Current Issue : April - June Volume : 2020 Issue Number : 2 Articles : 5 Articles
The next phase of industrialization in the world is the use of 3D printing technology. Various 3D printing technologies are\nemployed all over the world and for different purposes, from 3D printed houses to 3D printed food nutrients. Printer movement is\nachieved by carriages moving in a clearly defined X, Y, and Z orientation. The 3D printer has a lower work rate; subsequently,\nmany printouts consume a lot of time due to their complexity. This paper elaborates on the design and development of a faster and\nfixed build platform 3D printer (Delta 3D printer) using locally available materials and e-waste. The Delta 3D printer movement is\nfaster with a stable bed. Printer movement is achieved using three vertical axes placed 120° apart. Accuracy and speed are achieved\nwith the use of NEMA 17 stepper motors to drive the various carriages on the vertical axes. Design calculations show that the least\nforce delivered by the stepper motor is 1.73N which exceeds 0.8334 N, the weight of the load to be carried. Furthermore, a stepper\nmotor must turn 80 steps (rotational motion) in order to achieve 1mm advance (linear motion). This ensures a higher printout\nresolution. In place of traditional linear rails, locally sourced square pipes were adopted coupled with bearings and a 3D printed\ncarriage support, and a relatively cheaper but stable linear rail was developed. The goal of this research was to develop an\nalternative easy-to-build Delta 3D printer using locally sourced materials. This goal of this research was achieved, and the\ndeveloped prototype was test-run under load conditions. It is recommended that salvaged e-waste should be properly managed for\neasy acquisition....
The load characteristics for the flow regulator of a solid ducted rocket are discussed in this paper. The mechanism and the influence\nfactor of the load in the flow regulator were studied both theoretically and experimentally, and the system load and the working load\nwere divided according to the mechanism. Additionally, the load influence on the working quality of the flow regulator and the\nducted rocket were analyzed. System modeling of the flow regulator was carried out based on the working mechanism of the gas\ngenerator and the Stribeck friction model, and models of the actuator, gas generator, and load were built. Furthermore,\nconsidering the identification of the model parameters and the inapplicability of the conventional Stribeck identification method\nto the flow regulator, a new Stribeck model parameter identification method was proposed. A sine wave was used as the signal\nsource, and specially designed devices were used to accomplish the switch of the working condition. Through the use of the\ngenetic algorithm, the rotational inertia and parameters of the system load and working load were identified by stages. Finally,\nthe validation of the identification method was carried out with a simulation....
A two-dimensional numerical study of natural convection in a tunnel whose\nplane is sinusoidal with an opening on the horizontal ceiling is presented. In\nthis work, we study the thermoconvective instabilities of air in a tunnel closed\nat both ends and heated by the floor. The study was carried out for different\ncases of geometry by varying the thickness of the sinusoid and the height of\nthe tunnel. In order to create a transverse movement of the air, we heated the\nfloor to the temperature������...
Ocean thermal energy conversion (OTEC) uses the natural thermal gradient in the sea. It\nhas been investigated to make it competitive with conventional power plants, as it has huge\npotential and can produce energy steadily throughout the year. This has been done mostly by\nfocusing on improving cycle performances or central elements of OTEC, such as heat exchangers. It\nis difficult to choose a suitable heat exchanger for OTEC with the separate evaluations of the heat\ntransfer coefficient and pressure drop that are usually found in the literature. Accordingly, this\npaper presents a method to evaluate heat exchangers for OTEC. On the basis of finite-time\nthermodynamics, the maximum net power output for different heat exchangers using both heat\ntransfer performance and pressure drop was assessed and compared. This method was successfully\napplied to three heat exchangers. The most suitable heat exchanger was found to lead to a maximum\nnet power output 158% higher than the output of the least suitable heat exchanger. For a difference\nof 3.7% in the net power output, a difference of 22% in the Reynolds numbers was found. Therefore,\nthose numbers also play a significant role in the choice of heat exchangers as they affect the pumping\npower required for seawater flowing. A sensitivity analysis showed that seawater temperature does\nnot affect the choice of heat exchangers, even though the net power output was found to decrease\nby up to 10% with every temperature difference drop of 1 DegreeC....
Studies conducted over the past 10 years have demonstrated the technical suitability of the\nelectric arc furnace slag as an alternative to natural stone in several applications. Steel slag can be\nprofitably used as a road surface layer, for foundations and embankments, or for concrete aggregates.\nHowever, a strong limitation to their use is due to the presence of toxic metals (Ba, Cr, V, Mo, etc.) that\ncan be released into the environment in particular conditions, especially for unbound products in\nwhich the slag can come into contact with water. Recent studies have investigated the role of chemical\ncomposition and microstructure of slag on toxic metal leaching, allowing for the design of suitable\nstabilization treatments for hindering such leaching. In this work, four batches of electric arc furnace\ncarbon steel slag underwent a stabilization treatment and the obtained results were compared. In two\nbatches, the stabilizer was added directly in the slag pot and the slag was cooled down in the same\npot. The other two batches were stabilized during the downfall from slag door to slag pit. Several\nslag samples were collected before and after the stabilization treatment and were characterized by\nmeans of ED-XRF, XRD, and SEM analysis. Leaching tests were carried out in agreement with EN\n12457-2 standard on 4 mm granulated slag, and the leachate concentration was compared with the\ncurrent Italian limits listed in D.M. 3 August 2005 N. 201 and D.M. 5 April 2006 N. 186. The results\nclearly indicated that the cooling in the slag pot improved the efficiency of the stabilization treatment,\nleading to a complete transformation of the microstructure by a full development of homogeneous\ngehlenite matrix and a coarsening of Cr-spinels, assuring better toxic metal retention behavior. On the\ncontrary, stabilization in the slag-pit was rapid and reduced the interaction between slag and stabilizer,\nleading only to partial transformation of larnite into gehlenite, and also reducing the coarsening of\nCr-spinel. In addition, a layering effect was observed, resulting in an inhomogeneous product from\ntop to bottom in terms of chemical composition, microstructure, and leaching behavior....
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