Dead-space volume

TABLE 5.6 Effect of Dead Space Volume, Tidal Volume, and Breathing Frequency on Alveolar >fentllation at a Fixed Minute Ventilation (V = 58.0 Umin). Modified from Chemiack. ... 

Note that the dead space volume is treated as having a uniform well-mixed composition. 

Study the effects of fractional by-passing and fractional dead space volume on the steady-state conversion, X3, compared to that of the ideal tank, X4. 

Modify the program to allow for zero dead space volume and study the effect of fractional by-passing only. Compare the results to that of a perfectly stirred tank. 

Note that in the program that while the by-passing flow fraction ft (FRAC1) can be set to zero, the fractional dead space volume f2 ( FRAC2) cannot be set to zero without modifying the program. This would cause the derivative value for C2 to be divided by a zero value for V2. 

Columns for gel permeation chromatography must have both a minimal dead space volume at the outlet, to prevent broadening of the zones developed during the separation, and a suitable bed support, e.g. nylon mesh, which will retain the gel without becoming blocked. The length of the column affects the resolution,... 

The purpose of the Bohr equation is to give a ratio of physiological dead space volume to tidal volume. Dead space volume is normally around 30% of tidal volume and so the normal ratio is quoted as 0.3. Under abnormal conditions, the ratio will tend to increase and so make ventilation inefficient. 

Steps 3 and 4 are not required if the dead space volume is determined in another way. 

Determination of dead space volume by gas expansion into adsoiption bulb and measurement of new pressure another method is to determine the modified slope of the p versus t curve. 

When thermal equilibrium reached (i.e. after c. 3-5 hours), the dead space volume is determined as in Steps 3 and 4 of the discontinuous manometric procedure in Section 3.3.1. In the case of low-temperature calorimetry this must be done between Steps 2 and 3, by simply connecting the adsorption bulb to the manometric equipment. 

Steps 1-5 as for the discontinuous experiment. Dead space volume determination (Step 4) also possible by the discontinuous sonic nozzle procedure (Section 3.3.2). 

The determination of the dead space volume of the adsorbent bulb is not quite as straightforward as one might think. It is necessary to consider the following three questions (1) How do we define the remaining gas volume in relation to the volume occupied by the adsorbent (2) What is the most suitable procedure (3) If gas expansion is to be used, then which gas (e.g. He or Nj) should be adopted, and at what temperature ... 

The indirect route for determining the dead space volume makes use of an estimated volume of the adsorbent sample. This volume can be obtained in two ways ... 

Helium is often used in adsorption manometry for the determination of the dead space volume (see Chapter 3), but this procedure is based on the presupposition that the gas is not adsorbed at ambient temperature and that it does not penetrate into regions of the adsorbent structure which are inaccessible to the adsorptive molecules. In fact, with some microporous adsorbents, significant amounts of helium adsorption can be detected at temperatures well above the normal boiling point (4.2 K). For this reason, the apparent density (or so-called true density ) determined by helium pycnometry (Rouquerol et al., 1994) is sometimes dependent on the operational temperature and pressure (Fulconis, 1996). 

The establishment of the International Temperature Scale has been accomplished largely with the aid of measurements made with the helium gas thermometer. The most precise gas thermometry method is the constant-volume method, in which a definite quantity of the gas is confined in a bulb of constant volume Eat the temperature T to be determined and the pressure p of the gas is measured. A problem is encountered however in measuring the pressure a way must be found to communicate between the bulb and the pressure gauge. This is usually accomplished by connecting the bulb to the room-temperature part of the system by a slender tube and allowing a portion of the gas to occupy a relatively small, constant dead-space volume at room temperature. Thus, it is important that the gas volume in the pressure manometer be as small as possible. 

We can now develop the necessary equations for calculating the amount adsorbed from the p Fdata obtained during a run. Let us denote the known volume of the gas burette by Vb(= Vi + V2+ Fjor F2 + 14 as the case may be) and its temperature by 7g. Since the sample bulb is not completely filled by the solid adsorbent, we must also consider the so-called dead-space volume occupied by gas. Let us denote this volume by I4 and consider it to be at a single temperature T. If the burette is filled with gas at an initial pressure Pi and then stopcock B is opened, the pressure will drop to a new equilibrium value pi. The number of moles adsorbed is... 

The cryogenic adsorption system was specially developed to measure adsorption isotherms of H2 and D2. This system is equipped with a closed helium cycle two-stage Gifford McMahon refrigerator to operate under cryogenic conditions. The adsorption temperature can be kept constant within 0.03 K at 20 K. Adsorption isotherms are obtained by gas adsorption manometry. This method is based on the measurement of the gas pressure in a calibrated, constant volume, at a known temperature. The dead space volume was calculated from a helium calibration measurement at the temperature of interest. Thermal transpiration effect was calibrated according to the work by Takaishi and Sensui [41]. 

In (24-35) the term V /4 is influenced by many factors [Equation (24-14)], but mainly reflects the characteristics of a particular column and its mode of operation. This plate-munber factor is described in the preceding sections (24-2 and 24-3). The factors of relative retention and partition ratio in (24-35) depend on the solutes, the nature of the mobile and stationary phases, and the temperature. The factor A /(l -I- k) also strongly depends on the dead-space volume in a column. Figure 24-8 illustrates how it varies according to the dead-space volume per gram of stationary phase. When the specific retention volume of a solute is relatively low and a column... 

As it is known in real compressors, the percent of volume in the total displacement of a piston into a cylinder is called the dead space ratio, and it is defined as c = (volume of dead space) /(volume of displacement) [29]. In the Curzon-Ahlborn cycle, rc appears as the reciprocal of c. It is found that 3%rc>100/10 or 33>rc>10. Supposing power plants working as a Curzon-Ahlborn cycle, a linear approximation of efficiency, Equations (24) and (25), values of efficiency appear around the experimental values. As an example, Table 1 shows a comparison between real values and linear approximation values, y = 1.67, and the closeness of the linear approximation, in case of some modern power plants. 

The volume of the nasopharyngeal chamber and airways is 150 mL, that is, dead-space volume. Thus, with a resting tidal volume of 600 mL, only 75% of the air reaches the pulmonary air spaces. There is evidence to suggest that sequential breathing patterns occur that result in poorly ventilated regions [54-56],... 

Jet nebulizer (small volume) Volume fill (3-6 mL) Gas flow (6-12 L/min) Dead-space volume Open versus closed system Thumb-activating valve Mouthpiece versus facemask Inspiratory flow (slow, deep) Breath-holding Tapping nebulizer... 

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