In the present study, we report the results of the experiments conducted on the convective heat transfer of graphene nano-platelets dispersed in water-ethylene glycol. The graphene nano-suspension ...was employed as a coolant inside a micro-channel and heat-transfer coefficient (HTC) and pressure drop (PD) values of the system were reported at different operating conditions. The results demonstrated that the use of graphene nano-platelets can potentially augment the thermal conductivity of the working fluid by 32.1% (at wt. % = 0.3 at 60 °C). Likewise, GNP nano-suspension promoted the Brownian motion and thermophoresis effect, such that for the tests conducted within the mass fractions of 0.1%–0.3%, the HTC of the system was improved. However, a trade-off was identified between the PD value and the HTC. By assessing the thermal performance evaluation criteria (TPEC) of the system, it was identified that the thermal performance of the system increased by 21% despite a 12.1% augmentation in the PD value. Furthermore, with an increment in the fluid flow and heat-flux applied to the micro-channel, the HTC was augmented, showing the potential of the nano-suspension to be utilized in high heat-flux thermal applications.
Bio-fuel has come under consideration due to the effect of fossil oil crisis. Bio-fuels are acting as a renewable replacement of petroleum fuels due to some environmental and economic benefits. ...Bio-fuel can be produced from different kinds of raw materials. Researchers have seen that absolute utilization of bio-fuel is not appreciable as it will affect the food chain but the blend of bio-fuel with conventional fuel could precisely reduce its use and become beneficial to green house effect. It has been inferred that in the hot and cold environment bio-fuel is not fully convenient to replace fossil fuel. In the controlled environment with modified combustion equipment, biodiesel can be used as an alternate fuel. Research results reveal that bio-fuel has lower heating value in comparison to diesel fuel so it is consumed more in fuel-break mean effective power ratio and emits more NOx in comparison to the diesel fuel. Thus there remains a compromise between GHG emission and saving of fossil fuel energy by introducing bio-fuel either totally or as a blending component of engine fuel. Finally, bio-fuel could be considered as a replenishable energy source which might pave the future pathway management and planning of energy.
Solar-driven water desalination technologies are rapidly developing with various links to other renewable sources. However, the efficiency of such systems severely depends on the design parameters. ...The present study focused on using graphene oxide (GO) with the Φ = 0.2, 0.4 and 0.6 wt.% dispersed in paraffin, as phase-change materials (PCMs), to improve the productivity of a solar still for desalination applications. The outcomes showed that by adding more graphene oxide to paraffin, the melting temperature got reduced. Solar still with GO/paraffin showed 25% productivity improvement in comparison with the solar still with only PCM. The obtained Nusselt number during the melting time also represented that free convection heat transfer into the melted region of the solar still has been enhanced by adding dispersed GO to the PCM, compared to the base paraffin. Also, increasing the hot wall temperature augments the Nusselt number. Finally, an empirical equation was derived to correlate the average Nusselt number as a function of Rayleigh number (Ra), the Stefan number (Ste), the subcooling factor (Sb), and the Fourier number (Fo). The obtained correlation depicted that Nusselt number enhancement has a reverse relation with Fourier number.
In the present work, an experimental investigation is performed to assess the thermal and electrical performance of a photovoltaic solar panel cooling with multi-walled carbon nanotube–water/ethylene ...glycol (50:50) nano-suspension (MWCNT/WEG50). The prepared nanofluid was stabilized using an ultrasonic homogenizer together with the addition of 0.1vol% of nonylphenol ethoxylates at pH = 8.9. To reduce the heat loss and to improve the heat transfer rate between the coolant and the panel, a cooling jacket was designed and attached to the solar panel. It was also filled with multi-walled carbon nanotube–paraffin phase change material (PCM) and the cooling pipes were passed through the PCM. The MWCNT/WEG50 nanofluid was introduced into the pipes, while the nano-PCM was in the cooling jacket. The electrical and thermal power of the system and equivalent electrical–thermal power of the system was assessed at various local times and at different mass fractions of MWCNTs. Results showed that with an increase in the mass concentration of the coolant, the electricity and power production were promoted, while with an increase in the mass concentration of the nanofluid, the pumping power was augmented resulting in the decrease in the thermal–electrical equivalent power. It was identified that a MWCNT/WEG50 nano-suspension at 0.2wt% can represent the highest thermal and electrical performance of 292.1 W/m2. It was also identified that at 0.2wt%, ~45% of the electricity and 44% of the thermal power can be produced with a photovoltaic (PV) panel between 1:30 pm to 3:30 pm.
We present a numerical investigation of tapered arteries that addresses the transient simulation of non-Newtonian bio-magnetic fluid dynamics (BFD) of blood through a stenosis artery in the presence ...of a transverse magnetic field. The current model is consistent with ferro-hydrodynamic (FHD) and magneto-hydrodynamic (MHD) principles. In the present work, blood in small arteries is analyzed using the Carreau-Yasuda model. The arterial wall is assumed to be fixed with cosine geometry for the stenosis. A parametric study was conducted to reveal the effects of the stenosis intensity and the Hartman number on a wide range of flow parameters, such as the flow velocity, temperature, and wall shear stress. Current findings are in a good agreement with recent findings in previous research studies. The results show that wall temperature control can keep the blood in its ideal blood temperature range (below 40°C) and that a severe pressure drop occurs for blockages of more than 60 percent. Additionally, with an increase in the Ha number, a velocity drop in the blood vessel is experienced.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
In the present work, the boiling heat transfer coefficient (BHTC) and fluid flow characteristics of graphene oxide nanoplatelets (GONPs) nano-suspensions in an annular heat exchanger (AHEX) were ...experimentally investigated. The BHTC, pressure drop (PD) and the friction factor (FF) of the heat exchanger was quantified, and effects of various operating conditions including heat flux (HF), flow rate (FR), the temperature of the nano-suspension and the mass concentration (MC) of the GONPs on the HTC and the PD of the system was assessed. Results showed that by increasing the HF, the weight concentration of the GONPs, and the temperature of the working fluid, the BHTC of the system increases. Also, the presence of GONPs can augment the friction forces, viscosity, and, as a result, increase the PD and the FF of the system. For all the experiments, the BHTC of the system was more significant than water. A comparison between water-perfluorohexane and water- n-pentane nano-emulsions revealed that water-n pentane has better thermal performance and lower PD in comparison with perfluorohexane despite the presence of the GONPs within the bulk of the nano-emulsion.
In this paper, the effect of base fluid, temperature, solid volume concentration and nanoparticle type on electrical conductivity of nanofluid is reviewed for the first time. The work involves ...discussing the effect of base fluid, temperature, solid volume concentration and nanoparticle type on electrical conductivity of nanofluid among academic analysis of recent studies. The achievements imply that the electrical conductivity generally increases as temperature and solid volume fraction increases. Moreover it should be mentioned that the influence of temperature improvement is not as effective as the nanoparticles concentrations.
•A comprehensive statistical work on electrical conductivity of nanofluids.•Mechanism of changing the electrical conductivity in mixture production.•Study the effect of temperature, nanoparticles type and nanoparticles concentration.
Nowadays, due to the energy and environmental crisis, using renewable energy is considered to reduce environmental pollution. In this paper, a comprehensive review of geothermal source heat pumps ...(GSHPs) and air source heat pumps (ASHPs) are studied from various aspects including refrigerant change, single-stage heat pump and heat pump with an economizer. This study is conducted to meet the heating needs of the central laboratory of Hakim Sabzevari University. These cycles are analyzed using energy, exergy, and environmental and economic equations (4E analysis). The results show that the coefficient of performance (COP) and exergy efficiency values for the GSHP cycle are higher than the ASHP cycle, and the best refrigerant for both is R134A. The economic and environmental analysis also reveals that using the GSHP cycle can save the electricity to 239 MWh/year (by cycle equipment), which reduces CO2 emissions to 140 tons/year and saves costs 27,280 $/year, compared to ASHP.
Moreover, by using an economizer in the heat pump cycle, the COP of the GSHP cycle improved by 9%. The exergy efficiency about 6.8% and the COP of the ASHP cycle grew about 7.5% and its exergy efficiency by 7.4%. It is concluded that the economizer has a more significant impact on the GSHP cycle.
In this article, an experimental study was performed to assess the potential thermal application of a new nanofluid comprising carbon nanoparticles dispersed in acetone inside an evacuated tube solar ...thermal collector. The effect of various parameters including the circulating volumetric flow of the collector, mass fraction of the nanoparticles, the solar irradiance, the tilt angle and the filling ratio values of the heat pipes on the thermal performance of the solar collector was investigated. It was found that with an increase in the flow rate of the working fluid within the system, the thermal efficiency of the system was improved. Additionally, the highest thermal performance and the highest temperature difference between the inlet and the outlet ports of the collector were achieved for the nanofluid at wt. % = 0.1. The best tilt angle and the filling ratio values of the collector were 30° and 60% and the maximum thermal efficiency of the collector was 91% for a nanofluid at wt. % = 0.1 and flow rate of 3 L/min.
•CuFe2O4/SiO2 nanocomposites were synthesized and then, dispersed in W-EG (60:40).•Effect of T and φ on nanofluids’ ρ, µ and σ was evaluated experimentally.•Sensitivity analysis, enhanced ANN and ...curve fitting were employed to predict ρ, µ and σ values.•Values of density are decreased, by increasing temperature.•More temperature corresponds to mildly increase of electrical conductivity.
The new nanocomposite material of CuFe2O4 (copper ferrite) nanoparticles coated by SiO2 is synthesized. Then, this newly generated nanocomposite is dispersed in water/ethylene glycol (60:40) to make a new homogeneous nanofluid in order to avoid settling and agglomeration. Through suitable accurate experiments, density, viscosity and electrical conductivity of the mixture are measured at various temperatures and nanoparticles concentrations. Besides we empirical correlations for the same parameters developed via the curve fitting method. To have a better statistical view, the optimization procedure based on the enhanced artificial neural network (EANN), developed at present study, is performed. Furthermore, according to the obtained empirical results, the sensitivity analysis is provided and the margin of deviations is represented for each proposed correlation. Generation, stabilization and measuring the density, viscosity and electrical conductivity of the newly mentioned nanofluid, make present work different from the previous ones in this field. The highest amount of relative electrical conductivity is observed at T = 75 °C and φ = 0.02 (g/mL); however, the case of T = 30 °C and φ = 0.02 (g/mL) represents the maximum value of relative viscosity. Moreover, density is decreased by temperature augmentation, through all cases.
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