Experimentation, effective diffusivity residence time determination

The slope of the lines presented in Figure 5 is defined as k(q/v). The q/v term defines the turnover of the tank contents or what is commonly referred to as the retention time. When q is increased, the liquid contacts the carbon more often and the removal of pesticides should increase, however, the efficiency term, k, can be a function of q. As the waste flow rate is increased, the fluid velocity around each carbon particle increases, thereby increasing system turbulence and compressing the liquid boundary layer. The residence time within the carbon bed is also decreased at higher liquid flow rates, which will reduce the time available for the pesticides to diffuse from the bulk liquid into the liquid boundary layer and into the carbon pores. From inspection of Table II, the pesticide concentration also effects the efficiency factor, k can only be determined experimentally and is valid only for the equipment and conditions tested. 

In the case of less reactive pofymer ems, sudi as the meta-isomer of the PMDA/ODA based pol>(amic ethyl ester), mbmd results were obtained when investigating the pofymer imidization behavior of this pofymer in the presence of various amines as illustrated in Table 3. All spedmens were soft-baked at 80 C for S minutes, treated with the amine for 10 minutes and finalfy cured at 200 for IS minutes. Although imidization levels of base-treated spedmens are significantly higher as compared to the non-treated spedmen, no distinctive trend in the data is observable. This is most likety due to factors sudi as the ability of the amine to effectivety diffuse into the polymer film or the actual residence time of the amine in the film at elevated temperatures as determined by volatility considerations. Another aq[>ect not reflected tty the experimental IR imidization data relates to surface effects. Since the IR measurement determines bulk imidization levels, skin-core effects are completely ne ected. Thus, it is quite conceivable that in case of low imidization levels, the surface of the film could actually be completely imidized with little or no imidization in the underlying material. This skin-effect may then prevent the diffusion of catalyst into the bulk of the polymer film. 

---