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In this study, the performance of hybrid nanofluids in a flat plate solar collector was analysed based on various parameters such as entropy generation, exergy efficiency, heat transfer enhancement, pumping power, and pressure drop. Five different base fluids were used, including water, ethylene glycol, methanol, radiator coolant, and engine oil, to make five types of hybrids nanofluids containing suspended CuO and MWCNT nanoparticles. The nanofluids were evaluated at nanoparticle volume fractions ranging from 1% to 3% and flow rates of 1 to 3.5 L/min. The analytical results revealed that the CuO-MWCNT/water nanofluid performed the best in reducing entropy generation at both volume fractions and volume flow rate when compared to the other nanofluids studied. Although CuO-MWCNT/methanol showed better heat transfer coefficients than CuO-MWCNT/water, it generated more entropy and had lower exergy efficiency. The CuO-MWCNT/water nanofluid not only had higher exergy efficiency and thermal performance but also showed promising results in reducing entropy generation.

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The effect of the geometric parameters on the flow and heat transfer characteristics of a double-layer U-shape microchannel heat sink (DL-MCHS) for a high-power diode laser was investigated in this work. FLUENT 19.2 based on the finite volume method was employed to analyze the flow and heat transfer performance of DL-MCHS. A single variable approach was used to fully research the impact of different parameters (the number of channels, the channel cross-sectional shape, and the aspect ratio) on the temperature distribution, pressure drop, and thermal resistance of the DL-MCHS. The rectangular DL-MCHS heat transfer performance and pressure drop significantly increased with the rise in the channel's aspect ratio due to there being a larger wet perimeter and convective heat transfer area. By comparing the thermal resistance of the DL-MCHS at the same power consumption, it was found that the rectangular DL-MCHS with an aspect ratio in the range of 5.1180-6.389 had the best overall performance. With the same cross-sectional area and hydraulic diameter (AC = 0.36 mm, Dh = 0.417 mm), the thermal resistance of the trapezoidal microchannel heat sink was 32.14% and 42.42% lower than that of the triangular and rectangular ones, respectively, under the condition that the pumping power (Wpp) was 0.2 W. Additionally, the thermal resistance was reduced with the increment of the number of channels inside the DL-MCHS, but this would induce an increased pressure drop. Thus, the channel number has an optimal range, which is between 50 and 80 for the heat sinks in this study. Our study served as a simulation foundation for the semiconductor laser double-layer U-shaped MCHS optimization method using geometric parameters.

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Covalent-functionalized graphene nanoplatelets (CF-GNPs) inside a circular heated-pipe and the subsequent pressure decrease loss within a fully developed turbulent flow were discussed in this research. Four samples of nanofluids were prepared and investigated in the ranges of 0.025 wt.%, 0.05 wt.%, 0.075 wt.%, and 0.1 wt.%. Different tools such as field emission scanning electron microscopy (FE-SEM), ultraviolet-visible-spectrophotometer (UV-visible), energy-dispersive X-ray spectroscopy (EDX), zeta potential, and nanoparticle sizing were used for the data preparation. The thermophysical properties of the working fluids were experimentally determined using the testing conditions established via computational fluid dynamic (CFD) simulations that had been designed to solve governing equations involving distilled water (DW) and nanofluidic flows. The average error between the numerical solution and the Blasius formula was ~4.85%. Relative to the DW, the pressure dropped by 27.80% for 0.025 wt.%, 35.69% for 0.05 wt.%, 41.61% for 0.075 wt.%, and 47.04% for 0.1 wt.%. Meanwhile, the pumping power increased by 3.8% for 0.025 wt.%, 5.3% for 0.05 wt.%, 6.6% for 0.075%, and 7.8% for 0.1 wt.%. The research findings on the cost analysis demonstrated that the daily electric costs were USD 214, 350, 416, 482, and 558 for DW of 0.025 wt.%, 0.05 wt.%, 0.075 wt.%, and 0.1 wt.%, respectively.

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Coolants play a major role in the performance of heat exchanging systems. In a marine gas turbine engine, an intercooler is used to reduce the compressed gas temperature between the compressor stages. The thermophysical properties of the coolant running within the intercooler directly influence the level of enhancement in the performance of the unit. Therefore, employing working fluids of exceptional thermal properties is beneficial for improving performance in such applications, compared to conventional fluids. This paper investigates the effect of utilizing nanofluids for enhancing the performance of a marine gas turbine intercooler. Multi-walled carbon nanotubes (MWCNTs)-water with nanofluids at 0.01-0.10 vol % concentration were produced using a two-step controlled-temperature approach ranging from 10 °C to 50 °C. Next, the thermophysical properties of the as-prepared suspensions, such as density, thermal conductivity, specific heat capacity, and viscosity, were characterized. The intercooler performance was then determined by employing the measured data of the MWCNTs-based nanofluids thermophysical properties in theoretical formulae. This includes determining the intercooler effectiveness, heat transfer rate, gas outlet temperature, coolant outlet temperature, and pumping power. Finally, a comparison between a copper-based nanofluid from the literature with the as-prepared MWCNTs-based nanofluid was performed to determine the influence of each of these suspensions on the intercooler performance.

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This research was designed to experimentally study the influence of using three metal oxide nanofluids at different high flow rates with various mass concentration of nanoparticles as the working fluid, on the thermal efficiency and pumping power of heat pipe solar collector (HPSC). The volume flow rate of the working fluid was 5, 8, 11, and 14 L/min. Also, mass concentration of nanoparticles was 0.5 and 1.167 g/L. Co-precipitation technique was employed to prepare CuO, Al2O3, and MgO nanoparticles. The optical and structural characterization of the nanostructure were considered by using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), and UV-visible analysis. The thermal performance of the HPSC using metal oxide nanofluids and water was compared with the volume flow rate that varied from 5 to 14 L/min. It was observed that nanofluids improved the collector efficiency between 9 and 20% compared with deionized water. The present results revealed that the maximum efficiency was found to be 83% for a mass concentration of 1.167 g/L of CuO nanofluids and volume flow rate of 14 L/min. The HPSC efficiency shows better improvement with the increasing mass concentration of metal oxide nanoparticles and volume flow rate. Also, the increase rate of the pumping power and pressure drop is less than 0.9% for all of the nanofluids that were used as the working fluids. Results showed that the metal oxide nanofluids are appropriate for increasing the efficiency of HPSC.

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It is of both fundamental importance and practical value to measure the frequency of an LC resonator beyond the near-field region, especially when the resonator is used as a standalone capacitive sensor embedded inside a closed environment. To improve the coupling efficiency between the resonator and the external sniffer loop, we propose a novel method to integrate the LC resonator with a wirelessly-powered parametric resonator whose oscillation signal can be remotely identified in a noisy background. By measuring the minimum power level that is required for oscillation at different pumping frequencies, the resonator can be indirectly characterized by the frequency response curve. Starting from the basic principle of parametric oscillation, we will predict the measurable extremities in the frequency-dependent power curve under various circumstances that are classified based on the relative ratio between the lower and higher resonance frequencies. Our analytical models are validated by on-bench measurements performed on several parametric resonators with different circuit topologies. Their ability for remote characterization will make parametric resonators useful in structural health sensors or biomedical implants.

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In this paper, three different designs of a hybrid PV/T double-pass finned plate solar air heater (DPFPSAH) are investigated. The PV module is used to produce electricity needed to run the pump and blow the air into the solar collector. In the first design, the PV module is placed on the absorber plate of the air heater. In the second design, the PV module is placed beside the glass cover of the air heater; while, in the third one, the PV module is completely separated from the solar collector. The effects of mass flow rate of air, flow, and fan pumping powers are studied. The top losses of the third design are found to be higher than that of the first and the second designs by average values of 7.5% and 29%, respectively. The third design of the hybrid systems has the highest overall performance. The daily thermal efficiencies of the first, second, and third designs of the hybrid systems are obtained as 53%, 27%, and 64%, respectively, at mass flow rate of 0.02 kg/s.

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This research aims at studying the stability and thermophysical properties of nanofluids designed as dispersions of sulfonic acid-functionalized graphene nanoplatelets in an (ethylene glycol + water) mixture at (10:90)% mass ratio. Nanofluid preparation conditions were defined through a stability analysis based on zeta potential and dynamic light scattering (DLS) measurements. Thermal conductivity, dynamic viscosity, and density were experimentally measured in the temperature range from 283.15 to 343.15 K and nanoparticle mass concentrations of up to 0.50% by using a transient plate source, a rotational rheometer, and a vibrating-tube technique, respectively. Thermal conductivity enhancements reach up to 5% without a clear effect of temperature while rheological tests evidence a Newtonian behavior of the studied nanofluids. Different equations such as the Nan, Vogel-Fulcher-Tamman (VFT), or Maron-Pierce (MP) models were utilized to describe the temperature or nanoparticle concentration dependences of thermal conductivity and viscosity. Finally, different figures of merit based on the experimental values of thermophysical properties were also used to compare the heat transfer capability and pumping power between nanofluids and base fluid.