Pressure Build-Up

The constant container volume V consists of the variable shares for the liquid V and gaseous hydrogen volume V , in which the following applies  

The distribution of the mass in the boiling liquid m and saturated vapor m is described by the vapor fraction x  

Thermophysical property tables give the specific volumes for liquid i/ and saturated vapor v for each pressure so that the vapor fraction and the mass distribution can be determined  

With the vapor fractions of two states defined by a pressure increase Ap, the evaporated hydrogen mass Am is also determined. 

The reason for the pressure build-up is the heat input. The specific heat quantity can be read from the T-s-diagram as the area below the constant-volume change in 

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It is common practice to record the bottom hole pressure firstly during a flowing period (pressure drawdown test), and then during a shut-in period (pressure build-up test). During the flowing period, the FBHP is drawn down from the initial pressure, and when the well is subsequently shut in, the bottom hole pressure builds up. 

Addition of Inert Filter Aids. FUtet aids ate rigid, porous, and highly permeable powders added to feed suspensions to extend the appheabUity of surface filtration. Very dilute or very fine and slimy suspensions ate too difficult to filter by cake filtration due to fast pressure build-up and medium blinding addition of filter aids can alleviate such problems. Filter aids can be used in either or both of two modes of operation, ie, to form a precoat which then acts as a filter medium on a coarse support material called a septum, or to be mixed with the feed suspension as body feed to increase the permeabihty of the resulting cake. 

Electro osmosis often accompanies electrophoresis. It is the transport of Hquid past a surface or through a porous soHd, which is electricaHy charged but immovable, toward the electrode with the same charge as that of the surface. Electrophoresis reverts to electroosmotic flow when the charged particles are made immovable if the electroosmotic flow is forcibly prevented, pressure builds up and is caHed electroosmotic pressure. 

Pressure build-up Provide adequate venting and dust filtration on downstream of receiving vessel vent mill (risk of com-, Where liquefied gas (nitrogen or CO9 ) is used ponent failure, ensure adequate vent sizing and limit particularly in gas liquefied gas feed-rate to mill conveying systems). Internal pressure may also force product out of the mill. CCPS G-11 CCPS G-22 CCPS G-23 CCPS G-29... 

Vaporization in enclosed containers can produce significant pressure build-up and explosion. 

Many liquid phase or heterogeneous solid-liquid or gas-liquid reaetions result in gaseous produets or byproduets. These produets may be toxie (refer to Table 5.1) or flammable (refer to Table 6.1), or result in overpressurization of any sealed eontainer or vessel. Unless pressure relief is provided, relatively small volumes of reaetants - the presenee of whieh may not be expeeted - may generate suffieient gas pressure to rupture a eontainer. The eauses of pressure build-up may be ... 

Catastrophic failure of containers as cryogen evaporates to cause pressure build-up within the vessel beyond its safe working pressure (e.g. pressures <280 000 kPa or 40 600 psi can develop when liquid nitrogen is heated to ambient temperature in a confined space). 

The on-line filter on the wash headers manifold should be checked periodically for pressure build- up due to progressive blockage. Likewise, the nozzles on the wash headers should be kept clean in order to ensure overlapping for full coverage of the washed cake. 

The pressure build-up which occurs along a screw is illustrated in Fig. 4.2. The lengths of the zones on a particular screw depend on the material to be extruded. With nylon, for example, melting takes place quickly so that the compression of the melt can be performed in one pitch of the screw. PVC on the other hand is very heat sensitive and so a compression zone which covers the whole length of the screw is preferred. 

From equation (4.9) it may be seen that there are two interesting situations to consider. One is the case of free discharge where there is no pressure build up at the end of the extruder so... 

Now, as shown in previous example, for a constant flow rate situation the pressure build-up in the machine is given by... 

Trapped liquor may cause crystal fracture due to vapour pressure build-up on... 

The ASME code requires every pressure vessel that can be blocked in to have a relief valve to alleviate pressure build up due to thermal expan sion of trapped gases or liquids. In addition, the American Petroleum Institute Recommended Practice (API RP) 14C, Analysis, Design, Installation and Testing of Basic Surface Safety Systems on Offshore Production Platforms, recommends that relief valves be installed at vari ous locations in the production system and API RP 520, Design and Installation of Pressure Relieving Systems in Refineries, recommends various conditions for sizing relief valves. 

Conventional relief valves should only be used where the discharge is routed independently to atmosphere, or if installed in a header system, the back-pressure build-up when the device is relieving must be kept below 10% of the set pressure so the set point is not significantly affected. The set point increases directly with back-pressure. 

In canned pumps the rotor (the moving part of the electric motor) is immersed in the process liquid the stator (the fixed part of the electric motor) is separated from the rotor by a stainless steel can. If there is a hole in the can, process liquid can get into the stator compartment. A pressure relief plug is therefore fitted to the compartment and should be used before the compartment is opened for work on the stator. One day, an operator opened the pump without using the pressure relief plug. There was a hole in the can which had caused a pressure build-up in the stator compartment. When the cover was unbolted, it was blown off and hit a scaffold 6 feet above. On the way up it hit a man on the knee and the escaping vapor caused eye irritation. The worker was not familiar with canned pumps and did not realize that the pressure relief plug should be used before opening the compartment. 

Users are warned that a rupture disk wdll not burst at its design pressure if back pressure builds up in the space between the disk and the safety or safety relief valve which will occur should leakage develop in the rupture disk due to corrosion or otlier cause. 

Users are warned that an ordinary spring loaded safety relief valve will not open at its set pressure if back pressure builds up in the space between the valve and rupture disk. A specially designed valve is required, such as a diaphragm valve or a valve equipped with a bellows above the disk. 

Several types of valves used in compressor cylinders are shown in Figure 12-6. To function properly, a valve must seat uniformly and tighdy, yet must not have snap-action on opening or closing. Until pressure builds up to the discharge point, the valve must remain closed, open at dis-... 

Upon shutting in the well, the pressure builds up both on the drillpipe and casing sides. The rate of pressure buildup and time required for stabilization depend upon formation fluid type, formation properties, initial differential pressure and drilling fluid properties. In Ref. [143] technique is provided for determining the shut-in pressures if the drillpipe pressure is recorded as a function of time. Here we assume that after a relatively short time the conditions are stabilized. At this time we record the shut-in drillpipe pressure (SIDPP) and the shut-in casing pressure (SICP). A small difference between their pressures indicates liquid kick (oil, saltwater) while a large difference is evidence of gas influx. This is true for the same kick size (pit gain). 

Why does the pressure build up in a tire on a hot day Answer in terms of the kinetic theory. 

There are two points of the cycle at which velocity decreases very rapidly from a high value to zero. To give a.familiar analogy, the van der Pol oscillator for this value of y. behaves not as a decent oscillator but rather as a pneumatic hammer, which idles for some time while the air pressure builds up, delivers a hammer blow, losing its kinetic energy, and then begins a similar half-cycle. 

CautionI All reactions in which 50% or more concentrated hydrogen peroxide is employed must he conducted behind a safety shield. Beakers are recommended as reaction vessels to permit rapid escape of gas and avoidance of pressure build-up in the event of a rapid decomposition. 

The cyclization of 1,2-dicarbonyl compounds with aldehydes in the presence of NH4OAC to give imidazoles was employed in a combinatorial study that compared conventional and microwave heating in the preparation of a library of sulfanyl-imidazoles (Scheme 15). The study employed an array of expandable reaction vessels that could accommodate a pressure build-up system for heating without loss of volatile solvents or reagents. A 24-membered library of imidazoles (48 and 49) was prepared in 16 min instead of the 12 h required using conventional heating [45]. 

Since the pressure build up is primarily due to the evolution of CO as MDI is being decomposed to carbodiimide, the thermodynamic relationship PV = nRT may be applied to convert the pressure profiles to plots of moles of CO2 generated vs. time. This is shown for the 225 °C isotherm in Figure 3. The theoretical curve obtained through the application of zero-order kinetics is also shown in this plot and the data seem to be well accommodated by this rate law throughout the majority of the run. 

Table 3 shows the performance of the promoted-catalysts for the decomposition of methane to hydrogen at 5, 60, 120 and 180 min of time on stream. The results in Table 3 revealed that the activity of the parent catalyst and MnOx-doped catalyst remained almost constant until 120 min of time on stream. The activity of the other promoted-catalysts, on the other hand, decreased with an increase in the time on stream. The data for the CoO-doped catalyst and 20 mol%NiO/Ti02 could not be recorded at 120 min and 180 min, respectively because of the pressure build-up in the reactor. This finding indicates that adding MnOx enhances the stability and the resistibility of the NiO/Ti02 catalyst towards its deactivation. 

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