Experiments on the Electrical Conductivity of PEG 400 Nanocolloids Enhanced with Two Oxide Nanoparticles.

This paper aims to provide some insights into the pH and electrical conductivity of two classes of nanocolloids with PEG 400 as the base fluid. Thus, nanoparticles of two oxides-MgO and TiO2-were added to the base fluid in 5 mass concentrations in the range 0.25-2.5 %wt. The stability was evaluated in terms of pH at ambient temperature, while the electrical conductivity was discussed at both ambient temperature and up to 333.15 K. The electrical conductivity of PEG 400 was previously discussed by this group, while the behavior of the new nanocolloids was debated in terms of the state of the art. More precisely, the influence of MgO increases electrical conductivity, and an enhancement of up to 48% for 0.25% MgO was found, while the influence of TiO2 nanoparticles was found to be in similar ranges. In conclusion, electrical conductivity varies with temperature and the addition of nanoparticles to the base fluid, although the mechanisms that are driving the nanoparticle type and concentration influence are not yet entirely assumed in the available literature.

Thermophysical Properties of Nanocolloids and Their Potential Applications.

This Special Issue is a continuation of the previous successful Special Issue, entitled "Future and Prospects in Nanofluids Research", co-edited by the present Editor and dedicated to the topic of "Thermophysical Properties of Nanocolloids and Their Potential Applications" [...].

Heat Transfer Analysis of Nanocolloids Based on Zinc Oxide Nanoparticles Dispersed in PEG 400.

Cooling and heating are extremely important in many industrial applications, while the thermal performance of these processes generally depends on many factors, such as fluid flow rate, inlet temperature, and many more. Hence, tremendous efforts are dedicated to the investigation of several parameters to reach an efficient cooling or heating process. The interest in adding nanoparticles in regular heat transfer fluids delivered new fluids to the market, the nanofluids. In this paper, a new nanoparticle-enhanced fluid based on polyethylene glycol with ZnO nanoparticles is considered and its hydrothermal performance is investigated for HVAC applications. The thermophysical properties of PEG 400-ZnO and their variation with temperature at different nanoparticle loading are previously determined on experimental bases and here implemented in a numerical application. The numerical results are completed at Reynolds number from 200 to 2000, while the nanoparticle concentration varies from 0.5 to 5%. Results are discussed in terms of Nusselt number, friction factor, and dimensionless pressure drop ratio at different temperatures and ZnO loading in the PEG 400 base fluid. Additionally, the evaluation performance criteria (EC) are calculated and discussed. Concluding, the newly developed fluid enhances the heat transfer up to 16% with a 13% pressure drop penalty, while the performance evaluation criteria are enhanced. Plus, several correlations are developed for both Nusselt number and friction factor as a function of relevant operating conditions.

Are European marketed acyclovir 5% cream products similar? Comparison with EU and US reference product.

OBJECTIVE: The aim was to perform a comparative evaluation of composition and in vitro release performance of multisource acyclovir 5% creams. SIGNIFICANCE: The outcome was analyzed in relation with the principles of the Topical drug Classification System (TCS). METHODS: The in vitro drug release testing (IVRT) was based on selection of an inert artificial membrane and a medium providing sink conditions, and utilizing the vertical diffusion cells. US and European innovator products, with marked difference in excipients, were used as references for the assessment of the in vitro release similarity. The qualitative composition of the topical semisolid products was inventoried, with no quantitative details being available. A Principal Component Analysis was applied by either dichotomy ranking or grouping the individual excipients into categories according to their functional role. RESULTS: The results confirmed the sensitivity and discriminative characteristics of IVRT with respect to the qualitative composition, as well as its relevance in the comparative assessment of multisource drug products beyond the current strict requirements of Q1 and Q2 similarity. CONCLUSIONS: This is in line with the principles of the TCS and with the central role assigned to IVRT.

Rheological and in vitro release measurements of manufactured acyclovir 5% creams: confirming sensitivity of the in vitro release.

Previous evaluation of marketed acyclovir 5% creams using in vitro release testing (IVRT) and its correlation with the qualitative composition confirmed the discriminative characteristics of this methodology. This was in line with the principles of Topical drug Classification System (TCS). For the current research, experimental formulations were designed and prepared by applying controlled changes in manufacturing process, sources of raw materials, and amount of the excipients. The topical semisolids were representative for the four classes of TCS. The outcome of the IVRT and rheological assessments was evaluated in relation with the nature of the change and the functional role of the excipients. The variations in propylene glycol content from 5% to 40% impacted both the in vitro release rates (gradual decrease from 16.23 to 8.97 µg/cm2/min0.5) and the microstructural characteristics (proportional increase of yield stress from 17.98 to 46.40 Pa). The inert excipients e.g. cetostearyl alcohol or white soft paraffin altered majorly the rheological behavior, as their functionality is mainly related to vehicle properties. IVRT was discriminative for the microstructural differences induced by both categories of excipients according to TCS dichotomy. This simple, reliable, and reproducible test reflected the impact of difference in quantitative composition and characteristics of excipients.

Ionic Liquids-Based Nanocolloids-A Review of Progress and Prospects in Convective Heat Transfer Applications.

Ionic liquids are a new and challenging class of fluids with great and tunable properties, having the capability of an extensive area of real-life applications, from chemistry, biology, medicine to heat transfer. These fluids are often considered as green solvents. Several properties of these fluids can be enhanced by adding nanoparticles following the idea of nanofluids. These ionic liquids-based nanocolloids are also termed in the literature as ionanofluids or nanoparticles-enhanced ionic liquids. This review summarizes the findings in both areas of ionic liquids and ionic liquids nanocolloids (i.e., ionic liquids with nanoparticles in suspension) with direct applicability in convective heat transfer applications. The review presents in a unified manner the progress and prospects of ionic liquids and their nanocolloids from preparation, thermophysical properties and equally experimental and numerical works. As the heat transfer enhancement requires innovative fluids, this new class of ionic liquids-based nanocolloids is certainly a viable option, despite the noticed drawbacks. Nevertheless, experimental studies are very limited, and thus, extensive experiments are needed to elucidate ionic liquids interaction with nanoparticles, as well as their behavior in convective heat transfer.

State of the Art in PEG-Based Heat Transfer Fluids and Their Suspensions with Nanoparticles.

Research on nanoparticle enhanced fluids has increased rapidly over the last decade. Regardless of several unreliable reports, these new fluids have established performance in heat transfer. Lately, polyethylene glycol with nanoparticles has been demarcated as an innovative class of phase change materials with conceivable uses in the area of convective heat transfer. The amplified thermal conductivity of these nanoparticle enhanced phase change materials (PCMs) over the basic fluids (e.g., polyethylene glycol-PEG) is considered one of the driving factors for their improved performance in heat transfer. Most of the research, however, is centered on the thermal conductivity discussion and less on viscosity variation, while specific heat capacity seems to be fully ignored. This short review abridges most of the recent investigations on new PEG-based fluids and is dedicated especially to thermophysical properties of the chemicals, while a number of PEG-based nanofluids are compared in terms of base fluid and/or nanoparticle type and concentration. This review outlines the possibility of developing promising new heat transfer fluids. To conclude, this research is in its pioneering phase, and a large amount of experimental and numerical work is required in the coming years.

A Review on Electrical Conductivity of Nanoparticle-Enhanced Fluids.

This review discusses exclusively the recent research on electrical conductivity of nanofluids, correlations and mechanisms and aims to make an important step to fully understand the nanofluids behavior. Research on nanoparticle-enhanced fluids' electrical conductivity is at its beginning at this moment and the augmentation mechanisms are not fully understood. Basically, the mechanisms for increasing the electrical conductivity are described as electric double layer influence and increased particles' conductance. Another idea that has resulted from this review is that the stability of nanofluids can be described with the help of electrical conductivity tests, but more coordinated research is needed. The purpose of this article is not only to describe the aforementioned studies, but also to fully understand nanofluids' behavior, and to assess and relate several experimental results on electrical conductivity. Concluding, this analysis has shown that a lot of research work is needed in the field of nanofluids' electrical characterization and specific applications.

Electrical Conductivity of New Nanoparticle Enhanced Fluids: An Experimental Study.

In this research, the electrical conductivity of simple and hybrid nanofluids containing Al2O3, TiO2 and SiO2 nanoparticles and water as the base fluid was experimentally studied at ambient temperature and with temperature variation in the range of 20-60 °C. A comparison of the experimental data with existing theoretical models demonstrated that the theoretical models under-predict the experimental data. Consequently, several correlations were developed for nanofluid electrical conductivity estimation in relation to temperature and volume concentration. The electrical conductivity of both simple and hybrid nanofluids increased linearly with both volume concentration and temperature upsurge. More precisely, by adding nanoparticles to water, the electrical conductivity increased from 11 times up to 58 times for both simple and hybrid nanofluids, with the maximum values being attained for the 3% volume concentration. Plus, a three-dimensional regression analysis was performed to correlate the electrical conductivity with temperature and volume fraction of the titania and silica nanofluids. The thermo-electrical conductivity ratio has been calculated based on electrical conductivity experimental results and previously determined thermal conductivity. Very low figures were noticed. Concluding, one may affirm that further experimental work is needed to completely elucidate the behavior of nanofluids in terms of electrical conductivity.