Thermal profiles

Figure 2.7 Two alternative reactor designs for methanol production give quite different thermal profiles.

Figure 13.1a shows two possible thermal profiles for exothermic plug-fiow reactors. If the rate of heat removal is low and/or the heat of reaction is high, then the temperature of the reacting stream will increase along the length of the reactor. If the rate of heat removal is high and/or the heat of reaction is low, then the temperature will fall. Under conditions between the two profiles shown in Fig. 13.1a, a maximum can occur in the temperature at an intermediate point between the reactor inlet and exit. 

The thermal profile through the reactor will in most circumstances be carefully optimized to maximize selectivity, extend catalyst life, etc. Because of this, direct heat integration with other process streams is almost never carried out. The heat transfer to or from the reactor is instead usually carried out by a heat transfer intermediate. For example, in exothermic reactions, cooling might occur by boiling water to raise steam, which, in turn, can be used to heat cold streams elsewhere in the process. 

Also like distillation, the thermal profile of evaporators can be manipulated by changing the pressure. However, the degrees of freedom in evaporator design open up more options. 

Guenther P, Fischer U Ch and Dransfeld K 1989 Scanning near-field acoustic microscopy Appl. Phys. B 48 89 Williams C C and Wickramasinghe FI K 1986 Scanning thermal profiler App/. Phys. Lett. 49 1587... 

Fig. 7. Thermomagnetic recording, (a) A focused laser beam generates a thermal profile in the magnetic layer, (b) The coercive force in the layer is reduced and its magnetisation can be reversed by a small magnetic field, here 30 kA/m. At room temperature, the coercive force is high and the written domains are...

Normally for non-mechanical equipment the analysis parameter set will consist of the calculated values derived from measuring the thermal profile or process parameters. Each classification of equipment or system will have its own unique analysis parameter set. 

Before setting out to discuss the vertical structure of the atmosphere, we note that it is useful to have access to conventional nomenclature. Figure 7-1, based on the thermal profile of the atmosphere, includes a number of commonly used definitions. 

An example of integrated heat-transfer modehng and reactor design is shown in Figure 11.6. A predicted thermal profile for the reactor section of a combined reactor-heat exchanger is the solid line, while the discrete points are experimentally measured temperatures along the reactor length. The thermal profile is controlled... 

Molecular structure and weight Melting point Thermal profile Particle size and shape Hygroscopicity potential Ionization constant Light stability Optical activity pH solubility profile pH stability profile Polymorphism potential Solvate formation... 

Figure 20.1b shows two possible thermal profiles for endothermic plug-flow reactors. This time, the temperature decreases for low rates of heat addition and/or high heat of reaction. The temperature increases for the reverse conditions. Under conditions between the profiles shown in Figure 20.1b, a minimum can occur in the temperature profile at an intermediate point between the inlet and exit. 

In another study, thermodiffractometry was used to study phase transformations in mannitol and paracetamol, as well as the desolvation of lactose monohydrate and the dioxane solvatomorph of paracetamol [56]. The authors noted that in order to obtain the best data, the heating cycle must be sufficiently slow to permit the thermally induced reactions to reach completion. At the same time, the use of overly long cycle times can yield sample decomposition. In addition, the sample conditions are bound to differ relative to the conditions used for a differential scanning calorimetry analysis, so one should expect some differences in thermal profiles when comparing data from analogous studies. 

The seminal work by Maleki et al. in 1999 seemed to provide a direct answer to the question about which of the five possible processes was responsible for the thermal runaway of a lithium ion cell. Using ARC, they first determined the thermal runaway onset temperature in a lithium ion cell based on LiCo02/graphite with LiPFe/EC/DMC/DEC to be 167 °C. The thermal reaction, however, was found to start at 123 °C and continued to self-heat the system to the above onset temperature. Using DSC and TGA, they further determined the heat evolution as well as the thermal profile for the individual components of the cell in the presence of electrolytes, which included cathode, anode, and anode binder (PVdF). 

However, salinity values are easily obtained with a salinometer (which measures electrical conductivity and is appropriately calibrated with standard solutions and adjusted to account for T effects). The salinity of seawater increases if the loss of H2O (evaporation, formation of ice) exceeds the atmospheric input (rain plus rivers), and diminishes near deltas and lagoons. Salinity and temperature concur antithetically to define the density of seawater. The surface temperature of the sea reflects primarily the latitude and season of sampling. The vertical thermal profile defines three zones surface (10-100 m), where T is practically constant thermoclinal (100-1000 m), where T diminishes regularly with depth and abyssal... 

Table 9.12 Thermal profile of water along boiling curve (from Haas, 1971).

The rate of bleeding is dependent on several factors, including the permeability of the fiber bed, both vertically and horizontally, and the viscosity of the liquid resin. The permeability of the fiber bed will depend on the weave of the fabric, the fiber diameter, and the fiber volume fraction. The resin viscosity is determined by the chemistry of the resin and the thermal profile of the cure cycle. The cure cycle greatly affects resin viscosity and the flow process, both directly through the pressure application and indirectly through the effect of the thermal profile on resin viscosity. 

The original synthesis of triazole 3 began with the reaction of chloropyrazine 6 with hydrazine (Scheme 5.2). While these two compounds readily react at elevated temperature, the reachon possessed several unsafe aspects. First, heating 6 in isopropanol (IPA) with an excess of hydrazine allowed for a high potenhal for dangerous free hydrazine to be present in the head space.Second, the thermal profile of this step showed the potential for an uncontrollable reachon at elevated temperatures with a large amount of gas evoluhon. ) ) Lastly, the hydrazine adduct 7 was observed to crystallize from the reaction as a toxic and explosive hydrazine co-crystal. 

To attain control over the thermal profiles, four independent resistance heaters are utilized. 

To control the gas pressure of As precisely, a sodium heat pipe and an internal cooling gas distribution system are installed in the cool zone, which serve to establish a flat thermal profile and enhanced temperature stability. 

Two other factors could contribute to the observed departure of the growth thickness at long times from that predicted by equation 17. First, homogeneous nucleation in the melt and the subsequent growth of precipitates will act as sinks for solute atoms, just as film growth does. The exact location in the melt where homogeneous nucleation will occur depends on the melt compositional and thermal profiles (96). The precipitates are less dense than the melt and will rise to the top of the melt. Such precipitates... 

Harrison TM, Grove M, Lovera OM, Zeitler PK (2005) Continuous thermal histories from inversion of thermal profiles. Rev Mineral Geochem 58 389-409... 

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