Feasibility of Isotopic Power for Manned Lunar Missions. Volume 1. Summary. Page: 42 of 61
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lem was eased to a great extent by placing a spiral turbulator within the
tubing causing the vapor and mercury droplets to be thrown against the
boiler tubes. In a mercury vapor system, it is necessary to significantly
superheat the vapor before any expansion takes place. This is caused
by the negative slope of the temperature entropy diagram at points of
high entropy. Any expansion decreases the quality of the vapor. Thus,
superheating is required or serious turbine erosion can result. This
problem requires further analysis.
The fuel capsules required for the boiler of this system were not
designed for intact re -entry or abort integrity. To meet the fuel safety
requirements this boiler must be redesigned to incorporate the integrity
and ablator materials and the operating temperatures reduced to keep
the fuel core below 18000 F. These changes will further reduce the
overall efficiency of this system.
A two-stage turbine is used for this system; the first allowing 6%
vapor admission, the second 10%. This two-stage turbine was required
to optimize system performance at this power level. Reference to the
temperature entropy diagram (Volume 8) indicates that significant super-
heating would be required for the vapor quality to remain 100% as the
vapor enters the second-stage turbine. Stated in another way, as vapor
expansion takes place in the first-stage turbine, the tendency is for the
vapor to go through the saturation curve and be less than 100% quality.
This vapor must then drive the second-stage turbine without superheat-
ing. It is felt that this is an optimistic assumption and certainly requires
Hydrodynamic liquid film bearings are proposed for the mercury
Rankine cycle. A spiral groove axial thrust bearing is proposed while
a three-sector channel bearing takes the radial loads. Thompson has
run life tests up to 6500 hours on such bearings without failure.
c. Heat rejection system
One of the major problems associated with a Rankine cycle in a zero
g environment is that of adequate and stable condensation of the vapor
phase back to the liquid phase. Systems utilizing this conversion tech-
nique have generally proposed a tapered tube condenser. This concept
essentially assumes that liquid droplets form on the condenser walls,
converge into sheets of liquid and, as the tube diameter decreases,
eventually form a stable interface which does not vary in position within
the tube. A number of tests have been run on this concept, notably by
Thompson, Aerojet General, and Sundstrand, in various conditions of
condenser attitude ranging from one g in the vertical position to the
horizontal position to a slightly negative g field in a tilted position. In
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Feasibility of Isotopic Power for Manned Lunar Missions. Volume 1. Summary., report, January 1, 1964; Baltimore, Maryland. (https://digital.library.unt.edu/ark:/67531/metadc1032333/m1/42/: accessed May 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.