Convective Heat Transfer Coefficient Of Nanofluids Research Articles

An experimental study of the influence of Fe3O4, MWCNT-Fe3O4, and Fe3O4@MWCNT nanoparticles on the thermophysical characteristics and laminar convective heat transfer of nanofluids: A comparative study

In this study, the main objective is to investigate the impact of single, hybrid, and doped magnetic nanoparticles (NPs) on the convective heat transfer capabilities of a water/ethylene glycol (EG)-based nanofluid (NF) under the influence of a magnetic field (MF). The NFs were prepared by incorporating Fe3O4, Fe3O4-multi-walled carbon nanotubes (Fe3O4-MWCNT), and Fe3O4@MWCNT in concentrations of 0.05, 0.1, and 0.2 wt.%. The NPs were characterized using various techniques such as XRD, SEM, VSM, Raman spectroscopy, and FTIR to confirm their properties. The stability of the NFs was assessed through dynamic DLS and zeta potential measurements. The study then focused on evaluating the effects of these nano-additives on thermal conductivity (TC), viscosity at 25 °C, convective heat transfer coefficient (CHTC), and friction factor in a circular tube under laminar flow regime with a constant wall flux, both with and without the application of a MF. The results of present preliminary study with limited samples revealed that the CHTC of NFs containing Fe3O4 and Fe3O4@MWCNT NPs increased with NP concentration and application of a MF, with maximum increases of approximately 19.01 % and 32.84 %, respectively. However, in the case of NFs containing MWCNT-Fe3O4 NPs, the CHTC decreased when the MF was applied at concentrations higher than 0.1 wt.%. Furthermore, the NFs containing 0.2 wt.% of Fe3O4, MWCNT-Fe3O4, and Fe3O4@MWCNT NPs exhibited the highest friction when subjected to a 400 G MF, resulting in increases of 5.2 %, 9.2 %, and 5.9 %, respectively, compared to the base fluid. The performance index, which assesses the effectiveness of using NFs instead of the base fluid, indicated that all samples had a performance index greater than one, indicating their efficacy. The maximum performance index achieved was 1.343, corresponding to the NF containing 0.2 wt.% of Fe3O4@MWCNT NPs at a Reynolds number (Re) of 2200 and a MF strength of 400 G.

Experimental Investigation of the Effect of Graphene/Water Nanofluid on the Heat Transfer of a Shell-and-Tube Heat Exchanger

The most common type of heat exchanger used in a variety of industrial applications is the shell-and-tube heat exchanger (STHE). In this work, the impact of graphene nanoplate (GNP)/water nanofluids at 0.01 wt.%, 0.03 wt.%, and 0.06 wt.% on the thermal efficiency, thermal performance factor, pressure drop, overall heat transfer, convective heat transfer coefficient (CVHTC), and heat transfer characteristics of a shell-and-tube heat exchanger was examined. For these experiments, a new STHE was designed and built. The novelty of this study is the use of GNPs/water nanofluids in this new STHE for the first time and the fully experimental investigation of the attributes of nanofluids. GNP properties were analysed and confirmed using analyses including XRD and TEM. Zeta potential, DLS, and camera images were used to examine the stability of nanofluids at various periods. The zeta potential of the nanofluids was lower than -27.8 mV, confirming the good stability of GNP/water nanofluids. The results illustrated that the experimental data for distilled water had a reasonably good agreement with Sieder-Tate correlation. The maximum enhancement in the CVHTC of nanofluid with 0.06 wt.% of GNP, was equal to 910 (W/m2K), an increase of 22.47%. Also, the efficiency of the heat exchanger for nanofluid at 0.06 wt.% improved by 8.88% compared with that of the base fluid. The heat transfer rate of the nanofluid at maximum concentration and volume flow rate was 3915 (J/kg.K), an improvement of 15.65% over the base fluid. The pressure drops increased as the flow rate and concentration of the nanofluid increased. Although increasing the pressure drop in tubes would increase the CVHTC, it would also increase the power consumption of the pump. In conclusion, nanofluid at 0.06 wt.% had good performance.

Heat transfer and fluid flow characteristics of nanofluids with various filling ratios under synchronous vibration

In the combustion engine working process, significant heat energy is transferred to the combustion chamber, and particularly to the piston. Therefore, the piston must be efficiently cooled with increased thermal loading. When the piston power density exceeds 0.3 kW/cm2, it must be cooled by a cooling chamber. To assess nanofluid flow and heat-transfer characteristics in the cooling chamber, visualization experiments and numerical simulations were performed using water-based Al2O3 and SiO2 at 2% concentration by volume in a straight circular pipe under synchronous vibration with the piston. The filling ratio, vibration frequency, and nanoparticle shape all have important impacts on cooling. Experimental data verified numerical simulation results that the optimum heat transfer filling ratio = 53.4%, under which the convective heat-transfer coefficient of nanofluids reached the maximum 1914.4 W/(m2 K). The heat-transfer enhancement coefficient was proportional to the vibrational frequency. Within the experimental limits and with high filling ratio, the convective heat-transfer coefficient increased by 9.5% when the vibrational frequency increased from 2.55 Hz to 3.65 Hz. Nanoparticle shape also had a major impact on heat transfer. Heat transfer with rod-shaped Al2O3 nanoparticles was significantly better than with spherical SiO2 nanoparticles. Under the condition of 3.65 Hz, compared with water, the enhancement amplitude of spherical nanoparticles with the same volume concentration was 8.0%, but that of the rod-like nanoparticles could be increased by 13.4%. The fluids mixed best for a rotor rotation angle between 180 °C and 270 °C, and the degree of nanofluid chaos was better than that of purified water in a reciprocating vibration cycle, as verified by experiments and numerical simulations.

Experimental investigation on heat transfer characteristics and pressure drop of BPHE (brazed plate heat exchanger) using TiO2–water nanofluid

In this research, the effect of using TiO2–water nanofluid on heat transfer enhancement and pressure drop in a Brazed Plate Heat Exchanger used in domestic hot water system is investigated experimentally. TiO2 nanoparticles with 20nm diameter and 99+% purity are used for making the nanofluid at 0.3%, 0.8% and 1.5% weight concentration of suspended nanoparticles, in such experiments. This study is done on the brazed plate heat exchanger under turbulent flow condition. The effects of Reynolds number and weight concentration of nanoparticles on the heat transfer characteristics are investigated experimentally. This results in a significant increase in convective heat transfer coefficient through adding nanoparticles to distilled water. The results show that, the convective heat transfer coefficient and the overall heat transfer coefficient of TiO2–water nanofluid is increased with enhancement of Reynolds number and at a specified Reynolds number, heat transfer characteristics is enhanced by increasing weight concentration of nanoparticles in brazed plate heat exchanger. The maximum enhancement of the nanofluid convective heat transfer coefficient at 0.3%, 0.8% and 1.5% weight fraction of nanoparticles are about 6.6%, 13.5% and 23.7% respectively. Also the maximum enhancement of the nanofluid overall heat transfer coefficient at mentioned weight concentrations of nanoparticles are about 2.2%, 4.6% and 8.5% respectively. Finally, the nanofluid pressure drop at various levels of nanoparticles is measured experimentally. According to these results, increment in system pressure drop is negligible compared to the heat transfer improvement.

Experimental studies on the convective heat transfer performance and thermophysical properties of MgO–water nanofluid under turbulent flow

This study present results of experiments on thermal conductivity, viscosity and Turbulent heat transfer behavior of Magnesium Oxide–water nanofluid in a circular pipe, where the volume fraction of nanoparticles in the base fluid is less than 1% (low concentration). Pure water and nanofluid with particle volume fraction of 0.0625%, 0.125%, 0.25%, 0.5% and 1% are used as working fluid. It is observed that most conventional models fail to predict the thermal conductivity and dynamic viscosity of the MgO–water nanofluid accurately, especially in case of viscosity. Therefore a new correlation of the dynamic viscosity will be presented based on the obtained experimental results. The experiments are carried out in the fully-developed turbulent regime. The results indicate that addition of low value of nanoparticles to the base fluid motivates the heat transfer to increase remarkably. The measurements also show that the pressure drop of nanofluid is slightly higher than that of the base fluid and does not increase with increasing the nanoparticles volume fraction. In this paper, experimental results have been compared with the existing correlations for nanofluid convective heat transfer coefficient in turbulent regime. Also Nusselt number and friction factor were considered in definition of thermal performance factor. The results show that the thermal performance factor for all cases are greater than unity which indicate that this nanofluid enhances the heat transfer without huge penalty in pumping power. Hence, applying the methods studied here could be considered as a good choice in practical application.

Nanofluids thermal behavior analysis using a new dispersion model along with single-phase

A numerical study has been performed to analyze nanofluids convective heat transfer. Laminar α-Al2O3-water nanofluid flows in an entrance region of a horizontal circular tube with constant surface temperature. Numerical analysis has been carried out using two different single-phase models (homogenous and dispersion) and two-phase models (Eulerian–Lagrangian and mixture). A new model is developed to consider the nanoparticles dispersion. The transport equations for the tube with constant surface temperature were solved numerically using a control volume approach. The effects of nanoparticles volume fraction (0.5, 1 %) and Reynolds number (650 ≤ Re ≤ 2300) on nanofluid convective heat transfer coefficient were studied. The results are compared with the experimental data and it is shown that the homogenous single-phase model is underestimated and the mixture model is overestimated. Although the Eulerian–Lagrangian model gives a reasonable prediction for the thermal behavior of nanofluids, the dispersion single-phase model gives more accurate prediction despite its simplicity.

Investigation of turbulent convective heat transfer and pressure drop of TiO 2/water nanofluid in circular tube

Turbulent heat transfer behavior of titanium dioxide/water nanofluid in a circular pipe was investigated experimentally where the volume fraction of nanoparticles in the base fluid was less than 0.25%. The experimental measurements have been carried out in the fully-developed turbulent regime for various volumetric concentrations. The results indicated that addition of small amounts of nanoparticles to the base fluid augmented heat transfer remarkably. There was no much effect on heat transfer enhancement with increasing the volume fraction of nanoparticles. The measurements also showed that the pressure drop of nanofluid was slightly higher than that of the base fluid and increased with increasing the volume concentration. In this paper, experimental results have been compared with the existing correlations for nanofluid convective heat transfer coefficient in turbulent regime. Finally, a new correlation of the Nusselt number will be presented using the results of the experiments with titanium dioxide nanoparticles dispersed in water.

Experimental investigation of turbulent convective heat transfer of dilute γ-Al 2O 3/water nanofluid inside a circular tube

Turbulent convective heat transfer and pressure drop of γ-Al 2O 3/water nanofluid inside a circular tube were investigated experimentally. The volume fraction of nanoparticles in base fluid was less than 0.2%. Results indicated that addition of small amounts of nanoparticles to the base fluid augmented heat transfer remarkably. Increasing the volume fraction of nanoparticles in the range studied in this work did not show much effect on heat transfer enhancement. Measurements showed that pressure drop for the dilute nanofluid was much greater than that of the base fluid. Experimental results were compared with existing correlations for nanofluid convective heat transfer coefficient in turbulent regime.