| Summary: | A miniature reciprocating expander is being developed as part of a larger program
to develop a heat actuated heat pump for portable applications. By utilizing the higher
energy density of liquid hydrocarbon fuels relative to batteries, a heat actuated heat pump
would be able to provide cooling for much longer than motor driven units of equal
weight. A prototype expander has been constructed and demonstrated to produce up to
22 W of shaft power at 2500 rpm using 60 psig, room temperature nitrogen as the input.
Assuming adiabatic conditions, the expander appears to operate at up to 80% isentropic
efficiency. However, when heat inflow to the expander is accounted for, the resulting
polytropic efficiency is about 10% lower. In addition to experimental results, models of
expander performance with different loss mechanisms are presented. These mechanisms
include over- and under-expansion, in-cylinder heat transfer, clearance volume, friction,
and valve pressure drop. === Graduation date: 2005
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