Transient effects

The foregoing is an equilibrium analysis, yet some transient effects are probably important to film resilience. Rayleigh [182] noted that surface freshly formed by some insult to the film would have a greater than equilibrium surface tension (note Fig. 11-15). A recent analysis [222] of the effect of surface elasticity on foam stability relates the nonequilibrium surfactant surface coverage to the foam retention time or time for a bubble to pass through a wet foam. The adsorption process is important in a new means of obtaining a foam by supplying vapor phase surfactants [223]. 

Fypass Flow Effects. There are several bypass flows, particularly on the sheUside of a heat exchanger, and these include a bypass flow between the tube bundle and the shell, bypass flow between the baffle plate and the shell, and bypass flow between the shell and the bundle outer shroud. Some high temperature nuclear heat exchangers have shrouds inside the shell to protect the shell from thermal transient effects. The effect of bypass flow is the degradation of the exchanger thermal performance. Therefore additional heat-transfer surface area must be provided to compensate for this performance degradation. 

Transient effects are those where there is repair of toxic physical injury or the reversal of induced biochemical aberrations. 

Note For motors beyond 200 h.p., NEMA has not covered these data. It is, however, recommended that larger motors may be designed to have even lower locked rotor currents than the above to reduce the starling transient effects on the distribution system as well as on the motor windings. ... 

Design considerations should be examined by process design engineers when designing heat exchangers for stage 1 tube rupture transient effects, which includes the following ... 

The simplest, and by far the most common, detection scheme is the measurement of the current at a constant potential. Such fixed-potential amperometric measurements have the advantage of being free of double-layer charging and surface-transient effects. As a result, extremely low detection limits—on the order of 1-100 pg (about 10 14 moles of analyte)—can be achieved, hi various situations, however, it may be desirable to change the potential during the detection (scan, pulse, etc.). 

Figure 4.17. NO reduction by H2 on Pt/p"-AI203.52 Transient effect of applied constant negative current (Na supply to the catalyst) on catalyst potential (a) under reaction conditions (solid line) and in a He atmosphere (dashed line) and on the rates of formation of N2 and N20 (b). Potentiostatic restoration of the initial rates see text for discussion. Reprinted with permission from Academic Press.

Figure 4.49. Transient effect of constant applied current (I=+10 pA) on the rate (r) of C2H4 oxidation on Ir02/YSZ, on catalyst work function (AO) and on catalyst potential (Uwr)-Conditions T=380°C, pc>2 = f 5 kPa and PC2H4 =0.05 kPa.88 Reprinted with permission of The Electrochemical Society.

Figure 4.50. Transient effect of constant applied current (I=+300 pA) on the rate of C2H4 oxidation on Ir02 and on 75mol% Ir02 - 25%Ti02 and 25% Ir02 - 75%Ti02 composite catalysts deposited on YSZ. Note the decrease in p upon increasing the Ti02 content and the appearance of permanent NEMCA in all cases.124...

Figure 4.51. Transient effect of a constant applied current on the rates of C02, N2 and N20 production, on NO conversion (XN0) and on catalyst potential (Uwr) during NO reduction by propene in presence of gaseous 02 on Rh/YSZ.70 Reprinted with permission from Elsevier Science.

Figure 5.2. NEMCA and its origin on Pt/YSZ catalyst electrodes. Transient effect of the application of a constant current (a, b) or constant potential UWR (c) on (a) the rate, r, of C2H4 oxidation on Pt/YSZ (also showing the corresponding UWR transient)3 (b) the 02 TPD spectrum on Pt/YSZ4,7 after current (1=15 pA) application for various times t. (c) the cyclic voltammogram of Pt/YSZ4,7 after holding the potential at UWR = 0.8 V for various times t.

Figure 5.37. Transient effect of constant current application and interruption on the Pt/YSZ catalyst potential UWr and on the XPS signal at Eb = 528.8 eV (location of 8-0 Is peak) and at Eb = 181.7 eV (electrochemically shifted position of the Zr 3d5/2 peak).6 Reprinted with permission from the American Chemical Society.

Figure 8.27. Transient effect of current on the rate of CO oxidation on Pt (solid lines) and on catalyst potential (broken lines) inlet compositions and temperatures (a) pco=0.47 kPa, po2-10 kPa, T=412°C (b) pco=2.9 kPa, po2=0.40 kPa, T=555°C.33 Reprinted with permission from Academic Press.

Figure 8.39. Transient effect of electrochemical O2 pumping to (a) and from (b) a Ag catalyst film on selectivity and yield to ethylene oxide.42 Current applied at t=0 Pc2H4=1-5 kPa, p02= 10 kPa T=400°C. Reprinted with permission from Academic Press.

Figure 8.58. Transient effect of applied negative current on the rate of CH3CHO formation during CO hydrogenation on Pt.5,59 Acetaldehyde does not form under open-circuit conditions, thus p is nominally infinite P=12.5 bar, T=350°C. pH2/pco=l-8, flowrate 85 cm3 STP/min.5,59...

Figure 8.60. Transient effect of applied negative current on the rates of N2, C02, CO and N20 production on Pt/YSZ (solid curves) and on catalyst potential (dashed curve). Open circuit rates rN2=2.93xlO 9 mol C2H4/s, rco2=3.08x]0 9 mol C2H4/s, rco-0.77xl0 9 mol QH4/S, rN2o==0.92xlO 9 mol C2H4/s.64 Reprinted with permission from the Institute for Ionics.

Figure 8.68. Transient effect of applied positive current on the rate and turnover frequency of C2H4 oxidation on Pt/Ti02 (solid curve) and on catalyst potential (dashed curve) at high oxygen to ethylene ratios.24 Reprinted with permission from Academic Press.

Figure 9.10. Ethylene epoxidation on Ag/p"-Al203 Transient effect of a negative applied current (Na supply to the catalyst) on the rates of ethylene oxide and C02 formation and on catalyst potential (work function) and Na coverage22 T=260°C, P=5 atm, p02=17,5 kPa, Pc2H4=49 kPa, 0.6 ppm C2H4CI2. Reprinted with permission from Academic Press.

Figure 9.25. Transient effect of applied positive current (1=5 mA) on the rate of consumption of hydrogen (rH2) and oxygen (r0) gas molar flow rate fm=13x 0"s mol/s.35 Reproduced by permission of The Electrochemical Society, Inc.

Figure 12.4. Transient effect of an applied negative current (I=-20mA) on the reaction rate r of CyT, oxidation on Pt finely dispersed on Au supported on YSZ (solid curve) and on the catalyst potential Uwr (dashed curve). Conditions catalyst C2, T=42l°C, po2=14.8 kPa, pc2H4=0.l kPa, fiow=411 ml/min, open circuit rate ro=0.037xl0 6 mol/s.7 Reprinted with permission from Academic Press.

Figure 12.7. Transient effect of an applied current on the rate of ethylene oxidation (expressed in mol O/s) for three different electrode configurations of Fig. 12.6 config. 1, I=+20 pA (solid curve) config. 5, I=-20 pA (dotted curve) and configs. 6, I=+20 and -20 pA (dashed curves). Conditions T=353°C, Pc2h4=065 kPa, p02=17.5 kPa, flowrate=200 ml/min.8 Reprinted with permission from Academic Press.

Figure 12,9, Transient effect of an applied potential, UAP, between the two terminal gold electrodes (30 V) on the catalytic rate of ethylene oxidation (expressed in molO/s) for a multi-dotted platinum configuration.10 Reprinted with permission from Elsevier Science.

Design of vessel and vent line pipe supports is very important because very large forces can be encountered as soon as venting begins. Figure 4 shows the equations and nomenclature to calculate forces on pipe bends. The authors have heard of situations where vent line bends have been straightened, lines broken off, or vent catch tanks knocked off their foundations by excessive forces. For bends, the transient effects of the initial shock wave, the transition from vapor flow to two-phase flow, and steady state conditions should be considered. Transient conditions, however, are likely to be so rapid as to not have enough dura-... 

Nuclear bomb produced " 002 and (as HTO) have been used to describe and model this rapid thermocline ventilation (Ostlund et ah, 1974 Sarmiento et ah, 1982 Fine et al., 1983). For example, changes in the distributions of tritium (Rooth and Ostlund, 1972) in the western Atlantic between 1972 (GEOSECS) and 1981 (TTO) are shown in Fig. 10-10 (Ostlund and Fine, 1979 Baes and Mulholland, 1985). In the 10 years following the atmospheric bomb tests of the early 1960s, a massive penetration of F1 (tritium) into the thermocline has occurred at all depths. Comparison of the GEOSECS and TTO data, which have a 9 year time difference, clearly shows the rapid ventilation of the North Atlantic and the value of such transient" tracers. A similar transient effect can be seen in the penetrative distribution of manmade chlorofluorocarbons, which have been released over a longer period (40 years) (Gammon et al., 1982). 

If < fcpg, the time course of Cp is dominated by the slower rate of absorption. This is desirable when a drug is to be delivered over a prolonged period of time, for example in the relief of chronic pain. When a sufficiently large period of time has elapsed, the transient effect of elimination has decayed and the solution for the plasma compartment in eq. (39.16) becomes approximately ... 

Both naturally aging253 and electrically301 or thermally302 stressed anodic oxides exhibit characteristic nonstationary behavior. One can distinguish the following transient effects ... 

Transient effects in naturally aging samples occur with some delay and are very slow. Nazar and Ahmad274 have observed a slow decrease of A1-A1203-A1 capacitance that was attributed to neutralization of Al3+ cations in the vicinity of the internal boundary and a corresponding increase of the effective oxide thickness. However, the same effect may be due to neutralization of negatively... 

Bowyer, J.F., Tank, A.W., Newport, G.D. et al. The influence of environmental temperature on the transient effects of methamphetamine on dopamine levels and dopamine release in rat striatum. J. Pharmacol. Exp. Ther. 260 817, 1992. 

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