查看更多>>摘要：This paper proposes a novel stand-alone liquid air energy storage (LAES) system to enhance round-trip efficiency (RTE) using a thermal energy storage system. Thermal energy storage comprises sensible heat storage with quartz and latent heat storage with cryogenic phase change material (PCM) for recycling cold energy from the LAES discharge process. The liquid air in the pressurized tank was released during the discharge cycle and used to store energy using PCM and quartz. The cryogenic phase change material melts at 110 K based on experimental result, making it possible to provide cold heat of fusion 61.62 kJ/kg at a constant temperature for air liquefaction. Thus, proposed system can effectively increase the cold energy recycle. In addition, the two-dimension numerical model allowed us to estimate the outlet temperature of sensible heat store without isothermal assumption by Biot Number. The proposed process is modified from Linde-Hampson, and a sensitivity analysis is performed using ASPEN HYSYS. The analysis shows that the implementation of energy recycling from the compressor and thermal store leads to a high round-trip efficiency (60.6%) higher than base case (34.4%) of LAES system. Therefore, the proposed system is a promising process in terms of simplification and high efficiency, cognizant of the integration of waste heat from industrial plants.
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：The secondary heat transfer surface of the shovel-cut finned tube, called the flying-wing fin, eliminates the thermal contact resistance. In the present study, the thermal-hydraulic characteristics of the flying-wing fin at Reynolds number range of 1500-3000 were studied, including overall quantitative analysis and three-dimensional thermophysical field analysis. It was found that the ratio of Nu.eta o/f(1/3) of the flying-wing fin (Case A1) is about 8.6% larger than that of the wavy fin (Case B3). The fundamental reason is that the flying-wing fin has a smaller average field synergy angle than the wavy fin. There is a butterfly-shaped low-velocity zone at the root of the wave trough of the monitoring section on the acute-angled side of the flow channel. In addition, along the fin height direction, the influence range of this low-velocity zone on the flow field is less than around 1.34 mm. Similarly, there are butterfly-shaped zones for the temperature and field synergy angle distributions. The average value of the convective heat transfer coefficient on the left side of the flying-wing fin is greater than that on the right side. In general, the promising flying-wing fins show better thermal-hydraulic performances than the wavy fins with similar geometric parameters, which deserve further promotion and engineering application.
查看更多>>摘要：The representative composite overwrapped pressure vessel of vehicle-mounted composite compressed natural gas cylinder is taken as the research object. Based on the principle of double decentralized fuzzy inference with a temporal-spatial decoupling characteristic, an inversion scheme is established by which the infrared thermography of cylinder is employed to estimate the transient distribution of internal thermal excitation. In this scheme, the error vector of time series of the finite temperature measurement points on the surface of cylinder is processed by fuzzy inference, and then the transient distribution of internal thermal excitation is estimated. The influence of the number of measurement points and measurement errors on the inversion results is studied through numerical simulation. Furthermore, combined with the on-site gas cylinder inspection process, the internal thermal excitation of cylinder is estimated using the infrared thermography of cylinder under the steam flushing process obtained from the inspection site. According to the inversion results, the transient temperature field of cylinder is reconstructed, and the reliability of reconstruction results is also verified. The results show that under the experimental conditions in this paper, the maximum deviation of the surface temperature reconstruction results of cylinder is about 1.0 degrees C.
查看更多>>摘要：R134a will be phased out soon due to its high GWP. Replacing R134a with a low Global Warming Potential (GWP) and non- or slightly flammable fluids in the systems in stock should maintain the same level of system performance. This study focuses on the drop-in alternatives for R134a regarding a Mobile Air-Conditioning system. A simulation model coupled with a microchannel heat exchanger model is developed and validated for calculating the system Coefficient of Performance (COP) and capacity of the Mobile Air-Conditioning system. A comprehensive method is developed to evaluate the alternative candidates combining the performance simulation and the flammability estimated of mixtures. The evaluation includes the system performance, environmental impact, and flammability of alternative mixtures. 15 pairs of binary mixtures from six pure fluids (R134a, R1234yf, R1234ze(E), R32, R227ea, and R152a) with 99 compositions are evaluated as R134a drop-in replacements, and the results are discussed. There is no perfect mixture found that is nonflammable, has low GWP, and has higher system efficiency and capacity than R134a in this study. Using R152a as a drop-in replacement of R134a can increase the system efficiency and capacity, but R152a is flammable. By adding R134a or R227ea to R152a can reduce the flammability of the mixture. R152a/R134a, R152a/R1234yf, and R32/R152a have higher COP and capacity than R134a, but they are not safe or environmental friendly enough. The mixtures for replacing R134a as drop-in alternatives with low Global Warming Potential (less than 150 or 700), nonflammable or slightly flammable are listed and discussed. The method developed in this study can be extended to evaluate alternatives for replacing other working fluids in any thermal application that will be restricted.
查看更多>>摘要：Preheated kerosene injection is one of the fuel supply methods for a rotating detonation scramjet engine. The injection and evaporation of preheated kerosene were numerically investigated in an expansion configuration combustor with intake air at a speed of Mach 2 at various fuel temperatures for the first time. The EulerLagrangian method was used to describe the gas-liquid two-phase flow phenomenon. The random trajectory model was used to track the droplet movement process, and the infinite thermal conductivity model was used to describe the evaporation process. The numerical analysis of preheated kerosene injection atomization in supersonic inflow under constant liquid-gas momentum flux ratio was performed. The results reveal that the penetration depth of various thermal jets in the combustor changes slightly with a constant liquid-gas momentum flux ratio, independently of the kerosene temperature and liquid-gas coupling influence in the mainstream zone. The shape of the outer edge of the liquid mist evidently varies in a disordered manner. Using preheated kerosene as the fuel of the rotating detonation scramjet can increase the mixing degree of gas-liquid two-phase jets and accelerate the evaporation of droplets. Moreover, the fragmentation and atomization effects of thermal kerosene droplets are significantly improved. The analysis demonstrates that preheated kerosene injection may be beneficial to ignition and contributes to the self-sustainment of the detonation waves in the engine.
查看更多>>摘要：Although latent heat thermal energy storage using PCMs is widely used in the field of energy storage, a few challenges still remain. Among them, the PCM volume shrinkage during solidification has a serious impact on the current discharging process and the subsequent charging process. In this study, detailed analyses of unconstrained melting mode, especially solidification mode were studied, and an acceptable and reliable image processing technique with an uncertainty of about 0.9% was developed. In addition, the effects of cooling times (90-180 min), initial temperatures (42-60 degrees C), and cooling temperatures (12-30 degrees C), as well as the effects of heating times (30, 60 min), initial temperatures (18, 24 degrees C), and heating temperatures (54, 60 degrees C) were investigated. The results show that numerous shrinkage voids and porosity with attached air bubbles are formed inside the solidified PCM, which may reduce its effective thermal conductivity and hinder any heat transfer. The air bubbles attached to the shrinkage voids are released during the next melting process, forming several floating bubbles. The cooling and heating temperatures have a greater influence on the heat transfer rate than the initial temperature. Decrease of cooling temperature (18 degrees C) and increase of heating temperature (6 degrees C) will result in shorter solidification time (up to 46.51%) and melting time (up to 11.46%). The different solidification conditions have little effect on the subsequent melting process due to the same solidification mode.
查看更多>>摘要：Aircraft travel has quickly become the most enthusiastic and lowest-carbon mean of transportation for people to travel remotely. However, with the increase in the number of long-distance flights, at present, electric heating is widely used in domestic civil aircraft to supply hot water, which will challenge the energy system of aircraft. Especially, when the hot water requirement is huge. In this paper, a novel aircraft environmental control system coupled with hot water supplying is proposed. This novel system has two operating modes, self-circulation mode and hot water supplying mode. Results show that hot water with constant temperature of 55 degrees C can be provided and the temperature requirement of the aircraft environmental control system is met in the novel system. Compared with the current aircraft environmental control systems, the exergy loss of dominant components can be decreased in novel system. Compared with the current system, the exergy efficiency of the novel system with self-circulating mode is 3.18% higher, and the exergy efficiency of the novel system with hot water supplying mode is 5.6% higher. The novel system can save 1.17% of the aircraft's fuel consumption per hour, and the approach to reduce the exergy loss of the novel system is proposed.
查看更多>>摘要：In an adaptive optics system combined with a high-power laser radiation (HPLR) system, the thermal deformation of a deformable mirror (DM), which is induced by high-energy irradiation, is a significant factor influencing the optical performance of the system. In particular, the thermal deformation of the DM with a large diameter of more than a few hundred millimeters should be controlled to be on the order of 1 mu m in various HPLR environments. To satisfy these challenging criteria, we experimentally and numerically investigated the cooling performance of a large-diameter water-cooled DM (WDM) with U-shaped cooling microchannels (U-WDM) made of chemical-vapor-deposited SiC, which was designed first in our previous research. The fluid-thermal-structural coupling characteristics of the U-WDM were verified and analyzed through the verification process. In addition, the fluid-thermal-structural coupling characteristics of the DM and U-WDM were compared and analyzed by applying four different HPLR conditions: annular, circular, holed-square, and square beams. Under all the HPLR conditions, the comparative study demonstrated that the U-WDM had dramatic cooling performance, reducing the thermal deformation by more than 85% compared to that of the DM and achieving submicron-scale thermal displacement, which was lower than the targeted actuator deformation limit of 1.3 mu m.
Garcia-Afonso, OscarDelgado-Torres, Agustin M.Gonzalez-Diaz, Benjamin
15页
查看更多>>摘要：Waste Heat Recovery with Organic Rankine Cycle (ORC) in piston engine-based power plants placed in isolated systems is addressed in this paper. The power plant subjected to study is located in La Palma, Canary Islands, considered a representative example of small-to-medium isolated power system where the diesel engine is the solely or the main conventional technology for generation. In those systems, the power plant load control to cover the grid demand results in a noticeable variability of the available heat. This challenge is addressed in this paper through a performance and economic evaluation of an intermediate thermal energy storage system. A techno-economic analysis of the proposed power plant is performed taking as input the annual exhaust thermal energy available. The ORC-Diesel unit interaction is studied by means of an in-house developed plant load management model. An annual power plant fuel economy gain and pollutant emission reduction between 5% and 7% is estimated. In addition, the extra power and spinning reserve provided by the ORC allows the power plant to reduce its operational cost through the reduction of the number of diesel units starts.
NSTL
Elsevier