H2O, oxidation

The elemental reaction used to describe a redox reaction is the half reaction, usually written as a reduction, as in the following case for the reduction of oxygen atoms in O2 (oxidation state 0) to H2O (oxidation state —2). The half-cell potential, E°, is given in volts after the reaction ... 

The synthesis of other biologically active thiazoles was described by Ohsumi et al. [50] and is shown in Scheme 16. Condensation of phosphonium bromide and 4-methoxy-3-nitrobenzaldehyde gave a 1 1 mixture of (Z)- and (-E)-stilbenes. ( )-stilbene 64 was purified by crystallization and then converted to bromohydrin 65 by NBS-H2O. Oxidation of the bromohydrin by DMSO-TFAA gave the bromoketone intermediate 66, which was condensed with thiocarbamoyl compounds in the presence of Na2C03 in DMF to give the corresponding 2-substituted thiazole derivatives (67a and b). Compound 67a... 

Results of an experimental program in which aluminum particles were burned with steam and mixtures of oxygen and argon in small-scale atmospheric dump combustor are presented. Measurements of combustion temperature, radiation intensity in the wavelength interval from 400 to 800 nm, and combustion products particle size distribution and composition were made. A combustion temperature of about 2900 K was measured for combustion of aluminum particles with a mixture of 20%(wt.) O2 and 80%(wt.) Ar, while a combustion temperature of about 2500 K was measured for combustion of aluminum particles with steam. Combustion efficiency for aluminum particles with a mean size of 17 yum burned in steam with O/F) / 0/F)st 1-10 and with residence time after ignition estimated at 22 ms was about 95%. A Monte Carlo numerical method was used to estimate the radiant heat loss rates from the combustion products, based on the measured radiation intensities and combustion temperatures. A peak heat loss rate of 9.5 W/cm was calculated for the 02/Ar oxidizer case, while a peak heat loss rate of 4.8 W/cm was calculated for the H2O oxidizer case. 

Argon and oxygen for 02/Ar oxidizer tests were supplied from high-pressure gas bottles. Steam for H2O oxidizer tests was supplied by a 150 psig electric steam boiler and was superheated to 600 °F using electric heaters. To start a H2O oxidizer test run, the steam flow was first set to the required rate for the test condition. An amount of oxygen sufficient to complete combustion of the aluminum was then mixed with the steam, and a flow of propane into the combustor was initiated. 

Figure 8.3 Typical measured hemispherical emissive power distribution for the H2O oxidizer test. 1 — Port 7 Data, 2 — Fit T = 2609 K, EM = 0.42...

Figure 8.5 Measured temperature and radiation intensity distributions for the H2O oxidizer test in 48-inch long combustor. 1 — temperature, 2 — power, 400-800 nm...

Figure 8.6 Particle size distribution for combustion products collected during H2O oxidizer test... 

The size distribution for the large diameter fraction of the H2O oxidizer combustion products is shown in Fig. 8.8, along with the size distribution of the aluminum powder fuel. The mean particle size of the unburned fuel fraction in the combustion products is about 10.7 pm, while the mean size of the fuel particles is 17.4 pm. Most sources report that burning aluminum particles follow a rate law of the form d = do" — Pt, where / is a constant and the exponent n is between 1.5 and 2.0. In that case, the size distribution of the unburned fraction of the combustion products would be expected to be larger than that of the fuel. A size distribution of unburned aluminum smaller than that of the parent fuel is more consistent with particles that never ignited, since the larger particles would probably be undersampled. On the other hand, it seems unlikely that any particle could... 

Figure 8.8 Particle size distribution of fuel and unburned fraction in products from H2O oxidizer test 1 — fuel, 2 — products...

It was found that when using an 02/Ar oxidizer stable combustion could be maintained with cold combustor walls, while a warmup period of approximately two minutes assisted with O2 was required when using the H2O oxidizer before H2 0-only operation was possible. Apparently, with the lower heat release using the H2O oxidizer, the recirculated combustion products do not stay hot enough to ignite the incoming fuel when the combustor walls are cold. 

Measurements of combustion temperatures, radiation intensity distributions in the range from 400 to 800 nm, and particle size distributions of combustion products have been made for the reaction of aluminum powder with both 02/Ar and H2O oxidizers in atmospheric dump combustors. The fraction of unburned aluminum in the combustion products was also determined for the H2O oxidizer case. An analytical study was performed to determine if the measurements are consistent with each other and with theory, and also to estimate the rate of heat loss from the combustion products. A Monte Carlo technique was used to determine the expected spectral energy distribution that would be emitted from a viewport located in the side of a combustion chamber containing products of aluminum combustion. 

For the H2O oxidizer case, the average radiant heat loss rate for the entire combustor volume is estimated at about 1.9 W/cm, corresponding to a total radiant heat loss of about 19 kW, or 420 cal/g of combustion products. A heat loss of 420 cal/g, together with an estimated combustion products temperature of 2575 K, implies that the reactedness of the mixture is on the order of 85% to 95%, depending on whether we assume that the unburned aluminum never ignited or that the unburned aluminum is at the same temperature as the rest of the mixture. 

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