Alami, Abdul HaiRamadan, MohamadAbdelkareem, Mohammad AliAlghawi, Jawaher Jamal...
20页
查看更多>>摘要：Solar energy has witnessed a rapid development during the past three decades. However not all solar technologies have reached the same level of maturity. Photovoltaic (PV) technologies possess the lion share of development in all technical aspects including materials, output efficiency, prices and mass production. A remarkable decrease in the cost of such technologies has allowed their proliferation into energy markets as a synonym to renewable energy. In this framework, this paper offers a review of recent progress in PV applications that have not been categorized or reviewed before. The domains under investigation include transportation, domestic applications, street lighting and water applications. Moreover, an overview of the different sub-applications belonging to each family of applications is presented. In transportation domain, aircraft propulsion and maritime propulsion are reviewed. In domestic applications, heat pumps as well as indoor application are studied. The review also covers water applications including desalination irrigation and pumping. Having said that, the current investigation clearly projects the potential of photovoltaic technology in energy applications and provides an insight about the future progress of this domain.
查看更多>>摘要：The conical liquid sheet formed by a swirl nozzle was numerically investigated by volume-of-fluid (VOF) in this paper. With increase of Reynolds number (Re), the breakup process of the conical liquid sheet was dominated successively by rim, rim-perforation, perforation, perforation-wave and wave disintegration modes, which agreed well with the experiment results. For the perforation disintegration mode, several kinds of hole in the liquid sheet were successfully predicted, such as isolated holes and group holes. The expansion speed of the hole varied with the time in an exponential form at the initial stage of hole growing, and then kept constant at TaylorCulick speed. That was the reason why there were two views on the expansion speed of the hole. A model to predict the expansion speed and the rim radius of the hole was proposed and well validated by the numerical results. The flow instability in the conical liquid sheet was successfully predicted, and its wave length was corresponding with Reitz wave instability model. Based on such flow instability, the mechanism of perforation formation was revealed. At the superimposed position of surface wave troughs, fluid migration from this position to its surrounding stretched the liquid sheet thinner and thinner, and finally made it collapsing. Thus, the perforation of the liquid sheet was an intrinsic performance induced by flow instability of liquid sheet itself, rather than the environmental factors. Furthermore, based on the such perforation mechanism, a perforationtime model is proposed, which is reasonable to predict the formation process of hole.
查看更多>>摘要：Two novel composite adsorbents have been developed with porous home silica-gel to enhance the performance of the adsorption refrigeration system. The two types of thermal conductivity enhancers (TCEs) namely graphite and copper powder with a polymeric binder polyvinyl alcohol (PVA) are used to develop the high-performance composite adsorbents. The thermal stability, crystallinity and morphology of prepared composite adsorbents are analyzed. The porous properties such as specific surface area, pore volume and pore size distribution, and the thermophysical properties such as specific heat, thermal conductivity and thermal diffusivity are also investigated. A maximum specific surface area of 417 m(2)/g and pore volume of 0.3648 cm(3)/g is observed for a composite of 80% silica-gel + 10% graphite + 10% PVA. The copper-based composite adsorbents show lower specific heat values as compared to the graphite-based composite adsorbents. The thermal conductivity and diffusivity of composite adsorbents are significantly increased with the increased percentage of TCEs. A maximum thermal conductivity of 0.5 W/m K and diffusivity of 0.34 x 10(-6) m(2)/s is observed for graphite-based composite adsorbent with a composition of 50% silica-gel + 40% graphite powder + 10% PVA. This is 4.23 times and 2.12 times greater than the thermal conductivity and thermal diffusivity of the silica-gel respectively. Similarly, a maximum thermal conductivity of 0.433 W/m K and diffusivity of 0.214 x 10(-6) m(2)/s are observed for copper-based composite adsorbent with the same composition of TCE. This is 3.66 times and 33% greater than the thermal conductivity and diffusivity of the silica-gel respectively. The developed composite adsorbents show improved thermal and physical properties as compared to the conventional silica-gel.& nbsp;
查看更多>>摘要：This article presents a closed form analytical solution to estimate solar receiver surface and fluid temperatures. An approximation and its domain of validity (in term of the value of a small parameter) are also proposed. These simple models are then applied to a large and a small cylindrical cavity. Finally, the model is applied to an experimental hemispherical coiled cavity.
查看更多>>摘要：Rotor casing injection is one of the technical means for tip leakage flow control and casing thermal management. In the current investigation, a series of numerical simulations with the unsteady sliding mesh method are conducted to illustrate the effects of injection location, tip clearance, and shaped injection hole on the aerodynamic and cooling performance of casing air injection in an axial turbine cascade, under three injection mass flow ratios (0.15%, 0.30%, and 0.45%). The results indicate that the casing injection at X/C-a = 0.1 performs the best in reducing the tip leakage mass flow rate, but the highest isentropic efficiency appears when the injection holes are located at X/C-a = 0.3. The increase of the tip clearance is detrimental to the aerodynamic and film cooling performances of the casing injection scheme. Moreover, the application of shaped holes (converging slot hole and fan-shaped hole) plays a positive role in improving film cooling effectiveness and increasing isentropic efficiency. Especially under a large coolant to mainstream mass flow ratio of 0.45%, the results show that the fan-shaped hole improves the spatially-averaged casing film cooling effectiveness by approximately 16% relative to the cylindrical hole.
查看更多>>摘要：Nowadays, thanks to ever-increasing computational resources, a viable path to a robust and fast design strategy for both thermal machines and turbomachinery is the coupling of Computational Fluid Dynamics (CFD) and shape optimization algorithms. In general, numerical optimization approaches require less time than the trial and-error procedure traditionally employed, where the designer produces only a tentative initial geometry. This work assesses the capability of a shape optimization algorithm to enhance the design of a steam boiler mixing channel to guarantee negligible NOx production, avoid combustion instabilities especially at lower thermal powers, due to a bad mixing quality of the mixture, and thermal deformation on the burner surface mesh, due to a non uniform distribution of the flame. In particular, the effect of the mixing quality, flow uniformity and the pressure losses at the outlet section of the mixing channel are investigated. The shape optimization approach is here based on a Surrogate Based Optimization (SBO) with the Multi Objective Genetic Algorithm (MOGA), where response surfaces based on the Kriging meta-model are adopted to decrease the computational cost of the proposed approach.
Ramachandran, Abhilash VakkadaZorzano, Maria-PazMartin-Torres, Javier
15页
查看更多>>摘要：Environmental chambers are used to test the expected performance of space instrumentation and to investigate certain processes which are relevant in space or other planetary environments. In this study, a computational model of an existing Martian experimental facility is investigated numerically using COMSOL Multiphysics. For this purpose, we simulate the near surface water cycle under Martian temperature and pressure experimental conditions as tested inside the chamber and we compare the simulations with the experimental data. The model shows good agreement with experiments on the equilibration time scales and thermal gradients. Due to the imposibility to place sensors at multiple locations inside the chamber, we use the model to extrapolate the onepoint relative humidity of the experimental data to each grid points in the simulation. This model gives an understanding of the gradient in atmospheric water relative humidity to which the experimental samples such as deliquescent salts and Martian regolith simulants are exposed at different time intervals. The of the performance of HABIT instrument during the tests, of the ESA/IKI ExoMars 2022 robotic mission to Mars, when compared with the model shows the existence of an extra internal heating source of about 1 W which can be attributed to the hydration and deliquescence of the salts exposed to Martian conditions when in contact with atmospheric moisture. In addition, the presented model is used to predict the thermal gradients and understand the time response when the chamber is heated in vacuum conditions. Our analysis shows that for thermal vacuum tests, the chamber will take about 2.5 h to reach the test temperature of 420 K.
Abdelkareem, Mohammad AliMahmoud, Mohamed S.Elsaid, KhaledSayed, Enas Taha...
13页
查看更多>>摘要：A thermoelectric generator (TEG) is a device that can directly convert heat into electricity without any intermediate energy forms such as work in the conventional power generation cycles. Waste heat recovery (WHR) is looking to recover such energy and utilize it for useful applications. The heat transfer efficiency from a waste heat (WH) stream to TEG material, plays a determinant role in the TEG performance. Nanoparticle-based heat transfer fluids, i.e., nanofluids, have significantly improved the heat transfer process, enabling higher energy efficiency in TEG applications. In this respect, we discuss the unique utilization of nanofluids in TEG applications for WHR. The critical role of nanofluids in improving the performance of different TEG for WHR was discussed. Despite the proven improvement with the incorporation of nanofluids in TEG applications, further research is required on both the operational and material development sides to reach the full scale and commercialization of TEG systems.
查看更多>>摘要：A sweeping jet generated by a unique class of fluidic device commonly known as a fluidic oscillator is applied to the film cooling in this study. Unsteady Reynolds-averaged Navier-Stokes numerical simulations are conducted to reveal the film cooling mechanism of the sweeping jet. A comparative study of the sweeping jet and fan-shaped holes film is performed. The innovation and application of sweeping jets can improve the film attachment along flow and span-wise direction. Compared with the fan-shaped hole, the spatially-averaged film cooling effectiveness of the SJ hole increases 34% when the blow ratio is 0.5. Significantly, it is found that the rotating direction of the vortex pair induced by the sweeping jet is contrary to the conventional counter-rotating vortex pair. The anti-counter-rotating vortex pair prevents the wall intrusion of high-temperature flow. The effects of coolant incident angle (alpha = 10 degrees similar to 30 degrees), exit fan angle (beta = 30 degrees similar to 70 degrees) and coolant gas outlet width (L = 0.5D similar to 2D) on the sweeping jet film cooling characteristics are investigated. When the sweeping jet incident angle a is changed from 10 degrees to 30 degrees, the position of higher cooling effectiveness changes from the centerline to both sides of the film hole, and the effectiveness at the centerline is reduced. The sweeping jet spreading angle (beta(jet)) does not follow the exit fan angle beta after beta > 60 degrees, which implies that the jet would not spread any further. Reducing the sweeping jet outlet width can increase the lateral cooling effectiveness. However, the cooling effectiveness of the flow direction shows a decreasing trend when the sweeping jet outlet width is reduced to 0.5D.
查看更多>>摘要：Parallel micro/mini-channel heat sinks are widely used for the efficient cooling of electronic devices to avoid functional damage and lifetime shortening due to overheating. This study addresses the optimization of fluid flow distribution in parallel mini-channel heat sinks subjected to a non-uniform multiple-peak heat flux to eliminate the temperature hotspots. A 3D heat sink comprising of 16 parallel straight mini-channels is used as a model for study, each mini-channel having the dimension of 1 mm in width, 2 mm in height and 34 mm in length. In particular, an original optimization algorithm is developed to adjust the inlets of these mini-channels according to the temperature distribution on the heating base surface. The fluid flow distribution is thereby tailored, leading to the reduced peak temperature on the heating surface. The effectiveness and robustness of the optimization algorithm are tested and discussed.Results obtained show that the maximum temperature can be reduced by 10 K and 7 K for two-peak and five peak heat flux cases, respectively, by using the proposed optimization method. The heat sink configuration with optimized channel inlets could always provide smaller thermal resistance than that of the equal channel inlet configuration under different average heat flux or total mass flow-rate conditions. At the same pressure drop, tailoring the flow distribution of the cooling fluid is more effective in reducing the thermal resistance than simply increasing the mass flow rate of the cooling liquid. This optimization method could also be generalized as an efficient thermal management technology for electronic cooling.
NSTL
Elsevier