Liquid Volume Flow Rate Research Articles

Modelling deposit growth on tilted rotating cylindrical substrate in centrifugal spray deposition

Centrifugal spray deposition (CSD) using a tilted rotating cylindrical substrate may offer considerable technical benefits over the conventional CSD process using a reciprocating substrate in producing ring preforms. A model has been developed to calculate the deposit growth rate as a function of the liquid volume flowrate, the substrate radius, the tilt angle, the position of the atomising disc, and the longitudinal position at the substrate. The deposit band length is determined by the substrate radius and tilt angle. The distribution of the deposit growth rate is symmetrical provided the atomising disc is positioned on the substrate axis or displaced along the direction perpendicular to the tilt plane. For a tilt angle of <50·46°, the deposit thickness uniformity can be improved by increasing the displacement. A tapered deposit with a controlled gradient can be obtained if the atomising disc is positioned offcentre on the tilt plane.

Infiltration of a liquid finger down a fracture into superheated rock

A finger or ribbon of liquid water flowing down a fracture in an unsaturated rock matrix begins to boil when it passes the boiling‐point isotherm. The length of the infiltrating finger increases with time; boiling of the water in the fracture is maintained by heat conduction from the surrounding superheated rock. An intrinsic length scale in this problem is l3 = (ρlQ0h/kmβ)½, where Q0 is the volume flow rate of liquid across the boiling‐point isotherm, h is the enthalpy change on boiling, km is the thermal conductivity of the matrix rock, and β is the ambient temperature gradient. Initially, while (kt)½ &lt;b, the length l(t) of the water finger increases rapidly, proportional to l3 (kt)¼/b½, where k is the thermal diffusivity of the matrix and b is the ribbon width. A corresponding result is given for a cylindrical finger. If water continues to infiltrate beyond the time b2/k, the liquid penetration ultimately stabilizes at a distance l of order l3 below the boiling‐point isotherm, even though the temperature distribution continues to evolve. Numerical calculations show that l depends only weakly on the ribbon width or on the radius of a cylindrical finger.

Monodisperse Sprays for Various Purposes — Their production and characteristics

AbstractThe production of liquid sprays represents a key technology for a wide range of industrial proceses. Most applications currently use pressure or air‐assisted atomization, resulting in the production of polydisperese sprays. Recent advances in experimental and numerical techniques for investigating liquid spraying processes, however, have enabled a closer examination of parameter optimization, leading to the conclusion that in may cases, a much narrower size distribution, or even a monodisperse spray, may exhibit many advantages. Currently monodisperse droplet generators, or drop‐on‐demand generators, do not meet this challenge of producing monodisperse sprays, primarily owing to the very low volume flow rate of liquid which is atomized. In the present work, a monodisperse sprya generator is introduced, which overcomes this difficulty for many applications.

Digital sampling of low fluid flow: application to coronary flow measurements

A novel, simplified and inexpensive solution to the on-line monitoring of low fluid flow is reported. The method can utilise a variety of common liquid flow sampling devices (i.e. fraction collector volumeters) as a front-end, constant-volume dispenser coupled to a described sample-and-hold circuit. The latter, on triggering, samples a variably set ramp voltage which is directly proportional to liquid volume flow rate. The system is easily calibrated, has a wide dynamic range of volume flow rates, and can be configured accurately for high signal resolution of very low flow phenomena. An application to coronary flow measurement is provided as well as circuit descriptions and typical performance parameters which can be measured and adjusted for optimisation.

Decline in lung liquid volume and secretion rate during oligohydramnios in fetal sheep.

Reduced amniotic fluid volume often results in fetal lung hypoplasia. Our aim was to examine the effects of prolonged drainage of amniotic and allantoic fluids on lung liquid volume (Vl), secretion rate (Vs), and tracheal flow rate (Vtr) in fetal sheep. In five experimental animals, amniotic and allantoic fluids were drained from 107 to 135 days of gestation. The volume of fluid drained from the experimental animals was 411.8 +/- 24.4 ml/day (n = 140). In six control animals, amniotic fluid volume was 747.7 +/- 89.7 ml (n = 15). Wet and dry lung weights were 20-25% lower in experimental fetuses than in control fetuses. Fetal hemoglobin, O2 saturation, arterial PO2, pH, and hematocrit were unchanged by drainage. During the drainage period, Vl was up to 65% lower, Vs was up to 35% lower, and Vtr was up to 40% lower in experimental fetuses than in control fetuses. We conclude that prolonged drainage of amniotic and allantoic fluids decreases Vl, Vs, and Vtr in fetal sheep. These findings indicate that fetal lung hypoplasia associated with oligohydramnios may be the result of a prolonged reduction in Vl.

Field injection electrostatic spraying of liquid hydrogen

Uniform charged liquid-hydrogen drops are produced using the method of field injection electrostatic spraying. This method consists of forming a meniscus of liquid hydrogen at the end of a glass nozzle and injecting charge into the liquid using a sharp electrode raised to a high voltage. A small pressure drop across the nozzle results in a constant volume flow rate of liquid through the nozzle allowing a drop to form and drip off. As the amount of charge injection increases with the raised needle electrode voltage, the drop size decreases due to the increased electrostatic forces compensating for the surface tension forces. As a result, the drops drip off at an increased frequency. Eventually a charged jet forms which in turn breaks up into small uniform charged drops. A detailed description of the experimental apparatus is presented. Experimental results are presented and discussed.

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.

Performance of Air-Lift Pump

A basic equation of air-lift pump performance is derived from a simple momentum equation. In the analysis, frictional pressure drop in two-phase flow is expressed by means of liquid volume fraction of the mixture, and slug flow is assumed in order to obtain the relationship between liquid volume fraction and flow rates of both phases. The results predicted by the analysis are compared with experimental data of other investigators as well as of the authors. Good agreement with experimental data is shown in the ranges of 25 mm≤D (inner diameter)≤100 mm, 4 m≤L (length of pipe)≤42 m and 0.4<σ (submergence ratio)<0.8. To give a clear explanation for pump characteristics, the efficiency of air-lift pump is subdivided into two components, the pipe efficiency and the ideal discharge efficiency. A procedure of a pump design is proposed.

The investigation of a standing wave due to gas blowing upwards over a liquid film; its relation to flooding in wetted-wall columns

A theory is given to predict the shape and amplitude of a standing wave formed on a liquid film running down a vertical surface, and due to an upward flow of gas over the liquid surface. The wave is maintained in position by the pressure gradients induced within the gas stream by acceleration over the windward part of the wave; over the leeward part of the wave, the gas pressure is roughly constant due to breakaway of the gas flow.The wave amplitude is found to be very sensitive to gas velocity so that the theory predicts a critical gas velocity beyond which the wave amplitude becomes very large; this critical velocity is confirmed by experiment, and the experiments confirm the predicted wave shape. The critical gas velocity also agrees reasonably well with published values of the flooding velocity in empty wetted-wall tubes; this velocity is defined as the point at which countercurrent flow of gas and liquid becomes unstable. The phenomenon of flooding, which has puzzled chemical engineers for many years, may thus be due to wave formation on the liquid film.From the theory are derived three dimensionless groups, namely, Weber number $We \equiv \rho_g U_c^2t_0|T$, liquid-film Reynolds number $Re \equiv 4\rho_l Q|\mu, and Z \equiv T(\rho_l|\mu g)^{1/3}|\mu$. Here Uc is the critical gas velocity, Q is the liquid volume flow rate per unit wetted perimeter, ρg and ρl are the gas and liquid densities, μ is the liquid viscosity and T is its surface tension; $t_0 = (3\mu Q|\rho_lg)^{1/3}$ is the liquid film thickness in the absence of gas flow. We, Re and Z are uniquely related at the flooding point, and a diagram is presented to show this relation. This diagram will enable designers to predict flooding in wetted-wall tubes, though more experimental verification is required.