查看更多>>摘要：Dynamic hydrothermal management is the critical issue for improving the performance of Proton exchange membrane fuel cell (PEMFC). In this study, a multi-input and multi-output (MIMO) fuzzy control method is proposed for the hydrothermal management of PEMFC in real time. For PEMFC, stack temperature and relative humidity at cathode are chosen as the control objectives, and the cooling water flow rate and inlet gas humidity at cathode are set as the control variables. To establish the transient synergy control of temperature and humidity, a fuzzy logic controller is constructed. The input parameters of controller include the errors of temperature, humidity and their derivatives. The dynamic performances of temperature and humidity transient synergy control under the disturbance of load current and operating parameters are analyzed. The results show that the temperature and humidity transient synergy control based on MIMO fuzzy method presents faster response speed and better control performance than traditional Proportion Integration Differentiation (PID) control. The output voltage of the proposed control method is 3.14% and 4.21% higher than that of traditional PID controllers. Furthermore, the power density of THTSc is 9.37% higher than that of PID controller.
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：The aim of this paper is to thoroughly analyse the influence of condensation models on the modelling of condensation phenomena in transonic flows of moist air. The reason for the study was the fact that different condensation models are used by researchers to obtain satisfactory results of numerical modelling. The condensation models tested herein differ in the nucleation rate formula and the droplets growth equation. Four most often used condensation models were selected for detailed investigations. The results obtained from each model were compared with experiments for the internal flow through a nozzle and the external flow around an airfoil. The main focus was on the location of the onset of the nucleation process. Moreover, the droplet growth intensity was compared and discussed. The nozzle flow CFD calculations were performed using the ANSYS Fluent commercial tool. Finally, the condensation model which is the most suitable for the moist air transonic flow was recommended.
查看更多>>摘要：The drag reduction equipment (DRE) suffers dual environmental stress of high-speed spin and rapid depressurization during the launching process, disturbing the projectile intensely. To research the effect of this extreme process on heat and mass transfer, flow field development, as well as drag reduction performance of the DRE, a numerical model was established based on the MT-based pyrotechnics combustion mechanism and the H2-CO combustion mechanism. Simulation on the unsteady reacting flow was conducted to investigate the effect of high-speed spin on the performance of the DRE under depressurization. The results indicate that the wake flow field of the DRE transforms from a supersonic under-expanded jet into a subsonic swirling flow, and two recirculation zones with low-pressure appear at the base of the DRE. The transition region between propellant gas and igniter gas in the combustion chamber displays the Kelvin-Helmholtz instability, in which a vortex core forms with a high tangential velocity gradient. The igniter gas burns in the combustion chamber, resulting in an axial high-temperature region. And then the combustion products of igniter gas are mixed with propellant gas and inject outwards, reacting with the air near the jet boundary to be an intense post-combustion. High-speed spin improves the nozzle mass flow rate, enhancing the post-combustion. Eventually, compared with the nonspin case, the mass flow rate and base temperature in the case of 20,000 rpm are improved by 67.6% and 21.56%, respectively. And the base drag is reduced by 10.14%.
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.
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：The offshore floating storage and regasification unit (FSRU) is developing rapidly as a new type of storage and gasification system for liquefied natural gas (LNG), and the heat transfer and system stability of offshore LNG vaporizers are greatly affected by ocean rolling. To reveal the regular pattern and mechanism of supercritical methane heat transfer performance under ocean motion, this research numerically studied the flow and heat transfer characteristics of supercritical methane in a 1 x 1 x 100 mm mini channel under the additional inertial force by large radius rolling. Based on the non-inertial coordinate system, the normal inertial acceleration, radial inertial acceleration and Coriolis inertial acceleration were considered. Moreover, Nusselt number, degree of fluctuation and friction factor were investigated. The ranges of Reynolds number and Nusselt numbers are 15,000 to 45,000 and 35 to 130 respectively. The results show that the Nusselt number and friction factor violently fluctuate under rolling motion, and the fluctuation period is similar to the rolling period. Besides, the fluctuation degree of Nusselt number is greater than that of friction factor, and the largest fluctuation degree of Nusselt number is 27.9%. The effect of the fluctuation increases with the decrease of the rolling period and the increase of the rolling amplitude. Hysteresis exists in the coupling of rolling, flow fluctuation and temperature fluctuation. In addition, the degree of fluctuation is reduced with the increase of fluid temperature and mass flux. For the effect of rolling, the additional force in the mainstream direction plays a leading role. Besides, the influence of radial force is greater than that of normal force for horizontal flow condition.
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.
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.
NSTL
Elsevier