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CO2 foams often suffer from poor stability due to high coarsening and coalescence rates, limiting their effectiveness in various applications. While it is well-established that small amounts of insoluble vapours such as alkane or fluorocarbon vapours can impede coarsening and recent studies have demonstrated their impact on coalescence, their specific effect on the CO2 foams has not been studied. This research provides a comprehensive examination of stabilising effect of hexane on CO2 foams in the presence of sodium dodecylbenzenesulfonate (SDBS). We investigated the foam stability of CO2 foams, benchmarking them against N2 foams by analysing foam lifetime, liquid drainage rate, and the evolution of bubble size. Additionally, we quantified the stabilising impact of hexane by calculating the coarsening rate. To gain insights into the adsorption mechanism of surfactants in the presence of hexane, we conducted surface tension and interfacial dilational rheology measurements, which demonstrated an increased adsorption of surfactant molecules at the interface and increased dilational viscoelasticity of interface when n-hexane was present. The introduction of hexane significantly improved foam stability, reducing coarsening rates by more than an order of magnitude. This improvement in foam stability is attributed to inhibited CO2 diffusion from the bubbles, as well as enhanced surfactant adsorption and surface elasticity, resulting in an approximate 3.6-fold increase in foam half-life.

Frothers play a key role in froth flotation by stabilising bubbles, which serve as a platform for separation of minerals of interest. This paper presents D-a-Tocopherol Polyethylene Glycol 6000 Succinate (VitE_PEG6000), an eco-friendly green frother. VitE_PEG6000's frothing performance was evaluated and benchmarked against MIBC using metrics such as the dynamic and static foam stability index (DFI, SFI), decay rate index (DRI), and critical coalescence concentration (CCC). The results show VitE_PEG6000 offers relatively high DFI of ~ 405 s/mM and low CCC of ~ 0.008 mM, classifying it as a powerful frother. Furthermore, NaCl enhances the foaming properties of VitE_PEG6000 by further lowering the surface tension and increasing dilational viscoelasticity. The outcome from this work suggests VitE_PEG6000 as a viable green frother, minimising environmental impact and hazards. Moreover, the compatibility of VitE_PEG6000 with NaCl, as the most dominant salt in groundwater and seawater allows the use of this novel frother with various water sources, thus reducing ecological footprints and fresh water usage.

Pickering foams are available in many applications and have been continually gaining interest in the last two decades. Pickering foams are multifaceted, and their characteristics are highly dependent on many factors, such as particle size, charge, hydrophobicity and concentration as well as the charge and concentration of surfactants and salts available in the system. A literature review of these individual studies at first might seem confusing and somewhat contradictory, particularly in multi-component systems with particles and surfactants with different charges in the presence of salts. This paper provides a comprehensive overview of particle-stabilized foams, also known as Pickering foams and froths. Underlying mechanisms of foam stabilization by particles with different morphology, surface chemistry, size and type are reviewed and clarified. This paper also outlines the role of salts and different factors such as pH, temperature and gas type on Pickering foams. Further, we highlight recent developments in Pickering foams in different applications such as food, mining, oil and gas, and wastewater treatment industries, where Pickering foams are abundant. We conclude this overview by presenting important research avenues based on the gaps identified here. The focus of this review is limited to Pickering foams of surfactants with added salts and does not include studies on polymers, proteins, or other macromolecules.

Surfactant-stabilized foams have been at the centre of scientific research for over a century due to their ubiquitous applications in different industries. Many of these applications involve inorganic salts either due to their natural presence (e.g. use of seawater in froth floatation) or their addition (e.g. in cosmetics) to manipulate foam characteristics for the best outcomes. This paper provides a clear understanding of the effect of salts on surfactant-stabilized foams through a critical literature survey of this topic. Available literature shows a double effect of salts (LiCl, NaCl and KCl) on foam characteristics in the presence of surfactants. To elucidate the underlying mechanisms of the stabilizing effect of salts on foams, the effect of salts on surfactant-free thin liquid films is first discussed, followed by a discussion on the effect of salts on surfactant-stabilized foams with the focus on anionic surfactants. We discuss two distinctive salt concentrations, salt transition concentration in surfactant-free solutions and salt critical concentration in surfactant-laden systems to explain their effects. Using the available data in literature supported by dedicated experiments, we demonstrate the destabilizing effect of salts on foams at and above their critical concentrations in the presence of anionic surfactants. This effect is attributed to retarding the adsorption of the surfactant molecules at the interface due to the formation of nano and micro-scale aggregates.

The enhancement of heat transfer between parallel surfaces, including parallel plates, parallel disks, and two concentric pipes, is vital because of their wide applications ranging from lubrication systems to water purification processes. Various techniques can be utilized to enhance heat transfer in such systems. Adding nanoparticles to the conventional working fluids is an effective solution that could remarkably enhance the heat transfer rate. No published review article focuses on the recent advances in nanofluid flow between parallel surfaces; therefore, the present paper aims to review the latest experimental and numerical studies on the flow and heat transfer of nanofluids (mixtures of nanoparticles and conventional working fluids) in such configurations. For the performance analysis of thermal systems composed of parallel surfaces and operating with nanofluids, it is necessary to know the physical phenomena and parameters that influence the flow and heat transfer characteristics in these systems. Significant results obtained from this review indicate that, in most cases, the heat transfer rate between parallel surfaces is enhanced with an increase in the Rayleigh number, the Reynolds number, the magnetic number, and Brownian motion. On the other hand, an increase in thermophoresis parameter, as well as flow parameters, including the Eckert number, buoyancy ratio, Hartmann number, and Lewis number, leads to heat transfer rate reduction.

The current study deals with modeling of CO2 solubility in various deep eutectic solvents (DESs). Various artificial intelligent methods including PSO-ANN, PSO-ANFIS, LSSVM, and newly proposed correlation were developed, examined and comparatively evaluated. Comprehensive data were gathered from literature and LSSVM and MPR models were found robust and precise models for estimating CO2 solubility in DESs.

Air-breathing is known as a way to reduce the weight, volume, and the cost of PEMFCs. In this study, the thermal management of the high-powered air-breathing PEMFC stacks by applying different cathode flow channel configurations is carried out to improve the stack performance. In order to verify the thermal management results, numerical simulation is also performed. The research results show that a combination of the 50% and 58.3% opening ratios in the air-breathing stack reduces the stack temperature and enhances the temperature distribution uniformity, leading to a better and more stable stack performance. In addition, it is found that the stack performance is significantly improved under the assisted-air-breathing condition. Moreover, the simulation results and the experimental data are basically consistent. It is suggested to adopt the average temperature over the cross-sectional flow region from simulation as fitting the simulation results and the measured data.

Least square support vector regression (LSSVR) is a powerful data-driven method for simulation and forecasting, with two parameters to tune. In this study, these parameters were automatically tuned using the interior search algorithm (ISA) and genetic algorithm (GA). The main purpose is in situ simulation and forecast of monthly groundwater level in Karaj plain, Iran, using historical groundwater level, precipitation, and evaporation data. The results of the interior search algorithm-least support vector regression (ISA-LSSVR) and genetic algorithm-least support vector regression (GA-LSSVR) compared with genetic programming (GP) and adaptive neural fuzzy inference system (ANFIS). Based on average Nash-Sutcliffe criterion, the results revealed that the ISA-LSSVR improves the simulation and forecasting accuracy compared to other methods. Also, the results of the different model structure selection indicate that including precipitation and evaporation does not necessarily improve simulation and forecasting accuracy, but it would increase uncertainty. This increase suggests that groundwater level in the case study is affected by groundwater flow, recharge from leaky urban water infrastructure, and reduced recharge from precipitation due to impervious surfaces in urban areas rather than being solely governed by precipitation and evaporation. Finally, a sensitivity analysis was performed to assess the impacts of optimization algorithm parameters on the simulation and forecasting accuracy. The results indicate high and low sensitivity associated with GA and ISA, respectively. In conclusion, ISA-LSSVR was suggested as the best model due to computational efficiency, low sensitivity to its parameters, and high accuracy compared to other methods.

Industrialization and modernization have led to an increasing trend of greenhouse gas emissions entering the atmosphere. Consequently, many countries are imposing strict environmental regulations due to increasing concern on the climate change, and a significant amount of research is being conducted to tackle this problem. Carbon capture and sequestration are one of the major methods, which can remarkably contribute to this issue since a major greenhouse gas in Earth's atmosphere is carbon dioxide (CO 2 ). The general objective of this work was to investigate the significance of potential use of aqueous salt solutions for capturing CO 2 by developing an accurate model for estimation of this phenomenon. In particular, 608 experimental data of CO 2 solubility in aqueous solutions of salts as a function of temperature, pressure, salt solution concentration (molality), hydrogen bond acceptor count of salts, molecular weight of salts, and complexity value of the salts were collected from the literature. Four state-of-the-art computational methods (LSSVM, ANN, PSO-ANFIS and GA-ANFIS) were employed to examine their predictive capability for the problem. The results reveal that the LSSVM offers the highest accuracy with R 2 = 0.9927 and %AARD = 5.37. Although the neural network and fuzzy interface systems are more complex approaches, the superiority of the LSSVM method for the problem under study demonstrates the easy nature of this phenomenon. Thus, the LSSVM model is recommended for estimating the CO 2 solubility in aqueous salt solutions because not only it has more accuracy, but also it is easy to apply, has less mathematically complicated and less time-consuming.

This article aims to investigate the influence of imposed flow rate oscillation on the bubble behaviors of evaporative flow of R-134a in horizontal narrow annular ducts. Particularly, the effects of amplitudes and periods of the oscillating flow rates along with the vapor quality of the R-134a on the bubble characteristics are examined in details. Moreover, the R-134a flow photos captured at the middle axial location are presented to illustrate the shift between the annular two-phase flow pattern and the bubble nucleation at different operating conditions and time instances. The observations reveal that the imposed mass flow rate oscillation results in the fluctuation of bubble departure diameter and frequency along with the density of active nucleation sites with the same frequencies. The larger amplitudes and longer periods of the mass flow rate oscillation lead to the stronger fluctuations in bubble dynamics. Furthermore, it is found that the bubble nucleation on the heating surface is the dominant mechanism at the low vapor quality of 0.05. However, the annular two-phase flow prevails over a relatively large portion of the periodic cycle at the dryness fraction of 0.5 and over the entire cycle at the dryness fraction of 0.95. Finally, the evaporative heat transfer of R-134a subject to the flow rate oscillation is correlated as a function of the mass flow rate and the vapor quality.