Changes in optimal design of a dry-expansion evaporator when replacing R22 with R407C: Différences de configuration optimale pour un évaporateur à détente sèche lors du remplacement du R22 par le R407C

An investigation was made on whether the optimal number of tubes in a dry-expansion evaporator, for a given area or a given cost, will change when R22 is replaced with the non-azeotropic mixture R407C. A comprehensive computer program was used to simulate the tube-and-shell evaporator, under several sets of conditions. The simulations show that there are only small differences between R22 and R407C in the optimal number of tubes. However, the results indicate that one can allow a somewhat higher pressure drop for R407C, and that the number of tubes for a given area therefore can be smaller when R407C is used. For both fluids, the evaporator performance is more sensitive to the optimization for a given cost than for a given area.     

Selective determination of lithium and boron in minerals by means of an SSNTD-technique

A method has been worked out to identify lithium and boron in mineral samples by means of a solid state nuclear track detector technique. The samples have been irradiated with thermal neutrons which react with ¹⁰B and ⁶Li and give α-particles of different energies. The ranges of these α-particles in air are measured with the SSNTD-technique and found to be sufficiently different to make identification possible. A number of tests are made and the possibility for determining the distribution and the abundance of lithium and boron in a specific mineral in a rock sample is discussed.     

Surprising effects of combined vapour and liquid mass transfer resistances when condensing a mixture outside tube banks

Detailed calculations are carried out for condensation of a binary zeotropic mixture outside a tube bank to investigate combined effects of mass transfer resistances in the liquid and vapour phases. The question is how a change in mass transfer resistance in the vapour phase can influence the heat flux. The surprising result is that a decrease in resistance in the vapour phase by reducing the tube pitch, and thus increasing the vapour velocity, reduces the heat flux between 20% and 50% for the conditions studied. This is due to a combination of mass transfer resistance, depletion of the heavy volatile component, and a reduction of the phase interface temperature.     

Lignin gels as a medium in gel permeation chromatography

The preparation of spherical lignin gel beads, based on the crosslinking reaction between epichlorohydrin and kraft lignin (Indulin AT), is described. The lignin gels prepared were found to be an efficient resin in gel permeation chromatography. The separation of polystyrenes in dimethylformamide is described. The resin was found to separate polystyrenes with molecular weights up to 110,000. An inverse linear relationship between log M and elution volume or the partitioning coefficient was established.     

Performance modeling of distributed memory architectures

We provide performance models for several primitive operations on data structures distributed over memory units interconnected by a Boolean cube network. In particular, we model single-source and multiple-source concurrent broadcasting or reduction, concurrent gather and scatter operations, shifts along several axes of multidimensional arrays, and emulation of butterfly networks. We also show how the processor configuration, the data aggregation, and the encoding of the address space affect the performance for two important basic computations: the multiplication of arbitrarily shaped matrices and the Fast Fourier Transform. We also give an example of the performance behavior for local matrix operations for a processor with a single path to local memory and a set of processor registers. The analytic models are verified by measurements on the Connection Machine Model CM-2.     

Oxidation of sulphide in kraft black liquor and green liquor by residual oxygen in flue gas during precarbonation

Kraft black liquor/green liquor was continuously recirculated in a column (diameter 100 mm, height 450 mm) packed with 16-mm polypropylene Pall rings countercurrent to a gas stream containing N2 and O2 (O2–3.7%). The concentration of sulphide in the green liquor was not affected by oxygen in the gas; the latter, however, completely oxidised the sulphide in kraft black liquor over an 8 h recirculation period.     

Mass fragmentographic determination of docosenoic acid in rapeseed oils

A highly sensitive and accurate reference method for determination of docosenoic acid (mainly erucic acid, 22∶1n−9) in different rapeseed oils is described. A fixed amount of [1-¹⁴C]erucic acid methyl ester (about 1 μg) is added to a fixed amount of oil. After treatment with sodium methoxide/methanol reagent and extraction with hexane, the amount of unlabeled erucic acid is determined from the ratio between the recordings at m/e 320 and m/e 322 obtained after analysis with a combined gas chromatograph-mass spectrometer equipped with an MID (multiple ion detector). The two ions used correspond to the M-32 peak in the mass spectrum of unlabeled and [1-¹⁴C]labeled erucic acid methyl ester. The relative standard deviation of the method is about 1.8%. The method was compared with a gas chromatographic method for determination of erucic acid.     

Swelling and mechanical properties of cellulose hydrogels. IV. Kinetics of swelling in liquid water

The swelling kinetics of cellulose hydrogels have been studied in experiments where partially dried gels were reswollen to equilibrium in liquid water. The swelling interval studied was from the dry state to 3.6 g water/g dry gel, and the temperature range was from 15 to 65°C. The experimental arrangement and the theoretical analysis was based on the unidimensional, unsteady sorption of water into a swelling sheet. The effects of sheet thickness, temperature and the initial degree of swelling were investigated. The integral sorption curves obtained were sigmoid in shape when plotted as the sorbed amount of water versus the square root of time. These anomalous, non-Fickian sorption curves were analyzed under the assumption that the anomalous behavior is due to a slow establishment of concentration equilibrium at the boundary surfaces. Each sorption curve can then be described by a combination of a mutual diffusion coefficient and a surface relaxation rate. The sigmoidicity of the sorption curves is accordingly determined by the ratio of a characteristic diffusion time to a characteristic surface relaxation time. More classical, Fickian-type behavior is then explained by an increase in this ratio. The experimental sorption curves were found to become more nearly classical as the sheet thickness, the temperature and/or the initial degree of swelling was increased. The relaxation process was found to be associated with a higher apparent activation energy than the diffusion process.     

The effect of the oxygen pressure and the growth of whiskers on the oxidation of pure Fe

The weight increase curves of pure iron specimens cold-worked by abrasion with SiC and 7- diamond paste have been registered as a function of pressure and temperature. The oxidation rate increases with temperature and pressure when the pressure is raised from 0.02 to 0.2 bar. When the pressure is further increased to 1.02 bar at 500 and 625°C the oxidation rate decreases. This decrease is attributed to an orientation of the oxide grains in the -Fe₂O₃ surface.