Low-rate

Example 4.5 Given that a low rate of production is required, convert the continuous process from Example 4.4 into a batch process. Preliminary sizing of the equipment indicates that the duration of the processing steps are given in Table 4.7. ... 

LOW RATE OF HEAT TRANSFER AND/OR HIGH HEAT OF REACTION... 

Figure 13.16 shows two possible thermal profiles for endothermic plug-fiow reactors. This time the temperature falls for low rates of heat addition and/or high heat of reaction. The temperature rises for the reverse conditions. Under conditions between the profiles shown in Fig. 13.16, a minimum can occur in the temperature profile at an intermediate point between the inlet and exit. 

To reduce this tendency the well should be produced at low rate, and the perforations should be as far away from the OWC as possible. Once the unwanted fluid breaks through to a well, the well may be recompleted by changing the position of the perforations during a workover, or the production rate may be reduced. 

Figure 2.5 reveals that polymer viscosity approaches Newtonian behavior for sufficiently low rates of shear. From an empirical point of view, this simply means that m 1 as 7 0. From a molecular point of view, in the region of... 

Polymers display Newtonian behavior = constant) at sufficiently low rates of shear [Eq. (2.29)]. 

The bulk viscosity of polystyrene (M = 371,000) at 200°C was measured by Graessley and Segalt at different rates of shear. At low rates of shear Tjj = 330,000 P and drops off with 7 approximately as follows ... 

Propellants and explosives are chemical compounds or mixtures that rapidly produce large volumes of hot gases when properly initiated. Propellants bum at relatively low rates measured in centimeters per second explosives detonate at rates of kilometers per second. Pyrotechnic materials evolve large amounts of heat but much less gas than propellants and explosives (see Pyrotechnics). 

The limiting oxygen index of Tefzel as measured by the candle test (ASTM D2863) is 30%. Tefzel is rated 94 V-0 by Underwriters Laboratories, Inc., in their burning test classification for polymeric materials. As a fuel, it has a comparatively low rating. Its heat of combustion is 13.7 MJ/kg (32,500 kcal/kg) compared to 14.9 MJ /kg (35,000 kcal/kg) for poly(vinyHdene fluoride) and 46.5 MJ /kg (110,000 kcal/kg) for polyethylene. 

Under these conditions, a component with a low rate constant for propagation for peroxy radicals may be cooxidized at a higher relative rate because a larger fraction of the propagation steps is carried out by the more reactive (less selective) alkoxy and hydroxy radicals produced in reaction 4. 

At pH 4—6, the cure is slower than it is at pH 8 and higher, and much slower than at pH 1—3. Reactions at pH 4—6 resemble those on the more alkaline side, but with a substantial increase in side-products. This is partly the result of the low rates of the main reactions and partly the result of stable intermediates at this pH range. 

The phases present in products can differ from those predicted from equilibrium diagrams. Nonequilibrium metastable phases form at solidification rates experienced in commercial ingots. Because of the low rate of diffusion of iron in alurninum, equilibrium conditions can only be established by long heat treatments and are very slowly approached at temperatures below about 550 °C. Small additions of other elements, particularly manganese, can also modify the phase relations. 

Fig. 15. Temperature vs heat generation or removal in estabHshing stationary states. The heavy line (—) shows the effect of reaction temperature on heat-generation rates for an exothermic first-order reaction. Curve A represents a high rate of heat removal resulting in the reactor operating at a low temperature with low conversion, ie, stationary state at a B represents a low rate of heat removal and consequently both a high temperature and high conversion at its stationary state, b and at intermediate heat removal rates, ie, C, multiple stationary states are attainable, c and The stationary state at c ...

Another class of herbicides, the imida zolines, was discovered at American Cyanamid in the early 1980s. Extensive research has led to the development of four commercial compounds imazapyr, imazamethahenz-methyl, imazethapyr, and imazaquin (see Table 5). Like the sulfonylureas, the imidazolines are extremely active at low rates. 

At high temperature, the behavior is different. A stmcture designed according to the principles employed for room temperature service continues to deform with time after load apphcation, even though the design data may have been based on tension tests at the temperature of interest. This deformation with time is called creep because the design stresses at which it was first recognized occurred at a relatively low rate. 

Electrical Properties. Generally, deposited thin films have an electrical resistivity that is higher than that of the bulk material. This is often the result of the lower density and high surface-to-volume ratio in the film. In semiconductor films, the electron mobiHty and lifetime can be affected by the point defect concentration, which also affects electromigration. These effects are eliminated by depositing the film at low rates, high temperatures, and under very controUed conditions, such as are found in molecular beam epitaxy and vapor-phase epitaxy. 

ADI Process. The ADI is a low rate anaerobic process which is operated ia a reactor resembling a covered football field. Because of the low rate, it is less susceptible to upset compared to the high rate processes. Its disadvantage is the large land area requirement. 

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