查看更多>>摘要：Adsorption desalination (AD) is an emerging technology to reduce risk of freshwater scarcity, able to use renewable energy and applicable in decentralized areas. Only limited sorbents have been tested experimentally for AD systems. This study developed two composite sorbents based on LiCl as embedded salt and two matrices, namely, silica gel (LiCl@SG_30) and expanded vermiculite (LiCl@EVM_45). The performed analysis figured out how the trade-off between high sorption capacity and good mass transfer caused by their different pore structures influences the desalination operations. The results were compared against a standard microporous Siogel. The sorption isobars indicated that the sorption behavior of LiCl@SG_30 is the combination of silica gel and the embedded LiCl crystals, while for LiCl@EVM_45 is mainly the sorption process of the embedded LiCl crystals. LiCl@EVM_45 reached the highest sorption capacity. The Dubinin-Astakhov equation described the equilibrium capacities of the sorbents. The kinetics coefficient (k) was employed to evaluate the sorption rate. Microporous Siogel showed the highest sorption rate, followed by LiCl@SG_30 and LiCl@EVM_45. Finally, predicted specific daily water production (SDWP) were calculated, showing promising features for both LiCl@SG_30 and LiCl@EVM_45, with LiCl@SG_30 achieving SDWP ranging from 43 to 60 m(3)/tonne/day) for the selected conditions.
查看更多>>摘要：Since the early 1990s, the pulsating heat pipe (PHP) has emerged as one of the most innovative, effective and potentially more convenient passive two-phase heat transfer systems, thanks to its good performance, versatility, and construction simplicity. On the other hand, the PHP is characterized by complex thermohydraulic behaviour that still presents a true challenge to designers, which has led to significant interest by a growing number of researchers. The technological readiness level (TLR) of this technology is quite broad depending on the application: for instance, the industrial community is starting to consider the PHP as a reliable solution for electronic cooling in ground conditions, while implementations in the cryogenic temperature range and in space environments is also being extensively explored. This vision paper aims at shedding light on the current knowledge and prediction capability of PHP numerical models, on unsolved phenomenological issues, on the current technological challenges and the future perspectives of this fascinating heat transfer device. Specifically, after a general introduction and a brief overview of the current knowledge and the open issues of PHPs, special focus is devoted to the following topics: flat-plate PHP assessments; advancements in PHP modelling and simulation; flow stabilization techniques; non-conventional fluids subdivided into fluid mixtures, self-rewetting fluids, nanofluids; cryogenic applications, space applications, and finally the newest frontiers of flexible PHPs. Each section is accompanied by a brief roadmap providing directions for future research based on key challenges, which are also gathered and summarized in the final outlook section.
查看更多>>摘要：With the emerging demand of point-of-care microelectronics and lab-on-chip based bio-chemical sensors, it essentially requires the fully integrated and reliable solutions of flexible power supplies. Compared to well-demonstrated chip-based battery and capacitor, flexible fuel cell offers unique advantages such as high energy density, easy integration, potential cost effectiveness and portability, receiving the increased attentions and serving as an essential supplement for battery in past decade. This paper gives a brief perspective on the state-of-the-art trend of flexible fuel cells, focusing on the operational system, fabrication approach, power-generation property and application demonstration. The remaining challenges to achieve its commercialization are proposed including unsatisfactory power density, bulky fabrication process and incomplete flexibility.
查看更多>>摘要：Direct absorption solar collectors (DASC) are extremely attractive in solar energy utilization. In this paper, starting from these two aspects, graphene-based nanofluids, including single-layer graphene (SLG) and graphene oxide (GO), are prepared to enhance solar absorption and photothermal conversion performance. The influence of nanofluids' concentration and two different irradiation modes: traditional DASC and reverse radiation DASC (RI-DASC) on the photothermal conversion performance of graphene-based nanofluids has been studied. The addition of a small amount of SLG or GO significantly improves the photothermal conversion efficiency of base fluid, and it increases along with the increase of the concentration. Furthermore, the RI-DASC mode has a more uniform thermal field distribution and the higher photothermal conversion efficiency than the DASC mode. In DASC mode, the photothermal conversion efficiency of pure water is 17.00%. By changing the irradiation mode, the introduction of GO and SLG nanofluids (100 ppm) increased the photothermal conversion efficiency by about 172% and 189%, reaching 46.26% and 49.13%. According to the photothermal-thermoelectric conversion experiment, the positive correlation between the output power of the TE module and the heating state of the nanofluid makes it possible to adjust the nanofluid in real-time. This work presents a feasible way to enhance solar energy absorption and improve the photothermal conversion efficiency of nanofluids for DASC.
Avargani, Vahid MadadiZendehboudi, SohrabRahimi, AmirSoltani, Sara...
21页
查看更多>>摘要：Although obstacles on the absorber surface of a solar air heater (SAH) can increase the thermal efficiency by creating turbulent conditions, they might reduce the system's exergy efficiency due to an increase in the pressure drop. In the present work, a 3-dimensional computational fluid dynamics (3D CFD) model is first developed to simulate conical obstacles, and the developed model is then validated using the available experimental data. To find optimal design features, obstacles with various shapes/geometries such as cylindrical, spherical, hemispherical, pyramidal, and cubical are investigated. To attain this goal, a comprehensive study is conducted by including energy, exergy, enviro-exergy, and thermo-hydraulic analyses. The results reveal that vertical cylindrical obstacles have better performance than other geometries as well as a flat absorber without obstacles. The average daily thermal efficiency of the system is increased by 69.16%, and the exergy efficiency of the system is increased by 103.16%. The relative CO2 reduction potential (RCDRP) for a SAH with vertical cylinders is improved up to 168.7%. In addition, the vertical cylinder with a daily average thermo-hydraulic performance parameter of 1.2 shows the greatest thermo-hydraulic performance parameter (THPP) among other geometries, and the pyramidal obstacle with the THPP of 0.66 has the minimum performance.
Bandi, PrateekManelil, Neeraj PaulMaiya, M. P.Tiwari, Shaligram...
16页
查看更多>>摘要：Present work describes the thermal comfort of the driver in an automobile cabin under the effect of solar radiation for different cooling jet directions. Three-dimensional transient cooling simulations of the in-cabin flow and heat interactions have been carried out using commercial solver ANSYS Fluent 18.1. The surface to surface (S2S) radiation model embedded within the solver has been employed to simulate the internal conditions of radiative heat transfer. The transient behavior of the flow inside the cabin has been brought out using Fourier spectra of velocity signals. The spatial distributions of temperature and velocity for different values of driver-side vertical guide vane angle have also been presented. The interaction between cooling jets from the airconditioning vents with air inside the automobile cabin has been illustrated using iso-Q surfaces describing the vortex structures in the flow field. Variation of bulk average temperature with vertical guide vane angle is also reported in this study. The thermal comfort of the driver has been evaluated using Equivalent Temperature (ET) and Effective Draft Temperature (EDT) for different values of vertical guide vane angles. The ET and EDT values corresponding to different locations on the body of the driver have been compared to bring out the relative significance of draft and radiative heat transfer on the thermal comfort inside an automobile cabin. Optimal guide vane angle corresponding to enhanced mixing and thermal comfort has also been identified.
查看更多>>摘要：Based on the supercritical water-cooled reactor fuel assembly, a 19-rod bundle physical model with a hexagonal outer casing is established, and the four-wire structure is added to the bare bundle. To analyze the influence of wire spacers on the flow and heat transfer process, numerical investigations of supercritical water in the reactor under design conditions are performed by using the Reynolds stress model with enhanced wall treatment. The results show that the mass redistribution is the main factor affecting the distribution of thermal-hydraulic parameters regardless of the existence of wires. The wire plays a role in weakening the mass redistribution by reducing the cross-flow between the adjacent sub-channels. However, due to the large local hydraulic diameter of the side sub-channels and the sharp change of the supercritical water physical properties, the fluid gradually gathers in the external sub-channels. In addition, the four-wire structure drives the fluid to spiral upwards around the fuel rod, which significantly enhances the convective heat transfer between the fluid and the fuel rod. At the same time, the influence of the local hydraulic diameter on the circumferential non-uniformity is weakened by the wires, and the circumferential wall temperature gradient of the external fuel rod is significantly reduced.
查看更多>>摘要：Of the absorption heat transformer that useful to solve the problem of low-temperature heat utilization, the ejector heat pump is a good candidate because of its simple structure, flexible setting and single pure working fluid. This study aims to characterize the behavior of a novel design which replaces the traditional compression heat pump cycle with an ejector heat pump cycle and adds a waste heat recovery system to recover the heat in the flue gas. The evaluation approach takes into consideration four indices (the heating capacity per unit area of the system q(h) , gas consumption per unit heating capacity EC, gas heat utilization rate GUR and comprehensive heating coefficient R). The results show that the performance of this new designed system is good enough. Moreover, the influence of air and circulating water parameters on the performance of the system is studied, and it is pointed out that air parameters are the most important factors affecting the performance of direct-fired ejector air source heat pump.
查看更多>>摘要：Borehole heat exchangers (BHEs) are widely used in various building air conditioning and heating systems. It has always been the unremitting pursuit of researchers to provide solutions for energy conservation by improving the heat transfer efficiency of BHE. In this work, comprehensively considering groundwater seepage in the sur-rounding rock and soil and the difference of heat transfer performance between various layers of rock and soil, three-dimensional geometric models of double-U BHE and enhanced coaxial BHE with intermittently laid spiral ring fins were established. The established model was verified by the drilling, geothermal, thermal response data collected through filed tests and the actual operating data of the system. The heat transfer performance and influencing factors of the two BHEs models under different working conditions were simulated by improving and replacing the double-U BHE model by means of equivalent buried pipe cross-sectional area. The results showed that the linear meter heat transfer of the enhanced coaxial BHE was significantly better than the linear meter heat transfer of the equivalent U BHE. The average linear meter heat transfer of the enhanced coaxial BHE can reach 1.46 times and 1.45 times of the equivalent U BHE under winter and summer working conditions, respectively. Finally, the results of the sensitivity analysis of single factor showed that the inlet temperature/inlet fluid heating power is the most significant impact on the heat transfer performance, followed by the inlet flow rate, and the hydraulic gradient of groundwater seepage has the least impact. The results obtained can provide a new type of the buried pipe structure that can be used as a reference for improving the heat transfer performance of BHEs in the simulation and experiment conditions.
NSTL
Elsevier