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DOE/NASA/51 040-33 NASA TM-82727

ASA-TM-82727 19820004 120

Jet Impingement Heat Transfer Enhancement for the GPU·3 Stirling Engine

Douglas C. Johnson, Craig W. Congdon, Lester L. Begg, and Edward J. Britt Rasor Associates, Inc.

and

Lanny G. Thieme National Aeronautics and Space Administration Lewis Research Center

October 1981

Prepared for

r to liE

t Y C Y .J ~ J 1981

LANGLEY R[S~AR':H CENTER L BRA~y. NASA

HAMPTON, VIRGiNIA

U.S. DEPARTMENT OF ENERGY Conservation and Renewable Energy Office of Vehicle and Engine R&D

L __ ~_

https://ntrs.nasa.gov/search.jsp?R=19820004120 2018-08-11T19:34:01+00:00Z

NOTICE

This report was prepared to document work sponsored by the United States Government Neither·the United States nor its agent . the United States Department of Energy . nor any Federal employees. nor any of their contractors, subcontractors or their employees . makes any warranty . express or implied. or assumes any legal liability or responSibility for the accuracy, completeness, or usefulness of any information , apparatus . product or process disclosed , or represents that its use would not infringe privately owned rights.

------------------~

Jet Impingement Heat Transfer Enhancement for the GPU-3 Stirling Engine

Douglas C. Johnson, Craig W. Congdon, Lester L. Begg, and Edward J. Britt Rasor Associates, Inc. Sunnyvale, California 94086

and

Lanny G. Thieme National Aeronautics and SpacE? Administration Lewis Research Center Cleveland, Ohio 44135

Octobe r 1 981

Work performed for U.S. DEPARTMENT OF ENERGY Conservation and Renewable Energy Office of Vehicle and Engine R&D Washington, D.C. 20545

DOE/NASA/51 040-33 NASATM-82727

Under Interagency Agreement DE-AI01-77CS51 040

SUMMARY

In support of the Department of Energy's Stirling Engine Highway Vehicle Systems Program, this investigation demonstrated the benefits resulting from enhanced combustion-gas-side heat transfer using jet impingement in the GPU-3 Stirling engine. A computer model of the combustion-gas-side heat transfer was developed to predict the effects of a jet impingement system and the possible range of improvements available. A low temperature (315°C (600°F)) pretest was run on the GPU-3 heater head to verify the jet impingement model and to improve the correlation coefficients in the model. Utilizing the pretest data in an updated model, a high temperature silicon carbide jet impingement heat transfer system was designed and fabricated.

The system model predicted that at the theoretical maximum limit, jet impingement enhanced heat transfer can: 1) reduce the flame temperature by 275°C (500°F), 2) reduce the exhaust temperature by 110°C (200°F), and 3) increase the overall heat into the working fluid by 10%, all for an increase in required pumping power of less than 0.5% of the engine power output. Initial tests on the GPU-3 Stirling engine at NASA-Lewis demonstrated that the jet impingement system increased the engine output power and efficiency by 5% - 8% with no measurable in­crease in pumping power. The overall heat transfer coefficient was increased by 65% for the maximum power point of the tests.

Preliminary cost estimates indicate that addition of jet impinge­ment to the system will cost less than $50/unit on a production basis. On the basis of improved engine performance for minimal additional cost, jet impingement is an attractive addition to the design of advanced Stirling engines.

2

INTRODUCTION

This work was performed in support of the U.S. Department of Energy's (DOE) Stirling Engine Highway Vehicle Systems Program. The NASA Lewis Resea rch Center, through Interagency Agreement DEAIOl-77CS5l040 with DOE, is responsible for management of the project under the programmatic direct ion of the DOE Office of Vehicle and Engine R&D, Conservation and Renewable Energy.

The Stirling Engine Highway Vehicle Systems Program is directed toward the development of the Stirling engine as a possible alternative to the conventional spark-ignition engine. A part of this program is development of component technology that will improve engine efficiency and performance for advanced Stirling engine systems.

Of the many factors influencing the performance of a Stirling engi ne, that of transferring the combustion gas heat into the working flu id is crucial. In a conventional Stirling engine, the heat transfer coefficient on the combustion-gas-side of the heat exchanger, coupled with the combustion gas temperature and heater-tube metal temperature, determines the amount of heater tube surface area requi red. An increase in the heat transfer coefficient allows either the flame temperature or t he heater tube surface area and engine nonswept volume to be reduced. Al though the Stirling engine has relatively low exhaus t emissions, fur ther reduction is possible if the combustion temperature is reduced.

An illustration of the jet impingement concept is presented in Figure 1. Combustion gas inside a silicon carbide jet shell is forced through holes in the shell, impinging on the heater tubes. The purpose of the directed jets is to break up the boundary layer on the surface of the tubes and thereby reduce the resistance to heat tran sfer. The hot jet shell also provides some additional radiant heat transfer to the heater tubes.

Rasor Associates has applied jet impingement heat transfer to other high temperature combustion systems (ref. 1, 2). Figure 2 shows a combustion-heated silicon carbide jet impingement shell used in thermionic converter testing and Figure 3 illustrates the effect of tailoring the heat flux. Based on this experience, a jet impingement heat transfer system was designed for the GPU-3 Stirling engine on test at NASA-Lewis. The purpose of this effort was to verify the possible application of a jet impingement system to a Stirling engine and to quantitatively demon­strate the system performance.

The primary goal of this investigation was to enhance the combustion­gas-side heat transfer using the existing heater head, thereby improving the unmodified engine performance. Once the benefits of jet impingement were verified, a follow-on project would design a heater head to take full advantage of a jet impingement system. Because a smaller amount of heater tube area would be required, the redesign would reduce the non­swept volume in the engine. This would yield a greater performance improvement than retrofitting the existing engine system.

--------'

- - - ~- --- -><- - -, ---.------~ -

DESIGN OF THE JET IMPINGEMENT SYSTEM

A. Heat Transfer Design

In order to predict the gas temperatures and heat transfer rates necessary for the design of the jet impingement system, a computer model (for a HP9825 desk-top computer) of the combustion gas flow path was developed. In comparing the model to available data, it was noted that the calculated temperatures are a strong function of the preheater effectiveness. Figures 4 and 5 show the heat balance calculated for the NASA reference run, at two different values of preheater effectiveness. Note the decrease in the flame temperature and corresponding increase in heat transfer coefficient for a decrease in preheater effectiveness. The performance of the preheater degrades during operation due to fouling, and there is a corresponding decrease in the effectiveness. Therefore, in order to make a comparison of heat transfer coefficients, tests must be made both with and without jet impingement for a constant preheater condition.

As illustrated in Figure 1, the impinging jets break up the boundary layer on the surface of the heater tubes and cause relatively high local heat transfer coefficients (ref. 3, 4). For an average jet impingement heat transfer coefficient of 880 W/m 2 °C and an average tube temperature of 773°C (1423°F), a finite element analysis of the local temperatures under the jet was performed. The results are shown in Figure 6. Although the local heat transfer coefficient varies widely under the jet, the temperature variation in this region is less than 55°C (100°F).

B. Hardware Design To contain the hot combustion gases and form the jets which impinge

on the heater tubes, a silicon carbide jet shell was designed. Figure 7 shows the GPU-3 Stirling engine heater head/jet shell assembly. As shown in Figure 8, the jets impinge directly on the heater tubes. To compensate for differences in thermal expansion between the heater head and the silicon carbide jet shell, the shell expands to maintain proper alignment at all times. The alignment detail is shown in Figure 9, indicating both the assembled and operating conditions.

Silicon carbide was selected for the jet shell material due to its ability to sustain continued high operating temperatures and its excellent thermal shock resistance. The holes in the jet shell were drilled with a laser because silicon carbide cannot be machined economically by conventional techniques. A photo taken during the laser drilling opera­tion is shown in Figure 10.

-----

I I

3

4

PRETEST

Predictions of jet impingement heat transfer coefficients are based on correlations made in terms of Reynolds number, Nusselt number, Prandtl number, and geometric variables such as jet spacing and hole diameter (refs. 3-6). A pretest was performed on the GPU-3 heater head to verify and improve the correlation coefficients used to predict jet impingement heat transfer.

A stainless steel mockup jet shell (Figure 11) with geometric variables within the range expected in the final design was fabricated. In order to simulate the heater head operation without risk of damage to the heater head, air heated to 315°C (600°F) from an electrically heated pipe was blown past the heater tubes as shown schematically in Figure 12. Since the heater head consists of four identical sections, only one quadrant (1/4 of heater head) was used for the flow tests. The effect of jet impingement as measured in this pretest is shown in Figure 13, clearly showing the improved heat transfer with jet impingement.

Based on the pretest results, a new prediction of jet impingement heat transfer in the heater head was made for the NASA baseline case presented in Figure 14 for a preheater effectiveness of 80%. The engine conditions for this case were as follows: mean compression-space pressure, 6.9MPa (1000 psi); engine speed, 3000 rpm; air-fuel ratio, 26 to 1; and working fluid, hydrogen. The potential for enhanced heat transfer at this operating point is shown in Figure 15 assuming the same air and fuel flow rates and heater tube temperature. For a small penalty in pumping power (less than 0.5% of engine output), the computer model indicates that at the theoretical maximum limit, jet impingement enhanced heat transfer should: 1) reduce the ·flame temperature by 275°C (500°F), 2) reduce the exhaust temperature by 110°C (200°F), and 3) increase the overall heat into the working fluid by 10%. The theoretical maximum limit is defined as the point where the combustion gas temperature leaving the heater tubes equals the temperature of the tubes.

Based on the pretest results, the final design of the jet impinge­ment system was completed. Figu~e 16 shows the components of the jet impingement system (upper retaining ring is not shown), and Figure 17 shows the jet shell installed in the heater head. The final dimensions fo r the shell are given in Figures 8 and 9. There are 14 jet impingement holes per heater tube; the overall weight of the shell is 245 grams (0 . 54 1 b) .

DEMONSTRATION

To demonstrate the effects of the jet impingement heat transfer system, tests were performed at NASA-Lewis on the GPU-3 Stirling engine for similar operating points both with and without jet impingement. The operating points were 1500 rpm and 2500 rpm at 4.1 MPa (600 psi) mean compression-space pressure for helium work i ng fluid, and 2000 rpm and 3000 rpm at 6.9 MPa (1000 psi) helium pressure. All points were con­trolled to give 677°C (1250°F) working fluid temperature in the

---- -- --.---~

heater and the cooling-water inlet temperature was 21°C (70°F). The heater working fluid temperature was controlled to the maximum reading of thermocouple probes installed inside three of the heater-tubes and spaced circumferentially around the heater head. Data were obtained on the increase in pump power required and engine performance.

The GPU-3 engine tests with the jet impingement system indicated a substantial improvement in overall performance. Representative heat balance computer runs based on the experimental data are shown in Figures 18-19. Inputs for the heat balance are the air and fuel flow rates, the inlet air temperature, nozzle and preheater losses, preheater effectiveness, heat into the engine and the heater-tube metal tempera­ture. A preheater effectiveness of 71 % was chosen to give a reasonable match between the calculated and measured temperatures at positions 2, 4, and 5 shown in Figures 18-19. Based on the calculated temperatures at positions 3 and 4, the average measured heater-tube metal temperature and the heat into the engine, the effective heat transfer coefficient was determined. Table 1 summarizes the test results. The run numbers with a "JS" or "J" indicate the tests with the jet impingement shell.

The engine power is increased by 5.9 to 7.7 percent for the runs with jet impingement. The engine pressure, speed, cooling-water inlet temperature, and maximum heater-tube gas temperature were held constant for a given point with and without jet impingement. The increased power output and efficiency therefore were due to the jet shell smoothing the temperature profiles by providing a more uniform heat flux to the heater tubes and thereby raising the average gas temperature. F~gures 20 and 21 indicate that both the circumferential temperature profiles around the heater head and the tube vertical temperature profiles were more uniform. The increase in engine efficiency was about the same as the increase in engine output.

Figure 22 shows the increase in overall heat transfer coefficient with jet impingement for the demonstration tests. Both the demonstration test and the pretest (Figure 13) indicate a 65 - 70% increase in the effective heat transfer coefficient. The decrease in exhaust temperature and flame temperature for the jet impingement runs shown in Table 1 are due to this increase in the effective heat transfer coefficient. The absolute values determined from the test are significant only for comparison of the similar cases due to uncertainties in the measured system temperatures. At the maximum power point tested, the relative increase in the heat transfer coefficient was 65 percent and the increase in engine power was 7.4 percent.

Since the overall pumping power in the engine combustion system increases with jet impingement, cold flow tests of the required air pressure, both with and without the jet shell, were performed. In­spection of the data presented in Figure 23 shows that the increase in pressure for the jet impingement system was not discernible. Also, the data taken during the demonstration tests showed the increase in pump power to be insignificant.

5

6

CONCLUSIONS

Jet impingement heat transfer has been successfully demonstrated as a technique for enhancing the combustion-gas-side heat transfer in the GPU-3 Stirling engine. The combustion-gas-side heat transfer coefficient was increased by about 65%, along with an increase of the engine power and efficiency by 5 to 8% due to jet impingement. Both the circumferential temperatures around the heater head and the vertical tube temperatu res were made more uniform with the jet impingement system. The additional pumping power required with the jet impingement system was ins ignificant over that required for the baseline case. Preliminary cost esti mates indicate that a Stirling engine jet impingement system will cost less than $50 per unit on a mass production basis.

On the basis of improved engine performance for minimal additional cost, the jet impingement system is an attractive addition to the design of advanced Stirling engines. Further work should be undertaken to design a heater head to take full advantage of the jet impingemen t system.

REFERENCES

1. Begg, L. L. and Fitzpatrick, G. 0., "ZEPO - The World's Largest Thermionic Converter," Intersociety Energy Conversion Engineering Conference, 14th, Boston, Mass., Aug. 5-10, 1979, proceedings, Vol. 2, American Chemical Society, Washington, D.C., 1979, pp. 1868-1874.

2. Fitzpatrick, G. O. and Begg, L. L., "High Thermionic Converter Test Facility and Initial Converter Test Results," Rasor Associates, Sun­nyvale, Calif., "Topical Report NSR 2-10, Sept. 1978.

3. Gardon, R. and Cobonpue, J., "Heat Transfer Between a Flat Plate and Jets of Air," International Developements of Hea t Transfer, Proceedings of the 1961-1962 Heat Transfer Conference, American Society of Mech­anical Engineers, New York; 1963, pp. 454-460.

4. Martin, H., "Heat and Mass Transfer Between Impinging Gas Jets and Solid Surfaces," Advances in Heat Transfer, Vol. 13, Academi c Press, New York, 1977, pp. 1-60.

5. Kercher, D. M. and Tabakoff, W., "Heat Transfer by a Square Array of Round Air Jets Impinging Perpendicular to a Flat Surface Including the Effect of Spent Air," Journal of Engineering for Power, Vol. 92, No.1, 1970, pp. 73-82.

6. Hollworth, B. R. and Berry, R. D., "Heat Transfer from Arrays of Imping­ing Jets with Large Jet-to-Jet Spacing," ASME paper no. 78-GT-117, May 1978.

---.------

_._---- .~ ... -- .-.-- ----- - -l

TABLE 1. GPU -3 TEST RESULTS

PREHEATER EFFECTIVENESS = 71 %

HELlII~1 ENGINE TFMPERATURE (OC) HEAT INTO ENGINE EFFECTIVE % INCREASE DU E TO RUN PRESSURE SPEE D MEASURED CALLU LATED CALCULATED ENGINE pm4ER ENGINE HT . TRANS J ET IMPINGEMENT

NIJM[lU ~ (MPa) (RPM) EXHAUST EXHAU ST FLMIE TUBE (W ) (kW) EFFICIENCY COEF (W/m'OC) POWE R EFFICIE NCY HT . . TRANS

HE25-65 4.1 1500 244 234 1765 698 7791 1.871 1R.81 218

HE25-65JS 4.1 1500 239 230 1699 711 7852 2.015 19. 86 272 7. 7 5.6 24 .1

HE25-63 4.1 2500 251 239 1719 705 12301 2.306 14.86 417

HE25-63JS 4.1 2500 242 230 1722 719 12350 2.488 15.98 603 7.2 7.5 44 .5

HE25-104 6.9 2000 264 250 1726 717 15109 3.803 19.88 474

HE25-104J 6.9 2000 252 239 1704 729 15450 4.028 20.85 808 5.9 4. 9 70 .3

HE25-102 6.9 3000 291 273 1766 742 21214 4.025 14 .82 577

HE2S-102J 6.9 3000 270 254 1712 759 21462 4. 324 15 .84 954 7. 4 6. 9 65.3

-.....J

~

8

GPU-3 STIRLING

WORKING FLUID (HYDROGEN OR HELIUM)

t t

o o 0 () 0

000 0

ENGINE HEATER TUBES-- ~

0 00 0 () 0 0 o 0 p . (J

Fig. 1 Schematic of jet impingement concept.

Water Coo led _______ Top-Plate -----....... Tank

Water Cooled Jet She I I Support Coil

SiC Plates with Jet Ho l e Pattern

iC Slipport Rods

Fig . 2 Combustioh-heated SiC jet impingement shell used in thermionic converter testing. Th i s shell de­livered 193,370 Btu/ hr-ft2 (61 W/ cm2) at 1652°F (900°C).

1189

1278

1367

1456

1500

Temp . (K)

nat I nput Pov~r Profil e

T~ . (K)

1144

1144

1189

1100 1278

1367

1056 lead Region 1456

1011 --+-- 1544 967 Heat Input/Remova l

Reg; on

922

- Collector Emitter---

Opt l •• h ed Input Pover Prorilo

1100

1056

1011

967

922

Co nec tar

Fig. 3 Effect of t ailoring heat flu x prof ile on t emperatu re by using j et i mpi ng ement .

9

o

L

T =18°C 1

rna =24 r 00 g/ s

alr

5 exhaust

T = 278°C 5

m5 = 24.69 g/s

/

AIR PREHEATER

TJ = 80%

PREHEATER LOSS = 454 W

NASA REFERENCE RUN

PREHEATER ry = 80%

T 2 = 991°C rn 2 = 24.00 g/s

2

4

T - 1161 °C 4 -

rn4 = 24.69 g/s

mf = . 69 g/s

Q = 29738 W

fuel

COMBUSTOR

FUEL NOZZLE COOLING WATER LOSS = 569 W

3 ,~---+-T - 1840 °C 3 -. 24.69 g/s m =

3

HEATER TUBES

T = 773°C

h = 352 W/m2°C

HEAT INTO ENGINE = 22093W

Figure 4. NASA reference heat balance assuming a preheater effectiveness of 80%.

1

-' -'

Tl = lS'C

m = 24.00 g/s a .

air

5

exhaust

T = 278°C 5

m5 = 24.69g/s

AIR PREHEATER

." = 74%

PREHEATER LOSS = 454 W

NASA REFERENCE RUN

PREHEATER." = 74%

T = 2

748°C m2 = 24.00 g/s

2

4

T 4 = 944°C

m4 = 24.69 g/s

mf = .69 g/s

Q=29738W

fuel

COMBUSTOR

HEATER TUBES

T = 773 °C

h = 556 W/m2o C

FUEL NOZZLE COOLING WATER LOSS = 569 W

3 JJ----+-T3 = 1640°C

m3 = 24.69 g/s

HEAT INTO ENGINE = 22093 W

Fi~ure 5. NASA reference heat balance assuming a preheater effectivehess of 74%.

12

•

• •

Center of impinging jet

~Local area under consideration \ below

Average tube temperature

Average heat transfer coefficient

880 WI m20C

Local Temperatures and Convection Coefficients

h = 1192 h = 1050 h = 624 h = 426 T = 801 T = 791 T = 776 T = 767

h = 1164 h = 999 h = 454 h = 341 T = 798 T = 788 T = 772 T = 761

h = 1022 h = 903 h = 255 h = 85 T = 793 T = 783 T = 766 T = 757

h = 681 h = 545 h = 170 h = 57 T = 787 T = 778 T = 762 T = 753

Figure 6. GPU-3 Stirling Engine heater tubes. Local temperature distribution with jet impingement.

------ -------- J

...... w

I I

~' ~

I I ,

I I

IC RING

~ L' · . · · :· .1 "CERAMIC HEAT SHIEL U , .... ... J

SiC JET SHELl:

Figure 7. GPU-3 Stirling engine heater head/jet shell assembly .

l

~HEATER HEAD TUBES

TUBE SPACING RINGS

~

I l

B\

ICb . ~,

SEE DETAIL A

. _ _ =--S 1:....::· C:....-~~I tJP I~G E~.1 ~~I S~~Ll _

~'--O,\

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" \~, \\ 0

o u

Si C STANDOFF/ALIGNMENT SPACER - -.

I . /--·l ' 4.Bmm /JET IMPINGEMENT HOLE S I IN SHELL

~. 0 ~ - 0 0 0 0 5. 3mm

J~- O o 000

o ~ STANDOFF/A LIGNMENT

o ~ 0 0 SPACER

o

o

o o

: ~1.6mm o o SECTI ON A- A %\\> , . /fJ)

\~ /~JJU ~ ~~gTi~~E~EATER ('~J~ - fl.. ___ ._ .---- 00 cf 'O '( -/)"--"0 '

Figure B. Top view of jet shell assembly.

l __ ~

.0 ,/ HOLE PREDISPLACEMENT

POSISTION OF BEVEL JOINT AND PREDISPLACEM ENT OF HOLES IN liAS ASSEMBLED" CONDITION

------- ~-.. - - - ---

!l '-- 6.4mm

POSITION OF BEVEL JOINT AND HOLE ALIGNMENT DURING OPERATING CONDITIONS

Figure 9. Detail A illustrating hole alignment.

I I ,

-' 0\

---- ------ -

Figure 10. Laser drilling holes in SiC jet shell.

Figure 11. Stainless steel mockup jet shell.

......,

l _____ _

Combustion Chamber Manometer

Heating air Exhaust~--

, Jet shell __ _ assembly

./ /'

STIRLING ENGI NE PRETEST Test Set-up

((-II !t

-- Orifi ce I ~

~v- _ IJj \.

'i \1 I :-----Insulation \1 I I, ~II I 11 i ;;:c '~ . I , Hea tin 9 air ~~0j __ Stirling englne U.! ,! flow manometer ... ~ ;II}- -- heater head . .

I ·- . " I' 'II." __ ,_-{', It !i11 Pl ug (6 each)

//iiti ~- "Piston" seal ~ I~Jj -Cooling air exhaus t

L----------<rFTI 'I '!

•

, , , .

~-Cooling ai r f low mete r

o Thermocouple locations

Cooling air supply

, I -----..... - - - ---;: \ ..J

Fig . 12 Stirling engine pretest : Test schematic .

~

I

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- Blower

STIRLING ENGINE PRETEST RESULTS o With jet impingement o Without jet impingement

400r---------r-~--._--~~--r_~~~

3000 300

200 0 2000

u 0

N

0 E --:3: @

1000 ~

100 ..1::

0 900 ~

90 800 I-

80 :z:

0 w

700 .......

70 0 u .......

600 lL.

::::l 60

l.J... :z: w

0 500 u

50 0::: W

400 l.J...

40 (/)

:z: e::( 0::: I-

30 300 l-

e::( w :r: w ::>

200 .......

20 I-U W lL. lL. W

10~ ________ ~ ____ ~ __ ~ __ ~~ __ ~~~ 100

1 2 3 4 5 6 7 8 9 10

Re (x 10- 3)

Fig. 13 Heat transfer enhancement due to jet impingement.

18

~

T = 26°C 1

m = 1 7,. 51 g /5 a

air

5 exhaust

T = 293°C 5

m5= 18. 17 9/ S

AIR PREHEATER

." = 80%

PRE HEATER LOSS = 453 W

NASA REFERENCE RUN

PREHEATER ." = 80%

T2 = 1037 °C

m2 = 17.51 9/s

2

4

T4 = 1191°C

m4 = 18. 17 9/5

mf = .66 9/S

Q = 28990W

fuel

COMBUSTOR

HEATER TUBES

T = 760°C

h = 301 w/m2°C

FUEL NOZZLE COOLING WATER LOSS = 571 W

3 »)--....... -T = 2108 °C

3

m3 = 18. 17 g/ s

HEAT INTO ENGINE = 22454 W

Figure 14. NASA baseline case assuming a preheater effectiveness of 80%.

u o

N E "­::s:

20

140

1200

1000

800

600

400 ..

200

1 2

FLAME TEMPERATURE

EXHAUST TEMPERATURE

h

INCREASE IN HEAT IN TO ENG INE ABO VE PRESENT OPERATING POINT , %

ex: w l.L. I./)

~

.~ r-r-c::t: w :r: z >-I

W I./)

c::t: w cx: u Z >-I

:z ::::> L >-I

I~ L

l;i u

I~ w

18 :r:

Ir-

I 1 I I I

Fi gure 15 . PREDICTED EFFECTS OF JET IMP INGEMENT FOR THE GPU-3 STIRLING ENGINE .

11

2100

2000

1900 u o .. w

1800 ~

30

25

20

15

10

5

0

I-

~ W Q..

300 ~ I-

250

200

150

Z I-­..... w

'J W V1 a:: c:(o W LL a:: uo Z W ....... a::

........ ::;, Cf w a::

.-.---~---

L

. ~

~

OJ ..c til

+> OJ 0.....,

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OJ >­::::l CJ)

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c 0,-

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~ . OJ "0

..ccO til OJ

..c +> OJ >-0....., OJ

+> U cO ' r-' OJ (/) ..c

'""

21

f

N N

T = 21 DC 1

m = 16.93 g/s a

air

5

exhaust

T = 273 DC 5

m5 = 17.56 g/s

HE 25-102 3/26/81

3000 RPM 6.9 MPa

AIR PREHEATER

T} = 71 %

PREHEATER LOSS = 414W

T = 2 654 DC

m2 = 16.93 g/s

2

4

T = 836 DC 4

m4

= 17. 56 g/ s

mf = .63 g/s

Q = 27134 W

fuel

COMBUSTOR

HEATER TUBES

T = 742 DC

h = 577 W/m2DC

FUEL NOZZLE COOLING WATER LOSS = 526W

3 JJ---+-T =1766DC

3

m3 =17.56 g/s

HEAT INTO ENGINE =21214W

Figure 18. Heat balance based on experimental data. Baseline run without jet impingement.

N W

Tl = 19"C

HE 25-102 J 3/25/81

3000 RPM 6.9 MPa

m = 17.20 g/s a

air ci:; · AIR

PREHEATER

5

exhaust

T = 254°C 5

m5 =17.83 g/s

,/ PREHEATER LOSS = 376W

1] = 71 %

T = 2 610°C

m2 = 17.20 g/s

2

4

T = 779°C 4

m4 = 17.83 9/S

mf =.63 g/s

Q = 27281 W

fuel

COMBUSTOR

HEATER TUBES

T = 759°C

h = 954 W/m2°C

FUEL NOZZLE COOLING WATER LOSS =730W

3 )I----+--

T = 1712°C 3

m3 = 17.83 g/s

HEAT INTO ENGINE = 2l462W

Figure 19. Heat balance based on experimental data. Baseline run with jet impingement.

I ___ J

24

800

700

~I=~=--_'~~ without jet i mp ingement

600 u 0

uS 500 cr: ::> >--<>: cr: 400 w 0.. ::E w >--w 300 co ::> >--

200

100

0

2 3 4

THERMOC OUPLE POSITI ON

Figure 20. Circumferential heater-tube metal temperatures . Thermo­couples are located around the heater head at 90° intervals .

u 0 . Vl w cr: ::> >--<>: cr: w 0.. ::E w >--w co :::J >--

800

700

600

500

400

300

200

100

0

Top

rWith jet impingement

lWithout jet imp i ng ement

Center

THERMOCOUPLE POSITION Bottom

Figure 21. Vertical heater-tube metal temperatures.

--------------_.-

I --- - -

:::3 Z

l

NASA TEST RESULTS

o With jet impingement o Without jet impi ngement

40

0 1000 30 0

0

20

0

10 9 B 8

CO 7

6 -

5

4

3

2

1 2 3 5 6 7 8 9 10

Fig. 22 Heat transfer enhancement due to jet impingement in the GPU 3 Stirling engine.

900 800 700

600

500

400

300

200

100 90 80 70

60

50

40

u 0

N E ........ 3: .. L: .. ~ z w ....... u ....... u... u... w 0 U

0::: W u... V)

z c::x:: 0::: ~

I-c::x:: w :c w > ....... I-u w u... u... w

25

N 0'\

8.0

7.0

I 6.0~

I 5.0

<1:l

: 4.0~ a::: :::> (/') (/')

w

g: 3.0

2.01-

1.01-

OJ 0

00

5

[] WITH JET IMPINGEMENT

0 WITHOUT JET IMPINGEMENT o 0 [J 0

0

[]

8 [J

[J

0

~ []

[J

0

[J

0

[J 0

10 15 20 25

AIR FLOW RATE g/s

Figure 23. GPU-3 cold flow pressure drop results.

l

1. Report No. I 2. Government Accession No. 3. Recipient's Catalog No.

NASA TM-82727 4. Title and Subtitle 5. Report Date

JET IMPINGEMENT HEAT TRANSFER ENHANCEMENT FOR October 1981 6 . Performing Organization Code

THE GPU-3 STffiLING ENGINE 778-35-03 7. Author(s) 8. Perform ing Organization Report No .

Douglas C. Johnson, Craig W. Congdon, Lester L. Begg, and Edward J. Britt, Rasor Associates, Inc., and Lanny G. Thieme, Lewis Research Center 10. Work Unit No .

9. Performing Organization Name and Address

National Aeronautics and Space Administration 11 . Contract or Grant No.

Lewis Research Center

Cleveland, Ohio 44135 13. Type of Report and Per iod Covered

12. Sponsori ng Agency Name and Address Technical Memorandum

U. S. Department of Energy Office of Vehicle and Engine R&D 14. Sponsor ing Agency .code Report No , Washington, D. C. 20545 DOE!NASA!51040-33

15. Supplementary Notes /"'

Final report. Prepared under Interagency Agreement DE-AI01-77CS51040.

16. Abstract

Of the many factors influencing the performance of a Stirling engine, that of transferring the

combustion gas heat into the working fluid is crucial. By utilizing the high heat transfer rates

obtainable with a jet impingement heat transfer system, it is possible to reduce the flame temp-

erature required for engine operation thereby resulting in lower exhaust emissions, Also, the required amount of heater tube surface area may be reduced , resulting in a decrease in the en-

gine nonswept volume and related increase in engine efficiency, A jet impingement heat transfer system was designed 'by Rasor Associates, Inc., and tested in the GPU - 3 Stirling engine at the

NASA Lewis Research Center. For a small penalty in pumping power (less than 0,5% of engine

output) the jet impingement heat transfer system provided a higher combustion-gas-side heat

transfer coefficient and a smoothing of heater temperature profiles resulting in lower combustion

system temperatures and a 5 to 8% increase in engine power output and efficiency, On the basiS

of these results, the jet impingement system could be an important contribution to the design of

advanced Stirling engines.

17. Key Words (Suggested by Author(sl) 18. Distribution Statement

Jet impingement, Stirling engine, Heat trans- Unclassified - unlimited

fer enhancement STAR Category 85

DOE Category UC-96

19. Security Classif. (of this report) 20. Security Classi!. (of this page) 21. No . of Pages 22. Price

Unclassified Unclassified 27

. For sale by the National Techn ical Infor ma tion SerVice , Springf ield . Virginia 22161

NASA·C·168 (Rev. 10·75)

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