High performance turbine airfoils are typically cooled with a combination of internal cooling channels and impingement. In such applications, the jets impinge against a target surface, and then exit along the channel formed by the jet plate, target plate, and side walls. Local convection coefficients are the result of both the jet impact, as well as the channel flow produced from the exiting jets. Numerous studies have explored the effects of jet array and channel configurations on both target and jet plate heat transfer coefficients. However, most current studies use the plenum temperature as the reference temperature in heat transfer calculations. This presents some difficulty to designers who need to determine heat transfer rates based on the local bulk temperatures. This paper examines three different methods to determining the local bulk temperature in a steady state impingement channel heat transfer experiment. The various methods will be compared based on their ease of application as well as their accuracy in describing the results. One method proves to be the most accurate, while another proves to be more easily implemented. The methods are compared for a single case previously studied, on a 15 hole, single row impingement channel, with dimensions of $X/D=5$, $Y/D=4$, $Z/D=1$ and 3, and an average jet based Reynolds number of 17,000 and 45,000. Effects due to the choice of the reference temperature in heat transfer calculations are shown to cause significant variations in the calculated heat transfer coefficients. These results point to a transition between different flow regimes in the post-impingement flow.

1.
Florschuetz
,
L. W.
,
Truman
,
C. R.
, and
Metzger
,
D. E.
, 1981, “
Streamwise Flow and Heat Transfer Distributions for Jet Array Impingement With Crossflow
,”
ASME J. Heat Transfer
0022-1481,
103
, pp.
337
342
.
2.
Al-Aqal
,
O. M. A.
, 2003, “
Heat Transfer Distributions on the Walls of a Narrow Channel With Jet Impingement and Cross Flow
,” Ph.D. thesis, University of Pittsburgh, Pittsburgh.
3.
Chyu
,
M. K.
,
Ding
,
H.
, and
Downs
,
J. P.
, 1998, “
Determination of Local Heat Transfer Coefficient Based on Bulk Mean Temperature Using a Transient Liquid Crystals Technique
,”
Exp. Therm. Fluid Sci.
0894-1777,
18
, pp.
142
149
.
4.
Kercher
,
D. M.
, and
Tabakoff
,
W.
, 1970, “
Heat Transfer by a Square Array of Round Air Jets Impinging Perpendicular to a Flat Surface Including the Effect of Spent Air
,”
ASME J. Eng. Power
0022-0825, Jan., pp.
73
82
.
5.
Hilgeroth
,
E.
, 1965, “
Heat Transfer for Jet Flow Perpendicular to the Exchange Surface
,”
Chemie-Ing.-Techn.
,
37
(
12
), pp.
1264
1272
.
6.
Ricklick
,
M.
,
Kersten
,
S.
, and
Kapat
,
J. S.
, 2008, “
Effects of Channel Height and Bulk Temperature Considerations on Heat Transfer Coefficient of Wetted Surfaces in a Single Inline Row Impingement Channel
,” ASME Paper No. HT2008-56323.
7.
Ricklick
,
M.
,
Kersten
,
S.
, and
Kapat
,
J. S.
, 2008, “
Effects of Circumferential Heating Variations and Channel Height on Heat Transfer Coefficient of Wetted Surfaces in a Single Inline Row Impingement Channel
,” ASME Paper No. IMECE2008-67787.
8.
Florschuetz
,
L. W.
, and
Isoda
,
Y.
, 1983, “
Flow Distributions and Discharge Coefficient for Jet Array Impingement With Initial Crossflow
,”
ASME J. Eng. Power
0022-0825,
105
, pp.
296
304
.
9.
Incropera
,
F. P.
, and
DeWitt
,
D. P.
, 2002,
Fundamentals of Heat and Mass Transfer
,
Wiley
,
New Jersey
, pp.
491
493
.