【正文】 ??????????????????????????????? 5 9 T urbule nt kiic e ne r g y k μe/ σk ( ) (s e e E q n 5 1 3 for d e fi n a t i o n o f P )rP ??? 5 10 Dissi pa ti on ra te ? μe/ σε 12( / )( )(see E q n 5 1 3 fo r d ef i n at i o n o f P )r k c P c? ? ?? 5 11 Enthalpy h μe/ σh hprgSpwrrpvxpuq ???????????~1~~ 5 12 The production term (P) ? The production term (P) in the source terms for turbulent kiic energy (k) and dissipation (?) (eqns. 510 and 511 ) is given by (513) production term 產(chǎn)生項 eqn equation eqns equations 2 2 2 22221{211}eu v w v u vPx r r r r xu w v w wr x r r r??????? ? ? ? ?? ? ? ? ? ? ? ?? ? ? ? ? ???? ? ? ? ? ? ? ?? ? ? ? ?? ? ? ? ? ? ? ???? ? ? ?? ? ? ?? ? ? ? ?? ? ? ?? ? ? ?? ? ? ?The particle source terms ? The particle source terms for mass, axial momentum, radial momentum, tangential momentum, and enthalpy, are represented by , and respectively. ? These terms represent the additions of mass, momentum, and enthalpy per unit volume to the gas phase from the particles. axial 軸向的 radial 徑向的 tangential 切向的 momentum 動量 enthalpy 焓 addition 增加 m u v wp p p pS S S S， ， ， hpS? The Cartesian form is obtained by setting the radial coordinate (r) equal to unity. ? The 2D, axisymmetric form can be obtained by setting derivatives with respect to the angular coordinate (θ) equal to zero. unity （數(shù)學）一 derivative with respect to 對 … 的導數(shù) (ii) Turbulence Model ? Fundamental difficulties with the k? model ?The eddy viscosity is assumed isotropic . ?The eddy viscosity concept is derived by analogy with molecular viscosity, and there are important differences in the collision properties and mean free paths of molecules and eddies. isotropic 各向同性的 analogy 模擬，效仿 collision 碰撞 mean free paths 平均自由行程 anisotropic 各向異性的 PCGC3 treatment with turbulence 1 ? The nonlinear k? model has been adopted to account for nonisotropic eddy viscosity. ? Laminarization terms have also been included to more accurately model the dead zones in industrialscale furnaces. nonlinear 非線性的 laminarization層流化的 dead zones 死區(qū) PCGC3 treatment with turbulence 2 ? The extended k? model with laminarization correctly predict negligible eddy diffusivity at low Reynolds numbers and then revert to normal k? predictions at high Reynolds numbers. Advanced turbulence models ? The more sophisticated Reynolds transport and algebraic stress models have been used in FLUENT. ? Higherorder approaches such as direct numerical simulation (DNS) and largeeddy simulation (LES) have not yet been applied in prehensive modeling of coal bustion. Reynolds transport model(RSM)雷諾應力模型 algebraic stress model(ASM) 代數(shù)應力模型 direct numerical simulation 直接模擬 largeeddy simulation (LES) 大渦模擬 The effect of particles on gas turbulence ? The effect of particles on gas turbulence is modeled with the correlation of Melville and Bray (514) ? Eqn 514 results in decreased turbulence intensity with increasing bulk particle density o p a r t i c l e,p a r t i c l e s, )/1/( gbtgtg ???? ??b?(iii) Homogeneous Chemistry ? Assumption The chemical reactions for the major species to be limited by mixing rates. ? The local instantaneous gas properties are determined from equilibrium, without regard to chemical kiics. ? Mixing is modeled with two mixture fractions, and instantaneous properties are averaged over a probability density function (pdf) for the mixture fractions. Sources of mass to the gas phase ? At most three sources primary carrier gas secondary gas coal offgas Coal offgas ? consists of fluid atoms originating from the coal and is assumed to be independent of extent of devolatilization or burnout (referred to later as the constant coal offgas assumption). ? A coalgas mixture fraction is defined to account for the local mass fraction of coal offgas (515) cgsgpgcgmmmm????? If all of the inlet gas streams are identical in position and temperature, ? is the only required mixture fraction. ? Such is the case for bustors where both the transport (primary) and bustion (secondary) air streams are at room temperature. identical 同一的，完全相同的 Mixture fraction for advanced scheme ? Gasification processes and bustion processes with air preheating or advanced pollution control schemes (. reburning) require a second mixture fraction to predict inlet gas mixing (816) preheating 預熱 scheme 方案 reburning 再燃 sgpgpgmmmf??? Transport equations are solved to obtain the local, Favremean values of f, ? , and their variances (gf and g?) Instantaneous gas properties 1 ? The element mass fractions bk Assuming equal turbulent diffusivities for all species, the element mass fractions (bk) are conserved scalars and are functions of f and ? (517) diffusivity 擴散系數(shù) conserved scalars 守恒量 ? ?kskpkck bffbbb )1()1( ????? ???Enthalpy Enthalpy is deposed into a conserved portion (hf, ?) and a residual portion (hr) (518) Where depose 分解 Instantaneous gas properties 2 rf hhh ?? ?,])1()[1(, spcf hffhhh ????? ???Instantaneous gas properties 3 Hence, instantaneous gas properties are functions of f, ?, and hr (519) (520) (521) ),()],(),([),( rrkk hfThfhfbThbTT ??? ???),()],(),([),( rrkk hfhfhfbhb ??????? ???),()],(),([),( rirkikii hfyhfhfbyhbyy ??? ???Timemean gas properties ? Only the conserved portion (hf, ?) is allowed to