{"id":5379,"date":"2025-07-18T09:25:05","date_gmt":"2025-07-18T14:25:05","guid":{"rendered":"https:\/\/commons.princeton.edu\/josephhenry\/?page_id=5379"},"modified":"2025-08-18T22:41:54","modified_gmt":"2025-08-19T03:41:54","slug":"part-iii-estimation-of-fluid-drag","status":"publish","type":"page","link":"https:\/\/commons.princeton.edu\/josephhenry\/part-iii-estimation-of-fluid-drag\/","title":{"rendered":"Part III: Estimation of Fluid Drag"},"content":{"rendered":"

Ryan Yu | 8\/12\/25<\/p>\n

There are many experimental uncertainties that affect rotational velocity. Friction between the pivot and arms; Back EMF; fluid drag. We fixed this problem by remaking the pivot with 3\/56th pivot point and there was very little friction.<\/p>\n

\"\"<\/p>\n

Drag from the zinc conductor in the fluid was the most obvious source of experimental uncertainty, so I set out to model it in COMSOL, using an 2D Axisymmetric model and the laminar flow interface.<\/p>\n

\"\"<\/p>\n

I prescribed the rotational acceleration of our optimized configuration from Part II, .8962 rad\/sec^2, to the submerged zinc ring, and instructed COMSOL to solve for fluid disturbance. I then integrated the shear rate to across the surface of the zinc to get a value of 3.847E-4 (1\/s).<\/p>\n

Shear stress is shear rate times fluid viscosity (Newton’s law of viscosity<\/a>)\"\"<\/p>\n

The fluid viscosity of 35% sulfuric acid is .025, so shear stress is calculated to be 9.62E-06 Pascals<\/strong>.<\/p>\n

The opposing force (fluid drag) is torque (which is shear stress) times area. \"\"*Thank you ilearnengineering.com!*<\/a><\/p>\n

The formula for the lateral surface area of our zinc ring is 2(pi)(r)(h);<\/p>\n

A= 8.482E-3<\/span><\/span>(<\/span><\/span><\/span><\/span><\/span><\/span><\/span>m<\/span>2)<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/strong><\/p>\n

F*A=(9.62E-06)*(8.482E-3)=8.16E-8<\/strong><\/p>\n

So the force of drag, even for the most headstrong rotating zinc ring, is orders of magnitude lesser than our Lorentz forces, which are generally in the E-5 to E-4 range. The force of drag is (in my opinion) basically negligible!<\/p>\n

Unrelated but very cool visualization of the velocity in the sulfuric acid as the zinc rotates with optimal rotational velocity: (sped up, over a minute interval)<\/em><\/p>\n

https:\/\/commons.princeton.edu\/josephhenry\/wp-content\/uploads\/sites\/71\/2025\/07\/coolflow.mp4<\/a><\/video><\/div>\n

 <\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Ryan Yu | 8\/12\/25 There are many experimental uncertainties that affect rotational velocity. Friction between the pivot and arms; Back EMF; fluid drag. We fixed this problem by remaking the pivot with 3\/56th pivot point and there was very little friction. Drag from the zinc conductor in the fluid was the most obvious source of … Continue reading “Part III: Estimation of Fluid Drag”<\/span><\/a><\/p>\n","protected":false},"author":6918,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"categories":[],"tags":[],"class_list":["post-5379","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/pages\/5379","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/users\/6918"}],"replies":[{"embeddable":true,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/comments?post=5379"}],"version-history":[{"count":12,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/pages\/5379\/revisions"}],"predecessor-version":[{"id":5676,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/pages\/5379\/revisions\/5676"}],"wp:attachment":[{"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/media?parent=5379"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/categories?post=5379"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/commons.princeton.edu\/josephhenry\/wp-json\/wp\/v2\/tags?post=5379"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}