Abstract

Yield stress fluids resist flow unless an external force greater than their yield stress is applied to them.
The current thesis investigates the behavior of yield stress fluids subjected to a temperature gradient. We use
carbopol gels as a yield stress fluid to perform fluid flow characterization. The experimental setup includes a
cubical acrylic cell with aluminum sidewalls, 2 Thermoelectric units, thermocouples, and thermistors. Rheological
characterization of carbopol gels was performed, and yield stress was calculated by fitting the data
using the Herschel Bulkley equation. PIV (Particle Image velocimetry) technique was used for flow characterization.
Thermochromic liquid crystals (TLC) were used to visualize the temperature isotherms in the
flow field. Our experimental observations suggested an immediate flow onset with extremely slow sub yield
motions. The benchmark motionless experiments were compared with steady flow experiments to reveal
the immediate flow onset dynamics. The flow development curves showed rapid flow acceleration until it
reaches a maximum before decelerating to steady-state. The experiments with no steady flow developments
were compared with benchmark motionless experiments, supporting the presence of subyield motions in
yield stress fluids. The kinetic energy decayed exponentially to rest from the point when the supplied power
turned off during experiments.
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