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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. [ABSTRACT FROM AUTHOR]

In this work, thermal conductivity, viscosity, and boiling heat transfer coefficient of a biologically produced nano-coolant were experimentally quantified. The nanoparticles were produced from silver nitrate via the plant extraction method and by means of green tea leaf extract. The mean size of the particles was 50 nm, with spherical morphology and single-phase structure of Ag (silver). The synthesized particles were dispersed in coconut oil as base fluid. Thermal conductivity and viscosity of the nanofluid were experimentally measured and correlated based on temperature and concentration of nanoparticles via the regression analysis. Thermal performance of the nanofluid inside an annular heat exchanger with convective boiling conditions (in forced convection and nucleate boiling heat transfer regimes) was assessed. The results demonstrated a superior thermal performance in both heat transfer regions over the base oil, and revealed that this nanofluid can be used as a coolant as well as a lubricant in engines with high heat flux conditions, as its thermal conductivity and viscosity were enhanced due to the presence of Ag particles inside the oil. [ABSTRACT FROM AUTHOR]

Many experiments have been performed to investigate the thermal performance and thermal efficiency of a thermosyphon heat pipe charged with Al2O3-water/ethyleneglycol, (water-EG) and Al2O3-water/diethyleneglycol, (water-DEG) nanofluids. The heat pipe is fabricated from the high quality straight copper tube (with the outer diameter of 12 mm and length of 220 mm). The alumina spherical nanoparticles with mean size of 42-48 nm were well-dispersed, prepared and stabilized in water-EG and water-DEG base fluids at different particle concentrations using an ultrasonic homogenizer, magnetic stirrer as well as pH control in a constant temperature thermal bath. Influence of different operating parameters such as applied heat flux to the evaporator section, %charged value of working fluid, tilt angle of the heat pipe and volumetric concentration of nanoparticle on the thermal performance and efficiency of the heat pipe was experimentally investigated and briefly discussed. Results demonstrated that heat transfer coefficient of the heat pipe significantly increases, when nanofluids are used as possible working fluid and have a significant positive influence on the enhancement of thermal efficiency of the heat pipe. [ABSTRACT FROM AUTHOR]

this research, pool boiling heat transfer coefficient values were experimentally measured up to heat flux 115kW.m-2. Experiments were carried out for pool boiling of pure liquids, including of Formic acid, Propanol, 2-butanol on a horizontal smoothed cylinder, at atmospheric pressure. Applicability of the existing well-known and most common used correlations is comparatively discussed, with the present experimental data. The major predictions (over and/or under) were observed in some parameter range by the existing correlations. In this investigation the correlations of Stephan Abdelsalam, Boyko-Kruzhilin and Mostinski, have been compared with experimental data. [ABSTRACT FROM AUTHOR]

In this paper, nucleate pool boiling heat transfer coefficient of ternary mixtures of ethanol, monoethylene glycol (MEG) and diethylene glycol (DEG) as a new coolant with higher heat transfer coefficient has been investigated. Therefore, at varied concentrations of MEG and DEG and also at different heat fluxes, pool boiling heat transfer coefficients, α, have been experimentally measured. The results demonstrated higher heat transfer coefficient in comparison with water/MEG/DEG ternary mixture. In particular, at high heat fluxes, for ethanol/ MEG/DEG mixture, higher boiling heat transfer coefficient is reported. Additionally, experimental data were compared to well-known existing correlations. Results of this comparison showed that the most accurate correlation for predicting the heat transfer coefficient of ethanol/MEG/DEG is the modified Stephan-Preußer correlation, which has been obtained in our earlier work. [ABSTRACT FROM AUTHOR]

Nucleate pool boiling heat transfer coefficients of Al203-water and Ti02-water nanofluids have been experimentally measured on three horizontal tubes with different materials and similar roughness under atmospheric pressure. Results revealed that the presence of nanoparticles in the base fluid leads to an increase in pool boiling heat transfer coefficients on stainless steel and brass tubes in contrast to copper tube. The effect of different materials on excess temperature around the surface of the tubes has also been investigated. In addition, experimental investigations on the effect of different nanoparticles on nucleate boiling heat transfer have been conducted at volumetric concentra-tions of 0.1 %, 0.5 %, and 1 % of nanoparticles. Results indicated that the presence of nanoparticles have no effect on the pool boiling heat transfer coefficient for the copper tube. Variations of surface excess temperature for the copper tube were higher in comparison with that of the other tubes tested. [ABSTRACT FROM AUTHOR]

The subcooled flow boiling heat-transfer characteristics of water and ethanol solutions in a vertical annulus have been investigated up to a heat flux of 132 kW/m2. The variations in the effects ofheat flux and fluid velocity, and concen-tration of ethanol on the observed heat-transfer coefficients over a range of ethanol concentrations implied an enhanced contribution of nucleate boiling heat transfer in flow boiling, where both forced convection and nucleate boiling heat transfer occurred. Increasing the ethanol concentration led to a significant deterioration in the observed heat-transfer coefficient because of a mixture effect that resulted in a local rise in the sa tura ti on temperature of ethanol/water solution at the vapor-liquid interface. The reduction in the heat-transfer coefficient with increasing ethanol concentration is also attributed to changes in the fluid properties (for example, viscosity and heat capacity) of tested solutions with different ethanol content. The experimental data were compared with some well-established existing correlations. Results of comparisons indicate existing correlations are unable to obtain the acceptable values. Therefore, a modified correlation based on Gnielinski correlation has been proposed that predicts the heat transfer coefficient for ethanol/water solution with uncertainty about 8% that is lower in comparison to other well-known existing correlations. [ABSTRACT FROM AUTHOR]

The pool boiling heat transfer coefficient of monoethylene glycol (MEG), diethylene glycol (DEG) and water ternary mixtures has been experimentally measured up to heat flux 114 kW/m² at various volumetric concentrations of MEG and DEG. As expected, the heat transfer coefficient was strongly taken as a direct function of heat flux. Existing well-known correlations are shown to be unable to predict the acceptable values for the tested ternary mixtures, particularly at different concentrations of MEG and DEG. Furthermore, a new modified correlation is developed on the basis of the Stephan-Preusser correlation that predicts the values of heat transfer coefficients with an absolute average error of about 7% that is reasonable and acceptable values compared to other existing correlations. [ABSTRACT FROM AUTHOR]

This work investigates the use of iron oxide (III)–therminol 66 oil-based nanosuspensions in a convective heating system with potential heating applications in the buildings sector. In an experimental study, characteristics of nanofluids were measured, including heat capacity, thermal conductivity, and density. The influences of mass flow rate and concentration of nanofluid on various parameters were quantified, such as pressure loss, friction coefficient, and heat transfer rate. For a concentration of 0.3 wt.%, the heat transfer increased by 46.3% and the pressure drop increased by 37.5%. The latter is due to the higher friction and viscosity of the bulk of the nanofluid. Although the pressure drop is higher, the thermo-hydraulic efficiency still increased by 19%. As a result, iron oxide (III)–therminol 66 presented reasonable thermal performance, higher heat transfer coefficient, and a lower pressure drop value (19% better performance in comparison with water) for the air–liquid convective system. Results also showed that for nanosuspensions at 0.3 wt.%, the friction factor of the system increased by 10% in comparison with the performance of the system with water. [ABSTRACT FROM AUTHOR]

This study aims to numerically investigate the radiation heat transfer in a complex, 3-D biomass pyrolysis reactor which is consisted of two pyrolysis chambers and a heat recuperator. The medium assumes to be gray, absorbs, emits, and Mie-anisotropically scatters the radiation energy. The finite volume method (FVM) is applied to solve the radiation transfer equation (RTE) using the step scheme. To treat the complex geometry, the blocked-off-region procedure is employed. Mie equations (ME) are applied to evaluate the scattering phase function and analyze the angular distribution of the anisotropically scattered radiation by particles. In this study, three different states are considered to test the anisotropic scattering impacts on the temperature and radiation heat flux distribution. These states are as: (i) Isotropic scattering, (ii) forward and backward scattering and (iii) scattering with solid particles of different coals and fly ash. The outcomes demonstrate that the radiation heat flux enhances by an increment of the albedo and absorption coefficients for the coals and fly ash, unlike the isotropic case and the forward and backward scattering functions. Moreover, the particle size parameter does not have an important influence on the radiation heat flux, when the medium is thin optical. Its effect is more noticeable for higher extinction coefficients. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]