OCR Text |
Show as similar previous plots. Puff intensities are very weak. At long times, temperature profiles are similar to the case for toluene, but the gas phase concentration profile is lower by an order of magnitude (Figure 20). 5.4 Effect of Sorbent and Container Parameters In the experiment, sorbent amounts and characteristics were not varied. Therefore it is useful to exploit the model to extrapolate outside the test matrix and attempt to predict the effects of sorbent porosity, absorbency and container volume. It should be noted that sorbent porosity, mass, and container volume are not independent. Furthermore, porosity is equal to the volume fraction of the interstitial volumes between particles, while absorbency relates to the sorption properties within each grain. The effect of changes in porosity, changed by varying the mass of sorbent in a given container, but assuming that the sorbent was uniformly dispersed throughout the container is shown on Figure 21 and the puff trace for € = 0.13 is shown on Figure 22. Clearly, overall void fraction is important and should be minimized to minimize puffs. Calculations in which the thermal conductivity was varied were also completed. With ten times the base value the puff magnitude was 5.9 while with one tenth of the base value its value was 2.2 on the same arbitrary scale. Clearly, sorbents with high thermal conductivities should be avoided, because that would facilitate heat transfer into the sorbent aggregate. If sorbent masses are changed, and container volumes are reduced proportionately, keeping porosity the same, the model predicts little effect on the puff magnitude. Doubling the sorbent mass and the container length led to a modest puff magnitude change from 4 . 595 to 4 . 585, while increasing the 25 |