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.
查看更多>>摘要：Upgrading the energy density of lithium-ion batteries is restricted by the thermal management technology of battery packs. In order to improve the battery energy density, this paper recommends an F2-type liquid cooling system with an M mode arrangement of cooling plates, which can fully adapt to 1C battery charge-discharge conditions. We provide a specific thermal management design for lithium-ion batteries for electric vehicles and energy storage power stations. In addition, the influence of the type of liquid cooling system, discharge rate, inlet temperature and flow rate are investigated, along with the effect of cooling plate arrangement on the temperature uniformity, maximum temperature, cooling efficiency factor and comprehensive heat transfer performance of cooling systems. The experimental results showed that the F2-type liquid cooling system has more advantages in cooling efficiency and comprehensive heat transfer performance than other liquid cooling systems. The best arrangement mode is M and the optimal inlet temperature is approximately 18.75 degrees C The upper limits of cooling water rate of flow at different charging and discharging rates are also determined. Cooling water rates of flow should be no less than 6 and 12 L/h when batteries are discharged at the rates of 1 and 2C, respectively.
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：This study presents design, development and analysis of a novel integrated energy system based on renewable geothermal energy source with a Copper Chlorine (CuCl) thermochemical cycle for hydrogen production production and a multistage desalination subsystem for freshwater production. In the proposed system, five useful outputs are effectively generated, such as heat for space heating, electricity, freshwater, hot water and hydrogen. CuCl thermochemical cycle is used for hydrogen production. The need for achieving high-temperature levels for the thermochemical cycle is met by a CuCl cascaded heat pump configuration in the system. The presented system is further analyzed and assessed thermodynamically through energy and exergy approaches. A case study is conducted for the city of Vancouver, Canada. Some parametric studies are also performed to observe the effects of different ambient and working conditions for the overall system and subsystems. According to conducted thermodynamic analysis, 42.06% energy and 49.65% exergy efficiencies are obtained for the overall system. The total exergy destruction rate for the overall system components is determined to be 46.56 MW. In the CuClMercury cascaded heat pump configuration, the coefficient of performance values are obtained as 1.557 for energy and 1.128 for exergy.
查看更多>>摘要：The safety analysis of flow blockage accident is significant for plate-type fuel reactor, especially swelling of cladding, which is resulted from irradiation damage in high burnup condition and needs to be paid more attention. In this study, experimental and numerical researches have been conducted to study the convective heat transfer and flow structure within narrow rectangular channel, where exists different numbers and arrangements of spherical crown protrusions. Compared with the experimental data of single protrusion condition, the overall heat transfer capacity even deteriorates more than 20% when protrusions are aligned in streamwise direction. In contrast, the global Nu is nearly 10% higher when three protrusions are located in spanwise direction. Conclusions can be drawn that existence of protrusion can also significantly change convective flow condition in narrow channel, and the laminar flow is altered to transitional/quasi-turbulent even though Re is only nearly 1600. Besides, the local information, such as flow boundary layer separation, low-speed recirculation and vortex evolution etc., can also be acquired by the Computational Fluid Dynamics (CFD) method comprehensively. Combined with experimental data and numerical results, the distinct heat transfer behaviors and flow structures for different flow blockage conditions can be explained in detail. In summary, conclusions about the flow and thermal processes influenced by protrusions in narrow rectangular channel are fundamental to safety analysis and design criteria of plate-type fuel assembly for flow blockage condition. Besides, it also can be applied in other industry scene during convective laminar flow within narrow rectangular channel.
查看更多>>摘要：This work aims to reveal combined effect of intake angle and chamber structure on flow field, flame propagation, combustion characteristics and pollutants formation of a small-scaled rotary engine by using numerical simulation. For this reason, a three-dimensional dynamic simulation model was established by using a reasonable turbulent model and choosing a reduced reaction kinetic mechanism and was also validated by the experimental data. Simulation results showed that intake angle is more significant to the influence of flame propagation, in-cylinder pressure and heat release rate (HRR) in the front baffle combustion chamber (FBCC) and the rear baffle combustion chamber (RBCC) compared to that in the middle baffle combustion chamber (MBCC), but is an opposite trend for effect of flow field. The differences in the in-cylinder velocity field and turbulent kinetic energy magnitude were the intrinsic mechanism of combined influence of intake angle and chamber structure. Under larger intake angle, for the MBCC and the RBCC, higher pressure, HRR and power output were obtained, meanwhile the decreased HC and CO formations were obtained, while showed a contrary tend for the FBCC. And the amount of HC formation for these three combustion chambers at 15 degrees intake angle is relatively small. To sum up, considering combustion characteristics, engine cooling and pollutants formation, it can be concluded that the combination of 15 degrees intake angle and combustion chamber with a middle baffle was the optimum configuration for a small-scaled RE in engineering application.
Ali, MuzaffarHabib, Muhammad FarhanSheikh, Nadeem AhmedAkhter, Javed...
13页
查看更多>>摘要：Separate handling of sensible and latent components of building loads can be an energy efficient approach compared to simultaneous management of both. This paper presents a detailed experimental analysis of an energy efficient air conditioning system using solid desiccant integrated with absorption system for separate building thermal load handling. The experimental system consists of silica-gel based solid desiccant for latent load handling, whereas the gas fired air-cooled NH3-H2O absorption chiller is used to handle sensible load of the space. A chilled water-cooling coil heat exchanger is installed on the process side of desiccant cooling system to integrate it with the absorption chiller. The performance of integrated absorption- solid desiccant system is compared with a standalone conventional desiccant air conditioning system with a direct evaporative cooler considering it as baseline system under wide range of operating conditions including air temperature, air humidity, and regeneration temperature. The comparative analysis is performed in terms of supply air temperature, cooling capacity, and coefficient of performance. The experimental results exhibit that supply air temperature of the integrated system is 15.2 degrees C compared to 24.6 degrees C achieved by conventional desiccant system. Moreover, COPth of the integrated system is also 50-55% higher than its counterpart and it is almost comparable with double-effect absorption chiller. It is concluded that the integrated system using separate load management approach is more efficient for HVAC applications.
查看更多>>摘要：Research on nanofluids has increased markedly in the last two decades. Initial attention has focused on conventional or mono nanofluids, dispersions of one type of solid nano-sized particles in a base fluid. Despite various challenges such as dispersion stability or increased pumping power, nanofluids have become improved working fluids for various energy applications. Among them, convective heat transfer has been the main research topic since the very beginning. Hybrid nanofluids, dispersions of two or more different nanoadditives in mixture or composite form, have received attention more recently. Research on hybrid nanofluids aims to further enhance the individual benefits of each single dispersion through potential synergistic effects between nanomaterials. Multiple experimental studies have been conducted independently analysing the convective heat transfer performance of mono or hybrid nanofluids for single-phase and two-phase convective heat transfer applications. However, there are still no general conclusions about which nanofluids, mono or hybrid, present better prospects. This review summarizes the experimental studies that jointly analyse both hybrid and mono nanofluids for these applications and the results are classified according to the heat transfer device used. Based on this criterion, three large groups of devices were noticed for single-phase convective heat transfer (tubular heat exchangers, plate heat exchangers and minichannel heat exchangers/heat sinks), while one group was identified for twophase convective heat transfer (heat pipes). The main outcomes of these studies are summarized and critically analysed to draw general conclusions from an application point of view.
查看更多>>摘要：Liquid turbines can replace throttling valves to recover waste energy and reduce vaporization in various industrial systems, such as liquefied natural gas, air separation, supercritical compressed air energy storage (SCCAES) systems, et al. However, there were few studies about differences in the preliminary design method between general radial inflow turbines and liquid turbines. In this paper, a preliminary design method of liquid turbines was presented, and the performance of liquid turbines was predicted using CFD methods which were validated with experimental results. The efficiency of the designed liquid turbine was 92% and the output power was 65.7 kW. The performance of the turbine predicted by the preliminary method could agree with simulation results of prototype and model turbines near the design working condition, while there was a certain deviation when the flow rate was less than 70%. Through analyzing the presented preliminary design method, it could be found that distinctive differences in thermal properties of working fluids caused that typical design parameters for liquid turbines, like ratios of the blade height, the hub radius and the area, should be selected differently from empirical values for gas radial turbines. The results obtained in this paper could help guide the design of liquid turbines for various systems to promote energy conservation and improve system efficiencies significantly.
查看更多>>摘要：The stability of superheated steam temperature (SST) is severely challenged by the adjustment of thermal power plants under a wide-load range. Accurate and efficient prediction of SST plays an important role in the control of superheat system. To this end, an SST prediction model based on a multi-mode integrated method is proposed in this paper. Firstly, conservation of energy, as an equality constraint, is introduced into the loss function of the data-driven model based on Long Short-Term Memory (LSTM) architecture. Subsequently, the physical relationship between SST and the spray water flow, as an inequality constraint, is introduced into the above loss function. Finally, an individual hybrid model for each operating mode is developed and integrated with multimode switching strategies based on attention mechanism. Operating data with a wide-load range is sampled from a supervisory information system (SIS) to validate the superiority of the proposed method. The comparison results demonstrated that the predictive effect of the hybrid model with physics-based loss function is not only generalizable but also scientifically consistent with the dynamic characteristics of the step response. Furthermore, the results of the multi-mode integrated model prove the effectiveness of the mode switching strategy based on the attention mechanism.
NSTL
Elsevier