Buildup period

It is advisable to start a constant-pressure filtration test, like a comparable plant operation, at a low pressure, and smoothly increase the pressure to the desired operating level. In such cases, time and filtrate-quantity data shoulci not be taken until the constant operating pressure is reahzed. The value of r calculated from the extrapolated intercept then reflec ts the resistance of both the filter medium and that part of the cake deposited during the pressure-buildup period. When only the total mass of diy cake is measured for the tot cycle time, as is usually true in vacuum leaf tests, at least three runs of different lengths should be made to permit a rehable plot of 0/V against W. If rectification of the resulting three points is dubious, additional runs should be made. 

Figure 5.11 Typical kinetic curves obtained during propylene polymerization by TiCl3. is a decay-type curve 5 is a buildup or acceleration-type curve. I is the buildup period II is the decay period HI is the stationary period.

Example 5.3 In the buildup period of decay-type stereoregular polymerization, the rates are found to be different when catalyst is added first from the case when gas is introduced, followed by the catalyst. Show why this happens. 

In the buildup period of decay-type stereoregular polymerization, we find that the rate when propylene is introduced after TiCl3 and AlEt3 are allowed to equilibrate is different from the rate when AlEt3 is added after the gas is introduced. It is assumed that the following equihbrium exists in the former case ... 

The Z-spray inlet causes ions and neutrals to follow different paths after they have been formed from the electrically charged spray produced from a narrow inlet tube. The ions can be drawn into a mass analyzer after most of the solvent has evaporated away. The inlet derives its name from the Z-shaped trajectory taken by the ions, which ensures that there is little buildup of products on the narrow skimmer entrance into the mass spectrometer analyzer region. Consequently, in contrast to a conventional electrospray source, the skimmer does not need to be cleaned frequently and the sensitivity and performance of the instrument remain constant for long periods of time. 

Now suppose we consider another extreme of the same type of experiment. This time we alternate extremely short light and dark periods of equal duration. If we again start with [M-] =0 when the light goes on, we expect the type of behavior shown in Fig. 6.5d, where the radical buildup is interrupted by the extinction of the light before it reaches [M-] We could use Eq. (6.43) to evaluate the maximum radical concentration achieved, if that were the... 

Since membrane fording could quickly render the system inefficient, very careful and thorough feedwater pretreatment similar to that described in the section on RO, is required. Some pretreatment needs, and operational problems of scaling are diminished in the electro dialysis reversal (EDR) process, in which the electric current flow direction is periodically (eg, 3—4 times/h) reversed, with simultaneous switching of the water-flow connections. This also reverses the salt concentration buildup at the membrane and electrode surfaces, and prevents concentrations that cause the precipitation of salts and scale deposition. A schematic and photograph of a typical ED plant ate shown in Eigure 16. 

Most storage containers for ciyogens are designed for a 10 percent ullage volume. The latter permits reasonable vaporization of the contents due to heat leak without incurring too rapid a buildup of the pressure in the container. This, in turn, permits closure of the container for short periods of time to either avoid partial loss of the contents or to transport flammable or hazardous ciyogens safely from one location to another. 

Fouling on the outside of finned surfaces is usually rather small, but must be recognized. Values of 0.0001-0.0015 usually satisfy most fin-side conditions. Finned surfaces should be cleaned periodically to avoid excessive buildup of dust, oil films, bugs, etc. 

Thus, to control the buildup of sludge and scale (which may include the prevention of these foulants and deposits in the first place), it periodically becomes necessary to deconcentrate the BW by physically removing some of it from the boiler (blowing down or blowing off). This is achieved via a blowdown valve (BD valve) usually located at the bottom rear of the boiler vessel or WT mud drum. The BD water lost from the boiler is replaced by less concentrated FW. 

The furnace areas of WT boilers require the periodic deployment of retractable soot blowers to remove the buildup of soot and combustion products from water-wall tubes to maintain heat transfer and furnace cooling efficiency, as well as to minimize the interference of flue gas pathways. 

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