INFLUENCE OF VARIOUS FACTORS ON THE HEAT TRANSFER CHARACTERISTICS OF MINIATURE TWO-PHASE THERMOSYPHONS WITH NANOFLUIDS
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2022-12-20 |
| Journal | Energy Technologies & Resource Saving |
| Authors | V. Yu. Đravets, V.N. Moraru, D.I. Gurov |
| Institutions | National Academy of Sciences of Ukraine, National Technical University of Ukraine âIgor Sikorsky Kyiv Polytechnic Instituteâ |
| Citations | 3 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Diamond Nanofluids for High-Performance Thermosyphons
Section titled âTechnical Documentation & Analysis: Diamond Nanofluids for High-Performance ThermosyphonsâSource Paper: Kravets V.Yu. et al. âInfluence of Various Factors on the Heat Transfer Characteristics of Miniature Two-Phase Thermosyphons with Nanofluids.â (2022)
Executive Summary
Section titled âExecutive SummaryâThis research validates the superior thermal performance of diamond-based nanofluids (NFs) for miniature two-phase closed thermosyphons (TPCTs), a critical technology for high-density electronics cooling.
- Performance Breakthrough: Nanofluids utilizing Synthetic Diamond (CA) and Carbon Nanotubes (CNT) achieved a 1.5x to 2x increase in maximum transferable heat flux (Qmax) compared to pure water.
- Material Validation: The high intrinsic thermal conductivity of diamond ($\lambda$ ~2300 W/(m·K)) and CNT ($\lambda$ ~2000 W/(m·K)) is confirmed as the primary driver for enhanced heat transfer capacity.
- Mechanism Identified: The nanoparticles deposit on the heating surface, forming a porous structure that prevents the formation of a continuous vapor film, thereby suppressing the Critical Heat Flux (CHF) crisis during boiling.
- Optimal Operating Parameters: Peak performance (Qmax) was achieved at low fill factors (Kf ~0.4-0.5) and an inclination angle of 45°.
- 6CCVD Relevance: This study directly supports the use of high-quality MPCVD Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) materials, which are the source for the high-performance synthetic diamond nanoparticles used in this advanced cooling application.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental analysis, highlighting the performance gains achieved using diamond and CNT nanofluids (NFs).
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Thermosyphon Inner Diameter (din) | 5 | mm | All experimental samples |
| Thermosyphon Total Length (LÎŁ) | 700 | mm | All experimental samples |
| Nanofluid Concentration (SD) | 0.3 | mass % | Synthetic Diamond (CA) in water |
| Nanofluid Concentration (CNT) | 0.1 | mass % | Carbon Nanotubes (BHT) in water |
| Thermal Conductivity (SD/CA) | ~2300 | W/(m·K) | Source material property (Ref. 16) |
| Thermal Conductivity (CNT/BHT) | ~2000 | W/(m·K) | Source material property |
| Thermal Conductivity (Water) | 0.613 | W/(m·K) | Base fluid property |
| Max Heat Flux (Qmax) - Water | ~90 | W | Baseline performance |
| Max Heat Flux (Qmax) - SD NF | ~140 | W | 1.5x improvement over water |
| Max Heat Flux (Qmax) - CNT NF | ~180 | W | 2x improvement over water |
| Max Equivalent Thermal Conductivity ($\lambda_{eq}$) | Up to 120,000 | W/(m·K) | Achieved with CNT and SD NFs |
| Optimal Fill Factor (Kf) | 0.4 - 0.5 | Dimensionless | Yields maximum Qmax |
| Optimal Inclination Angle ($\Phi$) | 45 | ° | Yields minimum thermal resistance (R) |
Key Methodologies
Section titled âKey MethodologiesâThe experimental setup utilized miniature two-phase closed thermosyphons (TPCTs) to evaluate the impact of nanofluids on heat transfer efficiency.
- Thermosyphon Geometry: Copper thermosyphons were used with fixed dimensions: 700 mm total length, 5 mm inner diameter (din), 210 mm condensation zone (lc). The heating zone (lhz) was varied from 45 mm to 200 mm.
- Nanofluid Preparation: Nanofluids were prepared by ultrasonic dispersion (using a UZDN-2T disperser at 22 kHz, 500 W) of nanoparticles (CNT, Synthetic Diamond, Carbon Black) in deaerated distilled water, stabilized with an anionic surfactant.
- Nanoparticle Characterization: Particle size (davg), zeta potential ($\zeta$), specific electrical conductivity ($\chi$), and surface tension ($\sigma$) were measured to ensure dispersion stability.
- Heat Input: Heat flux (Q) was supplied via an ohmic heater and controlled by a laboratory autotransformer and wattmeter. Heat flux was varied from 0 W up to the CHF limit (Qmax).
- Thermal Measurement: Temperatures along the thermosyphon wall were measured using eight copper-constantan thermocouples. Cooling water temperatures (in/out) were measured by two additional thermocouples.
- Variable Testing: Experiments systematically tested the influence of:
- Coolant type (Water, CNT NF, SD NF, CB NF).
- Fill Factor (Kf): Varied from 0.44 to 1.93.
- Inclination Angle ($\Phi$): Varied from 5° to 90° relative to the horizontal.
- Performance Metrics: Thermal resistance (R), maximum heat flux (Qmax), and equivalent thermal conductivity ($\lambda_{eq}$) were calculated based on measured temperatures and heat input.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research confirms that diamond, due to its unparalleled thermal properties, is essential for achieving next-generation heat transfer performance in two-phase cooling systems. 6CCVD is uniquely positioned to supply the foundational diamond materials required for both research replication and industrial scaling of these high-performance nanofluids and heat spreaders.
Applicable Materials
Section titled âApplicable MaterialsâThe study highlights the necessity of high-purity, high-thermal-conductivity diamond material. 6CCVD provides the ideal source materials for both nanofluid synthesis and direct heat spreader integration:
| Application Requirement | 6CCVD Material Recommendation | Key Specification Match |
|---|---|---|
| Nanofluid Source Material | High-Purity Polycrystalline Diamond (PCD) | Provides bulk material for milling/grinding into high-$\lambda$ nanoparticles (as used in the paper). |
| High-Performance Heat Spreaders | Electronic Grade Single Crystal Diamond (SCD) | $\lambda$ > 2000 W/(m·K). Ideal for direct integration into electronic packages requiring extreme heat dissipation (e.g., GaN/SiC devices). |
| High-Density Heat Sinks | Thick PCD Substrates | Available up to 10 mm thickness and 125 mm diameter for large-scale, high-power cooling modules. |
| Electrochemical Applications | Boron-Doped Diamond (BDD) | While not the focus of this paper, BDD is available for related electrochemical cooling or sensing research. |
Customization Potential
Section titled âCustomization PotentialâThe miniature thermosyphons used in this study (5 mm din) represent a specific geometry. 6CCVDâs custom fabrication capabilities ensure that researchers and engineers can obtain diamond components tailored precisely to their thermal management systems.
- Custom Dimensions: 6CCVD supplies diamond plates and wafers up to 125 mm in diameter (PCD) and custom thicknesses (SCD/PCD from 0.1 ”m to 500 ”m). We can provide custom-sized diamond substrates for use as end caps or internal structures within TPCTs or heat pipes.
- Surface Engineering (Polishing): The paper emphasizes that surface structure (porosity) is critical for boiling intensification. 6CCVD offers ultra-precise polishing services:
- SCD: Surface roughness (Ra) < 1 nm.
- Inch-size PCD: Surface roughness (Ra) < 5 nm.
- Benefit: Precise control over surface roughness is essential for optimizing nanoparticle deposition and nucleation site density, directly impacting CHF performance.
- Metalization Services: For integrating diamond heat spreaders into electronic modules, 6CCVD offers in-house metalization capabilities, including standard layers like Ti/Pt/Au, W, Cu, and Pd. This ensures robust, low-thermal-resistance interfaces for high-power device integration.
Engineering Support
Section titled âEngineering SupportâThe complex interplay between nanofluid concentration (Kf), surface properties, and thermal performance requires specialized knowledge. 6CCVDâs in-house PhD team specializes in MPCVD diamond growth and characterization. We offer consultation services to assist clients in:
- Selecting the optimal diamond grade (SCD vs. PCD) for specific thermal applications.
- Defining surface preparation requirements (polishing, etching) to maximize heat transfer efficiency in similar two-phase cooling projects.
- Developing custom metalization schemes for reliable integration of diamond heat spreaders into high-power electronic packaging.
Call to Action: For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Currently, various types of nanofluids are of increasing interest as heat carriers for heat transfer in thermosiphons and other evaporative-condensation devices. This paper presents and analyzes experimental data on heat transfer characteristics (total thermal resistances, maximum transferable heat fluxes and equivalent thermal conductivity) of two-phase miniature thermosyphons with nanofluids. Geometric parameters of thermosiphons for all experimental samples were identical and were: total length 700 mm, inner diameter 5 mm. The length of the heating zone was changed stepwise from 45 mm to 200 mm. The length of the condensation zone was 200 mm for all investigated thermosyphons. The amount of coolant in the thermosiphons was the same, and its height in the heating zone before the start of the study was 88 mm. Distilled water and aqueous nanofluids with nanoparticles of carbon nanotubes, synthetic diamond, and carbon black were used as heat carriers. The main attention is paid to the study of the influence of the filling factor and the angle of inclination of the thermosyphon, the value of the transferred heat flux and the chemical nature of the coolant (nanofluid) on the heat transfer characteristics of thermosyphons. The strong influence of these factors on the efficiency of a miniature closed two-phase thermosyphon has been demonstrated. A more than twofold increase in the heat transfer characteristics of thermosyphons (the maximal transferred heat flux) was obtained with a sharp decrease in their thermal resistance. It is assumed that the significantly higher heat transfer capacity of such thermosiphons compared to those filled with water is explained not only by the higher thermal conductivity of the coolant, but also by the appearance of a peculiar porous structure that prevents the appearance of a vapor film and promotes the intensification of heat transfer processes during boiling. Bibl. 16, Fig. 10, Tab. 2.