Improving efficiency of the nuclear power plants has always been of interest for researchers. Recently, Nanofluid technology are developed to increase the heat extraction from a hot surface. Throughout this work, the thermal hydraulic behavior of Nanofluid was experimentally investigated and theoretically predicted. For this purpose, an experimental apparatus (setup) was designed and constructed to study the effect of the kind of Nanomaterial and the concentration of nanoparticles. Two kinds of Nanomaterial, Carbon Nano Tubes (CNTs) and Copper Oxide (CuO) were used. In an experimental investigation of CNTs, two nanoparticles concentration was used; 0.05 and 0.1% vol. CNTs/Water. CuO nanofluid was investigated experimentally with 0.1, 0.2, 0.3, 0.4, and 0.5% vol.CuO/Water. These concentrations of nanofluid were investigated at a constant mass flow rate and different heat fluxes, (1000, 3000 and 5000 W/m2). The test rig was modeled theoretically using ANSYS FLUENT 17.2 code and validated to predict the thermal hydraulic performance of the Nanofluid. The five concentrations of CNTs and CuO nanofluids were theoretically investigated. It was found that the measured wall surface temperatures of CNTs and CuO nanoparticles decreased remarkably as heat flux decreased and the nanoparticles concentrations increased. There was an increase in forced thermal efficiency of nanofluids as compared to base fluid. The experimental results showed a maximum heat transfer coefficient enhancement of 26.55% for a nanofluid prepared with 0.1% vol. CNTs and 20.6% with 0.5% vol. CuO. A good agreement was detected after comparing experimental results with the investigated model.
Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
Research funding: None declared.
Conflict of interest statement: The authors declare no conflicts of interest regarding this article.
Nanofluid preparation and characterization
Two nanoparticle materials, i.e., Copper Oxide (CuO) and Carbon Nano Tubes (CNTs), were selected for these experiments primarily due to their high chemical and colloidal stability. Water based nanofluids of these nanoparticles were prepared.
Preparation of nanofluid samples
A.1 Preparation of CuO nanoparticles
The preparation of CuO nanoparticles were performed by chemical reduction method of CuCl2.2H2O by eco-friendly material such as ascorbic acid. In a typical experiment, 0.01 mol of CuCl2.2H2O were dissolved in 100 ml deionized water in a 250 ml two neck round bottom flask equipped with a mantle heater, a small magnetic stirrer, and a thermometer. The solution was stirred rapidly at room temperature and the temperature was raised to 90 °C. After that the 2.2 g of ascorbic acid was then added gradually to the reaction. During the whole time of the reaction, some changes were found to the color of the solution from colorless to pale yellow to orange till deep brown black color. The reaction takes 17 h till obtaining CuO nanoparticles solution. To show high crystallinity and remove organic impurities, the obtained solution was dried at oven for six hand then finally calcined at 1000 °C in a furnace for 1 h. The resulted black powder of CuO nanoparticles was then characterized by an ultraviolet-visible (UV–Vis), X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscope analysis (TEM).
A.1.1 UV spectroscopy
Ultraviolet Spectroscopy is a first step for the characterization of a nanomaterial Figure A.1. The Cu peak appeared around 310 cm−1. Using this tool was a great benefit to determine the particle size of the prepared material. As with the knowledge of the peak intensity and using equation from which the particle size can be calculated it was 16 nm
where h corresponding to Planck’s constant, ν f is the Fermi velocity of electrons in bulk Cu nanoparticles. D is the particle size of Cu which found to be equal 16 nm.
A.1.2 X-ray diffraction (XRD)
X-ray diffraction device is a valuable method to calculate particle size and the structure of the prepared material. The maximum peak intensity appeared around θ = 26°, also the intense peaks appear at the same values 64, 74, 54, 35 as mentioned for other studies which ensure the preparation of metallic CuO (Umer et al. 2014)and using Scherrer’s equation revealed a crystallite size of about 66 nm in such powders as shown in Figure A.2. It shows perfectly the effect of different concentration effect which is observed from the resulted peaks and their values.
A.2 Preparation of carbon nanotube (CNTs)
For 5 gm. activated charcoal we add 50 ml sulfuric acid and 25 ml fume Nitric acid. Then let the mixture be cooled till its temperature become near to 10 °C using Ice bath, after that the mixture is stirred for 30 min, meanwhile the addition of sodium perchlorate (25 gm) to the mixture begins. It is preferably to be added gradually, after 30 min stop the mixing process and heat the mixture at 70 °C for 24 h then let it dry for three days. Remove the formed layer gently and let it dry for one day then repeat the above steps a gain for at least four times to increase number of the formed CNT starting from the step of mixing with Nitric acid and sulfuric acid. Then the final product has been examined using Raman Microscopy and TEM.
A.2.1 Raman microscopy analysis
Figure A2.1, vibrational modes are identified using Raman spectroscopy by measuring the energy of scattered photons generated by a sample exposed to intense laser light. CNT Raman spectra typically include a graphitic or G-band from highly ordered sidewalls, while disorder in the sidewall structure results in a D-band. The ratio of these two bands can be used to compute a quantifiable measure of defect density in the CNT sidewall (ID: IG). As a result, ID: IG band analysis can be used to obtain information about structural changes caused by functionalization.
A.2.2 Transmission electron microscopy (TEM)
Transmission electron microscopy (TEM) was used to characterize the cross-section of MWCNTs. Representative TEM overviews of the samples investigated are shown in Figure A2.2. From a qualitative point of view these samples mostly consist of nanotubes. As shown the figure, high concentration of the CNT but as mentioned on each the value of each for (a) its diameter is 50 nm and with amplitude of 0.5 μm and for other 0.2 μm.
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