Pressure Drop in Vacuum Systems

This method [54] is for applications involving air or steam in cylindrical piping under conditions of (a) turbu- 

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AP ae = Pressure drop in vacuum system due to friction, in. whaler/100 ft pipe... 

However, droplet systems can enable much higher energy input (via gas phase pressure drop in cocurrent systems) and, as a result, dominate applications where a quick quench is needed. See Examples 21 and 22. Conversely, droplet systems can also be designed for very low pressure drop which is advantageous in applications such as vacuum condensers. 

For ordinary laboratory work, a modified Hickman still (Fig. 1-39) is convenient. Volatile impurities and gases present in the liquid to be distilled must first be removed so that frothing wiU not occur in the still. This is done by placing the liquid in an ordinary flask, which is then evacuated and gently warmed. After all of the volatile impurities have been removed, the liquid is transferred to the still. The latter is connected to the vacuum system by means of a large connector in order to minimize pressure drop in the system. The still is heated by an aluminum block which is bored to accommodate the bottom of the still to a depth of about 15 mm and which is wrapped with nichrome wire serving as a heater. The wire is best insulated from the block by asbestos paper, and a layer of asbestos paper should be placed between the still and the aluminum block. As the liquid is heated, it evaporates and collects on the condenser from which it drips... 

The fluid dehvery in an air-spray system can be pressure or suction fed. In a pressure-fed system, the fluid is brought to the atomizer under positive pressure generated with an external pump, a gas pressure over the coating material in a tank, or an elevation head. In a suction system, the annular flow of air around the fluid tip generates sufficient vacuum to aspirate the coating material from a container through a fluid tube and into the air stream. In this case, the paint supply is normally located in a small cup attached to the spray device to keep the elevation differential and frictional pressure drop in the fluid-supply tube small. 

Vacuum distillation varies with the system tmd particularly with the absolute pressure required at the bottom of the column normally select low pressure drop in the range of 0.1 to 0.2 in. water/ft of packing. For in vacuum service of 75 mm Hg and lower, the pressure drop obtained from the GPDC,... 

In practice, a mixture of actinide dioxide and graphite powder is first pelletized and then heated to 2275 K in vacuum in a graphite crucible until a drop in the system pressure indicates the end of CO evolution. The resulting actinide carbide is then mixed with tantalum powder, and the mixture is pressed into pellets. The reduction occurs in a tantalum crucible under vacuum. At the reduction temperature, the actinide metal is vaporized and deposited on a tantalum or water-cooled copper condenser. 

Compute the size of the connection pipe. In usual vacuum-pump practice, the pressure drop in pipes serving mechanical pumps is not allowed to exceed 20 percent of the inlet pressure prevailing under steady operating conditions. A correctly designed vacuum system, where this pressure loss is not exceeded, will have a pump-down time which closely approximates that obtained under ideal conditions. 

The vacuum line is isolated from the forepump, and a liquid-nitrogen bath is put around trap D. The fluorine metering system is partially evacuated with the water aspirator, as discussed above. Then the vacuum line is completely evacuated with the forepump. Fluorine is allowed to expand slowly into the metal system by means of the needle valve 3. As the pressure increases above atmospheric, some fluorine is allowed to bleed into the vacuum line and storage bulbs until a pressure of 650-700 mm. is reached. First needle valve 1 on the metal system and then the fluorine control valve 3 are quickly closed. (Some fluorine may escape from the blowout manometer during this operation.) Approximately a 10% excess of fluorine (0.023 mole in this case) is condensed into the metal pressure reactor containing the thionyl fluoride. The amount of fluorine used is measured by the pressure drop in a calibrated volume in the pressure range of approximately 700-400 mm., since fluorine has a vapor pressure of approximately 400 mm. at —196°. 

Pressure drop across a mesh pad is usually less than 1 in. H20 and is of little concern except in vacuum operations or systems involving large flows with fans or blowers at near atmospheric pressure. Pressure drop is estimated by Ap pc,. where Ap is the pressure drop (in in. H50), Vc is the gas velocity (in fris), and pc (he vapor density (in Ibn/ft. C = 0.2 for a standard-density 4 in. thick pad, and C = 0,12 for a low-density 6 in. thick pad. For situations where pressure drop is critical, methods presented... 

The following calculation for the vacuum operation is based on the assumptions as (i) negligible pressure drop in fiber lumen (ii) no concentration and temperature gradients in the membrane module (iii) pure oxygen product and (iv) 10% heat loss for the membrane system. Figure 18.9 shows the flow patterns of the membrane system combined with heat exchangers for heat recovery where the parameters for energy calculation are also presented. 

If the lines cannot be kept short or relatively free of bends, then pressure drops will exceed 12 in. Hg, requiring more horsepower. Where the pressure drop is greater than 12 in. Hg, which is the normal operating and limiting pressure for most vacuum systems, it is necessary to use a positive pressure system. All these factors must be considered initially to obtain the best delivery system most economically. 

In addition to this, they also divide the mass spectrometer into several compartments. For each compartment closer to the analyzer, the pressure drops. The vacuum is created gradually throughout the system. Vacuum is essential for mass spectrometry the presence of air (gas molecules) hampers the ions to fly toward the analyzer. Performance of the mass analyzers can be summarized with the following parameters ... 

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