SEL Thermal Card Guide

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Sponsor: Schweitzer Engineering Laboratories
Duration: Fall 2017 - Spring 2018
Team Name Cooler Than Before
Faculty Advisor:
Consultants/Mentor:
  • Alex Olson
Team Members:
  • Marc Dobson
  • Collin Mabe
  • Nick Tobe
  • Michael Wendell

The goal of this project is to develop a card guide design that can be applied in SEL equipment that has a net thermal resistance less than 1 ⁰C/Watt between an aluminum tray (.05"-.1" thick) and the chassis (.05"-.1" thick).  This involves creating an instrumented test stand for measuring heat transfer across the card guide.  Results should be reconciled against an analytical model to assure accuracy.  The recommended solution should meet SEL standards for vibration.

Problem Definition[edit]

Deliverables[edit]

  • Experimental test set-up that can accommodate different guide configurations
  • Experiment design and test results that demonstrate which guide configurations are most effective
  • Comprehensive project documentation for easy future reference by client
  • Proof of Concept guide design
SEL Computer Model Description
Ctbmodel.jpg
  • This is the current SOLIDWORKS model of card guide and chassis.
  • The preferred method of heat transfer is conduction as it doesn't use moving parts.
  • The electrical components generate heat in the card which is transferred to the tray.
  • The tray then transfers heat to the chassis through the card guide.

Specifications[edit]

Sepcification Details
Thermal Performance Net thermal resistance of the guide must be ≤1°C/W between the tray it is supporting and the chassis it is fixed to.
Reliability Low DPU/Replaceable in case of failure.
Part Cost Card guide needs to cost less than $5.00/part.
Insertion Force Actual force of insertion.
Corrosion Resistance Must not promote galvanic corrosion.
Operational Simplicity How easy it is to use.
Dimensions The card guide is to be 5in* long, 0.38in wide, and 0.50in tall. Design able to support variable length and variable tray thickness.

Project Learning[edit]

SolidWorks Flow Simulation[edit]

To determine a suitable card guide deign our group used SOLIDWORKS to model heat transfer rates with Flow Simulation. This was then calibrated to match the experimental setup, so we could have a verified test apparatus once the guide was manufactured.

Test Setup Description
Ctbthermal.jpg
  • The testing apparatus was used to compare with our experimental model
  • A heat source was placed on the end of the guide to create a mock resistor
  • This model was the first assembly used to determine the thermal resistance through the card guide
  • This model was the first assembly used to determine the thermal resistance through the card guide
  • It was found to have too many variables and too much variation from experimental model

The testing aparatus was then simplified to a two plate study, so we could control temperature boundary condition and solve for varying surface area, thickness, contact pressure, and material properties. All these factors were varied in parametric studies to determine the point where thermal conduction is optimal.

Two Plate Test Description
CTB 2plate.jpg
  • This design allows for an easy set-up and controlled variables.
  • The temperatures are specified at each end of the plate assembly with goals specified throughout.
  • This model allowed us to solve for contact resistance in the experimental setup.
  • Parametric studies were able to be easily ran on this design with accurate results.

Experimental Setup[edit]

For our test setup we have created a scale version of the thermal card guide. This experiment would allow us to use thermocouples to measure temperature differences on the guide and determine the conductive power. To do so the resistance was calculated using R=L/kA, where R is resistance, L is length between two thermocouples, k is the thermal conductivity of the material, and A is the cross-sectional area of the tray. Once resistance is found we used Q =(T_1-T_2)/R, where Q is the conductive power, T is the temperature at a point, and R is the resistance calculated.

Initial Setup Thermocouple Figure Description
CTB expset.jpg
CTB expset2.jpg
  • Two power resistors are being used as a heat source for the system
  • The Bell Jar is a vacuum chamber will remove air from the system, thus reducing convection heat transfer
  • There are several thermocouples placed on the system to measure the gradient across the plate and through the guide
  • The measurements taken from this system can then be extrapolated for different sizes of card guides
  • The recorded measurements can be used to compare with the SolidWorks and math models
Pressure Test Setup Description
CTB ptest.jpg
  • Select masses were placed on the intersection of the two plates to create a pressure
  • The pressure between the plates was varied to record and find differences in contact resistance ans pressure increases
  • There are several thermocouples placed on the system to measure the gradient across the plate and through the guide
  • The measurements taken from this system can then plotted and effective pressure can be determined
  • The recorded measurements can be used to compare with the SolidWorks and math models

Experimental Results[edit]

After completing the experiments we were able to draw some conclusions from the data. However, these experiments still have some distance to cover as matching it to the SolidWorks Flow-Sim models have not been fully achieved. There was still 22% difference between the simulation and the actual experiment, but the simulation was conservative in estimating the resistance. With the pressure experiment there was only a 13% difference between the conductive resistances of the aluminum and brass, functionally the brass could replace the aluminum as material for the guide. That being said the brass would be much more expensive. Secondly in the pressure experiment, to reduce thermal contact resistance, pressure was found to be effective.

Guide Designs[edit]

Initial Designs[edit]

Guide Design Picture Description
One-Piece Guide
Ctb pguide.png
  • One of the first guide designs created for pressure application
  • Designed as one piece to create better conductivity and contact with chassis wall
  • Determined difficult to manufacture with extensive bends and spring fingers
End Capped Guide
CTB latchguide.jpg
  • Guide made with pressure application after insertion for easy of use
  • Base acts as heat sink to draw a large amount of heat
  • Determined to be too thick of base and difficult to manufacture with extruded base
End Latching Guide
CTB Guide1.png
  • Similar to the End Capped Guide, but differs with latching mechanism and plate thicknesses
  • Met specifications, but latch could only be oriented on one side, which would require left and right guides
Internal Pressure Guide
CTB Guide2.png
  • One of the more intricate guides where plate could be inserted and then pressure applied
  • Similar to current guides on the market
  • Interior bends were found too expensive to manufacture and again had some problem with left and right application

Final Design[edit]

For our final design we created a two piece card guide with one thermally conductive piece and another used to apply pressure to the tray when inserted. This will ensure better contact with the guide and decrease contact resistance, which was the biggest issue with our system.

Final Guide Design Description
CTB finaldesign.jpg
  • The top piece is made of cartridge brass which has a thermal conductance of 121.2 W/m
  • The bottom is made of spring steel, which can be stamped to have the spring fingers shown
  • When the tray is inserted into the guide the spring finger will exert a pressure upwards to contact the top part of the guide
  • This model was determined through simulation to have a thermal resistance of .8°C/W
  • This product wasn't able to be manufactured for expo so a 3D printed proof of concept was used

The Final Guide Design had intricate bends in the spring steel, so it couldn't be produced in the shop and its manufacturing required a 6 week lead time. As an alternative our group designed and 3D printed a PLA bracket to use as a proof of concept.

Proof of Concept Design Description
CTB proofcon.png
  • The PLA bracket has slightly flexible spring fingers that were able to apply similar pressure to the plate
  • This part will act similar to the Final Design, but wont perform as well
  • The guide was mounted using bolts with the cartridge brass top for proof of concept
  • The design was ran in a comparative test where it performed slightly better than the existing guide

Design Validation[edit]

Parametric Model Description
CTB para.png
  • Values found in the SolidWorks parametric study gave design parameters for surface area and thickness of the guide
  • In the parametric study the new guide design had a lower thermal resistance than desired 1°C/W
  • An experiment was ran with a heat source in the center of the plate and temperatures were measured at either side with a thermal camera
  • The new guide had about a two degree temperature difference determined through thermal pictures in ambient conditions

Team Information[edit]

Ctbteam.jpg
Team "CTB"
Member Biography Discipline
Marc Dobson

Team Orginizer

First generation college student, born and raised in Idaho. Anything outdoors is my game, but Netflix is also my friend. I choose to become an engineer to create a positive change in not only the world but my bank account as well. Mechanical Engineering
Collin Mabe

Treasurer

Born and raised in Boise Idaho I look forward to starting my career as an engineer in the near future. I enjoy fishing, hunting, hiking, and really anything that involves the outdoors. Using my skill set to help engineer a better world is the source of my drive, hopefully someday I will get to realize this dream. Mechanical Engineering
Nick Tobe

Primary Contact

Graduating senior at the University of Idaho from Eagle, Idaho. I plan to move to Auburn Hills, Michigan to pursue a mechanical engineering career in the automotive industry. I enjoy playing soccer and biking during the summer and in the winter I spend my free time snowboarding. Mechanical Engineering
Michael Wendell

Secretary

I am from Eagle, Idaho and am Senior in Mechanical engineering at the University of Idaho. I plan to graduate and move to Boise and find a career in engineering. My interests include golfing, playing soccer, and riding my motorcycle. Mechanical Engineering