steady flow velocity profile obtained in a laboratory experiment is calculated. It is shown that increasing the Reynolds number leads to the transition from polygonal convective cells to longitudinal rolls (elongated along the flow). The dependence of the transition Reynolds number on the temperature on the lower boundary of the layer is obtained. The calculation results are compared with experimental data.     

Measurement of the cyanogen concentration profile in a thermal boundary layer on models being destroyed by a heat flux

The distribution of the concentration of the CN radical across the boundary layer was obtained in experiments on metals made of high-temperature materials which were placed in an air stream heated to 8500K. The concentration was calculated on the basis of the measured absolute intensity of radiation of the rotational lines of CN with consideration of the temperature profile obtained in [1], A high-frequency electrodeless discharge was used for heating the air.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 139–141, May–June, 1976.     

Coupled fields in a deformable unsaturated medium

This paper considers several problems involving coupled heat–moisture–air flow indeformable unsaturated media. A set of coupled non-linear governing equations expressed in terms of displacements, capillary pressure, air pressure and temperature are used in the analysis. The mathematical model accounts for fully coupled heat and moisture flow, volume strain effects on water-air-heat flow, stress and temperature dependence of the water retention curve, heat sink due to thermal expansion, phase change between liquid water and vapour water, and compressibility of liquid water. Numerical solutions are obtained by using the finite element method. Comparisons with existing analytical and experimental results for problems involving infiltration, drying–rewetting (hysteresis effects) and heating confirm the general validity of the present mathematical model. Coupled fields in a confined clay cylinder are also examined. It is found that consideration of absorbed liquid flow due to thermal gradients (thermo-osmosis effect) results in increased drying and shrinkage near the heated boundary. The case of a confined clay cylinder under combined heating and infiltration is also studied. Important features of coupled fields are discussed.     

超音速气流中受热壁板的稳定性分析

采用Galerkin方法建立二维壁板的非线性气动弹性运动方程,用一阶活塞理论模拟壁板 受到的气动力. 基于李雅普诺夫间接法分析了平壁板的稳定性,得到了壁板失稳的边界 曲线;采用牛顿迭代法分析了壁板的屈曲变形,进而分析了后屈曲状态下壁板的稳定性; 在时域中分析了后屈曲状态下壁板的颤振边界. 分析结果表明,为了保证计算精度, 在二维壁板的静态失稳及过屈曲变形分析中,至少要取二阶谐波模态;在平壁板的超音速颤 振(动态失稳)边界分析中至少应取四阶模态. 还对壁板的温升,壁板长厚比、壁板密 度和气流马赫数作了无量纲变参分析,研究了这些参数的变化对壁板稳定性的影响规律. 研 究中发现,当气流速压较低时壁板一般会稳定在低阶谐波模态的屈曲变形位置,但是如果系 统出现多个渐近稳定的不动点,即使作用在壁板上的气流速压很低,壁板也有可能在较低速 压下发生二次失稳型颤振.     

Microwave drying of various shape particles suspended in an air stream

Fluidization is an efficient way to dry granular materials. Incorporating microwave heating into the fluidization makes the overall drying process shorter, and the quality of the final products can be improved. However, in order to understand the mechanisms of water removal, an exact knowledge of changes inside the dried material is necessary. The temperature and moisture distribution pattern within the heated material should be identified and analyzed. Unfortunately, the microwave environment makes the measurements very difficult. This paper gives new information on the temperature distribution inside small particles of various shapes dried with microwaves. The tests were carried out in a laboratory-scale, fluid-bed dryer equipped with a microwave source. Five different shapes were examined: sphere, cylinder, half-cylinder, rectangular prism, and prism with triangle base. All particles tested were suspended in an air stream and heated with microwaves. The internal temperature distribution has been analyzed in each case. The rate of drying is also presented and discussed for every case tested.     

Temperature field of a slightly heated jet in a cross flow

This paper deals with a temperature field of a slightly heated two-dimensional jet injected normal to a cold cross flow. At the blowing rates of 0.2, 1.5 and 3.0 in two kinds of approaching boundary layer, the thermal mixing characteristics of the heated jet with the cross flow are experimentally clarified. The correlation between the temperature field and the complex flow one in the downstream region of the jet is made clear, in relation to the typical jet flow patterns. Comparison of the present results with the existing experimental data are represented.     

Effect of Time Periodic Boundary Conditions on Convective Flows in a Porous Square Enclosure with Non-Uniform Internal Heating

The problem of unsteady natural convection in a square region filled with a fluid-saturated porous medium having non-uniform internal heating and heated laterally is considered. The heated wall surface temperature varies sinusoidally with the time about fixed mean temperature. The opposite cold wall is maintained at a constant temperature. The top and bottom horizontal walls are kept adiabatic. The flow field is modelled with the Darcy model and is solved numerically using a finite difference method. The transient solutions obtained are all periodic in time. The effect of Rayleigh number, internal heating parameters, heating amplitude and oscillating frequency on the flow and temperature field as well as the total heat generated within the convective region are presented. It was found that strong internal heating can generate significant maximum fluid temperatures above the heated wall. The location of the maximum fluid temperature moves with time according to the periodically changing heated wall temperature. The augmentation of the space-averaged temperature in the cavity strongly depends on the heating amplitude and rather insensitive to the oscillating frequency.