Concentration Of Al2O3 Nanofluid Research Articles

Numerical assessment of ceramic micro heat exchangers working with nanofluids by Taguchi optimization approach

The rapid advancements in microsystems technology have necessitated the exploration of innovative materials for efficient thermal management in micro heat exchangers. This research delves into the performance evaluation of three ultra-high temperature ceramics (UHTCs): ZrB2, BeO, and Si3N4 as alternative micro heat exchanger fabrication materials. The study systematically assessed the ceramics' interaction with Al2O3-nanofluids across diverse volume percentages and mass flow rates using the Taguchi optimization method. Beryllium oxide (BeO) emerged as the superior material, registering warm outlet temperatures as low as 64.86°C and cold outlet peaks at 31.68°C. Sensitivity analyses further underscored the critical role of inlet temperature on outlet dynamics, with warm and cold outlets showing significances of ~72% and ~99%, respectively. Additionally, the research pinpointed 0.75 vol% as the optimal Al2O3-nanofluid concentration, yielding the most favorable performance metrics across the ceramics.

The Effect of Threaded Rod Inserts and Aluminum Oxide–Water Based Nanofluids on Performance of a U-Bend Double Pipe Heat Exchanger

Double pipe heat exchangers, owing to their simplicity in construction and ease of maintenance, are being widely used in refineries, food processing units and pharma industries. However, they have a limitation that they can only operate at low heat loads. In order to make them suitable for higher loads, it is essentially required to enhance the rate of heat transfer. In this work, an attempt is made to this end using a combination of threaded rods and water-based aluminum oxide nanofluids. Experimental investigations were carried on a counter-flow double pipe return bend heat exchanger (DPHE) using water-aluminum oxide (Al2O3) nanofluids with threaded rod inserts. The volume concentration of Al2O3 nanofluid added in water was 0.03% and 0.05%. The entire analysis was carried out under turbulent flow regime by varying the mass flow rates of cold water from 3 to 15 LPM in steps of 2 LPM, with the hot water flow rate being fixed at 6 LPM. The Reynolds number range considered was from 3000 to 30000. From the obtained results, it was found that the maximum enhancement in the Nusselt number and friction factor for 0.05% concentration of the nanofluid and threaded rod inserts respectively is 89.95% and 32.46% more than the plain tube. The maximum thermal performance factor was found to be 1.75 for the combination of 0.05% nanofluid and inserts.

Tribological Performance of Different Concentrations of Al2O3 Nanofluids on Minimum Quantity Lubrication Milling

Nanofluid minimum quantity lubrication (NMQL) is a green processing technology. Cottonseed oil is suitable as base oil because of excellent lubrication performance, low freezing temperature, and high yield. Al2O3 nanoparticles improve not only the heat transfer capacity but also the lubrication performance. The physical and chemical properties of nanofluid change when Al2O3 nanoparticles are added. However, the effects of the concentration of nanofluid on lubrication performance remain unknown. Furthermore, the mechanisms of interaction between Al2O3 nanoparticles and cottonseed oil are unclear. In this research, nanofluid is prepared by adding different mass concentrations of Al2O3 nanoparticles (0, 0.2%, 0.5%, 1%, 1.5%, and 2% wt) to cottonseed oil during minimum quantity lubrication (MQL) milling 45 steel. The tribological properties of nanofluid with different concentrations at the tool/workpiece interface are studied through macro-evaluation parameters (milling force, specific energy) and micro-evaluation parameters (surface roughness, micro morphology, contact angle). The result show that the specific energy is at the minimum (114 J/mm3), and the roughness value is the lowest (1.63 μm) when the concentration is 0.5 wt%. The surfaces of the chip and workpiece are the smoothest, and the contact angle is the lowest, indicating that the tribological properties are the best under 0.5 wt%. This research investigates the intercoupling mechanisms of Al2O3 nanoparticles and cottonseed base oil, and acquires the optimal Al2O3 nanofluid concentration to receive satisfactory tribological properties.

THERMAL PERFORMANCE ENHANCEMENT OF A HELICAL COIL-IN-SHELL HEAT EXCHANGER WITH CIRCULAR FINNED TURBULATOR AND ALUMINA NANOFLUID-AN EXPERIMENTAL STUDY AND CORRELATION DEVELOPMENT

This paper discusses the conjoint effect of circular fin turbulators and alumina (Al2O3) nanofluid on the thermal performance of a helically wound coil-in-shell heat exchanger used for waste heat recovery. An experiment was conducted using three different coils: two with circular fin turbulators brazed to the annular coil surface at 45° and 90° orientations and one plain coil without a fin. The coil side fluid was Al2O3 nanofluid (0.05%, 0.1%, and 0.15% by volume concentrations) flowing in the coil under laminar and turbulent (500 ≤ Re ≤ 5500) conditions, while the hot air at different flow velocities from 1 to 3 m/s (i.e., 4500 ≤ Reh ≤ 13,500) was used as the shell-side fluid. The experiment revealed that the Nusselt number increased by 43.96% and 69.66% and the thermal-hydraulic performance increased by 16.92% and 35.71% for the 90° and 45° fin orientations, respectively, at 0.15% concentration of Al2O3 nanofluid and hot air velocity of 3 m/s. Furthermore, the thermal-hydraulic performance showed a nearly two-fold increase with 45° fin orientation/Al2O3 nanofluid combination. Based on the experiment, correlations were developed for the Nusselt number, friction factor, and thermal-hydraulic performance in the laminar and turbulent regimes, which are fairly in agreement with acceptable limits.

Reliability of Al2O3 nanofluid concentration on the heat transfer augmentation and resizing for single and double stack microchannels

The influence of using nanofluids on heat transfer augmentation and characteristics of fluid flow in rectangular cross sectional microchannel heat sink (MCHS) is numerically investigated for single and double stack microchannels at uniform heat flux, q̏ = 100 W/cm2 and Reynolds number ranging from 200 to 1500. In this study, alumina–water (Al2O3-H2O) nanofluid with different nanoparticle volume concentrations from 1% to 5% was used as a coolant for the MCHS. The three-dimensional steady, laminar flow and heat transfer governing equations are solved by finite volume method using ANSYS-Fluent 18.2. The MCHS performance is evaluated in terms of temperature profile, heat transfer coefficient, pressure drop, pumping power and volume reduction. The results reveal that increasing the nanoparticles concentration improves the cooling process. The maximum heat transfer augmentation in the current study was achieved at the highest concentration of 5%. For example, at this concentration the temperature was reduced by 7.3% using single stack microchannel. However, 33.5% temperature reduction was achieved using double stack microchannels. Also, it results in an increase in the heat transfer coefficient by 13.12% compare to that of the pure water. On the other hand, for a single stack at nanoparticle concentration of 5%, both pressure drop and power increased by 10% and 8%, respectively. Because of the significant influence of the nanofluid on the improvement of the cooling process, an estimation of the volume reduction was made. It was found that 62.6% volume reduction for single stake at concentration 5% can be achieved.

Influence of Al2O3 and TiO2 nanofluid on hard turning performance

The current paper emphasized on preparation methodology of aqueous Al2O3-water and TiO2-water nanofluids and its application as the coolant in hard turning operations. The nanofluids are prepared through the two-step process, dispersing nanoparticles of Al2O3 (average diameter 44 nm) and TiO2 (average diameter 27 nm) in deionized water at three different % weight concentrations (0.005, 0.01, and 0.05). Air-assisted nanofluid is impinged through spray impingement setup in hard turning of AISI D2 steel (55 HRC) using multilayer (TiN/TiCN/Al2O3)-coated carbide tool. Application of nanofluid through spray impingement technique in hard turning is a novel work which is rarely found in the literature. Also, there is no literature available which presented the comparative hard turning performance under lower weight % concentration of Al2O3 and TiO2 nanofluid although the cost of the nanoparticle is high. Further, flank wear (VBc), cutting temperature (T), average surface roughness (Ra), and chip morphology have been investigated as the cutting responses. Abrasion is the dominant wear mechanism identified for both types of nano cutting fluids. TiO2-water nanofluid attributes enhanced machinability compared with that of Al2O3-water nanofluid due to higher lubricious characteristics of TiO2 which significantly reduces the chip-tool friction thus reduces the cutting heat. The most favorable results are noticed at 0.01% weight concentration of TiO2 and at this condition, compared with the same concentration of Al2O3 nanofluid, 29% reduction in tool-flank wear, 9.7% drop in cutting temperature, and 14.3% reduction in surface roughness are found. Tool life at 0.01 wt% concentrations of TiO2 nanofluids is found to be 154 min taking flank wear criteria of 0.3 mm, which is 2.52 times more than the tool life obtained under dry cutting and 1.47 times higher than the tool life obtained under air-water spray impingement due to excellent wettability, lubrication, and heat dissipation capability of TiO2 nanofluid. However, the employment of deionized water-based TiO2 nanofluid in spray impingement cooling hard machining can be very promising for a practical manufacturing concern.

An Experimental Investigation of Properties of Nanofluid and Its Performance on Thermosyphon Cooled by Natural Convection

An attempt is made here to characterize thermal conductivity of water-based Al2O3 nanofluid and then use the same in a circular finned thermosyphon (TPCT) to measure its thermal performance. The concentration of Al2O3 nanofluid is varied within 0.05–0.25% by volume. The thermal conductivity of nanofluid is increased with concentration of Al2O3 nanoparticles as well as with temperature. A maximum of 26.7% enhancement of thermal conductivity is observed at 45 °C for 0.25% concentration by volume of nanofluid in comparison to that of de-ionized (DI) water. Variations of surface tension and contact angle of Al2O3 nanofluid are also compared with DI water. One of the smallest TPCT with different heat inputs (4 W, 8 W, and 12 W) and different inclinations (30 deg, 45 deg, 60 deg, and 90 deg) is tested for different concentration of Al2O3 nanofluid, which will find application in smaller electronic units. It is found that use of nanofluid decreases the wall temperature distribution of TPCT. Thermal resistance of TPCT decreases whenever TPCT is filled with nanofluid and a maximum of 36.4% reduction in thermal resistance is noted for 0.25% volume of nanoparticles at 4 W with an inclination of 60 deg. It is also found that performance of TPCT is higher at 60 deg inclination compared to other inclinations, especially for lower heat input.

Numerical Study of Thermofluid Characteristics of a Double Spirally Coiled Tube Heat Exchanger

In this study, the thermofluid characteristics of double spirally coiled tube heat exchanger (DSCTHE) were investigated numerically. A three-dimensional (3D) computational fluid dynamic (CFD) model was developed using ansys 14.5 software package. To investigate the heat transfer and pressure drop characteristics of DSCTHE, the Realize k–ε turbulence viscous model had been applied with enhanced wall treatment for simulating the turbulent thermofluid characteristics. The governing equations were solved by a finite volume discretization method. The effect of coil curvature ratio on DSCTHE was investigated with three various curvature ratios of 0.023–0.031 and 0.045 for inner tube side and 0.024–0.032–0.047 for annular side. The effects of addition of Al2O3 nanoparticle on water flows inside inner tube side or annular side with different volume concentrations of 0.5%, 1%, and 2% were also presented. The numerical results were carried out for Reynolds number with a range from 3500 to 21,500 for inner tube side and from 5000 to 24,000 for annular side, respectively. The obtained results showed that with increasing coil curvature ratio, a significant effect was discovered on enhancing heat transfer in DSCTHE at the expense of increasing pressure drop. The results also showed that the heat transfer enhancement was increased with increasing Al2O3 nanofluid concentration, and the penalty of pressure drop was approximately negligible.

Effect of nanofluid formation methods on behaviors of boiling bubbles

Understanding the boiling heat transfer characteristics of nanofluid suspensions containing nanoparticles is one of the challenging issues in the heat transfer research field. The addition of nanoparticles modifies both the surface characteristics and the thermo-physical properties of the suspension, including thermal conductivity, viscosity, and surface tensions. One of the critical features is the stability of nanoparticle suspension, which is strongly related to the formulation method of nanofluids. In this study, to investigate the effect of several formation methods, the pool-boiling bubble behaviors of Al2O3 nanofluid, with varying nanofluid formation methods, were systematically analyzed using an X-ray imaging system. The changes in the wettability of Al2O3 nanofluid suspensions and the variations of boiling bubble characteristics were analyzed to determine the relationship between boiling-bubble behaviors and examine the effects of heating the substrate. Before the heating substrate, the bubble generating ratio was increased by 1.4 times, when the concentration of Nanofluid 3 increased from 0.05 wt% to 1 wt% with adopting the electrostatic stabilization method and high-speed rotating procedure. On the other hand, at the end of heating process, the bubble generating ratio was decreased by 0.78 times for the same concentration change. Once the nanoparticle sedimentation occurred, the trend of wettability and bubble behaviors of nanofluids changed based on the surface modification, regardless of the nanofluid formation method. An increase in the Al2O3 nanofluid concentration results in a deterioration of the heat transfer characteristics, and the formulation method is not related to the boiling heat transfer performance when nanoparticles are deposited.

Experimental study on performance improvement of U-tube solar collector depending on nanoparticle size and concentration of Al2O3 nanofluid

In this study, the efficiency of a U-tube solar collector as a function of the concentration of Al2O3 nanofluid and the size of nanoparticles was investigated experimentally. Further, the efficiency of a U-tube solar collector with Al2O3 nanofluid as the working fluid was compared to that with water. The thermal conductivity of the Al2O3 nanofluid was found to increase with increase in its concentration and decrease in its nanoparticle size. When the inlet fluid and ambient environment are the same temperature, the solar collector with 1.0 vol% Al2O3 nanofluid of 20 nm-nanoparticles and a mass flow rate of 0.047 kg/s showed the highest efficiency, 24.1% higher than that of the solar collector with water. In addition, the efficiency of the solar collector with 1.0 vol% Al2O3 nanofluid was 5.6% and 9.7% higher than those with 1.5 vol% and 0.5 vol% nanofluid, respectively. For equal nanofluid concentrations, the maximum efficiency of the solar collector was 72.4% at the nanoparticle size of 20 nm–3.05% and 5.32% higher than those with nanoparticle sizes of 50 and 100 nm, respectively. Therefore, Al2O3 nanofluid was concluded to be effective in increasing the efficiency of the U-tube solar collector.

Theoretical analysis of pool boiling characteristics of Al2O3 nanofluid according to volume concentration and nanoparticle size

To investigate the effect of volume concentration and nanoparticle size on nanofluid boiling, a simulation with various concentrations of nanofluids and nanoparticle sizes was carried out using the HFP (heat flux partitioning) model with variations in the contact angle. The CHF (critical heat flux) of the nanofluid rose more than the base fluid. When the volume concentration was 0.025vol% and the size of the Al2O3-nanoparticles was 50nm, the maximum critical heat flux was 1515kW/m2 and gradually decreased with the concentration of the nanofluid. Since the Energy and K factor both improved as the Al2O3-nanofluid concentration increased, the frequency of bubble departure as well as the bubble departure diameter subsequently increased. However, the effect of nanoparticle size was not remarkable. The nucleate site density at the CHF increased from 32.97 to 30.53site/cm2 with the increase of volume concentration at 50nm-nanoparticle size but the increase was significantly lower than that of the base fluid, which was 65.90site/cm2. The temperature converted the natural convection boiling to the nucleate boiling increased and the dryout factor decreased as the concentration of the nanofluid increased. In addition, these parameters increased as the nanoparticle size became similar to the value for the surface roughness.

Heat transfer characteristics of Al2O3/water nanofluid in laminar flow conditions with circular ring insert

In this experimental investigation convective heat transfer, friction factor, and thermal enhancement characteristics of straight circular duct fitted with circular ring insert of constant heat flux boundary condition under fully developed laminar flow is presented. Tests have been conducted by using 0.1% volume concentration of Al2O3 nanofluid and water. Inserts of different pitch to diameter ratios of 6.25, 8.33, 12.5, and 16.67 with center core rod were used for this investigation. The circular ring insert shows a superior thermal performance than plain tube. The experimental results demonstrated that the Nusselt number, friction factor, and thermal enhancement factor increases with decrease in pitch to diameter ratio. The circular ring inserts of lower pitch to diameter ratio of 6.25 with nanofluid increases the Nusselt number by 165.38% compared to pure water and the friction factor, found to be 7.89 times higher than that of water. Empirical correlations are develope for Nusselt number and friction factor in terms of Reynolds number, volume concentration, and pitch ratio. The thermal performance factor was found to be greater than unity for all pitch to diameter ratios.

Heat transfer enhancement of nanofluids in a pulsating heat pipe for heat dissipation of LED lighting

The effect of nanofluids on the heat transfer performance of a pulsating heat pipe has been experimentally investigated. Water-based diamond nanofluid and aluminium oxide (Al₂O₃) nanofluid were tested in the concentration range of 0.5-5%. The pulsating heat pipe was constructed using clear Pyrex tubes of 1.85 mm in inner diameter in order to visualize the pulsating action. The total number of turns was eight each for heated and cooled parts. The supply temperatures of heating water and cooling water were fixed at 80oC and 25℃ respectively. The liquid charging ratio of the nanofluid was 50-70%. The test results showed that the case of 5% concentration of diamond nanofluid showed 18% increase in heat transfer rate compared to pure water. The case of 0.5% concentration of Al₂O₃ nanofluid showed 24% increase in heat transfer rate compared to pure water. But the increase of Al₂O₃ nanofluid concentration up to 3% did not show further enhancement in heat transfer. It is also observed that the deposited nanoparticles on the tube wall played a major role in enhanced evaporation of working fluid and this could be the reason for the enhancement of heat transfer by a nanofluid, not the enhanced thermal conductivity of the nanofluid.