Hot spots causes

Owing to the exothermic nature of hydrogenations, the avoidance of hot spots causing reductions in selectivity and catalytic activity is a second driver [11]. 

When a tube that has failed because of a hot spot caused by a coke deposit inside is cut in half, we would observe a pattern similar to that shown in Fig. 21.3. 

The various types of compound and their mechanisms of action have been reviewed by Mitchell . He concluded that the question of the extent to which the molybdenum additives decompose to produce molybdenum disulphide, if at all, was not yet resolved and certainly depended on the type of compound and the operating conditions. There was little doubt that molybdenum dithiocarbamates form molybdenum disulphide, probably by decomposition at hot spots caused by asperity interactions. It was less certain that molybdenum dithiophosphates form molybdenum disulphide, although mixtures of zinc dialkyidithiophosphate and molybdenum complexes had been shown to do so . 

Inspect the fryer pan and look for spots with discoloration. These indicate hot spots caused by localized heat. The pan and the heating element should be replaced if hot spots are noticed. 

Aside from process intensification, the enhanced transport rates may render a microscale system gradientless. This fact has important ramifications for operation and fundamental studies. Examples include elimination of detrimental hot spots caused by very exothermic reactions and the possibility of a microchemical system being isothermal and kinetically controlled. The latter makes microchemica] systems ideal for extraction of intrinsic chemical kinetics. 

Sharma, J., Forbes, J.W., Coffey, C.S., and Liddiard, T.P. (1987) The Physical and Chemical Nature of Sensitization Centers Left from Hot Spots Caused in Triaminotrinitrobenzene by Shock or Impact Journal of Physical Chemistry 91, 5139-5144. 

Direct resistance heating in which an electric current is passed directly through a section of the molten-salt piping has also been used successfully. Operating temperatures of this type of heater are limited only by the corrosion and strength limitations of the metal as the temperature is increased. Experience has indicated that heating of pipe bends by this method is usually not uniform and (jan be accompanied by hot spots caused by nonuniformity of liquid flow in the bend. 

Heat Transport Since a vast majority of the heat generated by fuel cell operation must be removed by the fuel cell and not through the exhaust gas, the landing-DM interface area carries much of the heat into the coolant Local hot spots caused by poor design can cause dryout and lead to premature membrane failure. The coolant and reactant flow channels should be designed in tandem to minimize flooding and hot spots. 

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