One of the great technological challenges in 21st century is the development of renewable energy technologies due to serious problems related with the production and use of energy. A new promising ...area of research grows rapidly which is called Nanotechnologies are considered nowadays one of the most recommended choices to solve this problem. This review aims to introduce several significant applications of nanotechnology in renewable energy systems. Papers reviewed including theoretical and experimental works related with nanotechnology applications in solar, hydrogen, wind, biomass, geothermal and tidal energies. A lot of literature are reviewed and summarized carefully in a useful tables to give a panoramic overview about the role of nanotechnology in improving the various sources of renewable energies. We think that this paper can be considered as an important bridge between nanotechnology and all available kinds of renewable energies. From the other side, further researches are required to study the effect of nanotechnology to enhance the renewable energy industry especially in geothermal, wind and tidal energies, since the available papers in these fields are limited.
Absorption refrigeration technology was introduced to address some serious issues such as the energy crisis, increased fuel prices, and environmental problems associated with the conventional ...compression refrigeration systems. It has attracted an increasing deal of interest thanks to such advantages as utilization of low-grade heat sources and environment-friendly working fluid pairs. Nevertheless, this technology suffers from two major obstacles including the usually too large size of the cooling unit and the low coefficient of performance (COP), preventing the absorption systems from being commercially successful. Numerous research works have been done to develop strategies in order to improve the COP of the absorption systems, so as to make the absorption refrigeration technology more competitive with the conventional compression refrigeration systems. In this paper, it is intended to conduct a literature review on various technologies implemented to improve the COP of absorption refrigeration systems. Among effective and promising workarounds for increasing the COP of absorption refrigeration systems, this work refers to cycle design improvement, heat recovery method, development of new working pairs, adding sub-components, and improvement of operating conditions.
This paper presents a numerical investigation of the natural convection in an inclined rectangular enclosure with a baffle filled with Cu/water and then with Al
2
O
3
/water nanofluids using the ...finite difference method for tracking the thermal behavior within it versus the baffle length. The horizontal enclosure walls are assumed to be adiabatic, while the vertical ones are supposed to be a differentially heated. A thin horizontal baffle was attached to its left sidewall and is assumed to be cold. The flow and thermal fields are computed, respectively, for various values of Rayleigh number (10
3
≤ Ra ≤ 10
5
), inclination angle (0° ≤
∅
≤ 60°), baffle length (0.25 ≤
L
b
≤ 0.5), solid volume fraction (0.02 ≤
ϕ
≤ 0.06), and aspect ratio (1 ≤ AR ≤ 2). It was found that as the Rayleigh number, solid volume fraction, baffle length, and aspect ratio increase, an enhancement in the intensity of fluid flow in the enclosure was observed. In comparison, it reduces when the inclination angle increases. Moreover, it was found that the local Nusselt number (Nu
c
) enhances with the rise in Rayleigh number and the solid volume fraction. In contrast, it reduces with the increase in the aspect ratio and the inclination angle.
A steady laminar two-dimensional magneto-hydrodynamics mixed convection flow in a square inclined cavity filled with Cu–water nanofluid is investigated numerically by using the finite difference ...method. The left and right vertical sidewalls of the cavity are considered adiabatic and move upward, while a partial slip flow condition is imposed on these walls. The horizontal top wall is considered cold and stationary, while a part of the stationary bottom wall is subjected to a uniform heat source and the remaining parts of it are considered adiabatic. An adiabatic obstacle is located in the center of the cavity and an external magnetic field is applied parallel to the horizontal
x
-axis. Parametric studies of the influence of various parameters such as Hartmann number, inclination angle of the cavity, dimensionless heat generation/absorption coefficient, obstacle aspect ratio, dimensionless length and location of the heat source, and solid volume fraction on the fluid flow and heat transfer have been performed. Comparisons with previously published numerical work are performed, and good agreements between the results are observed. It is found that the nanofluid was better than water to enhance the heat transfer when the effect of the magnetic field is weak, while the water is better than the nanofluid when its effect is strong. Moreover, the results indicated that the partial slip has a significant effect on the above-mentioned parameters.
An experimental and numerical investigation of a small linear Fresnel for water heating application has been carried out in Blida, Algeria. The numerical simulation with a 1D modeling in transient ...mode was performed by using the finite difference method. The thermal evaluation is based on the energy assessments characterized by the differential equations of pure water with a flow mass rate equal to 0.015 kg s
−1
and copper absorber tube temperature. Moreover, the Fluent code has been developed in order to conduct the CFD modeling at the absorber tube of the solar collector. SolTrace software has been used to determine the optical behavior of the linear reflector. The average optical efficiency of the device is about 42.97%, but the average value of the experimental thermal efficiency reached 29.21% for 22/01/2015 and 29.20% for 19/02/2015. The average value of pure water temperature for 22/01/2015 is 67.28 °C, while its value for 19/02/2015 is 70.99 °C. This solar experimental setup will reduce the consumption of liquefied natural gas by 88.9 m
3
, which will reduce the CO
2
emission by 187.93 kg. In addition, its manufacturing cost will be recovered 16 years from the date of use of this heater.
The laminar two-dimensional mixed convection in a trapezoidal enclosure with a rotating inner circular cylinder and a sinusoidal bottom wall is studied numerically. The fluid inside the enclosure is ...a CuO–water nanofluid layer in the top space of it, while the bottom space includes a CuO–water nanofluid saturated with a porous medium. Both the right and left sidewalls are assumed adiabatic, while the bottom and the top walls of the enclosure are maintained, respectively, at the hot and cold temperatures. The dimensionless governing equations are expressed for velocity and temperature formulation and modeled by using COMSOL code based on the Galerkin finite element method. Parametric studies on the effects of various significant parameters such as Rayleigh number, Darcy number, the inner cylinder radius, the porous layer thickness, the angular rotational velocity, the solid volume fraction and the number of undulations on the flow and thermal fields together with the heat transfer rate have been performed. The highest value of the stream function for (Ra = 10
3
and Ra = 10
5
) is seen at (
R
= 0.2 and
S
= 0.2). The same thing is observed, when the bottom wall is considered wavy. For (Ra = 10
3
and
N
= 0) and (0.5 ≤
S
≤ 0.8), it can be seen that as the inner cylinder radius increases from (
R
= 0.1) to (
R
= 0.3), the stream function values increase continuously. It is found that the average Nusselt number increases as the Rayleigh and Darcy numbers, the solid volume fraction, inner cylinder radius and the angular rotational velocity of the cylinder increase, while it decreases as the porous layer thickness and the number of undulations increase. Comparisons with previously published numerical works are performed, and good agreements between the results are observed.
This paper gives a comprehensive overview about the recent advances related with the application of the nanotechnology in various kinds of the solar collectors. Papers reviewed including theoretical, ...numerical and experimental up to date works related with the nanotechnology applications in the flat plate, direct absorption, parabolic trough, wavy, heat pipe and another kinds of the solar collectors. A lot of literature are reviewed and summarized carefully in a useful tables (Tables 1–7) to give a panoramic overview about the role of the nanotechnology in improving the various types of the solar collectors. It was found that the use of the nanofluid in the solar collector field can play a crucial role in increasing the efficiency of these devises. We think that this paper can be considered as an important link between the nanotechnology and all available kinds of the solar collectors. From the other side, further researches are required to study the effect of nanotechnology to enhance the solar collector industry over the next several coming years.
This numerical investigation effectively establishes a unique computing exploration for steady magnetohydrodynamic convective streams of tangent hyperbolic nanofluid traveling across a nonlinearly ...elongating elastic surface with a variable thickness. In addition, the importance of an externally imposed magnetic field of tangent hyperbolic nanofluid is comprehensively analyzed by considering the substantial impact of thermal conductivity and thermal radiation consequences. The governing PDEs (partial differential equations) are transmuted into a nonlinear differential structure of coupled ODEs (ordinary differential equations) using a series of variable similarity transformations. Furthermore, these generated ODEs (ordinary differential equations) are numerically set using a novel revolutionary Runge-Kutta algorithm with a shooting approach constructed in a MATLAB script. In this regard, extensive comparison studies are carried out to validate the acquired numerical results. The interactions between the associated profiles and the relevant parameters are rationally explored and shown using graphs and tabular forms. The velocity distribution declined with improving Weissengberg number We and power-law index m, while the reverse performance can be observed for temperature. As enhancement in Brownian motion, Thermophoretic and radiation parameters significantly rise in temperature distribution. The use of many different technological and industrial systems, including nano-bioconvective systems, nano-droplet evaporation, nano-ink jet printing, and microbial fuel cells, would benefit this research study.
The mathematical modeling of the activation energy and binary chemical reaction system with six distinct types of nanoparticles, along with the magnetohydrodynamic effect, is studied in this paper. ...Different types of hybrid nanofluids flowing over porous surfaces with heat and mass transfer aspects are examined here. The empirical relations for nanoparticle materials associated with thermophysical properties are expressed as partial differential equations, which are then interpreted into ordinary differential expressions using appropriate variables. The initial shooting method converts the boundary condition into the initial condition with an appropriate guess and finally finds out an accurate numerical solution by using the Runge–Kutta method with numerical stability. Variations in nanoparticle volume fraction at the lower and upper walls of porous surfaces, as well as the heat transfer rate measurements, are computed using the controlling physical factors. The effects of the flow-related variables on the axial velocity, radial velocity, temperature, and concentration profile dispersion are also investigated. The Permeable Reynolds number is directly proportional to the regression parameter. The injection/suction phenomenon associated with the expanding/contracting cases, respectively, have been described with engineering parameters. The hybrid nanoparticle volume fraction (1–5%) has a significant effect on the thermal system and radial velocity.
Natural convection visualization by heatlines in three types of inclined wavy cavities filled with Al2O3–water and Ag–water nanofluids and subjected to a discrete isoflux heating from its left ...sidewall is investigated numerically in this work. The right sidewall together with remaining regions in the left sidewall is insulated. The solution is based on the finite volume method. The upper and lower cavity walls are maintained at a constant cold temperature and follow a profile of sine wave. Numerical computations are carried out for various values of the solid volume fraction φ=0, 0.05, 0.1, 0.15 and 0.2, number of undulations N=1, 2 and 3, Rayleigh number Ra=103–107, the ratio of heating element length to the cavity height ε=0.2, 0.4, 0.6, 0.8 and 1.0, the cavity inclination angle Φ=0°, 30°, 60° and 90° and the wave amplitude γ=0.1, 0.15 and 0.2. The results are presented in terms of heatlines, isotherms, streamlines together with local and average Nusselt numbers. It is found that the geometry of the wavy cavity has a cursive role on the flow and thermal fields pattern. The results also explained that streamlines and isotherms were affected significantly for high Rayleigh number and vertical cavity position Φ=90°. Also, when the solid volume fractions and wave amplitudes increase, the local Nusselt number along the heat source increases. Furthermore, velocity profiles increase as ε increases near the left sidewall of the cavity while they decrease as ε increases near the right sidewall of the cavity. For all three types of horizontal wavy cavities the heat functions increase for both nano and base fluids when the wave amplitude increases. Finally, results of the present work indicated that both heatlines and heat functions techniques are applied efficiently to describe the natural convection heat transfer inside wavy cavities filled with nanofluid.
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