Piston-cylinder vessels

The two basic elements are (i) a container which is capable of withstanding 10-15 kbar or even higher pressures, and (ii) a means of reaching this pressure (two types of systems are in common use, piston-cylinder vessels... 

Typical piston-cylinder vessels are 2-5 cm in diameter and 20-30 cm in length thus, allowing for the space occupied by the piston typical volumes are in the range 50-300 cm. ... 

In practice, the high-pressure polycondensation of the salt monomers producing polyimides was carried out by using a piston-cylinder type hot-pressing apparatus with the use of a Teflon capsule as a reaction vessel (see Eq. 5) [34]. 

In Japan, Kobe Steel has sometime ago developed a high pressure crystallization technique known as Fine Cry Process in which m-, p-cresol mixture is introduced into a high pressure vessel of the piston-cylinder type and is crystallized adiabatically at 200 MPa. After draining off the mother liquor the system is decompressed and p-cresol emerges as the pure crystalline product [1]. 

Fig. 7.4 A piston-cylinder high-pressure apparatus (a) the pressure frame, (b) a 100 tonne hydraulic ram, (c) the piston, (d) the bottom plug, (e) high-pressure seals, (f) a double-walled pressure vessel, (g) the pressurizing fluid, (g) a 500 bar hydraulic fluid for pressurization, (i) hydraulic pressure used for piston extraction, (j) the sample. (Reproduced by permission from PSIKA Ltd).

While it is important to take proper precautions (see Appendix 2), properly built equipment offers few hazards if relatively small quantities of liquids are used under pressure. The energy stored in a compressed liquid is of the order of 0.2-0.5 kJ mor kbar" this is much less than in a gas. In the event of the catastrophic failure of a vessel, only around 10 per cent of the liquid would need to escape to reduce the pressure to the atmospheric value, and double-walled vessels are unlikely to suffer a failure of both cylinders. The author has experienced the failure of a piston-cylinder apparatus which led to nothing more than a sudden depressurization. On the other hand, hazards may arise from the low-pressure side, which is likely to be carrying oil at 500 bar or more a pin-hole jet at this pressure can penetrate the human body. The valve threads may become worn and the stems may then be forcibly ejected. So hose connections should be inspected and renewed regularly and, where possible, they should be shielded from personnel, the valves should be mounted with the stems pointing away from the operator, and the guidelines set out in the code of practice (see Appendix 2) should be followed. 

Hydrothermal- and carbonate-exchange techniques. The majority of available experimental fractionation data are for oxygen isotope fractionations involving minerals. Much of the data, particularly the early data, were obtained using water as the isotopic exchange medium. These experiments were either done at ambient pressure (typically synthesis experiments), or in cold-seal pressure vessels at pressures of 1 to 3 kbar (e.g. O Neil and Taylor 1967 O Neil et al. 1969 Clayton et al. 1972). Later experiments were done in a piston cylinder apparatus (at 15 kbar) to exploit the pressure enhancement of exchange rates (Clayton et al. 1975 Matsuhisa et al. 1979 Matthews et al. 1983a,b). 

Consider two systems, 1 and 2. System 1 is a one-phase mixture of C components, with mole numbers N. This mixture fills a rigid vessel of volume Vj, and the vessel is immersed in a heat bath maintained at temperature Tj. System 2 is another sample of the same mixture, having the same C components and the same mole numbers N. System 2 fills the cylinder of a piston-cylinder apparatus. The cylinder is immersed in a heat bath at T2. A constant external pressure is imposed on the mixture at equilibrium the system pressure P2 balances that external pressure. Therefore, system 2 is at constant pressure, while system 1 is at constant volume. 

The diffusion of H in San Carlos olivine single crystals was studied by performing experiments under hydrothermal conditions. The experiments were carried out at 1.5GPa, lOOOC for 1.5h in a piston cylinder apparatus, or at 0.2GPa, 900C for 1 or 20h in a cold-seal vessel. Polarized Fourier transform infrared spectroscopy was used to quantify the hydroxyl distributions. At high temperatures, hydrogenation was dominated by the coupled diffusion of protons and octahedrally coordinated metal vacancies. From the experimental data, Arrhenius expressions were determined ... 

A rigid tank of volume 0.5 m is connected to a piston-cylinder assembly by a valve, as shown below. Both vessels contain pure water. They are immersed in a constant-temperature bath at 200°C and 600 kPa. Consider the tank and the piston-cyhnder assembly as the system and the constant-temperature bath as the surroundings. Initially the valve is closed and both units are in equihbrium with the surroundings (the bath). The rigid tank contains saturated water with a quality of 95% (i.e., 95% of the mass of water is vapor). The piston—cylinder assembly initially has a volume of 0.1 m . 

A single-acting reciprocating pump has a cylinder diameter of 115 mm and a stroke of 230 mm. The suction line is 6 m long and 50 mm in diameter, and the level of the water in the suction tank is 3 m below the cylinder of the pump. What is the maximum speed at which the pump can run without an air vessel if separation is not to occur in the suction line The piston undergoes approximately simple harmonic motion. Atmospheric pressure is equivalent to a head of 10.4 m of water and separation occurs at a pressure corresponding to a head of 1,22 in of water. 

Aqueous hydrogen peroxide of a given concentration was poured into a vessel with a piston pump, which continuously injected it into the reactor. Methane was supplied from a gas cylinder with pressure sensors at the output. It was purified and dried, then heated and injected into the reactor. The reaction system is of a homogeneous (non-catalytic) flow type and operates in plug flow mode. 

The volume of a gas may be increased by allowing it to expand into an evacuated vessel, as shown in part (a) of the problem, by withdrawing a piston in a cylinder, as shown in part (b), or by other means. 

Hirn demonstrated that saturated steam when expand adiabatically in a cylindrical copper vessel with plate-glass ends deposits droplets of liquid, visible as a fog. Cazin connected the cylinder with another containing a piston, so that the vapour could be adiabatically compressed as well as expanded. Steam and carbon disulphide vapours (or"<0), condensed on expansion, but ether vapour (or">0) on compression. The inversion temperatures for benzene and cUoroform were about 120° and 127°C. respectively, agreeing with those calculated from Regnaulfs results, for CS2 790°, ether — 113°, CHCl3 123-5°, benzene 100° C. 

A streaming current detector based on a completely different principle than the above instruments is presented in [299], The dispersion is in a narrow space between a vertical cylindrical vessel and a coaxial piston, which moves back and forth along the axis. The potential between two gold electrodes on the wall of the cylinder at different heights is measured, and its zero value is identified with the IEP. The apparatus own response corresponds to the electrokinetic behavior of the piston and cell materials. In the presence of a colloid, the piston and the cell are assumed to be covered with colloidal particles. The above design has been utilized in some commercial instruments ... 

The streaming potential also may be determined by using a so-called particle charge detector, where the measuring unit consists of a cylindrical vessel made of synthetic material like teflon. The liquid movement is induced by a piston, which is moved up and down, and in dependence on its direction the mobile charges will be shifted. Electrodes at the top and near the bottom of the cylinder detect the induced streaming potential. 

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