I. Assessment of Hands-on Learning and Lecture II. Stability and Drag Reduction in Steady Capillary Flow Through Hydrophobic Channels with Minimal Helical Wire Supports.

Abstract

The expertise differential between instructor and student provides adequate potential for flow of expertise from the former to the latter during instruction. However, the intrinsic and extraneous cognitive loads (resistances to learning posed by the topic and instructional design/ implementation, respectively) need to be minimized. Multimedia learning and hands-on interactive learning are believed to reduce cognitive load over straight lecture. Several instructional configurations were compared in terms of important learning outcomes. Overall, students perceived that group miniaturized equipment-mediated instruction helped them more than lecture in terms of schema formation and aspects of competence-based education like group dynamics and hands-on skills.Stability and drag reduction during steady capillary fluid flow through hydrophobic extension springs were studied numerically and experimentally. Large-bore capillary channels formed from these springs are envisioned for phase separation and liquid-gas contacting in space and for small-scale terrestrial capillary transport. A practical realization of a structure with alternating transverse slip and no-slip boundaries that can give relatively large slip fractions and a large ratio of the length of slip sections to tube radius is a cylindrical capillary channel supported by a stretched hydrophobic spring. Some aspects of the flow in such a channel can be approximated by flow in the corresponding axisymmetric array of wire rings. Flow in such a channel is modeled by the finite element method on a periodic domain obtained by matching velocity fields at the extremities of the period. Drag reduction, measured by the slip length is found to increase with increasing pitch of the period and with increasing fraction of slip boundary, and to decrease with increasing roughness of the composite wire-plus-meniscus boundary and Reynolds number above 50. Overall, the highest drag reduction is found to occur for the highest contact angle studied (178o), Reynolds number below 50 and a smooth no-shear boundary. Stability and drag reduction during flow was studied experimentally in hydrophobic 1/4-inch and 1/8-inch springs. The ranges of stable pressures in the hydrophobic channels decreased with pitch and channel diameter. Consequently, relatively large flows up to 630 mL/min and slip lengths up to 140 µm were achieved at small pitches.