Liquid drop weight

It is to be noted that not only is the correction quite large, but for a given tip radius it depends on the nature of the liquid. It is thus incorrect to assume that the drop weights for two liquids are in the ratio of the respective surface tensions when the same size tip is used. Finally, correction factors for r/V < 0.3 have been determined, using mercury drops [37],... 

The surface tension of a liquid is determined by the drop weight method. Using a tip whose outside diameter is 5 x 10 m and whose inside diameter is 2.5 x 10 m, it is found that the weight of 20 drops is 7 x 10 kg. The density of the liquid is 982.4 kg/m, and it wets the tip. Using r/V /, determine the appropriate correction factor and calculate the surface tension of this liquid. 

The determination of the mechanical shock sensitivity or impact sensitivity is applicable to both solids and liquids. The principle involved is that a drop weight falls from a specified height onto the confined test sample. The load can be varied by changing the height of the drop and by changing the drop weight. 

This is one of the many detachment methods of which the drop weight and the Wilhelmy slide methods are also examples. As with all detachment methods, one supposes that, within an accuracy of a few percent, the detachment force is given by the surface tension multiplied by the periphery of the surface (liquid surface) detached (from a solid surface of a tubing or ring or plate). This assumption is also found to be acceptable for most experimental purposes. Thus, for a ring, as illustrated in Figure 2.12,... 

A return to a more rational expression of the relation between drop weight and surface tension has been made by Iredale Phil. Mag. XLV. 1088, 1923). This expression rests upon the fact that different liquids may form drops of similar shape from tubes of different diameters. From this and from the assumption that rupture occurs at the point of maximum concavity the equation... 

By reversing the position of liquid and gas assumed in the preceding section we obtain the bubble pressure method. The theory corresponds closely with that of the drop weight and has been developed by Cantor, Feustel and Schrodinger (Ann. d. Physih, xlvi. 413,1915). 

As we shall have occasion to note in dealing with solutions, the composition of the surface phase is very different from that of the bulk liquid. When a liquid interface is newly formed the system is unstable until the surface phase has acquired its correct excess or deficit of solute by diffusion from or into the bulk of the solution. This process of diffusion is by no means instantaneous and, as has been observed in discussing the drop weight method, several minutes may elapse before equilibrium is established. In the ripple method the surfece is not renewed instantaneously but may be regarded as undergoing a series of expansions and contractions, thus we should anticipate that the value of the surface tension of a solution determined by this method would lie between those determined by the static and an ideal dynamic method respectively. 

The shock sensitivity of materials are also frequently evaluated in a drop weight test. A variety of drop weight testers have been developed, but the standard device used to evaluate the sensitivity of liquid propellants is test No. 4 of the Joint Army-Navy-Air Force Panel on Liquid Propellants (2). A sample of material (usually less than 0.1 gram) is confined in an enclosed volume, and a calibrated weight is allowed to... 

There are numerous other methods for measuring surface tension that we do not discuss here. These include (a) the measurement of the maximum pressure beyond which an inert gas bubble formed at the tip of a capillary immersed in a liquid breaks away from the tip (the so-called maximum bubble-pressure method) (b) the so-called drop-weight method, in which drops of a liquid (in a gas or in another liquid) formed at the tip of a capillary are collected and weighed and (c) the ring method, in which the force required to detach a ring or a loop of wire is measured. In all these cases, the measured quantities can be related to the surface tension of the liquid through simple equations. The basic concepts involved in these methods do not differ significantly from what we cover in this chapter. The experimental details may be obtained from Adamson (1990). 

Trauzl Block and Drop Weight Test Values for Liquid Reaction Intermediates. U 22... 

Drop-weight method. Here, the liquid is allowed to flow out from the bottom of a capillary tube. Drops are formed which detach when they reach a critical dimension. The weight of a drop falling out of a capillary is measured. To get a precise measure, this is done for a number of drops and the total weight is divided by this number. 

Figure 2.9 Maximal bubble pressure and drop-weight method to measure the surface tension of liquids.

There are static and dynamic methods. The static methods measure the tension of practically stationary surfaces which have been formed for an appreciable time, and depend on one of two principles. The most accurate depend on the pressure difference set up on the two sides of a curved surface possessing surface tension (Chap. I, 10), and are often only devices for the determination of hydrostatic pressure at a prescribed curvature of the liquid these include the capillary height method, with its numerous variants, the maximum bubble pressure method, the drop-weight method, and the method of sessile drops. The second principle, less accurate, but very often convenient because of its rapidity, is the formation of a film of the liquid and its extension by means of a support caused to adhere to the liquid temporarily methods in this class include the detachment of a ring or plate from the surface of any liquid, and the measurement of the tension of soap solutions by extending a film. 

For rapid work, requiring an accuracy of about three-tenths per cent., Sugden s modification of the maximum bubble-pressure method is probably the most convenient very little apparatus is required, and a complete measurement can easily be made in 15 minutes. Two or three cubic centimetres of the liquid are all that is necessary. The drop-weight method (using Harkins s indispensable corrections) is also simple and equally accurate. 

Ring method — Method to determine the - interfacial tension in liquid-gas systems introduced by Lecomte du Noiiy [i]. It is based on measuring the force to detach a ring or loop of a wire from the surface of a liquid. The method is similar to the -> Wilhelmyplate method when used in the detachment mode [ii]. See also -> electrocapillarity, -r electrocapillary curve, -> Gibbs-Lippmann equation, - Wilhelmy plate (slide) method, - drop weight method, - Lippmann capillary electrometer. 

Beyond this, the combination of a high pressure optical cell with a magnetic coupling balance provides a possibility to measure the weight of the liquid drop and the related density difference between the drop phase and the surrounding fluid phase with time. Thus, a relation between the mass transfer across the fluid interface and the interfacial tension can be detected. 

Calculate the frictional pressure drop for a two-phase fluid flowing through a tube 0.62 in (0.0158 m) in inside diameter D and 20 ft (6.1 m) in length L at a rate of 100 lb/h (45.4 kg/h). The mixture is 50 percent gas by weight and 50 percent liquid by weight, having the following properties ... 

Only the two first methods allow measurement of the temperature coefficient of the surface energy. The maximum bubble pressure technique is well-adapted for metals with low and intermediate melting points and specially for oxidizable metals, while the sessile drop technique has been applied with success to measure ctlv values up to 1500°C. The drop weight method is particularly useful for very high melting-point metals because it avoids liquid contact with container materials. This is also true for the recently developed levitation drop technique that analyses the oscillation spectrum of a magnetically levitated droplet. 

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