Biomass has received wide attention as a substitute for fossil fuel in the generation of energy because of its renewability and carbon neutrality. However, raw biomass combustion is hindered by physical properties such as low energy density and high moisture content. Biomass torrefaction is a mild pyrolysis thermal treatment process carried out at temperature of 200 to 300°C under inert conditions to improve the fuel properties of parent biomass. This yields a higher energy per unit mass product but releases non-condensable and condensable gases which results in energy and mass losses. The condensable gases (volatiles), can result in tar formation on condensing hence, system blockage. Fortunately, the hydrocarbon composition of volatiles also represents a possible auxiliary energy source for torrefaction. The present study investigated energy recovery from volatiles through clean co-combustion with NG for feedstock drying and/or the thermal treatment process of pine wood chips. The research also studied the effect of torrefaction pretreatment temperatures on the amount of energy recovered for various combustion air flow rates. For all test conditions, blue visual flames and low CO and NOx emissions at the combustor exit consistently signified clean and complete premixed combustion. Torrefaction temperature at 283–292 °C had relatively low energy recovered from volatiles, mainly attributed to higher moisture content evolution and low molecular weight of volatiles evolved. At lowest torrefaction pretreatment temperature, smaller amount of volatiles was generated with most energy recovered from the volatiles. Energy conservation evaluation on the torrefaction reactor indicated that about 40% of total energy carried by the exiting volatiles and gases has been recovered by the co-fire of NG and volatiles at the lowest temperature while 20% and 22% of the total energy were recovered at the intermediate and highest torrefaction temperature respectively.

A multi-scale (in temporal domain) model was developed to study the ablation of dielectrics using a femtosecond (fs)-nanosecond (ns) dual-beam laser system. The model is an integration of the plasma model and improved two-temperature model for the fs laser ablation, and Fourier’s law for the ns laser ablation. The model is used to investigate the ablation for dielectrics when a fs pulse is shot at the peak of a ns pulse. It is found that the fs laser pulse can result in the increase of absorption of the ns laser energy, leading to a much higher material removal rate as compared to fs laser ablation alone or ns laser ablation alone. The enhancement of ns laser energy absorption is caused by the increased electron density and the formation of a tiny crater in the material created by the fs laser pulse. The corresponding experiment using a Ti:Sapphire fs laser (Legend-F, Coherent) and a Nd:YAG ns UV laser (Avia-X, Coherent) was also conducted and the results are consistent with the modeling predictions.

Combustion process is the major contributor to the air pollution, such as CO, unburned hydrocarbon, soot and NO x , etc. Porous media can be a good candidate for improving the combustion efficiency and reducing pollution formation. Premixed combustion has been extensively investigated in the literature, experimentally and computationally. However, investigation of non-premixed combustion in porous media is limited in the open literature, which is the topic of this paper. The present work deals with the numerical modeling of methane/air non-premixed combustion in porous media. Physical problem that is considered here is fuel jet which is injected to the air in free flame case and injected into a porous medium, in the porous medium combustion case. The flow is assumed turbulent and standard k-ε model with standard wall functions is used in the simulation. The solid porous structure is assumed to be composed of alumina fiber material with temperature dependent heat conductivity. Discrete Ordinate method is used to solve radiative transport equations. The governing equations are solved using finite volume method. The results show that the combustion in porous media has superior combustion efficiency and significantly lower NO x and CO emissions compare to the free flame. This is due to the lower maximum temperature in porous media combustion. In comparison with the free flame case where the combustion zone is narrow and long, the results shows the combustion zone in porous media is shorter in axial and wider in radial direction.

Severe plastic deformation (SPD) techniques have now successfully been applied to fabricate a large number of nanostructured metals and alloys. Most studies have so far focused on fcc materials, although some studies on Ti and Mg also exist. In this work we describe the nanostructures resulting from processing pure Zr by high pressure torsion (HPT) and accumulative roll bonding (ARB).

Recently, a new laser micromachining technique using multiple ultrashort pulses with a picosecond-to-nanosecond separation as a train group has demonstrated some promising application potential, which also has high scientific merits in micro-/nano-scale ultrafast energy transport. However, the underlying physics of this technique remain poorly understood. In this study, the improved two-temperature model recently developed by the authors is used to analyze the pulse train technology, in which the full-run quantum treatments are used to calculate the significantly varying properties, including the electron heat capacity, electron relaxation time, electron conductivity, reflectivity, and absorption coefficient. This paper reports the effects of the pulse number per train, pulse separation, and repetition rate. Results from the present study have demonstrated that 1) it can increase the photon efficiency and further reduces the heat-affected zone; 2) the number of bursts required for melting decreases with the repetition rate, but at tens of MHz or higher, the repetition rate has a negligible impact; 3) the lattice temperature right after the thermolization time first increases to a peak and then decreases as the pulse separation increases.

Two-phase microchannel heat exchangers are receiving increasing attention from the microprocessor industry as power density levels in microchips increase. Previous numerical investigations of convective boiling in microchannels assumed steady flow within the channels. However, experimental data shows that two-phase flows in microchannels are highly transient even under steady heat loads. Little work has been done to model the dynamics associated with vapor generation in microchannels. The present work simulates the periodic distribution of vapor within microchannels filled with water by solving one-dimensional homogeneous equations for the mass, momentum and energy transport in conjunction with a transient wall conduction equation. A wall superheat constraint is incorporated to account for the excess superheat temperature required for bubble nucleation. Boiling events reduce the local wall temperature and change the pressure and enthalpy distributions within the flow. The transient pressure fluctuations predicted here are consistent with those observed in experiments. This study provides insight into the significance of bubble nucleation for forced convective boiling in microchannels and will be useful for the optimization of microchannel heat exchangers.

Corrosion is the key factor responsible for the degradation of ship structures and in no place is this truer than water ballast tanks. Coating protection system is a continual research interest for classification societies and coating industries. Up to now, most coating performance analyses are qualitative not quantitative. Coating life prediction is almost always based on experience and various assumptions, due to unavailability of practical data support systems. This paper describes a preliminary impartial investigation of coating life carried out with interviewees from the Australian Defence Science and Technology Organization (DSTO), shipyards, coating supplier and an independent expert. Plate surface, edges and welds in ballast tank were considered and the influences of dry film thickness (DFT) and surface preparation (SP) are addressed. The investigation gives some insight into the life of practical coating systems for water ballast tanks. Coating life is proposed to be representable by a normal distribution when corrosion breakdown is below 10% of plate thickness, which is of practical implication.

In this paper, wave dynamics processes occurring in pulse detonation devices are analyzed both numerically and experimentally, including the propagation of detonation fronts, the motion of rarefaction waves in gas exhausting phase and the diffraction of shock waves at thrust nozzles. Numerical results are also compared with experiments to confirm the observed wave phenomena. In order to estimate operation roles of pulse detonation engines more accurately, the initiation of the air/hydrogen mixture is also examined experimentally at certain conditions. Numerical analysis indicates that pulse detonation devices can be operated in a quite high frequency, the gas-filling phase occupies a longer time in one detonation cycle, and decreasing the length of detonation chambers for the higher operation frequency is possible, but has its limitation.

This study develops a quantum mechanical model to investigate energy absorption in ultrafast laser of dielectrics. The model investigates the optical property variations, electron temperature, and density changes at femtosecond scales. The ionizations and electron heating are two major factors considered for pulse absorption occurring within the pulse duration. The flux-doubling model is employed to calculate the free electron generation mainly through impact ionization and photoionization. The quantum mechanical treatments are used to account for the specific heat and the relaxation time for free electrons. The time and space dependent optical properties of the dense plasma generated by the ultrafast laser pulse are calculated. The predictions of ablation threshold and ablation depth of fused silica and barium aluminum borosilicate (BBS) are in good agreements with published experimental data. The model greatly improves the accuracy in predicting the ablation depth and can predict the crater shape.

Recently, a new laser micromachining technique using multiple femtosecond pulses with a picosecond-to-nanosecond separation as a train group has demonstrated the ability to increase the ablation quality of dielectrics and semiconductors. However, the mechanisms involved in the technique are not fully understood. This study employs the plasma model recently developed by the authors to analyze the femtosecond pulse-train ablation of dielectrics. It is found that the transient significantly varying optical properties are the important reasons that lead to the advantages of the pulse-train technique. It has demonstrated that there exits a constant ablation-depth zone with respect to fluence, which has also been observed experimentally. By using the pulse-train technology, it is possible to obtain repeatable nanostructures, even when the laser system is subject to some fluctuations in fluences.