Lower Air Content Research Articles

Computer analysis of two-stage entrained bed coal gasifier. Characteristics of a 2T/D gasifier at various coal feed ratios.

A two-stage entrained bed coal gasifier has the feature that the entire coal gasifier can be operated at a low air content by controlling the coal and air feed rates to the combustor and the reductor section, respectively, independently. This paper describes the results of computer analysis on the different coal feed ratios to the combustor and the reductor before the test with our 2T/D coal gasifier. The main results are as follows: (1) We can expect a higher cold gas efficiency and calorific value at a lower combustor/reductor coal feed ratio, with the temperature of the raw gas at the combustor section kept constant; (2) In general, it is effective to lower the coal feed rate with the entire air feed ratios kept constant, for efficiently gasifying the high ash fusion temperature coal, but we assume that a high temperature cannot be obtained at the combustor section because the heat loss through the 2T/D gasifier wall tends to sharply increase at a lower combustor/reductor feed ratio.

Effect of concrete specifications and inspection practices on freeze–thaw resistance: a field study

In the late sixties significant durability problems were encountered in a major metropolitan center in Canada. A review of prevailing construction practices was undertaken, together with a rigorous statistical analysis of the air content and compressive strength results. The main outcome of that study was a conclusion that a significant amount of the concrete placed on the job site had an unacceptably low air content. It is understood that these results, coupled with a review of specifications used in other metropolitan centers, provided the basis for revising the concrete materials specification in 1970. A similar review of strength and air content results was carried out at the end of that year. It was evident that an increase of approximately 1% had occurred in the average measured air content together with a small increase in compressive strength as the result of the specification changes. To assess the effect of this specification and further changes that have occurred since 1970, a third review was carried out in 1987. It was noted that during the intervening period a further increase in air content had taken place. Reasons for these changes are reviewed with respect to current construction practices. Also included is a review of the current specifications for this class of concrete in use in Canada. Key words: air content, compressive strength, specifications, inspection, statistics, durability.

Cavitation Inception Tests on Axisymmetric Headforms

Six axisymmetric headforms were tested in the 350-mm dia water tunnel at China Ship Scientific Research Center (CSSRC) for observation and measurement of cavitation inception. Among them, three of the flow patterns were displayed and analyzed by holography. Results of the tests show that cavitation inception on the headforms was closely related to the structure of the near-wall flow past the body with different flow regimes corresponding to different features of cavitation inception. By carefully fitting a trip wire of suitable height on a hemispherical headform, it was observed that under conditions of low air content, this artificial means of boundary transition may bring about a significant reduction in cavitation inception number.

The influence of method and frequency of irrigation on soil aeration and some biochemical responses of apple trees

The effect of various irrigation regimes on soil aeration was tested in a two-year experiment with 15 year-old apple trees growing in soil containing 67% clay. Irrigation was applied by sprinklers at four intervals ranging from 3 to 18 days and by trickle irrigation every 7 days. Each treatment received a total of 800–850 mm water from May until September. Irrigation by sprinkling at 7 day intervals appeared to be optimal for fruit growth. Less frequent irrigations resulted in smaller fruits; sprinkling at 3–4 day intervals, as well as trickle irrigation reduced the fruit growth rate in July. Leaves from plots irrigated once every 3–4 days had a low chlorophyll content and accumulated relatively large amounts of ethanol, particularly when grafted on the Khashabi rootstock, which is highly susceptible to damage caused by inadequate soil aeration. With increasing intervals between irrigations, the resistance of the leaf surface to the diffusion of water vapour measured prior to irrigation increased, and water loss relative to that from an evaporation pan decreased. Sprinkling at intervals of 14 days resulted in maximal, and at 3–4 days in minimal, air contents of the soil when calculated as averages for the total period of irrigation. The decrease in soil air content with very frequent irrigations was particularly marked in the upper soil layer; this same layer also had a relatively low air content near the emitters in trickle irrigation. After each irrigation, relatively large amounts of ethylene accumulated in the soil atmosphere, indicating inadequate soil aeration, particularly with sprinkling intervals of 3–4 days and at a depth of 30 cm. However, the influence of the irrigation treatments on the oxygen and carbon dioxide contents of the soil atmosphere was small and not consistent.

The effect of fillers on strength of cement mortars

The effect of three fillers (ground limestone, dolomite and basalt) on the strength of cement mortars was studied on 1:2.75 mixes having a w/c ratio of 0.70. The filler content ranged from 10 to 40% of the cement weight and their fineness (specific surface) from 1,150 to 11,200 sq. cm per g. Results confirmed earlier conclusions that fillers effect on strength is primarily an accelerating effect on the cement hydration. The improvement in strength is essentially the same for all non-pozzolonic fillers increasing with both filler content and fineness. In part, this improvement in strength is attributable to the increase in the density of the mix (i.e. a lower air content) associated with the use of fillers. There is some indirect evidence that monocalcium carboaluminate is formed when the finest limestone filler (10,300 sq. cm per g) is used. This formation, however, apparently does not affect strength.

Soil-physical aspects of zero-tillage experiments.

Structural determinations (visual rating, penetro-meter resistance, core sampling) in zero-tillage experiments on various soils (marine loam, river clay, sand etc) showed greater soil densities in unfilled plots than after plowing (20 cm), while mean pore-space and standard deviation of pore-space were generally lower in untilled plots. Moisture content at pF2 was often lower on untilled plots, and the latter possessed many more spots of low air content than ploughed plots did. Satisfactory yields of potato of good quality were produced, at least on medium-textured soils, after several years of zero-tillage. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Growth reactions of carnation, measured by net photosynthesis, on different air contents of the soil.

In pot experiments, Dianthus caryophyllus plants grown for 2 1/2 months at soil-air levels of 20, 10 or 5% (v/v) produced approx. equal amounts of dry matter, but fresh-matter production at 5 and 10% soil air was 13 and 2% lower than at 20% soil air. The effect of aeration on growth (photosynthesis) increased with increasing light intensity. Decreasing content of soil air from 20, 10 and 5% to 5 and 2.5% respectively was accompanied by an immediate reduction of photosynthesis to a fairly constant level. This reduction increased with increasing light intensity. An increase in soil air from 2.5 to 20, 10 or 5% gave a recovery of photosynthesis which at the two lowest light intensities was complete within 1-3 days when the period of low air content was not >14 days. At the highest light intensity the recovery of photosynthesis was slower. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Corrosion Processes in Carbonated Beverage Cans★

Abstract Describes work undertaken to minimize occurrence of perforations and excessive iron pick up in carbonated beverage cans. Corrosion mechanism was one of attack on steel base of cans stimulated by reduction processes occuring at areas of exposed tin or other cathodic regions. Best solution was limiting galvanic current in the can through reducing corrosivity of beverage and control of metal exposure in the can. Short time test methods were devised to evaluate beverage corrosivity. A low air content was essential and control over other depolarizers in beverage led to lower corrosivities. Improvements made in organic coating systems and metal exposure in the side seam and double seam regions reduced corrosion currents so that perforations were no longer a problem and so that iron pick up was effectively reduced. 8.3.2