Unsteady Natural Convection in Condenser tank containing Al2O3–DI Water Nanofluids (original) (raw)

The new correlations for heat transfer in the cooling process of AL2O3: Water nanofluids in pipe

Istrazivanja i projektovanja za privredu, 2015

The aim of this experiment was to investigate convection heat transfer in the cooling processes of Al2O3-water nanofluid in concentrations of 0.15%, 0.25% and 0.5% by volume, respectively. The test section was a 1.25 m brass pipe with a 4.9 mm inner diameter and outer pipe of 38.5 mm diameter of a counter flow double-pipe heat exchanger. The temperatures at the nanofluid inlet in the inner pipe were a constant 40oC, and 23oC for the water at the inlet of the outer pipe. The results of this study indicated a more enhanced coefficient convective heat transfer of the cooling process than that of the heating process. The new equation of the Nusselt number obtained in the cooling process was Nu nf =0.75R e 0.846 P r-2.28 φ 0.03 at particle volume concentrations of 0.15%, 0.25% and 0.5%. The maximum ratio enhancement of the nanofluid heat transfer in the cooling process was 45.2% at a particle volume concentration of 0.25%, while for the heating process nanofluid heat transfer was same as that for distilled water.

Experimental investigation on cavity flow natural convection of Al 2 O 3 –water nanofluids

Thermo-physical properties of nanofluids have attracted the attention of researchers more than the heat transfer characteristic of nanofluids. On the other hand, contradictory results were reported on the thermal-fluid behaviour of nanofluids numerically and experimentally in the open literature. In addition to that, experimental natural convection has been investigated less than others. In this paper, characteristic and stability of Al 2 O 3 –water nanofluid (d = 30 nm) has been analyzed by using Malvern Zetasizer, Zeta potential, and UV–visible spectrosco-py. The natural convection of Al 2 O 3 –water nanofluids (formulated with single-step method) was experimentally studied in detail for volume fractions of 0, 0.05, 0.1, 0.2, 0.4 and 0.6% in a rectangular cavity, heated differentially on two opposite vertical walls for Rayleigh number (Ra) range 3.49 × 10 8 to 1.05 × 10 9. The viscosity of the Al 2 O 3 –water nanofluids are also measured experimentally in a temperature range between 15 °C and 50 °C and effect of temperature and volume fraction on viscosity have investigated. Detailed study on the influence of nanoparticle concentration on natural convection heat transfer coefficient was performed. It was found that increasing concentration of nanoparticles improves heat transfer coefficient up to an optimum value of 15% enhancement , at 0.1% volume fraction, then further increasing of concentration of the nanoparticles deteriorates natural convection heat transfer coefficient. This research also supports the idea of " for nanofluids with thermal conductivity more than the base fluids, there may exist an optimum concentration which maximizes the heat transfer in an exact condition as natural convection, laminar forced convection or turbulence forced convection " .

Experimental Studies of Natural Convection Heat Transfer of Al2O3/DI Water Nanoparticle Suspensions (Nanofluids)

Advances in Mechanical Engineering, 2010

The natural convection heat transfer characteristics of [Formula: see text] nanofluids comprised of 47 nm, [Formula: see text] and water, with volume fractions ranging from 0.5% through 6%, has been investigated through a set of experimental measurements. The temperature of the heated surface and the Nusselt number of different volume fractions of [Formula: see text] nanofluids natural convection tests clearly demonstrated a deviation from that of pure base fluids (distilled water). In the investigation, a deterioration of the natural convection heat transfer coefficient was observed with increases of the volume fraction of the nanoparticles in the nanofluids. The deterioration phenomenon was further investigated through a visualization study on a 850 nm diameter polystyrene particle/water suspension in a bottom heating rectangular enclosure. The influence of particle movements on the heat transfer and natural flow of the polystyrene particle/DI water suspension were filmed, and the...

CFD studies on natural convection heat transfer of Al2O3-water nanofluids

Heat and Mass Transfer, 2011

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Experimental Investigation of an Al2O3 / Distilled Water Nanofluid Used In the Heat Pipes of Heat Exchangers

gazi university journal of science, 2018

This study investigates the thermal performance of a heat pipe heat recovery system in air-to-air heat recovery systems using a nanofluid of Al 2 O 3 (aluminum oxide) particles and distilled water. The experimental setup used 15 wickless vacuumed copper pipes with a length of 1000 mm, a 10.5 mm inner diameter and a 12 mm outer diameter. The evaporator section consists of 450 mm of heat pipes, the condenser section is 400 mm, and the adiabatic section is 150 mm. In experimental studies, 33% of the evaporator volume of the heat pipes was filled with working fluids. Experiments were carried out at temperatures between 25 o C and 90 o C by using five different cooling air flows (40 g/s, 42 g/s, 45 g/s, 61 g/s and 84 g/s), and two different heating powers (3 kW and 6 kW) for the evaporation section, to determine the heat removed from the condensation section. Experiments were performed for distilled water and Al 2 O 3 nanofluid, respectively, and the results were compared with each other...

Effects of Nanoparticles Diameter and Concentration on Natural Convection of the Al2O3-Water Nanofluids.pdf

The effects of nanoparticles diameter and concentration on natural convection heat transfer of a nanofluid around a vertical cone embedded in a Darcy porous medium is theoretically investigated utilizing the drift-flux model. The thermal conductivity and the viscosity of the nanofluid are assumed as simultaneous functions of temperature and local volume fraction of nanoparticles using experimental correlations. In addition, the flux of nanoparticles on the surface of the cone is assumed to be zero. An efficient mathematical approach with a self-similar solution is utilized to theoretically analyze the boundary layer heat and mass transfer of an Al 2 O 3 -water nanofluid. The reduced system of ordinary differential equations are general and can be solved for any arbitrary functions of thermal conductivity and viscosity. The analysis of the nanofluid natural convection flow is accomplished for two cases of (i) T w > T 1 and (ii) T w < T 1 . The results show that using nanoparticles would not (would) enhance the heat transfer from the cone for the case of a cone with a hot surface (cold surface). A decrease in the size of nanoparticles or an increase in the volume fraction of nanoparticles causes a decline in the heat transfer rate from the cone when the cone surface is hot. Finally, a comparison between the non-homogenous model (drift-flux model) and the homogenous model of nanofluids is performed. The results demonstrate that the driftflux model tends to the homogeneous model as the size and volume fraction of nanoparticles increase.

Experimental investigation of forced convection of water/EG-Al2O3 nanofluids inside horizontal tube

E3S Web of Conferences

In this paper, forced convection of water/EG-Al2O3 nanofluids inside horizontal stainless steel tube is studied experimentally. As base fluid served water/EG mixture of two ratios (60:50 and 50:50). Nanoparticle mass concentrations was 0.1% or and 1%. Transition and turbulent flow regimes were tested. Average heat transfer coefficient and pressure drop values were determined for nanofluids and compared to base fluids. Deterioration of heat transfer for all tested nanofluids has been recorded compared to base fluid. Negligible increase of pressure drop for nanofluids compared to base fluids has been observed.

Experimental Investigations of Thermophysical Properties and Convective Heat Transfer of Al 2 O 3 and CuO Nanofluids in a Copper Tube: Proposing New Correlations

The performance of the Alumina/water and copper oxide/water nanofluids in a heat exchanger is experimentally investigated for particle weight concentrations ranging from 0.02 wt% to 0.5 wt%. The alumina/water and copper oxide/water nanofluids were prepared using two-step methods in an aqueous solution with 0.01 wt% CTAB (Cetyl Trimethyl Ammonium Bromide) as a surfactant at different concentrations and were characterized using HRTEM (High-Resolution Transmission Electron Microscopy) technique. Laminar forced convective heat transfer analysis using alumina and copper oxide nanoparticles suspended in water in a circular horizontal tube under constant heat flux boundary conditions was performed. The effect of various flow conditions and weight concentrations in the local heat transfer coefficient and pressure drop of both the nanofluids were investigated. Reynolds number varied from 1275 to 2200. Results show that 12.7 & 14.5 % thermal performance enhancement was observed with 0.5 wt% of Al2O3 and CuO nanofluids. Maximum, 50.62 % enhancement was observed in the average heat transfer coefficient by Al2O3 nanofluids, whereas 52.74 % was observed using CuO nanofluids using 0.5 wt% concentrations of the nanofluids and at Reynolds number of 2200. Correlations were proposed for thermal conductivity, viscosity, and Nusselt number for both the nanofluids with the maximum and minimum deviations of ±9 % and ±10 %, respectively.

Heat Transfer Performance in Heat Pipe Using Al2O3 –DI Water Nanofluid

Heat pipes are two-phase heat transfer devices with high effective thermal conductivity. This study presents the improvement of thermal performance of heat pipe using Al2O3 nanofluid. The nanofluids kept in the suspension of conventional fluids have the potential of superior heat transfer capability compared to the conventional fluids due to their improved thermal conductivity. The performance of the heat pipe greatly depends on the filling ratio of the working fluid. The Al2O3 – DI water is used as a working fluid. The temperatures at different places on the heat pipe are measured including the temperature of inlet and outlet of the cooling water. The results indicate that the variation of filling ratio, heat input and angle of inclination have a significant effect on its performance.

Performance analysis of turbulent convection heat transfer of Al2O3 water-nanofluid in circular tubes at constant wall temperature

Energy, 2014

The present paper analyzes the turbulent convection of Al 2 O 3 -water nanofluid inside a circular section tube subjected to constant wall temperature. The analysis is developed numerically by using the mixture model, which has been proved to be a convenient method to simulate nanofluids behavior. The numerical model is successfully validated by means of analytical equations and experimental correlations. The study is focused on the analysis of the performance of Al 2 O 3 -water nanofluid within the considered device. Performance indicators based on the first and second law of thermodynamics are taken into account and analyzed. At the increase of nanofluid concentration, the Nusselt number increases, but entropy generation and pumping power also increase, therefore the penalties overcome the benefits.