Phase equilibria data are presented for the helium-carbon dioxide system at 253", 273". and 293°K. and pressures to 139 atm. Equilibrium is established under flow followed by nonflow conditions, and liquid and vapor samples are isolated without disturbing equilibrium. Liquidand vapor-phase compositions are monitored with miniaturized copacitors, and compressibility factors are computed from resulting dielectric constants. The data are internally consistent and compore favorably with availableliterature values.Porter (1) did some early work on the phase equilibria of helium-carbon dioxide from 223" to 273°K. for design purposes for Bureau of Mines helium extraction plants, but the data are sparse. Barrick, Heck, and MacKendrick A new type of apparatus, which eliminates equilibrium disturbances upon sampling, is described and tested from 250" to 293°K. and pressures to 139 atm. Capacitors are used to monitor liquid-and vapor-phase compositions (via the density-dependent dielectric constants) as an aid is determining sample homogeneity and equilibrium. EXPERIMENTAL APPARATUS AND PROCEDURESThe experimental apparatus is shown in Figure 1. The main cell and the vapor and liquid traps are machined from 304 stainless steel. The nominal volume of the main cell is 350 cc.; the vapor and liquid traps are about 75 cc. each. Two fixed, parallel plate capacitors are located in the main cell and one in each trap. These stainless steel capacitors (I, 11, 111, and IV) are of reference standard type of design ( 3 ) but miniaturized to occupy less than 15 cc. bulk space and displace only 5 cc. volume. Six tension rods provide precise, parallel spacing ( 2 mm.) of the circular (15 mm. diameter) plates. Capacitances are measured with a transformer-ratio-arm capacitance bridge. A copper constantan thermocouple is located in the main cell; a pressure transducer is installed in a constant temperature enclosure. The cell system is suspended in an ethanol bath controlled to zt 0.03"K. A magnetic circulating pump moves fluids through the apparatus.The cell system is evacuated and purged with gaseous carbon dioxide. Carbon dioxide is introduced at a pressure above its saturated vapor pressure at cell tem erature. Liquefaction is Capacitors I and I1 read from 23 to 27 picofarads, depending on the temperature; I11 and IV read from 15 to 17 picofarads. Helium is admitted until the approximate datum point pressure is reached, and vapor is bubbled through the liquid with the magnetic circulating pump. The pump is stopped after about 15 min., and the system is permitted to stabilize. Pressure, temperature, and capacitances are monitored at intervals of 5 to 20 min. When these measurements are stable for 1 hr., e uilibrium is assumed and valves isolating the traps are closed; %e rest of the cell system is evacuated. The vapor trap is opened to an evacuated 500 cc. sampling bomb. The cell allowed to occur until the liquid leve P is above capacitor 11. system is then evacuated, except the liquid trap, so that the liquid-phase sample may be flashed i...
Equations are developed which satisfactorily describe the change in the pressure differential with time for a closed, constant-volume system which utilizes a coiled-capillary tube and a constant-rate pump to determine gas viscosities. Viscosities are computed at transient, unsteady, and apparent-steady-state conditions. As long as the flow rates are not too high and the pressure level is not too low, the computed viscosities appear to be reliable.
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