CAN you hear me all right?
I am glad to have the opportunity of making this presentation.
I shall be speaking today about The Model
Formulation of this article.DO you everyone have printed this article ? OK,good!
NOW, before we start our presentation, let's
answer some questions. Question 1:
What reactions can we find when carbon is
burning in the air？
Anyone? OK! These there reactions
Qestions 2: Can you translate it?
Yech, I can't either…
But, we can underline the Subject and
predicate.
Who wants to try??
ok...ignore! Next!
Second part is about what we've known about the model fomulation.
we know Kinetics models for the combustion of carbon particles are intended to reproduce major features of the process without having to account for underlying complexities.
2.The kinetic parameters of these models must be determined experimentally.
3. These large particles burn nearly as shrinking spheres and diffusion tends to control the burning rate rather than chemical kinetics.
Third part is What THEY have known.
THEY are the scientists who have studied the
model.Ragland and Yang [7] measured the time evolution of the mass of captive millimeter sized particles for different gas temperatures, gas velocities, oxygen concentrations, particle sizes, and coal types.
They found that the char burning rate normalized with the initial mass of the particle（最初的质量相等） is insensitive to gas temperature in the range 900 to 1200 K, increases slightly with gas velocity and markedly with oxygen concentration, and decreases with particle size.
Matsui and coworkers [8] experimentally studied the combustion of a heated carbon plate subjected to a stagnation (停滞的) point flow of air.
They determined the activation energy of the heterogeneous carbon oxidation reaction and the effect of the oxidation of CO in the gas, which interferes with (干扰) the heterogeneous reaction through the consumption of O2
Adomeit et al. [9] numerically solved the stagnation point flow problem and were able to match Matsui’s data by taking into account the heterogeneous reactions of O2 and CO2 with C and different approxi- mations to the gas-phase kinetics
Blake and Libby [10] quantified the enhancement (增强)of the burning rate of a char particle due to its motion.
Musarra et al. [11] carried out numerical computations (数值计算) using two competing reactions to model pyrolysis, and the heterogeneous reactions of O2 and CO2 with C to model char gasification.
little effect of the oxidation of CO during the
char gasification period.
SO
This paper extends the analysis of the flow around a moving char particle, removing some of the simplifying assumptions that have been made in previous works and covering a larger range of particle sizes and gas conditions.
Now,I'm going to be speaking about these there reactions :
The rates of the heterogeneous reactions are the following.
(mass of carbon consumed per unit surface area and per unit time)
AND the gas-phase reaction is assumed to be
infinitely fast and not taken into account.
In general, Ts and qs are not uniform on the surface, and the relation between them is not local or quasi-stationary.
However, if the conduction time in the solid, is short compared with the combustion time of the particle and the characteristic time of variation of the ambient conditions seen by the particle, then Ts is nearly uniform except is an initial period of order tc.
In these conditions,
the problem can be solved for a given value of Ts
These are the mass and energy equations which are used to determine the surface distribution of qs. ,and we can obtain the relation between a and m ,and between ts and qs.
these are the surface-averaged values.
NOW, let's have a conclusion:
Independent variables
the oxygen and the carbon dioxide mass
fractions of the gas ——YCO2
velocity——U
The surface temperature——Ts
Radius——a
And dependent variable——the time evolution of the mass m
第二篇：英语演讲稿.ppt03版
