No abstract

No abstract

The operation of a LN2 cryogenic heat pipe has been demonstrated experimentally in the range 78 K to 90 K. This heat pipe involves a totally new wick concept, viz., the “parallel capillary channel” wick, which affords a heat flux capability an order of magnitude higher than possible with the more conventional heat pipe wick structures. The experimental measurements were performed utilizing specially designed cryogenic heat pipe evaluation equipment which permitted heat flux measurements accurate to within 8 percent. The design and optimization of the cryogenic heat pipe is discussed including a description of the BCL generalized heat pipe computer program. A comparison of experimental data with analytical predictions is also provided.

A thermal conductivity measurement technique has been developed based on a novel design employing an ultrafine (0.02 cm dia) “traversing” thermocouple. This technique features the rapid determination of thermal conductivity as a function of temperature for specimens operating in the range from 300 up to 1200 K. In contrast to conventional “comparative” methods of thermal conductivity measurement, the present approach requires only one equilibrium condition, viz., the condition in which the specimen is maintained between the two temperature extremes of interest. The traversing-thermocouple measurement technique also permits the accommodation of a wide range of specimen sizes (e.g., 0.25 to 1.3 cm in diameter and 0.7 to 3.0 cm in length) and measurements accurate to within 5 to 7 percent. Although initially developed for use with semiconductors, the measurement technique is equally well suited to semimetals, metals, and insulators.

SPACECRAFTangles; a repetition of the analysis presented here at nozzle vector angles up to 15° would be required to explore this potential. This paper represents a comparative analysis of some of the technical considerations surrounding the use of Cm-244 and Pu-238 heat sources in radioisotope thermoelectric generators (RTGs). The principal considerations include radiological shielding, ground handling, and generator performance characteristics. The paper also describes a novel approach to RTG design and qualification which would facilitate the use of Cm-244 heat sources. This approach, which involves hermetically staled bellows-encapsulated thermoelectric elements, also features the potential for increased generator output pctwer stability and reliability and lower converter costs accruing from the advantages of a standardised approach to generator design, fabrication, and qualification.