Reference stream

A side stream from the cathode product mixture is passed over a room temperature alumina bed to remove HF. The nitrogen/hydrogen ratio is estimated, and from this ratio and the known flow rate of the nitrogen reference stream, the current efficiency for hydrogen production is calculated. 

These detectors sense the difference in refractive index between the column eluent and a reference stream of pure mobile phase. They are the closest thing in hplc to a universal detector, as any solute can be detected as long as there is a difference in ri between the solute and the mobile phase. 

There are several types of RI detector, all of which monitor the difference between a reference stream of mobile phase and the column effluent. Any solute whose presence alters the refractive index of the pure solvent will be detected, but sensitivity is directly proportional to the difference between the refractive index of the solute and that of the solvent. At best they are two orders of magnitude less sensitive than UV/visible detectors. All RI detectors are highly temperature-sensitive, and some designs incorporate heat exchangers between column and detector to optimize performance. They cannot be used for gradient elution because of the difficulty in matching the refractive indices of reference and sample streams. 

Note that (5.101) holds under the assumption that the initial/inlet conditions have been renumbered so that the first AW correspond to the mixture-fraction basis. By definition, the mixture-fraction vector is always null in the reference stream. 

FIGURE 10.6 Schematic diagram of flow and diffusion within the T-sensor at a 1 1 1 flow ratio. A reference solution enters the device from the left, a detection solution from the middle, and a particle-laden sample stream enters from the right. The inset shows (1) original flow boundaries, (2) reference stream, (3) particle-laden sample stream, (4) diffusion of detector substance into reference stream, (5) diffusion of reference substance into detector stream, (6) detection stream, (7) diffusion of sample analyte into detection stream, (8) diffusion of detector substance into sample stream, and (9) detector window [443]. Reprinted with permission from the American Association for the Advancement of Science. 

Total molar flow rate of reference stream... 

When the inlet stream is selected as the reference stream, Eq. 2.7.9 reduces to... 

Solution Note that the units of and Kg are (mol/L). We seleet the inlet stream as the reference stream. For gas-phase reactions, and asstrming ideal gas behavior. 

Using the conversion definition (Eq. 2.6.1b) and applying it to the reference stream, Fao-... 

To reduce die design equations of flow reactors to dimensionless forms, we select a convenient reference stream as a basis for the calculation. In most cases, it is convenient to select die inlet stream into the reactor as the reference stream, but, in some cases, it is more convenient to select another stream, even an imaginary stream. There is no restriction on the selection of the reference stream, except that we should be able to relate the reactor composition to it in terms of the reaction extents. Once we select the reference stream, we use the dimensionless extent, Z, of the mth-independent reaction, defined by Eq. 2.7.2,... 

The difficulty in analyzing flow reactors is that the transformations of chemical reactions take place over space (volume), whereas the reaction operation is a rate process. To relate the reactor volume to a time domain, we select a reference volumetric flow rate for the reference stream, vq, and define the reactor space time, t p, by... 

To solve these equations, we have to seleet a reference stream, define reference conceniration, Co, and characteristic reaction time ta, and then express the individual reaction rates in terms of t, Zi, Z3, and Z5. 

As in the case of batch reactors, dimensionless energy balance Eq. 5.2.53 is not conveniently used because the heat capacity of the reacting fluid, (FjCpj), is a function of the temperature and reaction extents and, consequently, varies along the reactor. To simplify the equation and obtain dimensionless quantities for heat transfer, we define the heat capacity of the reference stream and relate the heat capacity at any point in the reactor to it by... 

The specific molar-based heat capacity of the reference stream, Cp, is defined by... 

As discussed in Section 2.7, for gas-phase reactions, (Ttot)o is taken as the total molar flow rate of the reference stream, including inerts, and... 

To determine the correction factor of the heat capacity, CF(Zm, 6), we use Eq. 5.2.54 and the appropriate definition of the specific molar heat capacity of the reference stream, Eor gas-phase reactions. 

Note that when the inlet stream is taken as the reference stream, and assuming constant mass-based specific heat capacity, CF(Z , 0) = 1. 

For isothermal CSTRs with negligible shaft work, and selecting the inlet stream as the reference stream, 0out = 9in = 1. and, using Eq. 5.2.56, Eq. 5.2.68 reduces to... 

---