Enhancement Of Thermophysical Properties Research Articles

Confinement Effect of Graphene Interface on Phase Transition of n-Eicosane: Molecular Dynamics Simulations.

Phase change materials (PCMs) are widely used in thermal management and energy storage systems. Investigations on the thermophysical properties enhancement of organic PCMs by introducing carbon-based frameworks have received much attention in recent years. Studies of the phase transition in nanoconfinement are still in controversy with divergent opinions among researchers. In this article, the phase transition behavior of n-eicosane in slit-shaped pores between sheets of graphene is investigated by molecular dynamics simulation. It is found that the graphene interface makes the phase transition temperature of n-eicosane increase, under the initial slit widths of 1.5-5.3 nm. Impacted by interaction and size effects, the distribution and orientation of n-eicosane molecules are quite different from those of the bulk state. In the confinement of graphene, the molecules turn to a reversible layered distribution parallel to the graphene sheets after solidification. The contact layers are found in all the confined systems, which is harder to melt and easier to solidify compared with the main part of the systems. The melting points of different systems are obtained by analysis of the liquid ratio. Finally, the relationship between the dimensionless phase transition point and slit width is discussed.

Influence of solvents on the enhancement of thermophysical properties and stability of multi-walled carbon nanotubes nanofluid

Multi-walled carbon nanotubes (MWCNTs) are a contemporary class of nanoparticles that have a prominent thermal, electrical and mechanical properties. There have been numerous studies on the enhancement of thermophysical properties of nanofluids. However, there is only limited research on thermal and stability analysis of MWCNT nanofluids with various kinds of solvents or base fluids, namely propylene glycol, ethanol, ethylene glycol, polyethylene glycol, methanol and water. This paper reports the enhancement of thermophysical properties and stability of MWCNTs with six different base fluids in the presence of sodium dodecyl benzene sulfonate surfactant with a mass concentration of 0.5 wt%. Thermal and dispersion stabilities were determined using a thermogravimetric analyzer (TGA) and Zeta potential, along with a visual inspection method to evaluate the agglomeration or sedimentation of MWCNT nanoparticles over a period of one month. Ultraviolet–visible spectroscopy and Fourier transform infrared spectroscopy were utilized to identify the molecular components and light absorption of the formulated nanofluids at their maximum wavenumber (4500 cm−1) and wavelength (800 nm). In addition, thermophysical properties such as thermal conductivity, specific heat capacity, viscosity and density with a peak temperature of 200 °C were also experimentally evaluated. The TGA results illustrated that MWCNT/ethylene glycol nanofluid achieved maximum thermal stability at 140 °C and it revealed a maximum zeta potential value of −61.8 mV. Thus, ethylene glycol solution was found to be the best base liquid to homogenize with MWCNTs for acquiring an enhanced thermophysical property and a long-term stability.

Statistical and experimental investigation on flow boiling heat transfer to carbon nanotube-therminol nanofluid

In the present work, statistical, regression and experimental studies were conducted to assess the plausible application of an oil-based carbon nanotube nanofluid for high-temperature applications such as solar thermal receivers. Nanofluid was prepared at wt. %=0.1 and wt. %=3 using two-step procedure and was stabilized using ultrasonic together with the addition of surfactant. As a criterion for the stability of nanofluid, the zeta potential value was measured. Results showed that during flow boiling heat transfer, two distinguished heat transfer regions were identified namely forced convective and nucleate boiling heat transfer domains. Likewise, the presence of carbon nanotube within the oil increased the convective heat transfer coefficient (HTC) together with a significant increase in the nucleate boiling HTC. An increase in the heat and mass fluxes were found to enhance the flow boiling HTC both in convective and nucleate boiling regions. The sub-cooling temperature was also found to increase the HTC in convective and nucleate boiling regions due to the enhancement in thermo-physical properties of nanofluid. With an increase in the mass flux, the pressure drop of the system was increased. Heat flux was also enhanced the pressure drop within the system due to the increase in the rate of bubble generation and vapor blanket formation. Likewise, with an increase in the mass concentration of nanoparticles, higher pressure drop was registered in convective and nucleate boiling regions. Thermal performance index of the system showed that carbon nanotube can increase the thermo-hydraulic performance of the system by 56% in comparison with pure therminol 66. Equations were developed to predict the ONB points at various temperatures with A. A. D.% of ±0.9% to ±4.2% obtained with non-linear regression.

Effects of multi walled carbon nanotubes shape and size on thermal conductivity and viscosity of nanofluids

In this study, effective thermal conductivity and viscosity of multi walled carbon nanotubes water based nanofluids containing multi walled carbon nanotubes with various geometrical characteristics were investigated, with volume fraction 0.05 vol%. The experimental results demonstrated that thermophysical properties of the nanofluids depend on the geometrical characteristics of carbon nanotubes. The results were compared with some well-known models for thermal conductivity enhancement and relative viscosity and good conformities were observed. In this research, maximum enhancements of 36% and 5.5% were achieved for nanofluids effective thermal conductivity and dynamic viscosity respectively; these improvements were established in comparison to the base fluid at 45 °C. In addition, the results indicate that applying processes based on the surface modification on the nanotubes and improvement in nanoparticles dispersion can lead to enhancement in thermophysical properties in the nanofluids. During the experiments, the effective procedure of nanofluids stabilization was obtained. These findings combined with obtaining a pH value near the neutral state result an improvement in heat transfer and flow characteristics of the nanofluids.

Experimental investigation on stability and thermo-physical properties of Al2O3–SiO2/PAG nanolubricants with different nanoparticle ratios

The thermo-physical properties enhancement of nanolubricants can improve the heat transfer performance in refrigeration system. In this study, thermo-physical properties of Al2O3–SiO2/PAG nanolubricants were investigated at 30–80 °C temperatures for different nanoparticle ratios. Al2O3 and SiO2 nanoparticles were dispersed in the polyalkylene glycol (PAG 46) lubricant using the two-step method of preparation. Thermal conductivity and dynamic viscosity of the nanolubricants were measured by using KD2 Pro thermal properties analyser and LVDV-III Rheometer, respectively. All the hybrid nanolubricants are witnessed to behave as Newtonian fluids. A maximum thermal conductivity enhancement of 2.41% occurred at the temperature of 80 °C. Meanwhile for dynamic viscosity, the highest percentage increment was found up to 9.34% at 70 °C temperature. Increments in both properties were recorded for 50:50 nanoparticle ratio. The property enhancement ratio (PER) evaluation was suggested 60:40 as the optimum nanoparticle ratio with the lowest PER in comparison with other nanoparticle ratios at all temperatures by considering of both properties. Finally, new correlations have been proposed based on the experimental data to predict the thermo-physical properties of Al2O3–SiO2/PAG nanolubricants. As a conclusion, Al2O3–SiO2/PAG nanolubricants with nanoparticle ratio of 60:40 and volume concentrations of less than 0.1% are highly recommended for application in refrigeration system.

Advancement in phase change materials for thermal energy storage applications

In recent years the thermal energy storage applications with phase change materials have attracted wide interest. This has motivated a number of R&D efforts to develop novel materials and design new applications based on PCM. The efficient design of the new applications majorly depends on the quality of PCM employed. Numbers of reviews, reports have been written to compile the wide range of PCMs made available for different applications. This paper focuses on the development of next generation PCMs through the enhancement of thermophysical properties namely thermal conductivity, latent heat of fusion and sensible heat. The paper presents a detailed review of the research updates in this direction so as to produce PCMs with enhanced efficiency in terms of thermal energy storage and efficient heat transfer.

A facile, bio-based, novel approach for synthesis of covalently functionalized graphene nanoplatelet nano-coolants toward improved thermo-physical and heat transfer properties

In this study, we synthesized covalently functionalized graphene nanoplatelet (GNP) aqueous suspensions that are highly stable and environmentally friendly for use as coolants in heat transfer systems. We evaluated the heat transfer and hydrodynamic properties of these nano-coolants flowing through a horizontal stainless steel tube subjected to a uniform heat flux at its outer surface. The GNPs functionalized with clove buds using the one-pot technique. We characterized the clove-treated GNPs (CGNPs) using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). We then dispersed the CGNPs in distilled water at three particle concentrations (0.025, 0.075 and 0.1wt%) in order to prepare the CGNP-water nanofluids (nano-coolants). We used ultraviolet–visible (UV–vis) spectroscopy to examine the stability and solubility of the CGNPs in the distilled water. There is significant enhancement in thermo-physical properties of CGNPs nanofluids relative those for distilled water. We validated our experimental set-up by comparing the friction factor and Nusselt number for distilled water obtained from experiments with those determined from empirical correlations, indeed, our experimental set-up is reliable and produces results with reasonable accuracy. We conducted heat transfer experiments for the CGNP-water nano-coolants flowing through the horizontal heated tube in fully developed turbulent condition. Our results are indeed promising since there is a significant enhancement in the Nusselt number and convective heat transfer coefficient for the CGNP-water nanofluids, with only a negligible increase in the friction factor and pumping power. More importantly, we found that there is a significant increase in the performance index, which is a positive indicator that our nanofluids have potential to substitute conventional coolants in heat transfer systems because of their overall thermal performance and energy savings benefits.

Thermophysical properties enhancement of ternary carbonates with carbon materials for high-temperature thermal energy storage

Abstract Ternary carbonates in the form of Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 enforced by expanded graphite, graphene nanosheets and multi-walled carbon nanotubes are originally prepared though the solution-evaporation with the purpose of enhancing heat transfer for employment in concentrating solar power. FT-IR, XRD and SEM results indicate that three carbon materials are physically dispersed into composite carbonates with the effect of supporting structural support as well as improved thermal properties. The presence of carbon materials presents a slight effect on the melting and freezing temperature of ternary carbonates. It is apparent that enhancement of carbon materials on the heat transfer of the composite carbonates is mainly manifested in the aspect of thermal conductivity improvement. Expanded graphite, graphene nanosheets and multi-walled carbon nanotubes show respectively the enhancement of approximately 59.1%, 32.9% and 24.8% on average to thermal conductivity. Carbon materials also illustrate obvious improvement on the specific heat and the strengthening effect of liquid composite carbonates is generally better than that of solid carbonates. Average specific heat of composite carbonates modified by expanded graphene, graphene nanosheets and multi-walled carbon nanotubes is 1.278, 1.322 and 1.299 J/(g·°C) for solid and 1.502, 1.638, and 1.533 J/(g·°C) for liquid, respectively. Additionally, prepared composite carbonates exhibit superior cyclic stability and it is concluded that composite carbonates with carbon materials as effective latent heat storage materials will have great potential for application in thermal energy storage in terms of satisfactory thermal properties.

Thermophysical Properties and Morphological Changes of PEEK/LCP Blend System on Combined Effect of Polyphosphazene and HNT-COOH

ABSTRACTThis work explored the structural and morphological changes of poly ether ether ketone/liquid crystal polymer blend system, caused due to combined effect of polyphosphazene and acid-modified halloysite nanotubes. Surface modification of halloysite nanotubes gave these the adequate potential to make an effective combination with polyphosphazene. These were became the most promising factor on enhancement of thermophysical properties of blend system. Surface-treated halloysite nanotubes added nanocomposite drastically improves thermal stability than that of the other untreated nanofiller-based nanocomposites and pure blend. The storage modulus, tensile modulus, and tensile strength values increase due to the superior dispersion of the modified halloysite nanotubes in polymer matrix.

One-step amino-functionalization of milled carbon fibre for enhancement of thermo-physical properties of epoxy composites

Development of new chemical approaches for preparation of engineered carbon-based fillers is critical for high-performance applications. Herein, an efficient method for covalent functionalization of polyacrylonitrile-based carbon fibre through azo radical addition under mild condition is demonstrated. In this way, isobutyronitrile radicals in situ produced from thermal decomposition of 2,2′-azobisisobutyronitrile (AIBN), were covalently grafted on milled carbon fibre (MCF) surface, assisted by microwave irradiation, as evidenced by FTIR, Raman, and TGA analysis. The grafted isobutyronitriles on MCF surface (n-MCF) were applied for further MCF amino-functionalization (a-MCF) via nucleophilic reaction of an amine-rich compound. Then, both pure MCF and a-MCF were incorporated into epoxy matrix; and its curing process and thermo-physical properties were investigated using DSC, rheometry, DMA, TGA, and flexural analysis. The Tg and flexural strength of epoxy/a-MCF composites, compared to epoxy/MCF, increased by ∼3.5% and∼10.2%, resulting from good adhesion between a-MCF and epoxy matrix which confirmed by SEM observations.

A Review on Nanoparticle Addition in Base Fluid for Improvement of Biodegradable Ester-based Drilling Fluid Properties

Nanotechnology is increasingly capturing the attention of material researchers as this technology pushes the limits and boundaries of the pure material itself. Nanofluids usually contain enhanced physical properties such as thermal conductivity and electrical conductivity. The incorporation of such technology can be shifted to the oil and gas industry, especially areas relating to drilling fluid. However, most drilling muds have detrimental effects such as environmental pollution, low degradation of drilling mud and strenuous post-treatment. Thus, the need for the production of a biodegradable drilling fluid is emphasized. However, current limitations imposed on the said drilling fluid restrict its usage on conventional drilling operations. This paper aims to review the effects of addition of powder nanoparticles into base fluid to achieve required criterions of industrial drilling fluid. Generally, the addition of nanoparticles into base fluids will result in better thermophysical properties such as thermal conductivity and convective heat transfer coefficients. The enhancement of thermophysical properties in drilling operations are highly desirable as heat generated from the friction between of drilling bit and the wellbore can be circulated at a higher rate. The addition of nanoparticles also results in changes in electrical conductivity and viscosity of the base fluid. These parameters have been investigated by various researchers and a positive enhancing trend is observed. However, stability of nanofluids has been a wide concern as various researchers struggled to maintain the stability of nanoparticle suspension.

Thermal Diffusivity and Viscosity of Suspensions of Disk-Shaped Nanoparticles

In this work we conduct a transient heat conduction experiment with an aqueous suspension of nanoparticle disks of Laponite JS, a sol forming grade, using laser light interferometry. The image sequence in time is used to measure thermal diffusivity and thermal conductivity of the suspension. Imaging of the temperature distribution is facilitated by the dependence of refractive index of the suspension on temperature itself. We observe that with the addition of 4 volume % of nano-disks in water, thermal conductivity of the suspension increases by around 30%. A theoretical model for thermal conductivity of the suspension of anisotropic particles by Fricke as well as by Hamilton and Crosser explains the trend of data well. In turn, it estimates thermal conductivity of the Laponite nanoparticle itself, which is otherwise difficult to measure in a direct manner. We also measure viscosity of the nanoparticle suspension using a concentric cylinder rheometer. Measurements are seen to follow quite well, the theoretical relation for viscosity of suspensions of oblate particles that includes up to two particle interaction. This result rules out the presence of clusters of particles in the suspension. The effective viscosity and thermal diffusivity data show that the shape of the particle has a role in determining enhancement of thermophysical properties of the suspension.

A review of experimental investigations on thermal phenomena in nanofluids

Nanoparticle suspensions (nanofluids) have been recommended as a promising option for various engineering applications, due to the observed enhancement of thermophysical properties and improvement in the effectiveness of thermal phenomena. A number of investigations have been reported in the recent past, in order to quantify the thermo-fluidic behavior of nanofluids. This review is focused on examining and comparing the measurements of convective heat transfer and phase change in nanofluids, with an emphasis on the experimental techniques employed to measure the effective thermal conductivity, as well as to characterize the thermal performance of systems involving nanofluids.