摘要:

The purpose of this study is to predict the safe storage height of coal stockpiles. To accomplish this, a one dimensional non - steady - state model with the effect of stockpile height approximated by a heat sink in the one dimensional energy equation has been develepod. The model consists of conservation equations for oxygen, water vapour, inherent moisture of the coal, and energy for both gaseous and solid phases. The heal sink term taken from literature is based on an assumed sinusoidal variation in temperature in the vertical direction.

ISSN:0010-2202    

DOI:10.1080/00102200008947257

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The objectives of this study were to observe ignition events and to measure ignition times of a droplet array of n-decane placed in a high-temperature low-speed airflow under microgravity field. Due lo the difficulty of making droplets of the same size within a short period of time in a drop capsule, imitation droplets made of porous ceramic balls soaked with n-decane were used. Experimental conditions were a droplet diameter of 1 mm, droplet spacing within the range of 0 to 6 mm. airflow velocity of 0 to 10cm/s. and an airflow temperature of 925 K. According to OH emission images taken by a high speed camera with an OH band-path filter, ignition occurred around the droplets simultaneously at zero airflow velocity. At higher airflow velocities of more than several centimeters per second, however, ignition was initiated in the wake flow of the droplets and the flame spreads lo the forward region of droplets. A range of droplet spacing existed in which ignition times of droplet arrays were less than those of a single droplet and had a minimum ignition time at a certain spacing. The spacing of this minimum ignition time increased with an increase of airflow velocity.

ISSN:0010-2202    

DOI:10.1080/00102200008947258

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The heating and vaporization of a pure cold fluid package in a hot environment of the same fluid has been analyzed. The model applies to subcritical as well as supercritical fluid conditions and relics on the assumption of constant pressure and quasisteady conditions in the gas phase (in a reference system receding with the cold front). An asymptotic analysis is performed using the ratio of the hot fluid density to the density of the cold fluid package as the smallness parameter. Then, a transcendental equation is obtained which provides the evolution of the cold package radius. For longer times when isothermal conditions are achieved in the cold region, the d2law is obtained. Some deviations from this law. due to the unsteadiness of the heating process in the cold region, are evaluated and discussed.

ISSN:0010-2202    

DOI:10.1080/00102200008947259

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An experimental study on water mist extinction of turbulent premixed flames is described. The aim of the study is to compare the extinction limits of opposed jet turbulent methane/air flames with and without the addition of water mist, and to study the influence of several parameters including the structure of water mist in terms of droplet size and mass fraction of the condensed phase, mean strain rate and equivalence ratio. The effect of NaCI water solution on premixed flame extinction is also presented. An air assisted atomizer is developed to produce and control the water mist. The structure of the water mist is characterized by a Phase Doppler Anemometer. Water mist interaction with three different configurations of the opposed jet premixed flames is explored and the results arc discussed by introducing a parameter representing the water mist efficiency.

ISSN:0010-2202    

DOI:10.1080/00102200008947260

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The α-parameter is a variable appearing in the formulation of the Bray number, a dimensionless term that can be used to predict the behaviour of the turbulent scalar flux as counter-gradient or gradient in premixed combustion. However, the successful application of the Bray number is hampered by poor characterisation of the a-parameter. The results of previous laser-imaging studies of conditional mean velocities in turbulent premixed methane/air and propane/air Bunsen-flames are used to formulate an empirical description of a. The resulting description of a suggests that the behaviour of the scalar flux is dependent on the heal release parameter and the lengthscale ratio, I1/δL, rather than the velocity ratio, U1/SL.

ISSN:0010-2202    

DOI:10.1080/00102200008947261

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The structure of premixed methane-air flames is analyzed using the “laminar flamelet concept”. A new model based on one-dimensional set of transformed coupled second order differential conservation equations describing the species concentrations of CO2, CO, O2, CH4, H2O, H2and N2and the sensible enthalpy are presented in the present work. The equations are rigorously derived and solved numerically. In these equations, a reaction progress variable (c) is taken as the independent variable that varies from zero to one. A three-step chemical kinetic mechanism is adopted. This was deduced in a systematic way from a detailed chemical kinetic mechanism. The rates for the three steps are related to the rates of the elementary reactions of the full reaction mechanism. Calculations are made for different fixed values of the scalar dissipation rate (x) until the flamelet eventually reaches the extinction limit at different levels of pressure. Moreover, simultaneous and instantaneous l-D measurements of CO2, O2, CO, N2, CH4, H2O, H2, OH and temperature have been carried out in a premixed laminar methane-air flame. A one-dimensional UV Raman-Raylcigh and Laser Induced Predissociation (LIPF) technique has been applied in the present work. The spatial and temporal resolutions are limited to the signal-to-noise ratio and the laser pulse duration. The results of the calculations are assessed against the measurements and previous predictions based on the asymptotic approach of CI mechanism and a 4-step reduced mechanism. The burning velocity at different equivalence ratios was also deduced from the flamelet properties and assessed against available data.

ISSN:0010-2202    

DOI:10.1080/00102200008947262

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102200008947263

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The oscillatory motion encountered in a laminar spray flame as described in some experimental works is different from any reported previously in the literature. In the published works this phenomenon is associated with heat loss, droplet loading or gravity. In this paper a simplistic physical model for oscillations in the position of flame zone relative to the fuel nozzle is described. It is shown that this model is sufficient to demonstrate that the flame position instability may occurs due to some characteristics of the fuel stream warming at the entrance to combustion zone. An additional important advantage of this model is the easy possibility to graphical visualizes the effect of all of the flow properties and thermodynamic characteristic incorporated in the model.

ISSN:0010-2202    

DOI:10.1080/00102200008947264

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper describes the activities carried out for the development and the use of CRFD codes and related procedures for the design of industrial furnaces. The objective is to predict the emission of pollutants, such as nitrogen oxides, in combustion flue gases. This prediction may be correctly accomplished using a detailed kinetic mechanism, which cannot be directly implemented on CRFD codes due to actual computational limits (both in terms of memory and CPU time consumption). A new approach has been developed: analysing the 3D CRFD flow fields, an “equivalent” chemical reactors network model is extracted with corresponding residence time distributions and overall reactor properties, and the detailed kinetic calculation is performed on this simpler scheme.

ISSN:0010-2202    

DOI:10.1080/00102200008947265

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A stochastic model of combustion and NOXformation in premixed turbulent methane flames is described. The model is based on the combination of Computational Fluid Dynamics and Monic Carlo methods for the solution of the joint scalar Probability Density Function. Finite chemical rates are represented with several alternative reduced-chemistry systems, of both the global and systematically-reduced types.

ISSN:0010-2202    

DOI:10.1080/00102200008947266

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor