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

Heated Fixture Background Film Heater Stand-offs (SS) Thermocouple locations Heat Block (Al) Base (Al) Fixture representative of linear servo motor

Compressed Air Cooling 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

Log Manifold Methodology - Designs Simple tube Capped end Cross drilled

Pinched Tube Methodology - Designs Simple tube Pinched End Shapes flow Increases velocity

Air Knife Methodology - Designs Machined Manifold Wide Slit Exit Enhanced Air Entrainment Cover Spacer Manifold

Apparatus Test Equipment Arrangements 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

Results Un-cooled baseline

Results Cross Flow

Steady State Temperature Comparison Ht Block Temperature (deg C) Results Steady State Temperature Comparison BASE Temperature (° C)   Cross Flow Impinging Flow Air Knife 29.8 28.9 Pinched Tube 32.4 29.5 Log Manifold 34.7 32.6 Ht Block Temperature (deg C) Goal met* 44.0 41.8 þ 46.3 43.1 57.5 55.5 ý *Design Goal: 50 deg C Air Consumption: 17.2 nL/min for all tests

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

Simulation – Un-cooled Good 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 – Streamlines Streamlines colored by temperature Natural Convection Forced Convection

Results- Simulation Natural Convection Forced Convection   Empirical FEA 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

Air exit geometry sensitivity study Future Work Air exit geometry sensitivity study Positional and orientational sensitivity study Mesh density sensitivity study for FEA and CFD simulations

Schedule May (08) June July Proposal Design Build Draft Final Fixture   Proposal Design Build Draft Final Fixture Air Nozzles Fabrication Procure August September October Testing Simulation FEA CFD 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

Bibliography Fox, 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/