/*! 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 61 Water from a reservoir passes ov... [FREE SOLUTION] | 91Ó°ÊÓ

91Ó°ÊÓ

Water from a reservoir passes over a dam through a turbine and discharges from a \(70-\mathrm{cm}\) ID pipe at a point 55 m below the reservoir surface. The turbine delivers 0.80 MW. Calculate the required flow rate of water in \(\left.\mathrm{m}^{3} / \mathrm{min} \text { if friction is neglected. (See Example } 7.7-3 .\right)\) If friction were included, would a higher or lower flow rate be required? (Note: The equation you will solve in this problem has multiple roots. Find a solution less than \(2 \mathrm{m}^{3} / \mathrm{s}\).)

Short Answer

Expert verified
To deliver 0.80 MW power, the required flow rate of water is approximately 42.79 m^3/s. If friction were considered, a higher flow rate would be required to produce the same amount of power.

Step by step solution

01

Formulating the problem

Identify the water reservoir as the system since this is where the energy of water is being converted into mechanical energy by the turbine. The reservoir surface is point 1 from where water flows and the turbine represents point 2, 55 m below the point 1. The flow rate needed to produce 0.80MW of power can be found by setting up Bernoulli's equation for between these two points, neglecting friction.
02

Application of Bernoulli's Equation

Express Bernoulli's equation between the two points. \( P1+/rho * g * h1 + 1/2 * rho * V1^2 = P2 +/rho * g * h2 + 1/2 * rho * V2^2 \). Here, P1 and P2 represent pressure at point 1 and 2 respectively, h1 and h2 are the heights from a baseline, V1 and V2 are velocities of water at point 1 and 2 respectively, rho is the density of water, and g is acceleration due to gravity. Since we are neglecting friction, we can assume P1=P2. As the water is static at the reservoir surface, V1 is zero. Also V2, can be written as Q / A, where Q is the flow rate to be found and A is the cross sectional area of discharge pipe.
03

Solving Bernoulli’s equation

Solve Bernoulli’s equation as obtained in step 2. \(/rho * g * h1 = /rho * g * h2 + 1/2 * rho * (Q/A)^2 \), which simplifies to \(h1 = h2 + (Q^2/2*g*A^2) \). Rearrange equation to solve for Q. \( Q =sqrt[2*g*A^2*(h1-h2)] \). Substitute the values of known quantities and solve for Q.
04

Conceptual question - effect of friction

Think of what friction would do when water passes through the pipe. It would cause energy losses to overcome it, and hence, less energy would be available for the turbine to convert into mechanical energy. Therefore, if friction were included, a higher flow rate would be required to deliver the same power.

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 91Ó°ÊÓ!

Key Concepts

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

Energy Conversion
In the context of water passing through a turbine, energy conversion plays a significant role. Essentially, the gravitational potential energy of water stored in a reservoir is converted to mechanical energy by the turbine. This conversion process is understood through the lens of Bernoulli's equation. The potential energy due to the height of the reservoir surface is transformed into kinetic energy as water flows through the system. This kinetic energy is ultimately harnessed by the turbine to generate power.
For the exercise, this conversion needs to produce 0.80 MW of power, thus the flow rate is calculated by ensuring the kinetic energy at the point of discharge matches the mechanical energy output desired. Neglecting friction simplifies the scenario, allowing us to focus directly on the energy conversion without energy loss considerations.
This process highlights the efficient transformation of energy types in fluid dynamics systems and exemplifies the conservation of energy principle, enabling us to solve for other variables using the known power output.
Fluid Dynamics
Fluid dynamics encapsulates the study of the behavior of fluids in motion. When analyzing fluid systems like the reservoir and turbine scenario, several key factors come into play. We employ Bernoulli's equation, which is a fundamental principle in fluid dynamics.
Bernoulli's equation helps us account for different forms of energy in a flowing fluid. It equates the potential energy, kinetic energy, and pressure energy along a streamline. In this problem, because we assume frictionless flow, the fluid's pressure energy at the reservoir surface (point 1) and the discharge (point 2) remains constant, simplifying our calculations.
One essential aspect to understand is that the velocity of the fluid affects the energy states at various points in the system, such as at the point of discharge. By applying Bernoulli’s equation, we determine how these energies balance to find the necessary flow rate for desired power output without energy loss variations due to viscosity or surface roughness, as friction effects are not considered.
Hydraulic Systems
Hydraulic systems are a category of fluid dynamics that involve the transmission of power through pressurized fluid. In the scenario of a dam and turbine, we analyze a simple but effective hydraulic system where water from the reservoir serves as the fluid medium. This setup outlines the fundamental operation of many large-scale hydraulic systems found in civil engineering and resource management.
The turbine in the system converts hydraulic energy into mechanical energy. This conversion efficiency is key to understanding how hydraulic systems can be optimized. The ability to measure and calculate flow rates, as done in the exercise, shows how the system can ensure efficient energy transfer.
If we consider friction, which adds to the complexity of hydraulic systems, the energy losses would demand a greater volume of water to produce the same amount of energy, as the mechanical efficiency would decrease. This basic understanding highlights the importance of minimizing friction in real-world hydraulic applications to maximize efficiency and power output.

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

A fuel oil is burned with air in a boiler furnace. The combustion produces \(813 \mathrm{kW}\) of thermal energy, of which \(65 \%\) is transferred as heat to boiler tubes that pass through the furnace. The combustion products pass from the furnace to a stack at \(550^{\circ} \mathrm{C}\). Water enters the boiler tubes as a liquid at \(30^{\circ} \mathrm{C}\) and leaves the tubes as saturated steam at 20 bar absolute. (a) Calculate the rate ( \(\mathrm{kg} / \mathrm{h}\) ) at which steam is produced. (b) Use the steam tables to estimate the volumetric flow rate of the steam produced. (c) Repeat the calculation of Part (b), only assume ideal-gas behavior instead of using the steam tables. Would you have more confidence in the estimate of Part (b) or Part (c)? Explain. (d) What happened to the \(35 \%\) of the thermal energy released by the combustion that did not go to produce the steam?

Air is heated from \(25^{\circ} \mathrm{C}\) to \(140^{\circ} \mathrm{C}\) prior to entering a combustion furnace. The change in specific enthalpy associated with this transition is \(3349 \mathrm{J} / \mathrm{mol}\). The flow rate of air at the heater outlet is \(1.65 \mathrm{m}^{3} / \mathrm{min}\) and the air pressure at this point is \(122 \mathrm{kPa}\) absolute. (a) Calculate the heat requirement in \(\mathrm{kW}\), assuming ideal-gas behavior and that kinetic and potential energy changes from the heater inlet to the outlet are negligible. (b) Would the value of \(\Delta \dot{E}_{k}\) [which was neglected in Part (a)] be positive or negative, or would you need more information to be able to tell? If the latter, what additional information would be needed?

Saturated steam at \(100^{\circ} \mathrm{C}\) is heated to \(350^{\circ} \mathrm{C}\). Use the steam tables to determine (a) the required heat input (J/s) if a continuous stream flowing at \(100 \mathrm{kg} / \mathrm{s}\) undergoes the process at constant pressure and (b) the required heat input (J) if \(100 \mathrm{kg}\) undergoes the process in a constant-volume container. What is the physical significance of the difference between the numerical values of these two quantities?

One thousand liters of a 95 wt\% glycerol- \(5 \%\) water solution is to be diluted to \(60 \%\) glycerol by adding a \(35 \%\) solution pumped from a large storage tank through a \(5-\mathrm{cm}\) ID pipe at a steady rate. The pipe discharges at a point 23 m higher than the liquid surface in the storage tank. The operation is carried out isothermally and takes 13 min to complete. The friction loss ( \(\hat{F}\) of Equation \(7.7-2\) ) is \(50 \mathrm{J} / \mathrm{kg}\). Calculate the final solution volume and the shaft work in \(\mathrm{kW}\) that the pump must deliver, assuming that the surface of the stored solution and the pipe outlet are both at 1 atm. Data: \(\quad \rho_{\mathrm{H}_{2} \mathrm{O}}=1.00 \mathrm{kg} / \mathrm{L}, \rho_{\mathrm{gly}}=1.26 \mathrm{kg} / \mathrm{L} .\) (Use to estimate solution densities.)

A turbine discharges \(200 \mathrm{kg} / \mathrm{h}\) of saturated steam at \(10.0 \mathrm{bar}\) absolute. It is desired to generate steam at \(250^{\circ} \mathrm{C}\) and 10.0 bar by mixing the turbine discharge with a second stream of superheated steam of \(300^{\circ} \mathrm{C}\) and \(10.0 \mathrm{bar}\) (a) If \(300 \mathrm{kg} / \mathrm{h}\) of the product steam is to be generated, how much heat must be added to the mixer? (b) If instead the mixing is carried out adiabatically, at what rate is the product steam generated?

See all solutions

Recommended explanations on Chemistry 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.