The effects of applied load, sliding speed & temperature on the wear behavior of pure M50
alloy steel (M sample) and M50 reinforced with 10 wt.% Al2O3 (MA sample) & M50 hybrid
reinforced with Al2O3 and graphene (MAG sample) were studied. The powders were mechanically
mixed and sintered by spark plasma sintering (SPS) technique under Argon
atmosphere at 1000
C for 5 min under 35 MPa pressure. The sample surfaces were mechanically
prepared to study the wear & friction behaviors via applying mechanical polishing
using 0.05 mm diamond pastes and 1200 grit emery papers to enhance the surface
roughness. The phase structure and microstructure were estimated using XRD, Electron
Probe Micro-Analysis (EPMA, JAX-8230) and Energy Dispersive Spectroscopy (EDS, GENESIS
7000). The hardness and density of all samples were investigated according to HVS-1000
Vickers’ hardness test and Archimedes’ principles, respectively. Friction and wear tests
were carried on a high-temperature pin-on-disk tribometer (HT-1000). The investigated
samples were cut into disk-shaped specimens with 8 mm thickness and 25 mm diameter.
Then, the prepared specimens were sliding against silicon nitride (Si3N4) balls. The samples
were exposed to four different loads (2, 5, 8, and 11 N). Also, four different sliding speeds
(0.18, 0.36, 0.54, and 0.72 m/s) was performed at room temperature (RT). Another group of
samples were tested at constant applied load of 11 N and constant sliding speed of 0.72 m/s
for four different temperatures (RT, 150, 300, and 450
C). MAG exhibited enhanced tribological
properties compared with M and MA thanks to the synergic action between Al2O3

The main target of this paper is to allow renewable energy resources (RES) to participate effectively within hybrid micro
grids via an optimal proportional integral- derivative (PID) controller. This paper proposes two techniques of optimal PID
controllers in a hybrid renewable generation energy system. These techniques are particle swarm optimization (PSO) and
lightning attachment procedure optimization (LAPO). The hybrid renewable generation energy system in this study includes
a photovoltaic source, wind turbine, and battery storage, which are connected to a point of common coupling via DC/DC
boost converters. The controller at the inverter consists of a current controller and voltage source controller, which results in
three PID gains at each controller. In order to obtain the PID gains, a time domain objective function is formulated in terms
of the voltage, and current errors. The obtained results with the individual advanced optimization LAPO and PSO algorithm
are compared. The results display that the developed LAPO algorithms give better results compared to the conventional
PSO at the input and output current, voltage, and power. All the results have been taken under several operating conditions
of wind turbine (wind speed) and solar sun (changing irradiance and temperature).

The present study presents two techniques of Maximum Power Point
Tracking (MPPT) via DC/DC converter to enhance the performance of the
grid-connected Photovoltaic (PV) generation system to participate effectively
within microgrids. The two techniques of MPPT are Perturb-Observe (P&O)
and Incremental Conductance (IC). The variation of the solar radiation and
temperature is considered during employing the two MPPT techniques.
Besides, the performance of the system under the random variation of
solar radiation was investigated. The authors used two types of controllers
at the three-phase inverter, Proportional Integral (PI) and H-infinity Control
(H∞C). The output voltage, current, and power at each type of inverter
controller are compared along with the two techniques of MPPT. The effectiveness
of the developed controllers together with MPPT techniques is
demonstrated by comparing the obtained results with some previously
reported research in the literature. In the case of MPPT via P&O and IC
techniques along with the H∞C controller, the results show that the technique
of IC is more robust, and the obtained output power is well matched
with the references one as compared with the P&O technique which records
a 7% error from MPP. Besides, the P&O technique has a high voltage and
current ripple with a percentage of 20% at the starting time of the
simulation.

MWCNT/water nanofluid flow in a double pipe U-bend heat exchanger. The experiments were conducted at
different Reynolds number (3500–12000) and particle volume concentrations (0.05%–0.3%). The thermal
conductivity and viscosity are augmented by 15.27% and 9.15% at a temperature of 70 ◦C with respect to water
data. The Nusselt number, heat transfer coefficient, thermal performance factor are enhanced by 31.3%, 44.17%,
and 25.5% at a particle concentration of 0.3% and a Reynolds number of 10,005 over water data. The pressure
drop, pumping power, friction factor penalty are 17.05%, 15.96%, and 14.29%, at 0.3% particle concentration
and a Reynolds number of 10,005, compared to water. The effectiveness and number of transfer units are
increased by 2.49% and 2.75% at 0.3% particle concentration and a Reynolds number of 10,005 compared to
water data. The cost, weight, embodied energy, and CO2 emissions are analyzed based on the enhanced effectiveness
of the heat exchanger. The total embodied energy from the heat exchanger using water is 403.7 MJ and
it reduced to 393.1 MJ with 0.3% nanoparticle concentration. The heat exchanger cost is reduced to 61.46$ using
0.3 vol % of nanofluid whereas it is 63$ using water. The environmental CO2 emissions released from the heat
exchanger are reduced to 81 kg of CO2 using 0.3 vol % of nanofluid, whereas it is 83.3 kg of CO2 using water.

In the present study, the heat transfer, entropy, friction factor, exergy efficiency, pumping power, and performance
index ratio of nickel/water nanofluids flow in a corrugated plate heat exchanger are investigated
experimentally. The nickel nanoparticles were synthesized using the chemical precipitation method and characterized
by various techniques. The stable water based nickel nanofluids were prepared with particle volume
concentrations of 0.1%, 0.3%, and 0.6%. The experiments were conducted at nanofluids Reynolds numbers
ranged from 300 to 1000. The properties of nickel nanofluid are evaluated experimentally as well. The thermal
conductivity and viscosity enhancements are 33.92%, and 67.45% at a temperature of 60 ◦C compared to the
base fluid data. The increase of nanoparticle loadings and Reynolds number leads to an augmentation of the
overall heat transfer coefficient, heat transfer coefficient, and Nusselt number. The overall heat transfer coefficient,
convective heat transfer, and Nusselt number enhanced by 38.60%, 57.35%, and 42.68% at 0.6 vol % of
nanofluid and a Reynolds number of 707, respectively compared to water data. The thermal entropy generation
is decreased by 15.70%, while frictional entropy generation and pumping power are increased by 68.29% and
61.77%, respectively at 0.6 vol % of nanofluid and a Reynolds number of 707 against water data. The exergy
efficiency was enhanced by 42.27% at 0.6 vol % of nanofluid and a Reynolds number of 303 compared to water
data. The performance index ratio is decreased with the use of nanofluids due to the increase of viscosity, friction
factor, pressure drop, and pumping power.

Thermal efficiency, friction factor, heat transfer, and cost analysis of a flat plate collector operates with water-based nanodiamond
nanofluids under thermosyphon (natural circulation) conditions are investigated experimentally at 0.2%, 0.4%,
0.6%, 0.8%, and 1.0% particle volume concentrations. The thermophysical properties of the working fluids are analyzed
as well. Results show that the maximum thermal conductivity and viscosity enhancements are obtained by using 1.0 vol%
concentration of nanofluid and found to be 22.86% and 79.16%, respectively, compared to water at a temperature of 60 °C.
The maximum increases in Nusselt number are 19.53% and 36.17% using 1.0 vol% concentration of nanofluid compared to
water at Reynolds number of 140 and 345, respectively. The maximum increases of friction factor are attained by using 1.0
vol% concentration of nanofluid and found to be 1.14 times and 1.25 times of water friction factor at Reynolds number of
143 and 345, respectively. The collector thermal efficiency increases from 57.15% using water to 69.85% using nanofluid
with a concentration of 1.0%. The collector cost decreases approximately by 18.18% for 1.0 vol% nanofluid compared to
water. The relative deviations of the equations developed to evaluate Nusselt number and friction factor are within ± 2.5%.

The heat transfer, friction factor, and collector efficiency are estimated experimentally for
multi-walled carbon nanotubes+Fe3O4 hybrid nanofluid flows in a solar flat plate collector under
thermosyphon circulation. The combined technique of in-situ growth and chemical coprecipitation
was utilized to synthesize the multi-walled carbon nanotubes+Fe3O4 hybrid nanoparticles. The
experiments were carried out at volume flow rates from 0.1 to 0.75 L/min and various concentrations
from 0.05% to 0.3%. The viscosity and thermal conductivity of the hybrid nanofluids were experimentally
measured at different temperatures and concentrations. Due to the improved thermophysical
properties of the hybrid nanofluids, the collector achieved better thermal efficiency. Results show that
the maximum thermal conductivity and viscosity enhancements are 28.46% and 50.4% at 0.3% volume
concentration and 60 C compared to water data. The Nusselt number, heat transfer coefficient,
and friction factor are augmented by 18.68%, 39.22%, and 18.91% at 0.3% volume concentration and
60 C over water data at the maximum solar radiation. The collector thermal efficiency improved by
28.09% at 0.3 vol. % at 13:00 h daytime and a Reynolds number of 1413 over water data. Empirical
correlations were developed for friction factor and Nusselt number

The entropy generation and exergy efficiency of nanodiamond+Fe3O4 hybrid nanofluids in a circular tube are
inspected experimentally. The hybrid nanofluids were prepared in a 60% ethylene glycol and 40% water by
weight base fluid and their thermophysical properties were evaluated at different particle loadings and temperatures.
The pumping power, friction factor, and heat transferwere evaluated at various particle loading (0.05% to
0.2%) and Reynolds number (2000 to 8000) as well. The results indicated that the thermal conductivity and viscosity
are augmented by 14.65% and 79%, respectively at 0.2% particle loading and 60 °C compared to the base
fluid. At a particle loading of 0.2% nanofluid and a Reynolds number of 7218, the following results are obtained
compared to the base fluid data: theNusselt number, frictional entropy generation, exergy efficiency, friction factor,
and thermal performance factor are increased by 19.67%, 210.6%, 17.54%, 15.11%, and 14.19%, respectively;
while the thermal entropy generation is decreased by 22.93%. Newregression equations aremodeled to evaluate
the Nusselt number, friction factor, and thermophysical properties.

Screening for alternative refrigerants with high energy eciency and low environmental
impacts is one of the highest challenges of the refrigeration sector. This paper investigates the
performance and refrigerant screening for single and two stages vapor compression refrigeration
cycles. Several pure hydrocarbons, hydrofluorocarbons, hydrofluoroolefins, fluorinated ethers,
and binary azeotropic mixtures are proposed as alternative refrigerants to substitute R22 and R134a
due to their environmental impacts. The BACKONE equation of state is used to compute the
thermodynamic properties of the candidates. The results show that the maximum coecients
of performance (COP) for single and two stage cycles using pure substances are achieved using
cyclopentane with values of 4.14 and 4.35, respectively. On the other side, the maximum COP for the
two cycles using azeotropic mixtures is accomplished using R134a + RE170 with values of 3.96 and
4.27, respectively. The two-stage cycle presents gain in COP between 5.1% and 19.6% compared with
the single-stage cycle based on the used refrigerant. From the obtained results, among all investigated
refrigerants, cyclopentane is the most suitable refrigerant for the two cycles from the viewpoint of
energy eciency. However, extra cautions should be taken due to its flammability