Tracer computation errors

Potentiometric measurements give log(3/ values which are correct to within 10% but the relative accuracy is difficult to assess due to the successive, repetitive nature of the experiments. Probably the most significant source of error, as we have stated, is the variation of pH with time. At tracer concentrations the enthalpy AH0 can be determined only by the temperature differential method. However, the temperature differential method is not as precise as the calorimetric one. The enthalpy of formation for each complex is computed with the assumption that ACp is constant over the temperature range and that the range of error corresponds to 10%. 

The extent of gas dispersion can usually be computed from experimentally measured gas residence time distribution. The dual probe detection method followed by least square regression of data in the time domain is effective in eliminating error introduced from the usual pulse technique which could not produce an ideal Delta function input (Wu, 1988). By this method, tracer is injected at a point in the fast bed, and tracer concentration is monitored downstream of the injection point by two sampling probes spaced a given distance apart, which are connected to two individual thermal conductivity cells. The response signal produced by the first probe is taken as the input to the second probe. The difference between the concentration-versus-time curves is used to describe gas mixing. 

The bounce-back collision typically employed at fluid-solid boundaries, where fluid particles are turned back in the direction they came from following collision with a solid wall, causes the effective wall position to extend one half lattice unit into the fluid from the solid surface (Stockman et al., 1997). This is not a serious problem for velocity computations in slow flows, but has the potential to be a significant problem for tracer/dispersion simulations. Increasing the number of lattice points inside a flow channel can reduce this error, but is computationally very expensive. 

Computed values of Di for the smaller SDS and CTAB micelles (Mi) show excellent agreement with reported values (Table 2). Differences in Di for CTAB/KBr and CTAB/NaCl are greater than can be explained by experimental error. This is not surprising, since counter ion effects on the size of ionic micelles are well-known. For example, NMR tracer diffusion coefficient measurements in salt-free systems gave 1 x 10 cm s" ... 

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