COMPARING PLATE AND TUBULAR EXCHANGERS
In forming a comparison between plate and tubular heat exchangers, there are a number of guidelines which will generally assist in the selection of the optimumexchanger for any application. In summary, these are:
1. For liquid/liquid duties, the plate heat exchanger usually has a higher overall heat
transfer coefficient and often the required pressure loss will be no higher.
2. The effective mean temperature difference will usually be higher with the plate
heat exchanger.
3. Although the tube is the best shape of flow conduit for withstanding pressure, it is
entirely the wrong shape for optimum heat transfer performance since it has the
smallest surface area per unit of cross sectional flow area.
4. Because of the restrictions in the flow area of the ports on plate units, it is usually
difficult, unless a moderate pressure loss is available, to produce economic designs
when it is necessary to handle large quantities of low-density fluids such as vapors
and gases.
5. A plate heat exchanger will usually occupy considerably less floor space than a
tubular for the same duty.
6. From a mechanical viewpoint, the plate passage is not the optimum, and gasketed
plate units are not made for operating pressures much in excess of 300 PSIG.
7. For most materials of construction, sheet metal for plates is less expensive per
unit area than tube of the same thickness.
8. When materials other than mild steel are required, the plate will usually be more
economical than the tube for the application.
9. When mild steel construction is acceptable and when a close temperature
approach is not required, the tubular heat exchanger will often be the most
economic solution since the plate heat exchanger is rarely made in mild steel.
10. Plate heat exchangers are limited by the necessity that the gasket be elastomeric.
Even compressed asbestos fiber gaskets contain about 6% rubber. The maximum
operating temperature therefore is usually limited to 500°F.
