Co-production of power and urea from coal with CO<Subscript>2</Subscript> capture: performance assessment

Coal-based power plants are largest emitter of CO₂ as a single sector. To use fossil fuels (including coal), CO₂ capture and storage is a visible option. But large energy requirement for this process and risk associated with storage of CO₂ demand alternative solutions including recycling of captured CO₂. In this paper, a co-production of power and urea is proposed using coal with captured CO₂. Detailed ASPEN Plus^® model is developed for this plant. As shift reaction for producing H₂ has significant effect on output parameters, analysis is done for two different values of shift reaction, i.e., 90 and 95 % conversion. Plant consumes substantial auxiliary power (~19 % for the base case). Auxiliary power becomes a minimum for about 25 % captured CO₂ utilization for 95 % shift conversion. An economy factor is also defined to estimate the economic advantage of utilizing captured CO₂. Results show that economic advantage is obtained for CO₂ utilization beyond ~5 % for 95 % water gas shift reaction and it is beyond ~10 % for a 90 % shift reaction.     

Transport and relaxation properties of superfluid 3He. I. Kinetic equation and Bogoliubov quasiparticle relaxation rate

The kinetic equation for Bogoliubov quasiparticles for both the A and B phases of superfluid ³He is derived from the general matrix kinetic equation. A condensed expression for the exact spin-symmetric collision integral is given. The quasiparticle relaxation rate is calculated for the BW state using the s-p approximation for the quasiparticle scattering amplitude. By using the results for the quasiparticle relaxation rate, the mean free path of Bogoliubov quasiparticles is calculated for all temperatures.Also at Max-Planck-Institut für Physik und Astrophysik, München, Germany.     

Spatial estimation of snow water equivalent at different dates within the Adamello Park of Italy

Spatial estimation of snow water equivalent SWE at six different dates from February 1st to June 1st is tackled using Kriging from a sparse network of 14 snow stakes with density within the Adamello Natural Park of Italy. Therein, SWE is measured at these six dates for the period 1967-2009. Second order statistics of SWE are evaluated and linked to physiographic features. The covariance of the SWE field within the Park is studied, necessary for Kriging, and its regularization provided based upon geomorphic attributes. Seasonal dependence of the covariance of the SWE field is observed, and taken into account for optimal estimation. Then, a Kriging procedure based upon the so obtained covariance fields is developed and cross-validated. The accuracy of Kriging estimates is then compared against that of other commonly adopted methods for spatial interpolation. Kriged SWE maps are then produced at the six dates for two sample years, to demonstrate use of the method. Snow Cover Area SCA from the MODIS® satellite is used to constrain Kriging procedure upon snowed areas. The procedure provides well estimated, least variance SWE values and it is relatively simple and fast because it uses only information of physiography of the area. The so obtained maps can be used for spatial estimation of SWE within the investigated region for water availability conjectures, for constraining hydrological models simulating runoff at thaw, for ecological conjectures upon snow cover related species within the Park, and to evaluate snowpack dynamics for avalanche risk assessment.     

Magnetic Interaction Force and a Couple on a Superconducting Sphere in an Arbitrary Dipole Field

The calculation of the magnetostatic potential and levitation force due to a point magnetic dipole placed in front of a superconducting sphere in the Meissner state is readdressed. Closed-form analytical expression for the scalar potential function that yields the image system for an arbitrarily oriented magnetic dipole located in the vicinity of a superconducting sphere is given. Analytic expression for the lifting or levitation force acting on the sphere is extracted from the solution for a general dipole. A special case of our expression where the initial magnetic dipole makes an angle with the z-axis is derived. Our expression for the force in this particular case shows that a recently obtained result (J. Supercond. Nov. Magn. 21:93–96, 2008) for an arbitrary dipole is incorrect. A brief discussion of another erroneous result (J. Supercond. Nov. Magn. 15:257–262, 2002) for a transverse/tangential dipole–sphere configuration, corrected elsewhere recently, is reproduced. Correct expressions for the interaction energy with some limiting cases are also provided. The result derived here demonstrates that the value of the levitation force for a dipole that makes an angle with z-axis lies between the values for a radial dipole–sphere and transverse dipole–sphere configurations providing upper and lower bounds. It is found that for a magnetic dipole making an angle with z-axis, there exits a second force component along the negative y-direction, which influences a couple acting on the superconducting sphere. It is also shown that the couple is proportional to the second force component and that both the couple and second force components vanish for a radial dipole–sphere and transverse dipole–sphere configurations, respectively. These results appear to be new and have not had received due attention in the context of superconductivity.     

Determination of the relaxation modulus of a linearly viscoelastic material

In this paper, a numerical method for computing the relaxation modulus of a linearly viscoelastic material is presented. The method is valid for relaxation tests where a constant strain rate is followed by a constant strain. The method is similar to the procedure suggested by Zapas and Phillips. Unlike Zapas-Phillips approach, this new method can be also applied for times shorter than t ₁/2, where t ₁ denotes time when the maximum strain is achieved. Therefore this method is very suitable for materials that experiences fast relaxation. The method is verified with numerical simulations. Results from the simulations are compared with analytical solution and Zapas-Phillips method. Results indicate that the presented approach is suitable for estimating the relaxation modulus.     

Modified flux-vector-based Green element method for problems in steady-state anisotropic media

In this study we present a new numerical technique for solving problems in steady-state heterogeneous anisotropic media, namely the ‘flux-vector-based’ Green element method (‘$\mathit{q}$-based’ GEM) for anisotropic media. This method, which is appropriate for problems where the permeability has either constant or continuous components over the whole domain, is based on the boundary element method (BEM) formulation for direct, steady-state flow problems in anisotropic porous media, which is applied to finite element method (FEM) meshes. For situations involving media discontinuities, an extension of this ‘$\mathit{q}$-based’ GEM formulation is proposed, namely the modified ‘$\mathit{q}$-based’ GEM for anisotropic media. Numerical results are presented for various physical problems that simulate flow in an anisotropic medium with diagonal layers of different permeabilities or around faults and wells, and they show that the new method, with the extensions proposed, is very suitable for steady-state problems in such media.     

An automated composite table algorithm considering zero liquid discharge possibility in water regeneration–recycle network

In this study, a novel Automated Composite Table Algorithm (ACTA) is developed for targeting the water regeneration–recycle network of single contaminant problem. The ACTA is based on Pinch Analysis, but is automated by taking into consideration the possibility of zero liquid discharge (ZLD) for the water network. In the existing literature, the targeting procedure for ZLD network is based on the graphical tool of Limiting Composite Curve (LCC). However, identification of key parameters (i.e. freshwater, wastewater, regenerated water flowrates, along with pre-regeneration concentrations) is very tedious for highly integrated water network system. The magnification around the turning point of LCC is required to identify the correct pinch points and targeting procedure is done iteratively until the reliable network targets can be determined. These limitations are now overcome by the ACTA, which is an improved version of Composite Table Algorithm that is capable of identifying key parameters algebraically for a given post-regeneration concentration. The newly developed ACTA is capable of handling a wide range of problems including ZLD and non-ZLD network, for both fixed load and fixed flowrate problems.     

Multifrequency backscattering tomography for constant and vertically varying backgrounds

To improve the resolution and image quality of the SFDT (Sigle-Frequency Diffraction Tomography), a special fast multi-frequency imaging method: Multi-Frequency Backscattering Tomography (MFBT) is introduced in this paper. The method uses only the backscattered waves (after plane wave decomposition) while maintaining the merit of multi-frequency method. The method is formulated for both the constant and vertically varying backgrounds. For the latter case the WKBJ approximation is used for the background Green's function. Formulas are derived both for volume scattering using the Born approximation and for boundary scattering using the physical optics approximation. Two reconstruction methods are presented. The backpropagation method can be used and has the same computation speed for both the constant and vertically varying backgrounds. Meanwhile the direct FT method is only formulated for the constant background, in which the backpropagation in z-direction is implemented by FFT and therefore the computation speed is significantly increased. Compared with the SFDT using backpropagation reconstruction, the MFBT is nearly N_z/log₂N_z faster, where N_z is the number of grid points in z-direction, and at the same time has a much better resolution and image quality. When N_z is big, the time saving is remarkable. Compared with other multi-frequency methods such as the multi-frequency holography (prestack migration), the speeding factor becomes N_fN_z/log₂N_z, where N_f, is the number of frequencies used. Numerical simulations for both constant and vertically varying backgrounds are performed to demonstrate the feasibility of the method and the quality of reconstructed images for different situations. Examples are also given to show that when the reconstruction procedure of constant background is applied to the case of vertically varying background, the image quality will be greatly deteriorated.©1994 John Wiley & Sons Inc     

POP-IN AND CRACK ARREST IN AN HY80 WELD

It is generally thought that, when a material is in its brittle to ductile transition, it is more difficult to design for crack arrest than to prevent crack initiation (cleavage). This report shows that this is not always true for weldments. Comparison is made between compact crack arrest (CCA), K_a, and crack tip opening displacement (CTOD), K_Jc, toughness for the same HY80 weld. The value of K_a is shown to be much higher than the minimum K_Jc for pop-in fracture initiation. It is considered that the results support the conclusion of Japanese research workers (Arimochi and Isaka) that small pop-ins (in the CTOD test) propagate and arrest without load drop. It follows that prediction of structural failure for weldments need not be based on minimum pop-in toughness from CTOD tests.     

Application of the finite element technique combined with the collocation method to low supersonic lifting surface problems

In the present paper, a finite element technique combined with the collocation method is formulated to obtain numerical solutions of integral equations which determine the airload distributions acting on a wing oscillating sinusoidally in a uniform supersonic flow. This technique, which is formulated by the simultaneous use of two integral equations, is shown to be appropriate especially for the low supersonic regions, i.e., for 1 < M < 1·3, where M is the Mach number of the uniform flow. Although the formulation is made for a sinusoidally oscillating wing, it is obvious that the corresponding formulation for a stationary wing can be derived as a special case of that for the oscillating wing. Problems of determining the airload distributions for stationary as well as sinusoidally oscillating wings are treated, and it is shown that the accuracy of numerical results obtained by the present finite element technique is encouraging.     

Superconducting tunneling without the tunneling Hamiltonian

The theory of superconducting tunneling is extended to treat superconducting junctions with arbitrarily thin, but structureless tunnel barriers. An exact expression for the tunneling current is obtained, using standard, many-body, nonequilibrium Green's function techniques, assuming Fermi distributions in each electrode. The tunneling current result agrees with the recent theory of Blonder, Tinkham, and Klapwijk, but extends their results to treat strong coupling superconductors, proximity effect tunneling, and the effects of tunneling angle. Results for the Josephson critical current in S' INS (superconductor S', insulator I, metal N, superconductor S) junctions, where NS is a proximity effect double layer, are presented for barrier thicknesses ranging from zero to barrier thicknesses for which the tunneling Hamiltonian approach is correct, and for varying N metal thicknesses. Results forI-V curves are presented for normal metal (M)-INS junctions for a similar range of barrier thicknesses and N metal thicknesses. It is shown that the tunneling currentI is the sum of a supercurrentI _SUP carried solely by Cooper pairs through S, and a quasiparticle currentI _QP carried solely by quasiparticles. The influence of leakage on phonon structure observed on tunneling into strong coupling superconductors is described. The nonoscillating portion of the Josephson current is plotted as a function of voltage for the S' INS junction in the tunneling Hamiltonian limit.     

<Emphasis Type="Italic">SH</Emphasis>-wave intromission concept

The existence of an SH-wave incidence angle for which the reflected amplitude is zero (SH-wave intromission angle) is established for the case of plane-wave scattering by a planar interface joining two homogeneous, isotropic, and linearly elastic half-spaces. Such an incidence angle is numerically shown to exist for two combinations of bimaterial interface properties. The SH-wave intromission angle is roughly parallel to the electromagnetic Brewster angle and the acoustic P-wave intromission angle, and the concept should find new applications for non-intrusive characterization of interfaces.     

Computational study of transport processes in a single-screw extruder for non-newtonian chemically reactive materials

A numerical study of the transport phenomena arising in a single-screw extruder channel is carried out. A non-Newtonian fluid is considered, using a power law model for the variable viscosity. Chemical reaction kinetics are also included. Finite difference computations are carried out to solve the governing set of partial differential equations for the velocity, temperature and species concentration fields, over a wide range of governing parameters for the case of a tapered screw channel. The numerical treatment for this combined heat and mass transfer problem is outlined. A marching procedure in the down-channel direction is adopted and the validity of the scheme for practical problems discussed. For large viscous dissipation, the material heats up considerably due to the prevailing shear field, affecting the viscosity significantly, and results in large changes in the pressure development at the end of the channel. The rate of reaction controls the mass diffusion rate which in turn affects viscosity and the flow significantly. The dimensionless throughput,q _v , is one of the most important parameters in the numerical solution. The dimensionless pressure variation is very sensitive toq _v , and orders of magnitude changes are possible for small variations inq _v . Schemes for dealing with other important effects such as back flow, heat transfer by conduction in the barrel, and the effect of the die are also outlined. A list of symbols is given at the end of the paper This is publication No. F-10544-4-91 of the New Jersey Agricultural Experiment Station supported by State Funds and the Center for Advanced Food Technology (CAFT). The Center for Advanced Food Technology is a New Jersey Commission on Science and Technology Center. This work was also supported in part by the US Army Research Office.     

A multipurpose He refrigerator

We introduce a mini ³He refrigerator, operating at ∼300 mK starting from 4.2 K without pumping on the main ⁴He bath. The innovative idea is that the present one is suitable for a very fast operation; for its use, it is sufficient a storage ⁴He Dewar. In this way we drastically reduce the time required to cool it down, because there is no need for a classic cryostat. This prototype is particularly aimed for all those operations in which it is necessary to test a large number of samples that do not require long duration measurements at low temperature.     

Corrected optimum design of experiments on exponential absorption for materials in short supply

A corrected general expression is obtained for the statistical error in the absorption coefficient measured in an experiment on exponential absorption with n observations, making an allowance for a background measurement for each observation and using a fixed volume of absorber and a variable cross-sectional area for the incident beam. For n = 2 the design is optimised without constraint on the weighting of the points and also for equal weighting. With equally spaced values of absorber thickness, and with equal weighting on each point, the values of thickness interval and all the counting times are optimised for n = 3, 4, 6, 8 with relative backgrounds of zero and 0.001–100. For zero and very large backgrounds simplified formulae are obtained and optimised for any value of n. The results are compared with those for the simplest design with equal counting times for the transmitted beam plus background, equal counting times for each corresponding background count, and optimised absorber-thickness interval. For small backgrounds the loss of accuracy for this simplest design is relatively small, but is more significant for larger backgrounds and larger n values. For comparison, the optimum design is computed for unlimited absorber volume with equal counting times. It is shown that the unconstrained optimum design with limited absorber volume for two or more absorber thicknesses reduced to that for one thickness. The advantages of using the maximum available beam are are explored.     

Limited effect of diameter of fibres on spalling protection of concrete in fire

This study investigates the effect of diameter, length and melting point of fibres on spalling protection of concrete in fire. Three different diameters (0.012, 0.02 and 0.04 mm), three different lengths (9, 12 and 19 mm) and two different types (nylon and polypropylene) of fibres were investigated. Fibre volume (v%) or fibre weight per unit volume of concrete are commonly used parameters for fibre addition, but are dependent parameters on diameter of fibres. This study reports a better parameter for the expression of fibre addition which is independent of diameter, namely, number of fibres per cubic centimeter (N). When 12 mm length polypropylene fibre addition is expressed by v%, the minimum requirement for spalling protection is v = 0.20% for 0.04 mm diameter fibres and v = 0.05% for 0.02 mm diameter fibres. If the fibre addition is expressed in N, the minimum requirement is N = 133/cm³ for both cases regardless of fibre diameter. Hence, the diameter of fibres has limited effect on spalling protection of concrete. If the fibre addition is expressed in v%, the diameter seems to have an effect due to the fact that parameter v% is a function of diameter. In addition, increasing the length of fibres has the effect of reducing the required N for spalling protection. When fibre length is increased from 12 to 19 mm, the minimum requirement is reduced from N = 133 to 42/cm³. The melting point of the fibres also has an influence on spalling protection, which is discussed in detail by comparing nylon and polypropylene fibre results.     

Bose condensation of the localized pairs in two-band superconductors

Superconductor with two singularities inherent in high-T_c materials, low carrier density and overlapping of the energy bands on the Fermi surface, is considered. Provided T=0, the order parameter ‡_n and chemical potential Μ are determined in the mean-field approximation for the state with Bose condensation of the localized pairs (Μ < 0). The equation for the energy of the bound state ε_b is also obtained and the relationship ε_b = 2Μ is established. The method of functional integration concerning the two-band model is developed. On the basis of this method, the crossover between the Fermi picture and the Bose one of the elementary excitations is demonstrated for the system in the presence of the two-particle bound state. The expression for the temperature of Bose condensationT _k is obtained and the contribution of the residual interaction between bosons for the systems with arbitrary dimension is determined.     

Compositional effects on the fracture behaviour of alkali–silicate glasses

The two-point bend strength and the fracture toughness of a series of soda–potassia–silicate and soda–potassia–calcia–silicate glass fibres have been measured. There is a clear variation of mean strength with composition for the soda–potassia–silicate glasses, however, there is much less variation of mean strength with composition for the soda–potassia–calcia–silicate glasses. There is also a greater variation of fracture toughness with composition for the soda–potassia–silicate glasses than for the soda–potassia–calcia–silicate glasses. The mean strength, fracture toughness and inferred flaw sizes for the soda–potassia–calcia–silicate glasses are all less than the equivalent values for the soda–potassia–silicate glasses. These results are related to the structural models and durability of the glasses tested.     

J-integral evaluation for cases involving non-proportional stressing

Calculation of J for cases where the proportional stressing condition cannot be satisfied is investigated. A modified J definition is derived and implemented into an ABAQUS post-processing program for both 2-D and axisymmetric problems. The modified J-integral is path independent for cases of proportional and non-proportional stressing. For cases with proportional stressing, the modified integral gives the same value as does the standard ABAQUS J function. It is also found that the modified J is equivalent to the stress intensity factor for a linear elastic material and provides a measure of the intensity of the crack-tip fields for non-linear elastic and elastic-plastic materials. The modified J formulation is applied to the case of a cylinder with an external circumferential crack under various load conditions.     

Simulation of Magnetocaloric Properties of Antiperovskite Structural Ga1−X Al X CMn3

In this work, low-enhanced magnetic field magnetocaloric effect for Ga_1?X Al _X CMn₃ (X = 0, 0.05, 0.07, 0.12, and 0.15) system near a second-order phase transition from a ferromagnetic to a paramagnetic state is investigated theoretically. It is found that magnetic entropy change distribution is much more uniform than that of gadolinium, which is desirable for an Ericson-cycle magnetic refrigerator. Moreover, the results show that the magnetocaloric effect in this system is tunable by Al doping, which is beneficial for manipulating magnetocaloric refrigeration that occurs in various temperature ranges including room temperature. This makes the Ga_1?X Al _X CMn₃ samples potential candidates for practical applications.