Temperature Control and Heat Transfer

This paper describes work on equipment and instrumentation aimed at a computer-assisted lab-scale resin prep, facility. The approach has been to focus on hardware modules which could be developed and used incrementally on route to system integration. Thus, a primary split of process parameters was made into heat transfer and temperature control, and mass transfer and agitation. In the first of these the paper reports work on a range of temperature measurement, indicators and control units. On the mass transfer side most attention has been on liquid delivery systems with a little work on stirrer drives. Following a general analysis of different pump types the paper describes a programmable micro-computer multi-pump unit and gives results of its use. 

Another industrially important reaction of propylene, related to the one above, is its partial oxidation in the presence of ammonia, resulting in acrylonitrile, H2C=CHCN. This ammoxidation reaction is also catalyzed by mixed metal oxide catalysts, such as bismuth-molybdate or iron antimonate, to which a large number of promoters is added (Fig. 9.19). Being strongly exothermic, ammoxidation is carried out in a fluidized-bed reactor to enable sufficient heat transfer and temperature control (400-500 °C). 

After the dispersion leaving the reactor is separated in the settler (decanter), the liquid hydrocarbon product stream is partially flashed, forming a vapor phase, mainly isobutane. The remaining liquid is hence cooled, and it is used as the coolant in the tube bundle of the reactor. As heat is transferred there, more hydrocarbons vaporize, forming a liquid-gas mixture. Obviously, temperature gradients occur on both sides of the tube bundle as a function of reactor length. Heat transfer (and temperature control) is an important design consideration in contactors. 

The choice which of the phases is going to be the continuous phase determines to a large extent the choice of the reactor type in any case it limits the number of possible reactor types, as we shall see later (Chapters 9 - 13). And this choice has important consequences for the kinetics of the process (Chapter 5), and also for heat transfer and temperature control (Chapter 8). 

Vinyl chloride polymerization occurs via an exothermic radical reaction. In fact, the reaction is approximately 25% more exothermic than polyethylene polymerization. The highly exothermic nature of the reaction and the strong molecular weight dependence on temperature make heat transfer, and its control, critical to the manufacture of polyvinyl chloride. 

Possible coupling with microwave heating Optimized energy transfer and temperature control Expanded temperature range system. Issue incompatible with precipitating products... 

Temperature uniformity within a mixer should be controlled. In addressing temperature uniformity, one should consider the complex interaction among vat size, mixer speed, blade design, viscosity of contents, and rate of heat transfer. Where temperature control is critical, use of recording thermometers to continuously monitor and document temperature measurements is preferred to frequent manual checks. Where temperature control is not critical, it may be adequate to manually monitor and document temperatures periodically by use of handheld thermometers. 

As well as continuous development of machine design and especially machine control systems, there has been considerable development of molds. These may be quite simple or very sophisticated, with multiple cavities, moving parts. Since the molding of RTPs is essentially a question of the control of heat transfer, advanced temperature control systems are frequently used, which can repay their additional cost by... 

Lang, J., B. Erdmann, and M. Seebass, Impact of nonlinear heat transfer on temperature control in regional hyperthermia. IEEE Trans. Biomed. Eng., 1999,46 1129-1138. 

In the temperature control of mold plates made from conventional steel, CO2 is also passed into an expansion chamber and evaporates. However, the CO2 cannot flow through the steel, i.e. only the surface of the expansion chamber is available for heat transfer. The temperature-control performance, as opposed to applications with a sintered material, is correspondingly lower. Nevertheless, there are two key advantages ... 

Microreactors enable microscale reactions under continuous flow conditions. In recent decades, many studies were devoted to the development of new and efficient processes using flow microreactor systems in organic synthesis [36-38]. Compared to conventional batch methods, advantageous features of microreactor protocols include high mixing efficiencies, rapid mass and heat transfer (precise temperature control), and continuous operation and mixing. Recently,... 

Commercially, stabilization is accomplished by controlled heating in air at temperatures of 200—300°C. A variety of equipment has been proposed for continuous stabilization. One basic approach is to pass a fiber tow through heated chambers for sufficient time to oxidize the fiber. Both Mitsubishi and Toho patents (23,24) describe similar continuous processes wherein the fiber can pass through multiple ovens to increase temperature and reaction rate as the thermal stabiUty of the fiber is increased. Alternatively, patents have described processes where the fiber passes over hot roUs (25) and through fluidized beds (26) to provide more effective heat transfer and control of fiber bundle temperature. 

Homogeneous reactions. Homogeneous noncatalytic reactions are normally carried out in a fluidized bed to achieve mixing of the gases and temperature control. The sohds of the bed act as a heat sink or source and facihtate heat transfer from or to the gas or from or to heat-exchange surfaces. Reaclious of this type include chlorination of hydrocarbons or oxidation of gaseous fuels. 

Buildup of condensate in a heat exchanger can cause operating problems as well as water hammer. If the steam supply is controlled by a motor valve and the valve is not fully open, the steam pressure may be too low to expel the condensate, and its level will rise. This will reduce heat transfer, and ultimately the steam supply valve will open fully and expel the condensate. The cycle will then start again. This temperature cycling is bad for the heat exchanger and the plant and may be accompa-... 

Furnace temperatures (and in part, heat transfer rates) are controlled by the opening and closing of air and flue gas dampers and burner registers. 

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