An experimental study on the effect of conflict measurement criteria for heat transfer enhancement in nanofluidics (original) (raw)
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An experimental study on the proper criterion to judge the thermal performance of the nanofluids
International Communications in Heat and Mass Transfer, 2017
Available online xxxx This work is dedicated to finding a suitable measure to judge thermal performance of nanofluids. The importance of this issue arises from misleading claim of excess heat transfer of nanofluids compared to the base fluid, neglecting the hydraulic effects such as increase in pressure drop. To clarify the issue, the experimental setup with capability to create constant Reynolds number and constant pumping power is constructed. Thermal behavior of nanofluids of silicon oxide/water and aluminum oxide/water and distilled water in developing region of laminar flow regime is investigated. In this regard, the convective heat transfer coefficient within the finned tube heat exchanger is evaluated. According to the results, the concentration of nanoparticle in the base fluid will have a significant impact on the amount of deflection of these two criteria, so that by increasing the nanoparticle's concentration the difference between these two measures becomes greater.
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International Journal of Heat and Mass Transfer, 2016
The experiment investigation of turbulent forced convection of nanofluids with SiO2 and Al2O3 nanoparticles was carried out. Nanoparticle concentration varied in the range from 0.5 to 2 vol. % in the experiments. The nanoparticle size ranged from 10 to 100 nm. The dependence of heat transfer coefficient and pressure drop from the concentration, size, material of the nanoparticles and temperature was studied. It was shown that adding nanoparticles to the coolant significantly influences the heat transfer coefficient in the turbulent flow regime. It is shown that with increasing nanoparticles concentration, the local and average heat transfer coefficients at a fixed Reynolds number increase. Decrease in heat transfer coefficient with increasing particles concentration may take place at a fixed flow rate. It is shown that, the heat transfer coefficient of the nanofluid in turbulent regime increases with increasing nanoparticles size at a fixed flow rate, while has a certain maximum at a fixed Reynolds number. The effect of nanoparticles material on the heat transfer coefficient and pressure loss has been also demonstrated. It is found that the inlet temperature is another factor having a significant effect on turbulent heat transfer performance of nanofluids.
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TechConnect Briefs, 2007
Many recent studies have shown that nanofluids with metallic nanoparticles as suspension increase the thermal conductivity of base fluid by a substantial amount. First, we investigated the rheological properties of SiO 2 , Al 2 O 3 and CuO nanofluids at different volume percentages at varying temperatures. The fluids were tested over temperatures ranging from-35˚C to 50˚C. The viscosity trends showed the great influence of temperature on various nanofluids. Also, we investigated the particle diameter effect (20 nm, 50 nm, 100 nm) on nanofluid viscosity. Subsequent experiments were performed to investigate the convective heat transfer enhancement of nanofluids in a turbulent regime. During analysis of the convection coefficient, the measured viscosity values of the nanofluids were used as well as the thermal conductivity and specific heats were used from the available correlations in the current literature. Heat transfer coefficients of nanofluids increase with volume concentration, for example, a typical enhancement of a heat transfer coefficient of a 6% concentration of 45 nm CuO is about 54% at a Reynolds number of 8,000. Similar results were investigated for aluminum and silicon oxide nanofluids in ethylene glycol/water base fluid. Pressure loss was observed to increase with nanoparticle volume concentration and also with increasing particle diameter. It was observed that an increase in particle diameter increased the heat transfer coefficient. Applications of nanofluids will be in heating building and in automobiles in northern climates.
Experimental evaluation of heat transfer coefficient for nanofluids
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The paper reports the results of heat transfer experimental tests on nanofluids. Measurements were performed in a two-loop test rig for immediate comparison of the thermal performances of the nanofluid with the base-fluid. The convective heat transfer was evaluated in a circular pipe heated with uniform heat flux and with flow regimes from laminar to turbulent. Tests have been performed to compare the heat transfer capability of nanofluids and water at the same velocity or Reynolds number , and they have been compared with values calculated from widely used correlations. In particular ten different nanofluids and three base fluids (in addition to the water) have been used. The analysis of the experimental data shows a different behavior depending on the parameter used in the comparison, and, as a consequence, the addition of nanoparticles to the heat transfer fluid can result advantageous or not, depending on the specific point of view. Furthermore some classical correlations have been used to estimate the heat transfer coefficients, and the analysis shows that they are able to provide good agreement with the experimental data both for the nanofluid and water.
Heat Transfer Enhancement and Hydrodynamic Characteristics of Nanofluid in Turbulent Flow Regime
Turbulent forced convection of 𝛾-Al2O3/water nanofluid in a concentric double tube heat exchanger has been investigated numerically using mixture two-phase model. Nanofluids are used as coolants flowing in the inner tube while hot pure water flows in outer tube. The studies are conducted for Reynolds numbers ranging from 20,000 to 50,000 and nanoparticle volume fractions of 2, 3, 4, and 6 percent. Results showed that nanofluid has no effects on fully developed length and average heat transfer coefficient enhances with lower slope than wall shear stress. Comparisons with experimental correlation in literature are conducted and good agreement with present numerical study is achieved.
A CFD Study on Heat Transfer Performance of SiO2-TiO2 Nanofluids under Turbulent Flow
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A CFD model was performed with commercial software through the adoption of the finite volume method and a SIMPLE algorithm. SiO2-P25 particles were added to water/ethylene glycol as a base fluid. The result is considered a new hybrid nanofluid (HN) for investigating heat transfer (HT). The volume concentrations were 0.5, 1.0, and 1.5%. The Reynolds number was in the range of 5000–17,000. The heat flux (HF) was 7955 W/m2, and the wall temperature was 340.15 K. The numerical experiments were performed strictly following the rules that one should follow in HT experiments. This is important because many studies related to nanofluid HT overlook these details. The empirical correlations that contain the friction factor perform better with higher Reynolds numbers than the correlations based only on Reynolds and Prandtl numbers. When temperature differences are moderate, researchers may consider using constant properties to lower computational costs, as they may give results that are simila...
Energies
Theoretical analysis of the influence of nanoparticles and temperature on the average Nusselt (Nu) number and the average heat transfer coefficient (HTC) during the turbulent flow of nanofluid in a horizontal, round tube was carried out. The Nu number is a function of the Reynolds (Re) number and the Prandtl (Pr) number, which in turn are functions of the thermophysical properties of the liquid and the flow conditions. On the other hand, the thermophysical properties of nanoliquids are primarily a function of nanoparticle concentration (NPC) and temperature. Hence, the correct determination of the value of the Nu number, and then the HTC, which is needed for engineering calculations, depends on the accuracy of determining the thermophysical properties of nanofluids. In most cases, the thermophysical properties of the nanofluids are calculated as functions of the corresponding thermophysical properties of the base liquid. Therefore, the accuracy of the calculations of the thermophysi...
Comparison of the Heat Transfer Efficiency of Nanofluids
Chemical engineering transactions, 2015
The continuously increasing power involved in many applications, coupled with the very small size of a number of component devices, is pushing the technical community to look for more efficient heat transfer systems, to remove the heat generated and keep the system under controlled operating conditions. In particular, significant interest has been devoted to the use of the so-called nanofluids, obtained by suspending nano-sized particles in conventional heat transfer liquids. According to some literature, these suspensions present enhanced heat transfer capabilities, without the inconveniencies of particles settlement and clogging of the channels encountered using larger particles. However, other results show that the actual improvement in the heat transfer efficiency may depend on the adopted working conditions and on the reference parameters (fluid velocity, Reynolds number, pressure drop, etc.) assumed to compare the performances of the nanoparticles suspensions with those of the...
International Journal of Thermal Sciences, 2009
Turbulent flow and heat transfer of three different nanofluids (CuO, Al 2 O 3 and SiO 2 ) in an ethylene glycol and water mixture flowing through a circular tube under constant heat flux condition have been numerically analyzed. New correlations for viscosity up to 10% volume concentration for these nanofluids as a function of volume concentration and temperature are developed from the experiments and are summarized in the present paper. In our numerical study, all the thermophysical properties of nanofluids are temperature dependent. Computed results are validated with existing well established correlations. Nusselt number prediction for nanofluids agrees well with Gnielinski correlation. It is found that nanofluids containing smaller diameter nanoparticles have higher viscosity and Nusselt number. Comparison of convective heat transfer coefficient of CuO, Al 2 O 3 and SiO 2 nanofluids have been presented. At a constant Reynolds number, Nusselt number increases by 35% for 6% CuO nanofluids over the base fluid.