AHMED MOHSIN DHAYEA AJEENA

An advanced analysis of thermal behavior of three-dimensional conjugate heat transfer in a horizontal pipe with a fluid flow in a steady and transient states is performed. A numerical procedure of threedimensional conjugate heat conduction in a solid wall and heat convection in a laminar flow with radial radiation is developed by analyzing a computational modeling of the solid-fluid domains. The procedure is based on the assumption that the gradient of temperature and heat flux of the solid-fluid domains are dependent on the thermal equivalent between conduction, convection and radiation heat transfers, which is true since the thermal loads on the pipe are reasonably identified. Annealed stainless steel as a common solid pipe is used with two types of fluids (air and water) for sustainability assessment. The results of the thermal analysis are represented by various parameters in the steady and transient states to emphasize the effect of the three-dimensional conjugate heat transfer combined with radial radiation on the fluid flow. These parameters are the temperature distribution and the heat flux from the ambient to the fluid flow and the fluid velocity. The environmental impacts on the pipe are estimated in terms of Air Acidification and Water Eutrophication. It can be concluded from the thermal analysis that the computational modeling of the thermal loads recommends for different types of engineering devices such as a convergent-divergent nozzle.

The main reason behind the inefficient performance of heat transfer devices was the use of conventional fluids with poor heat transfer properties. However, remarkable improvement in efficiency was observed in thermal devices when these fluids were replaced by nanofluids with good thermal transfer properties. Various kinds of nanoparticles were used due to their increased thermal conductivity. Such nanofluids are particularly exploited in renewable energy systems like solar collectors. The most frequently used solar collectors in thermal appli cations are FPSCs. The current experimental research investigates how the use of nanofluids of SiC/DW impact the efficiency of a flat plate solar collector functioning in the climatic environment of G¨ od¨ oll˝ o, in Hungary. Firstly, the synthesis of nanofluid based on distilled water that contained nanoparticles of SiC (with a size 45–60 nm) at volume fractions of 0.025 %, 0.05 %, 0.075 %, and 0.1 % was performed. Various measurement in struments were used to test the thermophysical characteristics and stability. In the subsequent stage, thermal and exergy efficiencies tests were conducted on the solar collector with a range of mass flow rates including 0.025, 0.033, and 0.041 kg/s in which the collector’s efficiency was calculated according to the ASHRAE standard 93–2003. This developed collector was subjected to different flow rates, and nanoparticle concentrations to find out the effect of nanofluids on the thermal and exergy efficiencies of the solar collector. The findings indicated that an increase of up to 30.3 % was achieved in the fluid’s thermal conductivity through the addition of nanoparticles of SiC. The collector’s thermal efficiency was maximised at 77.43 % when the value of [(Ti – Ta)/ GT] was zero for a volume fraction (φ) of 0.1 % and mass flow rate of 0.041 kg/s, which represented a 35.53 % increase over the base liquid. Additionally, an increase of 37.4 % was recorded for the exergy efficiency at volume fraction (φ) of 0.1 % than its value in distilled water. Ultimately, the heat transfer properties of the device showed improvement.

It is becoming very difficult for the industrial and technological sectors to meet the ever-escalating fuel and energy demands of a growing population. Experts and scholars have emphasized studying the feasibility of using renewable energies specifically solar energy. In this regard, huge efforts have been invested lately to study the effects of adding nanofluids in solar-based devices. The hybrid nanofluid in this work is prepared by dispersion of ZrO-SiC particles in distilled water (DW). The nanofluid is employed into a Flat plate solar collector (FPSC) to identify the performance change of the collector. The study is conducted in solar energy laboratory, G¨ od¨ oll˝ o, Hungary. Next, various instruments are employed to evaluate the nanofluids’ stability and thermo-physical properties. Consequently, the ASHRAE standard 93–2003 is followed during the evaluation of the efficiency of solar collectors filled with nanofluids at mass flow rate of 0.025, 0.033, and 0.041 kg/s. The outcomes of the experiment revealed that the solar collector system showed greater energy and exergy efficiencies in the presence of a nanofluid as compared to the exergy and energy efficiencies shown by the system-based distilled water. The results indicated that at zero value of [(Ti – Ta)/GT], volume fraction of 0.1 % and mass flow rate of 0.041 kg/s, the collector showed maximum thermal efficiency equalling 75.21 %. Hence, nanofluid addition leads to a 31.64 % enhancement in thermal efficiency. It was found that the solar collector exergetic performance was evaluated which indicated a decline in exergy efficiency at a higher mass flow rate and also indicated a rise in the exergy efficiency at a higher concentration of nanoparticles in the nanofluid. At the concentration of 0.1 %, the system yielded maximum increase of about 28.31 % in the exergy efficiency.

Researchers, engineers, scientists, and other professionals have been focusing on the exploitation of nanotech nology with specific attention to nanofluids and their property of dynamic viscosity that can do wonders in the f ield of engineering. This study was aimed at determining the dynamic viscosity of the given hybrid nanofluid (distilled water based ZrO 2 /SiC) by studying the nanofluid's rheology. In this regard, a two-step method was employed for the dispersal of nanoparticles in the base fluid. The nano-powder was composed of ZrO ◦ 2 and SiC in a ratio of 1:1 (50% - 50%). The dynamic viscosity of solid volume fractions 0.025% - 0.1% was measured in temperatures 20–60 C by using DV2TRVTBG Brookfield digital viscometer. The research indicated the associ ation between the nanofluid's viscosity and the factors of temperature and solid volume fraction. At first, in order to assessment the characteristics and stability of nanoparticles into the base fluid, XRD, TEM, FESEM, EDX, UV–vis spectrometer, DLS, and zeta potential test were used on ZrO 2 and SiC nanoparticles. The results indicated an increase in dynamic viscosity at higher solid concentrations and falling temperatures. The dynamic viscosity increase of the nanofluid was recorded at 20 and 60 ◦ C, which showed a 29.6% and 64.2% rise in the viscosity

The main aim of this experiment was to determine the thermal conductivity of two nanofluids, ZrO 2 /DW and SiC/DW, under different temperatures and concentrations as compared to the base fluid. In this work, zirconium oxide and silicon carbide nanoparticles were obtained, and the nanofluids were prepared using a two-stage method by dispersing the nanoparticles in distilled water (DW) by the ultrasonic processor and a magnetic mixture. Field emission scanning electron microscopy (FESEM), Energy-dispersive x-ray spectrometer (EDX), Transmission Electron Microscope (TEM), and X-ray diffraction (XRD) techniques were used to microstructural and characterize the nanoparticles. Stability of nanofluids were examined by zeta potential test. After that, thermal conductivity was measured using the thermal hot wire method using a KD2-Pro thermal analyzer at temperatures ranging from 20 to 60 ◦ C. Solid volume fractions (φ) of 0.025%, 0.05%, 0.075%, and 0.1% were used. The results showed that the thermal conductivity of the nanofluid was enhanced with increased volume fractions and temperature. The highest recorded thermal conductivity was at the highest temperature 60 ◦ solid volume fraction 0.1%. The thermal conductivity enhancement for ZrO 2 C and /DW at the volume fraction of 0.1% was 20.455%, and that of SiC/DW was 30.303%. The enhancement was compared to that of the base fluid, distilled water. Finally, based on experimental data, A new mathematical correlations were obtained by curve- f itting. The correlations were used to estimate the thermal conductivity of ZrO 2 /DW and SiC/DW nanofluids at different solid volume fractions and temperatures. The results obtained were compared to a correlation to determine their accuracy. The deviations from the presented correlations were 1.49% and 1.2% for ZrO /DW and SiC/DW, respectively. The comparison between experimental results and correlation outputs showed a good agreement which signifies that the results were accurate.