Cell walls and lignin component disruption treatments are needed to enhance the hydrolytic phase and the overall biodegradability of lignocellulosics during an anaerobic digestion process. Given ...their abundant availability in nature, low impact on food market prices and low lignin content, aquatic plants result in being particularly suitable for biofuel conversion.
A preliminary study on the effects of a Hollander beater mechanical pretreatment has been conducted in batch mode focusing on biogas yields from five different species of Irish seaweeds in co-digestion with sludge. A second experiment on Laminaria Digitata species has been carried out using a Response Surface Methodology (RSM) with treatment times (0–10 min), mesophilic range of temperatures (35–39 °C) and sludge amounts (100–300 ml). Results from biogas yields of treated macroalgae have been found to be up to 20% higher when compared to untreated ones. A mathematical model of the biogas volume behaviour has been developed and the ideal conditions identified.
► Relates different seaweed species to biogas yield and evaluates extra biogas yield from mechanical pretreatment. ► Compares co-digestion of treated/untreated macroalgae to sludge-only digestion. ► Mechanically pretreated feedstock produced up to 13% extra biogas. ► No significant effect by temperature variations in the mesophilic range 35–39 °C. ► Contains optimisation conditions for fermentation of Laminaria sp. to biogas.
•The beating pretreatment speeds up the start of digestion.•After 3days of digestion, beating pretreatment enhances the methane yield by 37%.•Microwave and ball milling pretreatment impacts ...negatively on methane production.•At 25days of digestion the overall methane is not enhanced by beating pretreatment.
The objective of this study was to evaluate the effect of beating (BT), ball milling (BM) and microwave pretreatment (MW) on the conversion of the macroalgae Laminaria spp. into biogas by anaerobic digestion (AD). The AD was carried out in batch at 38±1°C, over an incubation time of 25days. After 3days of digestion the BT pretreated samples yielded the best result by achieving a methane increase of up to 37% with respect to the raw seaweed. At 25days, both BM and MW pretreatment lowered the methane yield with respect to the raw seaweed. Since BT produced higher methane yields with respect to the untreated sample, it was considered for energy balance analysis. After 3days of digestion, the BT resulted in an energy gain of 28%, while at the end of digestion the break-even point was reached.
Grass is being considered as a potential feedstock for biogas production, due to its low water consumption compared to other crops, and the fact that it can be cultivated in non-arable lands, ...avoiding the direct competition with food crops. However, biogas production is limited by the characteristics of the feedstock; in particular its complex lignocellulosic structure. Hence, different pretreatment methods are being investigated for grass structure disruption before undergoing the anaerobic digestion process. The aim of this paper is to review current knowledge on pretreatment techniques used for grassland biomass. Pretreatment techniques were categorized into mechanical, microwave, thermal, chemical and biological groups. The effect of the application of each studied methods on the biogas yield and on the energy balance is discussed. A further comparison between the covered techniques was revealed.
The European Commission opened a discussion about limiting first generation food based biofuels in favour of advanced biofuels. The main reason was to limit the uncertainty in estimates of indirect ...land use change emissions (ILUC) of food based biofuels. Brown seaweeds represent a valuable solution. The lack of lignin makes them suitable for degradation processes such as anaerobic digestion (AD). The main output of AD is biogas which can be upgraded to biomethane and used as a transport fuel. The most common Irish brown seaweeds namely Laminaria sp. and Ascophyllum nodosum were subject to AD. The effects of beating pretreatment time (5–10–15 min) and changes in the seaweeds volatile solids (VS) concentration (1–2.5–4%) on methane production were investigated through a response surface methodology (RSM). Laminaria sp. showed the highest methane yield of 240 ml CH4 g−1 VS when the pretreatment time was set at 15 min and at VS concentration of 2.5%. In the case of Ascophyllum nodosum, the best yield of 169 mL CH4 g−1 VS was found at the longest pretreatment time tested and at the minimum concentration of VS. The RSM analysis revealed that the VS concentration had the strongest impact on the methane yield.
•Laminaria sp. exhibited 40% more methane than Ascophyllum nodosum.•The VS concentration had a major impact on the methane yields of both species.•The pretreatment time had a marginal impact on the methane yields of both species.•Ascophyllum nodosum showed 30% more methane than the untreated sample.•Laminaria sp. showed the highest methane yield at 2.5% VS and 15 min of treatment.
The surface of nodular graphite cast iron samples was melted by 50% overlapping passes from a 3
kW CW CO
2 laser. The objective was to modify the microstructure and improve the hardness and erosion ...resistance of the surface. The results showed that laser melting led to complete dissolution of the graphite nodules which on solidifying created an inter-dendritic network of ledeburite eutectic with a very fine structure, good homogeneity, and high hardness. Sand particle erosion experiments were carried out at impingement angles of 30°, 60°, and 90° using angular particles of size between 300 and 600
μm. The velocity of the sand particles was 50
m/s, which was controlled by the gas pressure and measured by the double-disc method. The erosion resistance of the laser treated nodular cast iron was 110 times greater than the untreated material. The erosion mechanism of the untreated nodular cast iron under normal and oblique angles was by severe plastic deformation and ploughing; whilst the mechanism for the treated specimens was by fatigue cracking. The improvements of erosion resistance after laser treatment were considered due to the very fine structure, high micro hardness (650 Hv0.1) with the resistance to plastic flow and to the dissolution of the graphite nodules.
Laser butt-welding of medium carbon steel was investigated using CW 1.5
kW CO
2 laser. The effect of laser power (1.2–1.43
kW), welding speed (30–70
cm/min) and focal point position (−2.5 to 0
mm) on ...the heat input and the weld-bead geometry (i.e. penetration (
P), welded zone width (
W) and heat affected zone width (
W
HAZ)) was investigated using response surface methodology (RSM). The experimental plan was based on Box–Behnken design. Linear and quadratic polynomial equations for predicting the heat input and the weld-bead geometry were developed. The results indicate that the proposed models predict the responses adequately within the limits of welding parameters being used. It is suggested that regression equations can be used to find optimum welding conditions for the desired criteria.
► Defining the different methods of measuring residual stresses in manufactured components. ► Comprehensive study on the hole drilling, neutron diffraction and other techniques. ► Evaluating ...advantage and disadvantage of each method. ► Advising the reader with the appropriate method to use.
Residual stresses occur in many manufactured structures and components. Large number of investigations have been carried out to study this phenomenon and its effect on the mechanical characteristics of these components.
Over the years, different methods have been developed to measure residual stress for different types of components in order to obtain reliable assessment. The various specific methods have evolved over several decades and their practical applications have greatly benefited from the development of complementary technologies, notably in material cutting, full-field deformation measurement techniques, numerical methods and computing power. These complementary technologies have stimulated advances not only in measurement accuracy and reliability, but also in range of application; much greater detail in residual stresses measurement is now available. This paper aims to classify the different residual stresses measurement methods and to provide an overview of some of the recent advances in this area to help researchers on selecting their techniques among destructive, semi destructive and non-destructive techniques depends on their application and the availabilities of those techniques. For each method scope, physical limitation, advantages and disadvantages are summarized. In the end this paper indicates some promising directions for future developments.
Recently, laser welding of austenitic stainless steel has received great attention in industry. This is due to its widespread application in petroleum refinement stations, power plants, the ...pharmaceutical industry and also in households. Therefore, mechanical properties should be controlled to obtain good welded joints. The welding process should be optimized by the proper mathematical models. In this research, the tensile strength and impact strength along with the joint-operating cost of laser-welded butt joints made of AISI304 was investigated. Design-expert software was used to establish the design matrix and to analyze the experimental data. The relationships between the laser-welding parameters (laser power, welding speed and focal point position) and the three responses (tensile strength, impact strength and joint-operating cost) were established. Also, the optimization capabilities in design-expert software were used to optimize the welding process. The developed mathematical models were tested for adequacy using analysis of variance and other adequacy measures. In this investigation, the optimal welding conditions were identified in order to increase the productivity and minimize the total operating cost. Overlay graphs were plotted by superimposing the contours for the various response surfaces. The process parameters effect was determined and the optimal welding combinations were tabulated.
Laser cutting of medium density fibreboard (MDF) is a complicated process and the selection of the process parameters combinations is essential to get the highest quality cut section. This paper ...presents a means for selecting the process parameters for laser cutting of MDF based on the design of experiments (DOE) approach. A CO2 laser was used to cut three thicknesses, 4, 6 and 9mm, of MDF panels. The process factors investigated are: laser power, cutting speed, air pressure and focal point position. In this work, cutting quality was evaluated by measuring the upper kerf width, the lower kerf width, the ratio between the upper kerf width to the lower kerf width, the cut section roughness and the operating cost. The effect of each factor on the quality measures was determined. The optimal cutting combinations were presented in favours of high quality process output and in favours of low cutting cost.
► In this paper, we presented an overall review of developments and investigations in the tube hydroforming study. ► Factors affecting the output of the process were addressed by many studies which ...were categorized and reviewed. ► Different optimization algorithms were outlined.
Tube hydroforming is one of the most popular unconventional metal forming processes which is widely used to form various tubular components. By this process, tubes are formed into different shapes using internal pressure and axial compressive loads simultaneously to force a tubular blank to conform to the shape of a given die cavity.
In this paper, an overall review of developments in the tube hydroforming study is presented so that other researchers at different parts of the world can use it for further investigations in this area. Initially, analytical studies which predict the sufficient parameters in tube hydroforming process were summarized. Afterwards, a guideline for employing finite element modeling (FEM) in the process analysis was proposed. Factors affecting the output of the process were addressed by many studies which were categorized and reviewed in the present work. Moreover, common types of failure of the process were introduced and improvements to avoid them were mentioned. Furthermore, different optimization algorithms to choose the input parameters that would produce the desired hydroformed component were outlined.
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