Green Chemistry in Oscillatory Baffled Reactors - Process Intensification for Green Chemistry - page 161

Figure 5.4 Heat-transfer enhancement of OBRs. Reprinted from Mackley and Stonestreet
# 1995, with permission from Elsevier.

transfer coefficients associated with turbulent flows can be achieved at much lower net flow
rates. The lower dashed line, corresponding to Re o ¼

0, on the graph illustrates the heat
transfer enhancement due to the incorporation of baffles in the absence of oscillation, and
indeed orifice plate baffles, andmany other designs of 'flow inserts' are often used to enhance
heat transfer. Comparison of the Re o ¼

0 line with the other experimental data illustrates the
positive effect of the vortex generation in oscillatory flow on radial heat transfer.

5.1.2.5 OBR Design

Broadly, OBRs are designed along similar lines to shell-and-tube heat exchangers. The
visualization inFigure5.5 is aconcept design fora small industrial unit, illustrating thisprinciple.
The design procedure for OBRs was developed by Stonestreet and Harvey [5]. It was
based on following shell-and-tube design protocols, plus ensuring that the correct mixing
conditions are in place. The starting information required is: residence time, physical
properties of the reaction mixture - such as viscosity and density - and an estimate or
knowledge of the required Re o (to overcome any density differences in the system). The
design flowchart is given in Figure 5.6.
To briefly explain the design steps:

(1) Re o and c define the Re n . The value of c comes from knowledge of the required
degree of plug flow and the velocity ratio 'operating window'.
(2) Together with , various values of D, the tube diameter, are input to generate outputs

of u, the velocity. This is best implemented on a spreadsheet.
(3) Outputs for z (the length), m (the number of baffles), Q (the volumetric flowrate) and
e

t

t (the power) are then calculable (see Ref. [5] for more detail on these calculations).