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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Mechanical Engineering

Year Degree Awarded

Summer 2014

First Advisor

Robert Hyers

Second Advisor

David Schmidt

Third Advisor

Sanjay Arwade

Subject Categories

Heat Transfer, Combustion | Propulsion and Power | Systems Engineering and Multidisciplinary Design Optimization

Abstract

The desire to explore deep space destinations with high-power and high-speed spacecraft inspired this work. Nuclear Electric Propulsion (NEP), shown to provide orders of magnitude higher specific impulse and propulsion efficiency over traditional chemical rockets, has been identified as an enabling technology for this goal. One of large obstacle to launching an NEP vehicle is total mass. Increasing the specific power (kW/kg) of the heat radiator component is necessary to meet NASA’s mass targets.

This work evaluated a novel lightweight, high-temperature carbon fiber radiator designed to meet the mass requirements of future NEP missions. The research is grouped into three major sections: 1) a micro-scale radiation study, 2) bench-scale experimental and analytical investigations, and 3) large-scale radiator system modeling.

In the first section, a Monte Carlo ray tracing model built to predict the effective emissivity of a carbon fiber fin by modeling the radiation scattering among fibers showed that the added surface area of the fibers over a flat fin surface increases the effective emissivity of the radiator area by up to 20%. The effective emissivity increases as the fiber volume fraction decreases from 1 to about 0.16 due to increased scattering among the fibers. For fiber volume fractions lower than 0.10, the effective emissivity decreases rapidly as the effect of radiation transmission becomes significant.

In the second section, thermal analyses of the carbon fiber radiator fin predicted that these radiators could meet NASA’s performance targets by reducing the areal density to 2.2 kg/m2 or below. These models were validated through experimental tests conducted on sub-scale radiator test articles. This work elevated the technology readiness level (TRL) of the carbon fiber radiator fin from level 2 to 4.

In the last section, a radiator system model for an NEP vehicle was built to analyze the dependence of radiator mass on selected system parameters. The model was used to minimize the radiator mass for test cases. The results predicted that carbon fiber fins operated near 600°C reduced the radiator mass by a factor of 7 as compared with traditional radiators operating near 100°C. This significant mass-reduction could enable future NEP systems.

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