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CAMCOS Reports Day May 17, 2006

CAMCOS Reports Day May 17, 2006. Mathematical and Statistical Analysis of Heat Pipe Design. All heat pipes and data presented today are purely fictional. Any similarity with any heat pipe, functioning or not, is purely coincidental. Modern Day Microchips.

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CAMCOS Reports Day May 17, 2006

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  1. CAMCOS Reports DayMay 17, 2006

  2. Mathematical and Statistical Analysis of Heat Pipe Design All heat pipes and data presented today are purely fictional. Any similarity with any heat pipe, functioning or not, is purely coincidental.

  3. Modern Day Microchips • Microchips already contain millions of transistors • In three decades, circuit elements will be the size of a single atom • 40 – 60 °C

  4. Dealing with the Heat • Traditional stacked heatsink and fan set up not feasible in a laptop • Need to separate the two where you have more space

  5. Requirements for Cooling • Solid metal rods lose too much heat to the environment • Cannot use a powered cooling system, too much power consumption caused the problem

  6. What is a Heat Pipe? Kim Ninh

  7. Heat Pipe Background • 1800s – A. M. Perkins and J. Perkins developed Perkins tube • 1944 – R. S. Gaugler introduced the use of a wicking structure • 1964 – G. M. Grover published research and coined the “Heat Pipe” name

  8. Applications of Heat Pipes

  9. Transfer of Heat Heat Added Heat Released Heat Sink Heat Pipe Heat Processor *Drawing is not to scale.

  10. Heat Transfer within a Heat Pipe Container Heat Absorbed Heat Released Wick Structure Evaporation Condensation Wick Structure Heat Released Heat Absorbed Container *Drawing is not to scale.

  11. Components of a Heat Pipe Sergio de Ornelas

  12. Container • Metal Tubing, usually copper or aluminum. • Provides a medium with high thermal conductivity. • Shape of tubing can be bent or flattened.

  13. Working Fluid • Pure liquids such as helium, water and liquid silver • Impure solutions cause deposits on the interior of the heat pipe reducing its overall performance. • The type of liquid depends on the temperature range of the application.

  14. Examples of Working Fluid

  15. The Wicking Structure

  16. Axial Groove Wick • Created by carving out grooves on the interior core of the Heat Pipe.

  17. Screen Mesh Wick Utilizes multiple wire layers to create a porous wick. Sintering can be used.

  18. Sintered Powder Wick Utilizes densely packed metal spheres. Sintering must be used to solidify the spheres.

  19. Purpose of the Wick • Transports working fluid from the Condenser to the Evaporator. • Provides liquid flow even against gravity.

  20. How the Wick Works • Liquid flows in a wick due to capillary action. • Intermolecular forces between the wick and the fluid are stronger than the forces within the fluid. • A resultant increase in surface tension occurs.

  21. Mathematical Models for Liquid Flow Through the Wick • Brinkman Equation • Darcy's Law

  22. Permeability • Permeability, K, is a measure of the ability of a material to transmit fluids and depends on factors such as the wick diameter, wick thickness, pore size. • Porosity, φ, and the effective pore radius, R, contribute to an increase in permeability.

  23. Capillary Limitation • Wick must have minimum pressure difference between the condenser and the evaporator for liquid to flow. • Dry-out occurs when there is insufficient pressure difference.

  24. Evaporator Misako van der Poel

  25. Evaporator The evaporator section is enclosed in a copper block, which is placed on top of the CPU.

  26. What happens in the Evaporator Section • The working fluid is heated to its boiling point and converted into a vapor. • Pressure and temperature differences forces the vapor to flow to the cooler regions of the heat pipe.

  27. The Thermal Resistance = F (heat pipegeometry, evaporator length, flatness, power input, wick structure, working fluid….)

  28. Condenser Diem Mai

  29. Condenser`s operations Vapor gives up its latent heat of vaporization Vapor cools down and returns to its liquid state Working fluid then flows back to the evaporator through the wick. Condensation

  30. Pressure governs the condenser's operations • Capillary pressure at the liquid-vapor interface • Vapor pressure drop • Liquid pressure drop • Pressure drop at the phase transition

  31. Heat Exchanger • Dissipates heat into environment • High Thermal Conductivity • Improve heat exchanger's performance • Increase surface area with more fins • Include a fan

  32. Is a mathematical concept analogous to the electrical resistance Is a function of the temperature difference and the heat input Unit: C / W Reduce all thermal resistances to prevent heat loss along the heat pipe Thermal resistance θ

  33. Wick structure Pore size Working fluid Shape of heat pipes Liquid Charge Factors to Consider in Heat Pipe Design • Length • Diameter • Bending angle • Flatness • Material

  34. Data Characteristics Tracy Holsclaw

  35. The Data • 11 heat pipes - 6 test runs each • 8 combination runs, and 3 baseline runs • Minimize response - thermal resistance, Ө • 3 factors: • Powder Size • Wick Thickness • Liquid Charge • Attempt to improve previous results

  36. Box Plots Ө

  37. Experimental Design • 23 Factorial Design (three factors) • Set up for factor screening • Replicates only at the center point

  38. Analysis of Variance (ANOVA) Sandy DeSousa

  39. ANOVA • A procedure to determine whether differences exist between group means • Goals: • Identify the important factors • If differences exist, identify the best heat pipe among the given settings (choose best point of cube)

  40. ANOVA Findings

  41. Tukey's Comparisons of Treatments Individual 95% CIs For Mean HP Mean --+---------+---------+---------+----- 5 1.01 (-*-) 13 1.06 (-*-) 17 1.09 (-*-) 9 1.12 (-*-) 19 1.22 (-*-) 15 1.40 (-*-) 11 1.61 (-*-) 7 1.62 (-*-) --+---------+---------+---------+----- 1.00 1.20 1.40 1.60

  42. Regression Analysis Michelle Fernelius

  43. Regression • Regression analysis is used to model the relationship between the dependent (response) and independent variables (factors) • Goal: Optimize the experimental settings within the scope of the data (search entire cube for best setting)

  44. Regression Equation

  45. Response Surface The minimum occurs at: Powder size = 77.2 Wick thickness = 0.65 Liquid charge = 138 Ө= 0.5988 θ 39% Improvement

  46. Further Analysis &Recommendations Marian Hofer

  47. Nested Design • Does variability in the manufacturing process affect our analysis? • There are 3 heat pipes of “identical” construction

  48. Analysis of Nested Design Analysis of Variance for θ TermP-value Treatment 0.016 Heat Pipe (nested within Treatment) 0.039 Strong evidence of variability in the manufacturing process.

  49. Recommendations • Augment the design by adding more experimental settings at key locations (e.g. axial-settings) • Ensure testing conditions are uniform across experimental settings • Use more than one unit per experimental setting

  50. Break Q&A

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