Gasification effects in the heterogeneous ignition of a condensed fuel by a hot gas

An analysis is presented to describe the heterogeneous ignition of a condensed fuel suddenly exposed to a hot oxidizing atmosphere. The exothermic heterogeneous reaction, generating gaseous products, is considered to be of the Arrhenius type with an activation energy large compared with the initial thermal energy of the fuel. Instantaneously after contact with the gases the surface temperature rises to a jump value which is calculated allowing for variable transport properties of fuel and gas. The effect of the chemical heat release and the cooling effect due to the gasification flow are taken into account in obtaining an integral equation, involving a single parameter Δ, which is solved to describe the evolution of surface temperature with time. A runaway in surface temperature is found to occur at a well defined ignition time, which is calculated as a function of Δ. For values of Δ above a critical value no ignition occurs because the cooling effects of the gasification flow dominate over the effects of chemical heat release.     

Establishing satellite data bases in developing countries: A critical view

Remote sensing is a data gathering and analysis technique that offers the possibility of natural resource evaluation. Countries that have not yet evaluated their main resources owing to the lack of basic knoweldge of their territory, are attracted by the idea of rapidly creating data banks through the use of remote sensing. While such a technique offers advantages over traditional means of data acquisition, it requires special systems and methods of analysis that are not particularly easy to assimilate. The building of data bases is taken here as the framework for analyzing some problems confronted by developing countries when trying to incorporate the techniques of teledetection.