Chamber time constant

Sometimes, to get data from 4 K up to room temperature, the simplest and more economical way is to let the cryostat warm if the thermal insulation is good and the vacuum chamber is kept under pumping, the warm-up time can be several days. If the experiment thermal time constant is much shorter, data at practically constant temperature can be recorded. 

Note that increasing the flow rate of the analyte NO results in an increased signal according to Eq. (E4), but a complication arises in that the pressure (and therefore [M]) also increases. For a fixed pumping speed, the residence time within the reaction chamber is constant, and the pressure in the reaction cell will increase linearly with increasing flow rate of gas into the cell ... 

The ratio V/Sgj, is generally designated as a time constant x. Thus the pump-down time of a vacuum chamber from atmospheric pressure to a pressure p is given by ... 

While the transfer and process chambers are constantly evacuated, the entrance and exit chambers must be periodically vented and then evacuated again. Due to the large volumes of these chambers and the short cycle times, a high pumping speed is required. It is provided by combinations of rotary vane pumps and Roots pumps. For particularly short cycle times gas cooled Roots pumps are also used. 

According to Summerfield (Ref 12, p 442) The ideal rocket motor analysis rests on the following simplifications (a) the proplnt gas obeys the perfect gas law (b) its specific heat is constant, independent of temp (c) the flow is parallel to the axis of the motor and uniform in every plane normal to the axis, thus constituting a one-dimensional problem (d) there is no frictional dissipation in the chamber or nozzle (e) there is no heat transfer to the motor walls (f) the flow velocity in the chamber before the nozzle entrance is zero (g)combustion or heat addition is completed in the chamber at constant pressure and does not occur in the nozzle and (h) the process is steady in time. ... 

Before the sample is fed, the chamber is closed and current is applied for at least 3 hours, in case evaporation should cause disturbance of the pattern. After this equilibration period, the sample is applied without opening the chamber and constant working conditions for a field up to 12 volts/cm will be maintained for any length of time. When constant current is used, there is an initial voltage drop due simultaneously to the heating up of the substrate, to evaporation, and to ionophoresis. In a good run the experiment will start with a field of 14 volts/cm and fall to 10-12 volts/cm, where it remains constant. 

A time constant for an ionization chamber is in the order of 10 s for Geiger counters it can vary from a few seconds to more than 20 s. 

The time-based and pressure-based studies were carried out in a small experimental chamber (8). The experimental results (% mortality as a function of time or pressure) were analyzed by the methods of probit analysis presented by Finney (9). The time-based studies were analyzed first (see Appendix I). A statistical best fit was applied to the data once it had been determined that the percent mortality that occurred at the longest bottom time (90 minutes) was the same as at the saturation level (see Figure 7). From the statistically best fit line of percent mortality vs. bottom time, the time associated with a mortality corresponding to 99% of saturation mortality was determined. Assuming that r8iow characterizes a tissue that rises exponentially towards saturation, one may show that the time constant, t8iow> is a simple multiple of the time to reach 99% of saturation (called t99). From these experiments it was determined that r8iow = 25.5 minutes. 

Perkin-Elmer M 2100 atomic absorption spectrometer with deuterium lamp background corrector. Cadmium and lead hollow cathode lamps operated at 4 mA and 7 mA, and 228.8 nm and 283.3 nm wavelength respectively. Spray chamber used without impact system. Acetylene flow-rate 1.0 1 min , air flow-rate 10 1 min (extra-lean flame). Peak height evaluation with a time constant of 0.5 s. FI peaks recorded by a printer or chrrt recorder. 

Fig. 7. Run-time constant D as a function of the downstream chamber pressure.

To test the time response of the sensors, a 10% H2/90% Nj ambient was switched into the chamber through a mass flow controller for periods of 10,20 or 30 s and then switched back to pure Nj, Figure 5.9 shows the time dependence of forward current at a fixed bias of 2V under these conditions. The response of the sensor is rapid (< 1 s), with saturation taking close to 30 s. On switching off the hydrogen-containing ambient, the forward current decays exponentially back to its initial value. This time constant is determined by the transport properties of the test chamber and is not limited by the response of the diode itself. 

With respect to instrumentation, new and faster Monitrons (ion chambers and associated circuits) were added so that three were in operation at all times and all were connected to the control rod safety system. The time, constants of the safety circuits were about 0.2 to 0,5 sec. Eaterline>Angus recorders installed in the control room were driven by two of the Monitrons so that visual monitoring of the pile was provided. In addition, the usual array of counters, gamma ray and neutron, were in use with mechanical recorders for counting rate purposes and loud speakers for continuous auditory monitoring. 

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