INTRODUCTION 



As one of several activities supporting the Nuclear Division of 

 the Naval Facilities Engineering Command in developing a large 2-kw(e) 

 undersea radioisotope thermoelectric generator, the Civil Engineering 

 Laboratory undertook in late 1972 the design optimization, construction, 

 and testing of the' necessary heat rejection modules. 



All known methods of converting heat to electric power inherently 

 iiust reject a certain amount of the available heat to the environment. 

 Because of their relatively low efficiency, thermoelectric generating 

 elements reject a relatively large amount of heat, some 28 to 30 kw for 

 a 2-kw(e) unit. The cold waters of the deep ocean are excellent for 

 receiving heat, and the potential exists for attaining a near-mexteum 

 efficiency by keeping the cold junction of the thermoelectric conversion 

 units as near the ambient ocean temperature as is practicable. The colder 

 the cold junction, the better the efficiency and, probably, the life 

 of the elements. 



The practical foundation for convection heat transfer, entirely 

 adequate for the planned use here, is well laid in extensive theoretical 

 and empirical work in the open literature. This work was specialized 

 and extended for the ocean applications in a comprehensive study conducted 

 by and for the Civil Engineering Laboratory by Braun in 1965.* This study- 

 included resolution of former discrepancies in publi'hed works and extended 

 the resulting correlations to a design method and tests in shallow and 

 deep water in the ocean off Southern California. This work so completely 

 summarizes previous efforts that it is the only reference to be used 

 nere. It is far too comprehensive to be abstracted, so its results will 

 be used directly with a minimum of discussion; they relate to design, 

 corrosion, and marine fouling of heat transfer surfaces as well as consid- 

 eration of the probable height of a heated plume over a natural convector. 



Certain assumptions are made by Braun, page 11-25 "Optimiua Fin 

 Geometry in Free Convection," some of which, while appropriate for 

 industrial heat transfer devices, were not all appropriate in this appli- 

 cation. 



Assumption: 1. Steady-state heat f]ow. Valid, and realistic in the 

 ocean. 



Assumption: 2. Homogeneous fin material and constant fin thermal 

 conductivity. Valid, at least for the first trial 

 designs. The possibility of incorporating ducting 

 (heat pipe type passages) within the fins may be 

 considered later, which would invalidate this 

 ?ssumption. 



* C. F. Braun Co., Alhambra, CA. "Study of heat transfer and fouling 

 of heat transfer surfaces in the deep ocean-final report," Contract 

 NB 3227 A, 26 November 1965. 



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