Thermal and Physical Characterization of PEG Phase Change Materials Enhanced by Carbon-Based Nanoparticles

At a Glance

Metadata	Details
Publication Date	2020-06-15
Journal	Nanomaterials
Authors	David Cabaleiro, Samah Hamze, Jacek Fal, Marco A. Marcos, Patrice Estellé
Institutions	Laboratoire de génie civil et génie mécanique, Rzeszów University of Technology
Citations	64
Analysis	Full AI Review Included

Executive Summary

This study characterized Poly(ethylene glycol) 400 (PEG400) nano-enhanced Phase Change Materials (NePCMs) using five carbon-based nanostructures for cold thermal energy storage applications.

Sub-cooling Mitigation: The addition of nanoparticles significantly reduced the undesirable sub-cooling effect (the temperature difference between melting and crystallization). The raw Graphite/Diamond nanomixture (G/D-r) at 1.0 wt.% achieved the best result, reducing sub-cooling by 2.0 K compared to 4.0 K for neat PEG400.
Thermal Conductivity Enhancement: Graphite/Diamond nanomixtures (G/D-p and G/D-r) provided the highest thermal conductivity (k) improvements, reaching 3.3% to 3.6% enhancements over the base fluid.
Rheological Behavior: All carbon-based suspensions exhibited non-Newtonian, pseudo-plastic (shear-thinning) behavior in the liquid phase. This effect was strongest in Carbon Black (CB) dispersions, particularly at low shear rates.
Volumetric Properties: Nano-diamond suspensions (nD87 and nD97) showed the largest density increases, ranging from 0.64% to 0.66%. Density changes were accurately predicted using a weight-average mixing rule.
Surface Tension (SFT): Reductions in SFT were observed for the two nano-diamond nanopowders (nD87 and nD97), while other carbon structures showed slight increases within experimental uncertainty.
Latent Heat Trade-off: The presence of nanoparticles reduced the latent heat capacity (ΔH_melt) by 2.4% to 6.9%, attributed to a lower degree of polymer crystallinity.

Technical Specifications

Data extracted primarily from experiments conducted at 1.0 wt.% nanoparticle loading.

Parameter	Value	Unit	Context
Base Fluid (PEG400) T_melt	280.2	K	DSC measurement
Base Fluid (PEG400) T_cryst	276.2	K	DSC measurement
Base Fluid Sub-cooling (ΔT)	4.0	K	Neat PEG400
Minimum Sub-cooling (ΔT)	2.0	K	G/D-r (1.0 wt.%) NePCM
Base Fluid Latent Heat (ΔH_melt)	106.8	J·g^-1	Neat PEG400
Max Latent Heat Reduction	6.9	%	G/D-r (1.0 wt.%) NePCM
Max Thermal Conductivity Enhancement	3.6	%	G/D-p (1.0 wt.%) NePCM (Avg.)
Max Density Increase	0.66	%	nD97 (1.0 wt.%) NePCM (Avg.)
Minimum Flow Behavior Index (n)	0.77	-	CB (1.0 wt.%) at 318.15 K (Max shear-thinning)
Nanoparticle Size (nD87, nD97, G/D)	4	nm	Manufacturer declared average
Nanoparticle Size (CB)	13	nm	Manufacturer declared average
Base Fluid Viscosity (η) Reduction	75-79	%	Across 288.15 K to 318.15 K range
Base Fluid Isobaric Thermal Expansivity (α_p)	7.15-7.45 x 10^-4	K^-1	Calculated from density data

Key Methodologies

The NePCMs were characterized using a combination of thermal, rheological, and physical property measurements.

Nanofluid Synthesis: A two-step method was employed. Predefined mass concentrations (0.5 wt.% and 1.0 wt.%) of carbon nanopowders were mixed with PEG400, followed by 30 min vortex mixing and 200 min high-power sonication (450 W, 45 kHz) to ensure dispersion stability.
Phase Transition Analysis (DSC): Differential Scanning Calorimetry (Q2000) was used to determine crystallization (T_cryst) and melting (T_melt) temperatures and latent heats (ΔH_melt) at a constant scan rate of 0.5 K·min^-1.
Viscoelastic Analysis (Oscillatory Rheology): A stress-controlled rheometer (Malvern Kinexus Pro) was used with a plate-plate geometry. Temperature sweeps (0.5 K·min^-1) were performed at a constant frequency (1 Hz) and low strain (0.05%) to track the solid-liquid transition via changes in storage (G’) and loss (G”) moduli.
Dynamic Viscosity (Flow Curves): Non-linear viscoelastic tests determined dynamic viscosity (η) as a function of shear rate (up to 100 s^-1) across four isotherms (288.15 K to 318.15 K) using a cone-plate geometry.
Thermal Conductivity (k): Measured in the liquid phase (288.15 K to 318.15 K) using the Transient Hot Wire (THW) technique (THW-L2 meter), ensuring low power input (80 mW) to prevent convection.
Density (ρ): Determined using a vibrating U-tube densimeter (DMA 500) at atmospheric pressure across 288.15 K to 313.15 K.
Surface Tension (SFT): Measured using two independent methods for verification: the Pendant Drop technique (DSA-30 drop-shape analyzer) and the Du Noüy Ring tensiometer.

Commercial Applications

This research directly supports the development of advanced materials for energy management in low-temperature environments.

Cold Thermal Energy Storage (CTES): The primary application, leveraging the PEG400 phase change temperature (~277-281 K) for refrigeration, cold chain logistics, and industrial cooling processes.
Passive Thermal Management: Integration into electronic devices (e.g., high-performance computing, servers) or battery packs to buffer excessive temperature rises using the latent heat capacity of the NePCM.
Solar Thermal Systems: Use in solar energy harvesting where the NePCM acts as a storage medium, particularly benefiting from the enhanced thermal conductivity to accelerate charging/discharging cycles.
Heat Transfer Fluid (HTF) Design: The detailed rheological data (dynamic viscosity and shear-thinning behavior) is essential for engineers modeling fluid flow, pressure drop, and pumping power requirements in circulating heat transfer loops.
Nucleation Control: The ability of nanoparticles (especially G/D-r and CB) to reduce sub-cooling is critical for reliable and efficient operation of TES systems, ensuring the material crystallizes closer to its melting point.

View Original Abstract

This paper presents the preparation and thermal/physical characterization of phase change materials (PCMs) based on poly(ethylene glycol) 400 g·mol−1 and nano-enhanced by either carbon black (CB), a raw graphite/diamond nanomixture (G/D-r), a purified graphite/diamond nanomixture (G/D-p) or nano-Diamond nanopowders with purity grades of 87% or 97% (nD87 and nD97, respectively). Differential scanning calorimetry and oscillatory rheology experiments were used to provide an insight into the thermal and mechanical changes taking place during solid-liquid phase transitions of the carbon-based suspensions. PEG400-based samples loaded with 1.0 wt.% of raw graphite/diamond nanomixture (G/D-r) exhibited the lowest sub-cooling effect (with a reduction of ~2 K regarding neat PEG400). The influences that the type of carbon-based nanoadditive and nanoparticle loading (0.50 and 1.0 wt.%) have on dynamic viscosity, thermal conductivity, density and surface tension were also investigated in the temperature range from 288 to 318 K. Non-linear rheological experiments showed that all dispersions exhibited a non-Newtonian pseudo-plastic behavior, which was more noticeable in the case of carbon black nanofluids at low shear rates. The highest enhancements in thermal conductivity were observed for graphite/diamond nanomixtures (3.3-3.6%), while nano-diamond suspensions showed the largest modifications in density (0.64-0.66%). Reductions in surface tension were measured for the two nano-diamond nanopowders (nD87 and nD97), while slight increases (within experimental uncertainties) were observed for dispersions prepared using the other three carbon-based nanopowders. Finally, a good agreement was observed between the experimental surface tension measurements performed using a Du Noüy ring tensiometer and a drop-shape analyzer.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano10061168

References

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