An investigation of transient three-dimensional buoyancy-driven flow and heat transfer in a closed horizontal annulus
Abstract Buoyancy-driven flow and heat transfer in a horizontal annulus bounded by two impermeable boundaries in the axial direction are numerically investigated in this work. A transient three-dimensional analysis of the end effects on heat transfer and the corresponding flow field is presented. The effects of the axial impermeable boundaries are shown to be characterized by retardation of the flow field through the viscous shearing force in regions near the end walls. The results show that the temperature distribution remains unchanged in the core region provided that the annulus length to outer radius ratio is larger than a critical value. Flow and temperature fields are found to be symmetrical with respect to the mid-axial plane of the annulus. A number of interesting features resulting from the sudden heating of the inner cylinder are presented. Finally, a thorough presentation of formation of flow and temperature fields as a result of the sudden heating of the inner cylinder is given.
A CYLINDRICAL ANNULUS UTILIZING A POROUS PERTURBATION
In this work, free convective fluid flow and heat transfer are analyzed in a horizontal cylindrical annulus in the presence of a porous geometric perturbation. The flow in the porous region is modeled using the Brinkman-Forchheimer-Darcy model. The numerical scheme used in the present study is based on a Galerkin method of the finite element formulation. The nature of the three-dimensional flow field has been analyzed in detail, and the local and average Nusselt numbers have been obtained for a range of Rayleigh numbers of practical interest. In order to evaluate the effect of a porous perturbation, the flow and heat transfer characteristics were compared with those for a regular annulus without a perturbation and one with a solid perturbation. This study reports on the dependence of the flow and heat transfer characteristics on the governing parameters such as the ratio of the conductivity of the porous material to that of the fluid and the permeability. A correlation has been obtained that captures the variations of the overall heat transfer as a function of the Rayleigh number, the permeability, and the conductivity ratio. The results of this study show that both heat transfer retardation and enhancement can be achieved with the introduction of a porous perturbation.
Melanocins A, B and C, new melanin synthesis inhibitors produced by Eupenicillium shearii. I. Taxonomy, fermentation, isolation and biological properties.
New melanin synthesis inhibitors, melanocins A, B and C, were isolated from the fermentation broth and mycelium extract of Eupenicillium shearii F80695. Melanocin A, an isocyanide compound, inhibited mushroom tyrosinase and melanin biosynthesis of B16 melanoma cells with IC50 value of 9.0 nM and MIC value of 0.9 microM, respectively. Melanocin A also inhibited growth of Streptomyces bikiniensis. While, the structurally very related but non-isocyanide compounds melanocins B and C did not show inhibitory activity in these assays. Melanocins A, B and C showed potent antioxidant activity with scavenging activity of DPPH radical and superoxide anion radical.