A new formulation of Damkohler number for studying opposed-flow flame spread and extinction

1995 ◽  
Author(s):  
Kurt Sacksteder ◽  
James T'ien
Keyword(s):  
Flame Spread ◽  
Damkohler Number ◽  
Damköhler Number ◽  
Opposed Flow ◽  
New Formulation

Analysis of the Equilibrium Approximation in Chemical Ablation of Thermal Protective Systems

2012 ◽  
Author(s):  
B. W. Barr ◽  
O. A. Ezekoye
Keyword(s):  
Experimental Data ◽  
Complex Surface ◽  
Damkohler Number ◽  
Damköhler Number ◽  
Graphite Oxidation ◽  
Model Predictions ◽  
Surface Equilibrium ◽  
Carbon Combustion ◽  
New Formulation ◽  
Good Agreement

A quasi-steady-state ablation model is used to investigate the behavior of thermochemically ablating systems in equilibrium and nonequilibrium surface thermochemistry regimes. The model is simplified to allow extraction of relevant nondimensional parameters and comparison with existing experimental data on solid carbon combustion. Good agreement is found between model predictions and experimental data, and the data and model are collapsed in terms of the B number and surface Damkohler number. A new formulation for the surface Damkohler number is proposed, and a relationship between the B number and this Damkohler number is derived for the surface equilibrium and nonequilibrium regimes. The Damkohler formulation is applied to the reentry scenario, and the behavior of the B number in this context is explored. Nondimensional parameters governing behavior in the nonequilibrium regime are determined for graphite oxidation, and the results are extrapolated to more complex surface thermochemistry conditions.

Evaluation of the One-Well Uranium Leaching Test: Restoration

1982 ◽  
Vol 22 (01) ◽  
pp. 141-150 ◽  
Author(s):  
Muhammad I. Kabir ◽  
Larry W. Lake ◽  
Robert S. Schechter
Keyword(s):  
Acid Leaching ◽  
Leach Solution ◽  
Damkohler Number ◽  
Damköhler Number ◽  
Well Spacing ◽  
Number Of Factors ◽  
Well Pattern ◽  
Mineralized Zone ◽  
Selection Of

Abstract In-situ leach mining for uranium is an emerging technology. Currently, the selection of a well pattern designed to recover mineral values is governed primarily by arguments based on hydrological considerations. The effects of well pattern and well spacing on uranium recovery and oxidant utilization are considered in this paper. As expected, formation permeability heterogeneities and anisotropies are found to be important issues requiring careful consideration, however, it also is shown that chemical factors cannot be ignored. In particular, it is shown that the oxidant efficiency and the produced uranium solution concentrations are sensitive to the presence of other minerals competing with uranium for oxidant. If the Damkohler number for competing minerals, which measures the speed of the reaction, exceeds that for uranium, the competing mineral will have to be oxidized completely to recover a large proportion of the uranium. If the Damkohler number is smaller, it may be possible to achieve considerable selectivity for uranium by adjusting the well spacing. It also is shown that the oxidant efficiency is generally highest for well patterns that give streamlines of roughly equal length and that there is a minimum distance between injection and production wells to utilize oxidant most advantageously. Introduction In-situ solution mining is a process whereby uranium is recovered from permeable sandstone bodies by injecting and producing a leach solution through an array of wells penetrating the mineralized zone. It appears to have broad application and in many situations offers both economic and environmental advantages. The processes may be classified generally as acid or alkaline, but the general features of both are the same. The insoluble uranium in the mineralized zone is in the +4 state of oxidation. To be mobilized, the uranium must be oxidized to the +6 state and complexed either with sulfate in the case of acid leaching or carbonate in the case of alkaline leaching to form highly soluble uranyl sulfates or carbonates. The leach solutions, therefore, contain an oxidant (oxygen, hydrogen peroxide, ferric cations, sodium hyperchlorite, etc.) together with a complexing agent (anion). The choice of leach solution depends on a number of factors including selectivity and injectivity. For example, formations containing more than 1 wt% carbonates are not likely to be candidates for acid leaching because of the large acid requirement and because of permeability loss due to precipitation of calcium sulfate. It is the purpose of this paper to consider the technical factors (as opposed to economic) that govern the choice of well pattern to be used for leaching. The discussion is structured so that the conclusions apply to both alkaline and acid lixiviants and to any oxidant, although an occasional reference to a particular oxidant may appear. Considerable use is made of the computer simulator previously reported. The computational details are available in that paper. A number of factors that pertain to the selection of a well pattern are considered. It is shown that the effectiveness of the oxidant - i.e., the uranium recovered per unit of oxidant injected - is related to the well pattern, to the reaction rates, and to the permeability variations, especially if the formation is anisotropic. Furthermore, the spacing between wells is related to reactions with oxidizable minerals that compete for oxidant. These considerations can be quantified to some extent by studying linear systems. Linear Flow Systems SPEJ P. 132^

An Experimental and Theoretical Study of Heat Conduction and Vulcanization of Rubber Compounds in Molds

1987 ◽  
Vol 60 (1) ◽  
pp. 140-158 ◽  
Author(s):  
Dancheng Kong ◽  
James L. White ◽  
Frederick C. Weissert ◽  
Nobuyuki Nakajima
Keyword(s):  
Heat Conduction ◽  
Curing Kinetics ◽  
Damkohler Number ◽  
Fourier Number ◽  
Fundamental Study ◽  
Damköhler Number ◽  
Rubber Compounds ◽  
Cure Temperature ◽  
Black Other ◽  
Kinetics Of

Abstract A fundamental study on curing of rubber compounds in molds is presented. We have measured the thermal conductivity of a range of rubber compounds determining the influence of carbon black, other fillers, and oil. The heats of reaction associated with the curing kinetics of model compounds were measured. A mathematical model is proposed to predict the temperature profiles for curing a reactive slab. This involves inclusion of an energy generation rate, which depends on time and temperature. This is expressed through a Damkohler number. Solutions of the heat conduction equation are interpreted in terms of the Fourier number and the Damkohler number. Calculations are carried out using experimentally determined thermal conductivities and curing kinetics. Thick parts are shown to heat up more slowly (associated with the Fourier number) and to show greater overshoots of cure temperature (associated with the Damkohler number).

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