Measurement volume displacement

Flow, defined as volume per unit of time at specified temperature and pressure conditions, is generally measured By positive-displacement or rate meters. The term positive-displacement meter apphes to a device in which the flow is divided into isolated measured volumes when the number of fillings of these volumes is counted in some man-... 

Tlic density (p) of a substance is tlic ratio of its mass to its volume and may be expressed in units of pounds per cubic foot (Ib/ft ) or kilograms per cubic meter (kg/nv ). For solids, density can be determined easily by placing a known mass of the substance in a liquid and measuring tlie displaced volume. The density of a liquid can be measured by weighing a known volume of the liquid in a gradmitcd cylinder. For gases, tlie ideal gas law (to be discussed in Section 4.6) can be used to calculate tlie density from tlie temperature, pressure, and molecular weight of tlie gas. 

Determination of the porosity of a tablet presents the classic problem of defining the appropriate volume to be measured. The displacement medium may be able to penetrate the most minute crevices, as is the case for helium. Other displacement media, such as mercury, are unable to enter the smallest tablet crevices and thus produce different porosity values. Standardization of displacement media is therefore necessary for comparative evaluations. 

Nguyen et al. [205] designed a volume displacement technique that was used to measure the capillary pressures for both hydrophobic and hydrophilic materials. One requirement for this method is that the sample material must have enough pore volume to be able to measure the respective displaced volume. Basically, while the sample is filled wifh water and then drained, the volume of water displaced is recorded. In order for the water to be drained from fhe material, it is vital to keep the liquid pressure higher than the gas pressure (i.e., pressure difference is key). Once the sample is saturated, the liquid pressure can be reduced slightly in order for the water to drain. From these tests, plots of capillary pressure versus water saturation corresponding to both imbibitions and drainages can be determined. A similar method was presented by Koido, Furusawa, and Moriyama [206], except they studied only the liquid water imbibition with different diffusion layers. 

If the powder has no porosity the true density can be measured by displacement of any fluid in which the solid remains inert. The accuracy of the method is limited by the accuracy with which the fluid volume can be determined. Usually, however, the solid particles contain pores, cracks or crevices which will not be completely penetrated by a displaced liquid. In these instances the true density can be measured by using a gas as the... 

A routine method for determining relative crystallinity based on the amorphous bands in the spectrum has proved more rapid and precise than the x-ray method. In practice, the ratio of the 778 cm-1 (12.85 ft) and 2367 cm-1 (4.22 ft) band intensities is measured. Use of a ratio eliminates the thickness measurement and increases precision to about 1% at 50% crystallinity and considerably better at higher levels. A density measurement and an infrared crystallinity determination when combined give an estimate of the fraction of microvoids which can occur in molded specimens of polytetrafluoroethylene. The density of a sample is predicted on the basis of its crystallinity as measured by the infrared method and the difference between this density and the actual density measured by displacement in water is a measure of the microvoid content. This determination is precise to about 0,2% voids by volume. By the use of confirmatory infrared measurements, it is possible to check the possibility that the presence of a substantial percentage of voids may have led to erroneous indications of the molecular weight in the standard specific gravity test discussed earlier. 

Flow, defined as volume per unit of time at specified temperature and pressure conditions, is generally measured by positive displacement or rate meters. The term positive displacement meter applies to a device in which the flow is divided into isolated measured volumes when the number of fillings of these volumes is counted in some manner. The term rate meter applies to all types of flowmeters through which the material passes without being divided into isolated quantities. Movement of the material is usually sensed by a primary measuring element that activates a secondary device. The flow rate is then inferred from the response of the secondary device by means of known physical laws or from empirical relationships. 

This equation shows that R is given by the ratio of particle displacement velocity V to average carrier velocity , or equivalently to the ratio of channel void volume V° to the retention volume V. Thus R is experimentally accessible because V is the measured volume required to displace a given particle size" through the channel. However, the equation also shows that R is related to X, which is related to d through the previous equation. Thus a linkage is formed between particle diameter d and experimental retention volume V. It has been estimated that particle diameters accurate to 1-3% can be obtained by using this approach (2). 

We have seen above that mercury does not spontaneously penetrate the pores of the solid in the absence of pressure. This result is used to measure the volume displaced by the material + pores of a solid as a whole. The apparent density (or grain density) p is then calculated using the following expression ... 

Density of the Dry Cell Wall. The dry cell wall of wood has a density of approximately 1.5 g/cm when measured by pycnometric or volume-displacement methods. Somewhat higher values are obtained when using water as opposed to nonswelling displacement media such as toluene or benzene (22). 

The column is next washed with Milli-Q water to remove sea salt the wash is also directed to the waste container. The elution step follows the eluting solvent is delivered from a 50-mL syringe operated by a displacement pump (Sage Instrument Co.). In this manner, a precisely measured volume of solvent is directed through the column and through a special, low-dead-volume eluant path into a sealed, acid-cleaned linear polyethylene vial. 

The duration of the laser pulses is 0.3 ps the time interval between each shot of different wavelength is 20 ps. Thus, a set of the laser shots finishes in about 60 ps. At a towing speed of 5 knots, the displacement during 60 ps is estimated to cause a change of 3 % in the measurement volume thus, the four laser shots of different wavelengths irradiate almost the same volume. 

Some credence was given the latter of these alternatives by the observation that densities measured by displacement of helium in a gas pycnometry cell were essentially identical for the highest and lowest surface area products. The difference was less than 2Z. It is suggested that an intrinsically amorphous structure should have a range of void spaces due to inefficient filling of its volume, the net result of which should be a significantly diminished density compared to the highly crystalline form. Thus, we favor the view that the more amorphous products are composed of smaller, but essentially ordered, particles. 

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