Tham khảo tài liệu 'developments in heat transfer part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 150 Developments in Heat Transfer region whereas Ak and Ac are positive in the same region. Altogether there is a non-negligible effect of variable properties on the temperature distribution. a A c Ak b d Aa Fig. 9. A-values of temperature computed by RANS in a differentially heated cavity see Fig. 4 Ra 2 X108 a Ay b Aụ c Ak d A Variable Property Effects in Momentum and Heat Transfer 151 5. Conclusions Various methods to account for variable property effects in complex geometries and highly sophisticated numerical methods have been proposed. Due to the Taylor series expansions of all properties which are the starting point for all methods the influence of variable properties can be accounted for in a general manner . for all small heating rates and for all Newtonian fluids. For a special problem with A-values determined once the effect of variable properties can be found in the final result by fixing s the heat transfer rate and all K-values from the fluid of interest . This way of treating variable property effects is much closer to the physics than empirical methods like the property ratio and the reference temperature methods are. 6. Nomenclature Aa Ab A . A-values a b e p y v k cp a b cp specific heat capacity f friction factor g gravity vector haj h-values s Kaj j empirical parameter Ka K - Kan K-values a p y p k Cp k heat conductivity _ L characteristic length ma na empirical exponents Nu Nufielt number p pressure Pr Prandtl number Pa nondimensional properties about variable fluid property q heat flux Re Reynolds number T temperature u velocity vector V variables Greek symbols a p ơ s variables composed of fluid properties 7 expansion coefficient AT temperature difference s nondimensional temperature difference V dynamic viscosity p density subscripts cp constant properties R reference state .
