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

Biogas Production from Co-digestion of Pennisetum Pururem cv. Pakchong 1 Grass and Layer Chicken Manure Using Completely Stirred Tank

AbstractIn this research, the production of biogas from co-digestion of Pennisetum purpureum cv. Pakchong1 grass and layer chicken manure using completely stirred tank was investigated. The experiment was defined to examine effect of the change in carbon to nitrogen (C/N) ratios and the organic loading rates (OLRs) on biogas production and system steady-state performance. Primary analyses suggested that an approximate content of grass and manure was 50: 50% by weight to achieve C/N ratio of 20 and 70: 30% by weight for C/N ratio of 30 respectively. The experimental reactor was set to operate at a fixed total solid content of 4% with two cases of C/N ratio at four different OLRs of 1.1, 1.4, 1.7 and 2.2kg VS/(m3.d). Each condition was operated for 1.5 time of reactor retention time. The result suggested that maximum steady-state methane yield of 0.27 ± 0.01 L CH4/kg VSadded can be achieved at C/N ratio of 20 with OLR of 1.1kg VS/(m3.d). Moreover, the results also suggested that methane yield decreased for an increase in OLR. Nonetheless, the work presented herein can provide an insight information for design and operation optimization according to economical investment analysis

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

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

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