| OCR Text |
Show - 8 - fraction is constant, the increase in D is seen to be very strongly dependent on density. This would be contrary to the results of Yosida where a six- fold increase \ nf> did not lead to serious changes in D. The ratio in equation ( 13) varies between 2.15 and 23- 17 for the densities employed by Yosida. The measured increase in D was found to range between 3- 18 and 4.55- The calculated results are of the correct order of magnitude for this increase, but a variation in cross sectional gap area would have to be postulated to explain the constancy of measured values. If the least dense snow settled most strongly forming more gap area than the densest snow, the trend could be explained. More experimental data are needed to determine the role of the above factors. Any experimental method in which weight changes depend on mass flux across a narrow gap Is subject to the same considerations as discussed above. If the width of the gap is small compared to the container dimensions, the gap will not seriously disturb the normal temperature profile. The difference in mass flux from that normally expected will then be approximated by the ratio in equation ( 13). If one wishes to measure diffusion phenomenon without the disturbing effects of air gaps, it should be possible to record the weight at each end of a cylinder filled with snow and subject to a temperature gradient, and compare weight changes with those predicted by diffusion theory. |
