外文翻譯 煤低溫氧化模型

1、英文原文:Coal oxidati on at low temp eratures: oxyge n consump ti on,oxidati on p roducts, reacti on mecha nism and kin etic modelli ngThe conservation of mas and energy will be applied to the regions depicted in Figures 2a-2c. These con sist of the (a) the char, ) the vap orizati on in terface, and (c)

2、 the virg in solid. For mass con servati on with res pect to a con trol volume, the rate of cha nge of mass within the con trol volume p lus the net rate of mass flow out of the con tol volume is equal to zero. The con servatio n of en ergy for a con trol volume states that the rate of cha nge of in

3、 ternal en ergy within the con tol volume p lus the net rate of enthaIpy out is equal to the net rate of heat addition. Work is neglected, exceptfor flow work, and combustion energy can be treated as an effective heat addition. Constant properties will be assumed for each distinet media, i.e. char a

4、nd virgin material; and the in ternal en ergy is refere need at the in itial temp erature.The con servati on of mas for the solid in Figure 1 is give n by(1)1 dm . c+ m =0 A dtdmwhere is the mass of cha nge of the solid,A is the surface area,And m is the mas flow rate of the gasified products per un

5、it area.Hence, m is the mas loss rate per unit surface area, or which is more commomly referred to as the burning rate (per unit area). Eq.(1)is not esse ntial to the gover ning equati ons which follow, but is only p rese nted to show the relatio nship betwee n the rate of fuel gasses which flow out

6、 of the system and the rate of maw loss of the solid. Con servati on of mass for the charBy considering the conservation of mass for the char layer in Figure 2a, and assu ming that the vap orized fuel in sta ntan eously leaves the solid, it follows that d &.d JPdys =m：dt 0where pc is the char den si

7、ty, and xh, is the char mass flow rate per unit area from the vap orizati onplane. The accumulati on of the fuel gases in the char matrix is take n to be n egligible, so that the rate of gaseous fuel en teri ng from the vap orizati on in terface is equal to the rate of fuel gaseswhich leave the soli

8、d to be burn ed. Con servati on of mass for the vire in solidConsequently, a conservation of mass on the virgin fuel eleme nt in Figure 2c yields(3a)d岳審dt 嚴(yán)ys + gdcdvWhere p is the den sity of the virgin solid, and where the con trol volume surface dcdvmoves at the sp eed of the vap orizati on plane

9、, v = 一.It is assumed that thethick ness of the solid stays con sta nt as deco mp ositi on occurs.Con servati on of mass for the vaporizati on in terface.A mass bala nee at the vap orizati on plane together with Eq.(2), and assu ming pc iscon sta nt, givesPv =m + mc = Pm(3b)P=P/(P _Pc)This equati on

10、 states that the rate of mass from the virgin solid into the vap orizati on in terface is equal to the mass flow rate of char and fuel gases leav ing the vap orizati on in terface.The con servati on of en ergy for each regi on in Figure 2 is now con sidered. Con servati on of en ergy for the charFor

11、 the char regi on (2a),whereUccgCcqf,rqext,rqv1dUcAdt+ m Cg (Ts -T VmCc 仏-T 0 )=kdTg .dy 丿y=0A+ qf,r +q ext,r bTs7is the internal en ergy of the char layer,is the sp ecific heat of the vap orized fuel gas,is the char sp ecific heat,is the flame conv ective heat flux,is the flame radiative heat flux,

12、is the exter nal radiative flux to the surface,is the surface reradiative heat flux (assumed to be a blackbody),is the heat flux to the plane of vap orizati on,TsTois the surface temp erature, is the refere nee temp erature.Con servati on of en ergy for the vap orizati on in terfaceThe con servati o

13、n of en ergy app lied to the vap orizatio n plane of Figure 2b yields:(Pv 冷Hv =q；-qkwhere AH v is the heat of vaporization (pyrolysis) for the solid at temperature Tvq,is the heat loss per unit area to the virgi n solid.The left side of Eq. (5) relates to the en ergy required to cha nge the virgin s

14、olid to vapor and char, and can be take n as a defi niti on ofCon servati on of en ergy for the virgin solidAn en ergy bala nee on the virg in solid gives1 dU v , fT. /T-1- t W ”AIT fq)7 7where qb is the heat loss per unit area from the back of the solid,and Uv is the internal energy of the virgin s

15、olid.Since the density (p) and specific heat (c) of the virgin solid can be considered con sta nts.Uv = PcA J(T -T0 dysEquations (2)- (7)constitute the governing equations for the solid phase. It is not en tirely obviouswhat are the unknown variables, and what is the strategy of sol ving for them. F

16、or now it can be no ted that by assu ming approp riate p rofiles for the temp erature, the heat fluxes can be exp ress edi ng terms of temp erature by Fouriers Law. Also the variables involving the gas p hase heat tran sfer n eed to be devel oped from the gas p hase an alysis to follow in the next s

17、ection. Now a digression is introduced to illustrate another app roach for p rese nti ng the solid p hase equatio ns, and to offer a check on the above an alysis.Differential formulationCon sider pure con ductive heat tran sfer into the virgin solid with the sp ace coordi nate (x), had tothe moving

18、vap orizati on plane. This coord in ate system is show n in Figure 1,a nd is in troduced toavoid confusion with the ys coordinate system used above. If x0 is the initial fixed refere nee system,t(8)X = Xo - JV(T pT0where v is the velocity of the vap orizati on plane. The con duct ion equati on in th

19、e fixed frame of refere nee is(8)-ITwhich tran sforms ase丿xo-V(10) 2 -2 T c T=2& 丿丿tand Q00&t丿x(14)from Eq. (8). Hence in the movi ng frame of refere nee,-2ex丿t(11)with the con diti ons:-kcT“-=qkexandX = 6v,- kexpp=qb(12)t = 0 , T = To, the initial temperatureCase 1. Non-charring steady burningLet u

20、s con sider the ideal case of a non-charri ng material un dergo ing steady burnin g. If steady conditions prevail in the moving system, i.e., the temperature field is not cha nging in the virg in solid relative to the moving vap orizati on plane, and the back face con diti ons are n egligible,i.e.,

21、a very thick solid, the n Eq. (11) becomes-k立-k dx2(13)ddFrom Eq. (3) and since v =dtdT-m c一dxd2Twith con diti ons from Eq. (5) and (12)d 6X =0 ,-k。 -qv-mAHv ext =0,T =Tv(15b)(15c)Using Eqns (fib) and (Ec)T-T0=eTv -T0-|Ucmx k(16)and from Eq. (Ea)q；m b Hv+ c(TvT0)(17)The denomin ator of6/PeJ蘭Tdx=kcPm

22、dlTv -To y Pen ergy storage due to charri ng-”qbEn ergy flow through char d -Pc- J(T -T。dVsdt6back f a e heat Io.(21b)virgin SOU en ergy storage(The above labels are qualitative descri pti ons of the terms.)Equatio n (21b) gives the thermal boun dary con diti on for the g& p hase an alysis, Le.,=Pm

23、P kg、dy丿whered d HT -T0 dys + qSpcCc 4 J(T - % dysL dl LgfV+ m Cg (Ts -Tv )- Pc Pm & (L -T. y P + 叭4 _ q；十 qj(VPm(22)The form in Eq.(22)c on stitutes a boun dary con diti on for the gas p hase p roblem to中文譯文:煤低溫氧化模型氧氣消耗、氧化產(chǎn)物、反應(yīng)機(jī)理及動(dòng)力學(xué)模型在圖2a-2c種描述的區(qū)域應(yīng)用了質(zhì)量和能量守恒。其包括（a）炭化，（b） 氣化表面，和（C）原始固體。對(duì)于一個(gè)控制體的質(zhì)量守恒，

24、控制體內(nèi)的質(zhì)量變 化速率加上流出控制體的凈質(zhì)量流率等于零?？刂企w的能量守恒為控制體內(nèi)的內(nèi) 部能量變化加上流出控制體的凈能量流率等于凈增加熱流率。除了流動(dòng)做功，忽略了功的影響，另外燃燒熱可視為有效增加熱。 對(duì)每種特定媒介，如炭化材料和 原始材料，都為其假定常量，內(nèi)部熱量參考自初始溫度。總質(zhì)量圖1中的質(zhì)量守恒為A dt其中dm是固體質(zhì)量變化速率，A為表面面積，m為單位面積上氣化產(chǎn)物 dt的質(zhì)量流率。因此，m”是單位表面面積的質(zhì)量損失速率，或更普遍地被稱為燃燒速率（單 位面積）。方程（1）不是控制方程必須遵循的方程，但其可表現(xiàn)流出系統(tǒng)的燃燒 氣化速率和固體質(zhì)量損失速率之間的關(guān)系。炭化質(zhì)量守恒考慮圖2

25、a中炭化層的質(zhì)量守恒，并假定燃料氣化后即刻離開(kāi)固體，其遵循 下式：其中Pc是炭化層密度，m；為氣化平面單位面積炭化質(zhì)量流率。氣化燃料在 炭化層的積累可不加以考慮，從進(jìn)氣化表面進(jìn)入的氣化燃料質(zhì)量流率等于離開(kāi)固 體將要燃燒的氣化燃料的質(zhì)量流率。原始材料質(zhì)量守恒因此，在圖2C中標(biāo)出了原始燃料的質(zhì)量守恒。d備惰(3a)旦 f 田ys + Pv=Odt冠其中P為原始固體密度，其控制體表面移動(dòng)速率等于氣化平面移動(dòng)速率d6 d6ddt-TdT，假定固體的厚度在熱分界發(fā)生時(shí)保持不變。氣化表面的質(zhì)量守恒結(jié)合方程（2）在氣化平面存在質(zhì)量平衡，假定 Pc恒定，則Pv+ mc = Pm”其中 P=P/（P -Pc）此

26、方程表示從原始固體進(jìn)入氣化表面的質(zhì)量流率等于炭化和氣化燃料離開(kāi) 氣化表面的質(zhì)量流率。現(xiàn)在考慮圖2中的各個(gè)區(qū)域的能量守恒。炭化能量守恒對(duì)于（2a）區(qū)域，1 dU c L ” 斤 T L+ m Cg（Ts T V ）mcCc（Tv T 0 ）A dt(3b)&T+ qf,r +qext,r -bTs qv其中：UcCgCc炭化層內(nèi)部能量 氣化燃料比熱 炭化層比熱-kgdy火焰對(duì)流熱通量=0qf,rqext,rbTs4qV Tv Ts To可作為 Hv火焰輻射熱通量 對(duì)表面的外部輻射熱通量表面輻射熱通量（假定為黑體） 對(duì)氣化平面的熱通量氣化溫度表面溫度參考溫度氣化表面的能量守恒圖2b中表明了氣化平面

27、的能量守恒（Pv 處Hv=q；-q；（5）其中 Hv固體在溫度Tv下氣化（高溫分解）熱，qk單位面積散失到原始固體中的熱量。方程（5）的左項(xiàng)為把原始固體變?yōu)檎魵夂吞炕牧纤枘芰? 的定義。原始固體能量守恒原始固體有能量平衡：1 dUA”mq；其中q；Uv原始固體內(nèi)部能量從固體背面單位面積熱損失由于原始固體的密度（P）和比熱（c）可視為常量，U V = PcA（T -T 0 dy s6方程（2）（7）建立了固相的控制方程。不是很明顯能看出那些是未知變 量以及解出它們的方法?，F(xiàn)在可以假定溫度的大致分布，然后根據(jù)傅立葉定律就 可以用溫度來(lái)表示熱通量。而且和氣相換熱有關(guān)的變量在下一部分的氣相分析中

28、也可以得到解答?，F(xiàn)在介紹另外一個(gè)表征固相方程的公式，用以檢驗(yàn)以上分析。 微分公式假定給原始固體的凈傳導(dǎo)熱是沿著在移動(dòng)的氣化平面上建立的空間坐標(biāo) （X）的。 在圖1中標(biāo)出了坐標(biāo)系，為避免上面所用的 ys坐標(biāo)混淆。如果X0是固定初始參 考系統(tǒng)，t(8)(8)X = Xo - JV（T ）dT0其中V是氣化平面的移動(dòng)速度。在固定參考火焰下的傳導(dǎo)方程是-2oXo上式可變?yōu)樗栽趨⒖家苿?dòng)火焰為上式在下列條件下成立:互、dx =dt一 I -v(10)f 2、(2 、cTcT-2=-25丿t嚴(yán)丿t=k(11)x=0, kT=qkex啟，點(diǎn)T Jx =6v，-k= =qbext =0，T=T0，即初始溫度(

29、12)和第一種情況：非炭化穩(wěn)態(tài)燃燒讓我們考慮一種非炭化材料穩(wěn)態(tài)燃燒的理想情況。如果穩(wěn)態(tài)條件在移動(dòng)系統(tǒng) 中仍然成立，如溫度場(chǎng)不隨原始固體內(nèi)氣化平面的移動(dòng)發(fā)生變化，且忽略背部條 件的影響，如一塊非常厚的固體，則方程（11）變?yōu)?14)(13)-Pcvdl.kddx dx由方程（3）和2dT , d T -m c=k2dxdx2上式成立條件為方程（5）和（12）的條件：刃=6；-m3Hvx=0，-k(15a)t =0 , T =TvXT 處，T =丁0由(15b)和(15c)，可得(15b)(15c)T-T0Tv -T0cm_zXk(16)由方程（15a）可得(17)qV也Hv+ CTv -T。)方

30、程（17）中的分母一般稱為穩(wěn)態(tài)汽化熱（Lg = AH v+ c（Tv -T0 ）第二種情況：瞬間炭化大體上，下面要考慮的其他術(shù)語(yǔ)會(huì)影響質(zhì)量損失速率態(tài)的，我們可以在6上對(duì)每一項(xiàng)積分，考慮方程（11） 2 T亠fk 0 2 dx = 0 exexLg)(18)m”。如果過(guò)程不是穩(wěn)XT= (-q,)-(-dk)dx = -cm*Tdtk = PcU Ldx - PcT(5v,t)0 H dt 0=十 g：TdkamTbdt 0d首=Pc J(T T。dx + cm(Tb -T。) dt 0同樣對(duì)于在氣化平面的炭化情況v一理止，由方程（3b），m應(yīng)由Pm”替代，替換方程（11）的積分形式dt dtd

31、&PcfCT -T。dx + pm七(Tb -T。)-pmcTb -Tv)=q：-qbdt 0此方程與方程（6）相同，說(shuō)明原始固體能量守恒是符合微分公式的。 求解方法綜上，有對(duì)于炭化、氣化表面和原始固體的包含質(zhì)量和能量守恒的六個(gè)獨(dú) 立的方程。將這些方程合并后，只有兩個(gè)方程（4和6）與未知變量有關(guān)：炭化 厚度、表面溫度和一個(gè)將要介紹的可表征原始固體熱效應(yīng)的變量。原始固體厚度和質(zhì)量燃燒速率可以用來(lái)闡述炭化厚度，而熱通量可以用來(lái)闡述假定與炭化厚度 和原始固體厚度相關(guān)的溫度分布?？蓮臍庀嗷鹧娣治龅玫降谌齻€(gè)方程，其可以給 出燃燒速率的關(guān)系。火焰?zhèn)鲗?dǎo)和輻射熱通量可從氣相火焰分析的現(xiàn)有變量得出。 接下來(lái)，本

32、部分將基于上述守恒方程推導(dǎo)出火焰對(duì)流換熱量，這在下一部分研究的氣相分析中可以提供邊界條件。固相和氣相分析得到統(tǒng)一。由方程（5）和（6），可得到d各(19)代一fr -To dx + PmcfTv -To ）= qV - PmciH v -qb dt 0或者d 6pmtg =q；-q；-Pc-J(T-T0 dxdt 0此式偏離方程（17）給出的穩(wěn)態(tài)結(jié)果。當(dāng)qV被視為凈表面熱通量，且P = 0時(shí)， 此時(shí)可以應(yīng)用到非炭化情況。外,更多的普通炭化情況可以視為使用方程（4）從方程（19）中消除了 qV。另 炭化內(nèi)部能量可以表征如下：=J PcUcdys ,其中由炭化表面測(cè)得。單位內(nèi)部能量Uc可由Cc（T -To ）表示，其 0中Cc是炭化層比熱。由方程（2）可得到1 dUcA dt(20)d & =PcCc J(T 一T0 dys dt 0合并所有的固體能量方程，或從方程(4), (19)和(20)可得到怖Lg