OTEC performance tests of the Union Carbide flooded-bundle evaporator

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Abstract
Results of performance tests conducted on a Union Carbide flooded-bundle evaporator with High Flux titanium tubes are reported. At design operating conditions (a heat duty of 3.2 million Btu/hr, an inlet water temperature of 80/sup 0/F, and a water flow rate of 3200 gpm) the steady-state value of the overall heat transfer coefficient (U/sub 0/) was found to be 785 Btu/hr ft/sup 2/ /sup 0/F, and the ammonia-side and water-side heat transfer coefficients were 4800 and 1400 Btu/hr ft/sup 2/ /sup 0/F, respectively. The water-side pressure drop was 2.7 psi. Variations in heat duty (+-25%) and liquid ammonia feed temperature (over the range of 48 to 64/sup 0/F) did not affect thermal performance significantly. On the other hand, U/sub 0/ was reduced appreciably by operational shutdowns during which nonboiling ammonia remained in contact with the High Flux surface for periods of 30 minutes or more. During a one-hour shutdown the value of U/sub 0/ decreased to 690 Btu/hr ft/sup 2/ /sup 0/F, and values as low as 600 Btu/hr ft/sup 2/ /sup 0/F were reached for longer shutdowns. Such contact appears to deactivate some of the nucleate boiling sites, thus reducing the heat transfer coefficient. Although operation of the evaporatormore » under boiling conditions reverses this effect, reactivation takes place much more slowly than deactivation. Procedures for avoiding this problem in the operation of the High Flux flooded-bundle evaporator are given. « less

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