Comparative Cooling of Cylinders of Nonuniform Fin Width With Tight-Fitting Baffles and With Baffles That Provide Constant Flow-Path Areas Page: 3 of 27
[25] p. : ill.View a full description of this report.
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NACA AiR FD21
NL0RDUTIC
Most of the single-cylinder cooling tests ocanducted by the ACA
to date have been made using baffles that fitted tightly against the
fin tips because tests on electrically heated cylinder barrels (refer-
ence 1) indicated that the best cooling of the barrels was obtained
with this baffle condition. The cylinders of reference 1 had fine
of constant wi.th. Fin width at any point along the fin is defined
as the shortest distance between the fin base and tie fin tip at the
point in question, Flight tests of several baffles showed, moreover,
that best heat transfer eas obtained when the baffles were placed
close to the fin tips (refer nce 2).
Recent tests by the NACA on a Wright R-1820-H engine cylinder in
conjunction with baffles (of NACA desi n), which fitted tightly against
the fin tips around the rear half of the cylinder, showed several hot
spots on the cylinder head near the exbaust ear that resulted in high
average cylinder temperatures, Exa~ination of the cylinder showed a
large variation in the width of the individual fins fran the front to
the roar of the cylinder head, especially in the area around the exhaust
ear. For the baffles in close contact with the fin tips, the variation
of width of individual fins caused a similar variation in cross-
sectional area of the individual flow paths, At points the fin were
very narrow and the restrictions were very bad, reducing the area in
same cases to one fourth of the area upstream of the restriction. It
was believed that these large reductions in freo-flow area greatly
restricted the flow and, therefore, that +he cooling was impaired in
front of and behind the res rictions, where the fin wiLdth was large
and the local mass flow pv was small. The local mass flow pv, as
referred to heroin, is the product of the density p and the velocity v.
The tight-fitting bafflos wore therefore modified to oliminate
those restrictions for the Wright cylinder. These modified baffles
gavo a constarnt free-flow area throughout coach interfin air passage by
providing varying cloaranoo botwoon the bafflos and the fin tips.
Cooling ostc of the two typos of baffle wore made on the Wright cyl-
inder mountod on a singlo-cyliuder crankcase. As a result of these
baffle tosts for the right cylinder, the two types of baffle wore also
tested on a Pratt & Whitney R-2800-21 cylindor mounted on a singlo-
cylindor arankcaso.
The detrimental offoot of rostriotions in the interfin flow paths
was also noted in roeforenco 3. The baffles of a Pratt & Whitney
R-180-4 engine were modified to eliminate some of those restrictions
with a consoquont improvement in cylinder cooling.
The purpose of the present report; is to present a camP~atscn
between the cooling obtained with tight-fitting baffles and the cooling
obtained with baffles rovisoed to givo a constant free-flow area from_I
I.-
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Schey, Oscar W.; Rollin, Vern G. & Buckner, Howard A., Jr. Comparative Cooling of Cylinders of Nonuniform Fin Width With Tight-Fitting Baffles and With Baffles That Provide Constant Flow-Path Areas, report, April 1944; (https://digital.library.unt.edu/ark:/67531/metadc61906/m1/3/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.