Abstract
The sliding concentric cylinder technique has been discussed to evaluate the first normal stress difference of viscoelastic fluids. The entry pressure loss at the bottom of the bob was ignored in the previous study. In order to estimate the entry pressure loss, the three bobs were made. They have the same diameter but their length is different. The same technique of Berkley plot was applied in this study and therefore the effect of the bob length on the reactive force was measured. The evaluated N1 was close to the value predicted from the results measured by the rheometers. On the other hand, the result of N1 with the correction of the entry pressure loss was affected by the bob length. It seems that the validity is lacked in this result.
