查看更多>>摘要：Hybrid turbochargers can become an attractive solution for new built and retrofitted ship power plants, as their use can result in increasing the plant efficiency and reducing emissions. This study aims at computationally investigating the hybrid turbocharger effects on a large marine dual-fuel four-stroke engine performance and emissions characteristics as well as determining its electrical generator optimal size for the case of a ship power plant considering an actual operating profile. An existing model of a large marine four-stroke dual-fuel engine of the zero/one-dimensional type, which was developed in the commercial software GT-Power, is extended to include the hybrid turbocharger sub-model. This model is subsequently employed to carry out a parametric investigation considering a wide range for the hybrid turbocharger electric motor power. The derived results are analysed to identify the variations of the investigated dual fuel engine performance and emissions parameters in the whole engine operating envelope at both the diesel and gas modes, whilst taking into account the engine and its components operational limits. For the considered annual load profile, the results demonstrate that the optimal nominal size of the hybrid turbocharger electric motor power is 300 kW and leads to an annual energy surplus between 2% and 3% of the annually delivered engine mechanical energy. This study benefits the quantification of the hybrid turbocharger impact on large marine dual fuel four-stroke engines as well as the ship energy efficiency, thus providing useful decision support to facilitate the shipboard implementation of this technology.
查看更多>>摘要：Mobile, small-scale refrigeration applications for last-mile deliveries have gained increased importance in recent years. As they face disturbances and frequent door openings more extensively than long-distance transport, reliable temperature information is crucial for control concepts to comply with temperature regulations and increase efficiency. For desired ruggedness, sensors are typically integrated within the cooling unit, yielding substantial deviations between actual air temperature in the cooling chamber and measured one - particularly in periods of altered airflow conditions resulting from fan switching and the actual door opening status. This article introduces and compares two hybrid, online estimation procedures to overcome this issue: firstly, a Kalman-filter approach based on a simple lumped physical heat transfer model, and secondly, a graybox-model approach resulting from a realizable inversion of the physical model. Experimental investigations of typical operating profiles provide 14h of real-world data to parameterize (11.75 h data length), validate (2.25 h data length), and compare both estimators. The proposed concepts are based on a sensor setup available in state-of-the-art system architectures and provide satisfactory temperature estimates with more than 83 % overall fit. As the algorithms provide comprehensive process insight independent of the actual operating condition, sophisticated control schemes can be built upon the concept.
查看更多>>摘要：The operation optimisation of chilled water systems, comprising chillers and pumps, should consider variations in the cooling demand. Although a number of approaches have been proposed, achieving an overall optimum in actual operation is complicated. Herein, we propose a hybrid optimisation method for a chiller-pump system in parallel-arranged systems with non-identical chillers and pumps, which are commonly applied in engineering practice but are rarely considered in the literature. A holistic optimisation based on a multi-objective evolutionary algorithm was conducted for the overall minimum energy by solving the trade-off problem between chillers and pumps. The overall energy consumption and system flow violation were simultaneously minimised by optimising practical parameters, including binary (alpha(chiller,i), alpha(pump,j)) and continuous ((Q) over dot(chiller,i), omega(j), (m) over dot(chw,j)) variables. The proposed method was evaluated via a simulation. The results suggest that the optimisation is rational, and energy saving ratios of 7.3%, 5.3%, and 34.0% for overall, chillers, and pumps, respectively, can be achieved relative to the baseline.
查看更多>>摘要：Frosting researches under cryogenic conditions have great significance in liquefied natural gas (LNG) and aerospace applications. The investigation on the thermal resistance and the surface temperature of the frost layer is indispensable but insufficient due to the difficulty in experimental measurements. A novel computational fluid dynamics (CFD) model considering the change of the frost layer thermal conductivity was developed for the thermal resistance analysis of the frosting process of water-vapor-carried gas flowing over a cryogenic surface, and the change of the frost surface temperature over time was predicted. The calculated results were validated against the published experimental data and showed good agreements. Based on the validated model, the overall variation and local distribution of the thermal resistance and the surface temperature of the frost layer, as well as the growth behaviors, were studied. Furthermore, the influences of principal operating parameters on the averaged thermal resistance and the averaged surface temperature of the frost layer were analyzed, including the cryogenic surface temperature, the inlet gas flow temperature, the water vapor content of the inlet gas flow and the velocity of the inlet gas flow. Parameter sensitivity analysis was carried out and the averaged thermal resistance of the frost layer shows greatest sensitivity to the inlet gas flow temperature.
查看更多>>摘要：Passive devices based on water wicking and evaporation offer a robust, cheap, off-grid, energy-efficient and sustainable alternative to a wide variety of applications, ranging from personal thermal management to water treatment, from filtration to sustainable cooling technologies. Among the available, highly-engineered materials currently employed for these purposes, polyethylene-based fabrics offer a promising alternative thanks to the precise control of their fabrication parameters, their light-weight, thermal and mechanical properties, chemical stability and sustainability. As such, both woven and non-woven fabrics are commonly used in capillary-fed devices, and their wicking properties have been extensively modelled relying on analytical equations. However, a comprehensive and flexible modelling framework able to investigate and couple all the heat and mass transfer phenomena regulating the water dynamics in complex 2-D and 3-D porous components is currently missing. This work presents a comprehensive theoretical model aimed to investigate the wetting and drying performance of hydrophilic porous materials depending on their structural properties and on the external environmental conditions. The model is first validated against experiments (R-2=0.99 for the wicking model; errors lower than 14% and 1% for the evaporation and radiative models, respectively), then employed in three application cases: the characterisation of the capillary properties of a novel textile; the assessment of the thermal performance of a known material for personal thermal management when used in different conditions; the model-assisted design of a porous hydrophilic component of passive devices for water desalination. The obtained results showed a deep interconnection between the different heat and mass transfer mechanisms, the porous structure and external working conditions. Thus, modelling their non-linear behaviour plays a crucial role in determining the optimal material characteristics to maximise the performance of porous materials for passive devices for the energy and water sector.
Payri, RaulGimeno, JaimeCarvallo, CesarPeraza, Jesus E....
21页
查看更多>>摘要：Spray-wall interactions (SWI) directly affect fuel-air mixture and emissions formation. Therefore, they are considered among the most critical physical processes in engine research nowadays. However, the physics of the wall film formation, propagation, and breakup is not fully understood yet. This work aims to use a thermoregulated steel wall to study the spray-wall interaction phenomenon and its influence on the macroscopic spray behavior. A single-hole injector known as "Spray D"in the Engine Combustion Network was used. n-Dodecane was employed as fuel and the wall has been positioned in four different configurations, varying angle and distance respect to the injector tip. For this work, not only diesel combustion is reproduced in the test rig due to ambient gas engine-like thermodynamic conditions, but wall temperature has been controlled to emulate characteristic values that could be found in the piston of an internal combustion engine. This implies that the spray-wall heat transfer is simulated and its effects on ignition and spray development can be analyzed. Heat flux was measured by employing high-speed thermocouples fitted in the wall and by the use of an one-dimensional transient wall heat model. Three high speed cameras were simultaneously used to observe the SWI, one for the Schlieren optical technique which allows to study the vapor phase of the spray and to determine the ignition delay, another one to observe the natural luminosity of the flame, and finally, an intensified camera was used to determine the lift-off length by observing the chemiluminescence of the OH*. An interesting finding obtained in this work was a boundary layer formation due to the thermal diffusion that contributes to cool down the spray and to delay the high-temperature chemical reactions. Results show a substantial increment of the heat flux and the wall temperature variation with both ambient temperature and density by increasing the flame temperature and gas entrainment. The exposure to the cold wall affects the ignition delay variation with the injection pressure and the wall distance. It was found that the wall temperature (in the range of tested conditions) did not affect the lift-off length location.
Kim, YoungkunIl Kim, WoongMin, ByounghyoukSeo, Juhyeong...
13页
查看更多>>摘要：Interest in reducing greenhouse-gas emissions has increased in past decades because of global warming. In particular, research on alternative fuels for internal combustion engines is in progress for eliminating dependence on existing fossil fuels. Bioethanol-an alternative fuel-has attracted attention because it can be applied without major modifications to conventional internal combustion engines that use fossil fuels. However, further research is necessary, because gasoline and ethanol have different spray and combustion characteristics owing to differences in their physical properties. In this study, the penetration length, spray angle, and spray pattern were analyzed through spray experiments in which the blend ratio of ethanol-gasoline blended fuel was varied. In addition, a direct injection-type flex fuel vehicle engine test device was built, and the combustion and knocking characteristics were investigated with respect to the ethanol ratio through an engine test. Compared with the brake-specific fuel consumption and the combustion pressure of E0, those of E100 increased by 28.7% (because the lower heating value was lower for E100) and reduced by 11.2%, respectively. The heat-release rate of E22 increased faster than that of E0 owing to the characteristics of ethanol, which is an oxygen-containing fuel, and the high vaporization rate. The anti-knock properties of ethanol were superior to those of gasoline; therefore, knocking hardly occurred for fuel blend ratios above E50.
查看更多>>摘要：Currently, micro power generators have been widely drawing attention for various applications. In this study, the H-2-air micro combustor (MC) with a multihole baffle plate was combined with two power generators based on micro-thermophotovoltaic and micro-thermoelectric systems. The reacting flow and conjugate heat transfer including the MC wall were analyzed by the detailed reaction mechanism and the outer wall condition of convection and radiation. From the resulting thermal fields, the characteristics of heat emission and electrical potential were examined. Eight baffles with different numbers of air holes (Na) and three global equivalence ratios were selected, and a baffle with N-a = infinity was adopted to compare the multihole and annular air flows. The combustion characteristics depending on Na were explored by analyzing the changes in the reaction zone, the flammable range, reaction rate, and wall heat transfer rate. The N-a effect on wall and center recirculation zones was comparable to the variation due to other geometrical variables of the baffle plate. As N-a increased, the combustion efficiency increased to 20% of the N-a = infinity case. The combustion efficiency equivalent to the swirl MC was obtained for Na = 5-8, having enhanced preheating effects and large center recirculation zones. Compared to N-a = infinity the mean temperature of the multihole baffled MC increased by 6.4%-19.2% depending on Na. The emitter efficiency related a TPV system was comparable to the swirling flow MC. For a thermoelectric generator, the conversion efficiency of N-a = infinity was similar to that of a Swiss-roll MC, and the multihole baffled MC showed a high conversion efficiency of 1.55%-3.58% depending on N-a and the global equivalence ratio.
查看更多>>摘要：In this work, a theoretical study and a numerical performance analysis of a novel HumidificationDehumidification (HDH) desalination system, that simultaneously exploits an Indirect Evaporative Cooling (Maisotsenko cycle, IEC) device and a Vapour Compression Refrigeration cycle (VCR), are proposed. The IEC device is here employed as a very efficient saltwater evaporator-air humidifier, by an optimized mass exchange process between saltwater and working airstream. Both thermal exchanges of the VCR cycle are used: the hot coil pre-heats the inlet air to enhance the effectiveness of the evaporation process, while the cold one provides the cooling capacity to condense freshwater. The numerical model is based on data of actual commercial devices and considers their effective operational mode. The parametric analysis and the yearly simulations in different climatic areas show very promising results (GOR and RWA factor equal to 3.4 and 5.0.106 in the best operative condition, equal to 3.2 and 4.1.106 in the best climate situation) that lead to consider this technology as very competitive among HDH desalinations systems.
Kumar, AvnishSaxena, AbhishekPandey, S. D.Joshi, S. K....
18页
查看更多>>摘要：In the present work, the thermal performance of a low-cost solar box cooker (SBC) has been improved through the concept of extended fins and heat storage medium. To achieve the goal, about 144 aluminium made small capsule shaped containers have been filled with PCM and placed horizontally over the absorber. Experiments have been conducted on the three different configurations such as, SBC without any modification, SBC with hollow capsules and SBC with an encapsulated PCM. Experimental study mainly emphasizes on a high heat transfer rate and reduced cooking times through the applied modifications. Thermal performance has been found improved by using encapsulated PCM during the cooking trials. Results showed that the last configuration is the best among the three different configurations developed for cooking experiments. Thermal efficiency has been found improved by 52.2%, heat transfer coefficient improved by 301 W/m?, cooking power enhanced about 53.21 W, and the overall heat loss coefficient reduced about 4.11 W/m? on the third configuration. The modified SBC purposely designed for the people from hilly regions who are unable to access the clean cooking fuels. Present design is economic ($55.01) and feasible for cooking of common edibles available in Uttarakhand and nearby regions in India. The payback period ranges from 0.80 years to 4.01 years for different fuels. Notified that the modified cooker also meets the Bureau of Indian standards (BIS) developed for solar cookers.
NSTL
Elsevier