Different Concentrations Of Nanofluids Research Articles

Laminar forced convection effectiveness of Al2O3–water nanofluid flow in a circular tube at various operation temperatures: Effects of temperature-dependent properties

In this paper, effects of temperature-dependent thermophysical properties on laminar forced convection effectiveness of Al2O3–water nanofluids in a circular tube imposed to a constant heat flux are investigated numerically. The numerical study is supplemented with a scale analysis based on the integral energy equation. The analysis is conducted for various inlet temperatures and considering two cases for properties including (i) constant-properties, and (ii) temperature-dependent properties. The simulated results are presented for three different concentrations of nanofluids i.e. 0%, 5%, and 9%, volume flow rates in the range of 24–180cm3/min which correspond with Reynolds numbers between 120 and 2000, heat fluxes between 5.51×102 and 1.23×104W/m2, and various inlet temperatures in the range of 25–50°C. The effects of various inlet temperatures of nanofluids and different thermophysical models on the local and average Nusselt numbers in the tube have been investigated in details. It is found that with an increase in both nanofluid concentration and temperature rise in the heated section, the effects of inlet temperature and thermophysical properties on the Nusselt number are more pronounced.

Improving the rate of solar heat recovery from nanofluids by using micro heat exchanger

This work investigates the possibility of improving the solar heat recovery from copper–water nanofluids using a micro heat exchanger. This micro heat exchanger consisted of double brass tubes with a micro annular space. The effect of nanoparticles addition to the base fluid and its flow rate on the heat transfer characteristics and heating rate for both nanofluids in solar simulator section and water in shell side of micro heat exchanger were studied. The nanofluids was forced to flow in the tube side, while the fluid in the shell side was pure water. The effect of copper (Cu) weight fraction in nanofluids and the flow rate of nanofluids on the heat transfer coefficient (h), overall heat transfer coefficient (U), thermal resistance (R), and heating rate for both nanofluids in heating section and cold water in micro heat exchanger were studied. Four different concentrations of nanofluids in the range 0.01–0.1 wt.% had been used. The flow rate of nanofluids was changed in laminar region using a control valve. The temperature of heated nanofluids varied from 22 to 73°C. The heat transfer and overall heat transfer coefficients of the nanofluids 0.1 wt.% were found to increase by 49.9 and 42.08%, respectively, when it was compared with pure water. Also to be increased by increasing the nanofluid flow rate. Also, it was observed that the weight fraction has no significant effect on the final temperature of the nanofluid exit from heating section.

Experimental study on the effect of nanoparticle concentration on the lubricating property of nanofluids for MQL grinding of Ni-based alloy

The effect of nanoparticle concentration on the lubricating property of nanofluids for minimum quantity lubrication (MQL) grinding was experimentally investigated based on the status of nanofluid MQL. Different concentrations of nanofluids with molybdenum disulfide (MoS2), carbon nanotubes (CNTs), and their mixtures (MoS2-CNTs) were prepared. Difficult-to-cut Ni-based alloy was used as the workpiece material to explore the effect of mass fraction of nanofluids on grinding force ratio (G) and workpiece surface quality. The statistical analysis of grinding force ratio and surface roughness (Ra) were performed using one-way analysis of variance followed by Tukey’s post-hoc test with confidence intervals (CI) of 95%.Results showed that given the same mass fraction, MoS2-CNTs achieved lower G [GMix (8%)=0.274] and surface roughness (Ra=0.328μm) than MoS2 and CNTs. These characteristics were attributed to the physical collaboration of the mixed nanoparticles. For the same nanoparticle, G decreased initially, reaching the lowest value at 8% [GMix (8%)=0.274], and then increased with the increase in mass fraction of nanofluids because of the influence of agglomeration. Ra, increased gradually with the increase in viscosity of nanofluids. Autocorrelation analysis shows that MoS2-CNT nanofluid MQL achieved the lowest autocorrelation initial value (RMix=0.64) when τ=0. This result confirms that MoS2-CNT nanofluid MQL could improve machining precision and surface quality. Among different concentrations of nanofluids, the high-frequency continuous oscillation of the autocorrelation curve of the 8% MoS2-CNTs indicated improved workpiece surface quality. Combined friction coefficient, Ra, and autocorrelation analytical results show that 8% MoS2-CNTs was the optimum concentration for nanofluid MQL in the experiment. Autocorrelation analysis of the profile curves reveals the microstructural information of the workpiece surface and, combined with Ra analysis, provides a better method of analyzing the surface quality of a workpiece.

Heat transfer intensification in a shell and helical coil heat exchanger using water-based nanofluids

Nanofluids have been reported to be capable of heat transfer intensification. Performance of an agitated shell and helical coil heat exchanger has been experimentally investigated using three water based nanofluids (Al2O3, CuO and TiO2). The studies were carried out at different concentrations of nanofluid, nanofluid temperatures, stirrer speeds and coil-side fluid flow rates. Nanofluids of three concentrations 0.3, 0.6, 1, 1.5 and 2% by weight have been prepared for this purpose. Cetyltrimethyl ammonium bromide (CTAB) was used as stabilizer. Nanofluid was used as heating medium (shell-side) and water was used as coil-side fluid. It was found that heat transfer rate increases with increase in nanofluid concentration. Higher values of nanofluid concentration, stirrer speed and shell-side fluid temperature resulted in greater effectiveness of heat exchanger. A maximum increase of 30.37%, 32.7% and 26.8% in effectiveness of heat exchanger was observed for Al2O3, CuO and TiO2/water nanofluids respectively, when compared to water, indicating intensification of heat transfer.

Evaluation of acoustical parameters and thermal conductivity of TiO2-ethylene glycol nanofluid using ultrasonic velocity measurements

Abstract The nanosized titanium oxide (TiO2) nanoparticles (NPs) were synthesized via sol-gel method. The crystalline nature of the synthesized TiO2 nanoparticles was confirmed by X-ray powder diffractometry method. The surface morphology and particle size of the nanoparticles were analyzed by high-resolution scanning electron microscopic method. UV-visible spectroscopy was employed to determine its band gap energy value. The different concentrations of nanofluid samples of TiO2 NPs dispersed in ethylene glycol were prepared and mixed thoroughly by ultrasonication process. The value of ultrasonic velocity and density were measured for the different concentrations of TiO2 nanofluids. The acoustical parameters such as adiabatic compressibility, intermolecular free length, and acoustic impedance were calculated from the experimental data. It was observed that ultrasonic velocity showed linearity with particle concentration, and the results were discussed. In addition to the TiO2-ethylene glycol (particle-fluid) interaction studies, a new methodology was proposed to find the thermal conductivity of nanofluids using ultrasonic velocity.

Dispersion Stability of TiO2-H2O Nanofluids Containing Mixed Nanotubes and Nanosheets

Abstract Titanium dioxide nanotubes (TiNTs) and nanosheets (TiNSs) were synthesized according to the hydrothermal synthesis method. TiO2-H2O binary nanofluids were prepared by dispersing certain amount of both TiNTs and TiNSs in deionized water. Stabilities of nanofluids of different total concentrations were observed visually 1 hour later after preparation to classify stable and unstable nanofluids among nanofluids containing different ratios of TiNTs and TiNSs. Sedimentation heights variations with time were measured to indicate sedimentation velocities of nanoparticles of nanofluids of different concentrations as well. The preliminary results revealed that binary nanofluids stabilities could be improved effectively when concentration ratios of TiNTs to TiNSs are at suitable range compared with TiNTs or TiNSs alone, otherwise stabilities were deteriorated seriously. We consider the phenomenon is possibly concerned with electrostatic repulsion and depletion interactions in binary nanofluids.

Optimization of natural convection heat transfer of Newtonian nanofluids in a cylindrical enclosure

This study characterizes and optimizes natural convection heat transfer of two Newtonian Al2O3 and TiO2/water nanofluids in a cylindrical enclosure. Nusselt number (Nu) of nanofluids in relation to Rayleigh number (Ra) for different concentrations of nanofluids is investigated at different configurations and orientations of the enclosure. Results show that adding nanoparticles to water has a negligible or even adverse influence upon natural convection heat transfer of water: only a slight increase in natural convection heat transfer of Al2O3/water is observed, while natural convection heat transfer for TiO2/water nanofluid is inferior to that for the base fluid. Results also reveal that at low Ra, the likelihood of enhancement in natural convection heat transfer is more than at high Ra: at low Ra, inclination angle, aspect ratio of the enclosure and nanoparticle concentration influence natural convection heat transfer more pronouncedly than that in high Ra.

Supercooling and cold energy storage characteristics of nano-media in ball-packed porous structures

The presented experiments aimed to study the supercooling and cold-energy storage characteristics of nanofluids and water-based nano-media in ball-packed porous structures (BPS). Titanium dioxide nanoparticles (TiO2 NPs) measuring 20nm and 80nm were used as additives and sodium dodecyl benzene sulphonate (SDBS) was used as anionic surfactant. The experiments used different concentrations of nanofluid, distilled with BPS of different spherical diameter and different concentrations of nano-media, and were conducted 20 times. Experimental results of supercooling were analysed by statistical methods. Results show that the average and peak supercooling degrees of nanofluids and nano-media in BPS are lower than those of distilled water. For the distilled water in BPS, the supercooling degree decreases on the whole with the decrease of the ball diameter. With the same spherical diameter (8mm) of BPS, the supercooling degree of TiO2 NPs measuring 20nm is lower than the supercooling degree of distilled water in BPS. Step-cooling experiments of different concentrations of nanofluids and nano-media in BPS were also conducted. Results showed that phase transition time is reduced because of the presence of TiO2 NPs. The BPS substrate and the NPs enhance the heat transfer. Distilled water with a porous solid base and nanoparticles means the amount of cold-energy storage increases and the supercooling degree and the total time are greatly reduced. The phase transition time of distilled water is about 3.5 times that of nano-media in BPS.

The Application of Nanofluids for Enhanced Oil Recovery: Effects on Interfacial Tension and Coreflooding Process

Most oil reservoirs around the world are experiencing their second half of life. Hence, the necessity of appropriate enhanced oil recovery (EOR) method as a more efficient technology gets further importance. Nanotechnology is an advanced technology that has proved its potential to enhance oil recovery. In this study, some selected types of nanoparticles were used, which were aluminum oxide, iron oxide, and silicon oxide treated by silane, as EOR agents during different flooding scenarios and EOR experiments under surface conditions. For the first time, the application of propanol as a dispersing agent of nanoparticles and EOR agent in the formation was investigated by this research work. In order to examine the recovery mechanisms of nanofluids, interfacial tension (IFT), and contact angle measurements between different concentrations of nanofluids and crude oil were measured. Then, several coreflood experiments were conducted to investigate their impacts directly on recoveries. The experiment results show that the nanofluids can decrease the IFT between water and oil phases and make the solid surface more neutral wet. Results indicate that aluminum oxide and silicon oxide treated by silane are good agents for enhanced oil recovery, while silicon one changes rock wettability more in addition to reduction of interfacial tension between oil and water. According to the results the future expectation is that these nanoparticles with their dispersing agent could mobilize more oil in the pore network at field scale to improve oil recovery.

Thermal Performance of Automobile Radiator Using Carbon Nanotube-Water Nanofluid—Experimental Study

In the present study, the convective heat transfer enhancement of carbon nanotube (CNT)-water nanofluid has been studied experimentally inside an automobile radiator. Heat removal rate of the coolant flowing through the automobile radiators is of great importance for the optimization of fuel consumption. In this study, four different concentrations of nanofluids in the range of 0.15–1 vol. % were prepared with the addition of CNT nanoparticles into water. The CNT nanocoolants are synthesized by functionalization (FCNT) and surface treatment (SCNT) method. The effects of various parameters, namely synthesis method, variation in pH values and nanoparticle concentration on the Nusselt number are examined through the experimental investigation. Results demonstrate that both nanocoolants exhibit enormous change Nusselt number compared with water. The results of functionalized CNT nanocoolant with 5.5 pH exhibits better performance compared to the nanocoolant with pH value of 6.5 and 9. The surface treated CNT nanocoolant exhibits the deterioration in heat transfer performance. In addition, Nusselt number found to increase with the increase in the nanoparticle concentration and nanofluid velocity.

Heat transfer enhancement in a hybrid microchannel-photovoltaic cell using Boehmite nanofluid

Experiments were conducted to investigate the cooling performance of water-based Boehmite (AlOOH·xH2O) nanofluid in a hybrid photovoltaic (PV) cell. A Perspex plate consists of 40 parallel rectangular microchannels with a hydraulic diameter of 783μm, a length of 24cm, a width of 1.8mm and a depth of 500μm attached to the back of the cell. Cooling performances of water, as the base fluid, and three different concentrations of nanofluid (0.01, 0.1 and 0.3wt.%) were compared. The nanofluid thermal performance has been assessed from the obtained results for outlet flow temperature and the average PV surface temperature. The average PV surface temperature decreased from 62.29°C to 32.5°C at zero and 300ml/min of flow rate for 0.01wt.% nanofluid, respectively. Moreover, the highest improving in the electrical efficiency was achieved about 27% for 0.01wt.% concentration of the nanofluid at this flow rate.

Comparative Study of Cooling Performance of Automobile Radiator Using Al2O3-Water and Carbon Nanotube-Water Nanofluid

In the present study, the forced convective heat transfer performance of two different nanofluids, namely, Al2O3-water and CNT-water has been studied experimentally in an automobile radiator. Four different concentrations of nanofluid in the range of 0.15–1 vol. % were prepared by the additions nanoparticles into the water as base fluid. The coolant flow rate is varied in the range of 2 l/min–5 l/min. Nanocoolants exhibit enormous change in the heat transfer compared with the pure water. The heat transfer performance of CNT-water nanofluid was found to be better than Al2O3-water nanocoolant. Furthermore, the Nusselt number is found to increase with the increase in the nanoparticle concentration and nanofluid velocity.

Effect of Temperature and Concentration on the Molecular Interactions of Cu/ZnO-EG Nanofluids Using Ultrasonic Study

In this work, ultrasonic properties of copper (Cu) doped zinc oxide (ZnO) nanofluids are reported. Cu doped ZnO nanoparticles are synthesized by chemical precipitation method. The synthesized nanoparticles are characterized by X-ray powder diffractometry (XRD) and scanning electron microscopy (SEM) to find the crystallinity and surface morphology of the nanoparticles. Nanofluids are prepared by the dispersion of nanoparticles in ethylene glycol through the aid of ultrasonication. Ultrasonic studies are carried out for six different concentrations of nanofluids at 298 K, 303 K, 308 K, 313 K and 318 K. The acoustical parameters such as adiabatic compressibility, intermolecular free length and acoustic impedance are calculated from the experimental data. The intermolecular interactions responsible for the changes in acoustical parameters with respect to concentration and temperature are discussed.

Performance Investigation of an Automotive Car Radiator Operated With Nanofluid as a Coolant

Nanofluids are suspensions of metallic or nonmetallic nanopowders in base liquid and can be employed to increase heat transfer rate at various applications. In the present study, forced convective heat transfer in an Al2O3/water nanofluid has experimentally been compared to that of pure water in automobile radiator. Five different concentrations of nanofluids in the range of 0–1.0 vol. % have been prepared by the addition of Al2O3 nanoparticles into the water. The test fluid flows through the automobile radiator consisted of 33 vertical tubes with elliptical cross section and air makes a cross flow inside the tube bank with constant speed. The test fluid flow rate has been changed in the range of 3 l/min to 8 l/min to have fully turbulent regime. Obtained results demonstrate that increasing the fluid circulating rate can improve the heat transfer performance. The application of the nanofluid with low concentration can enhance heat transfer efficiency up to 40–45% in comparison with pure water. The increase in heat transfer coefficient due to presence of nanoparticles is higher than the prediction of single phase heat transfer Dittus Boelter correlation used with nanofluid properties. These results can be implemented to optimize the size of an automobile radiator.

Study of forced convection nanofluid heat transfer in the automotive cooling system

The heat transfer enhancement for many industrial applications by adding solid nanoparticles to liquids is significant topics in the last 10 years. This article included the friction factor and forced convection heat transfer of SiO2 nanoparticle dispersed in water as a base fluid conducted in a car radiator experimentally and numerically. Four different concentrations of nanofluids in the range of 1–2.5vol% have been used. The flowrate changed in the range of 2–8 LPM to have Reynolds number with the range 500–1750. The results showed that the friction factor decreases with an increase in flowrate and increase with increasing in volume concentration. Furthermore, the inlet temperature to the radiator has insignificantly affected to the friction factor. On the other side, Nusselt number increases with increasing in flowrate, nanofluid volume concentration and inlet temperature. Meanwhile, application of SiO2 nanofluid with low concentrations can enhance heat transfer rate up to 50% as a comparison with pure water. The simulation results compared with experimental data, and there is a good agreement. Likewise, these results compared to other investigators to be validated.

A coreflood investigation of nanofluid enhanced oil recovery

Abstract Recently nanoparticles have become an attractive agent for improved and enhanced oil recovery (IOR & EOR) at laboratory scale. Most researchers have observed promising results and increased ultimate oil recovery by injecting nanoparticle suspension (nanofluid) in laboratory experiments. The objective of this study is to reveal nanofluid possibility for EOR in low to high-permeability sandstone (ss) rocks and investigate suitable concentration. In this study, parameters involved in the structural disjoining pressure mechanism, such as lowering interfacial tensions (IFT) and altering wettability, were studied. Laboratory coreflood experiments were performed in water-wet Berea ss core plugs with permeability in range 9–400 mD using different concentrations of nanofluids. A crude oil from a field in the North Sea was employed and three nanofluid concentrations 0.01, 0.05 and 0.1 wt% were synthesized with synthetic brine. We observed that IFT decreased when hydrophilic nanoparticles were introduced to brine. The IFT decreases as nanofluid concentration increases and this indicates a potential for EOR. Increasing hydrophilic nanoparticles will also decrease contact angle of aqueous phase and increase water wetness. We have also observed that the higher the concentrations of nanofluids, the more the impairment of porosity and permeability in Berea core plugs. Despite that increasing nanofluid concentration shows decreasing IFT and altering wettability, our results indicate that additional recovery is not guaranteed. The processes and results are outlined and also further detailed in the paper to reveal the possible application of nanofluid EOR as a future or an alternative EOR method.

Viscosity studies on novel copper oxide–coconut oil nanofluid

Novel coconut oil based copper oxide nanofluids of various concentrations have been prepared by ultrasonically assisted two step method. Viscosity studies have been made experimentally and theoretically at various temperatures and shear rates for different concentrations of nanofluid ranging from 0% to 2.5%. Shear thinning, a non-Newtonian behavior is observed in all the samples. The shear thinning is higher at lower shear rates and higher concentrations. The shear thinning at low concentration is attributed to the non-Newtonian behavior of carrier liquid, but at higher concentration there is a considerable contribution from particle too. The measured viscosities of nanofluids are compared with existing theoretical models and found to have very slight deviation due to size, morphology and interactions. New empirical correlations are proposed for predicting viscosity of CuO–coconut oil nanofluid at various temperatures and concentrations.

Investigations on Boiling-Induced Nanoparticle Coating, Transient Characteristics, and Effect of Pressure in Pool Boiling Heat Transfer on a Cylindrical Surface

Pool boiling experiments were conducted to study the heat transfer characteristics using low concentrations (0.0015 to 0.0077 vol%) of CuO nanofluids at and above atmospheric pressure in distilled water. The study included the following. (i) effect of pressure and concentration on heat transfer using CuO nanoparticles in distilled water, (ii) investigations on nanoparticle coating formed due to boiling-induced precipitation tested in CuO nanofluid and distilled water, and (iii) pool boiling behavior of CuO nanofluid subject to transient characteristics. The experimental outcome indicated that different concentrations of nanofluids display different degrees of deterioration in boiling heat transfer coefficients at and above atmospheric pressure. Boiling-induced precipitation of nanoparticles resulted in coating of nanoparticles. When tested in pure water, the nanoparticle-coated heater showed significant increase in critical heat flux compared with the critical heat flux of a bare heater tested in pure water. Study of the transient characteristics indicated degradation in boiling heat transfer due to prolonged exposure of the heater surface in nanofluid. Based on the experimental investigations, it can be concluded that nanoparticle coating can also be a potential substitute for enhancing the heat transfer if used in controlled quantities.

NPIV velocity measurement of nanofluids in the near-wall region of a microchannel

Colloidal suspensions of nano-sized particles in a base fluid, nanofluids, have recently gained popularity as cooling fluids mainly due to their enhanced heat transfer capabilities. However, there is controversy in the literature on the reported properties of nanofluids and their applicability, especially since there is no fundamental understanding that explains these enhancements. A better understanding of these fluids and how they interact with a solid boundary may be achieved by a detailed near-wall fluid flow study at nanoscale. This work presents for the first time the near-wall velocity measurements for nanofluids using nanoparticle image velocimetry. This novel technique uses evanescent illumination in the solid–fluid interface to measure near-wall velocity field with an out-of-plane resolution on the order of O(100 nm). Nanofluids of different concentrations were prepared by dispersing silicon dioxide particles (10 to 20 nm) in water as the base fluid. Initially, viscosity measurements were conducted for the prepared nanofluids. The near-wall velocity data were then measured and compared with that of the base fluid at the same flow condition. It was observed that even though nanofluid viscosity had increased with particle loading, the near-wall velocity values were similar to that of the base fluid for a given flow rate. Together, these measurements vindicate the homogenous and Newtonian characteristics of the nanofluids in the near-wall region. Despite the low particle concentrations investigated, the present work also discusses the complexity involved in utilizing the methodology and possible errors arising during experimentation so as to implement this measurement tool more effectively in the future.

Use of Ultrasound Thermometry to Study Natural Convection in Opaque Nanofluids

Abstract Nanofluids are being evaluated as alternative heat transfer fluids, and thus their behavior during storage or low velocity applications in which natural convection can be significant has to be known and documented. Buoyancy induced flows in rectangular enclosures using nanofluids can be studied experimentally using thermocouples, thermistors, surface heat flux sensors, and ultrasound thermometry. The effects of the mass fraction concentration of nanoparticles, the enclosure aspect ratio, and the inclination have been studied experimentally, but more could be done. The opacity of nanofluids does not permit the use of particle image velocimetry, laser induced fluorescence, or any other means of flow visualization or visual temperature measurement of the local fluid temperature. However, the temperature field can be observed using a non-invasive method such as ultrasound thermometry. The experimental enclosure here was validated using water as the initial fluid; measured values of the local fluid temperature were compared with numerical simulations utilizing commercial software. Nanofluid mass fractions of 10% and 25% were used for comparative purposes to study the effects of concentration on the temperature field. Buoyancy force reversal effects were witnessed in both 10% and 25% concentrations. The nanofluid also prolonged the multicellular effects that occur in buoyancy inversion flows. A Rayleigh number inversion was observed with the 25% mass fraction nanofluid. The multicellular regime transitions to a boundary layer regime at about Ra = 1 × 107 when the aspect ratio is 2.625 and at about Ra = 2 × 108 when the aspect ratio is 1.000 for different concentrations of nanofluid. The observations could be physically explained. The current work confirms that temperature measurements of the flow field can be made to assess convective regimes and flow phenomena that induce significant temperature variations. The use of ultrasound thermometry is successfully demonstrated for opaque nanofluid.