*Corr. Author’s Address: Ankara Yildirim Beyazit University, Department of Mechanical Engineering, Turkey, hudaabdali973@gmail.com 395
Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410 Received for review: 2021-10-26
© 2022 The Authors. CC BY 4.0 Int. Licensee: SV-JME Received revised form: 2022-02-16
DOI:10.5545/sv-jme.2021.7454 Original Scientific Paper Accepted for publication: 2022-04-26
Enhancing the Performance  
of a Vapour Compression Refrigerator System  
Using R134a with a CuO/CeO
2
 Nano-refrigerant 
Mohamed, H.E. − Camdali, U. − Biyikoglu, A. − Actas, M.
HudaElslam Mohamed
1,*
 − Unal Camdali
1
 − Atilla Biyikoglu
2
 − Metin Actas
3
1
Ankara Yildirim Beyazit University, Department of Mechanical Engineering, Turkey 
2
Gazi University, Department of Mechanical Engineering, Turkey 
3
Ankara Yildirim Beyazit University, Department of Energy, Turkey
Most studies report that dispersing nanoparticles into refrigerants and lubricating oils leads to performance improvements in refrigeration 
systems, due to improvements in the thermal physics properties of a pure refrigerant, which leads to reduced energy consumption. Using 
nanoparticles in a refrigeration system is associated with many difficulties, such as the cost of preparing and obtaining a stable and 
homogeneous mixture with less agglomeration and sedimentation. Most current studies focus on the use of metals, metal oxides, and a 
hybrid of oxides as nanoparticles in refrigeration systems. In this research, nanoparticles were prepared in an inexpensive and easy way as 
a single oxide and as a mixture consisting of copper and cerium oxides. The results of nanoparticle preparation using X-ray diffraction and 
scanning electron microscopy prove that the particles of the samples were spherical in shape, with suitable average diameters ranging from 
78.95 nm, 79.9 nm, 44.15 nm and 63.3 nm for copper oxide, cerium oxide, the first mixture, and the second mixture, respectively. Cerium 
oxide has not been used in a refrigeration system; this study preferred the implementation of a theoretical study using Ansys Fluent software 
to verify the possibility of improving the performance of the refrigeration system. The results confirmed that copper oxide enhanced the 
coefficient of performance of the refrigeration system by 25 %, and cerium oxide succeeded in improving the performance of the. system by a 
lesser value. The mixture containing a higher percentage of copper oxide yielded better results.
Keywords: vapour compression refrigeration system, coefficient of performance, nano-refrigerant, nanoparticles 
Highlights
• 	 The performance vapour compression refrigeration system that works using R134a was studied experimentally and theoretically 
as a first step without nanoparticles, and the agreement between the experimental and theoretical results was close to 98 %.
• 	 This study provided an inexpensive method for preparing nanoparticles using distilled water, ammonia, copper nitrate, and 
cerium nitrate.
• 	 Nanoparticles were prepared as follows: CuO, CeO
2
; Mixture 1 consisted of 50 % CuO + 50 % CeO
2
; Mixture 2 consisted of 60 
% CuO + 40 % CeO
2
; Mixture 3 consisted of 70 % CuO + 30 % CeO
2
; Mixture 4 consisted of 40 % CuO + 60 % CeO
2
; Mixture 5 
consisted of 30 % CuO + 70 % CeO
2
.
• 	 The concept of nanoparticles as a mixture can improve the performance of refrigeration systems.
0 INTRODUCTION
The world is facing a major challenge in the energy 
sector, due to its diminishing resources and a large 
increase in energy consumption, especially in 
refrigeration and air conditioners. Various studies 
have improved the efficiency of thermal systems. This 
can be accomplished in two ways: first by improving 
the design of the heat exchanger to include thee shell 
and tube type, plate type, microchannel, and so on, 
and second by using new kinds of working fluids 
[1]. In 1873, Maxwell dispersed particles ranging in 
diameter from millimetres to micrometres into a pure 
to enhance the thermophysical properties of the fluid; 
however, this attempt encountered several problems 
including stability, clogging, and erosion. [2] to [4]. 
Nanofluids have attracted the attention of many 
researchers in various scientific fields in recent years. 
Researchers used a new concept of working fluids 
known as “nanofluids” for the first time, which contain 
particles of less than 100 nm, called “nanoparticles”, 
to improve the heat transfer characteristics of various 
fluids. Recently, the concept of nanofluids has been 
developed to include refrigerants [2] to [4]. A nanofluid 
is divided into three categories depending on the 
composition of nanoparticles: (i) mono-nanofluids, 
which consist of similar nanoparticles, (ii) hybrid 
nanofluids, which consist of dissimilar nanoparticles, 
and (iii) hybrid nanofluids, which consist of composite 
nanoparticles [1]. Four conditions are required for 
the successful preparation of the nanofluid: (i) the 
dispersibility of nanoparticles, (ii) the stability 
of nanoparticles, (iii) the chemical compatibility 
of nanoparticles, and (iv) the thermal stability of 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
396 Mo hamed,	H.E.	−	Camdali,	U .	−	Biyik o glu,	A .	−	A ctas,	M.
nanofluids. These conditions will create a nanofluid 
that has the best heat transfer properties between 
solid particles and fluids [5]. Practically, there are two 
methods to prepare the nano-refrigerants: a one-step 
method and a two-step method. The two-step method 
is commonly used for preparing nano-refrigerants, in 
which the nanoparticles are manufactured as a powder 
and then added to the base fluid, followed by several 
types of dispersion methods, such as agitation either 
by ultrasonic or magnetic force, homogenizing, and 
high shear mixing to disperse nanoparticles inside a 
mixture. The one-step method is based on condensing 
vapour nanophase powders into liquid by reducing the 
pressure and then dissolving them inside the liquid 
immediately [6]. 
The literature review is classified into two 
sections. The first evaluates the performance of the 
vapour compression refrigeration system based on 
nano-refrigerant and nano-lubricant, and the second 
evaluates the basic properties of nano-refrigerant and 
nano-lubricant such as thermal conductivity, viscosity, 
specific heat, and density. Vijayakumar et al. [7] 
evaluated the performance of refrigerators based on 
nano-lubricants consisting of an aluminium dioxide 
added to polyol ester oil, and 60 g of R602a was used 
as a refrigerant. The results showed that the 
refrigerating effect increased by 6.09 %, the 
compressor work decreased by 15.78 %, and the 
coefficient of performance (COP) increased by 20.09 
%. Choi et al. [8] evaluated the performance of 
refrigerators based on nano-lubricants consisting of 
0.1 wt.% multi-walled carbon nanotubes (MWCNTs) 
that were dispersed into the polyol ester oil, and 
R134a was charged as a refrigerant. The results 
showed that the power consumption of the compressor 
decreased by 17 %. Senthilkumar et al. [9] evaluated 
the performance of a refrigeration system based on 
nano-lubricants consisting of Al
2
O
3
 and SiO
2
 hybrid 
nanoparticles at two different concentrations of 0.4 g/l 
and 0.6 g/l; 40 g and 60 g of R600a were charged as a 
refrigerant. The results indicated that COP and the 
refrigerating effect increased by 30 % and 25 % 
respectively, while the power consumption decreased 
by 80 W. Senthilkumar et al. [10] evaluated the 
performance of a vapour compression refrigeration 
system based on hybrid nano-lubricants consisting of 
CuO and SiO
2
 at 0.2 g/l and 0.4 g/l concentrations, 
and 40 g and 60 g of R600a were charged as a 
refrigerant. The results indicated that the COP 
improved by 35 % and refrigeration effects by 18 % 
while the power consumption decreased by 75 W. 
Senthilkumar and Anderson [11] evaluated the 
performance of a refrigeration system based on nano-
lubricants consisting of 0 g/l, 0.2 g/l, 0.4 g/l, and 0.6 
g/l SiO
2
 mixed with polyol ester oil; 30 g, 40 g, 50 g, 
60 g and 70 g of R410A were used as refrigerants. The 
results indicated that 0.4 g/l SiO
2
 and 40 g refrigerant 
achieved a high refrigeration effect, decreased 
compressor work by 80 W, and enhanced COP by 1.7. 
Senthilkumar et al. [12] evaluated the performance of 
a refrigeration system based on hybrid nano-lubricants 
consisting of 0.4 g/l \ ZnO/SiO
2
 with 40 g R600a and 
0.6 g/l ZnO/SiO
2
 with 60 g R600a. The results 
indicated that 0.6 g/l ZnO /SiO
2
 achieved a high 
refrigeration effect of 180 W, and enhanced COP by 
1.7, while the lower compressor work was 78 W. 
Senthilkumar et al. [13] evaluated the performance of 
a vapour compression refrigeration system based on 
hybrid nano-lubricants consisting of 0.2 g/l, 0.4 g/l 
and 0.6 g/l CuO /Al
2
O
3
, and 70 g of R600a was used 
as a refrigerant. The results showed that the addition 
of CuO/Al
2
O
3
 enhanced COP by 27 % and increased 
the refrigeration capacity by 20 % while reducing the 
power consumption by 24 %. Javadi and Saidur [14] 
evaluated the performance of refrigerators based on 
nano-lubricants consisting of 0.1 wt.% Al
2
O
3
. The 
results indicated that 0.1 wt.% Al
2
O
3
 decreased the 
power consumption by 2.69 %. Gill et al. [15] 
evaluated the performance of a domestic refrigerator 
based on nano-lubricants consisting of 0.2 g/l, 0.4 g/l, 
and 0.6 g/l TiO
2
 added to Capella D oil as an 
alternative to R134a. Various charges of liquefied 
petroleum gas from 40 g to 70 g were used as 
refrigerants. The results indicated that the refrigeration 
effect and COP were higher than R134a by 
approximately 18.74 % to 32.72 % and 10.15 % to 
61.49 %, respectively. In addition, the compressor 
power input was lower than R134a by approximately 
3.20 to 18.1. Additionally, the results reported that 40 
g liquefied petroleum gas refrigerant with 0.4 g/l TiO
2
 
achieved the best energy performance of the 
refrigerator. Karthick et al. [16] evaluated the 
performance of a vapor compression refrigeration 
system based on four samples of nano-lubricant: 
Sample 1 (mineral oil + 0.02 vol.% Al
2
O
3
 + 0.01 
vol.% TiO
2
), Sample 2 (mineral oil + 0.01 vol.% 
Al
2
O
3
 + 0.005 vol.% TiO
2
), Sample 3(mineral oil + 
0.05 vol.% Al
2
O
3
), and Sample 4 (mineral oil + 0.02 
vol.% Al
2
O
3
 + 0.02 vol.% ZnO), and R600a was 
charged as a refrigerant. The results indicated that 
COP improved by 14.61 %. All nano-lubricants 
exhibited a higher COP, which reduces the power 
consumption. Adelekan et al. [17] Investigated the 
performance of a domestic refrigerator based on nano-
lubricants consisting of 0.2 g/l, 0.4 g/l, and 0.6 g/l 
TiO
2
. The safe mass charge of liquefied petroleum gas 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
397 Enhancing the Performance of a Vapour Compression Refrigerator System Using R134a with a CuO/CeO2 Nano-refrigerant   
was charged as a refrigerant. The results showed that 
all various concentrations of nanoparticles achieved a 
reduction in power consumption by 14 %, 9 %, and 8 
%, respectively. Mineral oil achieved the highest 
power consumption whereas 0.2 g/l TiO
2
 achieved the 
lowest. The refrigeration effects based on 0.4 g/l and 
0.6 g/l were higher, while those based on 0.2 g/l were 
lower. Subhedar et al. [18] evaluated the performance 
of a vapour compression refrigeration system based 
on nano-lubricants consisting of 0.05 vol.%, 0.075 
vol.%, 0.1 vol.%, and 0.2 vol.% Al
2
O
3
 mixed with 
mineral oil, and R134a was charged as a refrigerant. 
The results indicated that 0.075 vol.% achieved the 
maximum enhancement in COP of approximately 85 
% and saved approximately 27 % compressor power. 
Additionally, it was reported that 0.075 vol.% was the 
best concentration. Babarinde et al. [19] investigated 
the performance of a refrigerator based on nano-
lubricants consisting of 0.4 g/l and 0.6 g/l TiO
2 
mixed 
with mineral oil, and R600a was used as a refrigerant 
as an alternative to R134a. The results indicated that 
0.4 g/L TiO
2
 achieved the highest COP and lowest 
power consumption. Selimefendigil and Bingölbalı 
[20] evaluated the performance of a vapour 
compression refrigeration system based on nano-
lubricants consisting of 0.5 vol.%, 0.7 vol.%, 0.8 
vol.%, and 1 vol.% TiO
2
 mixed with poly alkylene 
glycol oil, and R134a was used as a refrigerant. The 
results indicated that 0.5 vol.%, 0.8 vol.%, and 1 
vol.% achieved improvements of COP of 
approximately 1.43 %, 15.72 %, and 21.42 %, 
respectively; 1 vol % reduced energy consumption by 
15 %. Sundararaj and Manivannan [21] investigated 
the performance of a vapour compression refrigeration 
system based on nano-lubricants consisting of 0.1 vol. 
% Au, 0.2 vol.% Au, 0.1 vol.% HAuCl
4
, 0.2 vol.% 
HAuCl
4
, 0.1 vol.% Au and 0.05 vol.% carbon 
nanotubes (CNT), 0.2 vol.% Au, and 0.02 vol.% of 
CNT added to poly alkylene glycol oil, and R134a 
was used as a refrigerant. The results indicated that 
0.2 vol.% Au and 0.02 vol.% CNT achieved the lowest 
power input compared to other compositions, the 
greatest cooling capacity, and the maximum value of 
COP. Therefore, it is preferred to run the system using 
0.2 vol.% Au and 0.02 vol.% of CNT as volume 
fractions. Peyyala et al. [22] investigated the 
performance of a vapor compression refrigeration 
system based on nano-lubricants consisting of 0.1 
vol.% to 0.2 vol.% Al
2
O
3
 mixed with mineral oil, and 
R410a was used as a refrigerant. The results indicated 
an increase in the COP value with increasing 
nanoparticle concentrations, and the maximum value 
was observed at 0.2 vol.% Al
2
O
3
. Babarinde et al. [23] 
investigated the performance of a vapor compression 
refrigeration system based on nano-lubricants 
consisting of 0.2 g/l, 0.4 g/l, and 0.6 g/l graphene 
added to mineral oil, and 50 g to 70 g of R600a which 
were used as a refrigerant. The results indicated that 
the nano-lubricant based on 60 g of R600a and 0.2 g/l 
graphene exhibited the lowest power consumption, 
and the highest COP. Adelekan et al. [24] evaluated 
the performance of a domestic refrigerator based on 
nano-lubricants consisting of 0.1 g/l, 0.3 g/l, and 0.5 
g/l TiO
2
, mixed with mineral oil, and 40 g, 60 g, and 
80 g of R600a were used as refrigerants. The results 
showed that the highest COP and refrigerating effects 
were 4.99 kJ/kg and 290.83 kJ/kg based on 40 g 0.1g/l 
nano-lubricant. Ajayi et al. [25] evaluated the 
performance of a vapor compression refrigeration 
system based on 0.5 g/l Al
2
O
3
 mixed with Capella D 
oil, and 100 g of R134a was used as a refrigerant. The 
results showed that nano-lubricants achieved a higher 
refrigeration effect, better performance, and improved 
energy consumption. Senthilkumar and Anderson [26] 
evaluated the performance of a vapor compression 
refrigeration system, based on nano-lubricants 
consisting of 0.2 g/l, 0.4 g/l, and 0.6 g/l SiO
2
, added to 
polyol ester oil, and 30 g, 40 g, 50 g, 60 g and 70 g 
R410A were used as refrigerants. The results indicated 
that 40 g of R410A and 0.4 g/l of SiO
2
 achieved better 
refrigerating effects and reduced power consumption. 
This leads to an enhanced COP. Pawale et al. [27] 
evaluated the performance of a vapor compression 
refrigeration system based on nano-refrigerant 
consisting of 0.5 wt.%, and 0.1 wt.% Al
2
O
3
, and a 
particle size diameter of 50 nm was dispersed into 
R134a. The results showed that 0.5 wt.% improved 
the performance; however, the increase in nanoparticle 
concentration will lead to a decrease the performance 
of the system. Kumar et al. [28] evaluated the 
performance of a vapor compression refrigeration 
system based on nano-refrigerant consisting of (1 g of 
ZnO / 1 g SiO
2
), (1.5 g of ZnO / 0.5 g of SiO
2
), and 
(0.5 g of ZnO /1.5 g of SiO
2
) dispersed into 0.5 kg of 
R134a. The results showed that COP increased 
approximately 26 %. Manikanden and Avinash [29] 
investigated the performance of domestic refrigerators 
based on nano-refrigerants consisting of CuO, pure 
nano-CuO, and Ag-doped nano-CuO dispersed into 
R290. The results indicated that Ag-doped nano-CuO 
achieved the best performance of the system compared 
to pure nano-CuO. The COP of Ag-doped nano-CuO 
increased up to 29 %, while the power consumption of 
a system reduced up to 28 %. Kundan and Singh [30] 
evaluated the performance of a vapour compression 
refrigeration system based on nano-refrigerant 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
398 Mo hamed,	H.E.	−	Camdali,	U .	−	Biyik o glu,	A .	−	A ctas,	M.
consisting of 0.5 wt.% to 1 wt.% Al
2
O
3
 dispersed into 
R134a, with a particle size diameter of 20 nm The 
results based on volume flow rates of refrigerants 
showed that 6.5 l/h and 11 l/h achieved improvements 
of COP from 7.20 % to 16.34 % respectively at 0.5 
wt.% Al
2
O
3
; however, 1 wt.% Al
2
O
3 
caused a 
reduction in COP at the same volume flow rates. 
Nagaraju and Reddy [31] evaluated the performance 
of a vapour compression refrigeration system based 
on nano-refrigerants consisting of 0.05 wt.% to 0.8 
wt.% CuO particle sizes ranging from 10 nm to 70 nm 
dispersed into R134a..The results showed that 0.8 
wt.% of CuO was the optimal concentration that 
achieved the highest heat transfer enhancement, 
enhanced COP, and reduced power consumption 
Kumar and Tiwari [32] evaluated the performance of a 
vapor compression refrigeration system based on 
R134a / poly alkylene glycol oil, R600a / poly 
alkylene glycol oil and Cu nanoparticles dispersed 
into R600a. The results showed that R600a achieved a 
higher COP and refrigeration effect of approximately 
27.12 % and 25 % respectively, while the reduction in 
power consumption was 1.69 % which was less than 
that of R134a. Moreover, dispersing 0.5 wt.%, 1 wt.%, 
and 1.5 wt.% Cu into R600a improved the COP and 
refrigeration effect compared to pure R600a, and 
reduced power consumption Kumar et al. [33] 
investigated the performance of a vapour compression 
refrigeration system based on 0.01 vol.% and 0.06 
vol.% ZrO
2
, and a particle size diameter of 20 nm was 
dispersed into both R134a and R152a. The results 
indicated an improvement in COP of 33.45 % based 
on the 0.06 vol.% ZrO
2
-R152a nano-refrigerant. The 
application of R152a as a refrigerant was 
environmentally beneficial due to its properties such 
as zero ozone depletion potential and very low global 
warming potential. Mahdi et al. [34] evaluated the 
performance of a vapour compression refrigeration 
system based on a nano-refrigerant consisting of 0.01 
vol.% and 0.02 vol.% Al
2
O
3
, and a diameter of 20 nm 
to 30 nm was dispersed into R134a. The results 
showed that the rising nanoparticle concentration 
caused the improvement of COP by 3.33 % to 12 %, 
respectively, and the reduction of power consumption 
was nearly 1.6 % and 3.3 %, respectively. Singh [35] 
evaluated the performance of a vapor compression 
refrigeration system based on 0.2 vol. %, 0.4 vol. %, 
and 0.6 vol. % TiO
2
, and a particle size diameter of 30 
nm to 50 nm was dispersed into R134a.The results 
showed that the nano-refrigerant based on 0.4 vol.% 
of TiO
2
 achieved an improvement of COP of by 
approximately 11.1 % at 20 °C, 25 °C, and 30 °C 
evaporator temperatures. Additionally, an increase or 
decrease in power consumption has not been observed, 
which shows that nanoparticles were completely 
dissolved in the refrigerant.
Thermal conductivity is the most important of the 
thermophysical properties of nano-refrigerants due to 
its effects on the boiling and convective heat transfer 
coefficients. This explains why most researchers focus 
on studying thermal conductivity. Recently, interest in 
the study of viscosity has begun to appear to extend 
to other thermophysical properties to form a clear 
idea of the heat transfer properties [4]. Kedzierski 
et al [36] evaluated the thermophysical properties of 
nano-lubricants based on nanoparticle size diameters 
of 127 nm and 135 nm of Al
2
O
3
 and ZnO respectively 
mixed with polyol ester oil at atmospheric pressure 
with temperatures ranging from 288 K to 318 K, 
and various mass fractions of Al
2
O
3
, and ZnO were 
used. The results showed that increasing nanoparticle 
concentrations led to increased viscosity, density, 
and thermal conductivity but decreased viscosity and 
density with increased temperature. Sanukrishna and 
Prakash [37] evaluated the thermal conductivity and 
viscosity of nano-lubricants based on 0.07 vol.% to 
0.8 vol.% TiO
2
 mixed with poly alkylene glycol oil 
at temperatures ranging from 20 °C to 90 °C. They 
found that increasing nanoparticle concentrations 
led to increasing these parameters; in contrast, they 
decreased with increasing temperature. Zawawi et al. 
[38] evaluated the thermal conductivity and dynamic 
viscosity of nano-lubricants based on 0.02 vol.% to 
0.1 vol.% Al
2
O
3
/SiO
2
, Al
2
O
3
/TiO
2
, and TiO
2
/SiO
2
 
mixed with poly alkylene glycol oil l at temperatures 
ranging from 303 K to 353 K. The results showed 
that 0.1 vol. % Al
2
O
3
/TiO
2
 poly alkylene glycol 
oil enhanced the viscosity by 20.50 % at 303 
K, while 0.1 vol. % Al
2
O
3 
/ SiO
2
 poly alkylene 
glycol oil improved the thermal conductivity by 
2.41 % at 303 K.
As per previous studies the addition of 
nanoparticles into the refrigerant or lubricant oil 
in a vapour compression refrigeration system was 
conducted to improve the COP and thermophysical 
properties of the fluid as a metal, metal oxide, and 
hybrid nanoparticles This research presents a new 
concept of nanoparticles as a single oxide and as a 
mixture that was prepared an inexpensive and easy 
way using, distilled water, ammonia, copper nitrate, 
and cerium nitrate. The nanoparticles were prepared 
as follows: CuO, CeO
2
: Mixture 1 consisted of 50 % 
CuO + 50 % CeO
2
; Mixture 2 consisted of 60 % CuO 
+ 40 % CeO
2
; Mixture 3 consisted of 70 % CuO + 
30 % CeO
2
; Mixture 4 consisted of 40 % CuO + 60 
% CeO
2
; and Mixture 5 consisted of 30 % CuO + 70 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
399 Enhancing the Performance of a Vapour Compression Refrigerator System Using R134a with a CuO/CeO2 Nano-refrigerant   
% CeO
2
. The application of nanoparticles in a vapour 
compression refrigeration system is challenging 
due to factors such as high cost, instability, and 
agglomeration. Fortunately, the method of preparation 
used in this research used materials from which 
nanoparticles are prepared can be commonly found 
in all chemistry laboratories. Therefore, the cost 
barrier, which is one of the major obstacles to using 
nanoparticles, is broken. Consequently, the desired 
increases in the thermal conductivity achieved by 
these nano particles can be obtained at a reasonably 
affordable cost.
1 MATERIALS AND METHODS 
This section is divided into three parts. In the first 
part, an experiment was conducted on a vapour 
compression refrigeration system using R134a as 
a refrigerant and SUNISO as a mineral oil of a 
compressor, and the coefficient of performance was 
calculated based on the change in the enthalpy of 
the refrigerant. Thereafter, Ansys Fluent software 
version 19.0 was used to calculate the coefficient of 
performance theoretically to make a comparative 
study between an experiment and theoretical results. 
In the second part, seven types of nanoparticles 
were prepared, and the preparation process will be 
explained in detail later, Finally, in the third part, the 
nanoparticles were added to the refrigeration system 
to verify their effect on the COP of the system.
 1.1 Experimental Work
An experiment was carried out in a laboratory under 
normal conditions at Yildiz Technical University 
in Istanbul, Turkey. The system was charged with 
refrigerant R134a and compressor oil. Digital meters 
were used to monitor the temperatures and pressures 
at the inlets and exits of a compressor, a condenser, 
and an evaporator. A digital wattmeter was used to 
monitor power consumption, and a digital flow meter 
was used to monitor the mass flow rate of R134a. 
Heat loss to the surroundings and the changes in the 
kinetic and potential energy were neglected. Every 
experiment was conducted three times to obtain the 
highest accuracy and steady-state performance. Table 
1 shows the technical details of the experimental 
system. An experimental set up and its schematic 
diagram are presented in Fig. 1. The experiment 
consists of a compressor, condenser, evaporator, and 
expansion valve.
Table 1. Technical details of the experimental system
No Components Characteristics
1 Compressor Bitzer compressor 1/2 HP
2 Condenser Air cooled condenser 1/2 HP
3 Evaporator Emersion coil 1/3 HP
4 Expansion valve Automatic expansion valve
5 Voltage rating 220V AC voltage supply
6 Suction line 3/8 inch copper pipe
7 Discharge line 1/4 inch copper pipe
8 Frequency rating 51 Hz
9 Defrost unit Automatic
10 Door type Single closed door
a) 
Expansion valve
↓   
↑   
Condenser
    ←
Compressor
Evaporator
     ←
b) 
Fig. 1. a) Experimental work and b) corresponding schematic 
diagram of the experiment

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
400 Mo hamed,	H.E.	−	Camdali,	U .	−	Biyik o glu,	A .	−	A ctas,	M.
1.1.1 Experimental Procedure
Using the Engineering Equation Solver (EES), the 
temperatures and pressure were measured at the 
inlet and outlet of the evaporator, condenser, and 
compressor to read the enthalpy of R134a. This 
software aids in determining the enthalpy of the gas 
and the change in the gas phase, where two states of 
the gas cycle were recorded in the system, specifically 
superheated vapour enthalpy (h1, h2) at the inlet 
and the exit of the compressor, superheated vapour 
enthalpy (h3) at the inlet of the condenser, compressed 
liquid enthalpy (h4) at the exit of the condenser, 
compressed liquid enthalpy (h5) at the inlet of the 
evaporator, and superheated vapour enthalpy (h6) 
at the exit of the evaporator The listed governing 
equations have been employed for analysis [33]. 
Characteristics of R134a utilized in the experimental 
setup are given in Table 2.
 

 Wm hh   21 , (1)
 Qm hh
evaporator
 
 65 , (2)
 Qm hh
condenser
 
 34 , (3)
 COP
hh
hh

 
 
65
21
. (4)
Table 2. Characteristics of R134a [39]
No Characteristics
1 Name
1,1,1,2 
tetrafluoroethene
2 Chemical formula CF3CFH2
3 Molecular weight 102.03 g/mol
4 Composition pure
5 ASHRAE safety classification A1
6 Ozone depletion potential zero
7 Lifetime in the atmosphere 13
8 Critical temperature 101.1 °C
9 Critical pressure 4.06.3 MPa
10 Normal boiling point NBP -26.4 °C
11 Saturated vapor pressure at 20 °C 774.3 kPa
12 Latent heat of vaporization 198.6 kJ/kg
13 Liquid density 1294.8 kg/m
3
14 Vapor density 14.43 kg/m
3
15 Liquid Cp 1.341 kJ/(kg °C)
16 Vapor Cp 0.90 kJ/(kg °C)
17 Liquid thermal conductivity at 25 °C 0.0824 W/(m K)
18 Vapor thermal conductivity at 25 °C 0.0145 W/(m K)
19 Liquid viscosity at 25 °C 0.202 mPa s
20 Vapor viscosity at 25 °C 0.012 mPa s
1.1.2 Simulation of Vapor Compression Refrigeration 
System
Ansys Fluent version 19.0 software was chosen to 
make the mathematical model of the refrigeration 
system based on the real dimensions of the condenser 
and the evaporator and these two parts of the system 
were chosen to study the effect of average the 
temperature of each of them on the performance of 
the refrigeration system. The stages of designing the 
mathematical model were as follows: 1) Geometry, 
where the evaporator and condenser were drawn 
based on the real dimensions using a solid works 
program, and the drawn models were exported to 
Ansys Fluent, where the solid works helped to draw 
quickly and accurately; 2) Mesh, where the tubes of 
the evaporator and condenser were divided into many 
elements and nodes, and the change in the number 
of elements stops when the temperature inside the 
tube does not change and is close to the experimental 
value. The equations that were used to calculate the 
theoretical temperatures and pressures and the amount 
of heat absorbed and rejected are the continuity, 
momentum, and energy equations. The dimensions 
of the condenser and evaporator and their theoretical 
models are shown in Table 3 and Fig 2. 
As shown in Fig. 2, the evaporator and condenser 
are designed so that the thermal gradient of the pipes 
appears at any point of entry. Also shown in the design 
is the gradient in the pressure and gradient in velocity 
to determine the velocity, pressure, and temperature 
of the refrigerant (R134a) while rotating inside the 
tubes. The colours shown in the drawing indicate that 
red gives the highest reading, blue the lowest reading, 
and the colours between red and blue are between 
the highest and the lowest in all cases of gradation, 
whether it is temperature, pressure, or velocity. 
1.2 Preparation of Nanoparticles
The nanoparticles were prepared with nitrates, 
distilled water, and ammonia. A specified amount of 
copper nitrate was weighed in the case of preparing 
copper oxide and dissolving it in a specified amount 
of distilled water or deionized water. Similarly, a 
specified amount of cerium nitrate was weighed, in 
the case of preparing cerium oxide; and dissolving it 
in a specified amount of distilled water or deionized 
water. Distilled water is considered one of the cheapest 
and best solvents for all materials laboratories. As 
for preparing the mixture, specific quantities of both 
copper nitrate and cerium nitrate are weighed and 
dissolved in a specific amount of distilled water to 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
401 Enhancing the Performance of a Vapour Compression Refrigerator System Using R134a with a CuO/CeO2 Nano-refrigerant   
Table 3.  Dimensions of condenser and evaporator
NO Condenser Measurements Dimensions NO Evaporator Measurements Dimensions
1 Length 35 cm 1 Length 33 cm
2 Width 17 cm 2 Width 10 cm
3 Height 28 cm 3 Height 28 cm
4
Diameter of copper tube inside the 
condenser 
0.25 inch 4
Diameter of copper tube inside the 
evaporator 
0.25 inch
5
The twists and copper tube inside a 
condenser 
18 5
The twists and copper tube inside an 
evaporator
18
6 Distance between one tube and another 5 cm 6 Area of evaporator 0.12 cm
2
7 Area of condenser 0.177 cm
2
7 Number of tubes 18
8 length of the tube inside the condenser 7.2 m 8 Fan speed 1300 rpm
9 The thickness of aluminium plate 0.3 mm 9 Air velocity 638 m/s
10 Number of plates 600 10 Evaporator type emersion coil
11 Single plate dimensions 35 cm × 17 cm × 34 cm 11 Distance between one tube and another 3 cm
12 Fan speed 1300 rpm 12 Length of the tube inside the evaporator 6.48 m
13 Air velocity 638 m/s
14 Condenser type Air cooler
a)        b) 
Fig. 2. a) Theoretical model of condenser, and b) theoretical model of evaporator without nanoparticles
begin preparation for the reaction until the oxide is 
obtained. The preparation process of the reaction is 
briefly described in the following steps:
1. Heating until 80 °C for 1 hour with a constant 
mixing speed of 375 rpm;
2. Adding ammonia at a constant temperature of 60 
°C and a constant mixing speed of 375 rpm to 
reach Ph = 10 ± 1
3. Raising the temperature to 90 °C until copper 
oxide is deposited;
4. Cooling the solution to room temperature;
5. Filtration;
6. Drying in an electric oven at 110 °C for 1 hour;
7. Milling;
8. Screening; and
9. Packing. 
According to the equations below, the 
nanoparticles were prepared as indicated clearly in 
Table 4 and their physical and chemical properties are 
shown in Table 5.
 M
W
M
W
= , (5)
 C
n
v
= , (6)
where M is mole [g/mol], W weight [g], M
W
 molecular 
weight [mol], C mole concentration [mol/l], n number 
of moles [-], and v volume [l].
Table 4 shows that the weights of substances 
involved in the reaction have been converted to moles 
by dividing the weight by the molecular weight as 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
402 Mo hamed,	H.E.	−	Camdali,	U .	−	Biyik o glu,	A .	−	A ctas,	M.
indicated in Eq. (5) then the molar concentration 
was calculated as indicated in Eq. (6) by dividing the 
number of moles by the volume of the solvent in litres. 
Note that the molecular weights of the reactants 
were as follows:
Cu (NO
3
)
2
 3H
2
O = 241.606
Ce (NO
3
)
3
 6H
2
O Ce = 434.22
CuO = 79.5
CeO
2
= 172.12
Table 4. The quantities obtained from the mixtures
Mixture 
number
Percentages Molar concentration
The 
Quantity 
[g]
CuO 
[%]
CeO
2
 
[%]
Cu(NO
3
)
2
 
3H2O
Ce(NO
3
)
3 
6H
2
O
1 50 50 0.20867 0.09673 12.67
2 60 40 0.250408 0.07753 11.44
3 70 30 0.300075 0.05834 10.97
4 40 60 0.16694 0.11622 13.07
5 30 70 0.125687 0.135569 13.85
Table 5. Nanoparticles properties [40]
No Nanoparticles
M
W 
[g/mol]
ρ 
[kg/m
3
]
K 
[W/(mK)]
Cp 
[J/(kgK)]
1 CuO 79.55 6320 32.9 536
2 CeO
2
172.1 6100 11.7 352
3 50 % CuO+50 % CeO
2
125.8 6210 22.3 444
4 60 % CuO+40 % CeO
2
116.5 6232 24.4 462
5 70 % CuO+30 % CeO
2
107.3 6254 26.5 481
6 40 % CuO+60 % CeO
2
135.1 6188 20.1 426
7 30 % CuO+70 % CeO
2
144.3 6166 18.0 407
where M
W
 is molar mass [g/mol], K is thermal 
conductivity [W/(m K)], ρ is density [kg/m
3
], and Cp 
specific heat [J/(kg K)].
1.3 Mathematical Models 
After completing the geometry and mesh stages that 
are referred to in Section 1.1.2, the refrigeration system 
for this study is ready to receive the nanoparticles. 
This stage is called “setup” where the multiphase is 
used as the best model for the solution. The properties 
of both R134a are entered in the liquid and gaseous 
phase, and the nanoparticles with the proportions 
specified for it depending on the nanofluid equations 
and dealing with nanoparticles and R134a based on 
becoming one homogeneous material as shown below.
 Keff kbf
kp kbfk pk bf
kp kbfk pk bf

 
  








22
2
)
)
,


 (7)
where Keff, Kbf, and kp are the thermal conductivities 
of the nano-refrigerant, base refrigerant in the liquid 
phase and particle, respectively, and φ is the particle 
volume fraction:
 
nr r

 
1
1
25 .
, (8)
where μ
nr
 and μ
r
 are the dynamic viscosities of the 
nano-refrigerant and refrigerant, respectively.
The density and specific heat of the nano-
refrigerant are shown in Eqs. (9) and (10).
  
efff np
    1, (9)
 C
cp bf cp np
bf np
pnf

   
 
1
1


, (10) 
where –Ø, ρbf, ρ
np
, np, cp are volume fraction of 
nanoparticles, density of base fluid, density of 
nanoparticles, specific heat of base refrigerant, and 
specific heat of nanoparticles, respectively, [41] and 
[42].
A multiphase model solves the momentum, 
continuity, and energy equations for the mixture, 
and solves the equation of volume fraction for the 
secondary phases [43] and [44]. A continuity equation 
for the volume fraction of one (or more) of the phases. 
For the q
th
 phase, this equation has the following form:
 
1
1

 
 

q
qq qqq
qq
n
t
Sm m
q












 





 , (11)
where  m
q ρ
 is the mass is transfer from phase ρ to q 
phase, –  m
q ρ
 the mass transfer from phase q to phase 
ρ. A single momentum equation is solved throughout 
the domain; it is dependent on the volume fractions of 
all phases through the properties ρ and μ. 
 


  
  






t
gF
T
 
 
 
 

. (12) 
The energy equation, is also shared among the 
phases
 


   



t
EE PK TS
effh
 

. (13)
The amount of nanoparticles that was added to 
R134a was 2.6 g, while the amount of R134a was 
1039 g, as this was the amount that the system was 
operating within the first part of the experiment to 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
403 Enhancing the Performance of a Vapour Compression Refrigerator System Using R134a with a CuO/CeO2 Nano-refrigerant   
become a mass fraction of 0.25 wt.%. The theoretical 
results obtained by adding a quantity of nanoparticles 
are presented and their effects on the performance of 
the refrigeration system are discussed in the discussion 
section.
2 RESULTS AND DISCUSSION
This section is divided into three parts; the first 
part includes a discussion of the results obtained by 
conducting an experiment on a vapor compression 
refrigeration system and comparing these results 
with a simulation that was done using Ansys Fluent 
19.0 software program and calculating the accuracy 
rate. The second part includes discussing the results 
obtained from the preparation of nanoparticles by 
presenting nanoparticle screening tests using X-ray 
diffraction (XRD) and scanning electron microscope 
(SEM) methods. The third part includes discussing 
the results obtained from the theoretical study 
where nanoparticles were introduced to a vapour 
compression refrigeration system to investigate 
their effects on the coefficient of performance of the 
system.
2.1 Comparison of Experimental and Theoretical Results of 
a Vapor Compression Refrigeration System 
A theoretical model was designed for the evaporator 
and condenser with specifications similar to the 
experimental system; the results obtained were 
illustrated graphically to show the effects of the 
average temperature of both the evaporator and 
condenser on COP, and W
comp
 as shown in Fig. 
3. The COP at varying evaporator temperatures 
is presented in Fig 3a; an increase in evaporator 
temperatures causes an increase in COP due to an 
increase in the refrigeration effect because of increase 
in both the enthalpy difference and mass flow rate 
of R134a through the evaporator, and a decrease 
in compressor work. The power consumption at 
varying evaporator temperatures is presented in Fig. 
a)      b) 
c)      d) 
Fig. 3. a) The effect of T
av,ev
 on COP b) the effect of T
av,ev
 on the power consumption W
comp
  
c) The effect of T
av,cond
 on COP, and d) The effect of T
av,cond
 on the power consumption W
comp

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
404 Mo hamed,	H.E.	−	Camdali,	U .	−	Biyik o glu,	A .	−	A ctas,	M.
3b; an increase in evaporator temperatures causes a 
decrease in power consumption, due to an increase 
in suction temperature, which causes an increase in 
both vaporization pressure and density suction vapor 
entering the compressor, which leads to an increased 
mass flow rate of R134a through the compressor for 
a given piston displacement and decreased power 
consumption. The effects of the average temperature 
of the condenser on the COP are presented in Fig. 3c; 
it decreases as the condenser temperature increases 
due to a decrease in the refrigeration effect and an 
increase in compressor work. Increased condenser 
temperatures cause an increase in the heat rejection, 
due to the rise in enthalpy difference and mass flow 
rate of R134a through the condenser. In contrast, 
the increase in condenser temperature will cause 
an increase in power consumption, as presented in 
Fig. 3d. To achieve high accuracy, the experiment 
was divided into several cases, in which each case 
included five experiments. Each experiment was 
repeated three times. The experiment which gave 
the most convergence with the theoretical value 
calculated using Ansys Fluent was chosen to then 
capture all these points to be plotted with the average 
temperatures of the evaporator and condenser. As 
shown by the results and in agreement with previous 
studies, our results confirmed the increase in COP 
with the temperature of the evaporator and its decrease 
with the increase in temperature of the condenser, 
as well the decrease in energy consumption with an 
increase in the average temperature of the evaporator 
and increased with increasing the average temperature 
of the condenser 
2.2  Characterization of Nanoparticles
Nanoparticle characterization was carried out at the 
Huazhong University of Science and Technology in 
China on September 24, 2019, by using XRD analysis 
and SEM images. The results of the nanoparticles 
are presented below in Fig. 4. The XRD pattern was 
scanned from 20 deg to 80 deg and the XRD profile 
confirmed the nanocrystalline nature of CuO. The 
characteristic diffraction peak was observed, and all 
of the peaks agreed in position and intensity with the 
database standard (JCPDS 00-045-0937) of the face-
centred cubic CuO crystal with the fluorite structure. 
The absence of additional diffraction peaks confirms 
a)           b) 
c)           d) 
Fig. 4.  XRD Pattern of a) pure CuO, b) pure CeO
2
, c) 0.5 % CuO, 0.5 % CeO
2
 , and d) 0.6 % CuO, 0.4 % CeO
2
 nanoparticles

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
405 Enhancing the Performance of a Vapour Compression Refrigerator System Using R134a with a CuO/CeO2 Nano-refrigerant   
the nanocrystalline nature and purity of the samples. 
The XRD pattern of CeO
2
 was scanned from 20 
deg to 80 deg, and the XRD profile confirmed the 
nanocrystalline nature of CeO
2
. The characteristic 
diffraction peak was observed, and all of the peaks 
agreed in position and intensity with the database 
standard (JCPDS 00-004-0593) of the face-centred 
cubic CeO
2
 crystal with the fluorite structure. The 
absence of additional diffraction peaks confirms the 
nanocrystalline nature and purity of the samples. The 
SEM images proved that the particles of the samples 
were approximately spherical in shape and the particle 
sizes of CuO, CeO
2
, 0.5 % CuO + 0.5 % CeO
2
, and 
0.6 % CuO + 0.4 % CeO
2
 were observed to be 78.95 
nm, 79.9 nm, 44.15 nm, and 63.3 nm, respectively, 
based on the SEM images, as shown in Fig. 5. This 
research succeeded in preparing nanoparticles with 
suitable diameters. Cerium oxide was used for the 
first time to determine its effect on the performance 
of refrigeration system. It is expected that this study 
will open the door to future research to reveal new 
properties of cerium oxide as a mixture with copper 
oxide; in particular, the mixture consisting of both 
oxides was prepared by the same method in this 
experiment as a homogeneous substance 
2.3 The Results Obtained from Adding Nanoparticles 
Theoretically into a Vapor Compression Refrigeration 
System
The results obtained from adding CuO are illustrated 
in Fig. 6 to show the effects of the average temperature 
of the evaporator on the COP, and W
comp
. As it appears 
from the results, the addition of 0.25 wt.% CuO caused 
an increase in the temperature of the evaporator at its 
entrance and exit, which led to a rise in both the COP 
and the amount of heat absorbed inside the evaporator 
and thus a decrease in the amount of energy consumed 
by the compressor. This conclusion is consistent 
with previous studies, and the main reason for the 
occurrence of these changes is the high thermal 
conductivity of the refrigerant due to its mixture with 
CuO, which records an average thermal conductivity 
of 20 W/(mK) to 40 W/(mK). The addition of the 
a)      b) 
c)      d) 
Fig. 5.  a) spherical CuO, b) spherical CeO
2
, c) spherical 0.5 % CuO + 0.5 % CeO
2
, and d) spherical 0.6 % CuO + 0.4 % CeO
2

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
406 Mo hamed,	H.E.	−	Camdali,	U .	−	Biyik o glu,	A .	−	A ctas,	M.
a)       b) 
c)       d) 
e)       f) 
g)       h) 

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
407 Enhancing the Performance of a Vapour Compression Refrigerator System Using R134a with a CuO/CeO2 Nano-refrigerant   
same amount of CeO
2
 caused an increase in the 
temperature of the evaporator at its entrance and 
exit, which led to a rise in both COP and the amount 
of heat absorbed inside the evaporator and thus a 
decrease in the amount of energy consumed inside 
the compressor. The main reason for the occurrence 
of these changes is the high thermal conductivity of 
the refrigerant due to its mixture with CeO
2
, where 
it records an average thermal conductivity of 11.7 
W/(mK). The addition of the same amount of 0.5 
% CuO with 0.5 % CeO
2
 caused an increase in the 
temperature of the evaporator at its entrance and 
exit, which led to a rise in both COP and the amount 
of heat absorbed inside the evaporator and thus a 
decrease in the amount of energy consumed inside 
the compressor. The main reason for the occurrence 
of these changes is the high thermal conductivity of  
the refrigerant due to its mixture with nanoparticles. 
The addition of the same amount of 0.6 % CuO with 
0.4 % CeO
2
 caused an increase in the temperature 
of the evaporator at its entrance and exit, which led 
to a rise in both the COP and the amount of heat 
absorbed inside the evaporator thus a decrease in the 
amount of energy consumed inside the compressor. 
The main reason for the occurrence of these changes 
is the high thermal conductivity of the refrigerant 
due to its mixture with nanoparticles. Since the most 
important factor in improving the performance of the 
refrigeration system after adding the nanoparticles is 
the temperature of the evaporator, all the results were 
plotted so that the effect of the average evaporator 
temperature on the COP of the system at a specific 
amount of nanoparticles is shown. Nagaraju and 
Reddy [32] proved that adding copper oxide to R134a 
improved the COP of the refrigeration system to 
a degree close to what was found in this study, and 
the method in which nanoparticles are prepared, the 
shape, diameter, and quantity added to the refrigerants 
play an important role in determining the result. 
3  CONCLUSION 
A new concept of nanoparticles was introduced in this 
research to open the door to answering many questions 
in the future, because cerium oxide was used with 
copper oxide as one material consisting of a mixture 
of both oxides. The results obtained for copper oxide 
agreed with previous studies, where copper oxide 
succeeded in improving the performance of the 
refrigeration system and increased COP by 25 %, and 
cerium oxide succeeded in improving the performance 
of the system by a lesser value. For the mixture, the 
results confirmed that the mixture containing a higher 
percentage of copper oxide gave better results. The 
door remains open for more experimental studies 
on the use of cerium oxide as a single oxide or as a 
mixture with other oxides to study its effect on the 
performance of the vapor compression refrigeration 
system and whether the refrigeration system will work 
safely. In addition, more experiments needed to study 
the effect of the mixtures mentioned in this research 
on the stability of nanoparticles with refrigerants and 
lubricant oils, as the problem of stability is one of the 
greatest obstacles to the application of nanoparticles 
in the refrigeration systems.
4  FUTURE WORK
In this study the method of preparing nanoparticles 
was simple and affordable and produced two types 
i) 
Fig. 6.  The effect of T
av,ev
  on COP and W
comp
 at constant mass fraction and comparing of the results of a vapor compression 
refrigeration system with nano and without nanoparticles

Strojniški vestnik - Journal of Mechanical Engineering 68(2022)6, 395-410
408 Mo hamed,	H.E.	−	Camdali,	U .	−	Biyik o glu,	A .	−	A ctas,	M.
of oxides and five types of mixtures. Subsequently, 
the field of research remains open. This method 
succeeds in obtaining other oxides, especially oxides 
with high thermal conductivity, because the cost of 
nanoparticles increases as their thermal conductivity 
increases. Nevertheless, the theoretical results in 
this research encourage researchers to move forward 
with experimental studies This study recommends 
conducting experiments to verify the behaviour 
of cerium oxide in refrigeration systems and to 
monitor its behaviour at different temperatures for 
the evaporator, especially because the results of 
this research show that cerium oxide improved the 
performance of the refrigeration system due to its 
good thermal conductivity This study recommends 
mixing materials that have been prepared with other 
refrigerants and compressor lubricant oils to study 
their effect on the thermophysical properties of 
refrigerants and oils. Since the problem of the stability 
of nanoparticles with refrigerants is so important, 
a hybrid consisting of oxides was recently used to 
solve this problem. The mixture prepared from oxide 
succeed in obtaining better results, especially since 
the mixture consisting of 50% copper oxide and 50 
% cerium oxide has already been mixed with R134a 
in the lab using the ultrasonic machine only for one 
hour; the result was a stable mixture for a whole day 
5  ACKNOWLEDGMENTS
I would like to thank Yildiz Technical University 
in Istanbul Turkey, where the first part of this 
research was carried out in Mechanical Engineering 
Laboratories under the supervision of Dr Ahamet 
Salim. I take an opportunity to express my sincere 
thanks and gratitude to Dr Jassim M. H. Alkurdhani 
who helped me to prepare the nanoparticles and 
showed me a different way to achieve my goal, and 
Dr Yusuf Bedeli who provided me with the laboratory 
so that I could prepare the nanoparticles. I also 
extend my thanks to Huajong University in China 
and Gazi University in Ankara/Turkey for their help 
in examining and identifying the properties of the 
nanoparticles.
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