Heat Transfer Simulation: Reporting and Analysis

Heat Sink Design Iterations

The design process of the heat sink involved a series of iterative enhancements aimed at optimizing thermal performance, manufacturability, and cost-effectiveness. Each iteration addressed key limitations discovered through analytical calculations, Python simulations, and ANSYS-based thermal analysis. This section discusses the two primary iterations—Version 1 and Version 2—highlighting the design evolution, key modifications, and performance improvements achieved.

Version 1: Baseline Design

Version 1 served as the baseline for evaluating thermal performance. This iteration featured two distinct configurations fabricated from aluminum alloy 6061 due to its high thermal conductivity:

• Straight Rectangular Fin Design: Uniformly spaced rectangular fins aligned perpendicularly to the base. Dimensions included a 50 mm × 50 mm base and 5 mm thick fins spaced 3 mm apart.
• Cylindrical Pin Fin Design: Evenly distributed vertical cylindrical fins with a 2 mm diameter, spaced 5 mm apart.

Performance Analysis of Version 1

Under forced convection conditions at 10 W/m²·°C and 150 W/m²·°C, Version 1 exhibited the following characteristics:

• Straight Fin Design: Demonstrated moderate thermal performance with a maximum temperature of 41°C. However, significant thermal gradients were observed along the fins, indicating inefficient heat dissipation.
• Pin Fin Design: Provided a larger surface area but showed higher heat accumulation near the base, limiting effective thermal spreading along the fins.

Key limitations identified in Version 1 included:

1. Insufficient convective efficiency under low airflow conditions.
2. Non-uniform temperature distribution, leading to localized hotspots.
3. Higher airflow resistance in pin fin configurations, resulting in increased pressure drops.

Figure 1 & 2: Thermal flux for Version 1 (Pin and Straight Fin) under forced convection at 10 W/m²·°C.

Version 2: Optimized Design

Version 2 introduced substantial design enhancements based on the findings from Version 1. Key modifications included:

• Base Expansion: The base dimensions were increased to 100 mm × 100 mm, effectively doubling the available heat dissipation surface area.
• Optimized Fin Spacing: Improved fin spacing reduced thermal gradients by enhancing airflow management and heat dissipation.
• Increased Fin Density: The number of fins was increased to boost convective surface area without significantly raising pressure drop.
• Material Consistency: Retained aluminum alloy 6061 for its balance of thermal performance and manufacturability.

Performance Improvements in Version 2

The enhancements in Version 2 resulted in significant performance gains:

• Straight Fin Design: Achieved uniform temperature gradients with maximum surface temperatures not exceeding 30.7°C.
• Pin Fin Design: Improved thermal performance with better heat flux distribution, although still less efficient than straight fins.
• Reduced Pressure Drop: Enhanced airflow pathways lowered pressure drops, improving overall system efficiency.

Figure 3 & 4: Heat flux for Version 2 (Pin and Straight Fin) under high convection conditions (150 W/m²·°C).

Comparative Analysis of Versions 1 and 2

Table 1: Performance comparison between Versions 1 and 2 under high convection conditions.

Key Takeaways from the Design Iterations

The iterative design process highlighted the critical role of base area, fin geometry, and airflow management in optimizing thermal performance. Version 2's straight fin design emerged as the most effective configuration, offering uniform temperature distribution, reduced pressure drops, and superior heat dissipation. These improvements underline the importance of design optimization in achieving efficient thermal management solutions for high-power electronic applications.

Analytical Calculations

The analytical calculations in this project were conducted to determine the thermal performance of the heat sink designs. Using fundamental heat transfer principles, the calculations focused on estimating key parameters such as heat dissipation, Reynolds number, airflow velocity, and pressure drop. These parameters provided a benchmark for validating simulation results and evaluating design effectiveness.

1. Convective Heat Transfer Equation

The primary equation used to calculate the heat transfer rate (Q) is:

Q = h × A × (T_surface − T_ambient)

Where:

• Q: Heat transfer rate (W)
• h: Convective heat transfer coefficient (W/m²·K)
• A: Effective surface area for heat transfer (m²)
• T_surface: Surface temperature of the heat sink (60°C)
• T_ambient: Ambient air temperature (25°C)

2. Reynolds Number Calculation

The Reynolds number (Re) determines the flow regime (laminar or turbulent):

Re = (ρ × v × D) / μ

Where:

• ρ: Density of air (1.225 kg/m³ at 25°C)
• v: Velocity of air (m/s)
• D: Hydraulic diameter (m)
• μ: Dynamic viscosity of air (1.81 × 10⁻⁵ kg/m·s)

Hydraulic Diameter Calculation:

For the rectangular fin design:

D = 4A / P

• A: Cross-sectional area for airflow = 2.5 × 10⁻⁴ m²
• P: Perimeter of the flow path = 2.05 × 10⁻² m

Result: D = 4.88 × 10⁻³ m

Reynolds Number Example:

Assuming v = 2 m/s:

Re = (1.225 × 2 × 4.88 × 10⁻³) / (1.81 × 10⁻⁵) = 660 (Laminar Flow)

3. Airflow Velocity for Sufficient Cooling

Using the Dittus-Boelter correlation:

h = 10.45 + 10√v

Example Calculation: Assuming v = 2 m/s, h = 24.57 W/(m²·K).

Required Airflow Velocity:

v = ((Q / (h × A × ΔT)) − 10.45)²

Result: v = 2.02 m/s (Sufficient for cooling requirements).

4. Surface Area and Heat Transfer Results

Table 1: Analytical results comparing surface area, heat transfer, temperature, and flow characteristics for both versions.

5. Key Insights from Analytical Calculations

• Version 2 straight fins: Provided the highest heat dissipation and uniform temperature distribution.
• Airflow requirements: Reduced in Version 2 due to optimized geometry and fin spacing.
• Flow behavior: Both designs exhibited laminar flow, suitable for efficient forced convection applications.
• Heat dissipation efficiency: Increased by 393.7 W in Version 2 compared to Version 1 under high convection.

6. Summary of Analytical Findings

The analytical calculations confirmed that Version 2's straight fin design is the most thermally efficient configuration, achieving high heat dissipation rates with minimal airflow requirements. The analytical results aligned closely with simulation data, validating the reliability of the design modifications.

Conclusion & Recommendations

Conclusion

This study analyzed air-cooled and water-cooled heat sink designs for a 75 W heat load, employing analytical calculations, Python-based simulations, and ANSYS Workbench validation. The Version 2 straight fin heat sink emerged as the most effective configuration, demonstrating superior thermal performance and operational efficiency.

Key Findings:

• Heat Dissipation: Version 2 straight fin design achieved a heat dissipation rate of 535.50 W, exceeding the required 75 W.
• Temperature Control: Maintained uniform surface temperatures below 30.7°C.
• Airflow Efficiency: Reduced pressure drops due to optimized airflow pathways.
• Water Cooling Potential: Water-cooled systems showed theoretical promise, though practical validation was limited by simulation complexities.

Recommendations for Future Work

While the Version 2 straight fin heat sink met the primary performance goals, further enhancements are suggested for broader applications:

1. Material Optimization

Investigate alternative materials such as copper or composite alloys to improve thermal conductivity and reduce temperature gradients.

2. Advanced Water-Cooling Systems

Refine water block geometries and address simulation challenges related to boundary conditions and complex fluid paths. Experimental validation is recommended to assess practical performance.

3. Airflow Optimization

Optimize fan placement and implement variable speed controls to enhance airflow management and reduce energy consumption.

4. Geometric Refinements

Explore alternative fin geometries, such as louvered or wavy fins, to enhance turbulence and improve convective heat transfer.

5. Experimental Validation

Construct physical prototypes for empirical testing, providing real-world data to refine simulation models and design assumptions.

6. Scalability Analysis

Evaluate the performance of the heat sink design under higher power loads and varied form factors to ensure applicability across diverse electronic systems.

Summary

The Version 2 straight fin design offers an efficient and scalable solution for thermal management in high-performance electronics. Future research should focus on material enhancements, airflow optimization, and advanced water-cooling integration to further improve performance and adaptability.