Experimental and Computational Investigation of Air Flow on a Hybrid Heat Sink

Abstract

Polymer-based heat exchangers can offer lower mass, corrosion resistance and manufacturing flexibility compared with conventional metallic designs, but the low thermal conductivity of unfilled polymers limits heat rejection. This study experimentally and computationally evaluates a hybrid finned-tube heat sink made from reprocessed high-density polyethylene (HDPE) reinforced with multi-walled carbon nanotubes (MWCNTs) and boron nitride (BN). Three fin materials were compared: neat HDPE, HDPE with 4% MWCNT and 2% BN, and HDPE with 6% MWCNT and 2% BN. Thermal conductivity was measured using the composite-wall method, and the fabricated heat sink was tested in an air–water loop at air-side Reynolds numbers of approximately 2,000–40,000. The reported thermal conductivities were 0.581, 0.86 and 1.18 W m?¹ K?¹, respectively. The higher-filled composite also produced the highest plotted heat-transfer rate and overall heat-transfer coefficient across the investigated Reynolds-number range. A three-dimensional steady-state ANSYS Fluent model was used to examine temperature distribution in a representative fin under a 65 °C heating condition and 26 °C room temperature. The computed temperature fields were qualitatively consistent with the observed material trend. The results indicate that hybrid MWCNT/BN reinforcement can improve the thermal response of reprocessed HDPE fins under the tested conditions. Further work should quantify uncertainty, repeatability, mechanical durability and model-to-experiment error before design-level performance claims are made.

Introduction

Heat sinks and compact heat exchangers are widely used in electronic, electrical, and industrial applications to dissipate heat. Although copper and aluminium provide excellent thermal conductivity, their high weight, cost, and corrosion-related limitations have encouraged research into polymer-based heat exchangers. However, the low thermal conductivity of conventional polymers restricts their heat-transfer performance.

Thermally conductive polymer composites offer a promising alternative by incorporating conductive fillers into polymer matrices. This study investigates the thermal performance of a finned-tube heat sink fabricated using reprocessed high-density polyethylene (HDPE) reinforced with multi-walled carbon nanotubes (MWCNT) and boron nitride (BN). The research combines experimental measurements, thermal conductivity testing, and three-dimensional numerical simulation using ANSYS Fluent.

Objectives of the Study

The primary objectives are:

• To prepare and compare neat HDPE and hybrid MWCNT/BN-reinforced HDPE composites.

• To measure the thermal conductivity of the prepared materials.

• To evaluate heat-transfer rate and overall heat-transfer coefficient at different air-side Reynolds numbers.

• To analyse temperature distribution in heat-sink fins using ANSYS Fluent.

Materials and Experimental Methodology

Three formulations were investigated:

The polymeric fins were fabricated using a machined die and assembled with copper tubes to develop a finned-tube heat sink. The experimental setup consisted of an air duct, blower, heated water tank, pump, flow-control valves, thermocouples, and manometer.

The experiments were conducted with water inlet temperatures ranging from 30°C to 75°C and air-side Reynolds numbers of approximately 2,000–40,000. Temperature and pressure measurements were used to calculate thermal conductivity, heat-transfer rate, and overall heat-transfer coefficient.

Numerical Simulation

A three-dimensional single-fin model was developed using ANSYS Fluent to investigate heat distribution in the three materials. The simulation considered steady-state heat transfer, an energy model, and the reported RNG k–ε turbulence model.

The heater temperature was maintained at 65°C, with the surrounding room temperature set at 26°C. Numerical temperature contours were compared to understand the effect of hybrid reinforcement on heat spreading.

Results and Discussion

1. Thermal Conductivity

The measured thermal conductivity increased with hybrid filler concentration.

The higher-filled composite exhibited approximately twice the thermal conductivity of neat HDPE. This improvement is attributed to the formation of conductive pathways through the polymer matrix. However, filler dispersion, agglomeration, interfacial resistance, and orientation can influence the measured conductivity.

2. Average Heat-Transfer Rate

The average heat-transfer rate increased with air-side Reynolds number for all three formulations. The 6% MWCNT + 2% BN composite exhibited the highest heat-transfer performance, followed by the intermediate composite and neat HDPE.

The difference between the highest and lowest heat-transfer cases was approximately 0.027 kW near Re ≈ 2,000, as reported in the thesis.

3. Overall Heat-Transfer Coefficient

The overall heat-transfer coefficient increased with increasing Reynolds number. The higher-filled composite consistently demonstrated the highest plotted values.

This behaviour indicates that improved solid-side thermal conductivity contributes to enhanced heat transfer. However, the overall performance also depends on air-side and water-side convection, fin geometry, contact resistance, and operating conditions.

4. Numerical Temperature Distribution

ANSYS Fluent temperature contours showed improved heat spreading in the reinforced composites compared with neat HDPE. The higher-conductivity formulation exhibited a broader temperature distribution, whereas neat HDPE showed more localized heat transfer.

The numerical results qualitatively supported the experimental observations. However, mesh-independence analysis, detailed validation against experimental temperatures, and uncertainty assessment are required before establishing quantitative predictive accuracy.

Engineering Significance

The combined experimental and numerical results demonstrate that hybrid MWCNT/BN reinforcement improves the thermal conductivity and heat-transfer performance of reprocessed HDPE heat-sink fins under the investigated laboratory conditions.

The findings indicate potential applications in lightweight and corrosion-resistant heat exchangers, HVAC systems, compact cooling equipment, and industrial thermal management.

Conclusion

An experimental and computational investigation was conducted on a hybrid finned-tube heat sink fabricated from reprocessed HDPE reinforced with MWCNTs and BN. Three formulations were compared: neat HDPE, 4% MWCNT + 2% BN / HDPE, and 6% MWCNT + 2% BN / HDPE. The main conclusions are as follows. • The reported thermal conductivity increased from 0.581 W m?¹ K?¹ for neat HDPE to 0.86 W m?¹ K?¹ and 1.18 W m?¹ K?¹ for the two hybrid composites. • Average heat-transfer rate increased with air-side Reynolds number, and the 6% MWCNT + 2% BN formulation produced the highest curve in the reported range. • The overall heat-transfer coefficient followed the same qualitative material ordering, with the higher-filled composite giving the largest plotted values. • The ANSYS Fluent temperature fields qualitatively supported the observed conductivity trend by showing more extensive heat spreading for the higher-conductivity material. The present evidence is limited to the tested specimens, apparatus and reported operating conditions. Further work should document the filler fraction basis and manufacturing protocol, repeat the conductivity and heat-transfer measurements with uncertainty estimates, test mechanical and thermal-cycle durability, and quantify CFD error using measured temperatures and mesh-independence checks. A direct comparison with a metal-fin reference under identical geometry and operating conditions would be needed to establish the practical trade-off between thermal performance, mass and cost.

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Copyright

Copyright © 2026 Macha Bhargav, SK. Meeravali, Lakshmi Tulasi Chavali, M. Suresh Kumar. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.