Purge controls, helium

Cooling Rate (°C/min) Liquid Nitrogen Coolant with Helium Purge, Controlled Cooling to... 

For the present experiment, gas chromatograph (DS 6200 model, Donam Korea) and thermal collect detector were used to measure NO conversion. Reactor temperature was sustain consteintly at 5000 using P.l.D. temperature controller (UP-350, Yokokawa) and gas flow rate was maintained 10 ml/min by mass flow controller, GMC 1000, MKS). All samples were heated under Helium purge at 15010 for 1 hour to remove residual H2O before NO conversion test. The NO conversion was determined from the concentration of NO at the outlet reactor. Prior to each analysis, NO standard curve was gained using 300, 600, and 1000 ppm NO gas. 

Dissolved oxygen from mobile phase solvents has to be removed. This is accomplished by passing helium gas through the solvent container or by passing the mobile phases through helium purging units. Currently, computers that control the pumps also control vacuum degassers, which are placed in between the pump and solvent reservoir. 

Dynamic mechanical analysis (DMA) was performed to determine the influence of the polymer constitution on tensile modulus and mechanical relaxation behavior. For this purpose, a Perkin Elmer DMA-7 was run in tensile mode at an oscillation frequency of 1 Hz with a static stress level of 5 x lO Pa and a superposed oscillatory stress of 4 x 10 Pa. With this stress controlled instrument, the strain and phase difference between stress and strain are the measured outputs. Typically, the resulting strain levels ranged from 0.05% to 0.2% when the sample dimensions were 8 mm x 2 mm x 0.1 mm. A gaseous helium purge and a heating rate of 3°C min" were employed. The temperature scale was calibrated with indium, and the force and compliance calibrations were performed according to conventional methods. 

He) was introduced into the column, and the column pressure reached the adsorption pressure Pa. This process took about 5 seconds. Valve V-2 was then opened, and adsorption in the column from the inlet gas took place (adsorption step). During this period, the flow rate and concentration of CO, Gu and C/ were measured. (2) Valves V-1 and V-2 were closed, V-4 was opened, and the column was evacuated (desorption step). At the end of the desorption step, the pressure was below 13 Pa after 600 seconds. (3) As V-3 was also opened under evacuation, helium was supplied as a countercurrent puige to remove CO thoroughly (countercurrent purge step). (4) With V-3 closed and V-4 still open, the column was re-pressurized to the adsorption pressure with helium. The measurement conditions are summarized in Table 1, and the samples that were screened are listed in Table 2. The adsorption temperature was one parameter examined in this study, and a sequence controller was programmed for each set of conditions, so that steps (1) ( 4) were repeated over more than 4 hours. The total amount of desorbed gas was determined from the gas collected at the exit of the rotary flowm er. 

Known size specimens are placed in the tube and are flooded with a purge gas, typically helium. The tube has been modified with a heater and controls, and is thus able to subject the specimen to a controlled elevated temperature environment. Should highly volatile compounds be suspected, pre-chilling of the sample and tube prior to purging is possible. The time of purge necessary to obtain an optimum sample has to be established experimentally and will vary with the nature of the specimen under test. 

Better heat transfer is achieved if helium is used as a purge gas. The heat capacity constant is very sensitive to small changes in the flow rate of helium and so helium should only be used as a purge gas if mass flow controllers are used to control the flow rate. 

Concentrations of ammonia as high as 29.3 /rM (880 nmol in 30 mL) were observed. Control experiments in which helium was substituted for nitrogen still showed apparent yields of ammonia upon irradiation of Agl. No ammonia was found after irradiation of Agl in Pyrex tubes or if purging with nitrogen was allowed to continue throughout the experiment. No hydrazine or oxidized nitrogen were detected. 

The DSC measurements reported in this book are performed with the power-compensating DSC-2 and DSC-7 systems from Perkin Elmer. The block surrounding the DSC sample holders is kept at -150°C + 1°C with the aid of a controlled liquid nitrogen supply, both cells are purged with helium (60 ml/minute). 

The test vessel was equipped with subsystems (shown schematically in Fig, 3) which provided (1) wall heating rates to 0.9 Btu/ft -sec, (2) fill and drain, and purge, (3) pressurization with either helium or hydrogen gas to ISOpsig, (4) throttled venting, (5) controlled electrohydraulic shaking to 15 cps, and (6) measurement of pertinent test parameters. 

---