OCR Text |
Show - 2 - Jansson found that }\ z o. oooo5 + OrOo\ 9p + o-° Q& pz while Devaux concluded that ^ : 7-(\ Jr lOOp1)' lO~ 5 In each case these expressions represent the average of data with considerable scatter, and later investigations Lfor instance, Kondrat'eva (* f) J have generally found a similar scatter. It appears that the dependency of conductivity on density may be broadly described by the expressions given above, or similar ones, but within this dependency there is considerable variation from one snow sample to another. This variation may be attributed to differences in the ice framework ( crystal character) for a given density and to the variable influence of water vapor transfer mentioned above. More recently the separate elements of heat transfer in snow have come under investigations. Using precisely characterized snow samples in a laboratory apparatus, de Quervain ( 3) was able to compare the relative amounts of heat transferred by conduction in the ice framework and by the air in the pores. This was done by substituting gases of different known heat conductivities for the air in the snow and extrapolating the accompanying change in snow conductivity to that which would accompany a theoretical gas of zero conductivity. For natural snow of density 0,33 g/ cnK, it was found that about 75$ of the heat flow could be accounted for by conduction in the ice. Working later with the same apparatus and similar snow samples, Mueller ( unpublished report) showed that this heat flow might amount to 85$. Both of these investigations intentionally disregarded the role of water vapor in the heat flow. From the described experimental conditions, it appears that the contribution of water vapor would be included in that portion of the heat flow attributed to conduction in ice. |