Effect of gas evolution

Effect of Gas Evolution on Current Distribution and Ohmic Resistance in Electrolyzers . 

The forces associated with slug flow of cryogenic fluids are considerably less than those calculated because of the effect of gas evolution. The compressible gas present in the flow stream absorbs energy and cushions the hammer at an elbow. Also, the elasticity of the pipe will reduce the effective velocity of a sonic pressure wave by about l io and consequently reduce the head rise at an elbow. The use of long-sweep elbows also reduces impact pressures by increasing the impact area. 

Nishiki, Y., Aoki, K., Tokuda, K., and Matsuda, H., 1986, Effect of gas evolution on current distribution and ohmic resistance in a vertical cell under forced convection conditions, J. Appl. Electrochem., 16 615-625. 

Effect of gas pressure on adsorption and surface permeation processes. In order to understand the nature of this gas evolution following a previous charge of the furnace tube with gases, it is necessary to study the extent of adsorption and permeation of the gases into the tube material as a function of the pressure with the intermediate chamber evacuated. The extent of these processes is measured by apparent leak rate measurement 10 minutes after evacuation of the gas. 

Ariga et al. [48] have investigated the behavior of the monolith reactor in which Echerichia coli with P-galactosidase or Saccharomyces cerevisiae was immobilized within a thin film of K-carragcenan gel deposited on the channel wall. The effects of mass transfer resistance and axial dispersion on the conversion were studied. Those authors found that the monolith reactor behaved like the plug-flow reactor. The residence-time distribution in this reactor was comparable to four ideally mixed tanks in series. The influence of gas evolution on liquid film resistance in the monolith reactor was also investigated. It was shown that at low superficial gas velocities, the gas bubble may adhere to the wall, which decreases the effective surface area available for the reaction. The authors concluded that the reactor was very effective in the reaction systems accompanied by gas evolution, such as fermentations. 

Many effects of gas bubbles released at electrodes (on electrolyte flow, mass and heat transport, conduction, etc.) have been well studied in the past. A text with an extensive treatment of this topic is that of Hine [38]. However, in Hall-Heroult cells these effects are worthy of special mention because the relatively high current density, of the order of 1 A cm-2, and temperature make the volumetric gas evolution rate from the anode large. Furthermore, difficulties of measurement on actual cells mean less knowledge of these effects than in many other electrochemical cells. Finally, one effect of the bubble is to make the task difficult in reducing the enormous... 

In order to characterize the effect of gas exposure on polyynes and polycumulenes, we have monitored the evolution of in films exposed to the different gases at the pressure of SOOmbar. Figure 2.8 shows the... 

Emmerich and Bayreuther (75) found that in their simultaneous TG-EGD apparatus, the EGD peak area was proportional to the sample mass for the evolution of EUO.CO. and COz from the thermal decomposition of CaC204-UNO. This proportionality is shown by the curves in Figure 8.24, which have a linearity of wiihin — 2%. They also studied the effect of gas flow quantity and peak height, half-width, and peak area using calibrated amounts of air injected into the carrier gas stream. The peak area and half-width decreased, whereas the peak height increased with an increase in gas flow. Thus, better... 

The model couples the effects of stress and flow and accounts for varying permeability and compressibility of the pore fluid and nonlinear stress-strain behavior of the reservoir rock. The major factor responsible for fluid production is the compressibility attained by the pore fluid as a result of gas evolution. Transient flow rate is a function of the reservoir... 

Solids production from these heavy oil reservoirs was first discussed in some detail by Smith (97). Smith developed an analytical model to predict production, decline, recovery, pressure, and pressure-transient behavior, together with the large solids volume production and its effect on oil rate and well productivity. Smith s model incorporated time-de-pendent properties of the oil as a result of gas evolution and treated the unconsolidated reservoir sand as a soil in which cohesion relies only on the tension of the wetting phase. This is a similar, though simpler, approach than Vaziri s (54) finite element method. Smith developed a Darcy law formulation for compressible fluid flow... 

The idea that excitons are involved in photodecomposition of azides was previously suggested based on the effect of temperature and intensity on rates of emission of N2 gas [80]. However, information deduced about the mechanism of decomposition of the azide ion from studies of kinetics of gas evolution is... 

Studies have also been made of the effect of photodecomposition on subsequent heat treatment of Pb(N3)2. The rate of gas evolution is altered by prior irradiation, and the results are interpreted, at least for the initial stages of decomposition, in terms of the same type of disorder production by both types of stimuli [170]. The reader is referred to Chapter 6 for additional discussion. In contrast, the kinetics of thermal decomposition of AgNa are reported to be unchanged by prior UV exposure [98]. 

An exact calculation of the amount of decomposition and its distribution within the sample must take into account the inhomogeneous absorption of the light the transport, if any, of free charges or excitons the diffusion of nitrogen and the effects on the decomposition reaction of radiation-induced defects. These complications have only recently been taken into consideration, but are clearly important in interpreting rate of gas evolution vs. time curves. 

Electrolytic gas evolution can be discussed on two scales of length. The macroscopic or process scale is important to the overall design of equipment and includes modeling the overall distribution of gas in the reactor and the effects of gas bubbles on the gross electrolyte flow pattern. The microscopic scale is where the details of bubble events and their consequences are found. In this review, I concentrate on the latter, microscopic scale. 

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