Effect of metal oxide nanofluids on the performance of passive solar still single slope for two different absorbent plates

This study aims to improve the performances of a solar still single slope using metal oxide nanofluid (Al₂O₃–water, Cu₂O–water, and TiO₂–water). The numerical study was carried out for the climatic conditions of Agadir, Morocco, with different concentrations of nanofluids inside a basin equipped with an absorber plate with two different absorptivities. The numerical study is based on thermal balance equations applied on different solar system components and solved using the Runge Kutta method. The numerical model is validated by comparing our results with the literature available data. A comparison study of the effect of these nanofluids on solar still productivity is done. The results show that the productivity of the solar still using nanoparticles Cu₂O, TiO₂, and Al₂O₃ are 7.38, 7.1, and 7.064 kg m⁻² day⁻¹, respectively. It is obtained that the maximum efficiency of the solar still is found to be 55.27% by using cuprous oxide nanoparticles. Furthermore, an enhancement in solar still productivity of 6.36%, 19.54%, and 33.25% is obtained by dispersing 1%, 3%, and 5% volume fraction of Cu₂O nanoparticles in pure water, respectively compared to the conventional solar. Moreover, the impact of the absorptivity of the absorber plate on the solar still effectiveness is investigated. Two types of coatings are considered to change the absorber plate absorptivity. The results indicate that the efficiencies of the solar system are 58.81% and 51.77% using an absorber plate with 0.95 and 0.85 of absorptivity, respectively.     

Cocurrent turbulent mixed convection heat and mass transfer in falling film of water inside a vertical heated tube

A detailed numerical study has been conducted in order to analyse the combined buoyancy effects of thermal and mass diffusion on the turbulent mixed convection tube flows. Numerical results for air-water system are presented under different conditions. A low Reynolds number k-ε turbulent model is used with combined heat and mass transfer analysis in a vertical heated tube. The local heat fluxes, Nusselt and Sherwood numbers are reported to obtain an understanding of the physical phenomena. Predicted results show that a better heat transfer results for a higher gas flow Reynolds number Re, a higher heat flux q_w or a lower inlet water flow Γ₀. Additionally, the results indicate that the convection of heat by the flowing water film becomes the main mechanism for heat removal from the wall.     

Investigation of elastic constants of polymer/nanoparticles composites using the brillouin spectroscopy and the mechanical homogenization modeling

A numerical model using homogenization techniques is proposed to simulate the evolution of elastic properties of nanocomposite polymer‐nanoparticles, depending on the concentration of nanoparticles and the rigidity of the particle–matrix interface. To validate this model, it was confronted to several physical systems having different interface behavior, the nanocomposite systems: poly(vinylidene fluoride trifluoroethylene)/Al₂O₃ (alumina nanoparticles incorporated into copolymer of vinylidene difluoride and trifluoroethylene to form nanocomposite), PMMA/CNT (carbon nanotube/poly(methyl methacrylate) composite) and PMMA/SiO₂ with nanoparticles with or without surface treatment of silanization. For all these systems, the Young's modulus (nanoparticles and matrix) has been obtained experimentally from the elastic modulus C₁₁ obtained by Brillouin spectroscopy. These macroscopic measurements coupled with the theoretical model allow a multiscale approach of the elastic behavior of nanocomposite systems, providing information on the global elastic properties of polymer‐nanoparticle material, and also indications about the strength of physical and chemical bonds between the nanoparticles and the matrix. Our results validate the hypothesis of the crucial role of the interface module, provided by numerical simulation which shows that incorporation of nanoparticles may lead to a strengthening or a weakening of the matrix. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers.     

Falling film evaporation of ternary mixture under three different modes of heating

This numerical study deals with heat and mass transfer by evaporation under mixed convection in three different configurations of a ternary liquid film in a vertical channel. The ternary liquid mixture water-methanol-benzene falls along the right plate of channel while the other plate is kept thermally insulated. In the first configuration, a heat flux density is applied to the wall carrying the trickle film, while in the other configurations this same amount of heat is used to preheat the liquid film or the air at the inlet of the channel. The implicit finite difference scheme is used to solve the system of equations in both liquid and vapor phases. According to this study, it was observed that the evaporation efficiency is high when the mass fraction of volatile components is high or in the preheating state of ternary film.     

Linear stability analysis of mixed convection flow in a horizontal channel filled with nanofluids

The convective instability driven by buoyancy in the Poiseuille–Rayleigh–Bénard flow through two infinite parallel horizontal plates filled with nanofluids is investigated using linear stability analysis. We considered water‐based nanofluids with different volume fractions of aluminum ( $\mathrm{A}{\mathrm{l}}_2{\mathrm{O}}_3$) and silver ( $\mathrm{A}\mathrm{g}$) nanoparticles. A spectral collocation method founded on Chebyshev polynomials is implemented and the obtained algebraic eigenvalue problem is solved. In this study, we have numerically determined the critical Rayleigh number of the onset of longitudinal and transversal rolls and the results are represented in the form of marginal stability curves. Critical wave numbers that describe the size of convective cells in the flow are also presented, analyzed, and compared with those of the Poiseuille–Rayleigh–Bénard flow without nanoparticles. The effects of the type and nanoparticle volume fractions on the onset of both longitudinal and transversal rolls are investigated.     

Channel Wall Cooling by Evaporative Falling Water–Ethanol and Water–Methanol Films

Abstract

The thermal protection by evaporative cooling is among the most efficient cooling methods, which provides higher wall temperature reduction owing to the phase conversion of the heat-transfer fluid. Thus, the purpose of this study is to investigate the capacity of pure water, water–ethanol, and water–methanol liquid mixtures to thermally protect a channel wall. To achieve the goals, an implicit finite difference in house code is developed and exploited to solve the coupled governing equations in both liquid and gas phases. The influence of water mass fraction in binary mixture is studied. The results revealed the convenient liquid and water mass fraction to have low wall temperature. It was found that both latent and sensible heat are important in this process. In addition, the presence of alcohols in the mixture with high concentration ensures a better cooling and thermal protection of the wall. A maximum wall temperature drop of 12?K was achieved by pure methanol liquid film versus an elevation of 6?K by pure water film. Moreover, it is highlighted that a pure ethanol film can be avoided by using only 25% of methanol with water, which permitted keeping approximately the same temperature drop.     

Numerical study of the evaporative cooling of liquid film in laminar mixed convection tube flows

A numerical study is reported to investigate the evaporative cooling of liquid film falling along a vertical tube. A marching procedure is employed for solution of the equation of mass momentum, energy and concentration in the flow. Numerical results for air-water system are presented. The effects of flow conditions on the film cooling mechanism are discussed. Results show that a better liquid film cooling is noticed for a system having a higher inlet liquid temperature T_L0, a higher gas flow Reynolds number Re or a lower liquid flow rate Γ₀. Additionally, the results indicate that the convection of heat by the flowing water film becomes the main mechanism for heat removal from the interface.     

Turbulent liquid film evaporation in a partially heated wall along a vertical tube

In this numerical study, the evaporative heat and mass transfer of a turbulent falling liquid film in a finite vertical tube are investigated. The liquid film flows in the tube's inner wall, whose outer wall is partially subject to thermal flux. Here, different configurations corresponding to thermal flux imposed on different external surface wall percentages are examined. External face zones where the heat flux is not applied are maintained insulated. The nonlinear set of parabolic mass, momentum, energy, and mass fraction conservation equations combined with boundary and interfacial conditions are treated numerically using implicit finite difference procedure. For falling liquid film analysis, an adapted Van Driest turbulence model is used. For the present work, it is supposed that gas flows in a laminar regime. We examine in this paper the impact of the percentage of heated surface area on flows as well as on heat and mass transfer. Obtained results for a partially heated wall are compared with those produced for an entirely heated wall.     

Parameters identification of photovoltaic solar cells and module using the genetic algorithm with convex combination crossover

To design a high-performance photovoltaic (PV) system, the parameters extraction of solar cell models is exceedingly crucial. A new variant of the genetic algorithm (GA) called Genetic Algorithm with Convex Combination Crossover (GACCC) is proposed to identify the unknown electrical parameters of different solar cell models, i.e. single diode, double diode, and PV module. GACCC is achieved by integrating a new crossover operation to maintain a good balance between the intensification of the best solutions and the diversification of the search space. To test the proposed GACCC, we have compared it to the basic GA and with other literature techniques. The results indicate a high performance of developed approach GACCC and a high accuracy of estimated parameters. In addition, the efficiency of the results is confirmed by the good agreement between the experimental I-V data and the simulated results in all cases.     

Thermodynamic Description of the Ce-Ga Binary System

The thermodynamic modelling of the Ce-Ga binary system was carried out with the help of the CALPHAD method. The liquid phase has been described with the association model with the Ce1Ga1 complex. The CeGa₂ over-stoichiometric intermetallic compound, which has a homogeneity range, was treated with the formula (Ce,Ga)_0.333(Ga)_0.667 by a two-sublattice model with Ce and Ga on the first sublattice and Ga on the second one while Ce₃Ga, Ce₃Ga₂, CeGa, and CeGa₆ have been treated as stoichiometric compounds. The calculated phase diagram and the thermodynamic properties of the system are in satisfactory agreement with the experimental data.