Local heat generation

Other gradient forces as in local heating generated by the exothermic hydrogen peroxide reaction were determined to be negligible because their contribution to velocity was less than a micron/second. Therefore, the interfacial force due to a concentration gradient appears to be the most reasonable dominant driving force for the Pt/Au nanorods. 

Equation 76 is valid for local heat generation and analysis. However, there are some models that treat only heat transfer in the gas channels and assume that the fuel-cell sandwich remains isothermal,I5i6,i07,i29 assumption that is arguably valid... 

The second test, developed by the Society of the Plastics Industry, involved preparing an amount of bacon that covered at least 50% of the dinner plate surface area [2], The plate with the bacon layer was heated in a microwave oven set at full power until the temperature at the center of the plate area reached 121°C ( 5°C). The time period required to reach this temperature within the bacon fat was 5 min on the microwave unit used for this test Immediately after the cooking cycle, the plate was cleaned on the lower rack of an automatic dishwasher. The dishwasher cycle was set at normal and included a heated dry cycle. The water temperature reached 66°C ( 5°C). Once the cycle was complete, the plate was inspected for surface blemishes such as cracks or blisters. This test is considered the most severe of the three due to the extreme localized heat generated, which causes the difference between the thermal coefficient of expansion for the two materials to shear the interface resulting in delamination. 

In the previous discussion of the one-dimensional nonisothermal simulation results it has been shown that for certain operating conditions the ethane conversion can be increased considerably in a PBMR compared to conventional fixed-bed reactors. The price, which had to be paid, was the higher local heat generation and insufficient heat removal. The problem is more pronounced in the large-scale apparatus. For illustration, the temperature profile in the PBMR calculated with the extended version of the a -model is depicted in Fig. 5.22. Accounting for the thermal resistance of the shell side and of the membrane, a temperature maximum of more than 20 K above the inlet and outer reactor wall temperature is predicted. For the sake of completeness it has to be noted that the thermal resistance of the shell side was calculated for an annulus filled with inert particles. This constructional modification is, compared to a reactor with an empty annulus, necessary, otherwise the reaction is becoming uncontrollable. Because of... 

The analysis of turbulent motion physics for a reaction mtjcture in tubular channels of various designs can open the way to a quantitative and scientifically grounded approach for the selection of the optimal geometry, for any fast chemical process, to reduce the diffusion limitation and create uniform conditions for making synthetic products. However, it is necessary to find a solution for another very important problem of theoretical and applied science the temperature mode control of fast chemical processes with high local heat generation in a reaction zone. 

During the dynamic crack growth, local heat generation takes place at the crack tip. If the temperature is high enough, a plastic zone is formed at the tip (Fig. 3) and its traces are the so-called "arrest lines" which appear on the fracture surface after... 

During a nail penetration test, an instantaneous internal short would result the moment the nail pierced into the battery. Enormous heat is produced from current in the circuit by the metal nail and electrodes. The contact area varies according to the depth of penetration. The shallower the depth, the smaller the contact area and therefore the greater the local current density and heat production. Thermal runaway is likely to take place as local heat generation induces electrolyte and electrode materials to decompose [18]. On the other hand, if the battery is fully penetrated, the increased contact area would lower the current density, and consequentiy would pass the nail penetration test. 

Polymerization of ethylene is quite exothermic (3.4 x 10 J/kg) and since the heat capacity of gas is much lower than that of liquid, removal of the heat of polymerization can be problematic compared to solution and slurry processes. This was usually accomplished by lowering the activity of gas-phase catalysts by say 50-75% to reduce the rate of local heat generated. To compensate, the residence time was then extended to several hours. As a result of these differences, gas-phase processes tend to have a much larger polymer inventory in the reactor. The gas-phase approach is also more rigid in its catalyst requirements. The kinetic profile of a catalyst for a gas-phase process should preferably have a steady activity lasting 2-3 h. The particle size for consistent fluidization is also sometimes important, and smaller particles are preferred for heat removal. 

Thermal therapies such as hyperthermia treatment rely on local heat generation rates several orders of magnitude greater than produced by the metaboHsm. Under these circumstances, the metaboHc heat generation is often neglected with Httle error. 

Even for a reactor in which all fuel elements are identical, the local heat generation rate will vary because of the variation of thermal neutron flux with position in the core. We illustrate by calculating the maximum local rate of heat generation as a function of total core power for the case of a bare reactor with vertical fuel elements, all of which contain fuel of the same enrichment. 

In the practical experiments, the influences of some essential and/or experimental factors for the reaction kinetics of hydrogen-metal systems have to be considered. The chemical potential of the surrounding hydrogen gas changed by pressure variation due to the reaction, the local heat generation caused by the formation of solid solution or hydride. The reaction mechanism (order) is also important in order to understand the essential kinetic properties of the reaction. As the experimental factors, the stabilities of the temperature and pressure in the experimental systems and/or the sample conditions, which are quality, quantity, particle size, porosity, thermal conductivity, and so on, also affect the kinetic properties. Thus, the reaction models and experimental situations should be considered in order to discuss the essential kinetic properties about the chemical reactions. 

The removal of heat from laser diodes or other small localized heat generating devices. 

It can produce large, accurate, distortion free surfaces due to low cutting forces and low local heat generation. 

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