The effect of inlet flow distribution on the performance characteristics of a catalytic converter is analyzed for two common inlet manifold designs. Three-dimensional steady-state computational fluid dynamics simulations are performed under isothermal and nonisothermal conditions for the entire converter comprising an inlet manifold, central monolith, and outlet section. The porous medium approximation is used for the catalytic monolith. The reaction mechanism for a diesel oxidation catalyst with five global reactions is employed. A parameter called the "flow distribution index" is defined in order to quantify the nonuniformity of the velocity profile within the monolith and hence analyze the effect of operating conditions for the two geometries. Under isothermal conditions, catalytic converters with straight and U-bend inlet manifolds behave similarly and closely match single channel predictions. However, under nonisothermal conditions, there is a considerable difference in performance between the two geometries because of temperature variations. The presence of heat effects in the nonisothermal case marginally improves the flow uniformity within the monolith. However, in the presence of heat effects, reactant conversion in the center of the monolith varies from the periphery and the single channel model slightly overestimates the conversion for both geometries.
A computational fluid dynamics model, consisting of a mixing chamber coupled with a catalytic converter, is developed for the selective catalytic reduction (SCR) of NO x using urea. The NH3 required for the SCR reactions is produced from the injection and decomposition of urea in the mixing chamber. The conversion efficiency and concentration distribution of NH3 from the mixing chamber are analyzed for a range of operating conditions. The flow and species distribution profiles from the mixing chamber are incorporated as inlet boundary conditions at the entrance of the downstream SCR convertor. The SCR convertor comprises a central catalytic monolith and inlet and outlet diffuser sections. Variations in NO x concentration were observed within the monolith due to heat losses and nonuniformities in ammonia concentrations. While heat effects under non-isothermal conditions slightly improved the NO x conversion efficiency, nonuniformities in ammonia concentrations did not significantly influence the SCR performance. Thus, the radial variations in NH3 concentrations, owing to nonuniformity at the outlet of the mixing chamber, did not considerably impact the overall performance of the SCR. The effects of temperature, NO:NO2 ratio, and inlet velocity were investigated.
Cell-free protein expression has become a widely used research tool in systems and syn- thetic biology and a promising technology for protein biomanufacturing. Cell-free protein synthesis relies on in-vitro transcription and translation processes to produce a protein of interest. However, transcription and translation depend upon the operation of com- plex metabolic pathways for precursor and energy regeneration. Toward understanding the role of metabolism in a cell-free system, we developed a dynamic constraint-based simulation of protein production in the myTXTL E. coli cell-free system with and without electron transport chain inhibitors. Time-resolved absolute metabolite measurements for M = 63 metabolites, along with absolute concentration measurements of the mRNA and protein abundance and measurements of enzyme activity, were integrated with kinetic and enzyme abundance information to simulate the time evolution of metabolic flux and protein production with and without inhibitors. The metabolic flux distribution estimated by the model, along with the experimental metabolite and enzyme activity data, suggested that the myTXTL cell-free system has an active central carbon metabolism with glutamate powering the TCA cycle. Further, the electron transport chain inhibitor studies suggested the presence of oxidative phosphorylation activity in the myTXTL cell-free system; the oxidative phosphorylation inhibitors provided biochemical evidence that myTXTL relied, at least partially, on oxidative phosphorylation to generate the energy required to sustain transcription and translation for a 16-hour batch reaction.
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