Sensitivity to pressure and temperature

Solvent Strength of Pure Fluids. The density of a pure fluid is extremely sensitive to pressure and temperature near the critical point, where the reduced pressure, P, equals the reduced temperature, =1. This is shown for pure carbon dioxide in Figure 2. Consider the simple case of the solubihty of a soHd in this fluid. At ambient conditions, the density of the fluid is 0.002 g/cm. Thus the solubiUty of a soHd in the gas is low and is given by the vapor pressure over the total pressure. The solubiUties of Hquids are similar. At the critical point, the density of CO2 is 0.47 g/cm. This value is nearly comparable to that of organic Hquids. The solubiHty of a soHd can be 3—10 orders of magnitude higher in this more Hquid-like CO2. 

Solid-Fluid Equilibria The phase diagrams of binai y mixtures in which the heavier component (tne solute) is normally a solid at the critical temperature of the light component (the solvent) include solid-liquid-vapor (SLV) cui ves which may or may not intersect the LV critical cui ve. The solubility of the solid is vei y sensitive to pressure and temperature in compressible regions where the solvent s density and solubility parameter are highly variable. In contrast, plots of the log of the solubility versus density at constant temperature exhibit fairly simple linear behavior. 

One steel diaphragm is exposed to the internal pressure, the other is exposed to the external pressure. Four gages are normally used. Two of them are sensitive to pressure and temperature, and two are sensitive to the temperature. A Wheatstone bridge is used for detection of the pressure. 

The rest of the system, valves, separators, heat exchanges, filters, and storage and piping for demanding applications is also fabricated using stainless steel. These components are also cost sensitive to pressure and temperature. 

The ultrasonic detector can only be used for GC separations. The eluent is excited to oscillations of 4-6 MHz in a small cell of 10-40 pL volume using an oscillator crystal. The phase displacement between the oscillator and the receiver (a phase meter) is influenced by the composition of the eluent and proportional to the molar fraction (carrier gas and eluted compound). The response factor is influenced by the differences of the specific heat ratio, Cp /Cv, between carrier gas and eluent. The main drawback of this detector is its high sensitivity to pressure and temperature changes so that a temperature stability of 0.001 °C is required. 

A general reference often consulted today for the physical and chemical properties of common chemicals is Lange s Handbook of Chemistry (Dean 1999), which lists many chemical compounds and their most important properties. It is organized into separate chapters of Physical constants of organic molecules with 4300 compounds and Physical constants of inorganic molecules, and lists each compound alphabetically by name. Some of these properties are very sensitive to temperature, but less sensitive to pressure, and they are listed as tables, or more compactly as equations of the form /(T) for example, liquid heats of evaporation, heat capacities of multi-atom gases, vapor pressures over liquids, liquid and solid solubilities in liquids, and liquid viscosities. Some of these properties are sensitive both to temperature and pressure. 

Some characteristic values of the pressure sensors mentioned here have been summarized in table 10. As mentioned before, the value r ldX/dp, denoting the sensitivity of the sensor with respect to a pressure change, is the highest for SrFCl Sm2+. However, if an experiment requires high pressures and high temperatures, a closer look at the value of r 1dX/dp/(dX/dT) is necessary. This value can be regarded as a measure for the overall performance of the sensor with respect to pressure and temperature. From this point of view YAIO3 Nd3+ would be the best sensor due to its extremely low temperature shifts. 

Musacchio et al. 1997 Novak et al. 1997 Chevrot van der Hilst 2000). Fp/Fs ratios are not sensitive to pressure and subsolidus temperatures, but depend on fluid pore pressure, fabric attitude and rock composition, specifically quartz content and plagioclase composition (Christensen 1996). In stable shield areas, high Fp/Fs ratios in the crystalline crust are generally explained in terms of composition. Mafic rocks have Fp/Fs ratios higher than 1.73 as a result of low quartz content and the abundance of mafic minerals (plagioclase, pyroxene, garnet, amphi-bole and olivine). 

Gases, unlike liquids and solids, occupy volumes that depend very sensitively on pressure and temperature. Special attention must therefore be given to factors influencing the volume of gases. 

Below we summarize some of the results obtained by Oran et al. (20), which used chemical models that had the ability to represent the change in chemistry due to pressure and temperature perturbations in the chemically sensitive regime. 

Fans and compressors are gas movers, analogous to pumps as liquid movers. The term "gas mover" will be used when discussing the characteristics of faiK and compressors collectively. The geometry of gas movers is somewhat similar to that of pumps however, operating parameters and safety considerations are quite different. Fans and compressors must handle gases that are compressible and extremely sensitive to temperature and pressure changes, while pumps handle liquids that are relatively insensitive to pressure and temperature changes and can be considered incompressible. 

The nucleate boiling heat transfer coefficient is independent of flow velocity. It is sensitive to pressure and the surface wall temperature. 

The above example is a simple one, and it can be seen that the individual items form part of the chain in the production system, in which the items are dependent on each other. For example, the operating pressure and temperature of the separators will determine the inlet conditions for the export pump. System modelling may be performed to determine the impact of a change of conditions in one part of the process to the overall system performance. This involves linking together the mathematical simulation of the components, e.g. the reservoir simulation, tubing performance, process simulation, and pipeline behaviour programmes. In this way the dependencies can be modelled, and sensitivities can be performed as calculations prior to implementation. 

Since aerothermal performance of compressors and turbines is very sensitive to inlet temperature and pressure variations, it is essential to normalize the aerothermal performance parameters such as flow, speed, horsepower, etc., to standard-day conditions. When these corrections to standard conditions are not applied, a performance degradation may appear to occur when in fact it was a performance change resulting merely from ambient pressure and temperature changes. Some of the equations for obtaining correction to standard-day conditions are given in Table 19-3. 

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