Numerical Study Of Heat Transfer Mechanism In Turbulent Supercritical Co2 Channel Flow

Direct numerical simulation (DNS) of supercritical CO2 turbulent channel flow has been performed to investigate the heat transfer mechanism of supercritical fluid. In the present DNS, full compressible Navier-Stokes equations and Peng-Robison state equation are solved. Due to effects of the mean density variation in the wall normal direction, mean velocity in the cooling region becomes high compared with that in the heating region. The mean width between high-and low-speed streaks near the wall decreases in the cooling region, which means that turbulence in the cooling region is enhanced and lots of fine scale eddies are created due to the local high Reynolds number effects. From the turbulent kinetic energy budget, it is found that compressibility effects related with pressure fluctuation and dilatation of velocity fluctuation can be ignored even for supercritical condition. However, the effect of density fluctuation on turbulent kinetic energy cannot be ignored. In the cooling region, low kinematic viscosity and high thermal conductivity in the low speed streaks modify fine scale structure and turbulent transport of temperature, which results in high Nusselt number in the cooling condition of the supercritical CO2.

Políticas públicas y desigualdades regionales en la distribución del ingreso en la Argentina

Resumen: El análisis de los indicadores de ingresos, desigualdad y pobreza en cada uno de los 32 centros urbanos muestra las grandes disparidades regionales de la Argentina. En la Zona Norte del país el ingreso per capita es un 35% inferior al promedio nacional, la pobreza es 4 veces mayor que en la capital y la distribución del ingreso es más desigual. Los datos estadísticos disponibles indican que el crecimiento económico y las políticas públicas que se han implementado recientemente han reducido los niveles de pobreza agregados, pero han tenido poco impacto en las regiones más pobres del país. Por otra parte, el impacto distributivo de las políticas y programas públicos en la Argentina es reducido cuando se los compara con lo que sucede en los países mas desarrollados. Se requiere el diseño y la implementación de nuevas políticas públicas de reducción de la pobreza que se focalicen en los problemas y dificultades específicas que enfrentan las regiones más pobres. Entre ellas se destaca la necesidad de políticas para disminuir la alta informalidad del empleo que caracteriza a estas zonas. Por otra parte, las nuevas políticas deberían transferir las responsabilidades y premiar los esfuerzos propios de los gobiernos locales, reemplazando la actual “cultura de la dependencia” de los programas del gobierno central por un desarrollo institucional local que enfatice la gestión eficiente de las administraciones públicas provinciales y el desarrollo del capital social local.

A note on the heat-transfer to nonspherical particles from plasma

Heat transfer from plasma to a nonspherical partical in the free-molecular regime is studied in the present paper under thin plasma sheath condition. Analytical expressions for the floating potential charge and heat fluxes of an ellipsoid particle of revolution are derived and curves are given for key parameters for arbitrary plasma flow direction. On the basis of these results, an equivalent sphere with the same surface area as the nonspherical particle is suggested to be used for calculating the total heat flux of nonspherical particle in engineering application with acceptable accuracy. Furthermore, the effects of particle rotation, which occurs in most aerosol systems, on the heat transfer are also discussed.

Basic equations for suspension flows with interphase mass-transfer

In the case of suspension flows, the rate of interphase momentum transfer M(k) and that of interphase energy transfer E(k), which were expressed as a sum of infinite discontinuities by Ishii, have been reduced to the sum of several terms which have concise physical significance. M(k) is composed of the following terms: (i) the momentum carried by the interphase mass transfer; (ii) the interphase drag force due to the relative motion between phases; (iii) the interphase force produced by the concentration gradient of the dispersed phase in a pressure field. And E(k) is composed of the following four terms, that is, the energy carried by the interphase mass transfer, the work produced by the interphase forces of the second and third parts above, and the heat transfer between phases. It is concluded from the results that (i) the term, (-alpha-k-nabla-p), which is related to the pressure gradient in the momentum equation, can be derived from the basic conservation laws without introducing the "shared-pressure presumption"; (ii) the mean velocity of the action point of the interphase drag is the mean velocity of the interface displacement, upsilonBAR-i. It is approximately equal to the mean velocity of the dispersed phase, upsilonBAR-d. Hence the work terms produced by the drag forces are f(dc) . upsilonBAR-d, and f(cd) . upsilonBAR-d, respectively, with upsilonBAR-i not being replaced by the mean velocity of the continuous phase, upsilonBAR-c; (iii) by analogy, the terms of the momentum transfer due to phase change are upsilonBAR-d-GAMMA-c, and upsilonBAR-d-GAMMA-d, respectively; (iv) since the transformation between explicit heat and latent heat occurs in the process of phase change, the algebraic sum of the heat transfer between phases is not equal to zero. Q(ic) and Q(id) are composed of the explicit heat and latent heat, so that the sum Q(ic) + Q(id)) is equal to zero.