The systematic experiments were performed for buoyancy driven heat transfer of zinc oxide (ZnO)-water nanofluids with volume fraction 0.5%, 1%, and 2% in rectangular (50×50×75mm) cavity heated from below. In addition to determining the convective heat transfer coefficients, this study also included experimental determination of density, effective thermal conductivity, and rheological behavior of nanofluids. For all the properties and natural convection behavior De-Ionized (DI) water was used as the baseline data. The results show that density measurements agree well with predicted values by equation, thermal conductivity enhanced by ∼14% for 2 vol% nanofluids, and shear thinning behavior of nanofluids. The natural convection behavior shows degradation of heat transfer and degradation increases with the volume fraction of nanoparticles. Probable reasons of degradation are discussed in the paper.
In this paper, experimental investigation has been performed to characterize the heat transfer behavior of CuO–water and ZnO–water nanofluids. Nanofluids containing different volume percent (vol %) of nanoparticle concentrations flowed over a flat copper plate under a constant heat load. The constant heat flux was maintained using evenly placed cartridge heaters. The heat transfer coefficients of nanofluids were measured and compared with the results obtained from identical experiments performed with de-ionized (DI) water. In order to thoroughly characterize the nanofluids, nanoparticle size was investigated to inspect for possible agglomeration. The particle size was measured by using both a transmission electron microscope (TEM) and a dynamic light scattering system (DLS). Enhancement of convective heat transfer of nanofluids was 2.5–16% depending on the nanoparticle concentrations and Reynolds number. The plausible mechanisms of the enhanced thermal performance of CuO and ZnO nanofluids will be discussed in the following paper.
Thermal characteristics of CopperII and Zinc-Oxide nanofluids have been investigated for flow over a heated flat plate. Fluid containing different volume-percents nanoparticles flow over a heated flat plate at specified laminar flow velocities. The heated plate experienced a constant heat flux from cartridge heaters spaced evenly along the length of the plate. The flow channel’s cross-sectional area was a square of dimensions 5cm × 5cm. Investigation of the heat transfer occurring in a plane along the centerline of the plate in the direction of the flow was performed. The heat transfer coefficients were calculated and plotted verses the Reynolds number and compared with the results obtained from distilled de-ionized water. Nanoparticle size from the fluids was investigated to inspect for possible agglomeration using both a transmission electron microscope (TEM) and a dynamic light scattering system (DLS).
Nanofluid has the promising potential for enhancing the heat transfer performance of conventional fluids. Several experimental and numerical attempts have been made earlier to investigate its important thermo physical properties like thermal conductivity and viscosity. The findings and results are quite disperse instead of reaching a definitive agreement. This paper presents effective viscosity measurements of CuO and ZnO nanofluids experimentally. A Brookfield viscometer model DV-I Prime with a CPE 40 cone has been used to determine the effective viscosity of nanofluids. The measurements have included the effect of volume concentration of nanoparticles and temperature. The experimental results are compared with several experimental and theoretical models available in the existing literature. From the obtained experimental results it can be concluded that the viscosity values of the above mentioned nanofluids has a tendency to increase with increase of nanoparticle concentration and follows a decreasing trend with an increase in temperature. Presented results can be used to define the above mentioned nanofluids within the experimental volume concentration range in CFD software package and hence to predict overall heat transfer performance using these nanofluids.
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