Experiments relative to heat exchangers for ocean thermal energy conversion (OTEC) systems have been completed for ammonia condensing on the outside of four aluminum tubes of three types: a smooth tube, a single (external) fluted tube, and two double (internal/external) fluted tubes. Composite heat transfer coefficients (coefficients that include vapor-side plus wall resistance) are reported for a smooth tube condensing horizontally and at various tilt angles, and for a single-fluted tube condensing vertically. Overall heat transfer data are given for both double-fluted tubes. The primary conclusions from this study were as follows: (a) smooth tube condensing performance was maximum for the horizontal orientation, where, for a given heat flux, composite coefficients were 2.1 times vertical smooth tube (1.2 m long) values; (b) a vertically oriented, single-fluted tube gave the highest performance among the tubes studied with composite condensing coefficients, at a given heat flux, up to 5.2 times the vertical smooth tube values; (c) overall performance for a tube with inside and outside flutes was 25 percent greater than observed for a tube having identical outside flutes but a smooth inside surface; (d) overall performance was virtually unchanged for a double-fluted aluminum tube as the number of external flutes was reduced from 45 to 36; and (e) overall heat transfer results from Oak Ridge National Laboratory (ORNL) double-fluted, vertical, single-tube tests were in approximate agreement with vertical, double-fluted condenser tube bundle data obtained by the Argonne National Laboratory (ANL).

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