Nonadiabatic PFR

In many tubular reactors cooling or heating occurs as the process fluid flows through the reactor. This produces a major difference between an adiabatic and a nonadiabatic tubular reactor. In an adiabatic reactor, with an exothermic irreversible reaction, the maximum steady-state temperature occurs at the end of the reactor. In a cooled reactor, the maximum steady-state temperature usually occurs at some axial position part way down the reactor. Thus the temperature does not change monotonically with length. 

The component balance and pressure drop equation do not change, but the energy balance contains a heat transfer term 

However, a small-diameter tube gives more pressure drop for a given flowrate through each tube and a given tube length. Of course, a larger number of parallel tubes that are shorter can be used to keep pressure drop at a reasonable level, but this increases the shell diameter of the reactor, which increases the cost. Mechanical problems also limit the minimum tube diameter. Typical tube diameter in cooled tubular reactors is 0.03 m. Typical tube diameter in a furnace-fired heated tubular reactor is 0.15 m. 

The overall heat transfer coefficient U (kW m-2 K-1) depends on the velocity through the tubes  

4 Given ceactor inlet conditions, dtube, ltube, ntube, T5t, Tin and dp cleat 

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