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Luleå tekniska universitet Övrigt
Some comments and extensions are given to the paper on statistics for testing exponentiality against the HNBUEE property (i.e. {Mathematical expression} ≦μ exp(-t/μ), t≧0) by Basu and Ebrahimi
N/A / Link / Bergman , Bo / 1987

Three-dimensional finite element simulation of electron beam welding of a large copper canister has been performed. The use of an automatic remeshing algorithm, based on a graded hexahedral element was found to be effective. With this algorithm the strongly nonlinear thermomechanical effects locally close to the moving heat source can accurately be modelled using a dense element mesh that follows the heat source.
N/A / Link / Lindgren , Lars-Erik / 1997

Luleå tekniska universitet Övrigt
80-85823-45-4 / Link / Kufner , Alois / 2000

Luleå tekniska universitet Övrigt
In recent years an increasing number of organisations use process capability studies on a regular basis. Contemporaneous with the increasing number of organisations using process capability studies, warnings have been launched that imprudent use of numerical measures of capability, the so-called process capability indices, might lead the user to make erroneous decisions. As a result, many practitioners of today are left with a somewhat ambivalent attitude towards process capability studies. In order to reduce these ambiguities, this paper outlines the advantages and disadvantages of the method. The results presented are based on a survey performed among 97 Swedish organisations that use process capability studies on a regular basis
N/A / Link / Deleryd , Mats / 1999

Luleå tekniska universitet Övrigt
N/A / Link / Klefsjö , Bengt / 1986

According to a mathematical model, each mineral has its own liberation-energy characteristic curve which can be plotted. The relations between liberation, mill speed and charge volume are also presented.
N/A / Link / Forssberg , Eric / 1985

Luleå tekniska universitet Övrigt
A method for the evaluation of friction models is described. A wedge is rolled to uniform thickness, a range of reductions being investigated thereby in one experiment. Finite-element simulations are performed in order to estimate the friction parameters that can be used in the simulation of hot rolling. The influence of the material parameters and the friction parameters on the calculated results are investigated and the latter are compared with experimental results. It is shown that it is possible to separate the influence of the material parameters and the friction parameters, thus enabling the friction parameters to be evaluated from a minimum number of experiments.
N/A / Link / Edberg , Jonas / 1994

0-444-70273-3 / Link / Ekblom , Håkan / 1987

Propagation bending waves are studied in a tube of steel and in a ring of aluminum. The waves are generated by the impact of a ballistic pendulum. Holographic interferometry, with a double-pulsed ruby laser as light source, is used to record the waves. A conical mirror is placed axially inside the tube. Axial illumination and axial observation directions, make it possible to view all sides of the tube simultaneously with a high sensitivity to radial deformation. The interferograms, which have an unusual perspective, are captured with a CCD-camera and then spatially transformed into an unwrapped strip of the tube wall. This makes the interpretation of the measurements simpler. The geometry of the tube causes the wave pattern to propagate with different speed and amplitude along and across the tube, even when the material itself is isotropic. A finite-element simulation of the impact is compared to the corresponding experiment. An impact on a ring with a defect is performed in order to study the effect on the wave pattern. The proposed method could be used in nondestructive testing of pipes.
N/A / Link / Olofsson , Kenneth / 1993

Many difficulties in welding result from the fact that heat input causes uneven heating of the welded object. This article reports on the results of an investigation carried out with the object to find out whether it is possible to predict residual stresses in welding and weld deformations with the aid of new computational methods used in continum mechanics. Butt welding of flat plates was studied in this investigation. Deformations, residual stresses, and gap width variations during the welding process were calculated.
N/A / Link / Jonsson , Mikael / 1986

Luleå tekniska universitet Övrigt
N/A / Link / Helgeson , Bo / 1987

Luleå tekniska universitet Övrigt
0-470-21351-5 / Link / Nikolova , Ludmila / 1989

The size and location of silver particles in K-glycerate/AgNO3 impregnated Swedish pine, green wood as well as high temperature dried, have been studied using TEM micrographs. The diameter of the silver particles was found to be 2-20 nm in the impregnated green wood and as large as 1000 nm (major axis) for the ellipsoid-shaped silver clusters in the impregnated dried wood. Studying the projected area of the silver particles in impregnated green wood indicated that there are a lot of particles (40%) in the compound middle lamella with fewer particles in the S2 (6-8%), S1 (4%) and S3 (2%) layers. The average distance between the silver particles, 50 nm (S2-layer), in impregnated green wood shows that the impregnant is distributed in the cell wall at the microfibrilar level. Experimental results show that the fastest diffusion path into the cell wall is from the lumen over the pit membrane through the compound middle lamella and not from the lumen through the secondary wall layer S3.
N/A / Link / Wallström , Lennart / 2000

N/A / Link / Nilsson , Per / 1997

Luleå tekniska universitet Övrigt
Gas turbines with air-water mixtures as the working fluid promise high electrical efficiencies and high specific power outputs to specific investment costs below that of combined cycles. Different humidified gas turbine cycles have been proposed, for example direct water-injected cycles, steam-injected cycles and evaporative cycles with humidification towers. However, only a few of these cycles have been implemented and even fewer are available commercially. This paper comprehensively reviews the literature on research and development on humidified gas turbines and identifies the cycles with the largest potential for the future. In addition, the remaining development work required for implementing the various humidified gas turbine cycles is discussed. This paper can also be used as a reference source that summarizes the research and development activities on humidified gas turbines in the last three decades.
N/A / Link / Jonsson , Maria / 2005

Luleå tekniska universitet Övrigt
N/A / Link / Haugum , Dag / 1989

Luleå tekniska universitet Övrigt
Biomass fuelled integrated gasification/gas turbines (BIG/GTs) have been found to be one of the most promising technologies to maximise electricity output in the sugar industry. However, biomass fuels contain alkali metals (Na and K) which may be released during the gasification processes and cause deleterious effects on the downstream hardware (e.g. the blades of gas turbines). Much research has therefore been focused on different kinds of gas cleaning. Most of these projects are using a fluidised bed gasifier and includes extensive gas cleaning which leads to a high capital investment. Increasing alkali retention/separation during the gasification may lead to improved producer gas quality and reduced costs for gas cleaning. However, very little quantitative information is available about the actual potential of this effect. In the present work, comparative bench-scale tests of bagasse gasification were therefore run in an isothermal fluidised bed gasifier and in a cyclone gasifier to evaluate which gasification process is most attractive as regards alkali retention/separation, and to try to elucidate the mechanisms responsible for the retention. The alkali retention in the fluidised bed gasifier was found to be in the range of 12-4% whereas in the cyclone gasifier the alkali separation was found to be about 70%. No significant coating of the fluidised bed's bed material particles could be observed. The SEM/EDS and the elemental maps of the bed material show that a non-sticky ash matrix consisting of mainly Si, Al and K were distributed in a solid form separated from the particles of bed material. This indicates the formation of a high temperature melting potassium containing silicate phase, which is continuously scavenged and lost from the bed through elutriation.
N/A / Link / Gabra , Mohamed / 2001

Reflection and transmission of waves by impedance transitions from a constant input to a constant output characteristic impedence are considered. Several fundamental properties are explored, primarily for impedance transitions with piece-wise constant characteristic impedance in an arbitrary number N of intervals of equal length. For example, the following properties are shown: (i) The relative momentum transmission depends only on the ratio of output to input characteristic impedance. (ii) For a given impedance transition there are at most, and generally exactly, 2N different transitions, including the original one, with identical transmission properties. (iii) For monotoneous impedance transitions the efficiency of energy transmission is minimized by one with an abrupt change in characteristic impedance. (iv) There exists an optimal impedance transition, with a certain antisymmetry, which maximizes the efficiency of energy transmission for a given incident wave of finite duration and energy. Several of the results can be extended to more general classes of impedence transitions. Simple illustrative examples are given.
N/A / Link / Andersson , L-E / 1984

Autogenous grinding produces rounded particles with higher degrees of liberation and equiaxiality and lower roughness. These properties result in a higher grade concentrate and better recovery. Autogenous grinding is consequently more economical.
N/A / Link / Forssberg , Eric / 1985

Samples were collected from the Stekenjokk and Malmberget concentrators, operated by Boliden Mineral AB and Luossavaara-Kiirunavaara AB respectively. The Stekenjokk ore consists of massive pyrite with disseminated chalcopyrite and sphalerite; it assays 1. 4 % Cu and 3. 2 P% Zn. The Malmberget ore mainly contains magnetite with a coarse-crystalline structure; run-of-mine ore assays are about 40 5 Fe and 0. 6 % P. Using an automatic image analyzer, it appears that fully autogenous grinding down to flotation fineness results in better liberation and particle shape for flotation than is obtained with a combination of primary autogenous and ball mill grinding. Fully autogenous grinding also creates smoother particle surfaces.
N/A / Link / Forssberg , Eric / 1985

To obtain an extensive understanding of the behavior of the key parameters in grinding processes, factorial design is applied to a ball mill test using four variables, each at three levels. This required a total of 27 tests. The influence of charge volume, mill speed, feed and pulp density on grinding fineness and net energy consumption were related and in order by multiple regression analysis. The computer-based response surfaces of the dependent variables demonstrated the combined effects of the operational parameters. They also provided a base for further tests on the multiple influence of the process variables on continuous grinding.
N/A / Link / Forssberg , Eric / 1986

Luleå tekniska universitet Övrigt
N/A / Link / Eriksson , Ulf / 1997

Luleå tekniska universitet Övrigt
 A large-scale continuous stirred media mill called the MaxxMill [registered trademark] system in dry mode was used to investigate the comminution characteristics. A limestone powder below 2 mm was used as a feed material. A statistical experimental design was prepared with the major influencing parameters of the MaxxMill [registered trademark] , such as rotational speed of stirrer, feed rate and bead size. The fineness of the ground products obtained under various conditions of the MaxxMill [registered trademark] and the corresponding energy utilisation have been evaluated and analysed. The results have been empirically correlated with the operating parameters. In addition, product size-energy input relations can be described empirically, independent of the parameters used.
N/A / Link / Wang , Yanmin / 2004

Luleå tekniska universitet Övrigt
82-595-6248-0 / Link / Lindgren , Antony / 1990

This paper summarizes measurements of starting torque and motion of the rollers in a roller bearing during start-up at a temperature of -30 °C. The bearing was lubricated with three different greases and the tests were carried out after a running-in procedure at +20 °C. The results were compared with measurements obtained at +20 °C and with results from one base oil at +20 °C. A model for the roller motion was also built and simulations of the roller motion were compared with the measurements. Independent of temperature and lubricant the rollers rolled in the loaded zone and slipped, more or less, in the unloaded zone. The degree of sliding in the unloaded zone was found to be governed mainly by the local lubricant distribution and the position of the roller in the cage pocket. Some differences are also seen in the slide-roll ratio between the lubricants. A roller diameter difference of 1.3 μm gave a significant difference in roller motion, with the slightly thinner roller slides more in the unloaded zone of the bearing.
N/A / Link / Östensen , J.O. / 1995

Numerical methods for obtaining (X|y), related to the linear model y = X + e, are presented. The user is allowed to specify the Lp or Huber solution vector B* and is also free to choose the conditioning and the structure of X.
N/A / Link / Ekblom , Håkan / 1990

Luleå tekniska universitet Övrigt
N/A / Link / Helgeson , Bo / 1984

To obtain a sustainable increased use of the CO2-neutral biomass fuels, the nutrient elements in the ashes formed have to be recirculated back to the forest and farm lands. During their growth, plants accumulate significant amounts of heavy metals of anthropogenic origin, normally enriched in the ashes during the energy conversion processes. If some kind of heavy metal separation technique could be applied during or after the processes, a more ecologically safe ash fraction may be produced for the recirculation of the nutrients. In addition, contaminated soils could be efficiently cleaned by controlled cultivation and combustion of biomass fuels. Previous experimental results from full-scale combustion plants have indicated that a significant fraction of a heavy metal-free ash may be obtained at high temperatures due to the lower volatilization temperatures of these metals. In the present work, the theoretical feasibility of a proposed high-temperature cyclone separation technique was evaluated by means of chemical equilibrium model calculations. The equilibrium behavior of both nutrient elements (Ca, Mg, K, Na, P) and heavy metals (Cd, Cu, Cr, Pb, Ni, Zn, As, V) as functions of temperature was determined. The results indicate that Cd, Cu, Pb, and possibly As and Cr may be volatilized, and thus separated, through a hot cyclone (800-850 °C), still keeping all Ca, Mg, and P and 75% of K and Na in a condensed form in the cyclone ash.
N/A / Link / Ljung , Anders / 1997

N/A / Link / Hermansson , Roger / 1997