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

Biomass is currently one of the world’s major renewable energy sources. Biomass in a
powder form has been recently proposed as the most encouraging of biomass contours, especially
because it burns like a gas. In the current study, biomass powder was examined, for the first time,
as a direct solid fuel in internal combustion engines. The aim of the current study was to investigate
modeling tools for simulation of biomass powder in combustion engines (CE). The biomass powder
applied was in a micro-scale size with a typical irregular shape; the powder length was in the range
of 75?5800 m, and the diameter was in the range 30?1380 m. Dierent mechanisms for biomass
powder drying and devolatilization/gasification were proposed, including dierent schemes’ and
mechanisms’ rate constants. Acomparison between the proposed models and experiments was carried
out and results showed good matching. Nevertheless, it is important that a biomass powder simulation
addresses overlapping/complicated sub-process. During biomass powder combustion, tar was shown
to be formed at a rate of 57 wt.%, and, accordingly, the formation and thermal decomposition
of tar were modelled in the study, with the results demonstrating that the tar was formed and
then disintegrated at temperatures between 700 and 1050 K. Through biomass powder combustion,
moisture, tar, and gases were released, mostly from one lateral of particles, which caused ejection of
the solid particles. These new phenomena were investigated experimentally and modeled as well.
Results also showed that all the proposed models, along with their rate constants, activation energies,
and other models’ parameters, were capable of reproducing the mass yields of gases, tar, and char at a
wide range of working temperatures. The results showed that the gasification/devolatilization model
3 is somewhat simple and economical in the simulation/computation scheme, however, models 1 and
2 are rather computationally heavy and complicated.

In recent years, the use of solar energy has been growing exponentially and applied in a wider range of
applications; one of the important applications for using solar energy is water desalination. The current
work investigates the proof of concept experimental setup for a novel solar multi-effect distillation
(MED) using alternate storage tanks. The experimental setup consists of a MED unit, two thermal
storage tanks, and a solar collector. One storage tank is used as a charging tank while the other tank is
used as a discharging tank. This unique dual-tank system stores the thermal energy to be used later in
the MED unit, which improves the control of the water mass flow rate and water temperature
throughout the MED process. The peak temperature achieved every day in the charging tank
determines the MED production capacity. This system is designed for the tanks to alternate roles every
24 hours. The testing of this design was carried out during May 2019 in Saudi Arabia. The experimental
results prove the novel concept design to work efficiently providing an average production rate of about
21 kg/day with total solar collector area of 2.7 m2 and average daily performance ratio of 2.5.

Skin damage exposes the underlying layers to bacterial invasion, leading to skin and soft tissue infections. Several pathogens have developed resistance against conventional topical antimicrobial treatments and rendered them less effective. Recently, several nanomedical strategies have emerged as a potential approach to improve therapeutic outcomes of treating bacterial skin infections. In the current study, nanofibers were utilized for topical delivery of the antimicrobial drug vancomycin and evaluated as a promising tool for treatment of topical skin infections. Vancomycin-loaded nanofibers were prepared via electrospinning technique, and vancomycin-loaded nanofibers of the optimal composition exhibited nanosized uniform smooth fibers (ca. 200 nm diameter), high drug entrapment efficiency and sustained drug release patterns over 48 h. In vitro cytotoxicity assays, using several cell lines, revealed the biocompatibility of the drug-loaded nanofibers. In vitro antibacterial studies showed sustained antibacterial activity of the vancomycin-loaded nanofibers against methicillin-resistant Staphylococcus aureus (MRSA), in comparison to the free drug. The nanofibers were then tested in animal model of superficial MRSA skin infection and demonstrated a superior antibacterial efficiency, as compared to animals treated with the free vancomycin solution. Hence, nanofibers might provide an efficient nanodevice to overcome MRSA-induced skin infections and a promising topical delivery vehicle for antimicrobial drugs.