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Healthy water, which is vital to humans’ health, is defined as a water that is free from chemicals and pathogens. Healthy water can also be used as a necessary raw material in various key industries including electronics, pharmacology and food industries. Nowadays, the world faces a lot of challenges to respond to the ever-growing demand for healthy water as a fresh water resource.  With the advent of new technologies, there are currently new techniques and achievements in different fields as well as wastewater and industrial wastewater treatment. Nanotechnology enjoys an especial place in understanding and controlling different organic pollutants. Recent treatment technologies have led to new techniques using nanotechnology and porous media which display high capacities in eliminating organic elements from water and wastewater. In this review study we focused on researches on nanomaterials including, removing organics from water using nanoparticles and active coal, transferring metal oxide nanoparticles in saturated porous medium, using zero valent iron nanoparticles to remove chrome from water, removing arsenic from water using zero valent iron on active carbon, effective bromate reduction in water using active carbon granules impregnated with iron nano-hydroxide, nitrate reduction using Fe/Cu nanoparticles, synthesis of porous nanocomposite natural charcoal-magnesium oxide in order to remove phosphate and nitrate from aqueous solution, development and characterization of micro-porous ceramic membrane, Ti3SiC2, to carry out microorganism filtration. The aim of this study was to review methods and chemicals that eliminate organics from liquids such as acids and other similar particles as well as presenting some nano materials applications in eliminating pollutants from water.

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This paper present, Based on the experimental results, two new non-dimensional parameters, namely thermal conductivity ( ) and dynamic viscosity ( ) are introduced. These new non-dimensional parameters indicate the enhancement of thermal conductivity and dynamic viscosity of nanofluids by utilizing nanoparticles, and they facilitates the general survey of convective enhancement of nanofluids. Using the presented non-dimensional parameters, the effect of working temperature of nanofluid, type of base fluid, size and type of nanoparticles have been studied on the heat transfer enhancement of nanofluids. The results show that utilizing nanofluid can lead to deterioration or enhancement of heat transfer. On the other hand, Decrease of the size of nanoparticles can lead to enhancement of heat transfer.

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One of the nanoscience applications is to control dispersion of pollutants. In the present era, pollutants in air such as aerosols are one of the more recent additions that considered. Since few studies in modeling nanoparticles filtration and the use of temperature gradient inside the enclosures has been done, the present study aims to analysis the effect of Lewis number (Ln) and thermophoresis parameter on the heat transfer characteristics and concentration of nanoparticles on the laminar natural convection in an enclosure. The results show that increasing the amount of Ln to 10³, reducing the average Sherwood number and for other values of Ln, the average Sherwood number remains almost constant. Average Nusselt number for circular cylinder also had a similar behavior; In the event that, left wall average Nusselt number remained almost constant. The results clearly show that the concentration of particles in the final time is reduced by reducing Ln. The results reveal that the variation of the thermophoresis parameter does not show any significant effect on the average Nusselt, Sherwood number and the final concentration of nanoparticles.

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Considering the importance of improving heat transfer in heat exchangers, the effect of simultaneous use of agitators and also zirconium oxide nanoparticles on the heat transfer of tubular heat exchanger is studied numerically. For this purpose, at first, a new type of incomplete conical agitator with two parallel rows of holes is presented. Then, using the computational fluid dynamics method, heat transfer equations have been solved in the range of Reynolds numbers 4000 to 24000 and also the amount of zirconium oxide nanoparticles from 0.01% to 0.2%. In order to increase the modeling accuracy, the nanofluid has been simulated in a two-phase form. The effect of parameters such as the number of agitators, the number of holes and the volume fraction of nanoparticles on the flow field, the average Nusselt number, the friction factor and the thermal performance coefficient have been investigated. The results show that the use of perforated agitators in the flow path leads to significant changes in the flow characteristics and heat transfer. Perforated conical agitators improve heat transfer by creating recirculation and separation currents in the presence of nanofluid as a result of disrupting the thermal boundary layer and causing more disturbance in the fluid flow during the tubular heat exchanger. The agitators presented in this research can increase the thermal performance by 76% compared to the smooth pipe if the parameters are determined properly. The maximum coefficient of thermal performance is 1.76 in the case of M=1, N=1 and Re=4000.

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In this study, the cooling of a photovoltaic system with a concentrator is done with the help of a heat sink containing phase change materials and copper oxide nanoparticles using a numerical method. The photovoltaic module has a two-dimensional concentrator, and n-octadecane is chosen as the phase change material, and the mass fraction of copper oxide nanoparticles is 3 and 5%. The results of this research show that adding copper oxide nanoparticles with a mass fraction of 3% and 5% to the basic phase change material reduces the temperature of the solar cell from 191 o C to 185 o C and 180 o C, respectively.