Volumetric Air Flow Rate Research Articles

空気圧が作用した排出管付ホッパからの混合粉体の流量に関する実験的研究

An experimental study was carried out in which an efflux tube is attached vertically to the efflux orifice of a hopper, and the flow rate of powders flowing out of the tube and the pressure in a tube are controlled. The air from a compressor is blown into the tube, and its position is fixed directly below the orifice. As samples, mixed powders, i. e., the same kinds of powders having different particle diameters (glass beads), different kinds of powders having the same particle diameters (glass beads and styrol resin) and additives of a flow-improving agent, talc to glass beads are used. A flow rate of powders and the pressure distribution in a tube are measured for various combinations with volumetric flow rates of air and mixing ratios of powders or additive rates of talc.It was found that a flow rate decreases if the volumetric flow rate of air increases, and their relationships become nearly a straight line both in the uniform down-flow state and in the discontinuous state for all samples and when tho gradients of those straight lines are affected by the mixing ratios and the additive rate of talc. The curve shapes of the pressure distribution differ with the volumetric flow rate of air, and its minimum values exist. The positions of these minimum values shift upward if the volumetric flow rate of air increases and differ with the kinds as well as with the mixing ratios of the powders and the additive rate of talc.

Some effects of pseudoplasticity on hold-up in aerated, agitated vessels

The flow curves of four pseudoplastic sodium carboxy methyl cellulose (CMC) solutions are reported. Each solution was air sparged at rates up to 1 vvm (vvm is the volumetric flow rate of air per minute per volume of liquid in the vessel) in a 0.56 m diameter agitated vessel of Rushton dimensions and power inputs (up to 2.0 W/kg) and hold-ups have been measured. The ratio of gassed to ungassed power versus aeration number is compared with similar data from the agitation of Newtonian fluids and is correlated by an empirical equation proposed by Kudrna. The reported hold-ups are in the range 1.5 – 8% and, for equivalent sparging and agitation conditions, increasing pseudoplasticity leads to decreasing hold-up. This decrease is due to an increasing proportion of large bubbles which have a short residence time. For each CMC solution, hold-up, aeration rate and power input can be related by ϵ H ∝ ϵ 0.3 V s 0.7 The technique for measuring hold-up allows surface topographies to be determined. These topographies suggest that when the level of agitation is well matched to the sparge rate, the upper surface of the dispersion is relatively level.

Application of Vortex Shedding and Fluidics to the Control of Volumetric Flow Rates

The phenomenon of vortex shedding behind a bluff body in a fluid stream was investigated to determine its applicability to the measurement of the volumetric flow rate of air. Laboratory tests were performed to determine the best bluff body configuration for generating vortex-dependent pressure signals which could be sensed and processed by fluidic circuits. The feasibility of using fluidics to sense the vortex shedding frequency and to produce a usable output signal was demonstrated by tests performed on a volumetric flow controller consisting of a rectangular bluff body, fluidic circuitry, and a diaphragm-actuated butterfly valve.

Heat-transfer characteristics of a bubble-induced water jet impinging on an ice surface

An experimental study on the heat-transfer characteristics of a bubble-driven water jet impinging on an ice surface was conducted. Two Lucite columns, one 1·829 m high and 0·286 m in diameter, and the other 1·219m high and 0·140m in diameter were used. Water levels were maintained at 0·762 and 1·524m in the large column and 0·840m in the small column. Hypodermic needles with openings 0·152, 0·406 and 0·838 mm were used in bubble formation covering a volumetric air flow rate from 7·39 × 10 −8 to 9·91 × 10 −7 m 3/ s. To simulate winter environmental conditions in Northern America, the water temperature at the column bottom was thermostatically maintained at its temperature of maximum density, i.e. about 4°C. Cylindrical blocks of ice having diameters slightly less than those of the columns were supported at the column top while maintaining a proper immersion of the melting surface in the water level. The experimental results can be well represented by Nu = 630( d n ) 0·4( Re n ) 0·391 (1) for 8 < Re n < 10 3. The Nu is defined in terms of heat-transfer coefficient over the sample cross sectional area, the sample diameter, and thermal conductivity of water, and Re n is defined in terms of the air flow characteristics at the nozzle exit. The effect of both water levels and column diameter were found to be absent in the correlation. Using a Reynolds number based on the bubble-induced water jet flow characteristics, the experimental results were compared with the limited results reported on heat transfer between a round air jet and a plane surface held normal to the jet flow (modified to apply to water flow). The least-square analysis expression, Nu = 0·00010( D s ) −1·2( Re α ) 1·311 (2) indicating the absences of both nozzle diameter and height of water level, was found to represent the data extremely well. The above expression under- and overestimates Nu for lower and higher Re a values than those predicted from the expression representing pure water jet Nu = 1·94( Re α ) 0·55. However, in view of the numerous assumptions and wide differences in experimental parameters, the agreement is still considered to be remarkably good.

A recycle flow flotation machine model

Residence time measurements were made on a Denver laboratory flotation machine with and without the DR ring assembly. Soluble and insoluble tracers were used (a dye and fine quartz, respectively), and the variables studied were tank liquid volume, V , water and air volumetric flow rates, Q and Q A respectively, and some geometric and design variables. By analogy with nominal residence time, t N (= V Q ) , a term “effective residence time” t E is defined by: f(t)= exp[− t t E where f( t) is the fraction of tracer remaining in the tank at time t. Perfect mixing is indicated if and only if: (i) data satisfies the exponential relationship; and (ii) t E t N = 1 . Using the soluble tracer the machine behaved substantially as a perfect mixer under all operating conditions, except with the DR ring at values of Q A nearly double the natural aeration capacity of the machine; condition (i) above was satisfied, but t E t N ∼ 1.1 . With the insoluble tracer the machine behaved as a perfect mixer only without air. As Q A increased, t E t N increased from unity to about 1.2, and the effect was emphasized by the DR ring. In all cases condition (i) above was satisfied. A model in which the flow pattern in the tank includes a large component of pulp recirculation through the impeller region is developed. This model can account for the experimental findings but the details remain to be elucidated.