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EXPERIMENTAL INVESTIGATION ON IMPINGEMENT HEAT TRANSFER FROM
RIB ROUGHENED SURFACE WITHIN ARRAYS OF CIRCULAR JET:
Effect of Geometric Parameters
Chang Haiping Zhang Jingyu
Department of Power Engineering
Nanjing University of Aeronautics and Astronautics
210016 Nanjing, CHINA
Huang Taiping
School of Engineering, Xiamen University
361005 Xiamen, CHINA
ABSTRACT
m
Impingement heat transfer from rib roughened surface within
two-dimensional arrays of circular jet with initial crossflow has been
investigated experimentally. The configurations considered are
intended to simulate the impingement cooled midchord region of the
gas turbine airfoils in case where an initial crossflow is present.
Many factors affect the heat transfer. The relative positions of the jet
hole to the ribs and the geometric parameters have the significant
effect on the heat transfer characteristics and have been
experimentally studied. The investigation on the effect of the relative
position of the jet hole to the ribs has been presented in an other
paper. The effects of the geometric parameters such as jet hole
spacing, jet-to-surface spacing, rib pitch-to-height ratio and rib
height-to-hole diameter ratio on the heat transfer characteristics are
considered in this paper. The experimentation is conducted under the
conditions of Reynolds number 7,000-15,000 and the crossflow-to-jet
mass flux ratio based on each channel/jet hole area 0--0.5. With three
jet hole spacing to jet hole diameter ratios, five jet-to-surface
spacings, three rib pitch-to-height ratios and three rib height-to-hole
diameter ratios, a great number of experimental data has been
obtained. Based on this, the effects of the geometric parameters on
the heat transfer characteristics have been obtained qualitatively and
quantitatively. It can be used for evaluating the efficiency of the
impingement heat transfer.
Nu
NOMENCLATURES
A
Cp
d
e
Gc
Gj
Heat transfer area
Specific heat
Jet hole diameter
Rib height
Crossflow mass flux average over channel cross-sectional
area at entrance to individual spanwise row domain
Jet mass flux at individual spanwise row based on jet
hole area
p
Pr
Q
Q*
Ref
T
Tmi
Tri
Twi
xn
Xn
yn
In
zn
Zn
dT*
S,
A
A,
p
subscript
C
Mass flux
Average Nusselt number
Rib pitch
Prandtl number
Convective heat flux
The heat dissipation
Jet Reynolds number
Temperature
Mixed temperature in the impinging cavity of each
copper segment
Fluid reference temperature
Average surface temperature of segment
Jet hole spacing in x direction
Nondimensional jet hole spacing in x direction, xn/d
Jet hole spacing in y direction
Nondimensional jet hole spacing in y direction, yn/d
Jet-to-surface spacing
Nondimensional jet-to-surface spacing, zn/d
Temperature difference between two sides of the
asbestos sheet.
thickness of asbestos sheet
conductive coefficient
conductive coefficient of asbestos sheet
Dynamic viscosity
Crossflow
Jet
INTRODUCTION
In high performance turboengines, the internal cooling for gas
turbine airfoils is very important because the gas temperature is too
high for the material of guide vane and blade to withstand without
proper cooling. The impingement heat transfer from rib roughened
surface is an effective approach for heat exchanging. This is of
Presented at the International Gas Turbine & Aeroengine Congress & Exhibition
Stockholm, Sweden — June 2–June 5, 1998
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interest not only in gas turbine but also in numerous industrial
applications such as electronic components and some aspects of
drying and evaporation, etc. because many surfaces which must be
cooled or heated are not smooth. The investigation here is intended to
include the flow and heat transfer characteristics of the jet impinging
on the rib roughened surface with initial crossflow for simulating the
impingement cooled midchord region of the gas turbine airfoils in
case where an initial crossflow is present.
Significant research works have been done by many researchers
on the impingement heat transfer and augmented heat transfer.
Kercher and Tabakofl'(1970) researched the heat transfer within an
array of impinging jets with small spacing-to-diameter ratio.
Hollworth and Berry(1978) studied the heat transfer within an array
of impinging jets with large spacing-to-diameter ratio without initial
crossflow. Florschuetz et al. (1981) and Florschuetz et al. (1984)
researched the heat transfer within arrays of impinging jets with the
initial crossflow. Obot and Trabold(1987) researched the effect of the
nondimenional jet-to-surface Zn/d on the heat transfer. The
augmented heat transfer by complex geometric surface has also been
investigated by many researchers. Hong and Hsieh(l 993) studied the
effect of the staggered and inline ribs on the flow and the heat
transfer characteristics. Han and Park(1988), Han et al. (1989) and
Han et al. (1991) researched the augmented heat transfer in
rectangular channel with parallel, crossed and V-shaped ribs.
Koyelev(1978) stated that the combination of the impingement heat
transfer and augmentation of the roughened surface will enhance the
heat transfer efficiency and reduce the coolant consumption. Obot
and Trabold(1987) and Jiang(1990) researched the impingement heat
transfer within arrays of circular jets and stated that the heat transfer
characteristics for the jet impinging on the rib roughened surface is
different from that on the smooth surface, and it is considerably
affected by the jet-to-surface spacing. Chang et al. (1996b) studied
the flow behavior by flow visualization and showed that the initial
crossflow, the relative position of the jet hole to the ribs and the
geometric parameters have a considerable effect on the flow behavior,
and it certainly will affect the heat transfer characteristics. The
effects of the initial crossflow and the relative position of the jet hole
to the ribs on the impingement heat transfer from rib roughened
surface within arrays of circular jets have been revealed by Chang et
al. (1996a) and Chang et al. (1997). In this paper, the effect of the
geometric parameters on the impingement heat transfer from rib
roughened surface within arrays of circular jets has been
experimentally studied.
EXPERIMENTAL FACILITY
The experimental facility is consisted of three parts: the
impingement jet system, the initial crossflow system and the
interchangeable geometry test section . The air of the impingement
1.jet plate, 2.rib roughened surface, 3.constantan heater, 4.insulation
layer, 5.a board for fixing rib roughened surface, 6.the asbestos
sheets, 7.the plenum, 8.initial crossflowentrance, 9.the spacer.
Fig. 1. The scheme of the geometrically interchangeable
test section.
jet system comes from the air compressor and passes through a plate
orifice meter and a manually operated valve for measuring and
regulating the flow rate. Afterwards, the air flows into a plenum
chamber then through the jet plate impinges on the rib roughened
surface. Another part of air passes through a by-pass pipe and a
manually operated valve for regulating the crossflow rate, then
through a rotometer for measuring the crossflow rate. Afterwards, the
airflow passes through a stabilizer then enters into the test section as
initial crossflow.
Fig. 1 shows the schema of the geometrically interchangeable test
section. The main part of the test section includes the jet plate 1, the
impingement plate with rib roughened surface 2, the electric heater 3
and the thermal insulation layer 4. The jet plates and the rib
roughened surfaces are changeable to form the different geometric
parameters. The rib roughened surface consists of 6 segments of
copper plate with thickness 10 mm. There are 6 pieces of asbestos
sheet between the copper segments for thermal insulation. Under the
copper plate, there are 6 pieces of constantan electric heater for
heating each copper segment independently. A layer of asbestos
covers the constantan sheets for insulation.
The geometric parameters of the test models are intended to
simulate the midchord region of the gas turbine airfoils. By changing
the jet plate and the rib roughened surface, the values of Zn, Xn, e/d
and p/e can be changed to meet the requirement.
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The Reynolds number of the jet is defined as
Re j =
GJ •d
'
(1)
For a given Reynolds number Rej. Gj can be determined under
certain parameter of d and p. Gj can be obtained by the manually
operated valve in accordance with the rotometer.
Under this condition, Gc can be determined in accordance with
the given value of Gc/Gj. Then, the manually operated value
regulates the crossflow mass flux to meet the requirement.
The data obtained from the measurement in the experiment are
reduced and the heat transfer characteristics can be obtained.
The local Nusselt number is defined as:
(O - O*) • d(2)
Nu _A•(T,,
-T, )•A
;
;
_
;
(3)
The heat dissipation Q* can be calculated as:
Q* 2 S AT * A
SS
The reference temperature Tri is defined as:
T,
=(Tmi +Tj )/2
(4)
where the mixed temperature in the impinging cavity of each copper
segment is determined as follows
1. thermocouple 2. asbestos sheet
Fig. 2 Impingement plate and thermocouple arrangement
M.
Tin; =(m ' T' C p (T^)+6' iTi C p (TJ )+i 6)/
Xn=Yn=5,7.5,10
Zn = 1.5, 2, 3, 4, 5
[
(me + m.
)Cp ( Tmi)
(5)
p/e = 5, 7.5, 9, 10, 12
e/d = 0.75, 1.15, 1.5
The relative position of the jet hole to the ribs has a significant
effect on the heat transfer characteristics and has been studied by
Chang et al (1997). In this study, the first line of jet always aim at p/2
in front of the first rib. The relative position of other jets to the ribs
are different and depend on the test models.
The temperature at rib roughened surface is measured by 12
thermocouples. These thermocouples are fixed on the surface of each
copper segment individually through the holes of 0.5 mm diameter as
shown in Fig. 2. The total temperature of the jet and the crossflow are
measured by thermocouples. Two thermocouples are fixed at each
side of the asbestos sheet for measuring the temperature difference.
Then, the heat dissipation can be calculated.
The heat flux is adjusted by a silicon-controlled rectifier and the
total input to the copper plate is obtained by the measured electric
current and voltage.
EXPERIMENTAL PROCEDURE AND DATA
REDUCTION
The experimentation is executed under certain condition of the
geometric and flow parameters. The geometric parameters are
determined by the fixed model, the jet plate and the rib roughened
surface. With the fixed jet plate and the rib roughened surface, the
geometric parameters such as Xn, Yn, Zn, p/e, and e/d are determined.
The flow parameters such as Rej. Gc/Gj are calculated before the
starting of the experiment.
The average Nusselt number Nu will be
Nu=ZN
u '
i=1,2.......6
(6)
=i 6
EXPERIMENTAL RESULTS AND DISCUSSION
For the impingement heat transfer from rib roughened surface
within arrays of circular jets with initial crossflow, there are two
main contributions to the average Nusselt number. The first one is
the impingement cooling and the other is the convective heat transfer
by the crossflow. When the crossflow is little, it just plays the role in
disturbing the impingement cooling and can not enhance the
convective heat transfer. When the crossflow is large, the convective
heat transfer will be enhanced due to the disturbance by the ribs,
therefore, the heat transfer characteristics will be improved.
As well known, the heat transfer characteristics is Rej dependent.
Generally, Nu increases as Rej increases as can be seen later.
Emphasis here in this paper is put upon the effect of the
geometric parameters on the heat transfer characteristics. The
influences of Rej and Gc/Gj on these effects are considered.
Effect of Zn
The jet-to-surface spacing, Zn, has a significant effect on the heat
transfer characteristics. It can be seen from Fig. 3, that the values of
Nu for Zn=2.0 are a little lower than that for Zn=1.5, and are
evidently higher than that for Zn=3.0 under the same other conditions
( the same Rej. Gc/Gj and other geometric parameters). The effect of
the jet impinging on the roughened surface is weak when Zn is too
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large. Therefore, Nu decreases as Zn increases.
For large Zn, when Gc/Gj is low, Nu decreases as Gc/Gj increases,
while when Gc/Gj is high, Nu increases as Gc/Gj further increases.
This is similar to the impingement heat transfer from smooth
surface(Chang et al., 1997). For small Zn, the effect of convective
heat transfer is enhanced due to the high velocity of crossflow at the
same Rej. Therefore, Nu increases monotonically as Gc/Gj
Effect of Xn and Yn
In this experimentation, the jet holes are arranged inline and the
jet hole spacing along streamwise (chordwise), Xn, is equal to that
along the spanwise, Yn.
Fig. 4 shows the effect of Xn (Yn) on Nu under the certain
conditions of Rej. Gc/Gj and other geometric parameters. Obviously,
Xn has a significant effect on Nu. For a certain value of Rej, the
increases.
140
Xn =7.5
Zn =1.5
e/d=10
e d=0.75
120
140-
00000 Rej=7000
• .. Rej=8500
--^^- Rej=12000
""' Red =12000
. ... .ReJ=15000
120
00000 Rej=7000
Xn =5
g000 ❑ Rel=8500
Zn =2
•*P&• Re =10000
p/d 0.
Rej=12000
• ..a
e/d=0.75 &A.
W
Rej=15000
100
100
Z
80
80
60
60
TTg
40
40
20 20
0.0
0.1
0.2
0.3
0.4
0.5
-
0
0.0
Gc/Gj
1401 Xn =7.5 Q.Q.Q Rej=7000
❑ ooa ❑ Rej=8500
Zn =2
Rej=10000
p/e=10
120
■ ■■■■ Rej=12000
e/d=0.75
.
....
ReJ=15000
100
140
120
0.1
0.2
0.3
Gc/Gj
0.4
0.5
Xn =7.5Q-o 0 Rej=7000
Zn =2g0000 Rej=8500
•^"• Rej=10000
p/e=10
M EMO Rej=12000
e/d=0.75
4AA" Rej=15000
100
80
Z
80
60
60
40
40
20
0.0
0.1
0.2
0.3
0.4
0.5
20
0.0
Gc/Gj
140
0Q
140
Rej=7000
Red =8500
• iAt• Re)=10000
' EN'• Re 12000
4.ReJj= 15000
Xn =7.5
.Q
Zn =3
120- p/e=10
e d=0.75
/
1 00
120
0.3
Gc/Gj
0.4
0.5
g0000 Rej=7000
Xn =10
Zn =2Q2 Rej=8500
e t&" Re1=10000
e=10
■^a^^ Re=12000
075 AA
e /d=.
AA_Re
d1= 15000
80 -
60
60
40
40
0.1
0.2
100
80
20
0.0
0.1
0.2
0.3
Gc/Gj
0.4
20
0.0
0.5
0.1
0.2
0.3
Gc/Gj
0.4
0.5
Fig. 4 the effect ofXn on Nu
Fig. 3 The effect of Zn on Nu
4
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decrease of Xn means the increase of the coolant flux on impinging
surface. Therefore, the heat transfer efficiency is improved as Xn
decreases, so that, Nu increases. For large Xn, Nu increases as Gc/Gj
increases due to the enhancement of convective heat transfer of the
crossflow. However for small Xn, when Gc/Gj is little, Nu decreases
as Gc/Gj increases, until Gc/Gj is large, Nu increases as Gc/Gj
further increases owing to the strong effect of the crossflow on the
impingement heat transfer.
140
Xn =10Q_O
0
Rej=7000
120
Zn =3c000 ❑ Rej=8500
p/e=10O" Rej =10000
e/d=0.75
■ oEN0 Rej= 12000
&A.A. Rej=15000
100
Z So
Effect of pie
It can be seen from Fig. 5 that p/e has a little effect on Nu. When
60
Gc/Gj =0, Nu for small p/e is little higher than that for large p/e.
With the increase of Gc/Gj, Nu considerably increases for small p/e
due to the disturbance of the crossflow compared to that for large p/e.
40
20 -1-
0.0
0.1
0.2
0.3
0.4
0.5
Gc/Gj
140
Xn =10 Q.2 00 Rej=7000
❑ oono Rej =8500
Zn =2
120
p/e=7.5
e/d=0.75
•stz0 Rej=10000
■ ■ ■ ■ ■ Red= 12000
&& *.# Rej= 15000
140
100
z
^
120
'/
80
100
60
80
40
60
20 'r
0.0
0.1
0.2
0.3
0.4
Xn =1000000 Rej=7000
a ooa ❑ Red=8500
Zn =3
p/e=10•tW Rej=10000
e/d=1.15
■ M E M. Rej= 1 2000
&^& Rej= 15000
40
0.5
Gc/Gj
20
0.0
0.1
0.2
0.3
0.4
0
Gc/Gj
140
120
Xn =100Q 0 Rej=7000
°-nnog Rej=8500
Zn =2
p/e=10W.. S Rej=10000
e/d=0.75 ■ M'O• Rej= 12000
4.... Rej= 15000
Fig. 6 The effect of e/d on Nu
100
80
The heat transfer characteristics obtained in this study is in quite
good agreement with that by Florschuetz et al (1981, 1984) while has
a little higher Nusselt number. This is due to the different
arrangement of the thermocouples and the different definition of the
reference temperature. In this study, the thermocouples are slightly
pressed on the surface in order to avoid protruding from surface.
Therefore, the temperature measured is a little lower than the surface
temperature, but is much closer to the surface temperature than that
measured by the thermocouples buried in the surface. The reference
temperature is defined by equation (4). It may be a little higher than
adiabatic temperature (Obot and Trabold, 1987).
The correlation equation for impingement heat transfer rib
roughened surface in accordance with the experimental data can be
60
40
20
0.0
0.1
0.2
0.3
0.4
0.
Gc/Gj
Fig. 5 The effect of p/e on Nu
Effect of e/d
This non-dimensional geometric parameter connects the
geometric parameters between jet plate and impingement plate. It is
rather complicated to analyze the interaction of these parameters in
detail. Fig. 6 shows the general effect of e/d on Nu. It can be seen that
Nu for e/d=0.75 is slightly higher than that for e/d=1.15, especially at
high Rej and Gc/Gj. Therefore, a suitable small e/d is preferred for
improving the heat transfer characteristics.
expressed as
Nu= f(Gc/Gj,R ej,Xn,Yn,Zn,e/d,p/e,Pr ) (7)
These parameters affect the heat transfer characteristics in
different ways. By analyzing the experimental results, the effect of
Xn, Yn, p/e, e/d and Rej on Nu is monotonically positive or negative
5
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Inline Ribs", Journal of Heat Transfer, Vol. 115, pp. 58-65.
Jiang Jun, 1990, "Experimental Investigation on the Comparison
of the Jet Impinging on Smooth and Roughened Surfaces"(in
Chinese), Master Thesis, Nanjing Univ. of Aero. & Astro., Nanjing.
Kercher, D. M., and Tabakoff W., 1970, Heat Transfer by a
Square Arrays of Round Air Jets Impinging Perpendicular to a
Surface Including the Effect of Spent Air, ASME Journal of
Engineering for Power, Vol. 92, No. 1, pp. 73-82.
Koyelev, S. Z., 1978, "Thermal Situation of Structural
Elements of AeroEngines"(in Russian), Machine Press.
Obot, N. T., and Trabold, T. A., 1987, "Impingement Heat
Transfer within Arrays of Circular Jets. Part I", Journal of Heat
Transfer, Vol. 109, pp. 872-879.
respectively. The effect of Gc/Gj on Nu is not monotonic. The effects
of the flow and geometric parameters on Nu are interactive.
Therefore, the correlation equation for impingement heat transfer
from rib roughened surface is quite complicated. It is not in the scope
of this paper and will be presented in another paper.
CONCLUSIONS
The geometry has a significant effect on the impingement heat
transfer from rib roughened surface within two dimensional arrays of
circular jet with initial crossflow. The effects of the jet hole spacing,
the jet-to-surface spacing, the rib pitch-to-height ratio and the rib
height-to-hole diameter ratio on the heat transfer characteristics have
been experimentally investigated.
Based on the numerous experimental data, the effects of the
geometric parameters on the heat transfer characteristics have been
obtained qualitatively and quantitatively. It can be used for
evaluating the efficiency of the impingement heat transfer from rib
roughened surface within two dimensional arrays (inline) of circular
jet with/without initial crossflow for the structures with different
geometric parameters
REFERENCES
Chang Haiping, Zhang Dalin, Han Dong and Huang Taiping,
1996a, "Impingement Heat Transfer From Rib Roughened Surface
Within Arrays of Circular Jet, Part I : The Effect of the Initial
Crossflow", Transactions of Nanjing University of Aeronautics and
Astronautics, Vol. 13, pp. 61-67.
Chang Haiping, Zhang Jingyu, Huang Taiping and Zhang Dalin,
1996b, "Flow Visualization of a Jet Impinging on a Ribbed Surface
with Crossflow", ASME TUBO ASIA'96, ASME paper 96-TA-003.
Chang Haiping, Zhang Dalin, and Huang Taiping, 1997,
"Impingement Heat Transfer From Rib Roughened Surface Within
Arrays of Circular Jet: The Effect of the Relative Position of the Jet
Hole to the Ribs", ASME TUBO EXPO'97, ASME paper 97-GT331.
Florschuetz, L. W., Truman, C. R., and Metzger, D. E., 1981,
"Streamwise Flow and Heat Transfer Distributions for Jet Array
Impingement With Crossflow", ASME Journal of Heat Transfer, Vol.
102, pp. 337-342.
Florschuetz, L. W., Metzger, D. E., and Su, C. C., 1984, "Heat
Transfer Characteristics for Jet Array Impingement With Initial
Crossflow", ASME Journal of Heat Transfer, Vol. 106, pp. 34-41.
Han, J. C. and Park, J. S., 1988, "Developing Heat Transfer in
Rectangular Channels with Rib Turbulators", Journal of Heat and
Mass Transfer, Vol. 31.
Han, J. C. and Lei, C. K., 1989, "Augmented Heat Transfer in
Rectangular Channels of Narrow Aspect Ratio with Rib
Turbulators", Int. Journal of Heat Transfer, Vol. 32.
Han, J. C. and Zhang, Y. M., 1991, "Augmented Heat Transfer in
Squared Channels with Parallel, Crossed and V-Shaped Angled
Ribs", Journal of Heat Transfer, Vol. 113.
Hollworth, B. R. and Berry, R. D., 1978, "Heat Transfer From
Arrays of Impinging Jets with Large Jet-to-Jet Spacing", Transactions
of ASME, Vol. 100, pp. 337-342.
Hong, Yinb Jong and Hsieh, Shou-Shing, 1993, "Heat Transfer
and Friction Factor Measurements in Ducts with Staggered and
6
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