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Abstract In this study, impingement/effusion cooling with cross-flow of in-line array of electronic components (ECs) is investigated numerically using RNG k-ɛ turbulence model. The cooling process is examined for two channel base configurations i.e., solid board (SB) and perforated board (PB). Effects of effusion perforation diameter (d/l) and its position (s/l) are considered on flow structure, temperature contours, heat transfer, and friction coefficient for different jet-to-cross Reynolds number ratios (ReR). Throughout the experiments, the jet position is kept at the third EC [1] . The results show that utilizing perforated board generates a new E vortex behind each component and the magnification of the wake vortex depends substantially on both perforation diameter and position. The ratio of average heat transfer coefficient ( h ¯ R ) on the rear faces of ECs decreases with increasing s/l; while, it increases with increasing d/l. As well, d/l has a significant effect on friction coefficient; while, ReR and s/l have inconsiderable effect. Furthermore, the highest value of performance evaluation criteria (PEC) that is accomplished at the largest perforation diameter for the closest one, equals to 1.36 at ReR of 0.5. Also, a proposed correlation is presented to estimate PEC for PB as a function of ReR, d/l, and s/l.

Abstract In the present study, the effect of the inclination angle (ɵ) of a shell and helically coiled tube heat exchanger (SHCT-HE) on its performance utilizing based water, Al2O3/water, and SiO2/water nanofluids is investigated experimentally. The hot based water as well as nanofluids with volume concentrations ( ϕ ) of 0.1 vol%, 0.2 vol%, and 0.3 vol% flow through the coiled tube with a coil Reynolds number (Rec) varied from 6000 to 15000. The inclination angle is measured from the horizontal axis of the SHCT-HE as 0°, 30°, 60°, and 90°. The results indicate that increasing the inclination angle enhances the coil Nusselt number (Nuc) and the effectiveness of SHCT-HE (e); while, it decreases the coil pressure drop (ΔPc). Where, at coil Reynolds number of 15000, changing the orientation of the SHCT-HE from the horizontal to the vertical orientation improves the coil Nusselt number by 11%, 8.3%, and 7.5% for based water, Al2O3/water, and SiO2/water nanofluids with 0.1 vol%, respectively. Furthermore, at vertical orientation of heat exchanger and coil Reynolds number of 6000, utilizing Al2O3/water nanofluid with 0.1 vol% intensifies significantly the coil Nusselt number and the effectiveness than those for the based water by 35.7% and 35.5%, respectively. In addition, increasing the inclination angle up to 30° keeping the performance evaluation criterion (PEC) almost constant and more elevating into the vertical orientation decreases the PEC. Using multiple regression analysis, empirical correlations are proposed to estimate the coil Nusselt number (Nuc) for based water, Al2O3/water, and SiO2/water nanofluids as a function of R e c , θ , a n d ϕ .

Unforeseeable growth in the global population needs growing technological advances in establishing power plants to overcome this critical issue by reducing greenhouse gases. In the present study, a thermodynamic analysis for a 626 MW supercritical oil-fired steam power plant under different operating loads of 50%, 75%, 100%, and 105% at a sliding-pressure operation is conducted. Based on the actual operation of the examined plant, the results show that the condenser has the highest energy loss. As well, at a 100% full load, 88.6% of the total exergy is destructed in the once-through steam generator, followed by the turbine, and then the condenser. Hence, a significant concern is introduced toward the steam generator since it has the largest exergy destruction percentage relative to other cycle components. The heat transfer sets inside a once-through steam generator are studied and analyzed. The exergy destruction in the combustion process represents 58.6% and 54% of the overall boiler exergy destruction at an operating load of 50% and 100%, respectively. In addition, the evaporator has higher exergy destruction in comparison with other heating surfaces in the furnace.

Abstract The efficiency, availability, and reliability of thermal management for various engineering applications present a crucial challenge facing the designers and engineers. The rapid development and sophisticated technological advancement require innovative devices possessing high operating capacities that are launched into the prodigious growing markets in all engineering sectors. As a result of pronounced advancements, the jet impingement required to transfer high heat fluxes with a target surface becomes one of the essential priorities for researchers. The intensification of jet impingement can be achieved with different techniques such as passive self-exciting jets, active exciting jets, and hybrid exciting jets. The active methods of self-exciting jets include annular, swirling, and sweeping jets, while the active ones contain pulsed and synthetic jets. In the current study, the heat transfer characteristics and the fluid flow behavior of jet impingement with recent modifications of jets are reviewed comprehensively. As well, the critical methods of passive and active exciting jets considering the jet geometrical and operating parameters are introduced. Moreover, the physical phenomena for each technique in comparison to the conventional circular straight jet as well as the published empirical correlations as available, are studied. The present work reviews the published numerical and experimental investigations considering the different modified jets and its application with various installation geometries that provide a higher efficiency with the augmentation of heat transfer rate. The jet excitation causes topological metamorphosis of flow and hence has a remarkable effect on the intensification of heat transfer.

Abstract In this study, experimental investigation has been conducted on fluid flow and heat transfer of rough mini-channels with rectangular cross sections. The mini-channel considered consists of twelve identical rectangular channels with 4 mm width, 8 mm height, and 80 mm length. Air is employed as the working fluid with Reynolds number varied from 1500 to 5000. Four mini-channels were examined with different values of relative surface roughness (ɛ) 1.6 ∗ 10−4, 3.45 ∗ 10−4, 6.15 ∗ 10−4, and 10.5 ∗ 10−4. The friction factor (f), average Nusselt number (Nu), pressure drop penalty factor (Ef), heat transfer enhancement factor (Ehn), and universal evaluation parameter (PEC) were evaluated to study fluid flow and heat transfer of rough mini-channels with rectangular cross sections. The results showed that increasing the Reynolds number (Re) of air passing through the rectangular rough mini-channel, increases the average Nusselt number (Nu) and the pressure drop penalty factor (Ef), while decreasing the friction factor (f) and the heat transfer enhancement factor (Ehn) which, has a great effect on the universal evaluation parameter (PEC) rather than the pressure drop penalty factor (Ef). Moreover, a correlation of the relative surface roughness (e) and the universal evaluation parameter (PEC) was obtained.