Investigation of nanofluids in alkaline electrolytes: Stability, electrical properties, and hydrogen production

Utilizing solar energy efficiently and manufacturing hydrogen economically are the primary goals in the energy industry. In this paper, we present a novel method to solve both issues by exploiting the electrolysis of electrolyte-based nanofluids under the illumination of solar light. The carbon black nanoparticles/sodium hydroxide solution mixture of electrolyte nanofluids were prepared, which were then electrolyzed in a Hoffman voltameter to produce hydrogen. The results showed the hydrogen production rate improved by 23.62% when carbon black was used in the electrolyte. The optimal carbon black concentration was 0.04% or 0.2% depending on the experimental set-up used. Finally, a theoretical model was built to evaluate the total hydrogen production, which showed a good agreement with the experimental results when the carbon black concentration was lower than 0.1 wt%.publishedVersio

Numerical investigation of direct absorption solar collectors based on carbon black nanofluids

A novel model of a rectangular direct absorption solar collector (DASC) based on carbon black (CB) nanofluids for concentrated solar power is presented herein. Distributions of temperature, velocity, volume fraction of nanofluid were analyzed as well as the effect of CB concentration. A mesh independence study was also conducted. The results show that the optimal temperature and efficiency were, respectively, 331.669 K and 0.7234, for the concentration of 0.05 wt. %. The main reason was that higher concentration of CB formed a “shield” that blocked the light. The distribution of temperature and velocity of the nanofluid, and the volume fraction of carbon black during the flow process were highlighted. The study reveals that the nanoparticle has huge potential to improve the efficiency of DASC.acceptedVersio

Photothermal conversion of biodegradable fluids and carbon black nanofluids

The paper is devoted to the topic of direct absorption solar collectors (DASCs). Various kinds of fluids can be used as heat transfer fluid in DASCs, and the main focus of our paper is on comparing nanofluids (water with carbon black nanoparticles, concentrations between 0.25 and 1.00% weight) and biodegradable coffee colloids. At first, these fluids were tested by exposing them to irradiation caused by artificial light in indoor experiments, and the corresponding temperature increase was recorded. The fluids were placed in a beaker with a relatively large size so that most of the fluid was not directly irradiated. In these experiments, the performance of the two studied fluids was similar: the resulting temperature increase varied between 46 and 50 °C. Our next experiments involved a smaller system subjected to irradiation obtained by using a solar collector. As a result, we detected an intense absorption on the nanoparticle surface so that the temperature rise in the nanofluid was higher than in the coffee colloids. Next, the process was analysed using a theoretical analysis that gave good correspondence with the experiments. Finally, we extended the theoretical analysis to a DASC with a flowing fluid. The model was validated against results from the literature, but it also supported our experimental findings.publishedVersio

Theoretical analysis of erosion in elbows due to flows with nano- and micro-size particles

The present paper focuses on the issue of erosion due to fluid flow laden with nano- and microparticles. We investigated the case of a pipe elbow using theoretical analysis and numerical simulations. For the case when the particles were large, that is, of micrometre size, we observed the expected behaviour in which the erosion rate was greater with increasing particle diameter. The same was seen for flow velocity, and higher velocities promoted the erosion process. For small particles, however, the erosion rate increased with decreasing particle size. This was explained by the formation of secondary flows in the elbow that centrifuged the particles towards the walls. For very small particles, the erosion rate decreased again, i.e. the particle distribution towards the wall was insufficient to erode the pipe wall due to the particles low mass.publishedVersio

Experimental study of hydrogen production using electrolyte nanofluids with a simulated light source

In this research, we conducted water electrolysis experiments of a carbon black (CB) based sodium sulfate electrolyte using a Hoffman voltameter. The main objective was to investigate hydrogen production in such systems, as well as analyse the electrical properties and thermal properties of nanofluids. A halogen lamp, mimicking solar energy, was used as a radiation source, and a group of comparative tests were also conducted with different irradiation areas. The results showed that by using CB and light, it was possible to increase the hydrogen production rate. The optimal CB concentration was 0.1 wt %. At this concentration, the hydrogen production rate increased by 30.37% after 20 min of electrolysis. Hence, we show that using CB in electrolytes irradiated by solar energy could save the electrical energy necessary for electrolysis processes.publishedVersio

Experimental and numerical investigation of direct absorption solar collectors (DASCs) based on carbon black nanofluids

Direct absorption solar collectors (DASCs) typically achieve high efficiency due to the volumetric heat absorption process facilitated by the working fluids. In this study, carbon black (CB) nanofluids were utilized as the working fluid to experimentally and numerically investigate the thermal performance of a rectangular DASC. The findings suggest that the nanoparticles have the potential to enhance the efficiency of the DASC. Direct absorption solar collectors (DASCs) are known for their high efficiency, which is achieved through the volumetric heat absorption process provided by the working fluids In this study, carbon black (CB) nanofluids were used as these working fluids to study the thermal performance of a rectangular DASC. The experiments were conducted using water and nanofluids with 0.05 wt.% nanoparticle concentration, at different flow rates and tilt angles, under a concentrated simulated solar power source. Our results show that the efficiency of the DASC increased as the flow rate increased. The DASC was more efficient when the receiving surface was facing downwards (tilt angle of 0°), and the efficiency was 35% higher than when the receiving surface was facing upwards (tilt angle of 180°). A computational fluid dynamics (CFD) model, which was validated against our experimental results, analyzed the DASC performance under different CB concentrations. According to the simulations, the highest efficiency occurred at a concentration of 0.05 wt.%. The study also highlighted the distribution of temperature and velocity of the nanofluids, as well as the volume fraction of carbon black during the flow process.publishedVersio

Direct absorption solar collector: Use of nanofluids and biodegradable colloids

In this paper, an experimental and numerical analysis was performed on both carbon black nanofluids and a biodegradable fluid in a novel pump-free direct absorption solar collector (DASC). In the experiments, the nanofluid consisted of carbon black nanoparticles in water with concentrations ranging from 0.005 to 0.020 wt%, while the biodegradable fluid was coffee colloid. The overall findings indicated a concurrence: the nanofluids exhibited the best thermal performance when compared to pure water. The optimum nanoparticle concentration of 0.010 wt% carbon black yielded a 102% thermal enhancement compared to the base fluid. Furthermore, a numerical analysis using computational fluid dynamics (CFD) software was performed to study the experimental rig. According to these simulations, the optimal nanofluid concentration showed a 76.6 - 90.9% increase compared to the base fluid. The biodegradable fluids did not show a significant enhancement in the experiments, which differs from what has been reported in the scientific literature. Nevertheless, from the computer simulations, the biodegradable fluids also slightly outperformed the case when the pure water was used.publishedVersio

Flow loop study of a cold and cohesive slurry. Pressure drop and formation of plugs

Slurries of cohesive particles constitute a significant risk during subsea petroleum production due to their potential to plug the flow. This article describes a flow loop study of a slurry consistent with 0.23-mm ice particles in decane. The experiments were conducted for the concentration of particles up to 20.3% vol. and Re 25000. The cohesion of ice was suggested by controlling the temperature of the slurry. The relative viscosity of the slurry was computed as a function of particle concentration using pressure drop measurements. The relative viscosity was 3.1 for the concentration of 20.3%. The Bingham-fluid model agreed with the empirical calculations within the discrepancy of 15.5%. Increased viscosity of slurry led to a higher pressure drop in the flow loop compared to the single-phase case. Pressure drops for 20.3% slurry flow were 5.2% and 44.4% higher than for pure decane at Reynolds numbers of 24778 and 4956, respectively. The test section of the loop was equipped with an orifice to induce the formation of plugs. The plugs were observed at particle concentrations below 7.0%. The article presents detailed experimental logs depicting the process of plug formation. The observed blocking cases partially agreed with flow maps from the literature. In addition, we note the applicability of the blockage risk evaluation technique from the Colorado School of Mines.publishedVersio

Cohesive collisions of particles in liquid media studied by CFD-DEM, video tracking, and Positron Emission Particle Tracking

This paper investigates the cohesive collision of ice in an oil phase at temperatures ranging from −15.7 °C to −0.3 °C. The new information on the coefficient of restitution (COR) was obtained using three different velocity measurement methods: high-speed experimental video recording, Positron Emission Particle Tracking (PEPT), and numerical simulations. A new type of PEPT tracer was developed for the experiments. The COR values were in the interval 0.57...0.82, with a maximum at around −10 °C. The CFD-DEM coupled approach was applied to reproduce experiments with an ice particle drop and its collision with an inclined ice surface in a decane. The particle–wall interaction is modeled using commercial software, considering particle cohesion, particle size, and shape. CFD-DEM predicted the COR with an average deviation 10% from the experimental data. The numerical model’s results agree with the experiments, demonstrating that the CFD-DEM method is suitable for describing multiphase cohesive interactions

Experimental investigation of erosion due to nanofluids

The demand for efficient and sustainable energy is continuously increasing. Among the many technologies with great potential within this field are nanofluids. Nevertheless, there is still a considerable lack of information regarding their erosive effects on systems materials. In this research, the tribological behaviour of aqueous 1.33 wt% TiO2 nanofluid was investigated when jet-impinged with an average velocity of 0.8 m/s at flat targets of various materials (plastic, copper, rubber). The target surfaces were analysed using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and X-ray diffraction (XRD). It was found that impinging TiO2 nanofluid caused erosion of 282 g/( yr.mm2) for copper and 212 g/( yr.mm2) for plastic. In addition, a deposition of nanoparticles was found for rubber at rate of 2.7 kg/(yr.mm2).publishedVersio