Experimental investigation on synthesis, characterization, stability, thermo-physical properties and rheological behavior of MWCNTs-kapok seed oil based nanofluid

Preparing epoxidized vegetable oil from waste generated by the kapok fiber industry and assessing its thermal stabilization effect as a co-stabilizer for polyvinyl chloride

This paper describes the epoxidation of vegetable oil derived from waste kapok seeds using performic acid, which was generated in situ with sulfuric acid acting as a catalyst. The mole ratio of formic acid to double bonds varied between 0.25 and 1.00. The completion of the reaction has been verified by analyzing FTIR and NMR spectra. The resulting epoxidized kapok seed oil (EKSO) has a maximum oxirane oxygen content of 2.7%, achieved at a formic acid to double bond mole ratio of 0.5. The study has also examined the potential use of EKSO as a co-stabilizer in the presence of Ca/Zn stearate for stabilizing polyvinyl chloride (PVC). Both static and dynamic tests demonstrated that incorporating EKSO into the Ca/Zn stearate system leads to a significant increase in the thermal stability of PVC. Moreover, the effectiveness of EKSO as a co-stabilizer was found to be comparable to that of epoxidized soybean oil (ESBO). However, the use of EKSO did result in a decrease in the strength of PVC due to an increase in plasticity, although this effect was minimal at low dosages and was also observed with ESBO. On the other hand, when utilizing small doses (<2 phr), there is a tendency for flowability to decrease, but the reduction is not significant either. Overall, these findings suggest that EKSO could be a valuable co-stabilizer for PVC in industrial applications, as it enhances PVC's thermal stability without significantly compromising its mechanical and flow properties.

Correlating the Dipolar Interactions Induced Magneto-Viscoelasticity and Thermal Conductivity Enhancements in Nanomagnetic Fluids

The effective thermal management of electronic system holds the key to maximize their performance. The recent miniaturization trends require a cooling system with high heat flux capacity, localized cooling, and active control. Nanomagnetic fluids (NMFs) based cooling systems have the ability to meet the current demand of the cooling system for the miniaturized electronic system. However, the thermal characteristics of NMFs have a long way to go before the internal mechanisms are well understood. This review mainly focuses on the three aspects to establish a correlation between the thermal and rheological properties of the NMFs. First, the background, stability, and factors affecting the properties of the NMFs are discussed. Second, the ferrohydrodynamic equations are introduced for the NMFs to explain the rheological behavior and relaxation mechanism. Finally, different theoretical and experimental models are summarized that explain the thermal characteristics of the NMFs. Thermal characteristics of the NMFs are significantly affected by the morphology and composition of the magnetic nanoparticles (MNPs) in NMFs as well as the type of carrier liquids and surface functionalization that also influences the rheological properties. Thus, understanding the correlation between the thermal characteristics of the NMFs and rheological properties helps develop cooling systems with improved performance.

A Bibliometric Analysis of Research and Development of Nanofluids

Nanofluid concept was defined over 28 years ago. Since then, a veritable science has been developed around this concept. From 1993 until 2020, up to 18021 articles were published in high-quality journals worldwide. The high scientific interest in nanofluids lies in their exceptional thermophysical properties and their possibilities to design more efficient processes and systems. Although the numerous articles, there is a lack of information on the scope, its social and economic impact, or its future trends. This study provides an overview through bibliometric methods that allow better knowledge of the research field. The main goal is to offer a more generalized and strategic vision to help those researchers interested in this topic with accurate information on its impact. In addition, this study helps to maximize international collaborations and provide relevant information to decision-makers. The analysis reveals that research in nanofluids in the last decade has experienced a great specialization in a wide variety of new applications, reaching more new sectors. The main research communities, the most productive authors, or the most relevant journals are some of the analyzed metrics that provide key parameters for contextualization, allowing a clear vision of the current state of the nanofluids research field.

A Review on Experimental and Numerical Investigations of Jet Impingement Cooling Performance with Nanofluids

Nanofluids offer great potential heat transfer enhancement and provide better thermophysical properties than conventional heat transfer fluids. Application of nanofluids in jet impingement cooling is used for many industrial and scientific purposes as it manages to effectively remove high localized heat. Owing to its tremendous improvement of the heat transfer field, the use of nanofluids in jet impingement cooling has caught the attention of many researchers. This paper reviews previous research and recent advancements of nanofluid jet impingement via both experimental and numerical studies. In experimental approaches, Al₂O₃-water nanofluids are the most used working fluids by researchers, and most experiments were conducted with conventional impinging jets. As for the numerical approach, the single-phase model was the preferred model over the two-phase model in obtaining numerical solutions, due to the lower computational time required. A deep insight is provided into nanofluid preparation and methods for stabilization. Parameters affecting the performance of the jet impinging system are also investigated with comparison to numerous publications. The main parameters for jet impinging include the jet-to-plate distance (H/D), the shape of the impinged plate (curved, flat or concave), nozzle configurations and the twisted tape ratio. Studies on conventional impinging jets (CIJs), as well as swirling impinging jets (SIJs), are presented in this paper.

Exploring the thermo-physical characteristic of novel multi-wall carbon nanotube-Therminol-55-based nanofluids for solar-thermal applications

This work aims to develop a novel nanofluid using Therminol-55 (T-55) as heat transfer fluid and multi-wall carbon nanotubes (MWCNTs) as dispersants with various volume concentrations of 0.05, 0.1, 0.3, and 0.5% and assess its thermo-physical properties for solar-thermal applications. The pH values of nanofluid MWCNT/T-55 with various particle loading were too far-flung from the pH (I) value, which confirmed the good dispersion stability of nanofluid. The measured density shows tremendous deviation from predicted density with increasing MWCNT loading owing to the non-considering of microstructural parameters in Pak & Cho correlation predication. The highest augmentation in nanofluid thermal conductivity was 16.83% for 0.5 vol. % MWCNT at 60 °C. The maximum improvement in dynamic viscosity of nanofluid with 0.5 vol. % of MWCNT is found to be 44%, and this rise is reduced at higher temperatures. The thermal effectiveness of the nanofluids demonstrates that nanofluid with all volume fractions of MWCNTs was favorable at higher temperatures in the laminar region. Mouromtseff number ratio decreases with a rise in temperature and MWCNT volume concentration. It is concluded that the excellent thermo-physical properties and prolonged thermal stability of the MWCNT will be highly beneficial in improving the overall performance of various kinds of heat transfer fluids (HTFs) for process heating and solar-thermal applications.

Physiochemical studies of functionalized MWCNT/transformer oil nanofluid utilized in a double pipe heat exchanger

The transformer-oil based nanofluid suspensions were prepared by adding 0.05 to 0.80 wt% multi-wall carbon nanotubes (MWCNTs) functionalized with a –COOH group. Sodium dodecyl sulfate (SDS) was used to stabilize the suspensions. The resulting material was used as a coolant in a double pipe heat exchanger operated under co- and counter-current flow conditions. The nanofluid thermo–physical features such as the thermal conductivity, viscosity, and density were determined at various temperatures and mass fractions. Then, pertinent semi-empirical relations were developed. To verify any MWCNT and SDS interactions with the material, the Fourier-transform infrared analysis was performed. Moreover, the stability of the nanofluid suspension was understudied through the UV–vis and thermogravimetric analysis techniques. In addition, the maximum heat transfer coefficient improvement was determined to be 86.7% at a MWCNT mass fraction of 0.8 wt%. Meanwhile, average increments of the overall heat transfer coefficient and thermal conductivity of the prepared nanofluid were revealed about 37.2% and 138%, respectively in comparison with that of the base fluid. Furthermore, the optimum thermal conductivity of 0.388 W/m.K was obtained at 45 °C and 0.8 wt% of the MWCNT. Ultimately, a sensitivity analysis emphasized that, the understudied system’s behaviors were within an accuracy limit of ± 97%.

Hybrid Materials Based on Carbon Nanotubes and Nanofibers for Environmental Applications

With the advances in material science, hybrid nanomaterials with unique mechanical, electrical, thermal and optical characteristics have been developed. Among them, hybrids based on filamentous forms of carbon, such as carbon nanotubes and carbon nanofibers, in combination with inorganic nanoparticles attract particular attention. Due to the structure and morphology, charge and energy transfer processes lead to synergistic effects that allow the use of less material with higher productivity. To clarify these issues, this review will summarize and discuss the relevant studies of the use of inorganic compounds of various chemical groups in modifying carbon nanomaterials for ecological applications.

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.