Bulk residence time

K, when the residence time of bulk water molecules exceeds those in the first ionic shell of Cl, K > and Rb. At temperatures higher than 373 K, the decay of the bulk residence times is sharper than the corresponding decay in the first shell of the ions, and the ratio bulk/ ion is reduced to a value similar to that at ambient conditions. 

The bulk residence time, 6b, which is the more commonly used parameter to correlate pyrolysis selectivity, expresses only the length of time that a mass of gas spends in the pyrolysis coil. Bulk residence time is not adequate to represent the combined effects of temperature and chemical reaction which take place in the pyrolysis coil as witness by the failure to correlate the available experimental data as a function of bulk residence time especially when data from pyrolysis coils of different configurations and, therefore, different temperature profiles are considered.(3)... 

When only one phase is forming eddy cunents, as when a gas is blown across the surface of a liquid, material is uansported from the bulk of the metal phase to the interface and dris may reside there for a short period of time before being submerged again in die bulk. During this residence time t, a quantity of matter, will be U ansported across die interface according to the equation... 

The NMR study by Wiithrich and coworkers has shown that there is a cavity between the protein and the DNA in the major groove of the Antennapedia complex. There are several water molecules in this cavity with a residence time with respect to exchange with bulk water in the millisecond to nanosecond range. These observations indicate that at least some of the specific protein-DNA interactions are short-lived and mediated by water molecules. In particular, the interactions between DNA and the highly conserved Gin 50 and the invariant Asn 51 are best rationalized as a fluctuating network of weak-bonding interactions involving interfacial hydration water molecules. 

Glaser and Lichtenstein (G3) measured the liquid residence-time distribution for cocurrent downward flow of gas and liquid in columns of -in., 2-in., and 1-ft diameter packed with porous or nonporous -pg-in. or -in. cylindrical packings. The fluid media were an aqueous calcium chloride solution and air in one series of experiments and kerosene and hydrogen in another. Pulses of radioactive tracer (carbon-12, phosphorous-32, or rubi-dium-86) were injected outside the column, and the effluent concentration measured by Geiger counter. Axial dispersion was characterized by variability (defined as the standard deviation of residence time divided by the average residence time), and corrections for end effects were included in the analysis. The experiments indicate no effect of bed diameter upon variability. For a packed bed of porous particles, variability was found to consist of three components (1) Variability due to bulk flow through the bed... 

Example 5.7 A CSTR is commonly used for the bulk pol5anerization of styrene. Assume a mean residence time of 2 h, cold monomer feed (300 K), adiabatic operation UAgxt = ), and a pseudo-first-order reaction with rate constant... 

The reason for the formation of anatase phase at such a high temperature might be explained as following. The as-prqiared ultrafine titania particles are liquefied at sufficimtly high temperature because melting point of nanoparticlra are lower than that of bulk titania (1850 C). The liquid titania particles are supercooled and became metastable states. The residence time in the flame is only in the order of miU-second so that the metastable phase has no time to become thermodynamically stable phase, rutile. 

Possible causes of sludge bulking include (a) absence of certain necessary trace elements in wastewater (b) wide fluctuations in wastewater pH (c) limited DO in the aeration tank (d) inadequate FIM ratio (e) inadequate mean cell residence time Tc (f) inadequate return sludge pumping rate (g) internal plant overloading and (h) poor sedimentation clarifier operation. 

The bulk of this chapter is devoted to a discussion of optimization with regard to selectivity considerations. In the sections that follow we will take 3 = 0 in order to concentrate on the primary effects and to simplify the discussion. Consequently, in this chapter, the terms space time, mean residence time, and holding time may be used interchangeably. 

It is desirable to calculate new bulk phase Z values for the four primary media which include the contribution of dispersed phases within each medium as described by Mackay and Paterson (1991) and as listed earlier. The air is now treated as an air-aerosol mixture, water as water plus suspended particles and fish, soil as solids, air and water, and sediment as solids and porewater. The Z values thus differ from the Level I and Level II pure phase values. The necessity of introducing this complication arises from the fact that much of the intermedia transport of the chemicals occurs in association with the movement of chemical in these dispersed phases. To accommodate this change the same volumes of the soil solids and sediment solids are retained, but the total phase volumes are increased. These Level III volumes are also given in Table 1.5.2. The reaction and advection D values employ the generally smaller bulk phase Z values but the same residence times thus the G values are increased and the D values are generally larger. 

This D value is IJbAwZ4, where UB, the sediment burial rate, is 2.0 x 10-7 m/h. It can be viewed as GBZB4, where GB is the total burial rate specified as Vs/tB where tB (residence time) is 50,000 h, and Vs (the sediment volume) is the product of sediment depth (0.01 cm) and area Aw. Z4, ZB4 are the Z values of the sediment solids and of the bulk sediment, respectively. Since there are 20% solids, ZB4 is about 0.2 Z4. There is a slight difference between these approaches because in the advection approach (which is used here) there is burial of water as well as solids. 

Continuous SSP plants are characterized by longer residence times and larger product hold-ups compared to the melt phase. This is due to the lower processing temperatures and the lower bulk density of the pellets compared to the melt. At today s standard bottle grade capacities of ca. 300 t/d, the typical plant hold-up is approximately 2501, which equates to around 300 m3 of product volume at a bulk density of 800kg/m3. Because the plants make use of gravity flow through the equipment they tend to be very tall - up to 50 m at 300 t/d. 

The interpretation of the data from bulk oozes and chalks, even if it is accepted that they are providing a global signal, is different depending on whether the timescales of interest are greater than or smaller than the residence time of Ca. Equation (5) can be written also in the following form ... 

---