Unusually High Pressure

A common cause of unusually high pressure is a plugged in-line filter. In-line filters are found at the very beginning of the flow line in the mobile phase reservoir, immediately before and/or after the injector, and just ahead of the column. With time, they can become plugged due to particles that are filtered out (particles can appear in the mobile phase and sample even if they were filtered ahead of time), and thus the pressure required to sustain a given flow rate can become quite high. The solution to this problem is to backflush the filters with solvent or clean them with a nitric acid solution in an ultrasonic bath. 

Other causes of unusually high pressure are an injector blockage, mismatched mobile and stationary phases, and a flow rate that is simply too high. An injector that is left in a position between load and inject can also cause a high pressure, since the pump is pumping but there can be no flow. 

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In extreme cases, very high pressure waves are encountered in which the time to achieve peak pressure may be less than one nanosecond. Study of solids under the influence of these high pressure shock waves can be the source of information on high pressure equations of states of solids within the framework of specific assumptions, and of mechanical, physical, and chemical properties under unusually high pressure. 

What is the most common cause of an unusually high pressure in an HPLC flow stream and how is the problem solved ... 

Plugged in-line filter is a typical cause of unusually high pressure. The solution is to backflush the filter or otherwise clean it. 

Unusually high pressure in column Cl (we need to investigate why... 

Recent work on the carbon dioxide system shows another unusual high-pressure behaviour. Raman spectra of carbon dioxide show that CO2 molecules remain the basis of the phases to more than 40 GPa at temperatures below a few hundred Kelvin [52]. These results, however, do not mean that the molecular crystals are the stable phases indeed, recent studies of the combustion of carbon at high pressures by Yoo et al [53] reach another conclusion. They initiated combustion of a mixture of carbon and oxygen at pressures between 7 and 13 GPa by heating the carbon with a Nd YAG laser, quenching the products to ambient temperature under pressure and recording their Raman spectra. As well as features of unreacted O2 and CO2 in some samples,... 

Skates have relatively sharp blades, so someone in skates exerts an unusually high pressure on the ground. An exceptional property of water ice is that its melting point decreases under pressure (most substances behave in exactly the opposite way). This may lead people to rash to the conclusion that ice melts under a skate, and the athlete (or the beginning skater) actually slides on a thin layer of water rather than the surface of ice. However, this is far from logical many drivers know that an icy road is more slippery than a wet one. 

Measurements of pressure drop and flow rate for dilute solutions of high molecular weight polymers flowing through a porous medium show an unusually high pressure drop. The excess pressure drop due to the presence of polymers was found to be very high with a marked non-Newtonian behaviour. 

In eqn [1], c is the fractional conversion and the subscript O -denotes the initial state. Of comse such an estimate heavily depends on monomers and experimental conditions. One can relax the limitation imposed on DP by carrying out experiments at, for example, an tmusually low [P ] or an unusually high pressure. In these conditions, one can expect unusually large DPn for both conventional and LRP systems, but, of course, at the cost of a long polymerization time or a complicated and costly experimental setup, respectively. 

The working temperature, 77 K, is well below the triple point of krypton, 116 K, but if the solid is taken as the reference state the isotherm shows an unusually sharp upward turn at the high-pressure end. The usual practice, following Beebe, is therefore to take p° as the saturation vapour pressure of the supereooled liquid (p° = 2-49 Torr at 77-35 K and 27-5 Torr at 90-2 K). 

Even though the rates of initiation span almost a 10-fold range, the values of k, show a standard deviation of only 4%, which is excellent in view of experimental errors. Note that the rotating sector method can be used in high-pressure experiments and other unusual situations, a characteristic it shares with many optical methods in chemistry. 

Iodine vapor is characterized by the familiar violet color and by its unusually high specific gravity, approximately nine times that of air. The vapor is made up of diatomic molecules at low temperatures at moderately elevated temperatures, dissociation becomes appreciable. The concentration of monoatomic molecules, for example, is 1.4% at 600°C and 101.3 kPa (1 atm) total pressure. Iodine is fluorescent at low pressures and rotates the plane of polarized light when placed in a magnetic field. It is also thermoluminescent, emitting visible light when heated at 500°C or higher. 

Silicone Excellent resistance over unusually wide temperature range [—100 to 260°C (—150 to 500°F)] fair oil resistance poor resistance to aromatic oils, fuels, high-pressure steam, and abrasion... 

Mesh strainers finer than 100 mesh/inch (<150 /rm) should be treated as microfilters. Coarser strainers up to 50 mesh/inch (300 /rm) may generate significant static when fouled with accumulated debris, so should be treated as microfilters except in cases where fouling is not expected or may be rapidly identified by either periodic inspection or monitored pressure drop. Clean strainers should nevertheless be placed as far upstream as practical for nonconductive liquid service. A theoretical model for the charging process in strainers (screens) is given in [119-120]. Viscous nonconductive liquids (5-2.5.4) may produce unusually high charging currents in strainers. 

For applications involving unusually high superimposed back pressure, a pilot operated valve may be the only possible balanced valve that is commercially available, because of the mechanical limitations which apply to bellows. 

Solid substances are forced into unusual and distinctive conditions when subjected to powerful releases of energy such that their inertial properties result in the propagation of high pressure mechanical waves within the solid body. The very high stress, microsecond-duration, conditions irreversibly force materials into states not fully encountered in any other excitation. It is the study of solids under this unique compression-and-release process that provides the scientific and technological interest in shock-compression science. 

Testing should address the maximum operating temperature and pressure normally seen at the arrester location. This does not include certain pressure upsets (such as emergency shutdown) that produce unusually high system pressures. In many cases it may not be possible to design an arrester that will function effectively during upset conditions, and other protective measures should be considered (e.g., venting, suppression). 

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