Overheating, elimination

Eliminate tramp metal and broken parts that may cause localized overheating... 

A further example is the effect of tube failure resulting from longterm overheating. Here it is likely that the principle contributing causes are a combination of deposit formation and stresses resulting from mechanical operation of the boiler in excess of design limits. To minimize or eliminate the risks of deposits and the subsequent effects they produce within the boiler, control again requires a twofold approach ... 

Control of long-term overheating requires modifying water chemistry and a close analytical monitoring protocol to minimize or eliminate the risks of deposits. In many cases, some significant change in boiler operating practices is also required. 

In the Diels-Alder condensation of the 2 neat endothermic dienes to give 5-ethylidene- and 5-methyl-6-methylene-bicyclo[2.2.1]hept-2-ene, there is a serious risk of explosive decomposition arising from local overheating of the reactor walls. This hazard is eliminated by the presence of various hydrocarbons and their mixtures as diluents. 

The human body can tolerate only a small range of temperature, especially when the person is engaged in vigorous activity. Heat reactions usually occur when large amounts of water and/or salt are lost through excessive sweating following strenuous exercise. When the body becomes overheated and cannot eliminate this excess heat, heat exhaustion and heat stroke are possible. 

In the 40 years since Olah s original publications, an impressive body of work has appeared studying carbocations under what are frequently termed stable ion conditions. Problems such as local overheating and polymerization that were encountered in some of the initial studies were eliminated by improvements introduced by Ahlberg and Ek and Saunders et al. In addition to the solution-phase studies in superacids, Myhre and Yannoni have been able to obtain NMR spectra of carbocations at very low temperatures (down to 5 K) in solid-state matrices of antimony pentafluoride. Sunko et al. employed a similar matrix deposition technique to obtain low-temperature IR spectra. It is probably fair to say that nowadays most common carbocations that one could imagine have been studied. The structures shown below are a hmited set of examples. Included are aromatically stabilized cations, vinyl cations, acylium ions, halonium ions, and dications. There is even a recent report of the very unstable phenyl cation (CellJ)... 

All the mentioned above examples prove that for the investigated reactions the influence of microwave irradiation was limited to pure thermal effects (i.e., higher pressure and/or bulk temperature of the reaction mixture, development of temperature gradient, overheating of solvents) that can be responsible for seemingly higher reaction rates under microwave conditions. However, a careful consideration of all the factors that influence the reactions under microwave conditions can eliminate most of these effects, there are several of reactions in which the influence of only thermal effects do not suffciently explain the enhancement of yield and rate of the reactions. 

In radical polymerization, particularly in the large-scale production of poly(methyl methacrylate), the monomer may boil hence the process should be carried out with continuous removal of reaction heat to eliminate overheating in the reactive volume. In this case, the choice of cooling method needs careful consideration.1 2... 

The small mismatch between required and achieved minimum operation temperature has the severe consequence that a special preabsorption stage has to be included in the reactor set-up in order to achieve the essential complete conversion. In this manner the partial pressure of the SO3 product is lowered before the last stage of conversion, rendering acceptable incomplete conversion of the overheated catalyst. If the reason why the catalyst docs not operate efficiently down to its solidification point could be eliminated one may circumvent the intermediate absorption stage and thus facilitate the reactor design considerably. 

An example of this type of trouble-shooting application was the addition of a molybdenum disulphide dispersion to the lubricating oil in a 400 ton metalforming press, which was reported to have eliminated overheating, increased unit production rate and reduced downtime. 

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