Challenges in Nano and Micro Scale Science and Technology is a quarterly, peer-reviewed academic journal published jointly by the University of Sistan and Baluchestan and the Iranian Society of Mechanical Engineers under full permission of the Ministry of Science, Research and Technology of Islamic Republic of Iran. It intends to provide an international forum for refereed original research works, technical notes, and state-of-the-art reviews pertaining to nano and micro-scale science and technology. This account is managed by the Director-in-Charge, Dr. Amin Behzadmehr.
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Challenges in Nano and Micro Scale Science and Technology, 2021
This article is concerned with study of the steady and incompressible three-dimensional flow of m... more This article is concerned with study of the steady and incompressible three-dimensional flow of magnetohydrodynamic couple stress nanofluids over a stretching sheet through a porous medium under influence of, non-linear thermal radiation and heat generation/absorption, taking into account effects of both Brownian motion coefficient and thermophoresis coefficient. On the other hand, the system of nonlinear partial differential equations governing the flow process has been transformed into a system of nonlinear ordinary differential equations using similarity transformations and dimensionless variables, knowing that the numerical method used to solve the new system of differential equations is the fourth-order Runge-Kutta method with the shooting technique in the code of MATLAB program. The effects of all physical parameters resulting from this study on the distributions of velocity, temperature and concentration of nanoparticles within the base fluid were studied by means of graphs that were made by the MATLAB program. Finally, some of the results of the current study showed that the effects of the magnetic field parameter and Darcy number on the velocity distribution were negative, while their effect on the concentration of nanoparticle distribution was positive.
Challenges in Nano and Micro Scale Science and Technology, 2021
Friction is created in the gas seals due to the relative motion of the two fixed and rotary surfa... more Friction is created in the gas seals due to the relative motion of the two fixed and rotary surfaces, causing power dissipation, erosion, heat generation and temperature rise of the surfaces so a distance between two surfaces should be created. In the structure of Dry Gas Seals (DGS), the grooves on the rotating surface are created, which is the key to the gas penetration between the surfaces. The geometrical parameters of grooves would have substantial effect on the amount of leakage, so it is of high importance to indicate the best shape and operating condition of grooves. In this research, the effect of geometric parameters of a DGS with trapezoidal grooves on the leakage rate and open force is investigated. The geometric parameters are the depth of the triangular and square sections, the length of the groove, the angle of the square part and the angle of the groove. The length of the groove has a substantial impact on leakage, and by doubling the length, the leakage rate is raised to 58%. It is concluded that when the angle of the square section is 7° and the angle of groove is 22°, the minimum leakage occurs in the range of parameters studied. Taguchi algorithm is also applied to optimize the shape parameters of the groove to minimize open force and leakage of the seal. Optimal dimensions for grooves in the range of operating conditions in this study are triangle depth = 3μm, quad − depth = 10μm, Length = 8mm, groove angle = 18°, rectangle angle = 5°. The same optimum conditions are obtained by considering energy and exergy terms.
Challenges in Nano and Micro Scale Science and Technology, 2021
The temperature of the phase change material remains almost constant when the phase changes. It m... more The temperature of the phase change material remains almost constant when the phase changes. It means that these materials have a high heat capacity during phase change. This property causes the particles containing these materials to act like distributed heat sinks throughout the field and result in heat transfer increment. However, if these particles are placed inside the thermal boundary layer, they will have a greater impact on the heat transfer rate. The vertical velocity component in the entrance length, prevents particles from being placed near the wall. On the other hand, in this study, the particle coating is iron oxide, which are able to move towards the wall by magnetic force. This magnetic field pulls the particles toward the heated wall and inside the thermal boundary layer. To solve the governing equations, twophase Eulerian-Lagrangian model has been used. The PCM is Paraffin wax with 30 microns diameter and, particle volume concentration is 10%. This study covers a wide range of Reynolds numbers (100<Re<500), subcooling numbers up to 0.75 and magnetic field strength (H0) up to 2.1e-8 A.m-1. The results show 16.56% increase in Nusselt number for Re=100 and, H0=2.1e-8 A.m-1 .
Challenges in Nano and Micro Scale Science and Technology, 2021
Recently, using volumetric receivers as a novel idea to collect solar energy was considered. Sola... more Recently, using volumetric receivers as a novel idea to collect solar energy was considered. Solar radiation volumetrically absorbers with a heat transfer fluid which flows through a transparent tube. Nanofluids as working fluids were proposed by different researchers because of their interesting absorption coefficient as well as an important heat transfer coefficient. However, conditions such as the severe temperature gradient in absorber tubes and high temperature of working heat transfer fluid, deteriorate stability of the nanofluids.
Considering the kinetic energy of nanoparticles, DLVO potential energy and steric repulsion between nanoparticles, a molecular approach is adopted to investigate the nanofluid stability for different nanofluids with polymeric surfactants and different operational conditions. Two types of polymeric surfactants were considered and stability diagrams introduced to show the conditions for which a nanofluid would be stable.
In the case of using PAA for a given temperature gradient, increasing the working fluid temperature required smaller nanoparticle diameters to result in a stable nanofluid (nanoparticles up to 13.2 nm diameter) and for PMAA, a stable nanofluid can be achieved with larger nanoparticle diameters (about 80nm) while increasing the working fluid temperature.
Challenges in Nano and Micro Scale Science and Technology, 2021
In this paper, multi objective Pareto optimization of frost formation in Micro Channel Heat Sink ... more In this paper, multi objective Pareto optimization of frost formation in Micro Channel Heat Sink (MCHS) with circular fins with square and triangular configurations is performed in three steps. In the first step, the fluid flow is solved numerically in a number of MCHS using CFD techniques. In numerical modeling, basic equations of humid air and frost, including continuum, momentum, energy and phase change mechanism are numerically solved. Flow type is transient and the microfluidic regime is slip flow. In the second step, CFD data is used to model the objective functions namely volume fraction of ice and the heat transfer in MCHS using GMDH type artificial neural networks. The accuracy of GMDH modeling of objective functions is investigated using different statistical models. Finally, polynomials extracted from the GMDH are used to multi-objective optimization of frost formation in MCHS using NSGA II algorithm. In this step, the Pareto front, which contains very useful information in the design of MCHS containing frost formation, will be extracted and deeply discussed. In the results section, points with unique features are introduced. It will be shown that the design information presented in the results about MCHS containing frost formation can only be extracted with a multi-objective optimization approach.
Challenges in Nano and Micro Scale Science and Technology, 2021
We investigate the phenomenon of electrokinetics in microchannels. Electroosmotic is one of the f... more We investigate the phenomenon of electrokinetics in microchannels. Electroosmotic is one of the four electrokinetic effects. Electroosmotic flow (EOF) is caused by the application of an electric field to an aqueous solution. The characteristics of the EOF depend on the nature of the surface potential distribution. EOF in microfluidic systems is limited to low Reynolds. As a result, species mixing in EOF systems is primarily due to diffusion. The surface heterogeneous of the microchannel walls causes the production of micro vortexes in the liquid. In this study, A two-dimensional microchannel is used to study the electroosmotic/pressure driven in Newtonian fluids. The equations governing the fluid flow in a rectangular microchannel are obtained based on the Lagrangian approach and using the densitybased weakly compressible smoothed particle hydrodynamics (WCSPH) method. We have analyzed the vortexes due to surface potential heterogeneity and investigated increasing the surface potential on the flow. The results show that increasing the surface potential causes the vortexes to grow and strengthens the velocity and mixing fields more.
Challenges in Nano and Micro Scale Science and Technology, 2021
In recent years, significant attention has been devoted to nanofluids to improve the thermal eff... more In recent years, significant attention has been devoted to nanofluids to improve the thermal efficiency of conventional cooling fluids. Copper nanoparticles are a proper candidate for this purpose due to their high thermal conductivity. In this study, stable copper nanoparticles with a 34.5 nm average diameter were synthesized via chemical reduction without an inert environment. The synthesized copper nanoparticles and also commercial copper nanoparticles with a 40 nm average size were used in ethylene glycol as the base fluid. Viscosity and rheological behavior of these nanofluids as important factors for assessment of flow behavior in heat exchange equipment were also investigated experimentally. The effects of volume fraction and temperature on nanofluid viscosity were investigated. Viscosity was measured in a 29.5-60 °C temperature range at low weight fractions of 0.0001, 0.0003, and 0.0005. The results were compared with the proposed models for the prediction of nanofluid viscosity, suggesting a correlation. The results show the Newtonian behavior of both nanofluids. Based on the results of a previous study, the heat transfer coefficient and thermal conductivity increased significantly (38.2 % for 0.03 wt. % nanofluid at Re=68 and 39.4% for 0.01 wt. %, respectively). Also, for both cases, nanofluid viscosity was smaller than the base fluid (for nanofluid B, 12.8% reduction at 1.06 vol. %). These results suggest copper nanofluid as an appropriate alternative for application in heat exchange equipment.
Challenges in Nano and Micro Scale Science and Technology, 2021
This paper examines experimentally the heat transfer of the internal convection of MgO-water nono... more This paper examines experimentally the heat transfer of the internal convection of MgO-water nonofluids in a copper tube for a fully turbulent regime under constant heat flux boundary condition. The Nusselt number and convective heat transfer coefficients of nonofluids in different volumetric concentrations (0, 0.05%, and 0.15%) of nonofluids were estimated. Local convective heat transfer coefficient was also observed at different points along the pipe at different Reynolds numbers. The results showed a larger heat transfer coefficient with nonofluids compared to the base fluid. Heat transfer coefficient increased with an increase in the flow rate of nofluids from 6 to 10 l/min and the concentration of nonofluids from 0 to 0.15 vol.%. Conversely, the heat transfer coefficient decreases with increasing the nanofluid inlet temperature from 30 to 40 °C .Nusselt numbers increased to 45.9% as a result of the implementation of nonofluids at concentration of 0.15 vol.% in comparison with the base fluid. The Taguchi method was also used to analyze the results statistically. The maximum Nusselt number in nonofluids, the effect of each operational parameter on the Nusselt number, as well as the optimal values of each parameter was determined.
Challenges in Nano and Micro Scale Science and Technology, 2021
In this study, the Multi-Objective Optimization (MOO) of HIV separation from blood sample in a La... more In this study, the Multi-Objective Optimization (MOO) of HIV separation from blood sample in a Lab on a Chip (LOC) is investigated using Computational Fluid Dynamics (CFD) and NSGA algorithm. The separation device consists of two horizontal microchannels separated by a porous layer. The flow is controlled by an infinitesimal channel section connected to one of the microchannels. First, using CFD approach, the fluid flow is studied in over 150 separation devices with different geometrical parameters. All performance parameters like separation efficiency and pressure drop are calculated. Then, already computed numerical results are targeted by a multi-objective genetic algorithm (NSGA II). In optimization process, eight different geometrical and process parameters are considered as optimization variables. Maximum separation efficiency and minimum pressure drop caused by separation are considered as two conflicting optimization objectives. Pareto front is presented to assist the design of the efficient separators. Optimization yielded the optimum configuration of the geometrical and process parameters for the highest efficiency and lowest pressure drop in HIV separation process.
Challenges in Nano and Micro Scale Science and Technology, 2021
The separation of micron-sized particles and their sorting is a critical issue in diagnosing canc... more The separation of micron-sized particles and their sorting is a critical issue in diagnosing cancer and biological analyses. For fast and accurate separation and sorting of circulating tumor cells (CTCs), various methods have been presented so far. CTCs which are responsible for cancer metastasis have the potential to provide significant prognostic and diagnostic values. In this paper, some procedures for the separation of CTCs are studied which are generally based on passive methods. These methods use the interaction between particles, flow field, and channel structure. In this study, various designs in connection with passive methods for separating and sorting CTCs are discussed, including filter/deformation, Pinched Flow Fractionation (PFF), Deterministic Lateral Displacement (DLD), inertia and Dean flow fractionation, tunable microfluidic systems, Hybrid microfluidics, and Carpet microfluidic chip technology. Overall, a list of challenges for the micro-fluidic-based cancer cell separation technologies needs to be dealt with to make them more applicable, useful, and ultimately more mature, from lab-oriented researches to real-world applications. It is suggested to perform numerical simulations by considering real shapes of rare cells. Besides, the impact of cell deformability, non-Newtonian impacts, and stretchable channels should be assessed in numerical examinations.
Challenges in Nano and Micro Scale Science and Technology, 2021
In this paper, forced convection flow and heat transfer of Cu-water nanofluid in U-Tube collector... more In this paper, forced convection flow and heat transfer of Cu-water nanofluid in U-Tube collector are studied. The three-dimensional governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE algorithm. Reynolds numbers are considered in laminar-turbulent range of 2000<Re<8000. The most efficient model was achieved by comparison of different parameters to reach the optimal case with the maximum exergy efficiency. From this study, it is concluded that in the case of using U-tube, instead of shell and tubes, the time that the fluid is inside the collector increases and leads to outlet temperature increase from the collector the exergy efficiency increases. Also, it is realized that enhance the outlet fluid temperature, energy efficiency and exergy efficiency. Generally, while the trend of exergy efficiency variation with effective parameters is increasing, applying the mixers precipitate the efficiency increment. In addition, for the case that the trend of exergy efficiency variation with changing these parameters is decreasing, the decreasing trend gets slow. The exergy efficiency of studied UTC at 14:00 has the maximum exergy efficiency among all studied times and about 71.54%. The received energy always reduces by increasing of operating temperature. The value of received energy at operating temperature of 23°C is about 0.347 kW/m 2. The nanofluid flow has higher thermal conductivity than the base fluid and can absorb more solar irradiances. But the nanofluid has also more dynamic viscosity than base fluid which increases the pressure drop penalty and friction factor in system. Finally, the highest exergy efficiency was obtained for the nanoparticle volume fraction of ϕ=4%. Therefore, the UTC with tube diameter of 8nm filled with Cu-water nanofluid with 4% volume fraction and 40nm nanoparticle diameter at Re=2000 is introduced as the best model in present study.
Challenges in Nano and Micro Scale Science and Technology, 2021
The present paper aims to study the effects of different mass fractions of silica nanoparticles o... more The present paper aims to study the effects of different mass fractions of silica nanoparticles on the tensile, compressive, and flexural mechanical properties of polymer composites via experimental methods and non-linear damage model. Epoxy polymers consist of two parts: the first part has a low viscosity, ML-506, as the epoxy base, and the second part contains a polyamide as a hardener, HA-11. Spherical silica nanoparticles with four different mass fractions of 0, 0.2, 0.5 and 1 % are dispersed into the epoxy polymer system under two different ultrasonic times. The tensile and flexural mechanical properties of the prepared samples are determined using standard tests. Experimental measurements show that the mechanical properties of polymer composites improve with increasing mass fraction of nanoparticles. In addition, increasing the ultrasonic time from half-an-hour to one hour is further improves the mechanical properties of polymer composites. A non-linear damage model based on the Weibull theory is used to interpret the flexural stress-strain relationships of the tested materials. The parameters in this model are tensile modulus E, Weibull scale parameter σ0 and Weibull shape parameter β. A good agreement is seen between the results of the stress-strain curve obtained from the above mentioned model and experimental results.
Challenges in Nano and Micro Scale Science and Technology, 2021
In this study, the efficacy of magnetic field on the two-phase nanofluid flow in the flattened tu... more In this study, the efficacy of magnetic field on the two-phase nanofluid flow in the flattened tube was numerically examined. Initially, the finite volume method was used to solve the flow field and temperature. Secondly, the two-phase flow model was utilized to simulate the nanofluid flow. The consequences are associated with previously published data and good agreement observed. Thirdly, the uniform magnetic field is presumed to be constant, non-uniform, and oscillating. The results indicate that heat transfer and friction coefficient enhance with growing flatness and the nanofluid volume fraction. In the case of the constant magnetic field is exerted in the three directions, the Nusselt number increases by about 2.5%. The 90° phase delay in the oscillating magnetic field improves the heat transfer coefficient by 2%. The non-uniform magnetic field of 0.5 Tesla rather than without magnetic field in volume fraction of 0.01-0.05 the heat transfer coefficient increases in about 1.6-2 times rather than the first mode. In addition, the velocity and temperature profile approached the uniform manner.
Challenges in Nano and Micro Scale Science and Technology, 2021
In this work, the energy and exergy efficiencies of a nanofluid-based direct absorption solar col... more In this work, the energy and exergy efficiencies of a nanofluid-based direct absorption solar collector (DASC) are examined experimentally. Attention is focused to analyze the consequences of installation of porous foam in the collector, concentration of the nanoparticles (NPs) in the working fluid, and volumetric flow rate of the nanofluid from the standpoints of the first law and second law of thermodynamics. The porous foam is made up of SiC while the nanofluid contains SiC NPs in water as the base fluid. The results indicate that the foam installation improves both efficiencies. The dominant parameter on the energy efficiency is recorded to be the volumetric flow rate of the nanofluid but the highest contribution on the exergy efficiency belongs to the NPs concentration in the working fluid. More precisely, maximum changes in the exergy efficiency due to the variation in the NPs concentration in the working fluid is recorded to be 63.2%. Meanwhile, it is found that the foam installation and the alternation of the volumetric flow rate of the nanofluid bring 38.2% and 25.3% variations in the exergy efficiency, respectively.
Challenges in Nano and Micro Scale Science and Technology, 2020
In this paper, the fully developed non-ideal gaseous slip flow in circular, parallel plates, and ... more In this paper, the fully developed non-ideal gaseous slip flow in circular, parallel plates, and rectangular microchannels is analyzed analytically by using Navier-Stokes equations to obtain the analytical exact solution. Van der Waals equation is used as the state equation of non-ideal gas. It is assumed that the flow is isothermal, incompressible, steady state, two-dimensional and fully developed, slip flow regime with consideration the first and second orders boundary conditions. It is developed the models for predicting the local and mean velocity, normalized Poiseuille number, and the ratio of density for the first and second orders boundary conditions. The results show that the rarefication process and Poiseuille number are a function of the Knudsen number and the cross-section geometry and Poiseuille number is independent of fluid material properties, velocity, and temperature. Also, for circular microchannel, the rarefication process occurs faster than the others.
Challenges in Nano and Micro Scale Science and Technology, 2020
This study investigates the effect of adding SiO2 nanoparticles to the amine solution on the mass... more This study investigates the effect of adding SiO2 nanoparticles to the amine solution on the mass transfer coefficients with the aim to obtain effective solvent in the CO2 capturing process. An aqueous mixture of the methyl di-ethanol amine (MDEA), activated by blending with Piperazine (PZ) (a-MDEA), was considered as base absorption solvent. The addition of SiO2 nanoparticles with six different concentrations to the base absorption solvent was then studied. The absorption process took place in an agitated batch reactor at 40 ºC. Considering the gas pressure drop in the reactor the CO2 absorption and mass transfer rates were obtained for all types of the solvents and were compared with each other. Results revealed that two regimes of fast and slow were involved in the CO2 absorption process, where the overall mass transfer of the fast regime was more than 100 times that of the slow one. The results indicated that the liquid phase controlled the mass transfer in the CO2 absorption process. Furthermore, the maximum increase in the absorption rate was happenned when the concentration of SiO2 nanoparticles was set at 25 ppm in the solvent. In this regard, the enhancement was at least 85% increase in the overall mass transfer coefficient. The findings of this study can be used to design new nanoparticle-based solvents and reduce the cost of the CO2 capturing process.
Challenges in Nano and Micro Scale Science and Technology, 2020
In this paper, by employing the Computational Fluid Dynamics (CFD) and applying the NSGA II algor... more In this paper, by employing the Computational Fluid Dynamics (CFD) and applying the NSGA II algorithm, the multiobjective optimization of frost formation in the interrupted Micro Channels Heat sinks (MCHS) is investigated considering microfluidic effects in slip flow regime. For numerical modeling, basic equations of humid air and frost including continuum, momentum, energy and phase change mechanism are numerically solved and results are compared with reported data and good agreements are observed. Knudsen number (Kn) is changed so that slip flow regime requirement is accomplished. The design variables are geometrical parameters of MCHSc. In the results section, the Pareto front, which simultaneously displays the changes of the heat transfer rate and the frost formation, will be presented, and it will be demonstrated that the Pareto front conveys very important results for the two phase thermal designing of MCHSc. Finally, the multi-objective optimization results computed in this paper are compared with the CFD data and very useful and valuable information is obtained.
Challenges in Nano and Micro Scale Science and Technology, 2020
In this research, a flat plate solar collector with a triangular geometry, which is designed and ... more In this research, a flat plate solar collector with a triangular geometry, which is designed and built by the author and based on the ASHRAE93-2010 standard, has been experimentally studied. The triangular solar collector has no riser and has spiral tubes containing fluid from the inlet to the outlet of the collector. To study water and Al2O3-water nanofluid in concentrations of 0.1, 0.2 and 0.3% and different flow rates from 0.0063 to 0.0378 lit/s have been used, which has been studied experimentally based on environmental criteria such as temperature and radiation and effective thermal parameters such as concentration and flow. Studies show that the triangular solar collector, due to its stable geometry and due to the reduction of the tube length in relation to the area, has a suitable performance for water heaters and can also be used. Time constant for triangular solar collector was between 2.5-4.5 minutes in flow rate ranges. The average efficiency increase when using nanofluids instead of water was about 12.4% and the maximum efficiency obtained at a concentration of 0.3% and a flow rate of 0.0378 was more than 68.3%. Also, in measuring the pressure drop in the collector, it was found that the pressure drop was very small and less than 0.1 bar.
Challenges in Nano and Micro Scale Science and Technology, 2020
Today, green synthesis method for manufacturing of the nanoparticles (NPs) is the common rout for... more Today, green synthesis method for manufacturing of the nanoparticles (NPs) is the common rout for biomedical application. In this article, ZnFe2O4 NPs are fabricated by solgel method in the presence of surfactants. The samples are studied by x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), field effect scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM), x-ray fluorescence (XRF) and fourier transform infrared spectroscopy (FTIR). The XRD results show hexagonal wurtzite structure of ZnO and spinel phase of rhombohedral α-Fe2O3. The crystallite size of annealed samples are calculated around 57 nm. The SEM images show that the NPs change from rod-shape to nanoparticle clusters of ZnFe2O4 by increasing temperature after annealing. The TEM studies show the formation of Fe2O3 shell around NPs with a diameter of 10 nm for as-prepared samples. The sharp peaks in FTIR spectrum indicate the stretching vibrations of Fe and Zn groups in the frequencies of 675, 602 cm-1 and 476 cm-1. The results of magnetic measurements show coercive field and saturation magnetism around 2298 G and 34 memu/g respectively, for as-prepared samples. The XRF analysis demonstrate the decreasing of the Fe weight percent from 41.28 %Wt. to 39.64 %Wt., by increasing temperature.
Challenges in Nano and Micro Scale Science and Technology, 2020
Many studies have shown critical heat flux (CHF) enhancement by adding metals and nonmetals nanop... more Many studies have shown critical heat flux (CHF) enhancement by adding metals and nonmetals nanoparticles to water in flow boiling. In this study, we investigated critical heat flux enhancement mechanism by adding multi-walled carbon nanotubes (MWCNTs) to pure water in flow boiling in a 2 m horizontal tube under atmospheric pressure. Also, the feasibility of MWCNTs-GA/water nanofluid as an advanced and economic coolant was assessed for cooling the high power thermal systems. For preparing this nanofluid, gum Arabic as a surfactant and MWCNTs as nanoparticles were used in the ratio 1:1 with concentrations of 0.001, 0.005, 0.01 wt%. The measuring zeta potential showed nanofluid stability. Results indicated the relative stability of suspension in all concentrations. Also the results of the experiments showed that the critical heat flux of the nanofluid increases with increasing in concentration and mass flux at the inlet temperatures of 60 and 70 °C. The CHF enhancement was observed for nanofluids and it was greater than that for pure water. It is due to the deposition of MWCNTs nanoparticles and improvement of wettability in the heat transfer surface. The maximum CHF enhancement was observed at 0.01 wt% concentration, a mass flux of 620 kg/m 2 s and the inlet temperature of 60 o C. The local exit equality of the nanofluid in a fixed mass flux at the inlet temperatures was less than that for pure water and the lowest local exit equality of nanofluid was at inlet temperature of 60 °C and concentration of 0.001wt%.
Challenges in Nano and Micro Scale Science and Technology, 2021
This article is concerned with study of the steady and incompressible three-dimensional flow of m... more This article is concerned with study of the steady and incompressible three-dimensional flow of magnetohydrodynamic couple stress nanofluids over a stretching sheet through a porous medium under influence of, non-linear thermal radiation and heat generation/absorption, taking into account effects of both Brownian motion coefficient and thermophoresis coefficient. On the other hand, the system of nonlinear partial differential equations governing the flow process has been transformed into a system of nonlinear ordinary differential equations using similarity transformations and dimensionless variables, knowing that the numerical method used to solve the new system of differential equations is the fourth-order Runge-Kutta method with the shooting technique in the code of MATLAB program. The effects of all physical parameters resulting from this study on the distributions of velocity, temperature and concentration of nanoparticles within the base fluid were studied by means of graphs that were made by the MATLAB program. Finally, some of the results of the current study showed that the effects of the magnetic field parameter and Darcy number on the velocity distribution were negative, while their effect on the concentration of nanoparticle distribution was positive.
Challenges in Nano and Micro Scale Science and Technology, 2021
Friction is created in the gas seals due to the relative motion of the two fixed and rotary surfa... more Friction is created in the gas seals due to the relative motion of the two fixed and rotary surfaces, causing power dissipation, erosion, heat generation and temperature rise of the surfaces so a distance between two surfaces should be created. In the structure of Dry Gas Seals (DGS), the grooves on the rotating surface are created, which is the key to the gas penetration between the surfaces. The geometrical parameters of grooves would have substantial effect on the amount of leakage, so it is of high importance to indicate the best shape and operating condition of grooves. In this research, the effect of geometric parameters of a DGS with trapezoidal grooves on the leakage rate and open force is investigated. The geometric parameters are the depth of the triangular and square sections, the length of the groove, the angle of the square part and the angle of the groove. The length of the groove has a substantial impact on leakage, and by doubling the length, the leakage rate is raised to 58%. It is concluded that when the angle of the square section is 7° and the angle of groove is 22°, the minimum leakage occurs in the range of parameters studied. Taguchi algorithm is also applied to optimize the shape parameters of the groove to minimize open force and leakage of the seal. Optimal dimensions for grooves in the range of operating conditions in this study are triangle depth = 3μm, quad − depth = 10μm, Length = 8mm, groove angle = 18°, rectangle angle = 5°. The same optimum conditions are obtained by considering energy and exergy terms.
Challenges in Nano and Micro Scale Science and Technology, 2021
The temperature of the phase change material remains almost constant when the phase changes. It m... more The temperature of the phase change material remains almost constant when the phase changes. It means that these materials have a high heat capacity during phase change. This property causes the particles containing these materials to act like distributed heat sinks throughout the field and result in heat transfer increment. However, if these particles are placed inside the thermal boundary layer, they will have a greater impact on the heat transfer rate. The vertical velocity component in the entrance length, prevents particles from being placed near the wall. On the other hand, in this study, the particle coating is iron oxide, which are able to move towards the wall by magnetic force. This magnetic field pulls the particles toward the heated wall and inside the thermal boundary layer. To solve the governing equations, twophase Eulerian-Lagrangian model has been used. The PCM is Paraffin wax with 30 microns diameter and, particle volume concentration is 10%. This study covers a wide range of Reynolds numbers (100<Re<500), subcooling numbers up to 0.75 and magnetic field strength (H0) up to 2.1e-8 A.m-1. The results show 16.56% increase in Nusselt number for Re=100 and, H0=2.1e-8 A.m-1 .
Challenges in Nano and Micro Scale Science and Technology, 2021
Recently, using volumetric receivers as a novel idea to collect solar energy was considered. Sola... more Recently, using volumetric receivers as a novel idea to collect solar energy was considered. Solar radiation volumetrically absorbers with a heat transfer fluid which flows through a transparent tube. Nanofluids as working fluids were proposed by different researchers because of their interesting absorption coefficient as well as an important heat transfer coefficient. However, conditions such as the severe temperature gradient in absorber tubes and high temperature of working heat transfer fluid, deteriorate stability of the nanofluids.
Considering the kinetic energy of nanoparticles, DLVO potential energy and steric repulsion between nanoparticles, a molecular approach is adopted to investigate the nanofluid stability for different nanofluids with polymeric surfactants and different operational conditions. Two types of polymeric surfactants were considered and stability diagrams introduced to show the conditions for which a nanofluid would be stable.
In the case of using PAA for a given temperature gradient, increasing the working fluid temperature required smaller nanoparticle diameters to result in a stable nanofluid (nanoparticles up to 13.2 nm diameter) and for PMAA, a stable nanofluid can be achieved with larger nanoparticle diameters (about 80nm) while increasing the working fluid temperature.
Challenges in Nano and Micro Scale Science and Technology, 2021
In this paper, multi objective Pareto optimization of frost formation in Micro Channel Heat Sink ... more In this paper, multi objective Pareto optimization of frost formation in Micro Channel Heat Sink (MCHS) with circular fins with square and triangular configurations is performed in three steps. In the first step, the fluid flow is solved numerically in a number of MCHS using CFD techniques. In numerical modeling, basic equations of humid air and frost, including continuum, momentum, energy and phase change mechanism are numerically solved. Flow type is transient and the microfluidic regime is slip flow. In the second step, CFD data is used to model the objective functions namely volume fraction of ice and the heat transfer in MCHS using GMDH type artificial neural networks. The accuracy of GMDH modeling of objective functions is investigated using different statistical models. Finally, polynomials extracted from the GMDH are used to multi-objective optimization of frost formation in MCHS using NSGA II algorithm. In this step, the Pareto front, which contains very useful information in the design of MCHS containing frost formation, will be extracted and deeply discussed. In the results section, points with unique features are introduced. It will be shown that the design information presented in the results about MCHS containing frost formation can only be extracted with a multi-objective optimization approach.
Challenges in Nano and Micro Scale Science and Technology, 2021
We investigate the phenomenon of electrokinetics in microchannels. Electroosmotic is one of the f... more We investigate the phenomenon of electrokinetics in microchannels. Electroosmotic is one of the four electrokinetic effects. Electroosmotic flow (EOF) is caused by the application of an electric field to an aqueous solution. The characteristics of the EOF depend on the nature of the surface potential distribution. EOF in microfluidic systems is limited to low Reynolds. As a result, species mixing in EOF systems is primarily due to diffusion. The surface heterogeneous of the microchannel walls causes the production of micro vortexes in the liquid. In this study, A two-dimensional microchannel is used to study the electroosmotic/pressure driven in Newtonian fluids. The equations governing the fluid flow in a rectangular microchannel are obtained based on the Lagrangian approach and using the densitybased weakly compressible smoothed particle hydrodynamics (WCSPH) method. We have analyzed the vortexes due to surface potential heterogeneity and investigated increasing the surface potential on the flow. The results show that increasing the surface potential causes the vortexes to grow and strengthens the velocity and mixing fields more.
Challenges in Nano and Micro Scale Science and Technology, 2021
In recent years, significant attention has been devoted to nanofluids to improve the thermal eff... more In recent years, significant attention has been devoted to nanofluids to improve the thermal efficiency of conventional cooling fluids. Copper nanoparticles are a proper candidate for this purpose due to their high thermal conductivity. In this study, stable copper nanoparticles with a 34.5 nm average diameter were synthesized via chemical reduction without an inert environment. The synthesized copper nanoparticles and also commercial copper nanoparticles with a 40 nm average size were used in ethylene glycol as the base fluid. Viscosity and rheological behavior of these nanofluids as important factors for assessment of flow behavior in heat exchange equipment were also investigated experimentally. The effects of volume fraction and temperature on nanofluid viscosity were investigated. Viscosity was measured in a 29.5-60 °C temperature range at low weight fractions of 0.0001, 0.0003, and 0.0005. The results were compared with the proposed models for the prediction of nanofluid viscosity, suggesting a correlation. The results show the Newtonian behavior of both nanofluids. Based on the results of a previous study, the heat transfer coefficient and thermal conductivity increased significantly (38.2 % for 0.03 wt. % nanofluid at Re=68 and 39.4% for 0.01 wt. %, respectively). Also, for both cases, nanofluid viscosity was smaller than the base fluid (for nanofluid B, 12.8% reduction at 1.06 vol. %). These results suggest copper nanofluid as an appropriate alternative for application in heat exchange equipment.
Challenges in Nano and Micro Scale Science and Technology, 2021
This paper examines experimentally the heat transfer of the internal convection of MgO-water nono... more This paper examines experimentally the heat transfer of the internal convection of MgO-water nonofluids in a copper tube for a fully turbulent regime under constant heat flux boundary condition. The Nusselt number and convective heat transfer coefficients of nonofluids in different volumetric concentrations (0, 0.05%, and 0.15%) of nonofluids were estimated. Local convective heat transfer coefficient was also observed at different points along the pipe at different Reynolds numbers. The results showed a larger heat transfer coefficient with nonofluids compared to the base fluid. Heat transfer coefficient increased with an increase in the flow rate of nofluids from 6 to 10 l/min and the concentration of nonofluids from 0 to 0.15 vol.%. Conversely, the heat transfer coefficient decreases with increasing the nanofluid inlet temperature from 30 to 40 °C .Nusselt numbers increased to 45.9% as a result of the implementation of nonofluids at concentration of 0.15 vol.% in comparison with the base fluid. The Taguchi method was also used to analyze the results statistically. The maximum Nusselt number in nonofluids, the effect of each operational parameter on the Nusselt number, as well as the optimal values of each parameter was determined.
Challenges in Nano and Micro Scale Science and Technology, 2021
In this study, the Multi-Objective Optimization (MOO) of HIV separation from blood sample in a La... more In this study, the Multi-Objective Optimization (MOO) of HIV separation from blood sample in a Lab on a Chip (LOC) is investigated using Computational Fluid Dynamics (CFD) and NSGA algorithm. The separation device consists of two horizontal microchannels separated by a porous layer. The flow is controlled by an infinitesimal channel section connected to one of the microchannels. First, using CFD approach, the fluid flow is studied in over 150 separation devices with different geometrical parameters. All performance parameters like separation efficiency and pressure drop are calculated. Then, already computed numerical results are targeted by a multi-objective genetic algorithm (NSGA II). In optimization process, eight different geometrical and process parameters are considered as optimization variables. Maximum separation efficiency and minimum pressure drop caused by separation are considered as two conflicting optimization objectives. Pareto front is presented to assist the design of the efficient separators. Optimization yielded the optimum configuration of the geometrical and process parameters for the highest efficiency and lowest pressure drop in HIV separation process.
Challenges in Nano and Micro Scale Science and Technology, 2021
The separation of micron-sized particles and their sorting is a critical issue in diagnosing canc... more The separation of micron-sized particles and their sorting is a critical issue in diagnosing cancer and biological analyses. For fast and accurate separation and sorting of circulating tumor cells (CTCs), various methods have been presented so far. CTCs which are responsible for cancer metastasis have the potential to provide significant prognostic and diagnostic values. In this paper, some procedures for the separation of CTCs are studied which are generally based on passive methods. These methods use the interaction between particles, flow field, and channel structure. In this study, various designs in connection with passive methods for separating and sorting CTCs are discussed, including filter/deformation, Pinched Flow Fractionation (PFF), Deterministic Lateral Displacement (DLD), inertia and Dean flow fractionation, tunable microfluidic systems, Hybrid microfluidics, and Carpet microfluidic chip technology. Overall, a list of challenges for the micro-fluidic-based cancer cell separation technologies needs to be dealt with to make them more applicable, useful, and ultimately more mature, from lab-oriented researches to real-world applications. It is suggested to perform numerical simulations by considering real shapes of rare cells. Besides, the impact of cell deformability, non-Newtonian impacts, and stretchable channels should be assessed in numerical examinations.
Challenges in Nano and Micro Scale Science and Technology, 2021
In this paper, forced convection flow and heat transfer of Cu-water nanofluid in U-Tube collector... more In this paper, forced convection flow and heat transfer of Cu-water nanofluid in U-Tube collector are studied. The three-dimensional governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE algorithm. Reynolds numbers are considered in laminar-turbulent range of 2000<Re<8000. The most efficient model was achieved by comparison of different parameters to reach the optimal case with the maximum exergy efficiency. From this study, it is concluded that in the case of using U-tube, instead of shell and tubes, the time that the fluid is inside the collector increases and leads to outlet temperature increase from the collector the exergy efficiency increases. Also, it is realized that enhance the outlet fluid temperature, energy efficiency and exergy efficiency. Generally, while the trend of exergy efficiency variation with effective parameters is increasing, applying the mixers precipitate the efficiency increment. In addition, for the case that the trend of exergy efficiency variation with changing these parameters is decreasing, the decreasing trend gets slow. The exergy efficiency of studied UTC at 14:00 has the maximum exergy efficiency among all studied times and about 71.54%. The received energy always reduces by increasing of operating temperature. The value of received energy at operating temperature of 23°C is about 0.347 kW/m 2. The nanofluid flow has higher thermal conductivity than the base fluid and can absorb more solar irradiances. But the nanofluid has also more dynamic viscosity than base fluid which increases the pressure drop penalty and friction factor in system. Finally, the highest exergy efficiency was obtained for the nanoparticle volume fraction of ϕ=4%. Therefore, the UTC with tube diameter of 8nm filled with Cu-water nanofluid with 4% volume fraction and 40nm nanoparticle diameter at Re=2000 is introduced as the best model in present study.
Challenges in Nano and Micro Scale Science and Technology, 2021
The present paper aims to study the effects of different mass fractions of silica nanoparticles o... more The present paper aims to study the effects of different mass fractions of silica nanoparticles on the tensile, compressive, and flexural mechanical properties of polymer composites via experimental methods and non-linear damage model. Epoxy polymers consist of two parts: the first part has a low viscosity, ML-506, as the epoxy base, and the second part contains a polyamide as a hardener, HA-11. Spherical silica nanoparticles with four different mass fractions of 0, 0.2, 0.5 and 1 % are dispersed into the epoxy polymer system under two different ultrasonic times. The tensile and flexural mechanical properties of the prepared samples are determined using standard tests. Experimental measurements show that the mechanical properties of polymer composites improve with increasing mass fraction of nanoparticles. In addition, increasing the ultrasonic time from half-an-hour to one hour is further improves the mechanical properties of polymer composites. A non-linear damage model based on the Weibull theory is used to interpret the flexural stress-strain relationships of the tested materials. The parameters in this model are tensile modulus E, Weibull scale parameter σ0 and Weibull shape parameter β. A good agreement is seen between the results of the stress-strain curve obtained from the above mentioned model and experimental results.
Challenges in Nano and Micro Scale Science and Technology, 2021
In this study, the efficacy of magnetic field on the two-phase nanofluid flow in the flattened tu... more In this study, the efficacy of magnetic field on the two-phase nanofluid flow in the flattened tube was numerically examined. Initially, the finite volume method was used to solve the flow field and temperature. Secondly, the two-phase flow model was utilized to simulate the nanofluid flow. The consequences are associated with previously published data and good agreement observed. Thirdly, the uniform magnetic field is presumed to be constant, non-uniform, and oscillating. The results indicate that heat transfer and friction coefficient enhance with growing flatness and the nanofluid volume fraction. In the case of the constant magnetic field is exerted in the three directions, the Nusselt number increases by about 2.5%. The 90° phase delay in the oscillating magnetic field improves the heat transfer coefficient by 2%. The non-uniform magnetic field of 0.5 Tesla rather than without magnetic field in volume fraction of 0.01-0.05 the heat transfer coefficient increases in about 1.6-2 times rather than the first mode. In addition, the velocity and temperature profile approached the uniform manner.
Challenges in Nano and Micro Scale Science and Technology, 2021
In this work, the energy and exergy efficiencies of a nanofluid-based direct absorption solar col... more In this work, the energy and exergy efficiencies of a nanofluid-based direct absorption solar collector (DASC) are examined experimentally. Attention is focused to analyze the consequences of installation of porous foam in the collector, concentration of the nanoparticles (NPs) in the working fluid, and volumetric flow rate of the nanofluid from the standpoints of the first law and second law of thermodynamics. The porous foam is made up of SiC while the nanofluid contains SiC NPs in water as the base fluid. The results indicate that the foam installation improves both efficiencies. The dominant parameter on the energy efficiency is recorded to be the volumetric flow rate of the nanofluid but the highest contribution on the exergy efficiency belongs to the NPs concentration in the working fluid. More precisely, maximum changes in the exergy efficiency due to the variation in the NPs concentration in the working fluid is recorded to be 63.2%. Meanwhile, it is found that the foam installation and the alternation of the volumetric flow rate of the nanofluid bring 38.2% and 25.3% variations in the exergy efficiency, respectively.
Challenges in Nano and Micro Scale Science and Technology, 2020
In this paper, the fully developed non-ideal gaseous slip flow in circular, parallel plates, and ... more In this paper, the fully developed non-ideal gaseous slip flow in circular, parallel plates, and rectangular microchannels is analyzed analytically by using Navier-Stokes equations to obtain the analytical exact solution. Van der Waals equation is used as the state equation of non-ideal gas. It is assumed that the flow is isothermal, incompressible, steady state, two-dimensional and fully developed, slip flow regime with consideration the first and second orders boundary conditions. It is developed the models for predicting the local and mean velocity, normalized Poiseuille number, and the ratio of density for the first and second orders boundary conditions. The results show that the rarefication process and Poiseuille number are a function of the Knudsen number and the cross-section geometry and Poiseuille number is independent of fluid material properties, velocity, and temperature. Also, for circular microchannel, the rarefication process occurs faster than the others.
Challenges in Nano and Micro Scale Science and Technology, 2020
This study investigates the effect of adding SiO2 nanoparticles to the amine solution on the mass... more This study investigates the effect of adding SiO2 nanoparticles to the amine solution on the mass transfer coefficients with the aim to obtain effective solvent in the CO2 capturing process. An aqueous mixture of the methyl di-ethanol amine (MDEA), activated by blending with Piperazine (PZ) (a-MDEA), was considered as base absorption solvent. The addition of SiO2 nanoparticles with six different concentrations to the base absorption solvent was then studied. The absorption process took place in an agitated batch reactor at 40 ºC. Considering the gas pressure drop in the reactor the CO2 absorption and mass transfer rates were obtained for all types of the solvents and were compared with each other. Results revealed that two regimes of fast and slow were involved in the CO2 absorption process, where the overall mass transfer of the fast regime was more than 100 times that of the slow one. The results indicated that the liquid phase controlled the mass transfer in the CO2 absorption process. Furthermore, the maximum increase in the absorption rate was happenned when the concentration of SiO2 nanoparticles was set at 25 ppm in the solvent. In this regard, the enhancement was at least 85% increase in the overall mass transfer coefficient. The findings of this study can be used to design new nanoparticle-based solvents and reduce the cost of the CO2 capturing process.
Challenges in Nano and Micro Scale Science and Technology, 2020
In this paper, by employing the Computational Fluid Dynamics (CFD) and applying the NSGA II algor... more In this paper, by employing the Computational Fluid Dynamics (CFD) and applying the NSGA II algorithm, the multiobjective optimization of frost formation in the interrupted Micro Channels Heat sinks (MCHS) is investigated considering microfluidic effects in slip flow regime. For numerical modeling, basic equations of humid air and frost including continuum, momentum, energy and phase change mechanism are numerically solved and results are compared with reported data and good agreements are observed. Knudsen number (Kn) is changed so that slip flow regime requirement is accomplished. The design variables are geometrical parameters of MCHSc. In the results section, the Pareto front, which simultaneously displays the changes of the heat transfer rate and the frost formation, will be presented, and it will be demonstrated that the Pareto front conveys very important results for the two phase thermal designing of MCHSc. Finally, the multi-objective optimization results computed in this paper are compared with the CFD data and very useful and valuable information is obtained.
Challenges in Nano and Micro Scale Science and Technology, 2020
In this research, a flat plate solar collector with a triangular geometry, which is designed and ... more In this research, a flat plate solar collector with a triangular geometry, which is designed and built by the author and based on the ASHRAE93-2010 standard, has been experimentally studied. The triangular solar collector has no riser and has spiral tubes containing fluid from the inlet to the outlet of the collector. To study water and Al2O3-water nanofluid in concentrations of 0.1, 0.2 and 0.3% and different flow rates from 0.0063 to 0.0378 lit/s have been used, which has been studied experimentally based on environmental criteria such as temperature and radiation and effective thermal parameters such as concentration and flow. Studies show that the triangular solar collector, due to its stable geometry and due to the reduction of the tube length in relation to the area, has a suitable performance for water heaters and can also be used. Time constant for triangular solar collector was between 2.5-4.5 minutes in flow rate ranges. The average efficiency increase when using nanofluids instead of water was about 12.4% and the maximum efficiency obtained at a concentration of 0.3% and a flow rate of 0.0378 was more than 68.3%. Also, in measuring the pressure drop in the collector, it was found that the pressure drop was very small and less than 0.1 bar.
Challenges in Nano and Micro Scale Science and Technology, 2020
Today, green synthesis method for manufacturing of the nanoparticles (NPs) is the common rout for... more Today, green synthesis method for manufacturing of the nanoparticles (NPs) is the common rout for biomedical application. In this article, ZnFe2O4 NPs are fabricated by solgel method in the presence of surfactants. The samples are studied by x-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), field effect scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM), x-ray fluorescence (XRF) and fourier transform infrared spectroscopy (FTIR). The XRD results show hexagonal wurtzite structure of ZnO and spinel phase of rhombohedral α-Fe2O3. The crystallite size of annealed samples are calculated around 57 nm. The SEM images show that the NPs change from rod-shape to nanoparticle clusters of ZnFe2O4 by increasing temperature after annealing. The TEM studies show the formation of Fe2O3 shell around NPs with a diameter of 10 nm for as-prepared samples. The sharp peaks in FTIR spectrum indicate the stretching vibrations of Fe and Zn groups in the frequencies of 675, 602 cm-1 and 476 cm-1. The results of magnetic measurements show coercive field and saturation magnetism around 2298 G and 34 memu/g respectively, for as-prepared samples. The XRF analysis demonstrate the decreasing of the Fe weight percent from 41.28 %Wt. to 39.64 %Wt., by increasing temperature.
Challenges in Nano and Micro Scale Science and Technology, 2020
Many studies have shown critical heat flux (CHF) enhancement by adding metals and nonmetals nanop... more Many studies have shown critical heat flux (CHF) enhancement by adding metals and nonmetals nanoparticles to water in flow boiling. In this study, we investigated critical heat flux enhancement mechanism by adding multi-walled carbon nanotubes (MWCNTs) to pure water in flow boiling in a 2 m horizontal tube under atmospheric pressure. Also, the feasibility of MWCNTs-GA/water nanofluid as an advanced and economic coolant was assessed for cooling the high power thermal systems. For preparing this nanofluid, gum Arabic as a surfactant and MWCNTs as nanoparticles were used in the ratio 1:1 with concentrations of 0.001, 0.005, 0.01 wt%. The measuring zeta potential showed nanofluid stability. Results indicated the relative stability of suspension in all concentrations. Also the results of the experiments showed that the critical heat flux of the nanofluid increases with increasing in concentration and mass flux at the inlet temperatures of 60 and 70 °C. The CHF enhancement was observed for nanofluids and it was greater than that for pure water. It is due to the deposition of MWCNTs nanoparticles and improvement of wettability in the heat transfer surface. The maximum CHF enhancement was observed at 0.01 wt% concentration, a mass flux of 620 kg/m 2 s and the inlet temperature of 60 o C. The local exit equality of the nanofluid in a fixed mass flux at the inlet temperatures was less than that for pure water and the lowest local exit equality of nanofluid was at inlet temperature of 60 °C and concentration of 0.001wt%.
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Papers by Challenges in Nano and Micro Scale Science and Technology
Considering the kinetic energy of nanoparticles, DLVO potential energy and steric repulsion between nanoparticles, a molecular approach is adopted to investigate the nanofluid stability for different nanofluids with polymeric surfactants and different operational conditions. Two types of polymeric surfactants were considered and stability diagrams introduced to show the conditions for which a nanofluid would be stable.
In the case of using PAA for a given temperature gradient, increasing the working fluid temperature required smaller nanoparticle diameters to result in a stable nanofluid (nanoparticles up to 13.2 nm diameter) and for PMAA, a stable nanofluid can be achieved with larger nanoparticle diameters (about 80nm) while increasing the working fluid temperature.
Considering the kinetic energy of nanoparticles, DLVO potential energy and steric repulsion between nanoparticles, a molecular approach is adopted to investigate the nanofluid stability for different nanofluids with polymeric surfactants and different operational conditions. Two types of polymeric surfactants were considered and stability diagrams introduced to show the conditions for which a nanofluid would be stable.
In the case of using PAA for a given temperature gradient, increasing the working fluid temperature required smaller nanoparticle diameters to result in a stable nanofluid (nanoparticles up to 13.2 nm diameter) and for PMAA, a stable nanofluid can be achieved with larger nanoparticle diameters (about 80nm) while increasing the working fluid temperature.