Variations in Temperature and Concentration

Differences in temperature and concentration can in principle lead to corrosion cell formation, but have little effect below the water line. On the other hand, they have to be taken into account in the interior corrosion of containers and tanks in relation to their service operation (see Section 2.2.4.2). Generally the action of corrosion cells can be reduced or eliminated by cathodic protection. 

In strong sunlight, water can evaporate at defects in coatings and surface films, and lead to concentration and crystallization of salts (e.g., in the upper decks of the ship). This can damage surface films, giving rise to local anodes. This is the case when a ship slowly rises in the water on unloading and is later reimmersed on loading. 

---

Alben, K.T., Shpirt, E., and Kaczmarczyk, J.H., Temperature dependence of trihalomethane adsorption on activated carbon implications for systems with seasonal variations in temperature and concentration, Environ. Sci. Technol., 22, 406-412, 1988. 

Since it takes only a very small fraction of the reaction time to reach the end of the induction period, at the moment of the sudden rapid rise in temperature (i.e., when explosion begins), not more than 1% of the initial mixture has reacted. This result justifies the inherent approximation developed that the reaction rate remains constant until explosion occurs. Also justified is the earlier assumption that the original mixture concentration remains the same from T0 to 7j. This observation is important in that it reveals that no significantly different results would be obtained if the more complex approach using both variations in temperature and concentration were used. 

In spite of variations in temperature and concentration, there was no evidence for the presence of the a-acetate II.At that time, we have no explanation for the formation of this nitronate ester although we may now have a possible rationalization which will be discussed later. 

The solid-state hexamers (2)—(4) at first appeared to dissolve intact in benzene (94). Cryoscopic rmm measurements over a range of concentrations (0.03-0.09 M, molarity expressed relative to the empirical formula mass) implied n values of 5.9-6.1. Furthermore, their room-temperature 7Li NMR spectra in c/8-toluene each consisted of broad singlets within the narrow chemical shift (6) range of + 0.6 to -0.2 ppm (relative to external phenyllithium in the same solvent). However, variations in temperature and concentration affected the 7Li NMR spectra of (2) and, in particular, of (4) (95). Figure 18a shows these spectra for three d8-toluene solutions of (4) at -100°C. The most concentrated solution has a dominant signal at 8 -+0.7, though five or six other signals (indicated by asterisks) are apparent. On dilution,... 

For the bulk polymerization of styrene using thermal initiation, the kinetic model of Hui and Hamielec (13) was used. The flow model (Harkness (1)) takes radial variations in temperature and concentration into account and the velocity profile was calculated at every axial point based on the radial viscosity at that point. The system equations were solved using the method of lines with a Gear routine for solving the resulting set of ordinary differential equations. 

A typical example of nonequilibrium spatially homogeneous systems is an isotropic system where a chemical reaction occurs. The apphcation of nonequibbrium thermodynamics for the consideration of chemically reactive systems has a few peculiarities. Indeed, heat and mass transfer pro cesses are characterized usually by continuous variations in temperature and concentration (see Section 1.5). On the other hand, the chemical transformations imply transitions between the discrete states that pertain to the individual reaction groups. 

This chapter negated radial variations in temperature and concentration. 

Partial differential equations describing a.tial and radial variations in temperature and concentration in chemical reactors are developed in... 

During the 1870 s, Carlo Marangoni, who was apparently aware of Carra-dori s work but not of Thompson s, formulated a rather complete theory of surface tension driven flow (M2, M3). He noted that flow could result from surface tension variations as they are caused by differences in temperature and superficial concentration, and that, conversely, variations in temperature and concentration could be induced by an imposed surface flow. Marangoni ascribed several new rheological properties to the surface (notably surface viscosity, surface elasticity, and even surface plasticity), while remarking that perhaps some of these properties could be associated only with surface contamination. Most present-day authors ascribe the first explanation of surface tension driven flow to Marangoni, and term such flow a Maragoni effect. ... 

Oscillatory States in the CSTR limit Cycles.— The nature of the diemically open system makes it an ideal vehicle for studying reactions which odiibit chemical oscillations. The continuous supply of reactants diminates damping from reactant depletion inevitable in closed systems and permits the experimental establishment of true limit-cycle behaviour. However, not all oscillations in the CSTR need be kinetically interesting in their origin (e.g. the periodic variations in temperature and concentrations in reactors run with feedback control More importantly from the combustion researcher s viewpoint, oscillations may arise between multiple stable steady states of any normal exothermic reaction because of restric-... 

As a rule of thumb, axial dispersion of heat and mass (factors 2 and 3) only influence the reactor behavior for strong variations in temperature and concentration over a length of a few particles. Thus, axial dispersion is negligible if the bed depth exceeds about ten particle diameters. Such a situation is unlikely to be encountered in industrial fixed bed reactors and mostly also in laboratory-scale systems. Radial mass transport effects (factor 1) are also usually negligible as the reactor behavior is rather insensitive to the value of the radial dispersion coefficient. Conversely, radial heat transport (factor 4) is really important for wall-cooled or heated reactors, as such reactors are sensitive to the radial heat transfer parameters. 

Local variations in temperature and crevices that permit the accumulation of corrosion products are capable of allowing the formation of concentration cells, with the result of accelerated local corrosion. 

The terpolymerizations described were carried out by a continuous feed method, unless stated otherwise, where both the monomer mixture and the initiator were added together continuously to the reaction kettle (18). The variables studied were (1) effects of initiators with different half-lives, (2) effects of variations in temperature, and (3) effects of variations in concentrations of initiators. Attempts were also made to study the extent of heterogeneity in the products. 

In principle one can also obtain data on refractive-index differences by measuring the indices of solutions, but this method suffers from a number of problems. Even for moderately concentrated solutions, the absolute index differences are small, and it is difficult to be certain that they are not masked by effects of small variations in temperature or concentration. 

---