<p dir="ltr">Current industrial processes are energy and carbon emission intensive. Amidst the growing demand for decarbonization, it is critical to utilize alternate sources of energy and innovative technologies that could improve efficiency and reduce power consumption. In this context, twin-screw compressors are used extensively in commercial and industrial applications. Profile optimization and capacity modulation solutions (e.g., slide valves, variable-speed, etc.) are continuously investigated to improve the performance and operation of the compressors. This study focuses on an exploratory investigation of an additively manufactured twin-screw compressor with internal cooling channels to achieve a near isothermal compression process by evaluating both the potential compressor performance improvement and the structural integrity by means of rotordynamics and fatigue analyses.</p><p dir="ltr">To predict the compressor performance, complex coupling between compression process and heat transfer during the operation of the compressor must be investigated. The interactions between solid (i.e., rotors) and fluid phases (i.e., air and coolant) were modeled using a transient 3D CFD model with conjugated heat transfer (CHT). The CFD model predicted compressor performance parameters such as isentropic efficiency, heat transfer rate, work input and compression forces on the rotors. The performance of the twin-screw compressor with internal cooling channels has been compared with a conventional twin-screw compressor for which experimental data was available. Further investigations have been conducted at different operating conditions, including various pressure ratios, rotational speeds, and mass flow rates to improve the compressor efficiency. The results of the CFD model were used to quantify compression loads, assess the characteristics of the heat transfer processes, and optimize the internal flow through the cooling channels. As the rotors can be affected by stress accumulation and deformations due to their hollowness and reduced wall thickness over time, this study also established a detailed rotordynamic simulation model and a fatigue model using the actual compression forces obtained from previous CFD studies. Both hollow and solid rotors have been analyzed and compared. The bearing loads have been verified against Campbell diagrams whereas the fatigue results have been compared with experimental testing. With the validated model, the hollow rotor compressor durability was analyzed and compared with the conventional rotors. Lastly, a general mechanistic model to better understand bearing loads and frictional losses in a twin-screw compressor is also established and studied.</p><p dir="ltr">The CHT study concluded that the hollow rotor with single-phase internal cooling yielded to an increase in isentropic efficiency of 1% for the higher pressure ratio and 2% for lower pressure ratio at 19,000 RPM. More importantly, the hollow rotors also showed a decrease of 40 K and 20 K in discharge temperatures for the two operating conditions respectively, thereby arriving closer to isothermal conditions and reducing the thermal stresses on the rotors. The rotordynamic study revealed that the male rotor would endure highest amount of von Misses stress reaching up to 338 MPa for the pressure ratio of 3.29 bar and 19,000 RPM. Because of this, a maximum fatigue factor of safety of 5 occurs on the male rotor. From the analyses, the rotors were deemed to be safe and optimized for the designed operating conditions and proof of concept rotors were additively manufacturers with an Inconel alloy through Direct Metal Laser Sintering.</p>

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<div>Powder Bed Fusion Additive Manufacturing enables the fabrication of metal parts with complex geometry and elaborates internal features, the simplication of the assembly process, and the reduction of development time. However, the lack of consis-tent quality hinders its tremendous potential for widespread application in industry. This limits its ability as a viable manufacturing process particularly in the aerospace and medical industries where high quality and repeatability are critical. A variety of defects, which may be initiated during the powder-bed fusion additive manufacturing process, compromise the repeatability, precision, and resulting mechanical properties of the final part. The literature review shows that a non-uniform temperature distribution throughout fabricated layers is a signicant source of the majority of thermal defects. Therefore, the work introduces an online thermography methodology to study temperature distribution, thermal evolution, and thermal specications of the fabricated layers in powder-bed fusion process or any other thermal inherent AM process. This methodology utilizes infrared technique and segmentation image processing to extract the required data about temperature distribution and HAZs of the layer under fabrication. We conducted some primary experiments in the FDM process to leverage the thermography technique and achieve a certain insight to be able to propose a technique to generate a more uniform temperature distribution. These experiments lead to proposing an innovative chessboard scanning strategy called tessellation algorithm, which can generate more uniform temperature distribution and diminish the layer warpage consequently especially throughout the layers with either geometry that is more complex or poses relatively longer dimensions. In the next step, this work develops a new technique in ABAQUS to verify the proposed scanning strategy. This technique simulates temperature distribution throughout a layer printed by chessboard printing patterns in powder-bed fusion process in a fraction of the time taken by current methods in the literature. This technique compares the temperature distribution throughout a designed layer printed by three presented chessboard-scanning patterns, namely, rastering pattern, helical pattern, and tessellation pattern. The results conrm that the tessellation pattern generates more uniform temperature distribution compared with the other two patterns. Further research is in progress to leverage the thermography methodology to verify the simulation technique. It is also pursuing a hybrid closed-loop online monitoring (OM) and control methodology, which bases on the introduced tessellation algorithm and online thermography in this work and Articial Neural Networking (ANN) to generate the most possible uniform temperature distribution within a safe temperature range layer-by-layer.</div>

Purdue School of Engineering and Technology, Indianapolis / Powder Bed Fusion Additive Manufacturing enables the fabrication of metal parts with complex geometry and elaborates internal features, the simplification of the assembly process, and the reduction of development time. However, the lack of consistent quality hinders its tremendous potential for widespread application in industry. This limits its ability as a viable manufacturing process particularly in the aerospace and medical industries where high quality and repeatability are critical. A variety of defects, which may be initiated during the powder-bed fusion additive manufacturing process, compromise the repeatability, precision, and resulting mechanical properties of the final part. The literature review shows that a non-uniform temperature distribution throughout fabricated layers is a significant source of the majority of thermal defects. Therefore, the work introduces an online thermography methodology to study temperature distribution, thermal evolution, and thermal specifications of the fabricated layers in powder-bed fusion process or any other thermal inherent AM process. This methodology utilizes infrared technique and segmentation image processing to extract the required data about temperature distribution and HAZs of the layer under fabrication. We conducted some primary experiments in the FDM process to leverage the thermography technique and achieve a certain insight to be able to propose a technique to generate a more uniform temperature distribution. These experiments lead to proposing an innovative chessboard scanning strategy called tessellation algorithm, which can generate more uniform temperature distribution and diminish the layer warpage consequently especially throughout the layers with either geometry that is more complex or poses relatively longer dimensions. In the next step, this work develops a new technique in ABAQUS to verify the proposed scanning strategy. This technique simulates temperature distribution throughout a layer printed by chessboard printing patterns in powder-bed fusion process in a fraction of the time taken by current methods in the literature. This technique compares the temperature distribution throughout a designed layer printed by three presented chessboard-scanning patterns, namely, rastering pattern, helical pattern, and tessellation pattern. The results confirm that the tessellation pattern generates more uniform temperature distribution compared with the other two patterns. Further research is in progress to leverage the thermography methodology to verify the simulation technique. It is also pursuing a hybrid closed-loop online monitoring and control methodology, which bases on the introduced tessellation algorithm and online thermography in this work and Artificial Neural Networking (ANN) to generate the most possible uniform temperature distribution within a safe temperature range layer-by-layer.