Vacuum Flow calculation methods

Nitrogen adsorption was performed at -196 °C in a Micromeritics ASAP 2010 volumetric instrument. The samples were outgassed at 80 °C prior to the adsorption measurement until a 3.10 3 Torr static vacuum was reached. The surface area was calculated by the Brunauer-Emmett-Teller (BET) method. Micropore volume and external surface area were evaluated by the alpha-S method using a standard isotherm measured on Aerosil 200 fumed silica [8]. Powder X-ray diffraction (XRD) patterns of samples dried at 80 °C were collected at room temperature on a Broker AXS D-8 diffractometer with Cu Ka radiation. Thermogravimetric analysis was carried out in air flow with heating rate 10 °C min"1 up to 900 °C in a Netzsch TG 209 C thermal balance. SEM micrographs were recorded on a Hitachi S4500 microscope. 

In vacuum technology, some calculations involve the steady flow of fluid through duct of changing circular cross-section (diffusers, jets, nozzles, etc.) and the methods of gas dynamics can be applied to calculate pressures, velocities and temperatures. (A criterion for the applicability of gas dynamics is that Kn < 0.01 although, according to ref. (d), the methods can be applied even at Kn values up to 0.3.)... 

The catalysts were characterised by BET surface area and CO-chemisorption (carried out at 25°C), An all-glass high vacuum unit capable of producing a vaccum of lO" torr was used for this. X-ray diffraction patterns were recorded on a Phillips PW-101 difractometer using CuKa radiation. Prior to CO chemisorption experiment the catalysts were reduced in hydrogen flow at 400°C for 4h, Irreversible CO uptake was obtained by the double isotherm method. Pd- dispersion was calculated considering a 1 1 stoichiometry between CO and Pd... 

The measurement of partial pressures over a liquid or solid mixture of two metals is not as simple. Mostly, it is restricted to higher temperatures or even to the molten phase. The direct measurement can be done, for example, in high or ultra high vacuum, using a Knudsen cell and a mass spectrometer for selective pressure determination. Dynamic measurements were developed, e.g., transportation methods. A steady stream of a reactive gas is passed over the sample transporting the reactive component to a cooled region of the apparatus. From the measured mass of the transported metal and the flow rate the vapor pressure can be calculated. Kubaschewski et alP have given a detailed description of the experimental possibilities. 

A very common layout for the assembly of condensers is barometric installation, the method in which no pump is needed to extract the liquid from under vacuum. The condenser is erected at such a height above the liquid drain level that the pressure difference between the vacuum inside the condenser and the atmospheric pressure is compensated by a liquid column. The height of this barometric leg must also overcome the flow resistance. In Figure 2.15, such a barometric installation is shown for a unit employing surface condensers. The height between the condensate outlet at the condenser and the liquid surface level in the collecting tank can be calculated by the necessary pressure difference and the specific weight of the... 

Calculating pressure drop is of considerable importance in atmospheric absorbers, heat transfer services, and vacuum distillations. Although pressure drop plots are available for most commercial types and sizes of random dumped tower packings, these data usually have been collected on air/water systems. While the air flow rate can be corrected for changes in gas density, no adequate method exists for handling the effect of liquid properties. 

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