Current Issue : January - March Volume : 2017 Issue Number : 1 Articles : 5 Articles
This paper is focused on the discussion and comparison of characteristics and behavior of\nthree low frequency ac (LFAC) transmission system configurations operating under the same control\nscheme and conditions to identify the most promising operation system for LFAC. Merits of LFAC\nover high voltage direct current (HVDC) are mentioned first. By changing power flow direction\nwithout auxiliary switches in multi-terminal application and easiness of short circuit protection are\nexplained. The three configurations of LFACs are described and applied by the control scheme with\nthe aid of the tool of the PSCAD/EMTDC software to consider the behavior of each LFAC system\non line frequency and low frequency sides. For two-phase system, no fluctuation occurs on the\nline frequency side, which is the advantage over single-phase system. Furthermore, current rating\non thyristor devices during operation and number of devices that used in each type of LFAC are\ncalculated and compared. These results can lead to determine the most suitable transmission system\nfor the LFAC system operation....
The importance of gold recovery from low grade ores and flotation tailings is continuously increasing\ndue to raising gold demand and thereby high gold prices. However, due to raising social awareness\nof the ecological impacts of cyanidic gold extraction and environ-mental specifications, the development\nand the implementation of alternative hydrometallurgical extraction processes have\nbeen a focus for many research institutions in last decades. Present work gives a comparison between\ncompatible extraction reagents, with focus on less harmful processes. The target of this review\nis to point out the best cyanide-free processes of following methods and reagents: Bioleaching,\nChlorination, Aqua Regia, Bromine, Thiocyanate, Thiosulfate and Thiourea leaching. For this propose,\nthe gold leaching reagents are described and discussed in terms of their environmental and\neconomical points of view. As result of this comparison, thiourea stands out as the most promising\nalternative gold leaching reagent to cyanide....
The market for process instruments generally requires low cost devices that are robust,\nsmall in size, portable, and usable in-plant. Ultrasonic torsional guided wave sensors have received\nmuch attention by researchers for measurement of viscosity and/or density of fluids in recent years.\nThe supporting electronic systems for these sensors providing many different settings of sine-wave\nsignals are bulky and expensive. In contrast, a system based on bursts of square waves instead of\nsine waves would have a considerable advantage in that respect and could be built using simple\nintegrated circuits at a cost that is orders of magnitude lower than for a windowed sine wave device.\nThis paper explores the possibility of using square wave bursts as the driving signal source for the\nultrasonic torsional guided wave viscosity sensor. A simple design of a compact and fully automatic\nanalogue square wave front-end for the sensor is also proposed. The successful operation of the\nsystem is demonstrated by using the sensor for measuring the viscosity in a representative fluid.\nThis work provides the basis for design and manufacture of low cost compact standalone ultrasonic\nguided wave sensors and enlightens the possibility of using coded excitation techniques utilising\nsquare wave sequences in such applications....
The first exploration oil well in any oil block consumes in general more time and cost than the\nother wells in the same block. Evaluating the drilled wells serves to improve the future operations.\nThis paper evaluates the drilled surface section through real field data for the first exploration oil\nwell drilled in one of the oil blocks, in Kurdistan north of Iraq. The surface section of the well was\ndrilled with the conventional method to penetrate many different geological formations with tight\nintervals. Drilling efficiency and the difficulties encountered are discussed and explained using\nvarious data sources. All daily drilling reports concerning a specific interval were studied. This includes\nweight on bit, string rotation, mud pump flow and penetration rate. Evaluation was carried\nout by analyzing the used controllable drilling parameters with the formations features. Penetration\nof the Pila Spi formation (Middle Eocene) was the most difficult formation in the drilled section.\nMicrosoft Office 365 Pro Plus used in making graphs and Excel tables. Evaluations showed\nthat the conventional technology used left many negative effects, like increase in None Productive\nTime NPT, cost and ground water pollution. Simultaneous Casing Drilling method proposed as an\nalternative method for the future campaign....
To address the problem of low frequency noise of the internal combustion engine,\nseveral existing muffler design methods, such as the theory of the quarter-wavelength\ntube and the Helmholtz muffler, were examined and compared. This paper proposes\na new type of muffler design method, which has the advantages of both the quarterwavelength\ntube and the Helmholtz muffler. An example is carried out to illustrate the\nanalysis of original signal, the design of the new muffler and the improvement of the\nin-car noise. The transmission loss of the new muffler is studied by theoretical method\nand finite element method. The vehicle test of the new muffler demonstrates excellent\nperformance with a wider noise elimination frequency band and smaller radial size....
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