Piezometric measurement

Conventionally, molecular uptake is recorded gravi-metrically [18-20]. Alternatively, for a limited supply of adsorbate, molecular uptake may also be calculated from a knowledge of the time dependence of the pressure (piezometric method [21, 22]) or composition of the gas phase. Changing the sorbate pressure by a step change of the gas volume has proved to be a very efficient method for following fast sorption processes (single step method [23, 24]). The sorption uptake may also be measured volumctrically by mans of a gas burette arrangement [25]. 

The level water reaches in an artesian well reflects its pressure, called the piezometric, or confined, water head (Fig 2.6). In boreholes drilled at altitudes that are lower than the piezometric head, water will reach the surface in a jet (or wellhead pressure) with a pressure that is proportional to the difference between the altitude of the wellhead and the piezometric head. The piezometric head is slightly lower than the water level in the relevant phreatic section of the system due to the flow resistance of the aquifer. Confined aquifers often underlay a phreatic aquifer, as shown in Fig. 2.7. The nature of such groundwater systems may be revealed by data measured in boreholes and wells. The water levels in wells 1 and 2 of Fig. 2.7 did not rise after the water was encountered, and both wells reached a phreatic aquifer. Well 3 is artesian, and the drillers account should include the depth in which the water was struck and the depth and nature of the aquiclude. The hydraulic interconnection between well 1 and well 3 may be established by... 

Measurement of the transient adsorption or desorption curve for a sample of zeolite crystals exposed to a step change in ambient sorbate concentration (pressure) provides, in principle, a simple and direct method of measuring the intracrystalline diffusivity (D). Such measurements are conveniently carried out by gravimetric, volumetric or piezometric methods. The... 

Sorption Rates in Batch Systems. Direct measurement of the uptake rate by gravimetric, volumetric, or piezometric methods is widely used as a means of measuring intraparticle diffusivities. Diffusive transport within a particle may be represented by the Fickian diffusion equation, which, in spherical coordinates, takes the form... 

Fig. 18. Self-diffusion coefficients of benzene in NaX at 458 K PFG NMR, O (97) and (92) (JENS, A (13) deduced from NMR lineshape analysis, (10). Comparison with nonequilibrium measurements T, sorption uptake with piezometric control (93) , zero-length column method (96) o, frequency-response and single-step frequency-response technique (98). The region of the results of gravimetric measurements with different specimens (92) is indicated by the hatched areas. Asterisked symbols represent data obtained by extrapolation from lower temperatures with an activation energy confirmed by NMR measurements.

Saturated zones are common in porous material, and provide significant pathways for the subsurface transport of water and solutes. The term "ground water" commonly refers to continuously saturated zones of appreciable thickness. Saturated conditions also occur on a small scale or short term basis in association with the infiltration and drainage of precipitation or surface runoff. As indicated previously, the pressure and elevation components are the primary contributors to the total moisture potential in the saturated zone. These two are commonly combined into a "piezometric head", representing the addition of the water pressure head to the elevation at which the pressure head is measured. The hydraulic conductivity does not change significantly with... 

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. 

Numerous hydraulic tests were carried out, during the various project phases, either in an isolated borehole or between boreholes. Hydraulic experiments consisted of pulse tests, constant head injection and/or extraction and constant rate injection/extraction using borehole intervals delimited in FBX 95001, FBX 95002, BOUS 85.001 and BOUS 85.002 (Figure 1). Both water flow and piezometric level measurements for borehole intervals are available. Continuous pressure monitoring has allowed detecting crosshole responses during pulse testing these have then been used to calibrate the hydraulic conductivities of fractures. 

Single-component equilibrium isotherms are commonly measured by gravimetric or piezometric methods (see Fig. 9). An alternative technique based... 

In both gravimetric and piezometric experiments it is generally desirable to make the measurement over a small differential concentration change in order to ensure that the assumption of system linearity is fulfilled. Under these conditions the transient sorption curve (expressed as fractional approach to equilibrium) should be independent of either the step size or direction (adsorption or desorption). Varying the step size and direction thus provides a simple and sensitive experimental test for system linearity. 

The piezometric method involves following the pressure response in a dosing cell connected to an uptake cell containing a sample of the adsorbent. According to the results reported in the hterature, the piezometric method can be used to accurately measure intracrystalline diffusivities for fast diffusing and strongly adsorbed species such as benzene on NaX [15,16]. Furthermore, it is also claimed to provide the required accuracy needed to study combined intracrystalline processes such as diffusion and first-order reaction [17]. 

We conclude that the piezometric technique is capable of yielding reliable diffusivity data provided that the pressures are monitored in the uptake cell and the limitations imposed by the time constant of the valve and finite heat dissipation rates are respected. For strongly adsorbed species theses restrictions limit the applicability to relatively slow processes (half times of at least several seconds). For weakly adsorbed species somewhat faster diffusion processes can be measured. A detailed assessment of the range of validity of this method, as a function of the system variables, has been presented by Schumacher and Karge [19]. In reviewing earlier reported piezometric diffusivity data, the values derived from measuring only the pressure in the dosing cell should not be accepted without further detailed analysis. 

Fig. 5 Loading dependence of corrected diffusivities (Do) for ethylbenzene in H-ZSM-5 at various temperatures, measured by piezometric technique. From Schumacher et al. [20] with permission...

Detailed test section is shown in Figure 6. The test section was provided with pressure taps (piezometric ring) at various points in the upstream section and downstream section, sometimes on the pipe fitting like bend, elbow, etc. The static pressure at the different points was measured by means of simple manometer or piezoresistive pressure transducers. The main idea of putting long upstream and... 

During this period, the results of detailed piezometric and acoustical measurements were published. These studies were performed at the Thermophysical Institute of the Siberian Branch of the Academy of Sciences of the USSR under the supervision of A. N. Soloviov and E. P. Sheludyakov [2.15-2.19]. In this investigation Freon-21 having a purity of 99.8% (moisture, 0.19% nonvolatile residue, 0.004%) was used. 

For the experimental investigation of compressibility of superheated and saturated vapors, the method of the constant-volume nonballasted piezometer was employed. The fundamental variables (pressure, temperature, and mass of the substance) were measured with instruments of the same class as those used in the work of MEI. The distinguishing feature of the piezometric rig was the use of a membrane zero indicator of pressure of the electrocontact type. The sensitivity of this instrument reached 1 mm water column, but the zero point drifted by 10 mm water column. The authors in Refs. [2.19, 2.21] evaluated the scatter of experimental points on the saturation curve as 0.4% for pressure, and the repeatability of presssure during the forward and reverse tracing along the constant-volume lines was 0.15%. 

The flow within the porous medium is produced by the head difference, A/f = AP- pgL, between the bottom and top of the porous medium. This quantity is easily measured using height difference H (i.e. A/f = pgH ) between the water levels in two piezometric tubes cormected to the bottom and top of the porous... 

The forces on the cone end and on the friction sleeve are continuously measured. When a so-called piezometric cone is used (CPTU), the pore water pressure is... 

The most widely used method for ionic liquid density measurement is the vibrating-tube densitometer a method which relies on a calibration as a function of temperature and pressure using appropriate reference fluid.For many reported ionic liquids this is not routinely performed and corrections for the case of viscous fluids (i.e., >100 mPas) are often ignored. Despite these factors the densities of ionic liquids measured with vibrating-tube densitometers have a standard uncertainty to within 0.1%. Alternative methods include the calculation of density through speed of sound measurements or piezometric methods. Both approaches are relatively complex technically but present the advantage of providing extra thermodynamic property data. 

This method is typically valid when effluent concentrations are measured. When using a measurement device that allows the measurement of pore-water concentrations, other boundary conditions apply to the advection equation and Equation 15.12is not valid anymore (Kreft and Zuber, 1978 van Genuchten and Parker, 1984). Attention must also be paid to experimental artifacts arising from specific laboratory devices. For example, if injection is performed in a volume of water outside of the column (like a device to maintain the piezometric head), the actual injection condition is not an instantaneous step variation. Due to mixing with the volume of water, the injection is actually exponential. Not accounting for such effects can result in a serious bias in the estimated values of dispersivity (Novakowski, 1992). 

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