Results of performance tests on a Union Carbide sprayedbundle evaporator with High Flux titanium tubes are reported. This unit performed satisfactorily and was free of operational problems. Under nominal operating conditions (3200 gpm water flow rate, 3.2 million Btu/hr heat duty, and 40 gpm ammonia feed rate), the overall heat transfer coefficient (U 0) was found to be 760 Btu/hr• ft2"°F and the ammonia-side and waterside coefficients were 4600 and 1300 Btu/hr"ft2"°F, respectively. The overall •water-side pressure drop in the heat exchanger was 4.0 psi; and the vapor quality measured at various heat duties and ammonia feed rates was 99.2 ±0.25%. Variations in heat duty (frQm 2.4 million-4.0 million Btu/hr) and ammonia inlet temperature (from 52-72°F) did not affect the value of U 0 , nor did changes in ammonia feed rate in the range of 40-100 gpm. However, a minimum ammonia feed rate below which U 0 decreased sharply was observed; this corresponded to a local tube loading of 20 lb/hr•ft and was essentially independent of heat duty. Finally, contact between the liquid ammonia and the High Flux surface under nonboiling .conditions appeared to deactivate nucleation sites, reducing U 0 to <700 Btu/hr•ft2"°F. The deactivated surface could be reactivated by drying out the tubes while maintaining warm water flow.

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The Argonne Heat Exchanger Test Facility was constructed to test promising designs for OTEC heat exchangers. The facility has a nominal rating of 1 megawatt thermal and comprises separate loops for warm water, cold water, and ammonia. Since 1978 a total of 21 tests have been carried out on 13 different heat exchangers. Much valuable information has been generated. Future plans include additional tests in support of the OTEC Pilot Plant program and possibly the installation of a separate loop for testing of the OTEC opencycle concept. Related efforts at ANL include studies of biofouling and corrosion and the development of complete criteria for the specification of OTEC heat exchanger systems.BACKGROUND

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