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1、文档来源为 :从网络收集整理.word 版本可编辑 .欢迎下载支持.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
2、 interface, and (c) the virgin solid. 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
3、of internal energy within the contol volume plus the net rate of enthalpy out is equal to the net rate of heat addition. Work is neglected, except forflow work,and combustion energy can be treated as an effective heat addition.Constant properties will be assumed foreach distinctmedia, i.e. char and
4、virginmaterial; and the internal energy is referenced at the initial temperature.The conservation of mas for the solid in Figure 1 is given by1 dm0(1)mdmA dtwhereis the mass of change of the solid,dtA is the surface area,And mis the mas flow rate of the gasified products per unit area.Hence,mis the
5、mas loss rate per unit surface area, or which is more commomlyreferred 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 m
6、aw loss of the solid. Conservation of mass 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 thatddtcc dysmc(2)0where pc is the char density, and xh, is the char mass flow rate per un
7、it area from the vaporizationplane. The accumulation 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 s
8、olidConsequently, a conservation of mass on the virgin fuel element in Figure 2c yields1文档来源为 :从网络收集整理.word 版本可编辑 .欢迎下载支持.dcv(3a)dtdy sv 0cWhere p is the density of the virgin solid, and where the control volume surfacemoves at the speed of the vaporization plane, v =d cd v .It is assumed that thedt
9、dtthickness of the solid stays constant as decomposition occurs.Conservation of mass for the vaporization interface.A mass balance at the vaporization plane together with Eq.(2), and assuming pc is constant, gives/c(3b)This equation states that the rate of mass from the virgin solid into the vaporiz
10、ationinterface is equal to the mass flow rate of char and fuel gases leaving the vaporizationinterface.The conservation of energy for each region in Figure 2 is now considered.Conservation of energy for the charFor the char region (2a),1 dU cm c g Ts T v mccc Tv T 0kgdTq f ,r qext,rTs4qvAdtdyy 0(4)w
11、hereU cis the internal energy of the char layer,c gis the specific heat of the vaporized fuel gas,ccis the char specific heat,kgdTis the flame convective heat flux,dyy 0q f ,ris the flame radiative heat flux,qext ,ris the external radiative flux to the surface,4is the surface reradiative heat flux (
12、assumed to be a blackbody),Tsqvis the heat flux to the plane of vaporization,T vis the vaporization temperature,Tsis the surface temperature,2文档来源为 :从网络收集整理.word 版本可编辑 .欢迎下载支持.T0is the reference temperature.Conservation of energy for the vaporization interfaceThe conservation of energy applied to th
13、e vaporization plane of Figure 2b yields:v H v qv qk(5)whereH vis the heat of vaporization (pyrolysis) for the solid at temperature Tvqkis the heat loss per unit area to the virgin solid.The left side of Eq. (5) relates to the energy required to change the virgin solid to vapor and char, and can be
14、taken as a definition of Conservation of energy for the virgin solidAn energy balance on the virgin solid gives1 dU vvc TvT 0qkqb(6)A dtwhere qbis the heat loss per unit area from the back of the solid,and U vis the internal energy of the virgin solid.Since the density (p) and specific heat (c) of the virginsolid can be consideredconstants,cvU vcATT 0dys(7)cEquations (2)- (7)constitu
