Experimental and Theoretical Investigation on Heat Transfer Enhancement in Micro Scale Using Helical Connectors

At a Glance

Metadata	Details
Publication Date	2024-02-26
Journal	Materials
Authors	Malyne Abraham, Zachary Abboud, Gabriel Herrera Arriaga, Kendall Tom, Samuel Austin
Institutions	Bradley University
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond Nanofluid Heat Transfer Enhancement

Executive Summary

This research successfully demonstrates a passive method for significantly enhancing heat transfer coefficients (HTC) in microchannels, a critical requirement for next-generation microscale electronics cooling. The core findings and value proposition are summarized below:

Synergistic Enhancement: Heat transfer efficiency is boosted by combining optimized helical channel geometry (inducing secondary flow/mixing) with the superior thermal properties of diamond nanofluids.
Material Performance: A deionized water-based nanodiamond (ND) fluid (0.1 wt%) showed a 10% increase in thermal conductivity compared to the base fluid (water) at 50 °C.
Geometric Optimization: The helical connector acts as an effective fluid mixer, enhancing molecular and nanoparticle random motion, leading to superior HTC compared to conventional nozzle geometries.
Optimal Configuration: Maximum HTC enhancement was achieved using a connector with L_c = 40 mm, D_c = 10 mm, d = 1.5 mm, and p = 4 mm, effective across a low Reynolds number range (Re = 12.5 to 400).
Application Relevance: This passive enhancement technique is highly relevant for powerful, miniaturized electronic devices operating under high thermal loads where low Reynolds numbers are common.
6CCVD Connection: The use of high-purity nanodiamonds underscores the critical role of synthetic diamond materials in advanced thermal management systems, both as a fluid additive and as a primary heat spreader (6CCVD’s core product).

Technical Specifications

The following hard data points were extracted from the experimental investigation:

Parameter	Value	Unit	Context
Nanoparticle Material	Diamond (ND)	N/A	Explosion synthesized, spherical morphology
Nanoparticle Purity	98.3	%	Used in nanofluid synthesis
Nanoparticle Size (Avg.)	3	nm	Average particle diameter
Nanofluid Concentration	0.1	wt%	Final mass concentration in deionized water
Base Fluid Thermal Conductivity	0.6381	W/m·K	Deionized water at 50 °C
Nanofluid Thermal Conductivity	0.7016	W/m·K	0.1 wt% ND nanofluid at 50 °C
Thermal Conductivity Increase	~10	%	Nanofluid vs. base fluid
Microchannel Inner Diameter (D)	116	µm	Stainless-steel channel ID
Microchannel Length (l_e)	165	mm	Length of each channel segment
Reynolds Number Range (Re)	12.5 to 400	N/A	Laminar flow regime tested
Maximum System Temperature	85	°C	Maximum measured temperature (to avoid boiling)
Optimal Connector Length (L_c)	40	mm	For maximum HTC enhancement
Optimal Helical Diameter (D_c)	10	mm	For maximum HTC enhancement
Connector Inner Diameter (d)	1.5	mm	Inner diameter of the helical channel
Helical Pitch (p)	4	mm	Pitch of the helix

Key Methodologies

The experiment utilized a two-microchannel system separated by a 3D-printed helical connector, focusing on passive heat transfer enhancement.

Nanofluid Synthesis:
- Diamond nanofluid (3 nm particle size, 98.3% purity) was purchased pre-dispersed in water at 5 wt%.
- The fluid was diluted with deionized water to achieve a final concentration of 0.1 wt%.
- Magnetic stirring for 45 minutes ensured homogeneous and stable dispersion.
Experimental Setup and Heating:
- A syringe pump introduced the working fluid (water or nanofluid) into the system.
- The system consisted of two stainless-steel microchannels (116 µm ID, 165 mm length) connected by the helical geometry.
- The microchannels were resistively heated using a DC power supply, manually adjusted to maintain a maximum temperature of 85 °C.
Connector Fabrication:
- Helical connectors were modeled using Creo Parametric.
- Connectors were 3D printed using a Form 3+ resin type printer.
- Four geometries were tested, varying length (L_c: 40, 60, 80 mm) and helical diameter (D_c: 5, 10 mm), while maintaining inner diameter (d = 1.5 mm) and pitch (p = 4 mm).
Data Acquisition:
- Temperature measurements were taken using 0.2 mm K-type thermocouples at the inlet/outlet and 82 µm K-type thermocouples along the microchannel surface (11 sensors, 10 mm apart).
- Pressure drop across the connector was measured using pressure transducers.
- Data was collected at steady-state conditions using an NI cDAQ-9178 system and LabVIEW software.
Heat Transfer Coefficient (HTC) Calculation:
- HTC (h) was calculated locally as a function of non-dimensional location (x/D) based on measured surface temperature (T_s) and calculated fluid temperature (T_f).

6CCVD Solutions & Capabilities

The research highlights the critical role of high-quality diamond materials in advanced thermal management, both as a nanofluid additive and as a foundational material for high-power electronic substrates. 6CCVD is uniquely positioned to supply the necessary CVD diamond components required to replicate, extend, and commercialize this technology.

Applicable Materials

To replicate or extend this research into commercial microelectronic cooling systems, engineers require high-purity diamond materials for both the fluid and the heat sink substrate:

Research Requirement	6CCVD Material Solution	Key Capability Match
Nanodiamond Precursors	High Purity SCD (Single Crystal Diamond)	While the paper used explosion-synthesized NDs, 6CCVD supplies high-purity CVD diamond plates that can serve as precursors for high-quality, defect-controlled nanodiamond synthesis, ensuring superior thermal properties.
Microchannel Substrates	Optical Grade SCD or Thermal Grade PCD	For fabricating the microchannels themselves, diamond offers the highest thermal conductivity (up to 2200 W/m·K), far surpassing stainless steel. 6CCVD provides plates up to 125mm for large-scale microchannel fabrication.
High-Power Heat Spreaders	Polycrystalline Diamond (PCD)	Essential for mounting the microscale electronics being cooled. 6CCVD PCD plates offer superior thermal management for high-flux devices.
Electrochemical Applications	Boron-Doped Diamond (BDD)	If the system requires integrated electrochemical sensors or heaters (like the resistive heating used in the experiment), BDD offers stable, conductive diamond films.

Customization Potential

The experimental setup utilized specific geometries (helical connectors) and required precise material properties. 6CCVD offers comprehensive customization services essential for scaling this research:

Custom Dimensions: 6CCVD supplies SCD plates (0.1 µm to 500 µm thickness) and large-area PCD wafers (up to 125 mm diameter) suitable for etching or machining complex microchannel structures. Substrates up to 10 mm thick are available for robust heat sink designs.
Precision Polishing: To minimize fluid friction and pressure drop in microchannels, surface quality is paramount. 6CCVD guarantees ultra-smooth surfaces:
- SCD: Ra < 1 nm
- Inch-size PCD: Ra < 5 nm
Integrated Metalization: The integration of microelectronics requires reliable contacts. 6CCVD offers in-house metalization services, including Au, Pt, Pd, Ti, W, and Cu layers, allowing for direct integration of resistive heaters or thermal sensors onto the diamond substrate.

Engineering Support

The optimization of heat transfer in microscale systems is highly dependent on the complex interplay between fluid properties (nanoparticle concentration, viscosity) and geometric parameters (L_c, D_c, d, p, Re).

6CCVD’s in-house PhD team specializes in CVD diamond material science and thermal applications. We offer consultation services to assist researchers and engineers in:

Selecting the optimal diamond grade (SCD vs. PCD) for high-flux Microchannel Cooling projects.
Designing diamond substrates with appropriate thickness and surface finish to minimize pressure drop and maximize heat transfer efficiency.
Developing custom metalization schemes for integrated heating or sensing elements, directly supporting the experimental methodology used in this paper.

Call to Action: For custom specifications or material consultation regarding advanced thermal management or nanodiamond precursor materials, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery worldwide.

View Original Abstract

Microscale electronics have become increasingly more powerful, requiring more efficient cooling systems to manage the higher thermal loads. To meet this need, current research has been focused on overcoming the inefficiencies present in typical thermal management systems due to low Reynolds numbers within microchannels and poor physical properties of the working fluids. For the first time, this research investigated the effects of a connector with helical geometry on the heat transfer coefficient at low Reynolds numbers. The introduction of a helical connector at the inlet of a microchannel has been experimentally tested and results have shown that this approach to flow augmentation has a great potential to increase the heat transfer capabilities of the working fluid, even at low Reynolds numbers. In general, a helical connector can act as a stabilizer or a mixer, based on the characteristics of the connector for the given conditions. When the helical connector acts as a mixer, secondary flows develop that increase the random motion of molecules and possible nanoparticles, leading to an enhancement in the heat transfer coefficient in the microchannel. Otherwise, the heat transfer coefficient decreases. It is widely known that introducing nanoparticles into the working fluids has the potential to increase the thermal conductivity of the base fluid, positively impacting the heat transfer coefficient; however, viscosity also tends to increase, reducing the random motion of molecules and ultimately reducing the heat transfer capabilities of the working fluid. Therefore, optimizing the effects of nanoparticles characteristics while reducing viscous effects is essential. In this study, deionized water and deionized water-diamond nanofluid at 0.1 wt% were tested in a two-microchannel system fitted with a helical connector in between. It was found that the helical connector can make a great heat transfer coefficient enhancement in low Reynolds numbers when characteristics of geometry are optimized for given conditions.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ma17051067

References

2008 - Thermophysical and Electrokinetic Properties of Nanofluids—A Critical Review [Crossref]
2007 - Temperature and Particle-Size Dependent Viscosity Data for Water-Based Nanofluids—Hysteresis Phenomenon [Crossref]
2010 - Effects of Temperature and Particle Size on the Thermal Property Measurements of Al2O3−Water Nanofluids [Crossref]
2010 - Volume Fraction and Temperature Variations of the Effective Thermal Conductivity of Nanodiamond Fluids in Deionized Water [Crossref]
2013 - Investigation of Thermal Conductivity and Viscosity of Fe3O4 Nanofluid for Heat Transfer Applications [Crossref]
2020 - Investigating Control of Convective Heat Transfer and Flow Resistance of Fe3O4/Deionized Water Nanofluid in Magnetic Field in Laminar Flow
2024 - Empirical Investigation of Nanofluid Performance in a Microchannel Heat Sink for Various Attributes in Low Reynolds Number Range [Crossref]
2023 - On the Assessment of the Thermal Performance of Microchannel Heat Sink with Nanofluid [Crossref]