Double pressure measurement

Gas adsorption manometry with reservoir and double pressure measurement. The corresponding set-up is shown in Figure 3.3. One pressure transducer is used to determine the amount of adsorptive remaining in the reservoir, while the second is used to determine the adsorption equilibrium pressure and also the amount of unadsorbed gas in the central cross and adsorption bulb. This arrangement gives an integral measure-... 

Figure 3 J. Gas adsorption manometry with reservoir and double pressure measurement.

Measurements in this held have been made by Berthelot and Ogier with nitrogen tetroxide Ann. de Chim. et Phys., [v.], 30, 382 (1883)), and with acetic acid ibid., 400), and some calculations with reference to steam have been made by Nernst Verhandl. Deutsch. Phys. Ges., 15, 313) and Levy ibid., 330), who utilised the vapour-pressure measurements of Holborn and Henning Ann. der Physik, (1906), 21 (1907), 22, 23). Wiedemann had previously observed that the specific heats of ethylbromide, ethyl-acetate, and benzene increase with temperature at about the same rate as that of nitrogen tetroxide at 200°. In the case of steam it was assumed that (i.) the polymerisation is to double molecules... 

If the hydrogen introduced into the tube were employed entirely to reduce silver chloride, the hydrochloric acid set free would exert a pressure exactly double that exerted by the hydrogen absorbed the inverse S3rstem of this one we have taken as starting-point in the preceding experiment is therefore formed of silver in the presence of hydrochloric acid, this latter exercising, at the ordinary temperature, a pressure measured by 760 millimetres of mercury. Let us take such a system heat it to 448 for a time h, which we lay off as abscissse, and lay off the value p as ordinates the following results are obtained ... 

If decomposition goes to completion, the initial pressure approximately doubles. It has been found that the rates determined on the basis of pressure change and by analytical methods were in reasonable agreement - °°. However, recently Mirta et pointed out that, at low initial pressures and at high temperatures, the progress of the reaction cannot be characterized strictly by pressure measurements. 

The agreement is better than the experimental error justifies. In Experiment VI the constant is double the previous values, but, as the error in measuring the oxygen pressure to values of 9 X 10 4, is not accurate to 20 per cent this is without great significance. A twenty-five per cent error in the pressure measurement at this pressure would double the velocity constant. It nevertheless serves to indicate that there is no great departure in the velocity constant when the initial pressure is reduced to V25 that of Experiment IV. 

The fluid static pressures were measured with calibrated Bourdon tube gages, and the differential pressures were measured with mercury-filled, double-legged glass manometers. These pressure measuring instruments were located on a single panel and their indications were recorded photographically. The fluid and wall temperatures were measured with copper-constantan thermocouples and recorded on multipoint temperature recorders. 

Pressure-Compensated Temperature Multicomponent Compositions Computed from Temperature and Pressure Measurements Double-Differential Temperature Average Temperature Composition Estimators... 

Common practice is to specify exchanger surface in terms of total external square feet of tubing. The effective outside heat-transfer surface is based on the length of tubes measured between the inner faces of tube sheets. In most heat exchangers there is little difference between the total and the effective surface. Significant differences are usually found in high-pressure and double-tube-sheet designs. 

Example A ventilation system (Fig. 9.64) handling 20 mVs of air needs to heat the supply air from 10 °C to 20 C. Doubling the number of heat exchangers from one to two increases the heat-recovery efficiency from 50% to 75% and introduces an extra pressure drop of 300 Pa. As we can see from Table 9.19, this is probably a cost-efficient measure. 

For convenience, the usual measurement of sound is expressed in decibels (dB), and ratings go from threshold of hearing to threshold of pain (135 dB). Figure 34.11 illustrates the common noise criteria, which can be expressed in sound-pressure levels (SPL). The human ear can detect 1 dB but 6 dB represents a doubling of the SPL, although it would need a 10 dB increase to make it sound twice as loud. 

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