Chapter 5: Problem 17
What is flow energy? Do fluids at rest possess any flow energy?
Over 30 million students worldwide already upgrade their learning with Vaia!
All the tools & learning materials you need for study success - in one app.
Get started for free
A building with an internal volume of \(400 \mathrm{m}^{3}\) is to be heated by a 30 -kW electric resistance heater placed in the duct inside the building. Initially, the air in the building is at \(14^{\circ} \mathrm{C},\) and the local atmospheric pressure is 95 kPa. The building is losing heat to the surroundings at a steady rate of \(450 \mathrm{kJ} / \mathrm{min}\). Air is forced to flow through the duct and the heater steadily by a \(250-\mathrm{W}\) fan, and it experiences a temperature rise of \(5^{\circ} \mathrm{C}\) each time it passes through the duct, which may be assumed to be adiabatic. (a) How long will it take for the air inside the building to reach an average temperature of \(24^{\circ} \mathrm{C} ?\) (b) Determine the average mass flow rate of air through the duct.
Consider a 35 -L evacuated rigid bottle that is surrounded by the atmosphere at \(100 \mathrm{kPa}\) and \(22^{\circ} \mathrm{C}\). A valve at the neck of the bottle is now opened and the atmospheric air is allowed to flow into the bottle. The air trapped in the bottle eventually reaches thermal equilibrium with the atmosphere as a result of heat transfer through the wall of the bottle. The valve remains open during the process so that the trapped air also reaches mechanical equilibrium with the atmosphere. Determine the net heat transfer through the wall of the bottle during this filling process.
The velocity of a liquid flowing in a circular pipe of radius \(R\) varies from zero at the wall to a maximum at the pipe center. The velocity distribution in the pipe can be represented as \(V(r),\) where \(r\) is the radial distance from the pipe center. Based on the definition of mass flow rate \(\dot{m}\) obtain a relation for the average velocity in terms of \(V(r)\) \(R,\) and \(r\).
A vertical piston-cylinder device initially contains \(0.01 \mathrm{m}^{3}\) of steam at \(200^{\circ} \mathrm{C}\). The mass of the frictionless piston is such that it maintains a constant pressure of \(500 \mathrm{kPa}\) inside. Now steam at \(1 \mathrm{MPa}\) and \(350^{\circ} \mathrm{C}\) is allowed to enter the cylinder from a supply line until the volume inside doubles. Neglecting any heat transfer that may have taken place during the process, determine ( \(a\) ) the final temperature of the steam in the cylinder and \((b)\) the amount of mass that has entered.
A 110 -volt electrical heater is used to warm \(0.3 \mathrm{m}^{3} / \mathrm{s}\) of air at \(100 \mathrm{kPa}\) and \(15^{\circ} \mathrm{C}\) to \(100 \mathrm{kPa}\) and \(30^{\circ} \mathrm{C}\). How much current in amperes must be supplied to this heater?
What do you think about this solution?
We value your feedback to improve our textbook solutions.
