If density doubles while average flow speed and tube diameter stay the same, Reynolds number will:

If density doubles while average flow speed and tube diameter stay the same, Reynolds number will:

• A. It doubles
• B. It remains unchanged
• C. It halves
• D. It quadruples

Answer: (A)

Reynolds number measures the ratio of inertial to viscous forces in a flow and depends on density, velocity, diameter, and viscosity: Re = ρ v D / μ. Here, the flow speed and the tube diameter stay the same, and viscosity is assumed constant. The only changing factor is density, which sits in the numerator. Doubling density doubles the numerator while the denominator and other factors stay fixed, so the Reynolds number becomes twice as large. In other words, Re increases proportionally with density when velocity, diameter, and viscosity are unchanged.

Reynolds number measures the ratio of inertial to viscous forces in a flow and depends on density, velocity, diameter, and viscosity: Re = ρ v D / μ. Here, the flow speed and the tube diameter stay the same, and viscosity is assumed constant. The only changing factor is density, which sits in the numerator. Doubling density doubles the numerator while the denominator and other factors stay fixed, so the Reynolds number becomes twice as large. In other words, Re increases proportionally with density when velocity, diameter, and viscosity are unchanged.