David Everest

Images of the strained flammable layer used to study the liftoff of turbulent jet flames

Images were obtained to visualize the flammable layer upstream of a lifted turbulent, non-premixed jet flame in order to (a) quantify the degree of premixing upstream of the flame base, (b) visualize the path along which the flame base can propagate, and (c) show how scalar dissipation layers, which identify high strain regions, overlap the flammable layer. It is found that a significant amount of premixing occurs at x/d =5 that creates a continuous, contorted flammable layer, appearing as thin as 70 microns or as thick as 3 mm, depending on the local strain. The structure of many larger wrinkles in the flammable layer is consistent with the structure predicted by the flame-vortex simulation of Ashurst and Williams: a vortex that moves radially outward tends to cause extensive strain and a thinning of the layer at the largest radial locations. Upstream of the vortex, compressive strain causes a local broadening of the flammable layer, as predicted. Where the dissipation layers are observed to overlap the flammable layer, the dissipation rate is larger than that required to extinguish either a premixed or a non-premixed strained flame. The dissipation layers have a distinet structure in the jet near field—they are aligned at approximately 45° to the jet axis, unlike the isotropically aligned dissipation layers downstream.

Effects of Finite Time Response and Soot Deposition on Thin Filament Pyrometry Measurements in Time-Varying Diffusion Flames

Prior work has shown that thin filament pyrometry (TFP) is a powerful approach for making highly precise, spatially and temporally resolved line measurements of temperature in time-varying laminar diffusion flames. The technique has been previously used to map out temperature distributions as a function of phase angle for acoustically locked flickering diffusion flames with two different levels of forcing. During these measurements two small errors in the temperature measurements have been identified for certain heights and phases. The first error source is shown to be due to the limited time response of the TFP to a rapidly changing temperature field by comparing temperatures determined by TFP with line measurements using Rayleight light scattering (RLS). The TFP measurements yield lower temperature readings when the flame front is moving at its fastest rate, but the RLS measurements show that these lower temperatures are an artifact which is attributed to the finite time response of TFP. The second source of error occurs for a limited number of cases in which soot is thermophoretically deposited on the filament and is not subsequently burned off. The soot modifies both the emissivity of the filament surface and, for large amounts of deposition, its diameter. These modifications lead to lower measured filament temperatures for low levels of soot deposition and to increasing measured temperatures as the soot builds up. Approaches are suggested for identifying the presence of these errors and minimizing their effects.

Lessons learned from industrial assessments of metal casting facilities

This article presents recommendations for saving energy that are based on ten industrial energy assessments performed at metal casting facilities and foundries. The facilities assessed produce castings of aluminum, copper, bronze, iron and steel. They utilize a variety of molding processes and require large amounts of energy. The energy sources used for melting were electricity, natural gas, and coke. Support activities involved the use of natural gas and electricity. Recommendations that are of interest to all foundries and metal casting companies are discussed. In particular, analysis is presented for improvements in: ○ Process melting energy ○ Operating combustion blowers, pumps, and exhaust fans ○ Opportunities for combining heat and power Process melting energy accounts for the majority of energy costs in all foundries, and can be significantly reduced by decreasing heat losses. The major heat losses observed were due to: i) high temperature exhaust gases, ii) cooling water losses for electric induction coils, and iii) lack of proper furnace insulation. Methods of reducing each of these losses are discussed. The energy usage by air exhaust fans, pumps, and combustion air blowers offers additional opportunities for savings. Improvement in these systems through the use of two-speed or variable speed drives is discussed. Finally, the simultaneous need for heat and electricity at most of these sites provides an opportunity for combined heat and power (CHP) systems. The potential applicability of a CHP system is explored to meet the needs of these metal casting facilities and foundries.