Comparison of Micro-Pin-Fin and Microchannel Heat Sinks Considering Thermal-Hydraulic Performance and Manufacturability

This paper summary is based on the article Comparison of Micro-Pin-Fin and Microchannel Heat Sinks Considering Thermal-Hydraulic Performance and Manufacturability presented at the IEEE TRANSACTIONS ON COMPONENTS AND PACKAGING TECHNOLOGY

1. Overview:

• Title: Comparison of Micro-Pin-Fin and Microchannel Heat Sinks Considering Thermal-Hydraulic Performance and Manufacturability
• Author: Benjamin A. Jasperson, Yongho Jeon, Kevin T. Turner, Frank E. Pfefferkorn, and Weilin Qu
• Publication Year: March 2010
• Publishing Journal/Academic Society: IEEE TRANSACTIONS ON COMPONENTS AND PACKAGING TECHNOLOGY
• Keywords: Micro heat sink, micro-manufacturing, micro-machining, pin-fin heat sink.

• Social/Academic Context of the Research Topic:
  • The increasing heat loads in micro-electronic devices demand highly efficient thermal management techniques for dissipating high heat fluxes from small areas.
  • Single-phase liquid-cooled miniature heat sinks with microscale enhancement structures have emerged as a solution. Parallel-plate fins have been widely studied.
  • Recent advances in microfabrication enable more complex 3-D enhancement structures like staggered micro-pin-fin arrays.
• Limitations of Existing Research:
  • While microchannel heat sinks have well-established thermal-hydraulic performance models, reliable models for micro-pin-fin heat sinks are lacking due to complex flow and heat transfer. Existing studies are mostly empirical.
  • Economics and realistic microfabrication options are critical for the viability of micro-pin-fin heat sinks compared to microchannel heat sinks.
• Necessity of the Research:
  • To compare the thermo-hydraulic performance of micro-pin-fin heat sinks with microchannel heat sinks.
  • To evaluate the manufacturability and cost-effectiveness of both designs using micro-end-milling.
  • To provide a comprehensive comparison considering thermal performance, hydraulic performance, and manufacturing cost.

3. Research Purpose and Research Questions:

• Research Purpose:
  • To simultaneously compare the thermo-hydraulic performance and manufacturability of micro-pin-fin and microchannel heat sinks as alternatives for dissipating high heat fluxes.
• Key Research Questions:
  • Does the micro-pin-fin design outperform the microchannel design in terms of thermo-hydraulic performance?
  • What are the manufacturing methods suitable for fabricating micro heat sinks out of metals?
  • What is the difference in manufacturing cost between micro-pin-fin and microchannel heat sink designs using micro-end-milling?
• Research Hypotheses:
  • Micro-pin-fin heat sinks have the potential for improved heat transfer compared to microchannel heat sinks, but with a trade-off in pressure drop and manufacturing cost.
  • Machining time is the primary factor determining the manufacturing cost difference between the two designs when using micro-end-milling.

4. Research Methodology

• Research Design:
  • Comparative experimental study of thermal-hydraulic performance for micro-pin-fin and microchannel heat sinks.
  • Case study on micro-end-milling to compare manufacturing costs.
  • Review of various manufacturing techniques for micro heat sinks.
• Data Collection Method:
  • Experimental measurements of thermal resistance and pressure drop for both heat sink designs using single-phase water cooling.
  • Analytical models for microchannel heat sink performance based on existing literature.
  • Cost analysis based on machining time and tool path calculations for micro-end-milling.
• Analysis Method:
  • Comparison of experimental thermal resistance and pressure drop data for both designs across varying flow rates.
  • Calculation of machining time and cost based on tool path length and manufacturing parameters.
  • Qualitative assessment of different manufacturing methods based on mass production suitability, prototyping suitability and cost.
• Research Subjects and Scope:
  • Copper (110) micro heat sinks with channel/pin width of 200 µm and height of 670 µm.
  • Micro-pin-fin heat sink: staggered array of 1950 micro-pins.
  • Microchannel heat sink: parallel channels.
  • Single-phase water as coolant.
  • Manufacturing method focus: micro-end-milling.

5. Main Research Results:

• Key Research Results:
  • Thermal Performance: Micro-pin-fin heat sink exhibits lower convection thermal resistance at liquid flow rates above approximately 60g/min compared to microchannel heat sink. Below 60g/min, microchannel heat sink shows lower thermal resistance. (Refer to Fig. 10. Comparison of micro-pin-fin heat sink and microchannel heat sink average convection thermal resistance).
  • Hydraulic Performance: Micro-pin-fin heat sink has a significantly higher pressure drop than microchannel heat sink across all tested flow rates. (Refer to Fig. 11. Comparison of micro-pin-fin heat sink and microchannel heat sink pressure drop).
  • Manufacturing Cost: Micro-pin-fin heat sinks are approximately three times more expensive to manufacture than microchannel heat sinks using micro-end-milling, primarily due to the longer machining time required for the more complex pin-fin geometry. Machining time is the primary cost factor. (Refer to Fig. 14. Total machining distance (tool path as a function of pin/wall width for a 1 cm x 3.38 cm area)).
• Statistical/Qualitative Analysis Results:
  • Analytical models for microchannel heat sinks show good agreement with expected trends.
  • Review of manufacturing techniques (Table I. POTENTIAL MANUFACTURING METHODS FOR MICRO HEAT SINKS) indicates micro-EDM, micro laser machining, and micro casting as viable for mass manufacturing.
• Data Interpretation:
  • The enhanced thermal performance of micro-pin-fin heat sink at higher flow rates is attributed to more tortuous flow and stronger vortices, improving heat transfer.
  • Higher pressure drop in micro-pin-fin design is due to increased drag from pin arrays.
  • Machining time difference is directly linked to the complexity of tool path, which is significantly longer for staggered pin-fin geometry.
• Figure Name List:
  • Fig. 1. Structure and dimension of (a) microchannel heat sink and (b) micro-pin-fin heat sink.
  • Fig. 2. Illustrations of three electrodischarge machining techniques: (a) wire EDM, (b) die sinking, and (c) EDM milling.
  • Fig. 3. Schematic of LIGA process.
  • Fig. 4. Schematic of die casting.
  • Fig. 5. Schematic of extrusion process.
  • Fig. 6. Schematic of micro powder injection molding.
  • Fig. 7. Schematics of milling: (a) slot milling and (b) end milling.
  • Fig. 8. Schematic of chip load.
  • Fig. 9. Photographs of (a) copper heat sink and (b) pin fin geometry created by micro-end-milling.
  • Fig. 10. Comparison of micro-pin-fin heat sink and microchannel heat sink average convection thermal resistance for (a) Tin = 30 °C and (b) Tin = 60 °C.
  • Fig. 11. Comparison of micro-pin-fin heat sink and microchannel heat sink pressure drop for (a) Tin = 30 °C and (b) Tin = 60 °C.
  • Fig. 12. Illustration of tool path for milling channel heat sink.
  • Fig. 13. Illustration of tool path for milling staggered pin heat sink.
  • Fig. 14. Total machining distance (tool path as a function of pin/wall width for a 1 cm x 3.38 cm area).

2. Research Background:

6. Conclusion and Discussion:

• Summary of Main Results:
  • Micro-pin-fin heat sinks offer better thermal performance at higher flow rates (>60g/min) but with increased pressure drop and manufacturing cost compared to microchannel heat sinks.
  • Micro-end-milling cost for micro-pin-fin heat sinks is approximately three times higher due to longer machining time.
• Academic Significance of the Research:
  • Provides a direct comparison of thermal-hydraulic performance and manufacturability for micro-pin-fin and microchannel heat sinks.
  • Offers insights into the flow behavior and heat transfer mechanisms in micro-pin-fin arrays.
  • Contributes to the understanding of cost factors in micro-manufacturing of heat sinks using micro-end-milling.
• Practical Implications:
  • Guides the selection of heat sink design based on application requirements, considering trade-offs between thermal performance, pressure drop, and cost.
  • Highlights the importance of machining time in micro-manufacturing cost and potential areas for cost reduction through process improvements (e.g., higher spindle speeds, advanced tool coatings).
  • Suggests casting as a potential cost-effective method for mass production of micro-pin-fin heat sinks, minimizing the cost difference compared to microchannel designs.
• Limitations of the Research:
  • Cost analysis is specific to micro-end-milling and may vary for other manufacturing methods.
  • Assumes constant feed rate and tool life for cost comparison, which may not be entirely accurate in real-world scenarios.
  • Focuses on specific geometries and may not be generalizable to all micro-pin-fin and microchannel designs.

7. Future Follow-up Research:

• Directions for Follow-up Research:
  • Explore other pin fin designs (diamond, circular, airfoil) to optimize thermal performance and pressure drop.
  • Investigate the impact of improved productivity (higher feed rates, spindle speeds, advanced tool coatings) on reducing manufacturing cost and the cost difference between designs.
  • Further research into casting and other mass production methods for micro-pin-fin heat sinks to reduce unit cost.
• Areas Requiring Further Exploration:
  • Optimization of micro-pin-fin geometry for specific applications and flow conditions.
  • Development of more accurate and comprehensive models for predicting thermal-hydraulic performance of micro-pin-fin heat sinks.
  • Detailed cost analysis considering various manufacturing methods and production volumes.

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9. Copyright:

• This material is "Benjamin A. Jasperson, Yongho Jeon, Kevin T. Turner, Frank E. Pfefferkorn, and Weilin Qu"'s paper: Based on "Comparison of Micro-Pin-Fin and Microchannel Heat Sinks Considering Thermal-Hydraulic Performance and Manufacturability".
• Paper Source: 10.1109/TCAPT.2009.2023980

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