Shell diameter

No. of passages/pass

Figure 7. Pass arrangement comparison: plate versus tubular.

Figure 7. Pass arrangement comparison: plate versus tubular.

Figure 5. Gasket showing separation of throughport and flow areas.

Figure 8. Diagonal and vertical flow patterns.

thermal duty without oversizing the exchanger. This results in the use of fewer plates and a smaller, less expensive exchanger frame.

To achieve mixing, plates that have been pressed with different corrugation angles are combined within a single heat-exchanger frame. This results in flow passages that differ significantly in their flow characteristics and thus heat-transfer capability from passages created by using plates that have the same corrugation pattern.

For example, a plate pack (Fig. 11) of standard plates that have a typical 50° corrugation angle (to horizontal) develops a fixed level of thermal performance (HTU) per unit length. As plates of 0° angle (Fig. 12) are substituted into the plate pack up to a maximum of 50% of the total number of plates, the thermal performance progressively increases to a level that typically is twice that of a pack containing only 50° angle plates.

Outside plate edge

Figure 6. Exclusive interlocking gasket.

plates are manufactured to the standard widths specified for the particular heat exchanger involved but are offered in different corrugation patterns and plate lengths.

Since each type of plate has its own predictable performance characteristics, it is possible to calculate heat-transfer surface that more precisely matches the required

Figure 9. Corrugations pressed into plates are perpendicular to the liquid flow.
Figure 10. Troughs are formed at opposite angles to the centerline in adjacent plates.
Figure 11. Low HTU passage.
Figure 12. High HTU passage.

Thus, it is possible for a given plate length to fine-tune the Paraflow design in a single or even multiple-pass arrangement exactly to the thermal and pressure drop requirements of the application.

Of more recent development are plates of fixed width with variable lengths that extend the range of heat-transfer performance in terms of HTU. This is proportional to the effective length of the plate and typically, provides a range of 3-1 from the longest to the shortest plate in the series. As shown in Figure 13, mixing also is available in plates of varied lengths and further increases the performance range of the variable-length plate by a factor of approximately 2.

This extreme flexibility of combining mixing and variable-length plates allows more duties to be handled by a single-pass design, maintaining all connections on the stationary head of the exchanger to simplify piping and unit maintenance.

Plate Size and Frame Capacity

Paraflow plates are available with effective heat-transfer area from 0.28 to 50 ft2, and up to 600 of any one size can be contained in a single standard frame. The largest Paraflow can provide in excess of30,000 ft2 of surface area. Flow ports are sized in proportion to the plate area and control the maximum permissible liquid throughput Figure 14. Flow capacity of the individual Paraflow, based on a maximum port velocity of 20-ft/s ranges from 15 gpm in the "junior" to 11,000 gpm in the Model SR235. This velocity is at first sight somewhat high compared to conventional pipework practice. However, the high fluid velocity is very localized in the exchanger and progressively is reduced as distribution into the flow passages occurs from the port manifold. If pipe runs are long, it is not uncommon to see reducers fitted in the piping at the inlet and exit connections of high-throughput machines.

Figure 13. Variable-length plates with mixing options.

Figure 13. Variable-length plates with mixing options.

Figure 14. Throughput versus port diameter at 14 ft/s.

resistance coupled with excellent sealing properties. These qualities are achieved by specifically compounding and molding the elastomers for long-term performance in the APV Paraflow.

Since the temperatures shown are not absolute, gasket material selection must take into consideration the chemical composition of the streams involved as well as the operating cycles.

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