Reactor heat transport

By solving Eq. (6) numerically, we are able to calculate the concentrations of each species at any point in a reactor heat transport circuit. In the actual numerical simulation, all of the parameters, except the flow velocity, circuit geometry, and temperature can be found in the published literature [6, 9,13,14, 34],... 

TAYLOR, D., Prototype fast reactor heat-transport system, paper presented in the IAEA Simp, on Sodium-cooled fast reactor engineering, 23-27 March 1970, Monaco. 

K.A. Burrill, Water chemistries and corrosion product transport in supercritical water in reactor heat transport systems, in 8th BNES Conference on Water Chemistry of Nuclear Reactor Systems, Bournemouth, UK, vol. 1, October 22—26 2000, pp. 357—363. 

Flow Regimes in Multiphase Reactors. Reactant contacting, product separations, rates of mass and heat transport, and ultimately reaction conversion and product yields are strong functions of the gas and Hquid flow patterns within the reactors. The nomenclature of commonly observed flow patterns or flow regimes reflects observed flow characteristics, ie, armular, bubbly, plug, slug, spray, stratified, and wavy. 

Reaction and Transport Interactions. The importance of the various design and operating variables largely depends on relative rates of reaction and transport of reactants to the reaction sites. If transport rates to and from reaction sites are substantially greater than the specific reaction rate at meso-scale reactant concentrations, the overall reaction rate is uncoupled from the transport rates and increasing reactor size has no effect on the apparent reaction rate, the macro-scale reaction rate. When these rates are comparable, they are coupled, that is they affect each other. In these situations, increasing reactor size alters mass- and heat-transport rates and changes the apparent reaction rate. Conversions are underestimated in small reactors and selectivity is affected. Selectivity does not exhibit such consistent impacts and any effects of size on selectivity must be deterrnined experimentally. 

Scale-Up Principles. Key factors affecting scale-up of reactor performance are nature of reaction zones, specific reaction rates, and mass- and heat-transport rates to and from reaction sites. Where considerable uncertainties exist or large quantities of products are needed for market evaluations, intermediate-sized demonstration units between pilot and industrial plants are usehil. Matching overall fluid flow characteristics within the reactor might determine the operative criteria. Ideally, the smaller reactor acts as a volume segment of the larger one. Elow distributions are not markedly influenced by... 

There is also another key parameter linked to the choice of the material for the reactor. First, the choice is obviously determined by the reactive medium in terms of corrosion resistance. However, it also has an influence on the heat transfer abilities. In fact, the heat transport depends on the effusivity relative to the material, deflned by b = (XpCp) the effusivity b appears in the unsteady-state conduction equation. 

Rractor type2 shown in Fig. 3, in which the steam vapor was first fed Iran the bottom of the reactor then transported throu an internal thin tube in the heated part of the reactor, and th v mixed with TEMS fed fiom flie top of the reactor without heating. Thus the shape of the reactor was improved to generate smaller partides than in Type 1. Furthermore, CO2 was also used instad of Ar to increase the heat capadty of carrier gas. 

Catalysts are generally developed for a particular process, i.e. for a certain reaction in a certain reactor under certain conditions. Mass and heat transport phenomena put their... 

The reaction was of a scouting nature, actually one of the most common investigations done concerning gas-phase reactions in micro reactors. Hence it addresses in a general way the investigation of general micro reactor properties such as mass and heat transport and residence time. 

This equation may be used as an appropriate form of the law of energy conservation in various pseudo homogeneous models of fixed bed reactors. Radial transport by effective thermal conduction is an essential element of two-dimensional reactor models but, for one-dimensional models, the last term must be replaced by one involving heat losses to the walls. 

For the discrete bubble model described in Section V.C, future work will be focused on implementation of closure equations in the force balance, like empirical relations for bubble-rise velocities and the interaction between bubbles. Clearly, a more refined model for the bubble-bubble interaction, including coalescence and breakup, is required along with a more realistic description of the rheology of fluidized suspensions. Finally, the adapted model should be augmented with a thermal energy balance, and associated closures for the thermophysical properties, to study heat transport in large-scale fluidized beds, such as FCC-regenerators and PE and PP gas-phase polymerization reactors. 

For a more detailed analysis of measured transport restrictions and reaction kinetics, a more complex reactor simulation tool developed at Haldor Topsoe was used. The model used for sulphuric acid catalyst assumes plug flow and integrates differential mass and heat balances through the reactor length [16], The bulk effectiveness factor for the catalyst pellets is determined by solution of differential equations for catalytic reaction coupled with mass and heat transport through the porous catalyst pellet and with a film model for external transport restrictions. The model was used both for optimization of particle size and development of intrinsic rate expressions. Even more complex models including radial profiles or dynamic terms may also be used when appropriate. 

The essential ingredients for producing heat in a thermal fission nuclear reactor are the fuel and a moderator. A heat transport system with its coolant is necessary to convey the heat from the reactor to boilers where steam is produced to drive the turbogenerator. The natural materials available for fuel and moderator are uranium ore and water natural uranium extracted from the ore comprises the fissionable isotope uranium-235 and water contains hydrogen which is a good moderator. (Table I)... 

Much research is done in the field of catalyst-design and reactor engineering in order to improve mass- and heat-transport properties [7], Another purpose is to improve the selectivity. This is, in some cases, strongly related to the transport properties, but in other cases the choice of catalytic material and design is essential. 

During normal operation, the main circulator transports hot helium at 1266°F (686°C) from the bottom of the core to the steam generator which, in turn, produces superheated steam at I005°F (541 °C) and 2500 psia. The cold helium at 496°F (258°C) is returned to the top of the reactor core. During normal shutdown and refueling, the non-safety auxiliary shutdown heat removal system removes core afterheat if the main heat transport system is not operational. 

Fig. 25. Series of towers comprising part of the heavy water production plant at Ontario Hydro s Bruce nuclear power complex near Tiverton on the shores of Lake Huron. Heavy water is a clear, colorless liquid that looks and tastes like ordinary water. It occurs naturally in ordinary water in the proportion of approximately one part heavy water to 7000 parts of ordinary water. While ordinary water is a combination of hydrogen and oxygen (H20), heavy water (D.-1.0) is made of up of deuterium—a form, or isotope, of hydrogen—and oxygen. Deuterium is heavier than hydrogen in that it has an extra neutron in its atomic nucleus, so heavy water weighs about 10% more than ordinary water. It also has different freezing and boiling points. It is the extra neutron that makes heavy water more suitable than ordinary water for use in CANDU nuclear reactors as both a moderator and a heat transport medium. (Ontario Hydro, Toronto, Ontario, Canada)...

The principle of thermal recycling is also used in reactors with a boiling layer, in which the heat from the hot region of the reactor is transported to the cold region by circulating solid particles suspended in the gas flow.15 Methods of the theory of chemical reactor regulation have been successfully used in other sciences as well. We note the model of Belousov-Zhabotinskii, proposed for the description of heart disease, of spasmatic contractions of the cardiac muscle. 

Growth of the film is a primary concern for both reactor types, but the transport phenomena in a CVD reactor are more difficult to analyze. Knowledge of the fluid mechanics and heat and mass transfers, often for a very complex geometry, is required. In a line-of-sight PVD reactor, the transport of molecular species to the substrate can be analyzed more easily. 

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