Dead spaces

This method is smiple but experimentally more cumbersome than the volumetric method and involves the use of a vacuum microbalance or beam balance [22], The solid is suspended from one ann of a balance and its increase in weight when adsorption occurs is measured directly. The dead space calculation is thereby avoided entirely but a buoyancy correction is required to obtain accurate data. Nowadays this method is rarely used. 

Following the pioneer work of Beebe in 1945, the adsorption of krypton at 77 K has come into widespread use for the determination of relatively small surface areas because its saturation vapour pressure is rather low (p° 2Torr). Consequently the dead space correction for unadsorbed gas is small enough to permit the measurement of quite small adsorption with reasonable precision. Estimates of specific surface as low as 10 cm g" have been reported. Unfortunately, however, there are some complications in the interpretation of the adsorption isotherm. 

A number of potential sources of error must be taken into account. In the volumetric method the following items need attention (a) constancy of the level of liquid nitrogen (b) depth of immersion of the sample bulb ( S cm) (c) temperature of sample (monitoring with vapour pressure thermometer close to sample bulb) (d) purity of adsorptive (preferably 99-9 per cent) (e) temperature of gas volumes (doser, dead space), controlled to 01 C. 

A variation to the top-feed dmm filter is the dual dmm filter which uses two dmms of the same size in contact with each other and rotating in opposite directions. The feed enters into the V-shaped space formed on top of the two dmms and the cake that starts forming initially contains coarser particles due to the settling which takes place in the feed zone. This is beneficial to the clarity of the filtrate because the coarser particles act as a precoat. Erom the point of view, however, of the final moisture content of the cake the stratification of the soHds in the cake may lead to somewhat wetter cakes. Utilization of the area of the dmms is poor since there are dead spaces under the two dmms. The primary appHcation of the dual dmm filters is in dewatering coarse mineral or coal suspensions at feed concentrations greater than 200 kg/m. ... 

Since there are no dead spaces in a SHE, the helical flow pattern combines to entrain any solids and create high turbulence creating a self-cleaning flow passage. 

First, a mechanism is assumed whether completely mixed, plug flow, laminar, with dispersion, with bypass or recycle or dead space, steady or unsteady, ana so on. Then, for a differential element of space and/or time the elements of a conservation law. 

Figure 4-14. Radial machines of one to eight stages with horizontally split casing, partcularly suitable for compressing nitrous gases. There are no dead spaces provoking buildup of an ammonium nitrate salt.

Figure 8-14. E-curve, F-curve, and A-curve for a typicai system with dead space.

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. ... 

Dead space The portion of each breath that does not participate in gas ex-... 

The piping around any facility, other than the straight pipe connecting the equipment, is made up primarily of a series of control stations. Flow from one vessel goes through a control station and into a piece of pipe that goe.s to another vessel. In addition to considering the use of block valves, check valves, etc., all control stations should be designed so that the control valve can be removed and any bypass valve is located above or on a level with the main control valve. If the bypass is below the con tiol valve, it provides a dead space for water accumulation and corrosion. 

Sharp changes in direction, especially where liquids are moving at high velocities, and re-entrant angles, dead spaces and other details where stagnant conditions may result should be avoided. This is particularly important if inhibitors are to be used. 

Moreover, it has been noticed that in clinical applications, devices such as catheters, which have to pass through the skin from the outside to the interior of the body. It always exposes the patient to the risk of infection. Because there are dead space between the catheter surface and the surrounding tissue, the bacteria can enter the body along the device surface in direct contact with the skin. Such dead space would not be formed if the material surface were able to bond to the skin tissue at the microscopic level. 

Definitions of flame parameters in channels. D, distance between channel walls effective in flame quenching (quenching distance). D, flame width dead space R, radius of curvature of the flame. 

The cooling effect of the channel walls on flame parameters is effective for narrow channels. This influence is illustrated in Figure 6.1.3, in the form of the dead-space curve. When the walls are <4 mm apart, the dead space becomes rapidly wider. This is accompanied by falling laminar burning velocity and probably lowering of the local reaction temperature. For wider charmels, the propagation velocity w is proportional to the effective flame-front area, which can be readily calculated. On analysis of Figures 6.1.2b and 6.1.3, it is evident that the curvature of the flame is a function of... 

Dead space and the radius of curvature of flame as functions of the distance between channel walls for flames shown in Figure 6.1.2. 

Dead space as a function of (a) quenching distance and (b) equivalence ratio. 

To examine the details of the structure of flames in channels under quenching conditions, numerical methods were used. Two-dimensional CFD simulation of a propane flame approaching a channel between parallel plates was carried out using the FLUENT code [25]. The model reproduced the geometry of the real channels investigated experimentally. Close to the quenching limit, the burning velocity, dead space, and radius of curvature of the flames were all close to the experimental values. 

Cleaning of the wellbore region through the acids and gas fi-om in situ fermentation The gas serves to push oil from dead space and dislodge dehris that plugs the pores the average pore size is increased and, as a result, the capillary pressure near the wellbore is made more favorable for the flow of oil... 

In this model of non-ideal reactor mixing, a fraction, fi, of the volumetric feed rate, F, completely by-passes the mixing in the reactor. In addition, a fraction, f2, of the reactor volume, V, exists as dead space. F3 is the volumetric rate of exchange between the perfectly mixed volume Vi and the dead zone volume V2 of the reactor. 

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