FLOW OF SAND-WATER MIXTURES AT VELOCITIES BELOW THE DEPOSITION CONDITION

An experimental study of sand-water flow in a horizontal pipeline has been conducted for the regime in which a stationary deposit was present. The particle diameter ranged between 0.2 mm and 0.01 mm and the particles were not flocculated. Axial pressure gradients and delivered concentrations were measured as functions of mean velocity and in-situ concentration.

A three layer model was found to be useful to predict the pipeline behavior at all but the lowest velocities. The Meyer-Peter sediment transport equation was satisfactory for very low velocities with the larger particles.     

Flow of suspensions in pipelines(Part 2: Two Mechanisms of Particle Suspension)

The distribution of sand and nickel particles with height in a horizontal channel of rectangular cross section has been measured and eddy diffusivities have been computed from these measurements. Turbulent suspension of particles appeared to occur where the concentration of solid particles was low, the particle diameter was small (< 0.2 mm.) and the ratio of the settling velocity of the particles to the friction velocity of the flow was less than 0.2. Where these criteria were not satisfied, concentration profiles were observed to deviate significantly from the shape associated with turbulent suspension. These deviations are attributed to the effect of particle interactions investigated by Bagnold.     

Sliding in inclined slurry pipelines at shutdown

The sliding phenomenon which is reported to impose a restriction upon the slope of slurry pipelines is investigated experimentally. Two different types of behavior which could be called “sliding” were observed. At pipe inclianations greater than 22° to the horizontal, fully settled layers of solid particles would slide with shear occurring at or near the pipe wall. The critical angle of inclination increased as the particle size decreased. When the slurry was not fully settled, a natural convective flow process was observed to move the slurry down a pipe incline. This flow occurred at much lower pipe inclinations. Concentration profiles measured near the bottom of a pipe incline showed little effect of slurry type or concentration, provided the slurry contained a significant amount of slowly settling solids. In this case, pipe slope was the most important variable.     

A lactation measure of somatic cell count

Adjustments and weights to combine individual sample day SCC into a lactation measure were developed from 182,446 Holstein lactation records completed in 1984 from herds primarily in the western United States. Data included 1,660,782 sample day SCC expressed as log base 2 scores. Stage of lactation effects were investigated within average lactation score. Curves for lactations with averages less than 3.5 were essentially identical, which indicated that effect of stage of lactation did not increase with average somatic cell score. Lactations with averages above 4.5 did not display the typical curve of an early minimum followed by a gradual increase and, therefore, were excluded from estimating effects of stage of lactation and season. Curve for lactations with an average somatic cell score of 4.0 was intermediate. Small season effects were detected; scores were lowest in February and March and highest in August, September, and October. Parties after first had similar curves for effect of stage of lactation, but first parity showed relatively little increase in late lactation. Weightings were developed to combine adjusted sample day scores into a lactation measure. Weights were squares of correlations (computed from sample days grouped by month) between adjusted score for a given sample day and average of adjusted scores from other sample days. Weights were lowest at start of lactation, highest in midlactation, and intermediate at end of lactation.     

Experimental investigation of some hydrodynamic factors affecting slurry pipeline wall erosion

Using a non-intrusive technique, particle velocities and concentrations have been measured as functions of position on the pipe wall for water slurries of two different sands. The experimental conditions correspond to both low (fine particles) and high contact load flows. Although the velocity and concentration distributions for the two sands were quite different, flux distributions computed from the product of velocity and concentration were similar. The flux distributions are used to interpret wall erosion distributions for sands of these sizes. In the case of the coarser sand, there is evidence that the contact load mechanism contributes significantly to abrasive wear. In this case, scaleup of erosion test results may be possible, using concepts provided by mechanistic flow models. For the finer sand, wall erosion rates appear to be reduced by a lubrication force.     

Wall sampling in slurry systems

An experimental study of the errors arising in side wall sampling has been conducted. A two-dimensional model provides qualitative explanation of these errors but, unlike probe sampling, quantitative prediction of sampling efficiency is not possible because the flow to the sampler is more complex. The experiments show that serious errors in concentration or particle size distribution can arise unless the particles are fine, the concentration is high and a very high sampling velocity is used. A projection extending from the pipe wall was found to improve sampling efficiency. However this improvement was of marginal value because the complex nature of the flow precluded a simple theoretical prediction.     

Genotype by environment interaction and genetic correlations among parities for somatic cell count and milk yield

Lactation measures of somatic cell concentration and total SCC production were developed. Data were separated into three parity groups. Within parity, five data sets were created: four subsets by herd-year average SCC, and one with all records. Records on lactation SCC, total SCC production, and 305-d milk were analyzed by a sire model separately in each subset within parity. Variance components estimates were by REML. For SCC and total SCC production, heritability estimates averaged .12 and were lowest in the highest level of herd-year average SCC. Estimates of genetic correlation between SCC and total SCC production were over .95; between SCC and 305-d milk were around .25 in first and -.15 in later parities; between total SCC and 305-d milk were around .50 in first and .15 in later parities. Product-moment correlations between sire effects in different levels of herd-year average SCC were obtained. Ratios of product-moment correlations to their expected value were above .80 for all traits in all parities. High ratios indicated little genotype by environment interaction. A sire by herd interaction was fitted in the model and accounted for less than 2% of total phenotypic variance for SCC and total SCC production, and 4% for 305-d milk. Estimates of genetic correlation of first with later parities were .71 to .86 for all traits. Between second and third parity genetic correlation estimates were around unity for all traits. Records from all parities should be used for sire evaluation.     

Parametric sensitivity study of operating and design variables in wellbore heat exchangers

A numerical study was conducted to evaluate the potential for using Wellbore Heat Exchangers (WBHX) to extract heat for use in electricity generation. Variables studied included operational parameters such as wellbore geometries, working fluid properties, circulation rates, and regional properties including basal heat flux and formation rock type. Energy extraction is strongly affected by fluid residence time, heat transfer contact area, and formation thermal properties. Water appears to be the most appropriate working fluid. The effects of tubing properties and casing lengths are of second-order.On the basis of a sensitivity study, a Best Case model was simulated, and results compared against the geothermal fluid requirements of existing power generation plants that use low-temperature geothermal fluids. Even assuming ideal work conversion to electricity, a WBHX cannot supply sufficient energy to generate 200 kWe at the onset of pseudo-steady-state (PSS) conditions. Using realistic conversion efficiencies it is unlikely that the system would be able to generate 50 kWe at the onset of PSS.     

Mathematical model of chalcocite particle combustion

A mathematical model has been developed to simulate the combustion of a single chalcocite particle (particle diameter between 10 and 100 microns) in air, oxygen, and oxygen-SO₂ mixtures. Neglecting temperature and composition gradients within the particle, the model computes the thermal and compositional changes of the particle as a function of time. Five chemical reactions were considered to describe the chemical interaction between the gas and particle and within the particle. Copper vaporization below the boiling point was calculated by a balance between the vaporization rate (characterized by the Langmuir-Knudsen equation) and mass transfer from the surface of the particle. The model calculations were verified by comparison with published mass loss data obtained in a stagnant gas reactor. The model revealed that for particles combusting in oxygen, copper vaporization below the boiling point does not limit particle temperature, and particles of all sizes between 20 and 100 microns can readily reach the boiling point of copper (2836 K). Thus, the particle explosions observed in an earlier study are likely due to copper boiling within a combusting particle. Calculations of particle combustion in air snowed that only small (<20-micron diameter) particles would be capable of exploding, which agreed generally with earlier observations. Consequently, in a commercial flash-converting furnace, careful control of particle size and oxygen atmosphere must be maintained to minimize particle explosions and concomitant dust formation. Formerly Graduate Student, The University of British Columbia. Formerly Associate Professor, The University of British Columbia.