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.
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：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：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：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：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：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.
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：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.
NSTL
Elsevier