Steady state flow systems

A gas flow techique was successfully used by Hacker et al. [66] in 1961, who studied the recombination of O atoms on quartz and platinum using ESR spectroscopy and isothermal calorimetry with mutually consistent results. However, only in the last few years has the technique been developed for the study of recombination under conditions far removed from those associated with static side arm systems. 

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Referring to Figure 2-35 (process diagram), the first law for this steady-state flow system becomes... 

Application of the general component balance, Equation (1.6), to a steady-state flow system gives... 

A chemical reaction is being studied in a laboratory scale steady-state flow system. The reactor is a well-stirred 1000 cm3 flask containing an aqueous solution. The reactor contents (1000 cm3 of solution) are uniform throughout. The stoichiometric equation and data are given below. What is the expression for the rate of this reaction Determine the reaction order and the activation energy. 

This is a number that goes from zero to unity as the selectivity improves. We can use the number of moles Nj, chosen on some basis for each species such that we divide each Nj by its stoichiometric coefficient to normalize them. For a steady-state flow system the molar flow rates Fj are appropriate. 

Each term in the preceding equations has units of energy/time. Note the signs on each term indicating that heat is removed or added to the reactor. We preserve the minus sign on A Hji because we are more interested in exothermic reactions for which A Hr < 0. The student can recognize each term on the right side from the steady-state enthalpy balance we derived in the previous section from the thermodynamics of a steady-state flow system. 

For a steady-state flow system, again neglecting changes in the PEs and KEs, the... 

Careful analysis of the reaction products in the HDN of the 2,6-lutidine (2,6-dimethylpyridine) and the 2,6-lupetidine (2,6-dimethylpiperidine) allowed Ledoux et al.37 to conclude that under these low pressure conditions (1 atm H2, 5-10 Torr amine, in a steady state flow system, at 300°C on Mo03/A1203 in a fixed-bed reactor) the hydrogenated product is not the intermediate for the HDN of the aromatic compound because the distributions of the products obtained by the reaction of the two amines are fundamentally different. 2,6-Lutidine gives at initial conversion 60% toluene, 21% C3 + C4 and 8% olefinic n-C7, while 2,6-lupetidine gives only 18% toluene, 4% C3 + C4 but 69% of olefinic n-C7. Under the same experimental conditions (but at 380°C), analysis of the pyridine and piperidine HDN products38 shows that... 

PRESSURE OF A STEADY-STATE FLOW SYSTEM (WITHOUT PRESSURE CONTROL)... 

Using a steady-state flow system, Levy has investigated the H2-Br2 reaction over the temperature range 600-1470 °K and has shown the Christiansen, Herzfeld and Polanyi free radical mechanism to be obeyed. Pressures of Br2 and HBr were measured after collection of products. Initial Br2 concentrations were obtained by material balance. Reactor residence times were calculated from measurements of total flow rate and reactor volume. 

Equation 1.39 is a special case of a far more general result. The mean residence time t is the average amount of time that a material spends in a reactor. The concept of mean residence time is most useful for flow systems. In a steady-state flow system 1 is equal to the mass inventory of fluid in the system divided by the mass flow rate through the system ... 

Equilibrium steady-state flow system Level II... 

This is a steady-state flow system, hence AH = Q + fV. Assuming that work done is negligible in comparison with the heating... 

C Overall Energy Balance for Steady-State Flow System... 

If continuous flow is used, the relaxation time is determined from the integrated relaxation signal amplitude A measured (on the steady state flow system during the flow) coaxially with the flow direction (7), using eq. (1)... 

The fluid age distributions defined above for steady state flow systems can be extended to non-steady situations. Nauman [1969] illustrated this for vessels with time-varying inflow, outflow, and volume, related by ... 

In a steady-state flow system there is a transfer of energy or matter in and out such that the system remains constant. In a cyclic system, the final state is identical to the initial state. That is, the heat absorbed is equal to the work done by the system. In an adiabatic process, there is no heat exchange with the surroundings. The process is therefore thermally isolated or the process is very rapid such that heat has no time to enter or leave the system. This is an idealized process since insulation is not perfect and there will be some transfer of heat. In an isothermal process, there is no exchange of temperature with the surroundings. The type of system may depend on the timeframe of interest. For example, a vessel containing volatile liquid can be considered to be closed for a very short period after which the system can be considered to be open. 

The first law of thermodynamics is a simple conservation balance for energy. In a steady-state flow system it is... 

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