Residence times calculation

Typical gaseous residence time calculated in absence of organics. 

The mean of this distribution—the mean residence time—is the true mean residence time calculated by dividing the separator volume by the flow rate. 

Fig. 6. Qdyn/Qmax for BSA adsorption to fluidized Streamline DEAE at different linear flow rates. Original capacity data from Hjorth et al. [51], liquid residence time calculated from bed expansion data provided in Ref. [51]...

Another type of experiment has been used to assess the chemical reactivity of pesticides in the air. This principally employs downwind sampling from a treatment site during application (for measuring conversion in the spray drift) and for several days following application (for conversions involving volatilized residues) (24). The principal data are in the form of product(s)/parent ratios with increasing downwind distance, from which estimates of the rate of conversion can be made knowing the air residence time calculated from windspeed measurements. 

The reactive transport of contaminants in FePRBs has been modeled using several approaches [179,184,186,205-208]. The simplest approach treats the FePRB as an ideal plug-flow reactor (PFR), which is a steady-state flow reactor in which mixing (i.e., dispersion) and sorption are negligible. Removal rates (and therefore required wall widths, W) can be estimated based on first-order contaminant degradation and residence times calculated from the average linear groundwater velocity [Eq. (27)]. The usefulness of... 

Residence time calculations are a direct result of manipulating the compartmental matrix K. Let = —K be the negative inverse of the compartmental matrix, and let be the ijth element of . The matrix 0 is called the mean residence time matrix. The following information given concerning the interpretation of this matrix comes from Coveil et al. (4) and Cobelli et al. (12). Further detail is beyond the scope of this chapter, and the interested reader is directed to these two references. 

Note that the residence time is a function of the temperature since the volumetric flowrate is linearly related to the absolute temperature. Thus, the higher the operating temperature the shorter the residence time. In addition, the gas residence time calculated above by dividing the volume of the incinerator chamber by the combustion gas flowrate is an approximate value. This does not include flowrate... 

Strube (1996) has shown that an increasing interaction of components or a decreasing number of columns per section results in significant deviations of both the calculated concentration profiles and purities. Model based optimal design requires a correct description of the dynamic behavior of the SMB process. Therefore, Diinnebier et al. (2000a) recommend the use of the detailed SMB model. These considerations are also valid for SMBR processes. Additionally, Lode et al. (2003a) have shown that the residence time calculated with the TMBR model differs from that in the SMBR model and, in consequence, different conversion rates are calculated. 

The first assumption is probably valid, since the other sources listed in Table 6.2 do not greatly alter the results derived by considering rivers alone. The issue of steady state cannot be verified for very long (millions of years) timescales, but the geological evidence does suggest that the concentration of major ions in seawater has remained broadly constant over very long time periods (Box 6.2). As an example of the residence time calculation, consider sodium (Na+) ... 

Figure 4 presents the results of one such study. Petcoke carbon conversion was plotted versus reactor gas-phase residence time calculated for the trial runs, and a trend line was extrapolated to 100% conversion. From this graph, it was... 

It should be kept in mind, however, that the residence time calculated in this way is the mean residence time. There is a distribution of residence times in a reactor. The flow speed of the fluid near the channel wall surface... 

Uir and t are the minimal length of the tube and the residence time calculated, via the plug-flow model L is the actual length of the tube (taking into account the defor-mation-of the profile of flow velocities) which provides the required conversion corresponding to the time t ). 

Rate constants of separation and residence times calculated for some cep and hep metals are shown in Table 7.1. 

Residence time Calculated maximmn retention period for waste species in an incinerator furnace, assuming all gases move with plug flow and are at uniform temperature and pressure. 

Results of equilibrium thermochemical calculations for the thermal destruction of nonplastic and plastic materials show the effect of material composition on the flame temperature, particulate emission, metals, dioxins, and product gas composition. The effect of waste composition has greater influence on adiabatic flame temperature, combustion air requirement, and the evolution of products and intermediate species. The combustion of waste in air produces higher flame temperature for 100% plastic than for nonplastic and mixtures. The 100% plastic requires lower number of moles of oxidant than 100% nonplastic and mixtures. Plastic produces HCl and H2S with concentration levels ranging from 1000 to 10,000 ppm. Emission of NO and NO2 from 100% nonplastic showed an increase with increase in moles of air while that from 100% plastic a slight decrease with increase in moles of air. The higher theoretical flame temperatures predicted with plastic waste corresponds to lower waste feed rate requirement of plastic at constant furnace temperature. This resulted in higher excess air operation with plastic waste and hence lower equivalence ratio. The gas residence time calculated for all the samples was found to be about 1 s. Variation of residence time more or less follows the same trend as excess air for all the samples. 

Figure 7 shows the residence times calculated for = 0 ps and ti = 4 ps as a function of the adsorption energy for water in contact with the model surface and also for water in contact with the mercury surface. Suppressing the contribution from short time oscillations leads to a substantial increase in the calculated residence time. The trends, however, are rather similar. Water near the mercury surface behaves differently from water near the surfaces described by model III where a linear correlation of residence time with adsorption energy is observed. The adsorption energy is obviously not the only parameter that determines the residence time. Lattice geometry, periodicity, corrugation, and the curvature of the interaction potential influence it as well. 

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