Thermal controlling

Staged reactions, where only part of the initial reactants are added, either to consecutive reactors or with a time lag to the same reactor, maybe used to reduce dipentaerythritol content. This technique increases the effective formaldehyde-to-acetaldehyde mole ratio, maintaining the original stoichiometric one. It also permits easier thermal control of the reaction (66,67). Both batch and continuous reaction systems are used. The former have greater flexibiHty whereas the product of the latter has improved consistency (55,68). 

Low-velocity ATD An air terminal device which is designed for thermally controlled ventilation, e.g., displacement flow applications. See also Air terminal device. 

Absorptivity.-emissivity ratio Alkyd silicone Thermal control coating... 

We have designed, manufactured and tested a prototype that may be applied in thermal control of electronic devices. It was fabricated from a silicon substrate and a Pyrex cover, serving as both an insulator and a window through which flow patterns and boiling phenomena could be observed. A number of parallel triangular micro-channels were etched in the substrate. The heat transferred from the device was simulated by different types of electrical heaters that provided uniform and non-uniform heat fluxes, defined here respectively as constant and non-constant values... 

Ferrouillat, S., Tochon, P., Della Valle, D., and Peerhossaini, H. (2006a) Open loop thermal control of exothermal chemical reactions in multifunctional heat exchangers. Int.J. Heat Mass Transfer., 49 (15-16), 2479-2490. 

In order to exemplify the potential of micro-channel reactors for thermal control, consider the oxidation of citraconic anhydride, which, for a specific catalyst material, has a pseudo-homogeneous reaction rate of 1.62 s at a temperature of 300 °C, corresponding to a reaction time-scale of 0.61 s. In a micro channel of 300 pm diameter filled with a mixture composed of N2/02/anhydride (79.9 20 0.1), the characteristic time-scale for heat exchange is 1.4 lO" s. In spite of an adiabatic temperature rise of 60 K related to such a reaction, the temperature increases by less than 0.5 K in the micro channel. Examples such as this show that micro reactors allow one to define temperature conditions very precisely due to fast removal and, in the case of endothermic reactions, addition of heat. On the one hand, this results in an increase in process safety, as discussed above. On the other hand, it allows a better definition of reaction conditions than with macroscopic equipment, thus allowing for a higher selectivity in chemical processes. 

Since in the literature such deachvation was attributed to a sudden temperature rise and decline under the same process condihons, it was assumed that the improved thermal control of micro channels is responsible for the higher stability. 

To achieve excellent thermal control, to use short residence times and to have no back-mixing were the main drivers for an industrial investigation of the methylation of an aromatic. The target molecule yielded thereby, a precursor for a crop-protection product, is temperature sensitive [127]. Accordingly, cryo-processing has to be applied to avoid decomposition when the reaction is conventionally performed. A driver for micro reactor processing would be to enable room-temperature processing or, at least, to increase the reaction temperature closer to ambient... 

Sulphuric acid at 93% was added to p-nitrotoluene. The temperature reached 160°C due to a failure of the thermal control system. The sulphonic acid formed decomposed violently at this temperature. The post-accident investigation showed that the decomposition started between 160 and 190 C. In fourteen minutes the temperature rose to 190-224°C and in one minute and thirty seconds to 224-270°C. A large volume of gas was then released during the eruption. The phenomena caused by the decomposition of nitrated derivatives in the presence of sulphuric acid will be addressed several times. What these incidents have in common is the formation of large carbonised volumes. This phenomenon is common with sulphonic acids. The nitro group role is to destabilise intermediate compounds and final compounds and to generate... 

The effect of the nitric acid/hydrogen peroxide mixture on acetone when it is hot gives rise to an explosive oxidation, especially when the medium is confined. This situation also applies to a large number of ketones, and in particular, cyclic ketones. Cyclic di- and triperoxides form compounds that detonate, if there is no strict and very delicate thermal control. Accidents have been reported with butanone, 3-pentanone, cyclopentanone, cyclohexanone and methylcyclo-hexanones. 

For liquid metal boiling, however, Eq. (2-67) showed poor agreement with the experimental results of Bobrovich et al. (1967). In Ivey s correlations, it is expected that the thermodynamic region will not normally be applicable to liquid metals, because their bubble growth is very rarely thermally controlled. Consequently, in this case, Eq. (2-64) for the hydrodynamic region is applicable and is combined with Eq. (2-62), leaving the ratio [tj(tw + td) as a variable ... 

A road tanker was loaded with l-chloro-2,3-epoxypropane and then driven 250 miles overnight to the delivery point. On arrival, the contents were found to have self heated (undoubtedly from polymerisation initiated by some unknown contaminant) to the boiling point (115°C at ambient pressure) and soon afterwards the relief valve lifted and discharged large volumes of vapour. Cooling with water sprays eventually restored thermal control over the remaining tanker contents [1]. The material is incompatible with strong acids, caustic alkalies, zinc, aluminium, aluminium chloride or iron(III) chloride, all of which catalyse exothermic polymerisation [2],... 

As shown in Fig. 13, a variety of metal carbonyls upon sonication will catalyze the isomerization of 1-pentene to cis- and tram-2-pentene (186). Initial turnover rates are about 1-100 mol 1-pentene isomerized/mol of precatalyst/hour, and represent rate enhancements of 102 5 over thermal controls (174). The relative sonocatalytic and photocatalytic activities of these carbonyls are in general accord. An exception is Ru3(CO)12, which is... 

Fluidized beds are widely used to achieve either chemical reactions or physical processing that require interfacial contact between gas and particles. Heat transfer is important in many of these applications, either to obtain energy transfer between the solid and gas phases or to obtain energy transfer between the two-phase mixture and a heating/cooling medium. The latter case is particularly important for fluidized bed reactors which require heat addition or extraction in order to achieve thermal control with heats of reaction. 

Many commercial split flow capillary LC systems incorporate a nano flow sensor mounted online to the capillary channel. The split flow system can be easily modified from a conventional system and performs satisfactorily for capillary LC applications. However, the split flow system may require thermal control and the LC solvent requires continuous degassing. In addition, the system may not work reliably at a high flow split ratios and at pressures above 6000 psi due to technical limitations of the fused silica thermal conductivity flow sensor. The split flow system based on conventional check valve design may not be compatible with splitless nano LC applications. The conventional ball-and-seat check valve is not capable of delivering nano flow rates and is not reliable for 7/24 operation at low flow. 

M. Berggren, G. Gustaffson, O. Inganas, M.R. Andersson, O. Wennerstrom, and T. Hjertberg, Thermal control of near-infrared and visible electroluminescence in alkyl-phenyl substituted polythiophenes, Appl. Phys. Lett., 65 1489-1491, 1994. 

Thermal control, silver in, 22 660-661 Thermal cracking, See also Cracking entries... 

In the thermally controlled regime, the radius increases with the square root of time. 

For the thermally controlled growth curve, Eq. (16) was used and the properties of liquid propane were estimated at Tq [328 K at 1 atm and 322 K at 5 atm]. Over this small temperature range, the variation in most properties was small. However, p, the density of the vapor in the growing bubble, is proportional to the pressure so that the Ja number [Eq. (17)]... 

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