COMPREHENSIVE, THEORETICALLY BASED, CORRELATING EQUATIONS FOR FREE CONVECTION FROM ISOTHERMAL SPHERES

Correlating equations are developed for the local and mean Nusselt number for free convection from an isothermal sphere as a function of the Rayleigh and Prandtl numbers. These expressions are based primarily on theoretical solutions for limiting cases, and hence are presumed to be more reliable than purely empirical correlations. The predictions of the proposed expressions are, however, validated by comparisons with prior experimental data. The expressions for the mean Nusselt number are shown to be applicable for all Ra and Pr. The expressions for the local Nusselt number are limited in applicability to the laminar boundary layer regime. The same equations are applicable to mass transfer and to combined heat and mass transfer in terms of the Sherwood, Schmidt and appropriately modified Rayleigh numbers.     

HEAT TRANSFER TO NON-NEWTONIAN LIQUIDS FLOWING THROUGH HORIZONTAL TUBES

Experimental and analytical investigation of heat transfer to single phase flow of pseudoplastic fluids under constant heat flux condition was carried out. Experimental data for laminar flow heat transfer in the thermally developing region over a wide range of rheological properties ( n from 0.54 to 0.84 and K from 0.07 to 2.41 Nsⁿ/m²) in 0.028 and 0.057 m diameter pipes were collected. Enhancement in heat transfer rate due to natural convection and temperature dependent rheotogy was observed. The temperature dependent viscosity effect is a function of flow behavior index and it contributes more towards heat transfer enhancement than natural convection does. A correlation (confidence level ±15%) for the entire set of data is also presented.     

RADIATION EFFECT ON FREE CONVECTION LAMINAR FLOW FROM AN ISOTHERMAL SPHERE

Natural convection laminar flow from an isothermal sphere immersed in a viscous incompressible optically dense fluid in the presence of radiation effects has been investigated. The governing boundary layer equations are transformed into a non dimensional form and the resulting nonlinear systems of partial differential equations are reduced to local non-similarity boundary layer equations, which are solved numerically by two distinct, efficient methods, namely, (i) implicit finite difference method together with the Keller box scheme and (ii) local non-similarity method. Numerical results of the velocity and temperature profiles of the fluid are presented. The results of the shearing stress and the heat transfer rate in terms of skin-friction coefficient and Nusselt number respectively are also presented for a wide range of the radiation-conduction parameter or Planck number R _d (=0.0, 1.0, 2.0, 3.0), the surface heating parameter θ _w (=1.1, 1.2, 1.4), and Prandtl number Pr (=7.0, 10.0, 15.0, 20.0).     

Shear rate dependence of thermal conductivity and its effect on heat transfer in a Non-Newtonian flow system

The purpose of this research was to investigate the extent to which the thermal conductivity of non-Newtonian fluids is affected by fluid motion, and then the effect of this shear-rate-dependent thermal conductivity, measured in Lee [1995], on the heat transfer for a typical convective system. Such information would have important implications in the design and analysis of non-Newtonian thermal systems such as are found in food processing operations, polymer processing, paint manufacturing, biological systems and many others. A simple parallel plate flow model with temperature-independent properties gave increases in heat transfer on the order of 30–80 % compared to the heat transfer with shear-rate-independent thermal conductivity in Newtonian fluid flow over the entire temperature range (20–50 °C) of CMC solutions depending on the inlet average velocity due to the effect of the shear-rate-dependent thermal conductivity.     

非共沸混合工质在水平管束上轴向流动冷凝传热强化的强究

研究了花瓣形翅片管强化非共沸混合工质在水平管束上轴向流动冷凝传热的性能,并建立了管束冷凝传热系数的计算模型。结果表明,该模型的计算值与实验结果吻合得较好。     

NATURAL CONVECTION HEAT AND MASS TRANSFER FROM A VERTICAL FLAT PLATE WITH VARIABLE WALL TEMPERATURE AND CONCENTRATION TO POWER-LAW FLUIDS WITH YIELD STRESS IN A POROUS MEDIUM

The problem of natural convection coupled heat and mass transfer of non-Newtonian power law fluids with yield stress from a vertical flat plate in a fluid-saturated porous medium is analyzed under boundary layer approximations. Similarity solutions are obtained for the general case of power law variations of the wall temperature and concentration. Velocity, temperature, and concentration profiles as well as local heat and mass transfer rates are presented and discussed for different values of the rheological parameters of a power-law fluid, the Lewis number, and the thermal and concentration buoyancy ratio.     

DEVELOPMENT OF OVERALL HEAT TRANSFER COEFFICIENTS FROM THE HETEROGENEOUS TWO DIMENSIONAL (2-D) MODEL FOR CATALYTIC FIXED BED REACTORS, A COMPARISON BETWEEN ID AND 2-D MODELS

Analytical expressions are developed for the evaluation of global heat transfer coefficients for the heterogeneous one-dimensional (Het l-D)-flxed bed reactor model. These expressions are evaluated from the associated two-dimensional (Het 2-D) model applied at the hot-spot conditions ocurring for exothermic reactions, and include the effect caused by the dependence of heat generation with temperature. The comparison between the Het 1-D and Het 2-D models covering an important range of typical industrial operating conditions, shows that very precise estimates can be achieved with the former, provided that conditions of parametric sensitivity does not occur. For instance, maximum differences in average gas temperature are less than 6°C