W

Plate Materials

Paraflow plates may be pressed from 304 or 316 stainless steels, Avesta 254SMO or 254SLX, nickel 200, Hastelloy B-2, C-276 or G-3, Incoloy 825, Inconel 625, Monel 400, titanium or titanium-palladium as required to provide suitable corrosion resistance to the streams being handled.

Gasket Materials

As detailed in Figure 15, various gasket materials are available as standard that have chemical and temperature where Nu is the Nusselt number hDJk, Re is the Reynolds number i>De//i, Pr is the Prandtl number Cp/z/k, De is the equivalent diameter (2x average plate gap), (fi//uw) is the Sieder—Tate correction factor, and reported values of the constant and exponents are

C = 0.15-0.40, m = 0.30-0.45 n = 0.65-0.85, * = 0.05-0.20

Typical velocities in plate heat exchangers for waterlike fluids in turbulent flow are 1-3 ft/s (0.3-0.9 m/s), but true

Approximate maximum

Gasket material operating temperature Application

Paracril (medium nitrile) 275°F (135°C) General aqueous service, aliphatic hydrocarbons

Paratemp (EPDM) 300°F(150°F) High temperature resistance for a wide range of chemicals and steam

Paradur (fluoroelastomer) 400°F (205°C) Mineral oils, fuels, vegetable and animal oils

Paraflor (fluoroelastomer) 400°F (205°C) Steam, sulfuric acids

Figure 15. Paraflow gasket guide.

velocities in certain regions will be higher by a factor of £4 due to the effect of the corrugations. All heat-transfer and pressure drop relationships are, however, based on either a velocity calculated from the average plate gap or on the flow rate per passage.

Figure 16 illustrates the effect of velocity for water at 60°F on heat-transfer coefficients. This graph also plots pressure drop against velocity under the same conditions. The film coefficients are very high and can be obtained for a moderate pressure drop.

One particularly important feature of the Paraflow is that the turbulence induced by the troughs reduces the Reynolds number at which the flow becomes laminar. If the characteristic length dimension in the Reynolds number is taken at twice the average gap between plates, the Re number at which the flow becomes laminar varies from about 100 to 400 according to the type of plate.

To achieve these high coefficients, it is necessary to expend energy. With the plate unit, the friction factors normally encountered are in the range of 10-400 times those inside a tube for the same Reynolds number. However, nominal velocities are low and plate lengths do not exceed 7.5 ft so that the term (V2)L/(2g) in the pressure drop equation is much smaller than one normally would encounter in tubulars. In addition, single-pass operation will achieve

'g 3000

0 1000 2000 3000 4000 5000 6000 7000 8000 Flow rate/passage (Ibs/h)

Figure 16. Performance details: Series HX Paraflow.

0 1000 2000 3000 4000 5000 6000 7000 8000 Flow rate/passage (Ibs/h)

Figure 16. Performance details: Series HX Paraflow.

many duties so that the pressure drop is efficiently used and not wasted on losses due to flow direction changes. The friction factor is correlated with the equations:

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