Heat transfer in cylinder spaces is important to the performance of many
reciprocating energy conversion machines, such as gas compressors and Stirling machines.
Work over the past 10 years has shown that heat transfer driven by oscillating pressure
differs from steady state heat transfer in magnitude and in phase; in-cylinder heat transfer
under this oscillating condition can be out of phase with the temperature difference. For
studies with closed piston-cylinder gas springs, this heat transfer phase shift has been
successfully predicted with the use of a complex Nusselt number; since a complex number
has both a magnitude and a phase, a complex Nusselt number can describe the phase shift
between temperature and heat transfer. Quasi-steady heat transfer models, such as
Newton's Law of Cooling, do not predict this phase shift.
This project studied the problem of in-cylinder heat transfer with inflow-produced
turbulence. Initial tests were conducted without the generated turbulence; this enabled the
researchers to compare the results of this apparatus to previous work. Then, an orifice
plate was added to the apparatus to generate simulated inflow-produced turbulence. The
tests from this configuration were compared to the previous set, without the turbulence, to
see how inflow-produced turbulence affected heat transfer and the heat transfer related
cyclic lost work. The complex Nusselt number, which had been used in previous studies to
model non-turbulent in-cylinder heat transfer, was applied to the turbulent data as well.
The tests conducted without generated turbulence (one space experiments)
matched previous results and also extended their range to lower volume ratios and higher
oscillating speeds. These tests also demonstrated that an analytical heat transfer model
based on low volume ratios (approaching 1.0) was valid over the range from 1 to 2.
The tests conducted with the generated turbulence (two space experiments) were
compared against the results from the one space experiments. These results indicated that
the in-cylinder heat transfer was increased due to the generated turbulence. The magnitude
of the complex Nusselt number compared favorably to an analytical model of in-cylinder
heat transfer with inflow-produced turbulence.
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