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Selective laser melting (SLM) is increasingly used for the manufacture of end‐use metal tools and parts, requiring the careful identification of a range of appropriate process parameters and conditions to achieve desirable properties and quality. Process conditions such as the relation between layout of parts and internal gas flow within the SLM platform can influence the consolidation of metal powers and therefore the quality and properties of the final parts. The purpose of this paper is to investigate the effect of part layout on quality and mechanical properties of cylindrical 316L stainless steel parts manufactured by SLM.

The cylindrical 316L stainless steel parts were manufactured in two directions, one perpendicular to the gas flow direction and one parallel to it. The investigation first focuses on visual inspection and porosity measurements to compare the quality factors such as delamination and porosity of the parts. A mechanical test procedure including tensile, compressive, and shear‐punch is used to assess the mechanical properties of the SLM specimens. Cross sectional analyses are carried out to better understand of material response under mechanical tests.

The results show that the part layout and gas flow condition have a negligible influence on porosity formation, however they notably affect the thermal stress and bonding strength between particles which consequently influences the mechanical properties of final parts. The manufacturing of parts perpendicular to gas flow seems to be more advantageous rather than parallel to gas flow.

This is the first work investigating the effects of the SLM layout on the quality and mechanical properties of stainless steel specimens. The results can be used in quality control purposes and for quality improvement of SLM parts.

Solid thin films have been deposited on stainless steel 314 (SS 314) substrates in a chemical vapor deposition (CVD) reactor at different flow rates of natural gas mostly methane (CH₄). The purpose of this paper was to investigate experimentally the variation of thin film deposition rate with the variation of gas flow rate.

During experiment, the effect of gap between activation heater and substrate on the deposition rate has also been observed. To do so, a hot filament thermal CVD unit is used. The flow rate of natural gas varies from 0.5 to 2 l/min at normal temperature and pressure and the gap between activation heater and substrate varies from 4 to 6.5 mm.

Results show that deposition rate on SS 314 increases with the increase of gas flow rate. It is also seen that deposition rate increases with the decrease of gap between activation heater and substrate within the observed range. These results are analyzed by dimensional analysis to correlate the deposition rate with gas flow rate, surface roughness and film thickness. In addition, friction coefficient and wear rate of SS 314 sliding against SS 304 under different normal loads are also investigated before and after deposition. The obtained results reveal that the values of friction coefficient and wear rate are lower after deposition than that of before deposition.

In this study, thin film deposition rate on SS 314 was investigated using CVD. The obtained results were analyzed by dimensional analysis to correlate the deposition rate with gas flow rate, surface roughness and film thickness. The friction coefficient and wear rate of SS 314 were also examined before and after deposition.

Powder bed fusion processes are common due to their ability to build complex components without the need for complex tooling. While additive manufacturing has gained increased interest in industry, academia and government, flaws are often still generated during the deposition process. Many flaws can be avoided through careful processing parameter selections including laser power, hatch spacing, spot size and shielding gas flow rate. The purpose of this paper is to study the effect of shielding gas flow on vapor plume behavior and on final deposition quality. The goal is to understand more fully how each parameter affects the plume and deposition process.

A filtered-photodiode based sensor was mounted onto a commercial EOS M280 machine to observed plume emissions. Three sets of single tracks were printed, each with one of three gas flow rates (nominal, 75% nominal and 50% nominal). Each set contained single-track beads deposited atop printed pedestals to ensure a steady-state, representative build environment. Each track had a set power and speed combination which covered the typical range of processing parameters. After deposition, coupons were cross-sectioned and bead width and depth were measured. Finally, bead geometry was compared to optical emissions originating in the plume.

The results show that decreasing gas flow rate, increasing laser power or increasing scan speed led to increased optical emissions. Furthermore, decreasing the gas cross-flow speed led to wider and shallower melt pools.

To the best of the authors’ knowledge, this paper is among the first to present a relationship among laser parameters (laser power, scan speed), gas flow speed, plume emissions and bead geometry using high-speed in situ data in a commercial machine. This study proposes that scattering and attenuation from the plume are responsible for deviations in physical geometry.

The aim of this paper is to find the optimal values of the reaction rates coefficients for the combustion of a methane/air mixture for a given reduced reaction mechanism which has a high appropriateness with full reaction mechanism.

A multi‐objective genetic algorithm (GA) was used to determine new reaction rate parameters (A's, β's, and E_a's in the non‐Arrhenius expressions). The employed multi‐objective structure of the GA allows for the incorporation of perfectly stirred reactor (PSR), laminar premixed flames, opposed flow diffusion flames, and homogeneous charge compression ignition (HCCI) engine data in the inversion process, thus enabling a greater confidence in the predictive capabilities of the reaction mechanisms obtained.

The results of this study demonstrate that the GA inversion process promises the ability to assess combustion behaviour for methane, where the reaction rate coefficients are not known. Moreover it is shown that GA can consider a confident method to be applied, straightforwardly, to the combustion chambers, in which complex reactions are occurred.

In this paper, GA is used in more complicated combustion models with fewer assumptions. Another consequence of this study is less CPU time in converging to final solutions.

The purpose of this paper is to demonstrate the utilization of the direct simulation Monte Carlo (DSMC) method for moving‐boundary/deforming‐domain micro‐scale gas flow problems. Furthermore, a hydrodynamic model, proposed in the literature, is used to compare its results with those obtained using the DSMC method.

A micro‐scale adiabatic piston problem is analyzed using a parallel DSMC implementation for deforming domains. Initially, pressures at both sides of the piston wall are different. Consequently, frictionless piston moves toward low‐pressure compartment, keeps oscillating from one side to the other. Eventually, the piston reaches the “Mechanical equilibrium” state. Although the temperatures are different, pressures are equal at this state. The unsteady problem is analyzed until it reaches this state. Three test cases, all with the same initial conditions but different piston masses are analyzed. The time variation of the piston position, conditions in the compartments separated by the piston, are presented and compared with the results obtained from a hydrodynamic model proposed in the literature.

The results show that the DSMC and hydrodynamic results agree for the case where the piston mass is much larger than the mass of the gas inside the cylinder. But for other two cases, where the piston mass is smaller, piston motion, and conditions in the compartments separated by the piston differ for the two methods. This is attributed to the linear velocity distribution assumption of the hydrodynamic model. The DSMC results demonstrate that this assumption is not valid for cases where the piston mass is equal or less than the mass of the gas inside the cylinder.

Implementation of the DSMC method for problems with deforming domain is presented and a limitation for applicability of hydrodynamic model for these problems is shown.

The purpose of this study is to investigate the influencing factors on the charring behaviour of timber, the char layer and the charring depth in non-standard fires.

This paper summarizes outcomes of tests, investigating the influences on the charring behavior of timber by varying the oxygen content and the gas velocity in the compartment. Results show that charring is depending on the fire compartment temperature, but results show further that at higher oxygen flow, char contraction was observed affecting the protective function of the char layer.

In particular, in the cooling phase, char contraction should be considered which may have a significant impact on performance-based design using non-standard temperature fire curves where the complete fire history including the cooling phase has to be taken into account.

Up to now, some research on non-standard fire exposed timber member has been performed, mainly based on standard fire resistance tests where boundary conditions as gas flow and oxygen content especially in the decay phase are not measured or documented. The approach presented in this paper is the first documented fire tests with timber documenting the data required.

The purpose of this paper is to present an improved model and its applied adaptive controller for a waste heat recovery generation system using a power turbine generator (PTG) with an accurate model on shipboard that is employed by an identification method on the basis of an overall system model.

The PTG system has been developed as a waste heat recovery type generation system making use of exhaust gas from the main shipboard diesel engines. Conventionally, control of a plant is exercised using the proportional‐integral‐derivative (PID)‐based controller. The PID controller, however, is difficult to keep in place because of fouling conditions and variations across time. Thus, the load bank controller is proposed using a PID‐based controller. The controller should take into account both the fouling conditions and variations across time because the exhaust gas contains considerable amounts of ash and soot. Hence, an accurate model needs to improve the dynamic characteristics of the PTG system. The identification method clarifies the PTG system. The unknown parameters of the PTG speed model can be estimated using the prediction error method after the mathematical model is transferred to the state‐space model.

Simulation results are verified with measured data of a prototype. In the transient response of the PTG speed, all the errors are within 0.23 percent. The proposed model using the identification method shows the error between the accurate model and the standard to be less than 10 percent. The proposed controller is evaluated by comparing it with the conventional controller. As a result of using the proposed controller, limit speed overshooting is improved by more than 25 percent. Hence, the proposed model is confirmed to have excellent property.

The PTG is an extremely effective system for fuel cost reduction in the face of rising fuel prices, and systems capable of providing several thousand kilowatts are being considered.

This study aims to investigate the influence of the gas-flow field distribution and design on the parts quality of 316L stainless steel and the vapor–spatter behavior.

Based on the hot-wire wind speed test method, the exact value of the gas velocity at different locations was accurately measured to establish the effect on the porosity and the mechanical properties of the parts. The influence of the placement of single or dual blow screens on the performance of the parts quality was also studied. Through scanning electron microscope and energy dispersive spectrometer, high-speed photography and other methods, the influence mechanism was explained.

It was found that too high or too low gas velocity both play a negative role, for 316L stainless steel, the range of 1.3–2.0 m/s is a suitable gas field velocity during the multilaser powder bed fusion process. And printing quality using dual blow screens is better than single.

The optimization of gas field design and optimal gas velocity (1.3–2.0 m/s) applied during laser melting can improve the quality of ML-PBF of 316L stainless steel.

This study showed the influence of the gas field on the spatter–vapor in the process during ML-PBF, and the unfavorable gas field led to the formation of pores and unmelted powders.

To facilitate future development of the cooled gas‐turbine, more test information is needed on the effectiveness of cooling in an actual turbine operating at high gas‐temperatures. Part I of this paper deals with some design aspects of a single‐stage experimental turbine built to enable an experimental investigation to be carried out on the air cooling of nozzles and blades. The turbine, built for operation at high gas‐temperatures, was fitted with internally air‐cooled blades having a large number of small cooling passages running the whole length of the blades. A description is given of the pressed powder technique used to introduce the small passages in blocks of heat‐resisting material from which the blades could be machined. Mention is made of some of the difficulties encountered in this method of manufacture and also of the need for careful consideration of suitable methods of disposal of the cooling air when internally cooled nozzles and blades of this form are used.

This paper aims to extend the hybrid atomistic-continuum multiscale method developed by Vu et al. (2016) to study the gas flow problems in long microchannels involving density variations.

The simulation domain is decomposed into three regions: the bulk where the continuous Navier–Stokes and energy equations are solved, the neighbourhood of the wall simulated by molecular dynamics and the overlap region which connects the macroscopic variables (density, velocity and temperature) between the two former regions. For the simulation of long micro/nanochannels, a strategy with multiple molecular blocks all along the fluid/solid interface is adopted to capture accurately the macroscopic velocity and temperature variations.

The validity of the hybrid method is shown by comparisons with a simplified analytical model in the molecular region. Applications to compressible and condensation problems are also presented, and the results are discussed.

The hybrid method proposed in this paper allows cost-effective computer simulations of large-scale problems with an accurate modelling of the transfers at small scales (velocity slip, temperature jump, thin condensation films, etc.).