Showing papers by "Stuart W. Churchill published in 1983"

Comprehensive, theoretically based, correlating equations for free convection from isothermal spheres

Abstract: 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.

Laminar Natural Convection in an Inclined Rectangular Box With the Lower Surface Half-Heated and Half-Insulated

Abstract: The pattern of circulation and the rate of heat transfer were determined experimentally and also by three-dimensional, finite-difference calculations for an inclined 2 × 1 × 1 rectangular enclosure with a 1 × 1 segment of the lower 2 × 1 surface at a uniform temperature, the other 1 × 1 segment and four side walls insulated, and the upper surface at a lower uniform temperature. As contrasted with an enclosure heated and cooled on the horizontal surfaces, a fluid motion occurs and the rate of heat transfer exceeds that for pure conduction for all temperature differences and orientations. The effects of elevation of the heated and insulated segments were investigated, as well as of inclination about the longer dimension. Despite differences in the Prandtl and Rayleigh numbers, the observed and predicted patterns of circulation are in good agreement, and the measured and predicted rates of heat are in qualitative agreement.

Laser-Doppler Measurements of the Velocity Along a Heated Vertical Wall of a Rectangular Enclosure

Abstract: Mesures par anemometrie laser Dopler et par thermocouple des champs de temperatures et de distributions de vitesse au voisinage de la paroi verticale chauffee d'une enceinte rectangulaire remplie d'eau. Visualisation des ecoulements a l'aide de phenolptaleine

Correlating equations for the recovery factor and the blasius functions for flow along a flat plate

Abstract: This paper describes the development of a complete set of continuous, comprehensive correlating equations for the recovery factor, and for the various functions of the velocity field which are required for calculation of heat transfer in the laminar boundary layer regime. These expressions are based on theoretical asymptotes and intermediate numerical values. Asymptotes were derived in the few instances for which they were not already known. Additional numerical values were computed to support the construction of the correlating equation for the recovery factor, but prior computed values were sufficient for the velocity functions.

Computer study of the constant pressure auto-ignition of mixtures of ethane, methane, carbon monoxide and hydrogen in air

Abstract: The autoignition of mixtures of ethane, methane, carbon monoxide and hydrogen in air at atmospheric pressure was studied theoretically using a detailed, free-radical, kinetic model. The elementary reactions for the model were chosen with the help of the sensitivity analysis of Rabitz et al., which utilizes a Green's function transformation. This technique was particularly helpful in identifying those reactions which are important during the induction period prior to ignition. The effects of equivalence ratio, initial temperature and constant rate of heating were investigated for various fuel compositions. Induction times from 10 microns to 11.5 microsec were calculated for adiabatic ignition with initial temperatures from 1300 to 2100 K. Mixtures of pure methane and air were found to have long induction times, but small additions of ethane and even lesser additions of hydrogen, produced dramatic reductions. The flamefront was broadened significantly by large initial concentrations of carbon monoxide, due to its relatively slow rate of oxidation even at high temperature. 11 references.

Combustion: a true interaction of fluid dynamics, chemical kinetics, heat transfer, and mass transfer

Abstract: Illustrative recent work and challenging problems in the field of combustion were identified for modeling. Recent progress in several aspects of the modeling of combustion is illustrated for selected processes. The idealizations of infinite reaction rates, local partial equilibrium, global kinetics, and a stationary state for free radicals should now be avoided or justified. Generally, diffusive, convective, and radiative mechanisms are all significant in combustion and, frequently, turbulent transport and buoyant mechanisms as well.