Constant volume method

The apparatus necessary for the constant volume method is described in ISO 1399 [22] and BS 903, part A17 [23]. It consists of a metal cell having two cavities separated by the test rubber sheet. The high pressure cavity is filled with the test gas at the required pressure, and this pressure is measured and should be kept constant during the measure. The increase in pressure on the low pressure side is measured as a function of time. The curve obtained follows the shape shown in Hgure 7.14. Thus 

FIGURE 7.14 Kinetics of drug transfer through the skin using a patch (transdennal system) for various values of the diffusivity in the polymeric device. 1 D = 4.4 10- 2 D = 

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The adsorption of carbon dioxide or oxygen on praseodymium samples was measured by a constant-volume method using a calibrated Pirani vacuum gauge. Praseodymium oxide was heated in oxygen (4 kPa) at 775°C for 1 h, then evacuated at 750°C for 0.5 h just before the measurement. The sample of praseodymium oxychloride was prepared from praseodymium chloride by heating under oxygen flow... 

The apparatus for constant volume method (Figure 17.1) consists of a metal cell having two cavities separated by the test piece. The high pressure cavity is filled with the test gas at the required pressure and this pressure must be measured to an accuracy of 1%. 

The test cell is similar to that for the constant volume method, the test piece dividing the cell into high and low pressure cavities. The essential difference is that the low pressure side is connected to a device to measure the volume increase as gas diffuses to the low pressure side whilst maintaining constant pressure. In ISO 2782, a graduated capillary tube is used to measure the volume change and the tube may be arranged either vertically or horizontally. In the vertical arrangement, a U-tube capillary... 

As commented in Section 2.1, the vertical capillary type of apparatus requires considerable care to set up and operate. A horizontal capillary results in a little more simple apparatus compared to a vertical capillary but in either case there is the extra necessity in the constant pressure method to accurately calibrate the capillary. Generally, the most convenient procedure is to use the constant volume method with an apparatus equipped with modern pressure transducers. 

ICUMSA Table Sucrose Correction to Be Applied in Lane Eynon Constant Volume Method... 

The establishment of the International Temperature Scale has been accomplished largely with the aid of measurements made with the helium gas thermometer. The most precise gas thermometry method is the constant-volume method, in which a definite quantity of the gas is confined in a bulb of constant volume Eat the temperature T to be determined and the pressure p of the gas is measured. A problem is encountered however in measuring the pressure a way must be found to communicate between the bulb and the pressure gauge. This is usually accomplished by connecting the bulb to the room-temperature part of the system by a slender tube and allowing a portion of the gas to occupy a relatively small, constant dead-space volume at room temperature. Thus, it is important that the gas volume in the pressure manometer be as small as possible. 

The adsorption isotherms of N2 and O2 were measured by constant volume method at ambient temperature. The adsorption properties deduced from the isotherms further confirmed the high crystallinity and Li exchange degree of LiLSX prepared in our lab. 

Zhao, H. Zheng, C. 2009b A new event-driven constant-volume method for solution of the time evolution of particle size distribution. Journal of Computational Physics 228, 1412-1428. 

Aromatic Compounds in NaX. Molecular transport of aromatic compounds in zeolite NaX has been studied by both nmr and uptake measurements. On the basis of Equation 4,and if surface barriers are absent, both methods should lead to comparable results. Though uptake measurements by the variable - pressure, constant - volume method by Biilow and coworkers (16,17) apparently are in satisfactory agreement with the nmr data (18), extensive uptake measurements including chromatographic methods are continuously found to yield diffusivities of about two orders of magnitude below these values (19,20). In principle, this discrepancy might be explained by the existence of surface barriers, which remain invisible for nmr studies of intracrystalline diffusion, but which may control the uptake rate. 

The intracrystalline diffusivities of llZSM-5 zeolite were directly measured for several hydrocarbons at higher temperatures (373-773 K) by the constant volume method. High silicious HZSM-5 zeolite, which has no activity for reactions, was used as the adsorbent. Aromatics benzene, xylene-isomers ortho-, meta- and para-xylene) and toluene, and paraffins n-hexane, n-pentane, p-octane and iso-octane, were used as adsorbates. Intracrystalline diffusivities of aromatics markedly depended on the minimum size of the aromatics and that of paraffins depended on the carbon number (molecular weight of the paraffins). A method was developed for predicting diffusivity in terras of pore diameter and molecular properties of hydrocarbons. This method was found to well represent the experimental results. 

High silicious HZSM-5 zeolites were synthesized from silica glass, and intracrystalline diffusivities of eight kinds of hydrocarbons within these zeolites in the temperature range of 373-773 K were directly measured by the constant volume method. A method was developed for predicting the diffusivity on the basis of the thermodynamics of an impure metal atom diffusing among metal atoms which form crystal lattices. Its validity was experimentally examined. 

The intracrystalline diffusivities of the hydrocarbons were measured under the conditions of the temperature range of 373-773 K and the pressure range of 0-1.33 kPa by the constant volume method [9]. The apparatus and the procedure are the same as employed by Hashimoto et al. [4,5]. Change in the total pressure caused by adsorption was recorded by use of a piezometric sensor with a transducer, the response of which is first enough to measure accurately the pressure change. To eliminate the influence of several factors (such as mass conductivity between the sorbate and the pressure sensor) on the pressure change, the blank tests were conducted without zeolites. Comparing these data obtained with those with zeolites, an uptake curve of the amount adsorbed was obtained. 

Detector response factors need to be accurately determined for good reproducible quantitative analyses [60]. They may be conveniently obtained by the constant volume method, that is, approximately 10 repeatable volumes of a sample containing an equal amount of the analytes are injected and the mean determined. Drf values are calculated hy normalising each peak area to that of the peak to be used as the reference. 

ISO 1399. 1976. Determination of Permeability to Gases—Constant Volume Method. 

BS 903, Part A 17.1973. Determination of the Permeability of Rubber to Gases (Constant Volume Method). 

BOO] Hydrogen solubihty measurements by a constant volume method 1600°C, < 22 mass% Cr, 0.1 MPa of hydrogen pressure... 

BOO] Hydrogen solubility, constant volume method, Fe rich alloys 1600°C, < 13 mass% Cu, 0.1 MPa H2... 

ISO 1399 Rubber, vulcanized - Determination of permeability to gases - Constant volume method... 

Monte Carlo methods for the artificial realization of the system behavior can be divided into time-driven and event-driven Monte Carlo simulations. In the former approach, the time interval At is chosen, and the realization of events within this time interval is determined stochastically. Whereas in the latter, the time interval between two events is determined based on the rates of processes. In general, the coalescence rates in granulation processes can be extracted from the coalescence kernel models. The event-driven Monte Carlo can be further divided into constant volume methods... 

Adsorption isotherm of nitrogen at liquid nitrogen temperature is determined by the gravimetric method (Fig. 2.13), or the constant volume method (Fig. 2.14). From the adsorption isotherm of nitrogen shown in Fig. 2.1S, the pore size distribution is calculated by Dollimore method (1964) and shown in Fig. 2.16. Cumulative pore size distribution is sometimes preferred when change of pore size distribution is involved, for example during thermal regeneration or activation of activated carbons. 

The ordinate of Fig. 6.2 represents this magnitude and the slopes of the straight lines in the figure can then be used to determine K Results obtained from Fig. 6.2 are compared with direct measurement by constant volume method in Table 6.1. 

Carbon dioxide solubility was also investigated in binary and ternary mixtures of esters, at high pressure. The goal of the study was to identify an appropriate system for CO2 capture. Solubility of CO2 was determined by the constant-volume method in mixtures of dimethyl carbonate (DMC) + diethyl carbonate, (DMC + propyl acetate, (DMC + propylene carbonate and DMC + ethylene carbonate, in the temperature range from 282.0 to 303.0 K. It is found that the solubility of CO2 in four mixed solvents follows the Henry s law, and the linear compound has a greater ability to dissolve CO2 than the cyclic compound at the same temperature [73]. 

The disk was mounted on the membrane-coupling holder, which can withstand up to a pressure of 150psi. The system ensures that there is no pressure drop or leak at any point. The transport properties of membranes were measured using the variable pressure constant volume method. Fig.l shows the experimental setup of gas permeation apparatus. The membrane holder or the diffusion cell has two compartments, the feed side and the permeate side. The permeate side was kept under vacuum for 24 hrs to remove residual gas molecules and to obtain accurate measurements. 

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