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1、.英文原文：Coal oxidation at low temperatures: oxygen consumption,oxidation products, reaction mechanism and kinetic modellingThe conservation of mas and energy will be applied to the regions depicted in Figures 2a-2c. These consist of the (a) the char, ) the vaporization interface, and (c) the virgin so
2、lid. For mass conservation with respect to a control volume, the rate of change of mass within the control volume plus the net rate of mass flow out of the contol volume is equal to zero. The conservation of energy for a control volume states that the rate of change of internal energy within the con
3、tol volume plus the net rate of enthalpy out is equal to the net rate of heat addition. Work is neglected, except for flow work, and combustion energy can be treated as an effective heat addition. Constant properties will be assumed for each distinct media, i.e. char and virgin material; and the int
4、ernal energy is referenced at the initial temperature.The conservation of mas for the solid in Figure 1 is given by (1)where is the mass of change of the solid,A is the surface area,And is the mas flow rate of the gasified products per unit area.Hence, is the mas loss rate per unit surface area, or
5、which is more commomly referred to as the burning rate (per unit area). Eq.(1)is not essential to the governing equations which follow, but is only presented to show the relationship between the rate of fuel gasses which flow out of the system and the rate of maw loss of the solid.Conservation of ma
6、ss for the charBy considering the conservation of mass for the char layer in Figure 2a, and assuming that the vaporized fuel instantaneously leaves the solid, it follows that (2)where pc is the char density, and xh," is the char mass flow rate per unit area from the vaporizationplane. The accum
7、ulation of the fuel gases in the char matrix is taken to be negligible, so that the rate of gaseous fuel entering from the vaporization interface is equal to the rate of fuel gases which leave the solid to be burned. Conservation of mass for the vire in solidConsequently, a conservation of mass on t
8、he virgin fuel element in Figure 2c yields (3a)Where p is the density of the virgin solid, and where the control volume surface moves at the speed of the vaporization plane, v =.It is assumed that the thickness of the solid stays constant as decomposition occurs.Conservation of mass for the vaporiza
9、tion interface. A mass balance at the vaporization plane together with Eq.(2), and assuming pc is constant, gives (3b)This equation states that the rate of mass from the virgin solid into the vaporization interface is equal to the mass flow rate of char and fuel gases leaving the vaporization interf
10、ace.The conservation of energy for each region in Figure 2 is now considered.Conservation of energy for the charFor the char region (2a), (4)whereis the internal energy of the char layer,is the specific heat of the vaporized fuel gas,is the char specific heat,is the flame convective heat flux,is the
11、 flame radiative heat flux,is the external radiative flux to the surface,is the surface reradiative heat flux (assumed to be a blackbody),is the heat flux to the plane of vaporization,is the vaporization temperature,is the surface temperature,is the reference temperature.Conservation of energy for t
12、he vaporization interfaceThe conservation of energy applied to the vaporization plane of Figure 2b yields: (5)where is the heat of vaporization (pyrolysis) for the solid at temperature is the heat loss per unit area to the virgin solid.The left side of Eq. (5) relates to the energy required to chang
13、e the virgin solid to vapor and char, and can be taken as a definition ofConservation of energy for the virgin solidAn energy balance on the virgin solid gives (6)where is the heat loss per unit area from the back of the solid,and is the internal energy of the virgin solid.Since the density (p) and
14、specific heat (c) of the virgin solid can be considered constants, (7)Equations (2)- (7)constitute the governing equations for the solid phase. It is not entirely obviouswhat are the unknown variables, and what is the strategy of solving for them. For now it can be noted that by assuming appropriate
15、 profiles for the temperature, the heat fluxes can be express eding terms of temperature by Fourier's Law. Also the variables involving the gas phase heat transfer need to be developed from the gas phase analysis to follow in the next section. Now a digression is introduced to illustrate another
16、 approach for presenting the solid phase equations, and to offer a check on the above analysis.Differential formulationConsider pure conductive heat transfer into the virgin solid with the space coordinate (x), had tothe moving vaporization plane. This coordinate system is shown in Figure 1,and is i
17、ntroduced toavoid confusion with the coordinate system used above. If is the initial fixed reference system, (8)where is the velocity of the vaporization plane. The conduction equation in the fixed frame of reference is (8)which transforms as (10)and from Eq. (8). Hence in the moving frame of refere
18、nce, (11)with the conditions:， (12)and ，the initial temperatureCase 1. Non-charring steady burningLet us consider the ideal case of a non-charring material undergoing steady burning. If steady conditions prevail in the moving system, i.e., the temperature field is not changing in the virgin solid re
19、lative to the moving vaporization plane, and the back face conditions are negligible,i.e., a very thick solid, then Eq. (11) becomes (13)From Eq. (3) and since (14)with conditions from Eq. (5) and (12)， (15a)， (15b)， (15c)Using Eqns (fib) and (Ec) (16)and from Eq. (Ea) (17)The denominator of Eq. (17
20、) is commonly referred to as the steady state heat of gasification （） (18)Case2. Transient charringIn general, other terms which will be considered below will affect the mass loss rate, .If theprocess is not steady,we can consider Eq. (11) by integrating each item over Also for the charring case sin
21、ce at the vaporization plane,and from Eq. (3b) it follows that should be replaced by the above. Substituting in the integrated form of Eq.(11) giveswhich is identical to Eq. (6). This demonstrates that the conservation of energy for the virgin solidis consistent with this differential formulation.So
22、lution strategyIn review, six independent equations have been presented consisting of conservation of mass andenergy for the char, vaporizing interface, and virgin solid. These can be combined so that only twoenergy equations (4 and 6) are considered with the unknown variables: char depth, surface t
23、emperature, and a variable to be introduced which represents the thermal effects in the virgin solid.The thickness of the virgin solid and the mas burning rate can be related to the char depth, and the heat fluxes can be related to temperature profiles to be assumed in terms of the thicknesses of th
24、e char and virgin solid. A third equation will be found from the gas phase flame analys is which will give a relationship for the burning rate. The flame convective and radiativeheat fluxes will be expressed in terms of the current variables from the gas phase flame analysis. Below, this section wil
25、l be concluded with a derivation of the convective flame heat transfer based on the above conservation equations which will serve as a boundary condition to the gas phase analysis developed in the next section. This couples the solid and gas phase analyses.From Eqns. (5) and (6) (19)orThis is a depa
26、rture from the steady state results given by Eq.(17). It applies to the non-charring case if is regarded as the net surface heat flux,and .The more general charring case is considered by eliminating ; from Eq.(19) by using Eq. (4). Furthermore, the internal energy of the char is represented as follo
27、ws:where is measured from the charring surface. The internal energy per unit mass, ,is represented as where , is the char specific heat. By Eq.(2) it follows that (20)Combining all of the energy equations for the solid, or from Eqns. (4), (19) and (20)(21a)Alternatively, convective flow external rer
28、adiationheat transfer radiation radiation (noncharring) serface reradiation energy storagedue to charring due to charring Energy flow through char back f a e heat lo. (21b)virgin SOU energy storage(The above labels are qualitative descriptions of the terms.)Equation (21b) gives the thermal boundary
29、condition for the g& phase analysis, Le.,where (22)The form in Eq.(22)constitutes a boundary condition for the gas phase problem to follow. 中文译文：煤低温氧化模型氧气消耗、氧化产物、反应机理及动力学模型在图2a2c种描述的区域应用了质量和能量守恒。其包括（a）炭化，（b）气化表面，和（c）原始固体。对于一个控制体的质量守恒，控制体内的质量变化速率加上流出控制体的净质量流率等于零。控制体的能量守恒为控制体内的内部能量变化加上流出控制体的净能量流率等
30、于净增加热流率。除了流动做功，忽略了功的影响，另外燃烧热可视为有效增加热。对每种特定媒介，如炭化材料和原始材料，都为其假定常量，内部热量参考自初始温度。总质量图1中的质量守恒为 (1)其中是固体质量变化速率，为表面面积，为单位面积上气化产物的质量流率。因此，是单位表面面积的质量损失速率，或更普遍地被称为燃烧速率（单位面积）。方程（1）不是控制方程必须遵循的方程，但其可表现流出系统的燃烧气化速率和固体质量损失速率之间的关系。炭化质量守恒考虑图2a中炭化层的质量守恒，并假定燃料气化后即刻离开固体，其遵循下式： (2)其中是炭化层密度，为气化平面单位面积炭化质量流率。气化燃料在炭化层的积累可不加以考
31、虑，从进气化表面进入的气化燃料质量流率等于离开固体将要燃烧的气化燃料的质量流率。原始材料质量守恒因此，在图2c中标出了原始燃料的质量守恒。 (3a)其中为原始固体密度，其控制体表面移动速率等于气化平面移动速率，假定固体的厚度在热分界发生时保持不变。气化表面的质量守恒结合方程（2）在气化平面存在质量平衡，假定恒定，则 (3b)其中此方程表示从原始固体进入气化表面的质量流率等于炭化和气化燃料离开气化表面的质量流率。现在考虑图2中的各个区域的能量守恒。炭化能量守恒对于（2a）区域， (4)其中:炭化层内部能量气化燃料比热炭化层比热火焰对流热通量火焰辐射热通量对表面的外部辐射热通量表面辐射热通量（假定
32、为黑体）对气化平面的热通量气化温度表面温度参考温度气化表面的能量守恒图2b中表明了气化平面的能量守恒 (5)其中固体在温度下气化（高温分解）热，单位面积散失到原始固体中的热量。方程（5）的左项为把原始固体变为蒸气和炭化材料所需能量，可作为的定义。原始固体能量守恒原始固体有能量平衡： (6)其中 从固体背面单位面积热损失原始固体内部能量由于原始固体的密度（）和比热（）可视为常量， (7)方程（2）（7）建立了固相的控制方程。不是很明显能看出那些是未知变量以及解出它们的方法。现在可以假定温度的大致分布，然后根据傅立叶定律就可以用温度来表示热通量。而且和气相换热有关的变量在下一部分的气相分析中也可以
33、得到解答。现在介绍另外一个表征固相方程的公式，用以检验以上分析。微分公式假定给原始固体的净传导热是沿着在移动的气化平面上建立的空间坐标（x）的。在图1中标出了坐标系，为避免上面所用的坐标混淆。如果是固定初始参考系统， (8)其中是气化平面的移动速度。在固定参考火焰下的传导方程是 (8)上式可变为 (10)和 所以在参考移动火焰为 (11)上式在下列条件下成立：， (12)和 ，即初始温度第一种情况：非炭化稳态燃烧让我们考虑一种非炭化材料稳态燃烧的理想情况。如果稳态条件在移动系统中仍然成立，如温度场不随原始固体内气化平面的移动发生变化，且忽略背部条件的影响，如一块非常厚的固体，则方程（11）变为
34、 (13)由方程（3）和 (14)上式成立条件为方程（5）和（12）的条件：， (15a)， (15b)， (15c)由(15b)和(15c)，可得 (16)由方程(15a)可得 (17)方程(17)中的分母一般称为稳态汽化热（） (18)第二种情况：瞬间炭化大体上，下面要考虑的其他术语会影响质量损失速率。如果过程不是稳态的，我们可以在上对每一项积分，考虑方程（11） 同样对于在气化平面的炭化情况，由方程（3b），应由替代，替换方程（11）的积分形式为此方程与方程（6）相同，说明原始固体能量守恒是符合微分公式的。求解方法综上，有对于炭化、气化表面和原始固体的包含质量和能量守恒的六个独立的方程。
35、将这些方程合并后，只有两个方程（4和6）与未知变量有关：炭化厚度、表面温度和一个将要介绍的可表征原始固体热效应的变量。原始固体厚度和质量燃烧速率可以用来阐述炭化厚度，而热通量可以用来阐述假定与炭化厚度和原始固体厚度相关的温度分布。可从气相火焰分析得到第三个方程，其可以给出燃烧速率的关系。火焰传导和辐射热通量可从气相火焰分析的现有变量得出。接下来，本部分将基于上述守恒方程推导出火焰对流换热量，这在下一部分研究的气相分析中可以提供边界条件。固相和气相分析得到统一。由方程（5）和（6），可得到 (19)或者此式偏离方程（17）给出的稳态结果。当被视为净表面热通量，且时，此时可以应用到非炭化情况。更多的普通炭化情况可以视为使用方程（4）从方程（19）中消除了。另外，炭化内部能量可以表征如下：，其中由炭化表面测得。单位内部能量可由表示，其中是炭化层比热。由方程（2）可得到 (20)合并所有的固体能量方程，或从方程（4），（19）和（20）可得到(21a)或者 对流换热 火焰辐射 外部辐射 二次辐射（非炭化） 由于炭化引起的表面辐射 由于炭化引起的能量储存 传过炭化层的能量流动 背部热损失 (21b)原始固体能量储存（以上标注为对变量的描述）方程（21b）给出了气相分析的热边界条件，如其中 (22)方程（22）建立了气相问题可以遵循的边界条件。: