Equilibrium fuel concentrations

Fig. 10-13. Equilibrium fuel concentrations and reactor dimensions for homogeneous systems operating at 280°C and producing 125 Mw electrical power.

Fig. 2 shows clearly that the quasi-equilibrium radical concentration sets the rate of fuel consumption and chemical heat release. It also shows the stability. Whatever the initial value of [r] it moves towards [R]e and remains there. It can only increase as [R]e increases with temperature. Thus, though the oxidation of methane is a branching chain reaction, fuel... 

Other observations of the reaction of hydrazine and nitrogen tetroxide substantiate the production of non-equilibrium combustion products. Non-equilibrium product concentrations were found in combustion gases extracted from a small rocket combustion chamber through a molecular beam sampling device with direct mass spec-trometric analysis (31) (39). Under oxidizer rich conditions excessive amounts of nitric oxide were found under fuel rich conditions excessive amounts of ammonia were found. A correlation between the experimentally observed characteristic velocity and nitric oxide concentration exists (40). Related kinetic effects are postulated to account for the two stage flame observed in the burning of hydrazine droplets in nitrogen dioxide atmospheres (41) (42). 

Isothermal chemistry in fuel cells. Barclay (2002) wrote a paper which is seminal to this book, and may be downloaded from the author s listed web site. The text and calculations of this paper are reiterated, and paraphrased, extensively in this introduction. Its equations are used in Appendix A. The paper, via an equilibrium diagram, draws attention to isothermal oxidation. The single equilibrium diagram brings out the fact that a fuel cell and an electrolyser which are the thermodynamic inverse of each other need, relative to existing devices, additional components (concentration cells and semi-permeable membranes), so as to operate at reversible equilibrium, and avoid irreversible diffusion as a gas transport mechanism. The equilibrium fuel cell then turns out to be much more efficient than a normal fuel cell. It has a greatly increased Nernst potential difference. In addition the basis of calculation of efficiency obviously cannot be the calorific value of the... 

In Appendix A, calculations show a status, for fuel cell isothermal Faradaic oxidation, of a high vacuum of reactants relative to a high concentration of product. That calculated status cannot even be approached in the laboratory, for lack of adequate semi-permeable membranes and circulators (concentration cells). The equilibrium fuel cell of Figure A.l is dead-ended, whereas the air-breathing open-ended design must have both of its electrodes swept by a parallel flow, with an inlet and an... 

A. 1.2 Steady Flow Equilibrium Fuel Cell Equilibrated via Concentration Cells with the Environment and both Internally and Externally Reversible... 

Additional physical phenomena influence rates of horizontal spread of flames over surfaces of liquid fuels [111]-[120]. If the equilibrium vapor pressure of the liquid fuel at its initial temperature is high enough for the fuel concentration in the gas mixture at the liquid surface to lie above the lower flammability limit, then premixed flame propagation occurs in the gas above the liquid, and flame spread is rapid. If the liquid is cold and... 

The equilibrium concentration in the coolant after a longer time of steady-state operation of the plant is controlled by the production rate and the penetration rate, on the one hand, and by the removal rate on the other. For this reason it can vary considerably from plant to plant. In PWR plants, the equilibrium activity concentration in the primary coolant usually is within the range of 10 to 30 GBq/ Mg, in BWR plants it is considerably lower (about two orders of magnitude). In a PWR, the most important source is the generation from the B dissolved in the coolant in addition, in the case of insufficient LiOH isotopic purity the Li reaction may become important. In BWR plants which contain neither boron nor lithium in the coolant (with the possible exception of inadvertently introduced impurities), neutron capture in deuterium is usually the main somce. Due to the low base level of activity in the BWR reactor water, the penetration from fuel and control rods gains a greater significance, the extent of which depends on plant-specific parameters. 

Typical of many organic pollutants, petroleum hydrocarbons are sorbed rapidly by aquatic invertebrates until a steady state or equilibrium in concentrations is achieved. The rate of uptake depends primarily on the exposure concentration, but temperature and other environmental factors may alter the metabolic rate of the animal and hence rate of uptake. Most petroleum hydrocarbons are lipophilic and thus the maximum level achieved during the steady-state phase depends on the body lipid content, as well as exposure concentration (Figure 7.7). Depuration from tissues is generally rapid but once again depends on temperature. Bums and Smith (1981), working in relatively warm Australian waters, found that 90% of hydrocarbons in the mussel Mytilus was eliminated within 3 weeks. By contrast, the same species required 14 weeks for 90% clearance of fuel oil under European winter conditions (Blackman and Law, 1980). 

Figures 18 to 20 show that the equilibrium cell voltage increases with the increase in fuel concentration. Although the cell performance increases initially but it does not increase proportionally with further increase in fuel concentration. This is because the increase in fuel concentration leads to the decrease in hydroxyl ion mobility. The hydrolysis reaction dominates with the increase in sodium borohydride concentration and thus the performance increases rather slowly. Further at higher concentration of NaBH4, viscosity of the fuel-electrolyte mixture increases leading to the rapid increase in concentration polarization at higher current densities and the performance decreases (Fig. 20). The maximum power density of 16.2 and 13.8 mW cm" were obtained for 3 M methanol and ethanol concentrations while 22.5 mW cm" for 2 M sodium borohydride. The fuel cell was operated at 25°C, 3 M KOH concentration and with 1 mg cm " of anode catalyst (Pt-black) loading catalyst and 3 mg cm" of cathode (Mn02) loading, respectively.

The development of models for HCSI combustion has been governed by the similarity of flame growth in HCSI engines and premixed turbulent flames. Thin laser-sheets of only 300 pm thickness were used to measure high-resolution cross sections of the temperature and OH radical distribution in flames of a propane-fueled engine. Figure 8.2.3 illustrates the structure where temperature and OH concentration are closely coupled with super equilibrium values for the OH radical close to the flame front [11]. 

In model equations, Uf denotes the linear velocity in the positive direction of z, z is the distance in flow direction with total length zr, C is concentration of fuel, s represents the void volume per unit volume of canister, and t is time. In addition to that, A, is the overall mass transfer coefficient, a, denotes the interfacial area for mass transfer ifom the fluid to the solid phase, ah denotes the interfacial area for heat transfer, p is density of each phase, Cp is heat capacity for a unit mass, hs is heat transfer coefficient, T is temperature, P is pressure, and AHi represents heat of adsorption. The subscript d refers bulk phase, s is solid phase of adsorbent, i is the component index. The superscript represents the equilibrium concentration. 

A typical simulation result is shown in Fig. 3. Under the given conditions, the concentration of fuel gas in bulk phase at the exit (Fig. 3a) is zero and the concentration of evaporative fuel gas at solid phase (Fig. 3b) at the exit did not reach the equilibrium concentration of activated carbon during adsorption. These results indicate that the canister of ORVR system is properly designed to adsorb the evaporative fuel gas. The temperature changes in canister (Fig. 3 c) during the operation remains in the acceptable range. The test results for different weather conditions showed that the canister design in this study can fulfill the required performance. 

The liquid temperature (Tl) corresponding to Xl is measured for practical purposes in two apparatuses known as either the closed or open cup flashpoint test, e.g. ASTM D56 and D1310. These are illustrated in Figure 6.3. The surface concentration (Xs) will be shown to be a unique function of temperature for a pure liquid fuel. This temperature is known as the saturation temperature, denoting the state of thermodynamic equilibrium... 

Up to now we have presented this example without any regard for consistency, i.e. satisfying thermodynamic and conservation principles. This fuel mass flux must exactly equal the mass flux evaporated, which must depend on q and h(g. Furthermore, the concentration at the surface where fuel vapor and liquid coexist must satisfy thermodynamic equilibrium of the saturated state. This latter fact is consistent with the overall approximation that local thermodynamic equilibrium applies during this evaporation process. 

Occupational exposures and the study with human volunteers indicate that exposures at low concentrations cause headaches and signs of central nervous system depression. No headaches were reported and no equilibrium disturbances were measured during occupational exposures of healthy workers to Otto Fuel II (measured as PGDN) at concentrations <0.22 ppm (average of approximately 0.06 ppm) for periods of 30-60 min, although subtle changes in eye movements were recorded (Horvath et al. 1981). In a study with healthy but previously unexposed male volunteers, the threshold for odor detection was 0.2 ppm (Stewart et al. 1974). Mild headaches were reported in one of three subjects after a 6-h exposure at 0.1 ppm, in two of three subjects after a 2-h exposure at 0.2 ppm, and in one of three subjects after a 1-h exposure at 0.5 ppm. Severe headaches occurred after an 8-h exposure at 0.2... 

The first reaction (Boudouard equilibrium) favors carbon formation at lower temperatures compared to POX. The hydrogen concentrations attained depend on the fuel used in POX but it never reaches the theoretical level [27],... 

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