Air Cooling Design for Machine Components

Air Cooling Design for Machine Components

Presenter: Peter van Emmerik

Faculty Advisor: Dr. LeRoy Alaways

Department of Mechanical Engineering Villanova University

Problem Statement Design a cooling system to reduce the

steady state temperature of a given heated structure from 100 C to 50 C using compressed air

Accomplish goal using less than 18 normal liters per minute.

Create both finite element analysis (FEA) and computational fluid dynamics (CFD) simulation models validated by empirical results

Background As the demands on modern machinery

used for high accuracy positioning systems grow, greater emphasis is placed on thermal control

Bearings systems can be sensitive to thermal gradations affecting life

Machine component C.T.E. differences coupled with uniform and non uniform thermal excursions may lead to accuracy issues

BackgroundHeated Fixture

Base (Al)

Heat Block (Al)

Film Heate

r

Stand-offs (SS)Thermocouple

locations

Fixture representative of linear servo motor

Methodology

Advantages of using compressed air Compressed Air Cooling

Low Cost

Packaging Efficiency

Reliable

Simple

Methodology

Three delivery methods examined Log Manifold Pinched Tube Air Knife

Two orientations to target surface Cross Flow Impinging Flow

Methodology - Designs

Log Manifold Simple tube Capped end Cross drilled

Methodology - Designs

Pinched Tube Simple tube Pinched End

Shapes flow Increases velocity

Methodology - Designs

Air Knife Machined Manifold Wide Slit Exit Enhanced Air

Entrainment

Manifold

Spacer

Cover

Apparatus Test Equipment

Thermocouples k-type Data Collection Box Air Flow Meter Heater Voltage Controller

Arrangements Cross Flow Impinging Flow

Test Procedure Apply power Reach un-cooled steady state temperature Turn on air delivery system Reach cooled steady state temperature Repeat for all designs and orientations

ResultsUn-cooled baseline

0 10 20 30 40 50 60 70 80 90 1000

20

40

60

80

100

120

Ambient Base Heat Block

Time (minutes)

Tem

pera

ture

(deg

C)

ResultsCross Flow

0 100 200 300 400 50020

30

40

50

60

70

80

90

100

110

Ambient Base Heat Block

Time (minutes)

Tem

pera

ture

(deg

C)

ResultsSteady State Temperature Comparison

*Design Goal: 50 deg CAir Consumption: 17.2 nL/min for all tests

BASE Temperature (° C)  Cross Flow Impinging Flow

Air Knife 29.8 28.9Pinched Tube 32.4 29.5Log Manifold 34.7 32.6

Ht Block Temperature (deg C)  Cross Flow Impinging Flow Goal met*

Air Knife 44.0 41.8 þPinched Tube 46.3 43.1 þLog Manifold 57.5 55.5 ý

Simulation Simulation used empirical data to build accurate

simulation model Determine thermal conductance at interfaces

2000W/m2-C Heat loading from heater

15.5 Watts Convective heat transfer coefficient (h)

6.5W/m2-C for natural convection

Simulation – Un-cooled Correlation Transient Un-cooled FEA vs Empirical

0 10 20 30 40 50 60 700

20

40

60

80

100

120

Base FEA Block FEA Base

Block Time (min)

Tem

pera

ture

(°C

)

Simulation – Un-cooledGood correlation between simulations and empirical results

CFD Tmax = 108 C Empirical Tmax = 107 C FEA Tmax = 110 C

Simulation – Heat Transfer Coefficient FEA predicted havg = 6.5 W/m2-C CFD predicts havg = 6.0 W/m2-C

Natural Convection 0-20 W/m2-K

Forced Convection 0-200 W/m2-K

Simulation – Cooled (pinched tube)Velocity distribution through tube center plane

Temperature distribution through tube center plane (top view)

Simulation – StreamlinesStreamlines colored by temperature

Natural Convection Forced Convection

Results- Simulation

Natural Convection Forced Convection

  Empirical FEA CFD Empirical CFD

Base 64 71 67  32.4  34

Ht Block 107 110 108  46.3  50

Average delta between CFD and empirical results is <5%

Conclusion Air knife and pinched tube met design goal

temperature of 50 C or lower Packaging and cost may dictate which

design is most practical FEA/CFD heat transfer simulation can be

correlated to empirical results and then used as model for future designs. Approximate 5% difference between CFD and empirical results

Future Work Air exit geometry sensitivity study Positional and orientational sensitivity

study Mesh density sensitivity study for FEA and

CFD simulations

ScheduleMay (08) June July

    Proposal Design Build    Draft Final Fixture Air Nozzles Fabrication Procure                       

August September OctoberTesting Simulation   Proposal    

        FEA CFD   Final                           

November December January (09)

   Report Draft   Mid Year              

       report website              

                       

February March April                          

May   Ongoing        Complete          Not started

Budget All test apparatus provided courtesy of Kulicke

& Soffa Industries. All materials for fixture fabrication provided

courtesy of Kulicke & Soffa Industries. Film heater only purchased item: $39.99 Total Expenditure: 39.99

All materials reusable or recyclable for minimal environmental impact.

No exposure to hazardous conditions during testing

BibliographyFox, McDonald and Pritchard, 2004, Introduction to Fluid Mechanics, John Wiley and Sons Inc.,

Incropera, Dewitt, Bergman and Lavine, 2007, Fundamentals of Heat and Mass Transfer, John Wiley and Sons Inc.,

D.-Y. Lee, K. Vafai, 1998, “Comparative analysis of jet impingement and micro channel cooling for high heat flux applications”, International Journal of Heat and Mass Transfer,

Material Web, materials data website, http://www.matweb.com/