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-AD-A193 594 NATURAL CONVECTION IMHERSION COOLING OF AN MRAY O ±4SIMULATED CHIPS IN AN ENCLOSURE FILLED WITH DIELECTRICLIQUID(U) NAVAL POSTGRADUATE SCHOOL MONTEREY CA

UN SIFIED T PAHK DEC 97 F/O 9/1

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MICROCOPY RESOLUTION TEST CHARTJRAU - 1ANARDR-1963-

NAVAL POSTGRADUATE SCHOOLMonterey, California

IDTIC

ELECTE

MAY 3 1 1 88,

THESISNATURAL CONVECTION IMMERSION COOLI NG

OF Al ARRAY OF SIIULATD "HIPSIN AN EJCLOSURE FILLED WITH DIELECTRIC

LIQUID

by

Turgay Pamuk

December 1987

Thesis Advisor M.D. KelleherCo-Advisor Yogendra Joshi

Approved for public release; distribution is unlimited.

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DISCLAIMER NOTICE

THIS DOCUMENT IS BEST QUALITYPRACTICABLE. THE COPY FURNISHEDTO DTIC CONTAINED A SIGNIFICANTNUMBER OF PAGES WHICH DO NOTREPRODUCE LEGIBLY.

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6& %A-VE :3- ;E;Q- 0%.'.2 6n 0;c; s e 5,VS. a %AVi OP V O7RING OR~GANZ. ONNaval Postgraduate School j(it apooicaoie) Naval Postgraduate School

cc A.OD2S5 .Crt State, and Z!PCooe, 7o ADDRESS tCity State, and ZIP Code)

tionterey, California 93943-5100 "onterey, California 93943-5100

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E.VENT No .4O %0AO~ s ON NO

.:iic, uae Securitk Class,tIcat,On,Natural convection immersion cooling of an array cf simulated chips in an enclosure filledwjith dielectric licuid

2 ;ESONA, A--OOS. Pamuk, Turgay

Nasters/Eng thesis 1,19E _____ ___mbrI

6 S-S E M CEV ontinue on reverse It ,ieCeSsar and faenetry DV oiocK numbeINtrlco ecticn free convection, cubical or rectangularIaua Gvecin

enclosures~electronic coolinch

Iii A~S7AC' Conronue on reverse It ncessaryv aria taentity oy bot~ m~r

~4r experimental natural convection heat transfer study; of asimulated electronic circuit board has been conducted. Tlhe board has anarray of 9 simulated chips , each dissipating up to 2. 5 Wat.s. The boardis immersed in FC75, a fluorocarbon liquid, in an enclosure whose topand bottom surfaces are constant temperature heat sinks. Theexp~erimental data have been enpressed in terms of ret.evant dimensionlessheat transfer parameters such as Nusselt and Rayl"%igh numbers. Thetrend is that, the chips located higher in the enclosure have lower heattransfer rates. Otherwise the chips in the same row beh~ave in a similar

* way which implies a quasi-two diesoaiy

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Natural Convection Immersion Coolingof an Array of" Simulated Chips

in an Enclosure Filled With Dielectric Liquid

by

Turgav 'aniukLieutenant Junior 6radc. Turkish Na\v"

B.S.. Turkish Naval Academy. 1981

Submitted in partial fulfillment of therequirements for the dcgrees of

MASTER OF SCIENCE IN MECHANICAL ENGINEERINGand

NMECHANICAL ENGINEER

from the

NAVAL POSTGRADLATE SCHOOLDecember 19S7

Author:'I urvzi%- |amuk

Approved by:_ _ _"D Kcileher. Thesis Adisor

,'gendra. Josi. Co-Advisor

J

iv, Chairman.Deparmn oKlechanical Engin ring

Gordon E. Schacher,Dean of Sciencc and Engineering

l2

ABSTRACT

An experimental natural convection heat transfer study of a simulated electronic

circuit board has been conducted. The board has an array of 9 simulated chips, each

dissipating up to 2.5 Watts. The board is immersed in FC75. a fluorocarbon liquid, in

an enclosure whose top and bottom surfaces are constant temperature heat sinks. The

experimental data have been expressed in terms of relevant dimensionless heat transfer

parameters such as Nusselt and Rayleigh numbers. The trend is that, the chips located

higzhcr in the enclosure have lower heat transfer rates. Otherwise the chips in the same

row behave in a similar way which implies a quasi-two dimensionalitv.

Aoession For%iis- R-lIDTIC TAB [

Unannounced fl

PL t r-ibut ton/. ....

3 -Availability CodesAvail ax/or

Dist Special

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' -

TABLE OF CONTENTS

IN TRO D UCTIO N .............................................. 9

A. DESCRIPTION OF THE PROBLEM ......................... 9

B. BACKG RO UN D .......................................... 9

C. STUDIES ON NATURAL CONVECTION COOLING OFELECTRONIC DEVICES .................................. 10

1. N um erical Studies ..................................... 10

2. Experim ental Studies ................................... 11

D . O BJECTIVES ............................................ 12

II EXPERIMENTAL APPARATUS ............................ 13

A. GENERAL CONSIDERATIONS ........................ 13

B. CO M PO N EN TS .......................................... 13

I. H eating Elem ent ...................................... 13

2. Therm ocouples ........................................ 14

3. H eaters .............................................. 174. Sim ulated Circuit Board ................................ 17

5. Test C ham ber ......................................... 17

6. H eat Exchangers ...................................... 18

7. A ssem bly ............................................ 21

C. INSTRUM ENTATION .................................... 21

1. Power to the Chips .................................... 21

2. Data Acquisition System ................................ 22

3. C om puter ............................................ 23 S

lII. EXPERIMENTAL PROCEDURE ................................ 24

A. APPARATUS PREPERATION ............................. 24

B. DATA ACQUISITION ............................... 24

C. DATA ANALYSIS ........................................ .25

1. Determination of Nusselt Number ........................ 25

4

h

2. Determination of Rayleigh number ....................... 27

3. Flux Based Rayleigh Number ............................ 27

IV . R E SU LT S .................................................... 29

A. TEMPERATURE DATA .................................. 29

B. HEAT TRANSFER RESULTS .............................. 43

V. DISCUSSIONS AND RECOMMENDATIONS .................... 53

A. DISCUSSIONS OF THE RESULTS ......................... 53

B. RECOM M ENDATIONS ................................... 53

APPENDIX A: SAMPLE CALCULATIONS ............................. 5,4

1. DETERMINATION OF INPUT POWER .................... 54

2. ESTIMATION OF CONDUCTION LOSS .................... 55

3. CALCULATION OF NUSSELT AND RAYLEIGHN U M B E R ............................................... 57

APPENDIX B: UNCERTAINTY CALCULATIONS ...................... 59

APPENDIX C: PROGRAM LISTINGS ................................. 62

I. DATA ACQUISITION PROGRAM ......................... 62

2. HEAT TRANSFER CALCULATIONS PROGRAM ............ 64

LIST O F REFEREN CES ................................................ 67

INITIAL DISTRIBUTION LIST ......................................... 70

5

LIST OF TABLES

1. TEMPERATURE DATA FOR INPUT POWER Qj,- = 0.34 W ........... 302. TEMPERAkTURE DATA FOR INPUT POWER QlN = 0.68 V ........... 303. TEMPERATURE DATA FOR INPUT POWER QIN = 1.07 W ........... 314. TEMPERATURE DATA FOR INPUT POWER Ql. = 1.65 W ........... 325, TEMPERATURE DATA FOR INPUT POWER Q.N = 1.95 W ........... 33

6. TEMPERATURE DATA FOR INPUT POWER Q . = 2.35 W ........... 34

7. HEAT TRANSFER CALCULATIONS FOR QI. 0.34 W .............. 44

S. HEAT TRANSFER CALCULATIONS FOR QI. = 0.68 W .............. 44

9. HEAT TRANSFER CALCULATIONS FOR Qj,- = 1.07 W .............. 44

10. HEAT TRANSFER CALCULATIONS FOR = 1.65 W .............. 45

11. HEAT TRANSFER CALCULATIONS FOR Qj\ = 1.95 W .............. 45

12. HEAT TRANSFER CALCULATIONS FOR QIN = 2.35 W .............. 46

13. THERMAL CONDUCTIVITIES OF THE MATERIALS ................ 56

14. THERMAL RESISTANCES TO CONDUCTION ...................... 56

15. UNCERTAINTIES OF THE VARIABLES USED IN THEEX PER IM EN T .................................................... 59

6

LIST OF FIGURES

2.1 Top View of the Enclosure ......................................... 14

2.2 Schem atic of the Circuit Board ...................................... 15

2.3 Schematic of the Simulated Chip .................................... 16

2.4 Photograph of the Foil Heater with Simulated chip ..................... 18

2.5 Photograph of the Simulated Circuit Board ........................ ... 19

2.6 Photograph of the Test Chamber .................................... 20

2.7 Photograph of the Assem bly ........................................ 224...4.1 Temperature Distribution for Qin = 0.34 W ........................... 38

4.2 Temperature Distribution for Qin 0.68 W ........................... 38

4.3 Temperature Distribution for Qin = 1.07 W ........................... 39



4.6 Temperature Distribution for Qn - 2.35 W ......................... 42

4.7 Nusselt vs. Rayleigh Number for BOTTOM ROW of the chips ........... 48

4.8 Nusselt vs. Rayleigh Number for MIDDLE ROW ofthe chips ........... 494.9 Nusselt Number vs. Rayleigh Number for TOP ROW of chips ............ 50

4. 10 Comparison of the Results with Fujii and Fujii Correlation ............... 51

A. I Electrical Network of Power Input ................................... 54

A.2 Thermal Resistance Network for Conduction Loss ...................... 55

7

NOMENCLATURE

SYMBOL DESCRIPION UNITS

A Area m2

Q Thermal Diffusivitv t- sec

Thermal Expansion Coefficient 1 (0 C)C Specific Heat J, kg-0 C

5 Urcertainty in the Variables Various

g Acceleration of gravity m. sec 2

Gr Grashof Number Dimensionlessh Heat Transfer Coefficient W. m2.oC

k Thermal Conductivity W. m-°C

L Characteristic Length m

Nu Nusselt Number Dimensionless

Nu* Nusselt Number at Center Dimensionless

v Kinematic Viscosity m sec

Pr Prandtl Number Dimensionless

Qcon Energy Loss by Conduction W

Qconv Energy Added to the Fluid W

Qin Energy Input to the Heater W

R Resistance of Precision Resistor 1's

Rcon Total Thermal Resistance oC, W

;',a Rayleigh Number DimensionlessRamc Modified Rayleigh Number at Center Dimensionless

p Density kg m3

Ta Ambient Temperature 0C

Tf Average Film Temperature °C

T Back Surface Temperature of Component 0C

Vi Input Voltage Volts

Vh Voltage Across Heater Volts

8

-. w . ~ % ~ ~ ~ %

,P ! %

I. INTRODUCTION

A. DESCRIPTION OF THE PROBLEM

Develepment of electronic packaging, starting with ENIAC, the first digital

electronic computer, has created a very urgent need to devise more sophisticated

cooling systems. In the last ten years, the remarkable advancement of very densely

packaged electronic components has brought about the necessity for enhancement of

heat transfer features applied to these thermal packages.

The first electronic packages in 1960's, SSI (Small Scale Integration) chips had

only a maximum of 20 devices per chip, whereas today's most advanced ULSI (Ultra

Hligh Scale Integration) chips have more than 100,000 devices per chip [Ref. 1.1 The

overall effect over the past 30 years resulting from this tremendous increase in the

packaging densities has been a trend towards ever increasing heat fluxes. While this has

always been the case for very high power modules, the same trend towards ver- high

heat fluxes in the microelectronic chips has also been observed. Heat fluxes reaching

lo' W, m2 on the chip surface have introduced a major cooling problem [Ref. 2J.

Inadequate cooling of these elements, coupled with the enviromental temperature rise.

often leads to failure of these components and decrease in reliability and performance.

B. BACKGROUND

Many papers on the electronic cooling area have proposed a very wide variety of

solutions to specific problems. Major digital technology firms such as IBM, Honeywell

and Mitsubishi have become the pioneers in this research area. For instance, air

cooling technology of the modules now often includes impingement air cooling to

enhance the heat transfer. Using liquid cooled cold plates to conduct heat away from

the sources has also been employed. Combined conduction and air cooling has been p

observed to provide a much higher enhancement when used with fins on the chip

surface [Ref. 31.

Some special chip outer surface features such as TPF (Turbulence Promoting

Fin) have provided significantly higher cooling enhancements, when used with special

gases such as Helium as the closed cycle coolant [Ref. 4]. By doing so. 300 0 greater

dissipation (cooling) level can be reached than when open cycle air is used as the

coolant. 0

9 9,'.r

p

Among the cooling techniques mentioned above, liquid forced convection has a

very important place since it is possible to attain heat transfe r coeflicients over an

orler of magnitude higher than those attainable with air cooling [Ref I1]. According to

TIME magazine, June 17, 19S5 issue, the Crav-2 super computer utilizes forced

convection with local boiling at some hot spots. In the same magazine it is stressed

that "20 gallons of liquid are used in the machine flooding the circuits wil a

continuous flow of Fluorinert." However, the use of forced convection leads to more

complex design features and brings along the possibility of vibration based failure risks.

Final, more recent advancements and growing use of largescalc and very large

scale integration (LSI and VLSI) microelectronic technologe.s with chip dissipation

cxceeding 1-2 W and chip surface heat fluxes exceeding 10S W m2 has focused

attention on natural convection liquid immersion cooling because of its advantages

over forced convection such as simplicity, higher reliability and lower cost [Ref. 5].

Lsing R-113 as the coolant, different immersion cooling schemes with submerged

condensers have been proposed by Bar-Cohen [Ref. 6]. These techniques are mainiy

based on pool boiling of R-113 or other fluorocarbon liquids in which the components

are immersed.

C. STUDIES ON NATURAL CONVECTION COOLING OF ELECTRONIC

DEVICES

1, Numerical Studies

Among the different convection heat transfer modes mentioned above.

inunersion cooling by means of natural convection has received much attention

recently because of its high dissipation capabilities, together with such added

advantages as no noise and high reliability [Ref. 7]. Starting in early 1960s, numerous

studies of natural convection in rectangular enclosures have been carried out. Many of

the initial studies were however motivated by applications such as energy transfer

within buildings, solar collection etc.. Only recently has computational attention been

focused on simulations of natural convection in electronic component cooling.

Acharya et. al [Ref. 81 have investigated the natural convection phenomenon

in an inclined square box shaped enclosure which has energy sources in it. Torok

[Ref. 91 used finite elements technique to predict component and board temperatures

and heat fluxes. Kuhn et. al [Ref. 10] have studied the three dimensional natural

cor.vection heat transfer in a rectangular enclosure with heating elements on the ',

vcrtiaIl wall inside the enclosure. They found that when two elements are

IC'I

. . .. .- . . . . . .

LML% N

symmetrically placed on the wall, the distance between them has only a little effect on

the mean heat transfer rate distribution, but has a significant effect on the local NusscIt

Numbers. Shakerin et. al [Ref. 11] have investigated numerically the effect of the

discrete roughness elements protruding from the wall of an enclosure. They repeated

the numerical procedure for both a single protruding element and two elements.

Liu et. al [Ref. 71 have carried out the fInite difference numerical studv ofnatural convection in a rectangular enclosure with an array of chips mounted on a

vertical wail. The side walls of the enclosure are assumed to be adiabatic. The result of

:1his numerical study have been presented as temperatures and velocity fields for the

enclosure widths of 18 and 30 mm. It was concluded that:

0 Temperature field in the enclosure is characterized by boundary layer regionssurrounding individual chips.

0 There is only small interference among the chips, especially for the lower rows.& The maximum temperatures on the chip surfaces are located on the upper

horizontal faces of the chips. Lesser temperatures have been found on the lowerhorizontal faces of the chips in the bottom row.

• The results for 30 rmm width are essentially the same as those for IS mm.,indicating only a minor dependence on enclosure width.

Liu et. al have also studied the local oscillatory surface temperature responses in the

same anclosure [Ref. 121. This numerical study has shown that the maximumn

temperatures of chip surfaces have a tendency to fluctuate within a range tip to almost" 3 'C with a period of 4 seconds.

2. Experimental Studies

Numerous experimental works relating to the enclosure flows have beenconducted along with the numerical studies mentioned above. Park et. al [Ref. 13] usedthin foil heaters to simulate both flush mcunted and protruding microelectroniccomponents. They obtained heat transfer coefficients for various heater heights andwidths. Knock [Ref. 2] studied the effect of :he location of a single protruding heater inan enclosure, using water as the working fluid. Experiments were conducted wih theheater near the bottom, at the center and near the top of a vertical side wall. Side wallswere insulated to insure adiabatic boundary conditions on them. He repeated theexperimental procedure for three heater locations. The heater position was varied fromclose to bottom of a side wall to near the top of the side wall. His results can bequantitatively summarized as a trend suggesting that as the heater is raised within theenclosure, the Nusselt number decreases.

11 I

. . ..* 1I ,' ;

Filis et. a! [Ref. 141 have investigated the effect of wall temperature

nonuniformity on natural convection in an enclosure. They have presented their results

stressing that the nonuniform wall temperature is a more realistic boundary c3ndirion.

Anderson et. al [Ref. 151 have studied the wall roughness effect on heat transfer

enhancement in a water filled cubical enclosure.

D. OBJECTIVESTle experimental work described here was motivated by the numerical study by

Liu et al. [Ref. 71 and is the basis of the experimental work of this thcsis. The

objcctives of this study are

* To design and build an enclosure to cool an array of nine simulated chipsimmersed in FC-75. These simulated chips are to be instrumented with anumber of thermocouples, which are to be monitored using a data acquisitionsystem.

* To analyze the data in terms of relevant dimensionless heat transfer parameterssuch as Ray!eigh vs. Nusselt number.

• To prepare a basis for similar future experiments, including various chipconfigurations and enclosure widths.

12

% -MPI x

II. EXPERIMENTAL APPARATUS

A. GENERAL CONSIDERATIONS

The apparatus used in the experiment consists of an enclosure filled with

dialectric liquid. The top and bottom surfaces of the enclosure are formed by two heat

exchangers maintained at prescribed temperatures through the use of a water

circulation bath. Simulated electronic components are mounted on one of the vertical

sidewalls. All other walls are exposed to ambient air. Top view of the enclosure is seen

in Flgure 2.1.

A simulated circuit board seen in Figure 2.2 contains a 3 by 3 array of

syn.metrically piaced heating elements. The heating element dimensions correspond

approximate!y to those of a 20-pin Dual-in-line-Package (DIP). The dimensions of the

heating element used in the present study were identical to those in [Ref. 7] and

[Ref. 121 to allow future comparisons between experiments and computations. The

heating element was a rectangular parallelopiped made of aluminum with a foil typed

heater attached to the bottom face.

The present study. dealt with temperature measurements on the surfaces ofvarious heating elements, for a number of different power levels. The temperatures

were measured by fine thermocouples attaced to each aluminum block surfaces. The

data was acquired using a micro-computer controlled data-acquisition system. Details

of the major elements of the experimental assembly are described next.

B. COM PONENTS

1. Heating Element

The heating element is 6 mm wide, 8 mm long and 24 mm high. (Figure 2.3).

In order to be able to measure the temperatures of the surfaces, the lateral surfaces are

grooved to a 0.5 mm depth to contain thermocouple beads. The front surface of the

chip is reached by a hole drilled through the thickness of the component. The beads

and other uninsulated parts of the thermocouples are insulated using a thin layer of

electrical insulating varnish to insure a high enough electrical resistance between the

beads and aluminum block. An electrical contact described above may cause extra

bimetallic junctions, resulting in false temperature read-outs. The rest of the groove left

from thermocouple bead was filled with a high thermal conductivity epoxy, OMEGA

BOND 101. The surfaces of the blocks were smoothed out before the epoxy cured.

13

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Figure 2.3 Schematic of the Simulated Chip.

2. Thermocouples

Because of the relatively small size of the aluminum blocks, a %ery fine, 3-nil

copper-constantan (Omega) thermocouple wire was chosen. By doing so. cnly a small

amount of aluninum had to be drilled out of tie entire block (Approximatel. - ,IUvitvs. 1152 m m3, or in other words 0.6o in volume or weight.i. Since it I quite licult

to handle these thermocouple wires, special care had to be taken when akIn'g the

thermocouples. On the thermocouple welder, current and arc time should be set to

minimum" and the argon gas pressure should not exceed 5 psig. The copper wire

holder of the welder should be cleaned of carbon build-up with a fine sand paper

frequently to maintain the high electrical conductivity to the arc path. Each bead

I (

ip

should be checked 6or strength before using, since after the cooling of', the bead

junction might get brittle and break even if it looks welded.

3. Heaters

Marchi Associates foil type heaters were used to provide a nearly constant

heat tILx boundary condition at the back of the block (Figure 2.4,. Each of the

resistances were measured to be between 10.5 to 11.8 .t's. The resistor loop conductor

material is Inconel-600. The back of the heater element is laminated with Kapton with

a maximum allowable operating temperature of about 250'C. The thickness of the

heater element is 0.18 mm. Each of the heater elements has holes at the same locations

as the back of the aluminum blocks to pass the thermocouple wire terminating on the

front face. In addition, the heating element has four slots on the sides to allow passage

of other thermocouples.

The power leads from the heater resistor loops are gold plated to insure low

electrical contact resistance on soldering. Wires are soldered to gold plated power lead

hook-ups. A length of 5 nm from the bottom of the fbil heaters had to be clipped off

in order to accomodate a 6 mm distance between blocks. Heaters were bonded to the

blocks using OMEGA BOND 100 adhesive epoxy, after making sure that the holes and

blocks were lined up by means of a piece of wire. They were then squeezed together in

a small hand vice. Teflon sheets were used on both ,aces of the vice to protect the

surfaces of the heater and aluminum block.

4. Simulated Circuit Board

The vertical sidewalls containing the heating element are made of a 5.5 mmthick plexiglass sheet. The 120 mm by 144 mm card was grooved at the heater

locations to a depth of 0.5 mm to eliminate the extra thickness that would have

resulted from the adhesive used to bond both heater to sinulated chip and chip to

circuit board. The components with heaters were bonded to the card using rubber to

metal cement. After placing the thermocouples and clipping off the extra length on the

foil heaters, the grooves were filled with OMEGA BOND 101 fast set epoxy and

smoothed out.

5. Test Chamber

The test chamber is made of 13 mm thick plexiglass which has the dimensions

of 120 num length, 144 mn height and 30 mm width. The spacing at the back is

provided to carry the wiring out of the test section. All the wiring was taken out

through a Tygon guide tube. Two 3 mm aluminum plates were used as lids for the

bottom and the top of the enclosure.

17

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'Figure 2.6 Photograph of the Test Chamber.

20

6. Heat Exchangers

The two aluminum heat exchangers measure 38 mm by 65 mm by 274 mrm.

The details of the heat exchangers are given in [Ref. 2]. The top and bottom aluminum "

lids were grooved to a 2.5 nun depth to provide thermocouple slots. This left a 0.5 nun

wall thickness of aluminum between the thermocouple bead and the other surface of

the aluminum platc. The thermal resistance of the 0.5 mm aluminum wall was

neglected. Ileat exchangers were fed with water as coolant (in series) by means of

tygon tubing. Four 10-rui thermocouples were used to read the top and bottom heat

exchanger temperatures.

7. Assembly

After sliding the card into the slot in the enclosure, both thermocouple and

power wires were run through a small 1'2 in. diameter extension pipe behind the

enclosure and then taken out through a 1 2 in. diameter tygon tube of 25 cm. length.

Top and bottom heat exchangers were bonded to the encloure using RTV 732

adhcsive sealant. The back space of the enclosure was filled with rubber pieces to

decrease conduction losses to the back of the card. After attaching the heat exchangers

to the enclosure, the bottom heat exchanger was fixed on an adjustable level aluminum

stand by means of two aluminum clamps. A 4 cm. thick rubber slab was placed

between the aluminum stand and the bottom heat exchanger to absorb the vibrations

from the ground. Finally, inlet and outlet tygon tubes from the constant temperature

bath were conncC7d to the heat exchangers. The level of the apparatus was adjusted

by means of the adjustment screws under the aluminum stand.

C. INSTRUMENTATION

i. Power to the Chips

Each of the nine heaters was connected in series with a seperate 2 Ohm

precision resistor. The nine elements were connected in parallel to the power supply.

Power input to each heating element was calculated from a simultaneous measurement

of the voltage drop across the precision resistor and the overall voltage drop. (see

Appendix A)

The power panel has one main input and 10 terminals, the last one being a

spare terminal in this study. The main input is fed from a DC power supply. (KEPCO

0-100 V. 0-5 A, Mod. JQE 100-5 type)

21

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2. Data Acquisition System

A Hewlett-Packard 3054A Automatic Data Acquisition Control System was

used to collect the data. The first 49 channels of the data acquisition system are for the

thermocoup!e readings. Of these, the first forty-five are used for teniperatare

measurements of the heating elements. Channels 46-49 are for the hcat exchanier

tcmperaure measurements. Channel 50 reads the main input voitage to the power

panel. Channels 51-59 read individual heating element voltages.

3. Computer

A Hewlett-Packard 9826 computer with HIewlett-Packard 2671A printer was

used as the controller for the data acquisition system. Two programs written in IP-

BASIC language have the data acquisition system collect the data and store in a data

file for each run.

V

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Ill. EXPERIMENTAL PROCEDURE

A. APPARATUS PREPERATIONAflcr asserbling the apparatus, the enclosure was filled through the wire lead

tubC folded 900 upward, using a small funnel. To damp disturbances from the

surroundings, the apparatus is placed on a seperate table. The bubbles inside theenclosure were driven out by laying the enclosure horizontally and tilting it around.

After insuring that the liquid is in contact with the top heat exchanger, the enclosurewas fixed on the aluminum stand using the aluminum clamps, with a rubber vibration

damper in between. The apparatus was then leveled by means of a bubbie level placedon the top heat exchanger. Tygon tubing feeding coolant water to the heat exchangers

were attached to them in series. In other words, outlet of the top heat exchanger wasthe inlet of the bottom one. Because of the very high coolant mass flow rate, the

temperature drop through the heat exchangers was negligible. Ten terminals on thepower panel were used to supply power to the heaters on the simulated chips. Tie first

terminal was the main input, the next nine are the terminals for each heater. They xcre

connected in parallel to the main input with 2fl resistors which were in series with

each heater.

B. DATA ACQUISITION

All the thermocouples were initially scanned to insure that they were reading the

same temperature at steady state, for a predetermined sink temperature. The heat

exchangers were brought to 21"C by means of the adjustment dial on the constant

temperature bath. The voltage on the power supply was next set to the desired level.

The volzage setting was calculated knowing that each heater and resistor have a total

resistance of approximately 1392's. Once the desired power was determined, voltage on

the power supply could be set to its approximate value.

Once the voltage on the power supply and the temperature on the constant

temperature bath was set to their desired values, all the readings were taken by running

the data acquisition program.

Maximum power per component was about 2.35 Watts. At higher values,degasing of the bonding material resulted in bubble formation at the heater blocks.

For each seperate power setting, sevcral runs with 1 hour time period were taken.

24

.,.!' . - * *S ~ , . - -- - -

When the temperature change between two successive readings was within 2',, steady

conditions were assumed. This process takes 2-4 hours for each run, depending on the

power level.

C. DATA ANALYSIS

For each scperate run, all data were stored in files created by the data acquisitionprogram. After tlc end of all the runs, steady state data were kept on the disk. These

were accessed by a program written for the heat transfer calculations.

All 'he raw data were used for determining Nusselt and Rayleigh numbers for

each chip at each power level.

1. Determination of Nusselt Number

Nusseit Number is defined as following

hL

NU (eqn 3.1)kr

Where L is the characteristic length, taken here as the component height. All the fluid

properties were taken variable with average film temperature. In order to evaluate the

heat transfer coefficient h, an estimate for conduction loss through the back of the test

surface has to be made. A series of conduction thermal resistances, together with a

convection boundary condition at the outside wall of the enclosure determines the total

heat resistance. (Appendix A )

Conduction resistance Rcon for each solid layer is determined from

L

Rcon -0 (eqn 3.2)

k A

Where L is the length along the conduction path, k is the thermal conductivity of the

material ( see Appendix A ) and A is the area normal to the conduction path. Then

the conduction loss is

25

Ts - T a

Q n = (eqn 3.Qcon 2~

R~of

Power input to each chip is calculated from

( Vn Vh)Vh

Qin =(eqn 3.4)

R

Where Vin is the input voltage appiied to both 2l resistor and the heater which is in

series with it. V is the voltage drop across the heater. The difference between V and

Vh gives the voltage drop on the 2P- resistor.

The net energy added to the fluid in the enclosure is the difference between

Qin and Qcon which is at the same time from Newton's law of cooling

Qconv A(Tavg -T)

= Qin- Qcon

where,

A = Total surface area of the chip.

Tavg = Area weighted average surface temperature.

TC = average heat exchanger temperature.

Also.

Tavg - (eqn 3.5)

VA.

where

Ti = temperature of h surface of the chip,

26

Ai = area of the iP surface of the chip. The summlation

index i. varies from 1 to 5.The above procedure is repeated for each of the nine chips at each power

level. Then, from Equation 3.1, Nusselt number is calculated.

2. Determination of Rayleigh number

The definition of Rayleigh number is

Ra - (Gr)(Pr)

Where

gPLT -Tavg Tc)

Gr (eqn 3.6)

V~.

and

Pr-- v a

a kr (pc)

All the properties in the above equations are calculated at average Fim n

temperature

Tavg + TcTr = - (eqn 3.7)

2

Functional relationships for the properties at the film temperatures are given

in Appendix A, together with the sample calculations. Uncertainty calculations are

given in Appendix B.

3. Flux Based Rayleigh Number

Another approach is to calculate a modified Rayleigh Number based on the

heat flux. This Rayleigh number is defined as:

RamC = (Grmc)(Pr)

Where "c'" stands for the center of the heated block.

27

L W"., V.

gflL'q"

Grm = (eqn 38

16k V-

where q" Q 'RCA is the heat flux at the surface of the chip and

h L

Nuc = -(eqn 3.9)

2 k

Here

h =q",,(Ta -Tr)

The above definition of Ramc and Nuc have been used to compare the results

with those of Fujii and Fujii [Ref. 231. Fujii and Fujii correlation of boundary layer

solution for a vertical surface with constant heat flux is given by

(eqn 3.10)

Nuc~ fPr)(GrmcPr)0

where

f(Pr) (Pr;(4+9V Pr+ lOPr))0 2'

X-*XAVii .0zl:I

IV. RESULTS

A. TEMPERATURE DATA

As indicated in Chapter III, the raw temperature data were kept in order to be

rrocessed later on by the heat transfer calculations program. Temperature outputs

belonging to 6 power levels are as following (see figure 2.2 for identification of' chip

numbers).

29

- S.-- *S .* ~ * ~ * * ' *~* .-

TABLE ITEMPERATURE DATA FOR INPUT POWER Q 0.34 WX

DATA IS STORED IN DATA FILE : DATA7

CENTER TOP RIGHT LEFT BOTTOM POWER(WATTS)

CHIP NO1: 29.4 29.7 29.7 28.9 29.8 .35

CHIP N02: 31.4 31.6 30.9 29.7 31.1 .35

CHIP N03: 31.9 32.0 31.9 31.9 32.0 .33

CHIP N04: 30.0 28.6 29.2 29.4 29.4 .35

CHIP NO5: 31.8 31.6 31.1 31.7 31.0 .35

CHIP N06: 32.3 32.5 31.4 31.6 32.5 .35

CHIP NO7: 30.1 32.0 29.4 29.4 32.0 .3_

CHIP N08: 31.2 31.1 30.5 30.8 31.3 .32

CHIP N09: 32.5 31.5 31.3 31.3 32.0 .3S

HEAT EXCHANGER TEMPERATURES: RIGHT LEFTBOT: 20.7 20.6TOP: 20.8 20.7 1

: .. ',. I'

TABLE 2

TEMPERATURE DATA FOR INPUT POWER QIN = 0.68 W



CHIP NOI: 34.2 34.8 34.8 33.5 35.0 .G8

CHIP NO2" 27.9 37.5 37.0 34.9 37.3 .69CHIP N03: 38.9 39.3 39.1 39.1 39.2 .66

CHIP N04: 35.4 33.0 34.0 34.3 34.3 .68

CHIP NOS: 38.4 38.0 37.3 38.2 37.0 .68

CHIP N06: 39.3 39.8 37.4 38.0 39.8 .69

CHIP N07: 35.6 35.1 34.2 34.2 35.4 .68

CHIP N08: 37.5 37.3 36.4 36.8 37.8 .64

CHIP N09: 39.8 38.0 37.2 37.2 39.2 .68

HEAT EXCHANGER TEMPERATURES: RIGHT LEFTBOT: 20.8 20.5TOP: 20.9 20.6

w

31

..

~% ' ~ ~ ' 4**V~-

ITABLE 3

TEMPEPATURE DATA FOR INPUT POWER QIN = 1.07 W

DATA IS STORED IN DATA FILE DATA16


CHIP NO1: 40.9 41.5 41.S 39.7 42.2 1.08

CHIP N02: 46.5 45.6 4S.2 42.3 46.0 1.09

CHIP N03: 48.1 48.9 48.5 48.5 48.7 1.0s

CHIP N04: 43.0 38.8 40.9 41.3 41.3 1.08

CHIP NOS: 47.5 46.4 45.7 47.1 45.2 1.08

CHIP N06: 48.6 49.2 45.5 46.2 49.3 1.09

CHIP NO7: 43.2 41.9 40.9 40.9 42.6 1.08

CHIP N08: 46.2 45.5 44.5 45.1 46.6 1.02

CHIP N09: 49.4 47.1 45.6 45.6 48.7 1.09


32

TABLE 4

TEMPERATURE DATA FOR INPUT POWER QI\ = 1.65 W



CHIP NO1: 50.0 50.4 50.4 48.8 52.1 1.65

CHIP N02: 57.5 56.5 56.5 3.6 56.8 1.67

CHIP N03: 60.0 64.2 62.1 62.1 63.1 1.63

CHIP N04: 53.5 47.0 50.3 51.3 50.8 1.65

CHIP NOS: 58.7 56.0 56.2 58.1 55.2 1.66

CHIP N06: 60.6 61.4 57.0 57.2 61.5 1.67

CHIP N07: 53.8 50.9 50.4 50.4 52.6 1.65

CHIP N08: 57.2 56.3 54.6 55.5 57.8 1.57

CHIP N09: 61.8 58.1 56.9 56.9 63.1 1.66


.33

3.4.

TABLE 5

TEMPERATURE DATA FOR INPUT POWER = 1.95 W



CHIP NO1: 55.1 55.7 56.2 52.3 57.6 1.95

CHIP N02: 63.5 62.4 62.3 59. 625 1.97

CHIP N03: 66.3 77 .2 71.8 72.5 74.3 1 .94

CHIP NO4: 59.1 51.8 55.5 56.3 56.0 1.95

CHIP NOS: 65.5 62.2 62.8 64.8 61.7 1.96

CHIP N06: 66.0 67.5 61.9 62.8 67.3 1.97

CHIP N07: 59.3 56.2 55.7 56.2 58.1 1.95

CHIP NO8: 63.8 62.4 60.2 61.9 64.3 1.88

CHIP N09: 68.2 64.7 63.1 63.7 75.5 i.97


.

34D

1- - Vm .rv Ju --1I 77. v Jy'.L

!9

TABLE 6

TEMPERATURE DATA FOR INPUT POWER Q 2.35 W



CHIP NOl: 64.9 64.9 65.5 61.8 67.4 2.35

CHIP N02: 73.2 71.8 71.8 08.: 7.O 2.38

CHIP N03: 75. 6 83.3 79.5 80 .2 81.7 2 .35

CHIP NO4: 68.6 iO. 4 64.8 64.9 65.2 2.36

CHIP NOS: 75.0 7,.5 72.1 .749 71.?

CHIP N06: 75 .6 76.7 70.7 721.4 76.6 _.8

CHIP N07: 70.3 65.5 65.5 66. 02-.2

CHIP NO8: 73.9 72.6 70.3 7'.8 7.. .26

CHIP N09: 77.9 72 5 72.9 7.6 ". .62.27

HEAT EXCHANGER TEMPERATURES: RIGHT i.EFTBOT: )-.6 2 •(1TOP: 21. 1 ,.

5I

°,.'

• 'W .m mr m ,," ," , r' " I % ." r .- ,," " w %. ,w" ." " ," . , '. " ,'",. .. . . .,,.,. m m iuWi ld dldldl ll i .... . ...5

Following, are the graphical representation of the temperature data givc:1 above.

The plots are prepared to include the center, maximium and miniMuIM temperatures "oreach chip at 6 power levels.

36 %

9 11? 11111111 1W (J.

0

C 0 -

Y9C~~~~~~~~~ 01CWEliii*CO*C06 09 *2 09;O

(J 0IU~ ii,.,, -

0 0 .......

* - * . -

2

-4

HZ~1 ~ 0 -4

-

C liii -

20<

o

C -~

~5 -'

C .~. -

<2

-r

0 -

< 00 -

I I I 0)~I' OTt 00i' O6~ O*Hf O~A~ O9~ O~C O*t~ O*~C O~ o*i~ivo~

(D) 3?JflIVMdVi3l

38 5

*,..~~.h.

.40 El Z 4; ,--- -o 0

0 0 i

0 -1 +

<0 0

i I I ' [ 10 .. w

0'O69 0"6 1,O0*9 tO"/-tf 0'9% o'g0f*9 O't 'r 0" 0 -Z" 0" T O'l 0 0"Of'0"6 C0 "O ,0 "

03

:4w4

o0 0

00 3

<0 0

4 0 0

OW OZ9 *090*990*9 olg OZ9 009 WI 9t vi 0 ) 4

Iu

II

13)

0 1

0 40

0oco

00 0

00<i

0'T90*-l0*0 0*40-40-4 -Z-0-4' -9 0 0V 0-G -0s3

B. HEAT TRANSFER RESULTS

The temperature data given in the previous section have been processed by the

heat transfer calculations program given in Appendix C. Following are the tabulation

of these heat transfer calculations

4.

'43

'V

a . ~ *~. a V 'V ~ ~ VV V.

- - '

r\BLE "-

HE.TTR\NSI" R CALCI. L.%TIONS FOR o\ i"1W

THE RAW EMF DATA ORE FROM FILE: DATA7ONET(W) TAVG-TS NU ;UNC. IN NU RA*I.E-7 7UNC. IN RA.335 8.72 25.38 26.76 5.59

.299 10.17 19.49 30. 7 6. -- I.84

277 1 1 26 1633.33-2, c, 7 -1, .3.224 8_.78_ 24.27 2_7.30 5. ,-* 2.39

29"2 10.84 17.81 ".7F. 7.10 2.:3

24 11 25 96.72 .97 74U

•.,3 0 9.2 8 c.__ 2.13 6 ' 6 .:38.28,3 I1 .26 !22 "' . ": -. ...

.2 80 11.08 6. 7,,

F.ABLE SHIEAr I R-ANSI ER CALCL LAIIONS FOR Q\= .(S %V

THE RAW EMF DATA ARE FROM FILE: DATA12ONET(W) TAVG-TS NU 7,INC.IN NU RA*I.E-7 %UNC.IN RA.662 13.58 32.33 22.10 9.1s 2.85

.600 16.16 24.67 25.09 11.16 2.91

.559 18.38 20.22 27.18 12.98 2.99

.639 13.83 30.67 22.01 9.34 ).85

.587 17.26 22.60 12.06 2.95

.574 17.88 21 .35 26.73 12.57 2.97

.636 14.17 29.75 23.16 9.60 2.86

.570 16.38 23.1 -2 26.11 t1.34 2.92

.564 17.63 21.26 .-4 12.36 2.96

.4 ,4

¢,.,,, ... ... ,, .

T..\ 1I3. E 9

HEAF TRANSFER CALCLLATIO\S FOR Q,= I W

THE RAW EMF DATA ARE FROM FILE: DATA16ONET(W) TAVG-TS NU %UNC.IN NU RA*I.E-7 %UNC.IN PA1.054 19.98 35.14 20.93 14.40 3.i7960.9604.1 I I26.60 23.65 18.07 1.25

.898 27.54 21.83 25.50 21.S '. s

1.016 20 . 64 32. 79 2 1 .86 i,4.36

.936 25.78 24. 24. 45 19. 63 ,..

921 &2.46 . .3 25. 1 20.24 .25

1. 010 20 .39 3',A. i7 2..01 15 .2 -7 3 .11

.908 ,4. 6 L7 U '4.75 E;. 499074 5 _....*

.906 26.32 '"2 .74 21-

TABLE 10

I EAT ITLANSFER CALCULATIO.S FOR .65 W

THE RAW EMF DATA ARE FROM FILE: DATA22QNET(W) TAVG-TS Nl %UNC.IN NU RA! I.E-7 %UNC.IN RA1.611 28.99 37.23 20.02 22.80 3.49

?.486 35.11 28.47 2.28 .9. 20 3.79

1.416 40.61 23-.54 23.65 35.48 4.08

1.547 30.)7 34. 16 211.01 24.18 65

1.458 3.9 26.96 22.'34 30.62 ".86

428 37.7 2 4 2.2 3.1.9

1 .540 30.72 3".: 1 •.57

?420 ;5.07 2.70~

,,1 .406 312., 1 2 4.86F 24. 19 3 7 5"

. .. ,, . g ,P ~ - % %%'%~%% ~ m *%*%

TABLE 11

1tEAT TIRNSFER CALCLLATIONS FOR Q\ = 1.95 \V

THE RAW EMF DATA ARE FROM FILE: DATA27ONET(W) TAVG-TS NU %UNC.IN NU RA*I.E-7 /UNC.IN RA1.897 33.49 38.08 19.87 27.73 3.77

1.759 40.40 29.39 21.99 3S.57 4.13

1.686 49 .27 23.23 3."246. 84 4.62

1.826 -. 06 25.05 20.82 2982 :3.85

1.714 42.53 27.26 27.77 38.15 4.24

1.713 42.35 27 .4 , .86 .. Sa ,4. 26

1.817 35 S.75 34.2- 20.94 30.2 .8P

.681 46 31 4.6. ,c ,.,- - 14 .3I E-

i.67) 4456 2.4? -_.70 ,rES 4.3

TABLE 12

11E.\T TRANSFER CALCULATIONi FOR 2.35 \V

THE RAW EMF DATA ARE FROM FILE: DATA32ONET(W) TAVG-TS NU %UNC.IN NLI RA*I.E-7 7UNC.IN RA

2. 257 42.01 36.37 20 .41 38.11 4 .22."

I 2_, .48.-3 -9.52 2.17 47.09 4.70

2.062 56.40 :'4 .97 -. 04 57.76 .14

2.192 4.-29 34.31 21.16 39.71 4.39

2.082 51.23 2-.67 ."77 2. o., 4.84

2.080 51.27 27.6-2 .86 SO. 4.4

2.159 44.96 ""2.1 41.84 4. 4

2.020 W4j 27.51 . ,7 S

2. 037 53.03 26 .18 "5 .81 4.34

-46

, , , iww Wh lm |Nll mlm mliil~m ill lllppl,

Following are the graphical representation of heat transfer calculations to Mincuje

Nusselt number versus Rayleigh number. The plots have been classified as BOTTOM

row of the chips. MIDDLE row of the chips and TOP row of the chips.

.47

Ss *w a. S-

-.. . . . . . .. . . .. . ...

0 0 - --

... .. ..... ...-.....-

. . . .. . . . . . . . . . . . . . .

- -94

....- ..- . .. . . . . . . . . .. . . .-

-0 T

-HIII IIHSI

IMWVNIFW~wWWWWWWWW'WZ~l~rVr'5LWMIP~rWnA~r XV6RWUMFUWFQ" wv-ilx~vwwvl 7v^,.w W

. . . . . . . .. . . . . . . . . . .

.. ........ ....... .. ..... ....

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

:~~~~~ ~~ .. . .. . . .. .. .. . . .. . . . . .. . . . . .. . . . .

..... ~ ~ ~ ~ .. .. .. . . . . . .

. . . . . . . . ... . . . . . . .

... .. ... . . .. .-.. . .. . . . . . . . . . . . . .

zo I z

0 ~., 70

U3111~~ -. IMIs~i

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

.......................... ....... ............ .. ....... ...

:3 0

. .. . . . .. . . . . . . . ... . .. . . .. .

. .. . .. . . . . . . . - - - - -

11 .2s .\

2:- i-tat - I.

C5C

. . .. . . . . . . . . . . . . . 0. . . . . . . .

7

. ..... . ...... .. .... .. .... ..... . ......0 ......

- ' - -- - - - - - - .. . . . . . . . . . . .

__ Z

.. . . .. . . .. . . .. . . . . . . . . . . . . . ... . .. . .. . . . ..-. . .

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

. . . . ......... ............. ........... . . . . . C

. . . . .. . .. . . . . .. . .. . .

DT pi

51

Figure 4.10 includes the comparison of the results for chip number 1, 2 and 3

with those of Fujii and Fujii JRef. 23] in the fashion defined at the end of Chapter Ill.

Fujii and Fujii correlation of boundary layer solutions for a vertical surface with

constant heat flux (Equation 3.10) has been applied to mid height of the components.

5

i*

II

I5

fN

-N ....

V. DISCUSSIONS AND RECOMMENDATIONS

A. DISCUSSIONS OF THE RESULTSFigures including the temperature distribution for different power levels show

explicitly that the temperatures of the simulated chips have a tendency to increase withthe height inside the enclosure. This suggests that the chips in the bottom row have thelowest temperatures while the top ones have the highest. This conclusion is alsoobvious from the figures that include Nusselt vs. Rayleigh number. Highest heattransfer rates or in other words highest Nusselt numbers are seen in the lowest row ofthe chips. Another trend is that the increase in Nusselt number (heat transfer rates)gets smaller with increasing Rayleigh numbers. It is supposed that, this results from thesignificant increase in the bulk temperature of the fluid. Comparison of the results withFujii and Fujii correlation [Ref 231. shows the weak effect of protrusion on the heattransfer. The bottom row of the chips have a little higher heat transfer rates than thosethe correlation gives. Especially the top row of the chips have significantly lower heattransfer coefficients. This is because the chips in the bottom row have free boundarylayer plumes whereas top row chips have boundary layer plumes confined by those of

lower rows.

B. RECOMMENDATIONSHigh uncertainty in the Nusselt number calculations results mainly from the

necessity to make a rough estimation for conduction losses to the back of the

enclosure. This requires that the enclosure walls be vcry well insulated to insure a verysmall amount of conduction loss so that the uncertainty is low.

A flow visualization technique for FC-75 should be established. Knowntechniques for water such as die injection, electro-chemical (because of the requirementfor maintaining the dielectricity) or floating particles (because of the requirement forneutral density) techniques are not suitable for FC-75. Repetition of the experimentwith different enclosure widths and component configurations will be worthwhile so faras the collection of data sets for general similar problems is concerned.

53

APPENDIX ASAMPLE CALCULATIONS

rhrough this appendix, rample calculations will be basecd on chip iuniber 2 .kLI,

power input 0.35 WV.

1. DETERMINATION OF UNPUT POWER

C: : C: C:

Ficure A.1 Electri ;aI \etv ark of Pow~er 1It.

From quatin 3.

2.3 7 - .0 2) 0.351

2. ESTIMATION OF CONDUCTION LOSS

According to Equation 3.3. we need to know F and Rom. 1 can h aiu,:cd

using the relationship between Q, and diference between F thack 'u rtacc tciperature

of the chip) and Te (center temperature of the -ihip) obtained from a prevIoUa sitoie

chip experiment:

in S

Since there are 9 chips. we tmght want to use an average T, . From Table 1.

Ts = 35.4"C lor chip no 2 and

average T. = 35.0 0C.

R

R

Rr R_., C V .

Rc

R_

RaR wa evlae from

RCa

Rc

Figure A.2 Thermal Resistance Network for Cor1dUtion Loss.

In order to esti mia e the total thernial re -ist nce IR on . we need to kno wv tilethermial conductivities of each material. as ie n Table 13.Ra was evaluated from:

.R a 11 a '\ - 1

,a"

where h = 3.S5 W m-C as an a.erage value, calculated from:

h I.-2(AT [ 1 ) - from (RefI 221.

55

or %

Nun .4.W

TABLE 13THERMAL CONDUCTIVITIES OF THE MATERIALS

Material k (W'm-0 C)

Rubber 0.03S9Plexiglass 0.1-421FC-75 0.06-40

TABLE 14THERMAL RESISTANCES TO CONDUCTION

Resistance Material Value ('C WV)

RCPlexiglass 54.979Rr Rubber 22.321R1 FC-75 54.253

RPlexiglass 4.073Ra Air 11.690

RCwas evaluated using a projected area of 16 x 32 nun2 instead of 8 x 24 nirn 2. R r andRiwere evaluated assuming they take up 80%/' and 20%/ of the total heat flow area,

respectively. Since all the R~ resistances are parallel to each other and, Rr and Reparallel to each other such that

Reqi 1 15.814 OC; W and,

Req 6.109 0 C,'Wwere used. Then the total resistance:

=cn 37.686 0C XVfrom Equation 3.3

Qco = (35.0 - 20.0),37.686 =0.398 WV.Since, at the same time,

=cn (T - T) R1

5 6

xp

where T1 is the temperature of the back of the circuit board and,

Rt = Ro n - Req2

= 31.577 'C.W.

T= 32.57'C. Then, for chip 2,

Qcon = (35.4- 32.57) 54.979 = 0.052 W.

3. CALCULATION OF NUSSELT AND RAYLEIGH NUMBER

From the definitions given in Chapter III,

T 20.7 0 C

Tavg = 30.87'C and,

Qconv= 0.351 -0.052 = 0.299 W, the net power.

Then from Equation 3.3,

h = 0.299(5.76 x 10- )(30.87 - 20.7)= 51.042 W,.m12.OC0,

From Equation 3.7,=12

Tf = (30.87 + 20.70),2 = 25.790 C

Using the functional relationships given in [Ref. 7] for properties of FC-75,

kf= 0.1(0.65- 7,8947 x 10- 4 Tf)= 0.0629 W, m-0 C

p 1000(1.825-0.00246Tf)

- 1761.6 kgm 3

cp = 4180(0.241111+3.7037 x 10- 4Tf)

= 1047.8 J,'kg- 0C

v 10-6(ao+aITr +a 2T"'f+ a3T 3 +a 4Tf4)

= 0.8526 x 10- 6 m 2: s

where

a0 = 1.4074

aI = 2.964x10-2

a, = 3.8018x10-4

a3 = -2.7308 x 10-6

a4 = S.1679 x 10 - 9

= 0.00246(1.825-0.00246Tf)

- 0.0014 (0 C)

Then, from Equation 3.1

57

Nu = (51.042)(0.024) 0.0629 = 19.48

t = (0.0629) (1761.6)(104.S) - 3.4077 x 10 m s

Pr (0.8526 x 10 6 (3.4077 x I o 25.()2

From Equation 3.6,

Gr (9.S1)(0.001-4)(0.02-1)k30.S7 - 20. -0) .$526 x 10- 6),'

- 2.651 x 106

then,

Ra = (2.65 1 x 106) 25.02) = 6.63 x 10"

Following is to show how Ramc and Nu c are calculated;

From Table 7 ,

Qnet = 0.299 W.

q = 0.299 5.76 x 10' = 519.1 W in,

from Equation 3.8,

Grmc = 3.70 x 106 and,

Ramc = 9.26 x 107

From Equation 3.9,Nuc -- 19.4

in whichh - 102.2 W,'rn2-°C

From Equation 3.10,

Nuc -- (0.6088)(39.201) -- 23.9

58 v

'I. , -zg . .v .- ,.--. . , -.-. .. ,. ,, . . ,4 ,

APPENDIX BUNCERTAINTY CALCULATIONS

Uncertainties in the experiment were evaluated using the root mean square

method of KlIM and McClintock [Ref. 21.

Followina is a sumrmary of the uncertainties used in the experiments

TABLE 15UNCERTAINTIES OF THE VARIABLES USED IN THE EXPERIMENT

Variable Uncertainty Reference

L 10--s m Resolution of measurement device

T 0.2 0C Thermocouple reading

kr 5%0 [Ref. 2[

k 7% [Ref. 21

R 0.0612 3%,, variation

kf 4% [Ref. 7]

Uncertainty in thermal resistances is given by

6R/R = ((SL;-L) 2 +(Sk~k) 2 +(SA,'A) 2 )05

where

6A/IA = ((8L 1'L,) 2 +((61, 2, L2 )2 )05S

For R P

;9

N.,* *.

L 0. 120 M.

L 0. 144m

A =1.72 x10 mn

.6A A =0.000 1, and;

6R, R = 0.07

6RP = (4.073)(0.07) = 0.2851 0 CWNN.

IfC similar method is repeated for all the thermal resistances

Son= ((SReqi )2 +(SRe q2) 2 +(6Rp)2 +(SR) 2)0 .5

Uncertainty in Q is dominated by the uncertainty in the 292 resistance since

voltage readings done by the acquisition system have a very low uncertainty.

'QnQn= 0.03

For the chip chosen for calculations;

8Qj, = (0-03)(0.351) = 0.01053 W

Uncertainties for other variables are calculated as following

where

S(T 5 - T1) ((6T,)' + (6T 1) 2 )1. 1

Uncertainty in net power

6Qon = ((6Q.n)2 +(6Q) 2 ) 0

Uncertainty in h

6h,,h -((6Qc... Qcon,) 2+ (6(TaVg -Td ), (Tav.g -TF)) 2 )0 -5

Uncertainty in Nusselt number;

60

IW! S

&Nu Nu = ((Sh h,)2-f (6k k)2-4+ (6L, L) 2 0 .5

-((0.3047) +(0.010)2 +(105 0.014)2)0. 5 =0. 3073.

Uncertainty in Rayleigh number is calculated the same method

6 RaRa = ((6Gr r)2 +(6Pr Pr) 2)0 .5

whcre

6Pr'Pr -((6vv) 24+ (6aa)2)0 .5

6Ra, Ra =0.0284

61~

!1 1 ZQ 6: 11 A

APPENDIX C

PROGRAM LISTINGS

1. DATA ACQUISITION PROGRASNI

: I !FILE- NAME:T 4E-ISl20 !EIE YIRGAI PAMUK. TJC,. URKI-l N64VY3040so !PROGRPM FOR GATHERING AND REDUCING DATA60 IFOR 49 THERMOCOUPLE AND VOLTAGES FOR POWER70 !SUPPLY.7HERtIOCOUPLE- TO 4S ARE ON THE80 !BLOCKS.46 TO 49 ARE ON THE HEAT EXCHANGERS.90100!1O COM /Ca/ D(7120 DIM Emi(59k.Power!9,.T(4q913)01 4u I:3RRE'-AT:ON WC-C~s-c 'C :01VERT E!4c TO DEiR-

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0: 1 NPIJ T "ENTE; NAME CP 4iEW DATA -- LE.Newii1#S20 PPTNT UJSING- 20;'. D)ATA ITRD N DATA ;7:LE :-30 BEEP

>U:J EN4D

360 IF Im-, THEN ASSIGN isiiie 70OlQdfiieti: MJ IF tfn-I) THN'380 CREATE BDAi PNewiiieS.S390 ASSIGN *File TO Newt jieS'400 END IF

-320 IINOW THE ACQUISITION SYSTEM WILL READ DATA

*4O BEEP4Er, BEEz.60 IF IM-1 THEN470 OUTPUT 709:-AR AF00 AL513'480 OUITPU T 7^2:*F? R1 T', Z,'90 rop 1-0 To 585-10O UTPUT 709:AS*1510 ENTER 72..:EmitI1520 BEEPS30 NEXT Ir40 OUTPUT iFie:Emi'*1SSO ELSS63 ENTER %Fie:Em0*. f

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57 END - -

I P,0 01 TP T 09:'TO

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620 FOR I-1) TO 78

610 Sum-Sum

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36t PPNT USING HPN:.£..2.X..D T.,.1

P TN T 'jS INC- ;'X. 'fH~ Nr 02: 5£22'. -'X).4X. 2D. r).:Si.6.T7 .().

i0 PRrNTl USI!J '12X.CHIPN :.tD .2 .tX2 D.,!0 t(JT 2.

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* 370980 PRINT USING *SX.**HEAT EXCHANGER TE4PERATURES: RIIHT LEFT .990 PRINT USING. '29X.'BOT:".2X.3..2'X':T'4£..T4."1410') PRINT USING 27-'X. TOP: 2.X.23(ID.D.2X*:T(47).7'481010j BEEP

10 30I 040 PR INTER IS I1050 A3SIGrq IiL~ TO1060 END

63

Copy available to DTIC does notpermit hily lecibl, reproduction

- *, .

2.HEAT TRANSFER CALCULATIONS PROGRAM%*

20 'ED:7TED BY:TURCA -PAMUI..LTJG;.TIJRKi3-; NAHVY.3040 11s0 !PROG~RAM TOj ANALYZE THE RAW DATA IN THE DATA60 !~..SOBTAINED FROM TEST RUNS7080 COM /Co/ D(7)90 DIM EmtS9).P6wer9)T(49).Tav(9.Ts(9).Tfi~M9).net(9).H(9).K(9, .Rhoi9)

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200 IIIIPIT "C7fJTE? ,4pME I F TLE.0 lei

240 PRIT sIGp0. TiE P(h~w EMc Dari: ARE FROM r:*E:ie250 BEED260 BEE-0270 ASS:IGN iFile '0 OldiieS280 EVE; '"Lie:Ei-'90NO FOR I-1) TO4

310 Sum-O R320 FOR j-1) TO 7330 Sjm-SumD(J*Emi):I'j34(j NEA X

36o) NEXAT)uS70 I2:30 J-1390 VoiV-miUI91400 FOR >5.C TO 52410 Poaa..,-Emi I.-Vit-Em IT) I/Rp420 Donwtj)-.O'.Potj)430 !BECAUJSE OF THE U14CERTAINTY IN RP4.J0 J-j+1450 NEX T

470 Acen-'.92C-4490 Aie*-i .44E-4490 Ari',1.44E-4S00 Atop.4.8E-5510 Aoot-a.8E-5-520 Atot-5.76E-4530 Taal-TO*4e*()Ao>T,)Al+()Ae#()Ao)Ao540 Tav(21.-(T(S*AcenT(6.Mtop+T7*r(3Tflie-()Ato)Ao %I50 Tava(3I-(T( 10I*Acen.T II )eAtoo*T(121.Arig.T) 13)eAlet.T 14''Abot)/Atot560 Tava(4.-Tr15.okcenT16,.ato0 .fl77.Arlq.Ts13J.Ai+T19.ibot)/Atot

580 T daygb. .T(25I.*Hcen.T2l6.*Atoo*.T27?.r~g.T(2)Aiet.T(29.Atot/Atot

o'4

z~7101

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60'0 Ta<C.G670 !UNCEqTAINTY OF AMRIENT TEM~PERATURE630 Dta-1.630 Totr-37.686700 Dtotr-8.8324

720 Dr3.2730 gec- .109740 Dreq-.8620.750760 !CHi" BACK SuRFACE TEMPER4TIJRE570 -;. TC739 Tsk-;) * Powk j / .08 .1 + ( j-!' .790 TsuTsiuT ji900 Dts.)1145.'SJ1 04 t>

21 u Dsavqsqr-Dtsavs:.rt3s -320 NEXT9310.30 7savc- ssilmi3

850 D tsa v (Dt3avasr S5)/9R60 Qrotioss.'Tsavc-Ti/Torr:170 DQto tJtotioss~i(Dtsavco2Dt.2Ta',of.sv-7aV'IDtotr/7otr; -!.§30 T .tt 'oss* *-'.i

.3 0 D r i t-,D to zr '2-D r -: i .900 uttt T t- J(O tor. 2.310 Dt!-Dmu-,.0ta'21.S320330 ICONDUCTION LOSS CALCULATION940 FO;i..3W3 0iosslJ)--sj)-'''/Rc

30'4vE-AGE SZN 7E~sPERATURE CALCLLATIONi

!010 Aakwn. 3,E-31020j ALfl-2 .448E-."

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* 0?3 PRINT USING. "X.-ONETiW) TAV(.-TS Mu X/.NC. IN NU RA*' E-7 7U

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1210 Dk-7.8947E-5-Dtilim1 220 <( J).- J)/10.1250 Rnotj)-I.825-.00246.rT; m(J)1240 0ro100.#.00246*btfiim1250 Rho( J )Rho( J)*1 Duo.!260 Cp~J?-.24l11 1-'J.7037E-4*Tfi1ruj)1270 Dco-ifl8G.*3.7037E-4*Dttiim?280 Cp(,J)CptJ*4180.1 290 N(J)-1 A074-2.964E-2*rfllm(J)+3.8018E-4*rfLlm(j) 2-2.73O8E-6*rf1ImLj)*3+S.1679E-9*fL Im~j)*4

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480 NEXT -1.49(1 'S I N 4F L'e To:SOO EN D

606

;i&- NO

LIST OF REFERENCES

1. Chu, R.C., "Heat Transfer in Electronic Systems", Hemisphere Publisher Inc.,Heat Transfer 1986, v.6, pp. 293-306.

2. Knock, R.H., "Flow Visualiation Study of Natural Convection from A HeatedProtrusion in a Liquid Filled Enclosure", Master's Thesis, Naval PostgraduateSchool, Dec. 1983.

3. Kohara, K. Nakao, S. Tsutsumi, K. Shibata, H. and Nakata, H., "High ThermalConduction Package Technology for Flip Chip Devices", IEEE Transactions onComponents, Hybrids and Manufacturing Technology, v.6, no.3, Sep. 1983.

4. Kishimoto, T. Sasaki, E. and Moriya, K., "Gas Cooling Enhancement Technologyfor Integrated Circuit Chips", IEEE Transactions on Components, Hybrids andManutacturing Technology, v.7, no.3, Sep. 1984.

5. Kraus, A. D.. "Thermal Analysis and Control of Electronic Equipment",[.lemisphere Publisher Inc., pp.377-407, 1983.

6. Bar-Cohen, A. "Thermal Design of Immersion Cooling Modules for ElectronicComponents", Heat Transfer Engineering, v.4, nos. 3-4, Jul.-Dec. 1983.

7. Liu, K.V., Yang.K.T., and Kelleher,M.D., "Three Dimensional Natural ConvectionCooling of an Array of Heated Protrusions in an Enclosure Filled with a DielectricFluid" Proceedings of International Symposium on Cooling Tecnhology ofElectronic Equipment, March 17-21 1987, pp. 486-497, 1987.

8. Acharya, S. and Goldstein, R.J., "Natural Convection in an Externally HeatedVertical or Inclined Square Box Containing Internal Energy Sources", Journal ofHeat Transfer, November 16. 1983.

9. Torok, D., "Augmenting Experimental Ifethodsfor Flow Visuali-'ation and ThermalPerfomance Prediction in Electronic Packaging Using Finite Elements", 2 2ad

national heat transfer conference and exhibition, August 5-8 1984, ASME HTDv.32, pp. 49-57, 1984,

10. Kuhn, D. and Oosthuizen, P.H., "Three Dimensional Transient Natural ConvectiveFlow in a Rectangular Enclosure With Localized Heating", Winter Annual Meetingof ASME, 12-17 December 1986, ASME HTD v.63, pp. 55-62. 1986.

67

11. Shakerin, S., Bohn, M. and Loehrke, R.I., "Natural Convection in an Enclosurewith Discrete Roughness Elements on a Vertical Heated Wall", Proceedings ofInternational Heat Transfer Conference, 17-22 August 1986, v.4, pp. 1519-1525.1986,

12. Liu, K.V., Yang, K.T., Wu, Y.W. and Kelleher, M.D., "Local Oscillatory SurfaceTemperature Responces in Immersion Cooling of a Chip Array by NaturalConvection in an Enclosure" Proceedings of the Symposium on Heat and MassTransfer, October 1-2 1987, pp. 309-330, 1987

13. Park, K.-A. and Bergles, A.E., "Natural Convection Heat Transfer Characteristicsof Simulated Ificroelectronic Chips", Journal of Heat Transfer, v.109, pp. 90-96,Feb. 1987:

14. Filis, P. and Poulikakos, D., "An Experimental Study of the Effect of WallNonuniformity on Natural Convection in an Enclosure Heated from the Side", Int.J. Heat and Fluid Flow, v.7, no. 4, pp. 258-265, Dec. 1986,

15. Anderson, R. and Bohn, M., "Heat Transfer Enhancement in Natural ConvectionEnclosure Flow", Winter Annual Meeting of ASME, 9-14 December 1984 Journalof Heat Transfer, v.108, no. 2, pp.330-336, May 1986.

16. Yang, R. and Yao.L.S., "Natural Convection Along a Finite Vertical Plate",Journal of Heat Transfer, v.109, pp. 363-413, May 1987.

17. Beckermann, C., Ramadhyani, S. and Viskanta, R, "Natural Convection Flow andHeat Transfer Between a Fluid Layer and a Porous Layer Inside a RectangularEnclosure", Journal of Heat Transfer, v.109, pp. 363-413, May 1987,

18. Kulkarni, A.K., Jacobs, H.R. and Hwang, I.J., "Similarity Solution for NaturalConvection Flow over an Isothermal Vertical Wall Immersed in Thermally Stratifiedmedium", Int. J. Heat Mass Transfer, v.30, no. 4, pp. 691-698, 1987,

19. Lankford, K.E. and Bejan, A., "Natural Convection in a Vertical Enclosure Filled .With Water near 4 *C', Journal of Heat Transfer, v.108, pp. 755-763, Nov. 1986.

20. Bohn, M.S. and Kirkpatrick, A.T., "High Rayleigh Number Natural Convection inan Enclosure Heated from Below and From the Sides', Natural Heat TransferConference, 24-28 July 1983 ASME HTD, v.26, pp. 27-33, 1983.

21. Kline, S.J.and McClintock, F.A., "Describing Uncertainties in Single-sampleExperiments", Mechanical Engineering , p.3, Jan. 1953.

22. Holman, J.P., "Heat Transfer", Mc-Graw Hill, pp. 265-305, 1981.

68

01

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23. Kavs.. W.M. and Crawford., M.E., 'Convective Fleat and Mass Transfrr . Mc-Graw Hill, pp. 313-331, 1980.

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INITIAL DISTRIBUTION LIST

No. Copies

Defense Technical Information Center 2Cameron StationAlexandria, VA 22304-6145

2. Library. Code 0142 2Naval Postgraduate SchoolMonterey, CA 93943-5002

3. Professor M. D. Kelleher, Code 69KKDepartment of Mechanical EngineeringNaval Postgraduate SchoolMonterey, CA 93943

4. Professor Y. Joshi, Code 69JIDepartment of Mechanical EngineeringNaval Postgraduate SchoolMonterey, CA 93943

5. Department Chairman Code 69Department of Mechanical EngineeringNaval Postgraduate SchoolMonterey, CA 93943

6. Deniz Kuvvetleri K.ligi 4Personel ve Egitim Daire BaskanligiBakanliklar, ANKARA-Turkey

7. Istanbul Technical University IMakina Muhendisligi FakultesiIsi Transferi Kursusu

N

Macka, ISTANBUL-Turkey

8. Bosphorus UniversityMakina Muhendisligi FakultesiIsi Transferi KursusuISTANBUL-Turkey

9. Middle East Technical UniversityMakina Muhendisligi FakultesiIsi Transferi KursusuANKARA-Turkey

10. Turgay PamukOgretmenler SitesiOdul Sok., A Blok, No= 11AmbarliI STANBU L-Turkey

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