This study presents a machine learning-based approach to predict blockage in multiphase flow with cohesive particles. The aim is to predict blockage based on parameters like Reynolds and capillary numbers using a random forest classifier trained on experimental and simulation data. Experimental observations come from a lab-scale flow loop with ice slurry in the decane. The plugging simulation is based on coupled Computational Fluid Dynamics with Discrete Element Method (CFD-DEM). The resulting classifier demonstrated high accuracy, validated by precision, recall, and F1-score metrics, providing precise blockage prediction under specific flow conditions. Additionally, sensitivity analyses highlighted the model’s adaptability to cohesion variations. Equipped with the trained classifier, we generated a detailed machine-learning-based flow map and compared it with earlier literature, simulations, and experimental data results. This graphical representation clarifies the blockage boundaries under given conditions. The methodology’s success demonstrates the potential for advanced predictive modelling in diverse flow systems, contributing to improved blockage prediction and prevention.

The concept of direct absorption solar collector (DASC) was introduced in the 1970s. Multiple laboratory studies proved that nanofluid-based DASCs presented a fruitful alternative to conventional solar collectors. However, due to environmental and cost limitations of nanofluids, there are few records of real-size DASCs operating in field conditions. Filling the gap, we report a 5-month seasonal field study for a full-scale DASC with an eco-friendly and low-cost nanofluid. Throughout the experiments, the DASC competed with a commercial flat-plate solar collector mounted in the exact location. The results showed that the commercial collector had an average daily efficiency of about 65.9%, while the direct absorption collector had a daily efficiency of 57.7% to 86.1%. The most important parameters influencing the efficiency of the DASC are the flow rate and the extinction coefficient of the nanofluid. They alter the efficiency by 9.2% and 6.2%. Finally, the article briefly notes the technical and economic features of the DASC operation.

Flow regimes leading to clogging of pipes exist for most multiphase flows with cohesive particles. Although plugging is critical in many industrial and medical applications, there are few records describing the details of the process. To address the problem, we conduct a computed tomography (CT) study of plugging in a cohesive ice slurry. We run experiments for ice concentration of 15%, Re∼3500, particle size 0.2-0.4 mm, and their surface energy ∼150 mJ/m2. The CT scans, combined with experimental logs of the main flow parameters, revealed the formation of deposits around the orifice inserted into the pipe, with a complete blockage formed downflow the orifice. The deposition efficiency of ice was relatively low ∼ 10−3. Reproducing the experimental deposition efficiency with the Lagrangian CFD model, we extracted the probability of particle capture at the orifice, which was about 0.5%. The simulation results illustrated how inter-particle interactions hindered the plugging.

Slurries of solid particles in a liquid medium are common in chemical and petroleum industries. They possess significant clogging risks when transported in pipes during a process. This paper presents a simple and low-cost method to decrease the plugging risk in a flow system. For this, we streamline the pipes' internal geometry, significantly reducing the volume of stagnation zones in pipes' dead legs. We test the approach experimentally and consider how the plugs are formed before and after the geometry modification. The experiments were carried out in a flow loop with the cohesive ice particles suspended in decane. The particle concentration was 2.2…15 % vol., and Reynolds numbers were below 20,000. After we reduced the dead zones with inserts, the particle concentration of a plug-free regime was increased by 8 % vol., and the minimum transport Reynolds number decreased by 74 %.

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.

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.

The paper presents a performance study of a lab-scale geothermal coaxial heat exchanger with an aqueous nanofluid with the nanoparticles of Al2O3. The concentration of nanoparticles was in the interval 2% wt. to 8% wt. We describe the nanofluid production method resulting in samples that are stable in static conditions for 50 days. The average size of the particles was 183 nm in−situ. We found that the thermal conductivity of the nanofluid may increase up to 13%, and the maximum apparent viscosity grows to 20% relative to the base fluid. The nanofluid was tested in a lab-scale geothermal heat exchanger. The best thermal performance of the heat exchanger with nanofluid was 9% higher than for the experiments with the base fluid.

Nanofluids are promising receivers for solar collectors with volumetric absorption. These solar collectors are 1.2...1.4 times more efficient than conventional technology. However, most of the considered nanofluids are expensive and toxic. This work demonstrates how to treat instant coffee to produce inexpensive and environmentally friendly nanofluids for solar collectors. Our nanofluid contains particles with an average size below 100 nm. The nanofluid extinction coefficient is up to 300 1/m when 2% wt. of coffee is used. The toxicity of the nanofluid is of the same order as for the conventional coolants.

A method for calculating the coefficient of hydraulic resistance of a coaxial heat exchanger with different roughness of opposite walls is proposed. According to the technique, the annular section of the heat exchanger channel is divided by a line of zero shear stress into two non-interacting annular layers. The balance equations in the layers and the channel together with the condition of matching the velocities of the layers on the zero shear stresses line form a closed system of equations. The solution of the system allows calculating the coefficient of hydraulic resistance of the channel as a whole, the position of the line of zero shear stresses, average velocities in each of the layers, the value of the second constant of the universal velocity profile. The method was verified in several ways, which showed the maximum deviation of the calculated values from the data of other authors and the results of our experiments, no more than 7%. In our experiments, we used three two-dimensional artificial roughness profiles: rectangular, trapezoidal, and triangular. (c) 2022 Elsevier Ltd. All rights reserved.

Nanofluids have great potential for solar energy harvesting due to their suitable optical and thermophysical properties.One of the promising applications of nanofluids is utilization in solar collectors with the direct absorption of light (DASC).The design of a DASC requires detailed knowledge of the optical properties of nanofluids, which can be significantly affected by the particle size distribution.The paper presents the method to take into account the particle size distribution when calculating nanofluid extinction spectra.To validate the proposed model, the particle size distribution and spectral absorbance were measured for aqueous suspension with multi-walled graphite nanotubes; the minimum size of primary nanoparticles was 49 nm.The proposed model is compared with experiments demonstrating the concentration averaged and maximum discrepancies of 6.6% and 32.2% against 12.6% and 77.7% for a model assuming a monosized suspension.

The paper presents the experimental measurements of thermal efficiency of a tubular direct absorption solar collector (DASC) with a hybrid nanofluid based on magnetite (Fe3O4) and multi-walled carbon nanotubes (MWCNT). The volumetric concentration of Fe3O4 and MWCNT was 0.0053% and 0.0045%, respectively. The experiments were carried out for the flow rates of 2–10 L/min and a temperature difference up to 20 ∘C between the environment and the DASC. The performance of the DASC with a hybrid nanofluid was in the range of 52.3–69.4%, which was just beyond the performance of the collector with surface absorption. It was also found that using a MWCNT-based nanofluid with an equivalent total volumetric concentration of particles (0.0091%), the efficiency was 8.3–31.5% higher than for the cases with the hybrid nanofluid.

Direct absorption solar collectors (DASC) with nanofluid represent a new direction in solar thermal technology that is simpler yet more efficient than conventional equipment. In this work, we report details of performance for a custom tubular DASC with a carbon-based nanofluid. The collector was tested experimentally following a standard procedure and using a multiphase CFD-model of the device. The experiments were carried out in a range of flow rates 2... 10 l/min, nanoparticle concentrations 0.0015... 0.082%wt., temperature differences (up to 29.3 degrees), and radiant heat fluxes. We found that, at a particle concentration of 0.01%, the collector demonstrated the average thermal efficiency of 80%. For the comparable temperature differences, the efficiency of DASC was 5.8... 37.9% higher than a collector with similar geometry but a surface absorption of light energy. The CFD-model, validated against our experiments, depicts flow patterns in the DASC focusing on nanoparticles' deposition. Less than 5% of particles deposit under local flow restrictions at flows above 6 l/min. The deposition patterns from the CFD-model correlate to the experimental observations. (c) 2021 Elsevier Ltd. All rights reserved.

Due to the high light absorption and the possibility of localizing boiling to the interior of the receiver, nanoparticles are promising for solar-driven desalination. The paper presents an experimental study of the nanoparticle-based photothermal boiling of water with sea salt. The experiments were carried out using a laboratory-scale system with a transparent photothermal receiver of light and a closed condensate cycle. In this study, we tested three types of nanoparticles: multiwall carbon nanotubes with two main sizes of 49 nm and 72 nm, 110 nm iron oxide particles Fe3O4, and a commercial paste based on carbon nanotubes. The concentration of nanoparticles was varied up to 10% wt. We found that the nanoparticles enhance the steam generation by 23%, relative to a conventional desalinator with a black-body receiver. The best result was obtained for the 5% wt. concentration of carbon nanotubes.

The direct photothermal boiling in suspensions of nano- and microscopic particles finds multiple applications in concentrated solar power: turbine-based combined heat and power (CHP) generation, solar distillation, energy storage, and chemical synthesis. However, the most promising application is solar desalination. There have been multiple studies aimed at the evaporation of suspensions using simulated solar light, but there is neither a theory describing the process nor a well-documented prototype study. This article aims at the development of an experiment and a theory, that describe the photothermal boiling in aqueous suspensions of graphite. We develop a laboratory scale steam-fluid loop with continuous condensation that recycles the water back to the process. We clarify how the concentration and incident radiant heat influence the steam generation. The optimum concentration of graphite particles - 1 wt% - was found experimentally at 17.4 suns. We studied the granulometry of the suspension and dynamics of steam bubbles. We document how the particle size distribution and bubbles evolve in boiling suspension. The theoretical description of the process is based on a heat balance analysis for an individual steam bubble. The developed model is validated against three independent experimental datasets, exhibiting accuracy with the lowest average discrepancy of 10%. (C) 2020 Elsevier Ltd. All rights reserved.

Photo-thermal evaporation of nanofluids has potential applications in solar desalination, micro-CHP (combined heat and power) and domestic off-grid disinfection. In this research, we reproduced the process experimentally using 110-nm iron oxide particles dispersed in water. At an initial lab-scale stage, under the artificial radiation of 6.9 suns, we observed that the boiling nanofluid destabilizes to a suspension of 6pm agglomerates of nanoparticles and that up to 30% of the particles escape the system with the steam. At the prototype stage, we boiled the fluid in a solar concentrator producing 35 g/min steam with an efficiency of around 60%, which is sufficient to drive a small turbine. The optimum concentration of the nanoparticles was 3 wt%. To supplement the experiments, we developed a simplified model for engineering calculations of the solar steam generation rate. The model corresponds well to the experiments deviating by only 8%. (C) 2020 Elsevier Ltd. All rights reserved.

The paper describes the effect of sodium dodecyl sulfate (SDS) on the steam generation during photothermal boiling of carbon nanofluids. The considered process finds promising applications for e.g. solar desalination where SDS may boost steam generation. Our study was carried out in a lab system boiling aqueous suspensions of carbon by means of artificial thermal radiation. The experiments demonstrate that the newly-produced nanofluids turn into suspension when no SDS is present in the fluid. The agglomeration of nanoparticles reduces the stability of the system yet degrades the steam generation by no more than 8.2%. The optimum particle concentration was about 2% wt. independently of whether SDS was present in samples. The steam was superheated by up to 12 K when using the surfactant which was 5-7 K higher than without SDS. The experimental data was supported by a theoretical analysis. (c) 2020 Elsevier B.V. All rights reserved.