Localized Preheating Approaches for Reducing Residual Stress in Additive Manufacturing

Uniform preheating can be used to limit residual stress in the solid freeform fabrication of relatively small parts. However, in additive manufacturing processes, where a feature is deposited onto a much larger part, uniform preheating of the entire assembly is typically not practical. This paper considers localized preheating to reduce residual stresses, building on previous work using a defined thermal gradient through the part depth as a metric for predicting maximum final residual stress. The building of thinwalled structures is considered. Two types of localized preheating approaches are compared, appropriate for use in laser- or electron beam-based additive manufacturing processes. In evaluating the effectiveness of each approach, a simplified thermomechanical model is used that can be related directly to analytical thermomechanical models for thermal stresses in unconstrained thin plates. Results are presented showing that one of the methods yields temperature profiles likely to yield reduced residual stresses at room temperature. Mechanical model results confirm this, showing a significant reduction in maximum stress values. A more complete thermomechanical simulation of thin wall fabrication is used to verify the trends seen in the simplified model results.Mechanical Engineerin

Transient Changes in Melt Pool Size in Laser Additive Manufacturing Processes

Mechanical Engineerin

Process Scaling and Transient Melt Pool Size Control in Laser-Based Additive Manufacturing Processes

This modeling research considers two issues related to the control of melt pool size in laser-based additive manufacturing processes. First, the problem of process size scale is considered, with the goal of applying knowledge developed at one processing size scale (e.g. the LENSTM process, using a 500 watt laser) to similar processes operating at larger scales (e.g. a 3 kilowatt system under development at South Dakota School of Mines and Technology). The second problem considered is the transient behavior of melt pool size due to a step change in laser power or velocity. Its primary application is to dynamic feedback control of melt pool size by thermal imaging techniques, where model results specify power or velocity changes needed to rapidly achieve a desired melt pool size. Both of these issues are addressed via a process map approach developed by the authors and co-workers. This approach collapses results from a large number of simulations over the full range of practical process variables into plots process engineers can easily use.This research was supported by the National Science Foundation Division of Design, Manufacture and Industrial Innovation, through the Materials Processing and Manufacturing Program, award number DMI-0200270.Mechanical Engineerin

Melt Pool Size and Stress Control for Laser-Based Deposition Near a Free Edge

Thermomechanical models developed in this research address two experimental observations made during the deposition of thin-walled structures by the LENSTM process. The first observation (via thermal imaging) is of substantial increases in melt pool size as a vertical free edge is approached under conditions of constant laser power and velocity. The second observation (via neutron diffraction) is of large tensile stresses in the vertical direction at vertical free edges, after deposition is completed and the wall is allowed to cool to room temperature. At issue is how to best control melt pool size as a free edge is approached and whether such control will also reduce observed free edge stresses. Thermomechanical model results are presented which demonstrate that power reduction curves suggested by process maps for melt pool size under steady-state conditions can be effective in controlling melt pool size as a free edge is approached. However, to achieve optimal results it is important that power reductions be initiated before increases in melt pool size are observed. Stress simulations indicate that control of melt pool size can reduce free-edge stresses; however, the primary cause of these stresses is a constraint effect which is independent of melt pool size.This research was supported by the National Science Foundation Division of Design, Manufacture and Industrial Innovation, through the Materials Processing and Manufacturing Program, award number DMI-0200270.Mechanical Engineerin

Optimization of hydrothermal conditioning conditions for Pennisetum purpureum x Pennisetum americanum (Napier PakChong1 grass) to produce the press fluid for biogas production

This study focused on the optimization of hydrothermal conditioning conditions for Napier PakChong1 grass to produce press fluid for biogas production. The integrated generation of solid fuel and biogas from biomass (IFBB) process was adopted to separate press fluid from the biomass. Napier PakChong1 grass was hydrothermally pretreated and then mechanically pressed. The press fluid was used for biochemical methane potential (BMP) test while the press cake could be utilized as the solid fuel. The full factorial design of experiment with center points and the Central Composite Design (CCD) were developed to obtain the best possible combination of harvesting time, grass to water ratio, temperature and soaking time for the maximum organic substance (as COD) in press fluid. It was found that the obtained model could satisfactorily predict the mass of COD in press fluid used as the model response. The optimum hydrothermal conditioning conditions were as follows; harvesting time 75 d, ratio of grass to water of 1:6 (by weight), ambient temperature (about 25°C) of the water and the soaking time of 355 min. The mass of COD obtained in these conditions was 226.42 g equating to 71.5% of the value predicted by the model (316.68 g). The microbial kinetic coefficients and biogas yield potential of press fluid at these optimum conditions were properly fitted with the modified Gompertz equation (adjusted R2= 0.995). The methane yield potential (P), the maximum methane production rate (Rm) and lag phase time (λ) were 412.18 mlCH4/gVSadded, 51.47 mlCH4/gVSadded/d and 4.36 days, respectively

COD, TSS, nutrients and coliforms removals in UASB reactors in two stages treating swine wastewater

The performance of two upflow anaerobic sludge blanket (UASB) reactors was evaluated in pilot scale (908 and 188 L), installed in series (R1 and R2), fed with swine wastewater with TSS around 5 and 13 g L-1. The UASB reactors were submitted to HDT of 36 and 18 h with VOL of 5.5 to 34.4 g COD (L d)-1 in the R1 and HDT of 7.5 e 3.7 h with VOL from 5.1 to 45.2 g COD (L d)-1 in the R2. The average removal efficiencies of COD ranged from 55 to 85% in the R1 and from 43 to 57% in the R2, resulting in values from 82 to 93% in the UASB reactors in two stage. Methane concentrations in the biogas were 69 to 74% with specific production from 0.05 to 0.27 L CH4 (g removedCOD)-1 in the R1 and of 0.10 to 0.12 L CH4 (g removedCOD)-1 in the R2. The average removal efficiencies were 61 to 75% for totalP, 39 to 69% for KN, 82 to 93% for orgN and 20 to 94% for Fe, Zn, Cu and Mn. The amN concentration were not reduced indicating the need to post-treatment for effluent disposal into water bodies. There were reductions of total coliforms from 99.8123 to 99.9989% and of thermotolerant coliforms from 99.9725 to 99.9999%. The conditions imposed to the UASB reactors in two stage provided high conversions of removedCOD into methane (up to 77%) and reductions of organic an inorganic pollution loads from swine wastewater.Foi avaliado o desempenho de dois reatores anaeróbios de fluxo ascendente com manta de lodo (UASB) em escala-piloto (908 e 188 L), instalados em série (R1 e R2), para o tratamento de águas residuárias de suinocultura com concentrações médias de SST em torno de 5 e 13 g L-1. Os TDH foram de 36 e 18 h com COV de 5,5 a 34,4 g DQO (L d)-1 no R1 e TDH de 7,5 e 3,7 h com COV de 5,1 a 45,2 g DQO (L d)-1 no R2. As eficiências médias de remoção de DQO variaram de 55 a 85% no R1 e de 43 a 57% no R2, resultando valores de 82 a 93% nos reatores UASB em dois estágios. As concentrações de metano no biogás foram de 69 a 74%, com produções de 0,05 a 0,27 L CH4 (g DQOremovida)-1 no R1 e de 0,10 a 0,12 L CH4 (g DQOremovida)-1 no R2. Os valores médios de eficiência de remoção de Ptotal foram de 61 a 75%; de NK de 39 a 69%; de Norg. de 82 a 93%, e de Fe, Zn, Cu e Mn de 20 a 94%. As concentrações de N-am. não foram reduzidas, indicando a necessidade de pós-tratamento para disposição do efluente em corpos d'água. Houve redução de coliformes totais de 99,8123 a 99,9989%, e de coliformes termotolerantes de 99,9725 a 99,9999%. As condições impostas aos reatores UASB em dois estágios propiciaram reduções acentuadas da carga poluidora orgânica e inorgânica das águas residuárias de suinocultura, com conversão de até 77% da DQO removida em metano.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)TIGRE S. A.Centro Universitário de São José do Rio Preto (UNORP)Universidade Estadual Paulista Faculdade de Ciências Agrárias e Veterinárias Programa de Pós-Graduação em Microbiologia AgropecuáriaUNESP Faculdade de Ciências Agrárias e VeterináriasUniversidade Estadual Paulista Faculdade de Ciências Agrárias e Veterinárias Programa de Pós-Graduação em Microbiologia AgropecuáriaUNESP Faculdade de Ciências Agrárias e Veterinária

Effects of Ionic Liquid and Biomass Concentration to Partial Vapour Pressure Change in Hydrothermal Carbonization

Abstract This study aims to investigate the effects of ionic salt liquid and biomass concentration to partial vapour pressure change in hydrothermal carbonization system. The durability of reactor and safety aspect are crucial point for constant volume system which pressure is independence and important in scaling up hydrothermal process. The ionic salt including calcium propionate with the molality of 0.33, 0.43 and 0.65 and sodium chloride with the molality of 0.86, 1.14 and 1.71 were used. The suspension of corncob biomass and deionized water with the ratio 1:20 and 1:10 also were evaluated. The partial vapour pressure of the solution of sodium chloride with the molality of 1.71 decrease for 12.5 %. The partial vapour pressure of corncob biomass concentration with 1:20 decrease for 2.8%. The hydrochar produced from the 240 °C of reaction temperature and 100 minutes reaction time demonstrated the gradually decrease of hemicellulose constituent corresponding with higher biomass concentration.</jats:p

Physical and chemical characteristics of carbonized corncob through hydrothermal and pyrolysis conversion

Abstract Thailand and south-east Asia have been struggled with agriculture biomass residues management for decades where open burning causes severe air pollution affecting millions of people every year. Thermal carbonization is one of the most cost-effective and environmentally friendly techniques which converted the low value residues such as straw, corn stovers and corncob into a more valuable material such as solid biofuel, chemical adsorbent feed stocks. This study aims to explore crucial characteristics of carbonized corncob including fibre composition, BET surface area and FT-IR spectrums. The characteristics can be used to identify the potential of the material for further surface enhancement or surface activation to produce the bio-based activated carbon. The carbonization process in this work includes mild temperature hydrothermal technique and high-temperature pyrolysis process. The hydrothermal carbonization temperature is set at 250°C in a pressurized reactor where a pyrolysis is operated at 480°C and 380°C at atmospheric pressure. The BET surface area of “hydrochared” corncob derived from hydrothermal is 11.53 compared with 16.13 m2 g−1 of the raw materials. The pyrolized biochar at 480°C and 380°C yields surface area of 7.66 and 6.12 m2 g−1. The oxygenated functional groups on char surface and BET surface area are also compared to provide baseline for carbon activation.</jats:p

ความสามารถในการดูดซับก๊าซไฮโดรเจนซัลไฟด์ของถ่านชีวภาพที่ผลิตจากชีวมวลเหลือใช้Hydrogen Sulfide Adsorption Capability of Biochar Produced from Residual Biomass

การวิจัยนี้มีวัตถุประสงค์เพื่อทดสอบความสามารถในการดูดซับก๊าซไฮโดรเจนซัลไฟด์ด้วยถ่านชีวภาพ ประกอบด้วย ถ่านซังข้าวโพดจากกระบวนการคาร์บอไนเซชัน (C), ถ่านซังข้าวโพดจากกระบวนการคาร์บอไนเซชันภายใต้บรรยากาศก๊าซ CO2 (CA), ถ่านกะลามะพร้าวจากกระบวนการคาร์บอไนเซชัน (CO), ถ่านกะลามะพร้าวจากกระบวนการคาร์บอไนเซชันภายใต้บรรยากาศก๊าซ CO2 (COA), ถ่านกิ่งไม้จากกระบวนการคาร์บอไนเซชัน (B) และถ่านกิ่งไม้จากกระบวนการคาร์บอไนเซชันภายใต้บรรยากาศก๊าซ CO2 (BA) ชีวมวลผ่านกระบวนการคาร์บอไนเซชันที่อุณหภูมิ 500 ± 10 องศาเซลเซียส ถูกนำไปทดสอบความสามารถในการดูดซับโดยป้อนก๊าซชีวภาพที่ผลิตจากน้ำเสียเอทานอลสู่เครื่องปฏิกรณ์อย่างต่อเนื่องที่อัตราภาระบรรทุกก๊าซไฮโดรเจนซัลไฟด์ 4,300 ± 20 กรัมไฮโดรเจนซัลไฟด์ต่อลูกบาศก์เมตร-ชั่วโมง พบว่า ความสามารถในการดูดซับก๊าซไฮโดรเจนซัลไฟด์ของถ่าน C, CO และ B เท่ากับ 2.33 ± 0.09, 3.66 ± 0.63 และ 5.56 ± 0.77 ตามลำดับและความสามารถในการดูดซับก๊าซไฮโดรเจนซัลไฟด์ของถ่าน CA, COA และ BA เท่ากับ 1.58 ± 0.90, 1.84 ± 0.75, 1.26 ± 0.20 กรัมไฮโดรเจนซัลไฟด์ต่อกรัมวัสดุดูดซับ ตามลำดับ ดังนั้นจะเห็นได้ว่าถ่าน B มีค่าความสามารถในการดูดซับสูงกว่าถ่าน C และถ่าน CO และพบว่า กระบวนการคาร์บอไนเซชันภายใต้บรรยากาศก๊าซ CO2 ไม่มีผลต่อการเพิ่มค่าความสามารถในการดูดซับอีกทั้งยังก่อให้เกิดผลเสียต่อกระบวนการนี้This study aimed to investigate the adsorption capacity of hydrogen sulfide (H2S) by biochar prepared from agricultural waste. The biochar samples include carbonized corn cob (C), carbonized corn cob under CO2 rich atmospheres (CA), carbonized coconut shell (CO), carbonized coconut shell under CO2 rich atmospheres (COA), carbonized woodchips (B) and carbonized woodchips under CO2 rich atmospheres (BA). All samples were carbonized at the controlled temperature (500 ± 10 °C). H2S adsorption capability were evaluated in a continuous manner using actual biogas produced from ethanol waste with controlled H2S loading rates of 4,300 ± 20 g/m3-h. The experimental measurement of the H2S adsorption capacity of C, CO, and B were 2.33 ± 0.09, 3.66 ± 0.63, and 5.56 ± 0.77 g H2S/g Adsorbent material, respectively. The adsorption capacity of CA, COA, and BA were 1.58 ± 0.90, 1.84 ± 0.75, and 1.26 ± 0.20 g H2S/g Adsorbent material. It is thus clear that carbonized woodchip (B) has significantly higher adsorption capacity than carbonized corn cob (C) and coconut shell (CO). Concisely, carbonization under CO2 rich atmosphere cannot enhance adsorption capacity; instead it induces negative effects in most cases