Meniscus height

The last two equations relate the fractional conversion and the meniscus height. For first or second order mechanisms,... 

Ap is the difference between the densities of liquid and vapor g is the gravitational constant h is the meniscus height a is the liquid-gas surface tension of water. 

Therefore, the contact angle can be calculated from the experimentally measured meniscus height. 

The capillary rise technique is considered to be very useful for DL materials, especially if the angle is less than 90° and/or for measurements that are taken under different temperature conditions [192]. In this method, a sample material is immersed in a container filled with water and the meniscus height is measured with a microscope (see Figure 4.23). Contact angles between the water and DL are calculated using Equation 4.1 and by measuring the... 

Whether the meniscus height is measured with a cathetometer or a meter stick, it is important to have good illumination of the meniscus and to do the illumination in a consistent manner throughout a set of measurements. A sheet of white paper behind the manometer often provides good definition of the meniscus. Under many lighting conditions, illumination of this paper from behind may further improve the visibility of the meniscus. 

Fig. 7.7. The McLeod gauge. The principles of operation follow. Let the unknown pressure in a system be P when the Hg level is below point 1. Let the volume of the bulb and closed capillary above I be V, which is known. When the mercury is allowed to rise past point I, the gas is trapped and finally compressed into the capillary. Suppose that when the mercury in the reference capillary is at 0, the mercury in the dead-ended capillary is B mm below 0 (i.e., the pressure of the compressed gas is B mm). Since the initial pressure-volume product equals the final pressure-volume product, PV = pv, the volume in thecapillary v will be the height B times the area of the capillary bore A. Thus P = pv/V = B (A/V). Since A and V are known and B is measured, the original pressure (P) may be calculated. Most commercial gauges are provided with a calibrated scale which presents pressures directly. Alternatively, it is possible to devise a linear scale for the McLeod gauge, in one such method the mercury height in the closed capillary is always adjusted to the same point (B0), and then the difference in meniscus heights between the two capillaries is measured (AB). For this case the pressure being measured is P = pv0/V = (B0A/V)AB. As in the previous example, the quantity in parentheses represents the gauge calibration constant.

Consider a vertical solid wall of a crucible consisted of two macroscopic phases a and / separated by a plane intersecting the solid wall by an horizontal straight line (Figure 1.29.a). The intrinsic contact angles on the two phases are such that 0 > 6P, and for the sake of simplicity 0 > 90° and 0P < 90°. Moreover, we assume that the level of liquid in the crucible far from the wall is such that h2 <3C z p, where z p is the maximum meniscus height on the p phase i.e., z p would be the meniscus rise on a homogeneous vertical plate of j3 (equation (1.23)). During... 

Slit-lamp examination without dyes or anesthetic Observe tear meniscus height Observe quality of tear film Evaluate integrity of ocular surface Evaluate lids, lashes... 

Meniscus height Sediment layer height Spacing between parallel flat plates, charged flat plates, and flat electrodes in electrolytic cell Specific enthalpy... 

If the capillary is circular in cross section, the meniscus will be approximately hemispherical with a constant radius of curvature a/(cos 0), where 6 is taken to be the static contact angle (Fig. 10.2.1). Departure from hemisphericity is associated with the variation in liquid pressure over the surface due to the difference in gravitational force over the meniscus height h. A measure of the hydrostatic gravitational force to surface tension force is given by the Bond-number... 

A volume V of a liquid of density p and surface tension a is contained between two parallel, concentric circular disks that are oriented horizontally and separated from each other by a distance a. A thin circular capillary tube of radius a is connected to the upper disk at its center and oriented vertically. The liquid level in the tube measured upward from the center of the space between the disks (all) to the meniscus is H (the meniscus height itself is taken to be small). The distance the liquid extends radially outward between the disks, measured from the centerline of the... 

It was necessary to make the correction for the meniscus height, z, since z is of the same order of magnitude as h for this system, and its neglect could produce an error as large as 30%. 

Meniscus Height Changing in the Capillary and Ultraviolet Spectra of Ascorbic Acid and Paracetamol High-diluted Solutions... 

Meniscus height reduces on an average by 13.75%. Lowering of menisctts height by 23.7%, in comparison with more concentrated solution, is also observed for the sample with ascorbic add content of 10" mole/1. 

FIG LIRE 1 Values of meniscus height in the capillary of ascorbic acid solutions (concentration, mole/1). 

The same dependence is observed for dilution of paracetamol solution with concentration of 10" mole/1. So, at this concentration meniscus height is 0.7 nun. 

Growth of meniscus height in the capillary is observed further for solutions with the following dilution. This process is motivated by very high dilution that is the solution, according to its composition and properties, tries to attain the state of pure solvent. 

We have studied solutions of ascoibic acid and paracetamol mixture. It is necessary to note that not uniquely deOied change of meniscus height is observed in solutions containing simultaneously two active substances. Meniscns of one-component solutions is narrower than that of water, but in two-component solutions both reduction and increase of meniscus height values are possible in comparison with water (Figure 3). 

Increase of meniscus height in comparison with the solvent is observed in solutions with concentrations of diluted compounds of 10" , 10" , 10 , and lO" mole/1. Growth of meniscus height above such value of the solvent can be explained by the change in SSD effect display. 

Ascorbic acid Electronic spectroscopy Meniscus height changing Paracetamol solution Supersmall doses... 

Interfacial Electrokinetic Flow, Fig. 4 Spatiotemporal evolution profiles of the electrospray meniscus height R showing the initial stages of microjet formation obtained through an axisymmetric longwave model [11]... 

A similar axisymmetric model to that described above, assuming the jet to be slender such that the longwave approximation holds (Ro < L, in which Rq is the initial meniscus height and L the characteristic length scale of... 

Figiire 2. (a) A section of the numerically generated surface profile, (b) The possible apparent contact an es(0=7O°) for system in a and in (c) for a different surface. The lines indicate the meniscus height at a constant immersion depth with varying apparent contact angle the intersections are the available equilibrium positions for the contact lineOl. 

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