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Chapter One APPLICATIONS Conventionalheat exchangers use copper alloy tubes to transport seawater as a cooling medium. The copper-nickel tubes have high heat transfer rates, but they are subject to corrosion, erosion and fouling. The deteriorating tubes force operators to run the equipment at reduced flow rates, which in turn reduces the overall effectiveness. Composite materials offer the potential to eliminate corrosion and erosion problems, as well as reduce the weight of heat exchanger assemblies. An ongoing study by Joseph Korczynski, Code 823, NSWC, Annapolis is looking at candidate composite materials that were optimized to increase thermal conductivity, a characteristic not usually associated with these types of materials. Figure 1-32 illustrates the encouraging results of this program. Thermoplastics Figure 1-32 Ranking of Effectiveness (Allowable Stress, Conductivity over Density) of Various Materi- als Considered for Heat Exchangers [Joseph Korc- zynski, Code 823, NSWC, Annapolis] Thermosets Metal Alloys Composite piping system fire survivability has also been evaluated using glass reinforced epoxy and vinyl ester piping systems with various joining methods and under dry, stagnant water, and flowing water conditions. The results of these tests have been compared with metallic alt.ernatives For example, 90-10 Cu-Ni Sil-brazed joints survive 2-3 minutes with dry pipe and less than 20 minutes with stagnant water in the pipe. Epoxy pipe assemblies survived less than 3 minutes in a full-scale fire when pressurized to 200 psig stagnant water. The joints failed catastrophically. However, application of a promising fire barrier around the pipe joints improved survivability time to 23 minutes, and a completely insulated assembly survived for 30 minutes with no leaks after the fire. One of the most successful Navy composites machinery program to date involves the development of a standard family of composite centrifugal pumps. The pumps employ a limited number of housing sizes, impellers, and drives to cover a wide range of pressure and flow rate requirements. The pump housing can be fabricated from glass-reinforced epoxy, vinyl ester, or polyester. High velocity erosion investigations with various fiber reinforced polymer matrix composite pump materials showed excellent corrosion-erosion performance of composites relative to gun metal bronze (widely used in marine centrifugal pumps) over a velocity range of 0 to 130 ft/sec. However, the composites did not fare as well under cavitation condition,swhere they showed generally inferior performance to the bronze. In most marine pump applications, however, cavitation is not expected to be a problem. [1-30] 37PDF Image | Marine Componsites
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