/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 99 Concrete is pumped from a cement... [FREE SOLUTION] | 91影视

91影视

Concrete is pumped from a cement mixer to the place it is being laid, instead of being carried in wheelbarrows. The flow rate is \(200 \mathrm{L} / \mathrm{min}\) through a 50.0 -m-long. 8.00-cm-diameter hose, and the pressure at the pump is \(8.00 \times 10^{6} \mathrm{N} / \mathrm{m}^{2} .\) (a) Calculate the resistance of the hose. (b) What is the viscosity of the concrete, assuming the flow is laminar? (c) How much power is being supplied, assuming the point of use is at the same level as the pump? You may neglect the power supplied to increase the concrete's velocity.

Short Answer

Expert verified
The resistance of the hose is \(2.40 \times 10^{9} \, \mathrm{N} \cdot \mathrm{s}/\mathrm{m}^{5}\), the viscosity of the concrete is \(1.2 \times 10^{-3} \, \mathrm{Pa} \cdot \mathrm{s}\), and the power supplied is 26.6 KW.

Step by step solution

01

Calculate the resistance of the hose

Resistance in a fluid can be calculated by Poiseuille's Law, rearranged to solve for resistance (R): \( R = \Delta P / Q \) where 鈭哖 is the pressure difference and Q is the volumetric flow rate. The given pressure at the pump is \(8.00 \times 10^{6} \mathrm{N} / \mathrm{m}^{2}\) and the flow rate is 200 L/min or \(200 \times 10^{-3} \mathrm{m}^{3}/60 \, \mathrm{s} = 3.33 \times 10^{-3} \mathrm{m}^{3}/\mathrm{s}\). Substituting these values into the equation for R gives \( R = (8.00 \times 10^{6} \mathrm{N} / \mathrm{m}^{2}) / (3.33 \times 10^{-3} \mathrm{m}^{3}/\mathrm{s}) = 2.40 \times 10^{9} \, \mathrm{N} \cdot \mathrm{s}/\mathrm{m}^{5}\)
02

Calculate the viscosity of the concrete

Viscosity (畏) can be calculated by Poiseuille's Law rearranged to solve for 畏: \( \eta = \frac{R \cdot \pi \cdot r^{4}}{8 \cdot l}\) where r is the radius of the pipe, l is the length of the pipe. First, convert the diameter to radius: r = d/2 = 8.0 cm / 2 = 4 cm = 0.04 m. Note: the length was provided in the problem statement as 50.0 m. Substituting these values and the resistance calculated in step 1 into the equation for 畏 gives \( \eta = \frac{2.40 \times 10^{9} \, \mathrm{N} \cdot \mathrm{s}/\mathrm{m}^{5} \cdot \pi \cdot (0.04 \mathrm{m})^{4}}{8 \cdot 50.0 \, \mathrm{m}} = 1.2 \times 10^{-3} \mathrm{Pa} \cdot \mathrm{s}\)
03

Calculate the power being supplied

In fluids, power (P) is given by the formula P=螖P*Q where 螖P is the pressure difference (same as the pressure provided in the problem since the use-point and pump are at the same level) and Q is the volumetric flow rate. We substitute the given values into the formula to get: \(P=(8.00 \times 10^{6} \, \mathrm{N} / \mathrm{m}^{2})(3.33 \times 10^{-3} \, \mathrm{m}^{3}/\mathrm{s})=26.6 \, per kilowatt (KW)\)

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

Key Concepts

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

Poiseuille's Law
Poiseuille's Law is a critical principle in fluid mechanics that allows us to predict the flow of fluids through a pipe. It is predicated on the understanding of a few key variables, and is typically applied to scenarios where the flow is laminar, meaning the fluid flows in parallel layers without disruption between them. A laminar flow has a smooth, constant motion, as opposed to a turbulent flow where the motion is chaotic.

Poiseuille鈥檚 Law quantitatively describes the relationship between the pressure difference in the fluid (螖P), the viscosity (畏), the length of the pipe (l), the radius of the pipe (r), and the volumetric flow rate (Q). The law can be represented mathematically as:
Q = (蟺螖Pr鈦)/(8畏l)
Which can be rearranged to solve various unknowns 鈥 for example, the resistance of the hose in the exercise. To calculate resistance, Poiseuille鈥檚 Law is instead represented as:R = 螖P/Q
This form allowed us to determine how much the hose resists the flow of concrete by dividing the pressure by the volumetric flow rate.
Viscosity
Viscosity is a property of fluids that signifies their resistance to deformation or, more practically, their 'thickness'. A high viscosity indicates a thicker fluid, such as honey, while a low viscosity indicates a thinner fluid, like water.

In the context of our exercise, viscosity has a direct impact on how easily concrete flows through the hose. For a fluid flowing in a pipe, viscosity can be thought of as the 'internal friction' of the fluid, which affects the ease of movement and the energy required to maintain a certain flow rate. Mathematically, viscosity (畏) can be calculated using the rearranged form of Poiseuille's Law, as demonstrated in step 2 of the solution.
  • It should be noted that temperature often plays a role in changing a fluid's viscosity 鈥 higher temperatures usually decrease viscosity, making fluids runnier.
  • Viscosity is also a key factor in determining that the flow remains laminar; high viscosities tend to suppress turbulent flows.

The calculated value reflects the resistance of concrete to shear or flow under the given conditions, playing a crucial role in practical applications like pumping concrete for construction.
Pressure
Pressure in fluid mechanics is the amount of force exerted per unit area within the fluid or on the boundaries of its container. It plays a pivotal role in determining the flow of fluids through pipes, as well as in an array of industrial and natural phenomena.

In our exercise, we refer to the pressure within the hose provided by a pump (螖P), which pushes the concrete through the hose. It's crucial for driving the flow against resistance produced inherently from the viscosity of the fluid and the physical characteristics of the hose.
  • Pressure difference is what propels the fluid; without it, there would be no flow.
  • Pressure also affects the required power to maintain the flow, with greater pressures indicating higher energy demand.

By understanding pressure and its implications on fluid flow, we can design more efficient pumping systems and better anticipate the energy needs for various fluid transport scenarios.
Flow Rate
Flow rate, often represented as Q, is a measure of the volume of fluid that passes a particular point within a unit of time. It is a crucial concept in many areas of fluid dynamics as it indicates how swiftly a fluid moves through a system.

In the exercise example, we're dealing with a flow rate measured in liters per minute, which tells us how much concrete is transferred from the pump to the construction site within each minute. A higher flow rate signifies more volume being moved in less time, which is often sought after to increase efficiency in many industrial processes.
  • The volumetric flow rate is directly related to the speed at which the fluid moves, which depends on several factors including pressure and hose dimensions.
  • Calculating flow rate is essential for sizing equipment, designing systems, and determining operational costs.

Understanding flow rate aids in optimizing processes, ensuring sufficient quantities are transported, and mitigating potential bottlenecks within fluid transport systems.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

What force must be exerted on the master cylinder of a hydraulic lift to support the weight of a 2000-kg car (a large car) resting on a second cylinder? The master cylinder has a 2.00-cm diameter and the second cylinder has a 24.0-cm diameter.

(a) Verify that a \(19.0 \%\) decrease in laminar flow through a tube is caused by a \(5.00 \%\) decrease in radius, assuming that all other factors remain constant. (b) What increase in flow is obtained from a \(5.00 \%\) increase in radius, again assuming all other factors remain constant?

Assuming bicycle tires are perfectly flexible and support the weight of bicycle and rider by pressure alone, calculate the total area of the tires in contact with the ground if a bicycle and rider have a total mass of \(80.0 \mathrm{kg}\) and the gauge pressure in the tires is \(3.50 \times 10^{5} \mathrm{Pa}\)

Every few years, winds in Boulder, Colorado, attain sustained speeds of \(45.0 \mathrm{m} / \mathrm{s}\) (about \(100 \mathrm{mph}\) ) when the jet stream descends during early spring. Approximatelywhat is the force due to the Bernoulli equation on a roof having an area of \(220 \mathrm{m}^{2}\) ? Typical air density in Boulder is \(1.14 \mathrm{kg} / \mathrm{m}^{3},\) and the corresponding atmospheric pressure is \(8.89 \times 10^{4} \mathrm{N} / \mathrm{m}^{2}\). (Bernoulli's principle as stated in the text assumes laminar flow. Using the principle here produces only an approximate result, because there is significant turbulence.)

A trash compactor can compress its contents to 0.350 times their original volume. Neglecting the mass of air expelled, by what factor is the density of the rubbish increased?

See all solutions

Recommended explanations on Physics Textbooks

View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.