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The speed of flow of water through a long cylindrical pipe of diameter \(2 \mathrm{~cm}\) so that flow become turbulent, is: (Assume at temperature of \(20^{\circ} \mathrm{C}\), viscosity \(\eta=1 \times 10^{-3} \mathrm{~Pa} .\) second, Reynold number \(=3000\) ) (a) \(1.5 \mathrm{~m} / \mathrm{s}\) (b) \(0.15 \mathrm{~m} / \mathrm{s}\) (c) \(2 \mathrm{~m} / \mathrm{s}\) (d) \(1 \mathrm{~m} / \mathrm{s}\)

Short Answer

Expert verified
The speed is 0.15 m/s, option (b).

Step by step solution

01

Understand the formula for flow speed

To find the speed at which the flow becomes turbulent, recall the formula for the Reynold's number, given by \( R_e = \frac{\rho v d}{\eta} \), where \( R_e \) is the Reynold's number (3000 in this case), \( \rho \) is the density of water which is approximately \(1000\, \mathrm{kg/m^3}\) at \(20^{\circ} \mathrm{C}\), \( v \) is the speed of water, \( d \) is the diameter, and \( \eta \) is the viscosity.
02

Substitute known values

Substitute the known values into the formula to solve for \(v\). The diameter of the pipe \(d = 2\, \mathrm{cm} = 0.02\, \mathrm{m}\), viscosity \(\eta = 1 \times 10^{-3} \mathrm{~Pa} \cdot s\), and the Reynold's number \( R_e = 3000\). The density of water \( \rho = 1000 \mathrm{~kg/m^3} \).
03

Solve for the velocity \(v\)

Rearrange the formula \( R_e = \frac{\rho v d}{\eta} \) to solve for \( v \) as follows: \[ v = \frac{R_e \cdot \eta}{\rho \cdot d} \] Substituting the numbers gives \[ v = \frac{3000 \cdot 1 \times 10^{-3}}{1000 \cdot 0.02} \].
04

Calculate the result

Calculate the expression: \[ v = \frac{3000 \times 1 \times 10^{-3}}{1000 \times 0.02} = \frac{3}{0.02} = 0.15 \mathrm{~m/s} \]. This is the speed at which the flow becomes turbulent.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Turbulent Flow
Turbulent flow in fluid dynamics is when the fluid flow pattern is chaotic and irregular. Unlike smoother laminar flow, turbulent flow has swirls and eddies caused by unpredictable changes in speed and direction. Imagine the difference between gently pouring milk into coffee, creating smooth streaks, and rapidly stirring the coffee with a spoon, causing a chaotic mix. Turbulence is important because it affects how substances mix in a fluid. It also influences drag on objects moving through the fluid, like ships and airplanes.

In the context of our exercise, turbulent flow occurs in a cylindrical pipe when the fluid velocity crosses a certain threshold. This is measured using the Reynold's number, where values above 3000 typically indicate turbulence. It provides crucial insight into various natural and industrial processes, determining efficiency and performance of fluid systems.
Viscosity
Viscosity refers to a fluid's resistance to flow. You can think of it as the 'thickness' or internal friction of the fluid. For instance, honey has a higher viscosity than water and flows much slower. In our exercise, the viscosity of water serves as a key factor in determining the flow rate needed to reach turbulence.

The viscosity (\(\eta\) in our formula) in fluid mechanics often depends on the fluid's temperature. For example, the viscosity of water at 20°C is approximately \(1 \times 10^{-3}\, \text{Pa·s}\). Higher viscosity implies more resistance, influencing how easily a fluid can flow through pipes and channels. This knowledge helps in designing systems such as pipelines, where maintaining an efficient flow is crucial.
Cylindrical Pipe
A cylindrical pipe is a common pathway for fluid transport in many systems. The shape allows for efficient flow and ease of manufacture. In fluid dynamics, the diameter of the pipe is a crucial parameter, impacting flow characteristics like velocity and pressure. When water flows through a cylindrical pipe, as in our exercise, the diameter influences the Reynold's number, which indicates whether the flow is laminar or turbulent. A smaller diameter can lead to a higher probability of turbulent flow if the fluid's velocity is high enough. Knowing the diameter facilitates predictions of flow behavior and optimization of the pipeline's design in industrial applications.
Fluid Dynamics
Fluid dynamics is the study of how liquids and gases move. It covers various phenomena like flow rates, pressure changes, and energy transfer within fluids. To solve problems in fluid dynamics, engineers often use principles and equations, such as Bernoulli's equation or the continuity equation. Understanding fluid dynamics helps in solving practical problems like predicting weather patterns or designing efficient piping systems. In our problem, the use of Reynold's number is essential to determine when the flow in a pipe will become turbulent. Calculations based on fluid dynamics principles ensure that systems are designed to minimize energy loss and manage pressure efficiently, critical for industries involving fluid transport like water supply, gas production, and oil pipelines.

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Most popular questions from this chapter

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