ME 111 · Fluid Dynamics
Fluid Dynamics Experiment: Water Flow from Jar to Straw
An experimental analysis of water draining from a sealed jar through a glass straw — analyzing head loss, velocity, and flow regime.
ME 111 · Fluid Dynamics · April 29, 2025
Analyzing Head Loss, Velocity, and Flow Regime
Course
ME 111
Type
Experimental Study
Date
April 29, 2025
Result
Re = 2828 · Transitional
Topic Overview
An experimental study of water draining through a glass straw from a sealed 500 mL jar, used to compute flow rate, exit velocity, head loss, and flow regime from real measurements.
Objective
Compute the volume flow rate, exit velocity, head loss, pressure difference, and Reynolds number for the jar-to-straw system, and classify the flow as laminar, transitional, or turbulent.
Method
The setup used a 500 mL jar sealed at the top draining through a smooth glass straw of 0.295 in (0.00749 m) diameter, with a 0.3642 m drop from water surface to straw exit and water at 20°C. Measured volume and drain time fed an energy balance using Bernoulli's equation, with minor losses and a Reynolds number calculation determining the flow regime.
Key Insight
Measured flow rate was 1.67×10⁻⁵ m³/s at an exit velocity of 0.378 m/s, with total head losses of 0.0182 m. The Reynolds number came out to 2828 — placing the flow in the transitional band but behaving close to laminar because of the smooth glass surface. The takeaway: a simple gravity-driven system can be analyzed accurately with Bernoulli and Reynolds relations, and minor losses, while small, are measurable.