Question

10A.7 Viscous heating in a ballpoint pen. You are asked to decide whether the apparent decrease in viscosity in ballpoint pen inks during writing results from "shear thinning" decrease in viscosity because of non-Newtonian effects) or "temperature thinning" (decrease in viscosity because of temperature rise caused by viscous heating). If the temperature rise is less than 1 K, then "temperature thinning" will not be important. Estimate the temperature rise using Eq. 10.8-9 and the following estimated data: Clearance between ball and holding cavity Diameter of ball Viscosity of ink Speed of writing Thermal conductivity of ink (rough guess) 5x 10-5 in. 1 mm 0 cp 100 in./min 5 x10-4 cal/s . cm . "C

Answer 1