Effective elastic properties for unpoled barium titanate

Piezoelectric devices with complex electrode geometries may contain regions of ferroelectric material that remain unpoled. It is desirable to account for these non-piezoelectric regions for device optimization, since the unpoled and poled material properties differ. The lack of published elastic properties for unpoled ferroelectrics, specifically the numerous commercial PZT compositions, reflects the difficulty of experimental measurement. In this work, a method was developed to predict unpoled properties from more commonly available poled material data. Barium titanate was chosen for study as a representative ferroelectric, with both single crystal and polycrystalline (ceramic) properties available. Finite element micro-mechanical models were created with a focus on computational economy. This allowed larger ensembles of results to be computed, providing accurate effective compliances when averaged. The modelling methodology predicted the elastic properties for unpoled barium titanate to within ∼10% of measured experimental values.     

Combustion characteristics of SI engine fueled with methanol-gasoline blends during cold start

A 3-cylinder port fuel injection (PFI) engine fueled with methanol-gasoline blends was used to study combustion and emission characteristics. Cylinder pressure analysis indicates that engine combustion is improved when methanol is added to gasoline. With the increase of methanol, the flame developing period and the rapid combustion period are shortened, and the indicated mean effective pressure increases during the first 50 cycles. Meanwhile, a novel quasi-instantaneous sampling system was designed to measure engine emissions during cold start and warm-up. The results at 5°C show that unburned hydrocarbon (UHC) and carbon monoxide (CO) decrease remarkably. Hydrocarbon (HC) reduces by 40% and CO by 70% when fueled with M30 (30% methanol in volume). The exhaust gas temperature is about 140°C higher at 200 s after operation compared with that of gasoline. __________ Translated from Transactions of CSICE, 2007, 25(3): 235–240 [译自: 内燃机学报]     

Effects of cavitation in a nozzle on liquid jet atomization

Cavitation in two-dimensional (2D) nozzles and liquid jet in the vicinity of the nozzle exit were visualized using high-speed cameras to investigate the effects of cavitation on liquid jet under various conditions of cavitation and Reynolds numbers σ and Re. Liquid velocity in the nozzle was measured using a laser Doppler velocimetry to examine the effects of cavitation on the flow in the nozzle and liquid jet. As a result, the following conclusions were obtained: (1) cavitation in the nozzles and liquid jet can be classified into the four regimes: (no cavitation, wavy jet), (developing cavitation, wavy jet), (super cavitation, spray) and (hydraulic flip, flipping jet), (2) liquid jet near the nozzle exit depends on cavitation regime, (3) cavitation and liquid jet are not strongly affected by Re but by σ, and (4) strong turbulence induced by the collapse of cavitation clouds near the exit plays an important role in ligament formation.     

A numerical model for thermoelectric generator with the parallel-plate heat exchanger

This paper presents a numerical model to predict the performance of thermoelectric generator with the parallel-plate heat exchanger. The model is based on an elemental approach and exhibits its feature in analyzing the temperature change in a thermoelectric generator and concomitantly its performance under operation conditions. The numerical simulated examples are demonstrated for the thermoelectric generator of parallel flow type and counter flow type in this paper. Simulation results show that the variations in temperature of the fluids in the thermoelectric generator are linear. The numerical model developed in this paper may be also applied to further optimization study for thermoelectric generator.     

Thermodynamic analysis of an LNG fuelled combined cycle power plant with waste heat recovery and utilization system

This paper has proposed an improved liquefied natural gas (LNG) fuelled combined cycle power plant with a waste heat recovery and utilization system. The proposed combined cycle, which provides power outputs and thermal energy, consists of the gas/steam combined cycle, the subsystem utilizing the latent heat of spent steam from the steam turbine to vaporize LNG, the subsystem that recovers both the sensible heat and the latent heat of water vapour in the exhaust gas from the heat recovery steam generator (HRSG) by installing a condensing heat exchanger, and the HRSG waste heat utilization subsystem. The conventional combined cycle and the proposed combined cycle are modelled, considering mass, energy and exergy balances for every component and both energy and exergy analyses are conducted. Parametric analyses are performed for the proposed combined cycle to evaluate the effects of several factors, such as the gas turbine inlet temperature (TIT), the condenser pressure, the pinch point temperature difference of the condensing heat exchanger and the fuel gas heating temperature on the performance of the proposed combined cycle through simulation calculations. The results show that the net electrical efficiency and the exergy efficiency of the proposed combined cycle can be increased by 1.6 and 2.84% than those of the conventional combined cycle, respectively. The heat recovery per kg of flue gas is equal to 86.27 kJ s^?1. One MW of electric power for operating sea water pumps can be saved. The net electrical efficiency and the heat recovery ratio increase as the condenser pressure decreases. The higher heat recovery from the HRSG exit flue gas is achieved at higher gas TIT and at lower pinch point temperature of the condensing heat exchanger. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of uncertainties in physical properties on forced convection heat transfer with nanofluids

Nanofluids are considered to offer important advantages over conventional heat transfer fluids. However, at this early stage of their development, their thermophysical properties are not known precisely. As a result, the assessment of their true potential is difficult. This fact is illustrated by analyzing their thermohydraulic performance for both laminar and turbulent fully developed forced convection in a tube with uniform wall heat flux. Two different models from the literature are used to express these properties in terms of particle loading and they lead to very different qualitative and quantitative results in two types of problems: replacement of a simple fluid by a nanofluid in a given installation and design of an elementary heat transfer installation for a simple fluid or a nanofluid.     

Determination of the anisotropic radiative properties of a porous material by radiative distribution function identification (RDFI)

The anisotropic extinction and absorption coefficients of a high porosity material with a semi-transparent solid phase are directly obtained from identification of the statistical cumulated distribution function of extinction distances in the material, linked to that of the chords, and the corresponding function in the equivalent semi transparent medium. The bidirectional phase function is then determined without any hypothesis. The model only requires the knowledge of the material morphology, given by a X-ray tomography and the phases local radiative properties.     

Electromagnetic compatibility analysis in buildings affected by lightning strike

In this paper, we present the electromagnetic compatibility (EMC) analysis of a telecommunication building struck by a direct lightning stroke based on a simulation model. For this purpose, the resulting magnetic and electric fields have been determined as a function of time considering potential points where lightning is expected to strike. These potential points correspond to places where highly susceptible equipment is installed in the telecommunication building. For illustration purposes, electromagnetic interference inside a telecommunication building is calculated using the newly proposed three-dimensional cell model and finite difference discretization technique. Some illustrations are presented to point out the advantages of the proposed electromagnetic interference prediction model used during the design of the electrical and electronic installations by considering the lightning effects. Finally, examples of electric and magnetic fields inside the building as well as lightning-induced over voltages due to side return stroke were given at various distances in the simulation results.     

A critical review of using the Peukert equation for determining the remaining capacity of lead-acid and lithium-ion batteries

In many applications it is essential to predict the remaining capacity of a battery reliably, accurately and simply. Several existing techniques for predicting the remaining capacity of a lead-acid battery discharged with a variable current are based on variants of Peukert's empirical equation, which relates the available capacity to a constant discharge current. This paper presents a critical review of these techniques in the light of experimental tests that were carried out on two lead-acid commercial batteries. The relevance of these Peukert's equation based techniques to lithium-ion batteries is also discussed in the light of tests carried on a lithium-ion power battery. The basic conclusion of the paper is that Peukert's equation cannot be used to predict the state of charge of a battery accurately unless it is discharged at a constant current and constant temperature.     

2-Cyanofuran—A novel vinylene electrolyte additive for PC-based electrolytes in lithium-ion batteries

In this contribution, we focus on propylene carbonate (PC)-based electrolytes for lithium-ion batteries. In order to avoid solvent co-intercalation into graphite the presence of a solid electrolyte interphase (SEI) is required. This film is formed due to a film-forming species, i.e. a film-forming electrolyte additive. In this contribution, we focus on a vinylene compound, 2-cyanofuran (2CF) which proves to perform well in propylene carbonate electrolytes. 2CF is investigated by in situ Fourier transform infrared (FTIR) spectroscopy in a specially developed IR cell. We conclude that the cathodic reduction of the vinylene groups (=via reduction of the double bond) in the electrolyte additive is the initiating, and thus an important step of the SEI formation process. The possibility of an electropolymerization reaction of the vinylene monomers in the used electrolytes is critically discussed on the basis of the obtained IR data.