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Investigates the flowfield and aerodynamic performance of a turbine stator cascade with bowed blades. Impact of the loss near the cascade endwalls on the overall cascade loss; Usefulness of the bowed blade concept in reducing the loss of turbine cascades; Utilization of a suction-type low-speed linear cascade wind tunnel; Illustrations on mass-averaged energy loss coefficient and yaw flow angle.

An adaptive cycle engine is an evolutional aero-engine that can achieve low fuel consumption and high efficiency by adjusting the thermodynamic cycle; however, few studies have been conducted on adaptive cycle engine performance at low speeds. A high-fidelity ground starting model of an adaptive cycle engine is established by correcting the low speed characteristics of the components, while considering the effects of rotor inertia, volume, combustion efficiency, and the thermal inertia of the combustor and turbine. By employing a physically enhanced prediction method, three operating states of the compressor at low speeds are obtained: compressor, stirrer, and turbine state. The matching mechanism of the adaptive cycle engine and the detailed influence of the variable geometries on the engine's performance during the starting process are explored. The study shows that the third bypass duct has little effect on the engine starting time, and opening the mode select valve can reduce the starting time. Compared with the initial settings, the starting time decreases by 3.98 s after optimization with the variable geometries. The detailed impact of the variable geometries on the engine's starting performance provides an engineering reference value for the control strategies. • A high-fidelity ground starting model of an adaptive cycle engine is established by correcting the low speed characteristics of the components, while considering the effects of rotor inertia, volume, combustion efficiency, and the thermal inertia of the combustor and turbine. • A physically enhanced prediction method based on PSO-SVR for extrapolating the low-speed characteristics of compressors is proposed to solve the problems of low accuracy and discontinuous isentropic efficiency at low-speeds. • The detailed impact of the variable geometries on the adaptive cycle engine's starting performance provides engineering reference value for the optimum designing of adaptive cycle engine start control strategies. [ABSTRACT FROM AUTHOR]

Adaptive cycle engines (ACEs) represent a sophisticated class of power units, embodying numerous variable geometry components, marking them as pivotal for the advancement of next-generation high-speed civil and military engines. Nonetheless, this variability introduces substantial complexity into the engineering of control laws. Contemporary research predominantly relies on either manual methodologies or global optimization algorithms. The former rarely achieves peak performance, while the latter incurs substantial computational expenses. This research introduces an accelerated methodology by using variable-step gradient with boundary constraints (VGB) algorithm tailored for the nuanced optimization challenges posed by multi-variable, multi-constraint nonlinearities inherent in ACEs. Recognizing that ACE's peak performance is typically boundary-constrained, the algorithm strategically manipulates variable geometries to widen the operational gap from the most disadvantageous boundary (MDB), thereby inching closer to the engine's ideal operational nexus. This strategy culminates in a decease in computational overhead, diverging significantly from conventional global optimization approaches. Empirical findings represent the method's efficacy, with a maximal performance deviation of just 3.78 % across three steady-state missions. Post transient control law refinement, engine's starting time contracted by 5.93 s via VGB algorithm, opposed to baseline design point configurations. Collectively, this approach serves as a versatile and efficient blueprint for designing control laws. [ABSTRACT FROM AUTHOR]

Abstract A cryogenic air separation unit (ASU) with the implementation of vapor recompression column (VRC) and LNG cryogenic energy is proposed and investigated. To this end, three types of cryogenic rectification column for air separation are first illustrated, and their thermodynamic characteristics are evaluated by the first and second thermodynamic laws. The results show the purity and recovery ratio of product are determined by the total amount of heat duty and the scheme of heat distribution. Compared with the conventional double rectification column and internally heat-integrated distillation column, the VRC is the most suitable column for the ASU with use of LNG cryogenic energy as its lower demand of shaft work and minimum energy of separation. Based on the above analysis, adopting the cryogenic energy from product to cool the reflux and feed air is beneficial for producing vapor product in the proposed process. The operating pressure of ASU could be reduced by about 24%, and the cryogenic energy of LNG can be used efficiently and sufficiently with respect to the supercritical thermophysical property. By adding the air-aid refrigeration process, the proposed process also has the ability to produce liquid oxygen. Under the same oxygen purity and recovery ratio, the optimal results show the power consumption is about 6.9% and 11.1% lower than that in the previous studies in producing vapor and liquid product respectively, and the minimum energy of separation is improved by use of LNG cryogenic energy. Highlights • The unified governing equations of air separation is deduced. • The vapor recompression column has the lowest shaft work and minimum energy of separation. • The cryogenic energy of LNG can be used efficiently and sufficiently. • Energy consumption of the proposed process is less than that of conventional processes. [ABSTRACT FROM AUTHOR]

Due to strong nonlinear variation of supercritical liquid nature gas (LNG) and nitrogen (N 2 ) isobaric heat capacity with temperature and pressure, pinch point analysis is conducted for heat exchange process between LNG and N 2 and its effect on the air separation unit cooled by LNG cryogenic energy (CEASU) is studied in the present study. The effect of pinch point value, temperature difference at the cold end and pressure of N 2 on mass flow ratio (N 2 to LNG), approach temperature difference, energy consumption of CEASU and cryogenic energy utilization rate are analyzed in detail. For the heat exchanger process between LNG and N 2 , the different value of pinch point have little effect on its location, and increasing the temperature difference at the cold end effectively increases the mass flow ratio and decreases the approach temperature difference, while rising the pressure of N 2 leads to a valley value of the mass flow ratio, in contrast to a peak value in the approach temperature difference. For the energy consumption of CEASU, choosing the lower temperature difference at the cold end is good for the energy consumption and equivalent energy consumption per kilogram liquid production, but a large amount of LNG is needed and cryogenic energy could not be fully used; while the influence of pressure of N 2 on the energy consumption presents different variation trend. The result shows the energy consumption per kilogram liquid production of proposed CEASU is roughly 5–12% lower than that of convectional processes which the cryogenic energy is only used for cooling the nitrogen or the feed air. [ABSTRACT FROM AUTHOR]

This paper is devoted to the study of numerical computation for a kind of time optimal control problem for the tubular reactor system. This kind of time optimal control problem is aimed at delaying the initiation time τ of the active control as late as possible, such that the state governed by this controlled system can reach the target set at a given ending time T. To compute the time optimal control problem, we firstly approximate the original problem by finite element method and get a new approximation time optimal control problem governed by ordinary differential equations. Then, through the control parameterization method and time-scaling transformation, the approximation problem becomes an optimal parameter selection problem. Finally, we use Sequential Quadratic Program algorithm to solve the optimal parameter selection problem. A numerical simulation is given for illustration. [ABSTRACT FROM AUTHOR]

A method to estimate the mode III stress intensity factor (SIF) of kinked crack under anti-plane load is presented. The SIF of the kinked crack can be estimated by an expression derived from the stress field series of the original crack include first three order terms by the weight function (WF) method. The coefficients of the WFs were obtained by a fitting procedure based on the solutions of the weight function problem, which were solved by a conformal mapping method. The influence of the WFs in the estimation was evaluated as a function of the kink angle and the kink length ratio. The application to the case of a kinked crack shows good agreement with the analytical results. [ABSTRACT FROM AUTHOR]

A method for estimating the stress intensity factors (SIFs) of kinked crack with finite kink length is presented. This method is based on an estimation expression which is derived by He et al. according to the work of Cotterell and Rice from the stress field series of the original (unkinked) crack tip to the second order by using weight function (WF). In order to increase the estimation accuracy for the kinked crack with finite kink length, the third order coefficients of the stress field series of the original crack tip are introduced into this expression and these parameters can be obtained by a fitting procedure. Application of this modified expression to the cases of singly-kinked, edge kinked and doubly-kinked cracks reveals a good approximation with the finite element (FE) results of SIFs and showed that the accuracy is increased. [ABSTRACT FROM AUTHOR]

In order to reduce the cost of thermal energy recovery, a packed bed closed loop thermal energy storage system has been proposed and is investigated. The main components of the system include a closed air cycle, a heat exchanger, and a packed bed storage column. This paper is aimed at analyzing the performance of the packed bed in the system. Packed bed column experiments have been carried out to provide a basic understanding of the thermal energy storage process in the closed loop system with different flow directions in the packed bed and different energy storage temperatures. The detailed temperature distributions in the interior of the packed bed and the temperature differences along the axial and radial directions are presented. The influence of flow direction within the packed bed and structure of the gas distributer on the temperature distribution are also analyzed. The performance of packed beds in the closed loop thermal energy storage system is then evaluated based on energy and exergy analyses. These experimental results would be useful in the optimal design of the structure of packed bed columns and thus closed loop thermal energy storage systems. [ABSTRACT FROM AUTHOR]

An uninterruptible power supply (UPS) system based on supercapacitor and liquid nitrogen (LN2) hybridization is first introduced in this paper. Of the newly designed UPS, the supercapacitor reacts instantaneously once the main supply fails, and it also starts the LN2 power system to produce continuing electricity for the customer. This hybrid UPS system is of environment cleanness, long life time, easy maintenaince, etc. A 10kW model is analyzed in this study. A two-stage nitrogen expander is designed with the rated speed of 900rpm as the long time power generation device of the LN2 cycle. The UPS starting process calculation is carried out. The results reveal that commercial supercapacitors could fulfill this request. This UPS could be a competent choice for the UPS application. Further discussion indicates the LN2 power system could be used widely from UPS to low carbon vehicles. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a new type of solar energy based power generation system using supercritical carbon dioxide and heat storage. The power generation cycle uses supercritical carbon dioxide as the working fluid and integrates the supercritical carbon dioxide cycle with an efficient high-temperature heat storage. The analysis shows that the new power generation system has significantly higher solar energy conversion efficiency in comparison to the conventional water-based (steam) system. At the same time, the heat storage not only overcomes the intermittent nature of solar energy but also improves the overall system efficiency. The study further reveals that the high temperatures and high pressures are favorable for solar energy storage and power generation. Moreover the expander and the heat storage/regenerator are found to be the key components that determine the overall system performance. [Copyright &y& Elsevier]

Highlights: [•] Techno-economical and social analysis of energy storage is conducted for commercial buildings. [•] Methodologies for demand analysis, technical, economical and social evaluations are developed. [•] An illustrative example is analyzed for three kinds of energy storage systems. [Copyright &y& Elsevier]

Abstract: H2 production from glycerol steam reforming by the Ni–Cu–Al, Ni–Cu–Mg, Ni–Mg catalysts was evaluated experimentally in a continuous flow fixed-bed reactor under atmospheric pressure within a temperature range from 450 to 650 °C. The catalysts were synthesized by the co-precipitation methods, and characterized by the elemental analysis, BET, XRD and SEM. The GC and FTIR were applied to analyze the products from steam reforming of glycerol. The coke deposited on the catalysts was measured by TGA experiments during medium temperature oxidation. The results showed that glycerol conversion and H2 production were increased with increasing temperatures, and glycerol decomposition was favored over its steam reforming at low temperatures. The Ni–Cu–Al catalyst containing NiO of 29.2 wt%, CuO of 31.1 wt%, Al2O3 of 39.7 wt% performed high catalytic activity, and the H2 selectivity was found to be 92.9% and conversion of glycerol was up to 90.9% at 650 °C. The deactivation of catalysts due to the formation and deposition of coke was observed. An improved iterative Coats–Redfern method was used to evaluate the non-isothermal kinetic parameters of coke removal from catalysts, and the results showed the reaction order of n = 1 and 2 in the Fn nth order reaction model predicted accurately the main phase in the coke removal for the regeneration of Ni–Mg and Ni–Cu–Al catalysts, respectively. [Copyright &y& Elsevier]

Abstract: About 10wt.% of glycerol can be produced during the conversion of vegetable oils or animal fats into biodiesel fuel by the transesterification process. To make use of glycerol and increase its values, H2 production from catalytic steam reforming of glycerol by Ni–Mg–Al based catalysts was evaluated experimentally in a fixed-bed reactor under atmospheric pressure within a temperature range of 450–650°C. The thermodynamic analysis was conducted by using a non-stoichiometric methodology based on the minimization of Gibbs free energy. The Ni–Mg–Al based catalysts were synthesized by the co-precipitation method with rising pH technique. The synthesized catalysts were characterized by the elemental analysis, BET, XRD and SEM methods. All the metals in the catalyst remained in oxide forms and the catalysts had the specific surface areas from 98.542 to 126.777m2/g for different compositions. The results showed that glycerol conversion and H2 selectivity were increased with increasing temperatures from 450 to 650°C. The formations of CH4 and CO in the glycerol steam reforming were almost negligible. Carbon formation in glycerol steam reforming was serious in low temperatures. The catalyst containing NiO of 24.1wt.%, MgO of 26.1wt.% and Al2O3 of 49.8wt.% performed appreciable catalytic activity, and the H2 selectivity was found to be 78.5% and conversion of glycerol was up to 88.0% at 650°C. The effects of the operating conditions including temperature, the ratio of steam to carbon (S/C), glycerol inlet concentration and flow rate of carrier gas on glycerol steam reforming by the optimized catalyst were tested. Based on a kinetic model assuming the power law with a first reaction order, the activation energy and the frequency factor for glycerol steam reforming by the Ni–Mg–Al based catalysts were calculated. [Copyright &y& Elsevier]

To solve the problems of high cost and low efficiency of conventional co-production system of hydrogen and electricity with low hydrogen-to-electricity ratio, a novel co-production system based on coal partial gasification with CO 2 capture is proposed and thermodynamically analyzed. The new system integrates the conceptions of cascade conversion of coal and cascade utilization of syngas to realize the system with high efficiency, low cost, environmental friendliness and flexible hydrogen-to-electricity ratio. The performance of the new system is evaluated by an Aspen Plus model and effects of the operating conditions are also studied. It is found that the system with capturing CO 2 of 59.7% and hydrogen-to-electricity ratio of 4.76 holds a high exergy efficiency of 54.3% when the carbon conversion ratio of the pressurized fluidized bed (PFB) gasifier is equal to 0.7. The carbon conversion ratio of the PFB gasifier is a dominant factor to decide the performance of system. In comparison with the series-type co-production system, the parallel-type co-production system and separate production system, the new system proposed in this study has exergy-saving efficiency of 17.7%, 15.1% and 8.9%, respectively. [ABSTRACT FROM AUTHOR]

Abstract: To solve the problems of high cost and low efficiency of conventional co-production system of hydrogen and electricity with low hydrogen-to-electricity ratio, a novel co-production system based on coal partial gasification with CO2 capture is proposed and thermodynamically analyzed. The new system integrates the conceptions of cascade conversion of coal and cascade utilization of syngas to realize the system with high efficiency, low cost, environmental friendliness and flexible hydrogen-to-electricity ratio. The performance of the new system is evaluated by an Aspen Plus model and effects of the operating conditions are also studied. It is found that the system with capturing CO2 of 59.7% and hydrogen-to-electricity ratio of 4.76 holds a high exergy efficiency of 54.3% when the carbon conversion ratio of the pressurized fluidized bed (PFB) gasifier is equal to 0.7. The carbon conversion ratio of the PFB gasifier is a dominant factor to decide the performance of system. In comparison with the series-type co-production system, the parallel-type co-production system and separate production system, the new system proposed in this study has exergy-saving efficiency of 17.7%, 15.1% and 8.9%, respectively. [Copyright &y& Elsevier]

Abstract: In this paper, the pyrolysis characteristics of sucrose biomass were investigated in a tubular reactor at different temperatures and also using a thermogravimetric analyzer at the heating rate of 10°Cmin−1 from room temperature to 1200°C. The gas products in the pyrolysis process were measured using an Agillent 6890N GC analyzer. The results showed that the temperature greatly affected the product yields. The pyrolysis gas consisted of a major amount of CO, CO2, H2, and CH4, and its yield increased greatly with increasing temperature. Tars occurred mainly at 200–300°C under isothermal measurements in tubular reactor. The amounts of solid residue and tars decreased with increasing temperature. The presence of CaO responsible for the pyrolysis phase was shown to increase the conversion of sucrose and capture the CO2 produced. The kinetic analysis indicated that the reaction order model (first order) predicted accurately the conversion of 0.102–0.901 during the isothermal pyrolysis of sucrose in tubular reactor, and Arrhenius parameters and prediction of the pyrolysis time were obtained from isothermal kinetic results. [Copyright &y& Elsevier]

SUMMARY This work reports a newly proposed system for electrical energy storage. The new system combines a direct open nitrogen (cryogen) expansion cycle with a natural gas-fuelled closed Brayton cycle and the CO2 produced in the system is captured in the form of dry ice. Thermodynamic analyses are carried out on the system under the baseline conditions of 1 kg s−1 natural gas, a combustor operating pressure of 8 bars and a cryogen topping pressure of 100 bars. The results show that the exergy efficiency of the proposed system is as high as 64% under the baseline conditions, whereas the corresponding electricity storage efficiency is about 54%. A sensitivity analysis has also been carried out on the main operating conditions. The results indicate that the baseline performance can be enhanced by increasing the gas turbine (GT) inlet temperature, decreasing the approach temperature of the heat exchange processes, operating the combustor at an optimal pressure of ∼7 bars and operating the cryogen topping pressure at ∼90 bars. Further enhancement can be achieved by increasing the isentropic efficiency of the GT and the liquefaction process. The results of this work also suggest that the power capacity installation of peak-load units and fuel consumption could be reduced by as much as 50% by using the newly proposed system. Further work is suggested for an economic analysis of the system. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: New porous heterostructured nanohybrid of MgO–TiO2–Al2O3/montmorillonite has been successfully synthesized by an inflating, intercalation, and reassembling method under the ultrasonic vibration. The synthesized material was characterized by TGA–DTG, XRD, TEM and elemental analysis. The results showed that the material had a specific surface area of 156m2 g−1 with an average pore diameter of 2.68nm and pore volume of 0.6627cm3 g−1, and that the MgO, TiO2 and Al2O3 nanoparticles were introduced in the montmorillonite by the heat treatment of 500°C. It was found that the intercalation and deposition of mixed oxides nanoparticles expanded the basal spacing of montmorillonite, and the crystallites of the nanohybrids were assembled to form a heterostructured composite. [Copyright &y& Elsevier]

Abstract: This study examined the performance and emission characteristics of a household size trigeneration based on a diesel engine generator fuelled with hydrogen comparing to that of single generation, cogeneration using ECLIPSE simulation software. In single generation simulation, the engine genset is used to produce electricity only and the heat from the engine is rejected to the atmosphere. In cogeneration and trigeneration, in addition to the electricity generated from the genset, the waste heat rejected from the hot exhaust gases and engine cooling system, is captured for domestic hot water supply using heat exchangers and hot water tank; and a part of the waste heat is used to drive absorption cooling in trigeneration. Comparisons have been made for the simulated results of these three modes of operation for hydrogen and diesel. The results prove that hydrogen is a potential energy vector in the future which is a key to meeting upcoming stringent greenhouse gases emissions. The study show that hydrogen has very good prospects to achieve a better or equal performance to conventional diesel fuel in terms of energetic performance, and a near zero carbon emission, depending on the life cycle analysis of the way the hydrogen is produced. The results also show enormous potential fuel savings and massive reductions in greenhouse gas emissions per unit of useful energy outputs with cogeneration and trigeneration compared with that of single generation. [Copyright &y& Elsevier]

Abstract: Road transportation using air as a fuel has attracted much attention over the past decade. The fuel (air) can be in two forms, compressed gas form and cryogenic liquid form and engines based on both forms of air have been investigated. Prototypes of air powered road vehicles are expected to emerge over the next few years. However, there have been debates over the advantages and disadvantages of the two technologies. This paper aims to compare the two technologies from the technological point of view. Engines for a typical small scale passenger car are used for the analyses and the comparison is based on the shaft work, coolth, efficiency and energy density. It is shown that the shaft work outputs and the coolth available to engines powered by both fuels increase with increasing working pressure and temperature. Given the working pressure and temperature, liquid air powered engines have a slightly lower specific work outputs than compressed air powered engines. The volumetric energy density of liquid air, however, is much higher than that of compressed air, and liquid air has much higher coolth than compressed air. On the other hand, the efficiency of the compressed air powered engines is higher than that of liquid air powered engines mainly because of the higher energy consumption of liquefaction plants. The analyses also suggest that an effective use of coolth be a key to improve the overall efficiency of liquid air powered engines. [ABSTRACT FROM AUTHOR]

Abstract: Electrical energy storage technologies for stationary applications are reviewed. Particular attention is paid to pumped hydroelectric storage, compressed air energy storage, battery, flow battery, fuel cell, solar fuel, superconducting magnetic energy storage, flywheel, capacitor/supercapacitor, and thermal energy storage. Comparison is made among these technologies in terms of technical characteristics, applications and deployment status. [Copyright &y& Elsevier]

Abstract: Titanate nanotubes of an aspect ratio of ~10 are synthesized, characterised and dispersed in water to form stable nanofluids containing 0.5, 1.0 and 2.5 wt.% of the nanotubes. Experiments are then carried out to investigate the effective thermal conductivity, rheological behaviour and forced convective heat transfer of the nanofluids. The results show a small thermal conductivity enhancement of ~3% at 25 °C and ~5% at 40 °C for the 2.5 wt.% nanofluid. The nanofluids are found to be non-Newtonian with obvious shear thinning behaviour with the shear viscosity decreasing with increasing shear rate at low shear rates. The shear viscosity approaches constant at a shear rate higher than ~100–1000 s−1 depending nanoparticle concentration. The high shear viscosity is found to be much higher than that predicted by the conventional viscosity models for dilute suspensions. Despite the small thermal conduction enhancement, an excellent enhancement is observed on the convective heat transfer coefficient, which is much higher than that of the thermal conductivity enhancement. In comparison with nanofluids containing spherical titania nanoparticles under similar conditions, the enhancement of both thermal conductivity and convective heat transfer coefficient of the titanate nanotube nanofluids is considerably higher indicating the important role of particle shape in the heat transfer enhancement. Possible mechanisms are also proposed for the observed enhancement of the convective heat transfer coefficient. [Copyright &y& Elsevier]

Abstract: Systematic experiments have been carried out on the thermal and rheological behaviour of the ionic liquid, 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide, [C4mim][NTf2], and, for the first time, on the forced convective heat transfer of an ionic liquid under the laminar flow conditions. The results show that the thermal conductivity of the ionic liquid is ∼0.13Wm−1 K−1, which is almost independent of temperature between 25 and 40°C. Rheological measurements show that the [C4mim][NTf2] liquid is a Newtonian fluid with its shear viscosity decreasing with increasing temperature according to the exponential law over a temperature range of 20–90°C. The convective heat transfer experiments demonstrate that the thermal entrance length of the ionic liquid is very large due to its high viscosity and low thermal conductivity. The convective heat transfer coefficient is observed to be much lower than that of distilled water under the same conditions. The convective heat transfer data are also found to fit well to the convectional Shah’s equation under the conditions of this work. [Copyright &y& Elsevier]

Abstract: Ethylene glycol based nanofluids containing titania nanoparticles up to 8wt% show the Newtonian behaviour over a shear rate range of 0.5–104 s−1 at 293–333K. The shear viscosity of the nanofluids (η) depends strongly on temperature and particle concentration (φ). The normalized shear viscosity with respect to the based liquid viscosity (η 0) is found to be independent of temperature and can be given as η/η 0 −1=10.6φ +(10.6φ)2. Such rheological behaviour is explained by the aggregation mechanism. A combination of the aggregation mechanism with the Maxwell and Bruggeman models gives a good prediction of the effective thermal conductivity of the nanofluids. [Copyright &y& Elsevier]

Review: 81 refs. [ABSTRACT FROM AUTHOR]