Density Reactors

Solution In a real problem, the individual values for k, V, and Qi would be known. Their values are combined into the dimensionless group, kVIQi . This group determines the performance of a constant-density reactor and is one of the two parameters needed for the variable-density case. The other parameter is the density ratio, r = Pmommer/Ppoiymer- Setting kVIQtn = 1 gives T = 0.5 as the fraction unreacted for the constant-density case. The individual values for k, V, Qi , Pmommer, and Ppoiymer can be assigned as convenient, provided the composite values are retained. The following... 

The ongoing work on sludge-blanket and draft-tube reactors requires demonstration of sufficient gas-liquid mass transfer to provide the necessary oxygen needed in high cell density reactors. 

We will work out the solution to variable-density reactors for a simple example where the number of moles varies with conversion. 

In a variable-density reactor the residence time depends on the conversion (and on the selectivity in a multiple-reaction system). Also, in ary reactor involving gases, the density is also a function of reactor pressure and temperature, even if there is no change in number of moles in the reaction. Therefore, we frequently base reactor performance on the number of moles or mass of reactants processed per unit time, based on the molar or mass flow rates of the feed into the reactor. These feed variables can be kept constant as reactor parameters such as conversion, T, and P are varied. 

Reactors have volume V. Continuous-flow reactors have volumetric flow rate V, and constant-density reactors have residence time X = V/v. Until Chapter 8 all continuous reactors are either completely mixed (the CSTR) or completely unmixed (the PFTR). 

The molar flow rate of a species in a flow reactor is Fj = vCj. The batch reactor is a closed system in which v = 0. The volumetric flow rate is ti, while thelinear velocity in a tubular reactor is u, We usually assume that the density of the fluid in the reactor does not change with conversion or position in the reactor (the constant-density reactor) because the equations for a constant-density reactor are easier to solve. 

T residence time in a reactor, defined as T = V/p for a constant-density reactor and also... 

We first derive the energy balance in a CSTR. For the mass balance in a constant-density reactor we wrote an integral balance on the rate of change of the number of moles Nj of species j in the reactor to obtain... 

When we assume a steady-state constant-density reactor, we obtain the simple form of this equation (V. pu = 0 or pu constant), which is just total mass conservation as required from stoichiometry. 

Most reliable are the data on neutron fluxes which are determined by the plasma power density, reactor geometry and structural parameters. Most of the conceptual power reactor design studies contain a detailed neutronics analysis giving the energy as well as the spatial distribution of neutron fluxes. 

The density change in this example increases the reaction rate since the volume goes down and the concentration of the remaining A is higher than it would be if there were no density change. The effect is not large and would be negligible for many applications. When the real, variable-density reactor has a conversion of 50%, the hypothetical, constant-density reactor would have a conversion of 47.4% (7 = 0.526). 

Jp = Catalytic density (Reactor volume/ Flow rate)... 

Typical range values for plasma parameters in rf diode and high density reactors, (calculation is done for a CF4 plasma assuming Maxwell-Boltzmann distributions)... 

Liquid sodium has attractive properties for its application as a working fluid in a fast neutron reactor with the ability to breed plutonium fuel by the reaction of ura-nium with the fast neutrons. Sodium does not act as a neutron moderator, its liquid state at atmospheric pressure reaches from 97.8 °C to 892 °C, its heat transfer properties are excellent and its nuclear reactions do not cause a long lasting activation. Sodium is the medium which is able to transfer the energy generated in the high density reactor core better than any other heat transfer fluid... 

Low operating temperature and pressure, and low power density reactor design which provided increased operating margins and improved fuel economy ... 

Enrichment Power density Reactor Temperature Average burnup... 

We insert some fixed process and physical data, after which we select a current density and initialize the variables which will change as the calculation proceeds. We go through an integration loop (current density reactor model- AS) repeatedly until the required number of loops has been completed. The increments of S are accumulated, and the final value is printed out or fed directly into the main chart (Fig. 6.7). 

Rate constant Average residence time Concentration of A at the inlet Concentration of B at the inlet Molecular diffusion coefficient of A Dynamic viscosity Density Reactor length Reactor diameter... 

The two major weaknesses of the fermentation process for propionic acid production are the low final product concentration and the extremely low productivity due to the sensitivity of the bacterial cells to organic acids and their slow fermentation and growth rates. Two developments in fermentation technology that improve the process are the high cell density reactor and improved ultrafiltration membranes for recovery of the product. 

This appendix summarizes thermal-hydraulic considerations for a plutonium-burning reactor and recommends for this purpose a low-power-density reactor that is cooled with low-temperature, low-pressure light water flowing at... 

Because only a low power density reactor is being considered, there is little chance that the molten aluminum will reach a temperature high enough to cause chemical ignition to occur. From an energetic standpoint Pu-Al fuel material is a logical first choice as a fuel material. 

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