Calculate Time to Fill Bathtub with Volume Flow Rate

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SUMMARY

The discussion focuses on calculating the time required to fill a bathtub using the volume flow rate of water from a tap. The key formula derived is time = volume of the bathtub (x m³) divided by the outlet area (A) multiplied by the velocity (v m/s), resulting in time = x / (A * v) seconds. The outlet area is calculated using the radius of the pipe (r), leading to A = πr². Additionally, if temperature variations are considered, the problem evolves into a differential equation involving an exponential coefficient.

PREREQUISITES
  • Understanding of fluid dynamics concepts, specifically volume flow rate.
  • Knowledge of geometric calculations for area (A = πr²).
  • Familiarity with basic differential equations for temperature variations.
  • Ability to manipulate units of measurement (m³, m/s).
NEXT STEPS
  • Learn about fluid dynamics principles and the Bernoulli equation.
  • Study the derivation and applications of differential equations in thermal dynamics.
  • Explore practical examples of calculating flow rates in plumbing systems.
  • Investigate the impact of temperature on fluid flow and its mathematical modeling.
USEFUL FOR

Engineers, physicists, and anyone involved in plumbing design or fluid mechanics who seeks to understand the calculations involved in filling containers with varying flow rates and temperatures.

Angello90
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Ok another stupid/smart question,

I got a bath with x m^3 volume. And a water flow rate of a tap is y m/s. I also know pressure and velocity. How can I calculate time to fill up bathtub? I know it's simple but I can not figure it out!
 
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You need to know the volume of water coming in per second, then it is easy. If you know the velocity you don't need to know the pressure. However that is not enough, you can have any volume of water at the same velocity/pressure.
 
Ok, so let's say the radius of pipe is r. This would give the area of outlet. Multiplying Q by A would give me (m/s) by (m^2), thus giving me volume of water coming out.

Does it make any sense?
 
Exactly, so you have m^3/s. If the bathtub fills up at x cubic meters then it takes x/Av seconds.

Now if it is hot or cold water then you have to account for the room temperature difference and it becomes a differential equation with an exponential coefficient in the solution.
 
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