查看更多>>摘要：A study presents new model of the artificial neural network to predict friction factor and heat transfer coefficients for the turbulent flow in tubes with inner helical-finning. A fin geometry differs in its form, shape and fabrication method. The generalized equations, correlating thermal performance in such tube, available in earlier works by other authors primarily apply to a single type of inner helical-finning. In present work, we compile experimental results of other authors to an extended database that has been used further for artificial neural network training procedure. The presented model of artificial neural network applies to all types of inner helical tube finning. The mean average percent error values of 11.8% for friction factor and 16.3% for Nusselt number values for the ANN model over the whole database have been achieved. The performance validation of the obtained model was based on a comparison of predicted data with the independent experimental results obtained by authors, yielding excellent accuracy.
查看更多>>摘要：This work proposes a simultaneous approach for the synthesis and design optimization of industrial refrigeration cycles integrated with heat exchanger networks. Given the process hot and cold streams, the methodology determines the economically optimal refrigeration cycle configuration (number of evaporation/condensation levels, compressor intercooling, multiple throttling, etc.),cycle variables and heat exchanger network. The methodology includes a novel refrigeration cycle superstructure capable of reproducing a wide range of cycle architectures and an effective solution algorithm (based on the decomposition of the problem on two levels) to tackle the challenging Mixed Integer Non-Linear Program. The application to four literature case studies indicates that the proposed approach returns solutions which are considerably better both in terms of efficiency and economics than those published in literature. The application to four literature case studies indicate that the required computation time is tractable even for problems with thousands of variables and constraints (up to 87,000 real variables, 29,000 binary variables and 129,000 equations). Moreover, compared to previous literature studies, the optimized solutions feature a total annual cost reduction up to 40% and a decrease in compression power consumption up to 52%.
查看更多>>摘要：Accurate temperature predictions and cooling structure design for permanent magnet machines are essential to ensure safe and stable operation. In this paper, a cooling system with circulation between rotor holes for enclosed permanent magnet synchronous machines is proposed. The modified lumped parameter models of airflow network and thermal network are established, respectively, so as to predict the air velocity and temperature distribution quickly and accurately. In the airflow network model, the calculation method of deflector pressure is proposed based on blade element theory. The equation for the pressure drops in the rotor holes is modified, and the influence of rotor rotation on air velocity is better considered. To improve the accuracy of the thermal network model, each part of the motor is equivalent to three typical heat transfer surfaces, and the corresponding calculation methods of the convective heat transfer coefficient are listed. The parameters of the cooling structure are analyzed and designed based on the lumped parameter models. Compared with the original motor without the deflector, the maximum temperature-rise of the rotor is decreased by 16%. The accuracy of the calculation models is verified by experiment and simulation.
Jeong J.Benchikh Le Hocine A.E.Croquer S.Poncet S....
12页
查看更多>>摘要：The present work reports the numerical simulation of the heat transfer inside a refrigerated truck trailer equipped with three eutectic plates and fans. The numerical model solves the conjugated heat transfer inside the trailer under unsteady conditions. The conservation equations of mass, momentum and energy are solved in 3D and closed using the k-ω Shear Stress Transport (SST) model. It is first favorably validated against the numerical and experimental data of Lafaye de Micheaux et al. (2015). The results are then extended to investigate the performance of a refrigeration system equipped with eutectic plates for the transport of frozen food products. As no significant 3D effects are reported, a 2D model is adapted to analyze the configurations with the plates placed in series on the roof of the trailer or vertically at its back. During the door opening period, the configuration with the plates placed on the roof without the cargo leads to noticeably lower area-averaged temperatures inside the trailer than the configuration with the plates placed on the back due to the presence of recirculation zones and the cold plates located near the doorway. However, the presence of the cargo eliminates the formation of these zones that limits the infiltration of the outside atmospheric air. Also the configuration with the plates placed in the roof allows the outside atmospheric air to infiltrate earlier, resulting in an overall higher temperature observed for the cargo.
查看更多>>摘要：In this work, implicit method is used to solve the building heat transfer equations in order to improve the speed and stability of calculation. It only takes 161.906 s to calculate the annual data when the time step is 6 min in the specific calculation example. In addition, the effective heat capacity method is used to independently model the building module containing phase change materials (PCMs), which can accurately simulate the temperature distribution of each node inside PCMs. Therefore, the temperature changes of different nodes in PCM and the utilization efficiency of PCM can be analyzed. Radiative heat transfer in buildings can be considered separately so that it can be distinguished from convective heat transfer. The radiation characteristics of the envelopes can also be modified, which means that smart windows can be studied by changing the radiation characteristics of the transparent envelope. Combined with these calculation characteristics, a software called BuildingEnergy is proposed. At present, the reliability of the software has been proved by ANSI/ASHRAE Standard 140–2001. A set of experimental device was set up in Hefei (China), and through the comparison with the simulation results, it was found that the software has high reliability under both active and passive mode. Moreover, it has a high accuracy in simulating the performance of phase change materials and vanadium dioxide films in buildings.
查看更多>>摘要：The design of a wet cooling tower involves a number of trade-offs including the efficiency of the device to remove waste heat (thermal performance) and environmental aspects (emissions level). This paper deals with the experimental characterisation of a new cooling tower prototype. The novelty of the work relies on the study of a cooling tower designed to avoid the emission of airborne particles to the atmosphere. The experiments were conducted in a pilot plant built ad hoc for this purpose. The sensitive paper method was used in the environmental impact assessment (emissions level). The comparison between the obtained results and those found in the literature for similar cooling towers indicates that performance of the inverted cooling tower in terms of emissions is remarkable: D=1.47?10?6 (0.00015% of the circulating water). This value is up to 300 times lower than the limits imposed by several international standards and involves a reduction in terms of emissions ranging from 40.21% to 82.54% compared to commercial towers. The maximum size of the measured escaping droplets is dd = 50 μm, and the Sauter Mean Diameter of the ensemble of droplets is 31.42μm. Concerning thermal performance, the observed results are more modest. Operating at nominal conditions, the inverted cooling tower cools the water up to 33.5 °C. The efficiency of the tower is similar to that of a commercial tower equipped with a film-flow distribution system (up to 6.98% better). The difference is larger (41.16% lower) when compared to the same tower equipped with a splash distribution system.
查看更多>>摘要：Adsorbed natural gas (ANG) technology is considered a cost-effective and sustainable energy storage system that can offer a leading clean and environmentally friendly combustion fuel. Despite the benefits of ANG systems, still, there are some challenges in simulation of these systems accurately under actual conditions. The actual charging condition of ANG vessel with variable gas flow rate was simulated and experimentally validated for the first time. For this purpose, we proposed a new time-dependent equation to monitor methane's variable injection flow rate into the vessel. Dynamic methane storage was experimentally tested to validate the simulation results using a custom-built pressurised ANG vessel (～300 cm3) filled with various in-house prepared adsorbents (i.e. AC1 and AC2) under the loading condition of 40 bar and 298 K. Also, the thermal behaviour of the ANG vessel was studied via experimental observations. A 2D distributed dynamic model, solved by COMSOL Multiphysics software, was developed to assist the simulation in predicting pressure and temperature variations inside the ANG bed. Analysis of the ANG vessel's performance exhibited higher thermal fluctuations attributed to the adsorbent with superior isothermal methane storage capacity. Due to the low thermal conductivity of both adsorbents, a significant temperature rise was observed in the central region of the bed. Sensitivity analysis shows that increasing the length and diameter of the ANG tank leads to a longer required time for charging the tank up to the desired pressure and relative decreases in the temperature profile. Moreover, increasing heat capacity of adsorbent from 800 to 1350 J/kg.K caused 37% reduction in the temperature variations and 7.7% enhancement in gravimetric methane storage efficiency.
查看更多>>摘要：Two-phase flow modeling is important in well construction field for well planning and real-time applications. In this paper, a new non-isothermal two-phase flow model is presented that improves upon the simulation accuracy and capability of historical reduced drift-flux models (RDFM) while still retaining high computational efficiency. Built on the “no pressure wave” assumption of the RDFM, our new RDFM achieves improvements through calculating the temperature dynamics, considering interface mass transfer (i.e., gas-in-oil solubility behavior), and introducing a new lumped pressure dynamics model. By including these physical factors that are critical for practical applications, the proposed RDFM shows higher simulation accuracy and capability compared to historical RDFMs. The validity of the proposed model is proven by comparing it to field measurements, benchmark models, and the classical drift-flux model. Moreover, the proposed RDFM successfully retains the high computational efficiency of historical RDFMs even with the addition of the aforementioned complex physical dynamics. When conducting full-scale gas influx simulations, the proposed RDFM achieves a computational speed at more than two orders of magnitude faster than real-time. Due to its good performance on both computational efficiency and simulation accuracy, the proposed model is suitable for real-time applications in most well construction scenarios. It is especially superior to historical RDFMs when simulating more complicated but still common scenarios, e.g., deepwater wells drilled in high-pressure high-temperature environments, and wells experiencing gas-in-oil solubility behavior.
查看更多>>摘要：Bionic structure has become a popular tool to design heat pipes for its ability of heat transfer enhancement and liquid transport. Inspired by the powerful water collection and transfer capability of pitcher plant surface, this paper presents a new flat heat pipe design with bionic grading microchannels (BGFHP) based on special high-low structured surface. Firstly, the performance advantages of BGFHP are revealed by comparing the heat transfer performance and visible internal flow characteristics of BGFHP and conventional FHP. Secondly, the performance variation and influence trend of BGFHP are investigated experimentally with inclination angle and thermal power as variables. Finally, thermal management effects of natural cooling, FHP and BGFHP in fuel cells are compared to demonstrate the practical application of BGFHP. Results show that the high-low channel structure of BGFHP has the advantages of micro-channel hydraulic transport, and the small channel increases the heat transfer area, circulation efficiency and gas phase flow area, resulting in better start-up time and heat transfer capacity than the traditional FHP. The thermal resistance of BGFHP is reduced by 22%, while the thermal conductivity is increased by more than 40%. In the load range of 10–26 W and inclination angle range of 0–90°, the overall thermal resistance and temperature uniformity of BGFHP decreases and then increases as the inclination angle increases. With the increase of heat power, the thermal resistance of BGFHP gradually decreases, whereas the temperature uniformity first decreases and then increases. The optimal working condition of BGFHP is 45° and 24 W, with a minimum thermal resistance of 0.21 K/W. In the fuel cell temperature control test, the BGFHP was able to maintain the temperature below 52 °C, which is 5 °C lower compared to the FHP. This result shows the advantage of the BGFHP in terms of temperature control.
查看更多>>摘要：Solar cooling technologies have considerable potential in reducing the energy consumption of buildings to realise carbon neutrality. However, they typically suffer during off-design operations due to variations in meteorological data and cooling demand. Hence, system optimization is extremely important to achieve the best thermo-economic performance considering all varying conditions. However, optimizations based on the two widely used approaches, i.e., annual simulation and exergoeconomics, can not fully resolve the aforementioned problems. Accordingly, the so-called full-condition exergoeconomic optimization is proposed and applied to a solar absorption-subcooled compression hybrid cooling system, which has potential for building cooling. First, a full-condition exergoeconomic model is formulated, and the impact of critical component size is subsequently analyzed. Finally, the size of key components is optimized based on the trade-off between capital investment and performance in all-working condition. Further, the variation among optimal sizes based on different meteorological data is compared. The total cost rate of the optimal case for the system utilized in Haikou is found to be 13.6% lower than that of the base case. The scales of the solar device and compression subsystem are found to be positively related to the local solar radiation intensity and cooling load. The study is anticipated to aid in rendering solar cooling facilities to be cost-effective in all-working condition.
NSTL
Elsevier