Pressure/volume scanning

B) Changing the pressure or volume Pressure/volume scanning... 

Nowadays, for a thermodynainicist, /pVT-calorimetry (further referred to as scanning transitiometry, its patented and commercial name ) is the most accomplished experimental concept. It allows direct determinations of the most important thermodynamic derivatives it shows how, in practice, the Maxwell relations can be used to fully satisfy the thermodynamic consistency of those derivatives. Of particular interest is the use of pressure as an independent variable this is typically illustrated by the relatively newly established pressure-controlled scanning calorimeters (PCSC). - Basically, the isobaric expansibility Op(p,T) =il/v)(dv/dT)p can be considered as the key quantity from which the molar volume, v, can be obtained and therefore all subsequent molar thermodynamic derivatives with respect to pressure. Knowing the molar volume as a function of p at the reference temperature, Tg, the determination of the foregoing pressure derivatives only requires the measurement of the isobaric expansibilities as... 

For prediction of mold filling and flow-through dies, computer modelling is increasingly used. In addition to viscosity, measurements may be needed for specific heat, shrinkage, thermal conductivity, and pressure- volume -temperature (PVT) relationship. A differential scanning calorimeter (DSC) can be used for specific heal measurements. 

One way to discriminate between the possible problems is to perform a Beta Scan survey of the compression cylinders. A Beta Scan is a pressure-volume diagram describing the actual compressor cylinder end performance. The pressure inside the cylinder is plotted against the piston position. A piston position of 0% corresponds to the piston position closest to the cylinder head. A perfect pressure-volume diagram is shown in Figure 25-7 This is the Carnot Cycle. Figure 25-8 shows Beta Scans for several maladies affecting compressor valves. 

Simultaneous measurements of the rate of heat evolution and volume changes by phase transitions were carried out with a pressure-volume-temperature controlled scanning calorimeter up to 175 MPa. No pressure-temperature phase diagram for the compound under test 4-n-pentylphenyl-4-n-decyloxythiobenzoate, which has a nematic and three smectic phases, is given. 

The expoimental methods of measuring transition temperatures, wh her for crystal to mesophase, mesophase to mesophase, or mesophase to isotropic liquid, fall into four categories. A high pressure cell with optical detection is a common method [1,2]. High pressure diff ential thermal analysis (DTA) systems have been built [3]. In some cases DTA has been combined with optical cells for visual as well as thermal detection [4]. A variation of thermal detection of phase transitions is the high pressure differential scanning calorimetry system [5]. The technique that provides pVT data is based on measuring volume or density as a function of pressure for various isotherms [6-10]. A unique method is based on the thermobarometer developed by Busine [11]. 

Reviews on the activation of dioxygen by transition-metal complexes have appeared recently 9497 ). Details of the underlying reaction mechanisms could in some cases be resolved from kinetic studies employing rapid-scan and low-temperature kinetic techniques in order to detect possible reaction intermediates and to analyze complex reaction sequences. In many cases, however, detailed mechanistic insight was not available, and high-pressure experiments coupled to the construction of volume profiles were performed in efforts to fulfill this need. 

The authors have found similar stepwise intrusion on other materials. The low pressure (0.5-15 psia) intrusion curve in Fig. 11.5 was obtained using a scanning porosimeter which continuously plots the pressure and corresponding intruded volume on an XY recorder. Only in this continuous manner can the exact position and height of each intrusion step be fully determined. 

In those cases where pores are ink-bottle in shape, a method, proposed by Reverberi for calculating the sizes of the narrow and wide portions of the pore from intrusion-extrusion curves can be used. The method involves scanning the hysteresis loop by means of a series of pressurization and partial depressurization cycles in order to determine the volume of the wide inner portion of pores having neck radii in various radius intervals. 

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