Reactant supply pressure

Aside from the original assumption of a lumped analysis, thus far there have been no other assumptions or approximations to the model. The model relies completely on basic thermodynamic principles, a known cell performance R(I), and rigorous mathematical operations. To solve the model, we need to know the bulk mass and heat capacity of the cell, M and C, respectively the reactant supply flow rate (m = fuel flow + air flow) the inlet temperature and pressure and the change in stream composition due to the electrochemical reaction, AX, so that the change in enthalpy can be calculated the electrical load current, / and the inlet and exit temperatures, Tm and rout. 

Batch reactors can also be used for studies of gas-liquid reactions. A common procedure, sometimes called "semibatch," is to conduct the reaction as batch with respect to the liquid and bubble the gas through at constant composition and pressure. Effective gas-liquid contacting is essential in order to avoid mass-transfer limitation with respect to the reactant supplied by the gas phase. Good ways of introducing the gas are through a fine-pore sieve plate or through the hollow shaft and arms of a stirrer. 

Maintaining the continued efficiency of all three reactions in a three-way catalytic converter is a delicate matter. It requires control of such factors as the O2 supply pressure and the order in which the reactants reach the catalyst Modern automobile engines use microcomputer chips, based on an O2 sensor in the exhaust stream, to control air valves. 

A representative scheme of a low pressure FCS plant for automotive application is shown in Fig. 4.9. The reactant supply sub-systems could directly interact with thermal and water management sub-systems, by means of a simultaneous transfer of heat and mass into the humidifier devices, which should be inserted at the entrance of the stack for both reactants. Thermal sub-system includes an internal coolant circuit that is essentially constituted by a liquid pump, a radiator necessary to reject the stack waste heat, and a liquid reservoir. Other minor but equally important components are the de-ionizer filters, thermostat, and valves. 

Both rigs use existing Cranfield facilities for reactant supply and metering, rig pressure control, and gas analysis. The gas fuel and combustion air are fed from bottled storage through PC-controlled mass-flow controllers. 

A rather dangerous situation arises when individual fuel cells of a multicell fuel-cell stack deviate. Such nonuniformity is most often because of problems in reactant supply. Two systems of gas supply exist parallel and series. In parallel supply, the gas reaches each fuel cell through a narrow channel coming from a common manifold. The pressure in these channels is the same for all elements where they leave the manifold, but on account of differences in gas flow resistance, the amounts of gas (or the pressure) reaching each fuel cell may differ. In series supply, gas is fed to a first individual cell, flows through it, and continues to the next cell, and so on. In each fuel cell in series the amount of gas needed for the... 

Reactant supply and water removal is optimized by so called interdigitated flow fields where gas flow is forced across the ribs separating the flow field channels through the macroporous part of the gas diffusion electrodes at the expense of high pressure drop between reactant inlet and outlet. 

MPa is nearly absent, which is true also for the pMe powders [81]. Thus, gaseous reactant supply to the combustion wave at low pressures and, consequently, the temperature of the process are determined by the porosity of the CCP. 

A further problem in DMFC operation is due to the evolution of gaseous CO2 at the anode (Ye et al 2005b). Then gas bubbles that can locally interfere with the flow of the aqueous methanol solntion may form in the flow field on the anodic side of the bipolar plates. This leads to a nonuniform distribntion of the reaction (and thus current) across the MEA snrface. This effect is particularly noticeable when the solution is snpplied passively (e.g., by free flow from a tank above). To overcome it, one shonld nse an active reactant supply at flow rates several times in excess of the stoichiometric requirements (Cowart, 2005). This raises the question of how to dimension the means of pumping the solution through (and what energy they wonld consnme). The dimensions would depend on the pressure drop within the flow field channels between solution input and outlet (Yang et al., 2005). 

In which 100 cc could be polymerized. We used a pressure gage, rated from 0 to 140 pounds per square Inch. There were 3 type J thermocouples - one In the center of the solution, one In the reactor wall, and the third near the heater outside the reactor. The experiments were conducted In a high pressure bay and observed on closed circuit television. The Initial polymer concentrations of the test reactants were either 0 or 15 or 30 percent by weight. An electric heater controlled the ambient temperature of the nitrogen - purged reactor, and supplied heat to Initiate the reaction. 

Heat is applied to the reactor to further concentrate the reactants and to supply the energy to activate the polymerization reactions. At the outset, the reactor temperature and pressure rise rapidly. Sensor measurements indicate the existence of a temperature gradient having as much as a 40°C difference between material at the top and at the bottom of the reactor. Shortly after the pressure reaches its setpoint, the entire mixture boils and the temperature gradient disappears. The solution is postulated to be well mixed at this time. The cumulative amount of water removed is one indication of the extent of polymerization. 

As shown in Figure 1-1, the fuel cell combines hydrogen produced from the fuel and oxygen from the air to produce dc power, water, and heat. In cases where CO and CH4 are reacted in the cell to produce hydrogen, CO2 is also a product. These reactions must be carried out at a suitable temperature and pressure for fuel cell operation. A system must be built around the fuel cells to supply air and clean fuel, convert the power to a more usable form such as grid quality ac power, and remove the depleted reactants and heat that are produced by the reactions in the cells. 

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