Coupling of wrinkled laminar flames with gravity

The overall objective of our research is to understand flame-gravity coupling processes in laminar and low turbulent Reynolds number, Re(sub l), premixed flames (i.e. wrinkled- laminar flames). The approach we have developed is to compare the flowfields and mean flame properties under different gravitational orientations. Key to our study is the investigation of microgravity (mu g) flames. These mu g experiments provide vital information to reconcile the differences between flames in normal gravity (+g, flame pointing upward) and reverse gravity (-g, flame pointing downwards). Traditionally, gravity effects are assumed to be insignificant or circumvented in the laboratory, therefore, not much is available in the literature on the behavior of -g flames

Enhanced Evaporation of Microscale Droplets With an Infrared Laser

Enhancement of water droplet evaporation by added infrared radiation was modeled and studied experimentally in a vertical laminar flow channel. Experiments were conducted on droplets with nominal initial diameters of 50 lm in air with relative humidities ranging from 0% to 90% RH. A 2800 nm laser was used with radiant flux densities as high as 4 Â 10 5 W/m 2 . Droplet size as a function of time was measured by a shadowgraph technique. The model assumed quasi-steady behavior, a low Biot number liquid phase, and constant gas-vapor phase material properties, while the experimental results were required for model validation and calibration. For radiant flux densities less than 10 4 W/m 2 , droplet evaporation rates remained essentially constant over their full evaporation, but at rates up to 10% higher than for the no radiation case. At higher radiant flux density, the surface-area change with time became progressively more nonlinear, indicating that the radiation had diminished effects on evaporation as the size of the droplets decreased. The drying time for a 50 lm water droplet was an order of magnitude faster when comparing the 10 6 W/m 2 case to the no radiation case. The model was used to estimate the droplet temperature. Between 10 4 and 5 Â 10 5 W/m 2 , the droplet temperature changed from being below to above the environment temperature. Thus, the direction of conduction between the droplet and the environment also changed. The proposed model was able to predict the changing evaporation rates for droplets exposed to radiation for ambient conditions varying from dry air to 90% relative humidity

The Effects of Mixing, Reaction Rates, and Stoichiometry on Yield for Mixing Sensitive Reactions—Part I: Model Development

There are two classes of mixing sensitive reactions: competitive-consecutive and competitive-parallel. The yield of desired product from these coupled reactions depends on how fast the reactants are brought together. Recent experimental results have suggested that the mixing effect may depend strongly on the stoichiometry of the reactions. To investigate this, a 1D, dimensionless, reaction-diffusion model at the micromixing scale was developed. Assuming constant mass concentration and mass diffusivities, systems of PDE's were derived on a mass fraction basis for both types of reactions. Two dimensionless reaction rate ratios and a single general Damköhler number emerged from the analysis. The resulting dimensionless equations were used to investigate the effects of mixing, reaction rate ratio, and reaction stoichiometry. As expected, decreasing either the striation thickness or the dimensionless rate ratio maximizes yield, the reaction stoichiometry has a considerable effect on yield, and all three variables interact strongly

The Effects of Mixing, Reaction Rates, and Stoichiometry on Yield for Mixing Sensitive Reactions—Part II: Design Protocols

Competitive-consecutive and competitive-parallel reactions are both mixing sensitive reactions where the yield of desired product depends on how fast the reactants are brought together. Recent experimental results have suggested that the magnitude of the mixing effect may depend strongly on the stoichiometry of the reactions. To investigate this, a 1D, dimensionless, reaction-diffusion model was developed at the micromixing scale, yielding a single general Damköhler number. Dimensionless reaction rate ratios were derived for both reaction schemes. A detailed investigation of the effects of initial mixing condition (striation thickness), dimensionless reaction rate ratio, and reaction stoichiometry on the yield of desired product showed that the stoichiometry has a considerable effect on yield. All three variables were found to interact strongly. Model results for 12 stoichiometries are used to determine the mixing scale and relative rate ratio needed to achieve a specified yield for each reaction scheme. The results show that all three variables need to be considered when specifying reactors for mixing sensitive reactions

Fabrication of Binary Opal Lattices in Microfluidic Devices

We have studied growth and fabrication of opal lattices made from polystyrene and silica particles by an on-chip colloidal self-assembly (CSA) approach. An optical microscopy method was used to analyze the lattice growth behavior. A mathematical model was also adopted and modified to describe the growth behavior of the silica system. On the basis of these studies, silica and polystyrene systems demonstrate different growth dynamics that originate from a sedimentation process in the microfluidic chip reservoir fractionating large and small particles. Binary lattices of silica particles were fabricated by a periodic chip rotation method. The effect of particle number ratio on the opal stoichiometry was also studied for the polystyrene system. By increasing the number ratio from 2.5 to 11, different structural stoichiometries were achieved

Assessment of potential effects of injected salt water and hydrochloric aerosols on efficiency of lab-scale flares

The composition and behavior emissions of a single fuel comprised of 88.18% CH4, 8.08% propane, and 3.74% butane flowing at 109. 45 standard L/min. The effect of two aqueous NaCl mixtures and HCl on combustion products of a vertical diffusion flame was considered. The addition of distilled water on aerosols as a co-flow into fuel stream significantly decreased soot production and less remarkably decreasing NOx emissions. Aerosolized NaCl solutions of 5.0 wt% and 9.1 wt% demonstrated a significant and somewhat unexpected effect on CO yields. At ≈ 20 wt% liquid loading, the CO and CH4 yields peaked and the peak emissions rate increased with solution strength. HCl loading had no significant alterations from distilled water in terms of gaseous and solid phase combustion emissions. This is an abstract of a paper presented at the 108th AWMA Annual Conference and Exhibition (Raleigh, NC 6/22-25/2015)