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

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

Transient Changes in Melt Pool Size in Laser Additive Manufacturing Processes

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

Potential of Fermentable Sugar Production from Napier cv. Pakchong 1 Grass Residue as a Substrate to Produce Bioethanol

AbstractBioethanol is one of the most significant renewable fuels. The major sources of bioethanol production are food crops such as corn, sugarcane, rice, wheat and sugar beet. However, utilization of food crops to produce bioethanol could affect the food sources and disrupt the food to population ratio. To overcome these issues, the utilization of lignocellulosic materials such as wheat straw, grass and crop residues to produce bioethanol has been developed for second-generation fuel, since those resources are abundant, cheap and renewable. Napier Pakchong 1 grass (NPG) residue is a lignocellulosic waste obtained from the process of biogas production that can be used as an alternative material for bioethanol production. This research aims to study on the potential of fermentable sugar production from NPG residue. The materials were pretreated with different concentrations of sodium hydroxide (NaOH), followed by enzymatic hydrolysis for saccharification. The results suggested that pretreatment with 3.0% (w/v) NaOH solution at 121̊C for 60 minutes provided the highest lignin removal of 86.1% (w/w) and enriched cellulose fraction from 36.4 to 75.6% (w/w). The enzymatic hydrolysis was conducted by varying enzyme loading volume and total solid contents (TS) at pH 4.8, 50̊C for 72h. The hydrolysis with enzyme loading volume of 2.0 ml/g of substrate and 10% (w/v) of TS were optimal for saccharification giving the reducing sugar yield of 768 mg/g of pretreated biomass or equal to 64 g/L and glucose yield of 522 mg/g of pretreated biomass or equal to 43 g/L. The reducing sugar will be used as a starting material for yeast to produce bioethanol

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

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

การเพิ่มประสิทธิภาพการผลิตก๊าซชีวภาพจากน้ำเสียอุตสาหกรรมเอทานอลโดยการเติมโลหะไอออนEfficiency Increasement of Biogas Production from Vinasse by Trace Element Addition

งานวิจัยนี้มีวัตถุประสงค์เพื่อเพิ่มประสิทธิภาพการผลิตก๊าซชีวภาพจากน้ำเสียอุตสาหกรรมเอทานอลโดยการเติมโลหะไอออน ได้แก่ เหล็ก นิกเกิล และสังกะสี จากการเดินระบบของถังปฏิกรณ์ชนิดกวนสมบูรณ์ขนาด 10 ลิตร ที่อัตราภาระบรรทุกสารอินทรีย์ 0.50–7.42 กิโลกรัมซีโอดีต่อลูกบาศก์เมตรต่อวันพบว่า ระบบที่ไม่เติมโลหะไอออน (R1) ระบบที่เติมโลหะไอออนในทุกวันที่มีการเดินระบบ (R2) ระบบที่เติมโลหะไอออนในการหมักย่อยครั้งแรกของทุกอัตราภาระบรรทุกสารอินทรีย์ เมื่อร้อยละของก๊าซมีเทนน้อยกว่า 50% หรือเมื่ออัตราส่วนปริมาณกรดไขมันระเหยต่อค่าความเป็นด่าง (VFA/Alkalinity Ratio) มากกว่า 0.3 (R3) และระบบที่เติมโลหะไอออนในการหมักย่อยครั้งแรกของทุกอัตราภาระบรรทุกสารอินทรีย์, เมื่อร้อยละของก๊าซมีเทนน้อยกว่า 50% หรือเมื่ออัตราส่วนปริมาณกรดไขมันระเหยต่อค่าความเป็นด่าง (VFA/Alkalinity Ratio) มากกว่า 0.5 (R4) โดยมีอัตราการผลิตก๊าซมีเทนเท่ากับ 198.90 ±33.56, 165.90 ±12.19, 229.40 ±19.89 และ 195.44 ±24.98 มิลลิลิตรต่อกรัมของแข็งระเหยที่ป้อนเข้า ตามลำดับ ซึ่งผลดังกล่าวแสดงให้เห็นว่า R3 ให้ผลดีที่สุด โดยระบบสามารถรองรับอัตราภาระบรรทุกสารอินทรีย์ได้สูงสุด 4.94 กิโลกรัมซีโอดีต่อลูกบาศก์เมตรต่อวัน และมีประสิทธิภาพการผลิตก๊าซมีเทนเพิ่มขึ้นร้อยละ 15.33 เมื่อเปรียบเทียบกับการไม่เติมโลหะไอออนThe objective of this study is to investigate the effects of Trace Elements (TE) addition to increase efficiency of biogas production from vinasse. Multiple experiments were conducted to obtain the optimal feeding dosage of TE, which mainly consisted of iron, nickel and zinc. Experiments were performed in 10-litre lab-scale continuous stirred tank reactors at the organic load rates of 0.50–7.42 kgCOD/m3•d. The experiments included a control group and experimental groups as follows: The control case without TE addition (R1); the experimental groups with TE addition daily during system operation (R2); intervention with TE addition at the first fermentation stage in each organic load rate when the methane percentage was lower than 50% or when the volatile fatty acid/alkalinity ratio was more than 0.3 (R3); and the intervention with TE addition at the first fermentation stage in each organic load rate; when the methane percentage was lower than 50% or when the volatile fatty acid/alkalinity ratio was greater than 0.5 (R4). Observed specific methane production was198.90 ±33.56, 165.90 ±12.19, 229.40 ±19.89 and 195.44 ±24.98 ml/gVSadded. The results showed that R3 yielded the maximum organic loading rate of 4.94 kgCOD/m3•d, with 15.33% enhanced methane production efficiency as compared with the no-treatment control group

Bioenergy development in Thailand based on the potential estimation from crop residues and livestock manures

Bioresource evaluation is prerequisite and important to reduce cost of feedstock collection and avoid battle for feedstock to promote the healthy development of bioenergy industry. This study estimated Thai bioresources from arable field crops, horticultural plants and livestock with product quantity or livestock number, residue product ratio or manure productivity, and moisture content. Rice straw and husk, para rubber residues and cattle manure separately have the top amount in arable field crop biomass, horticultural residues and livestock manures. The northeastern region has the most amounts of arable field crop biomass and livestock manures, and the southern region possesses the largest quantities of horticultural residues. The available energy potentials from residues of arable field crops and horticultural plants can reach to maximum of 4.91 x 10(5) TJ and 7.65 x 10(5) TJ, respectively, which can theoretically share 21.67% of current total primary energy supply. The available biogas potential from livestock manures is nearly ten times than its current generation. After analysis the status of technologies and government policies for Thai bioenergy industry, it indicates that the utilization of bioenergy in the form of electricity, heat and transportation fuels has promising prospect in Thailand. The provinces of Thailand which are more suitable for developing bioenergy industry are suggested. This work may guide the reasonable layout of bioenergy industry in Thailand via the presence of bioresouces distribution in every province