Chapter 5: Problem 41
Will the temperature of air rise as it is compressed by an adiabatic compressor? Why?
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
Air at \(300 \mathrm{K}\) and \(100 \mathrm{kPa}\) steadily flows into a hair dryer having electrical work input of \(1500 \mathrm{W}\). Because of the size of the air intake, the inlet velocity of the air is negligible. The air temperature and velocity at the hair dryer exit are \(80^{\circ} \mathrm{C}\) and \(21 \mathrm{m} / \mathrm{s},\) respectively. The flow process is both constant pressure and adiabatic. Assume air has constant specific heats evaluated at \(300 \mathrm{K}\). (a) Determine the air mass flow rate into the hair dryer, in \(\mathrm{kg} / \mathrm{s}\). ( \(b\) ) Determine the air volume flow rate at the hair dryer exit, in \(\mathrm{m}^{3} / \mathrm{s}\).
Refrigerant-134a at \(1.4 \mathrm{MPa}\) and \(90^{\circ} \mathrm{C}\) is throttled to a pressure of 0.6 MPa. The temperature of the refrigerant after throttling is \((a) 22^{\circ} \mathrm{C}\) \((b) 56^{\circ} \mathrm{C}\) \((c) 82^{\circ} \mathrm{C}\) \((d) 80^{\circ} \mathrm{C}\) \((e) 90^{\circ} \mathrm{C}\)
Refrigerant 134 a enters a compressor with a mass flow rate of \(5 \mathrm{kg} / \mathrm{s}\) and a negligible velocity. The refrigerant enters the compressor as a saturated vapor at \(10^{\circ} \mathrm{C}\) and leaves the compressor at \(1400 \mathrm{kPa}\) with an enthalpy of \(281.39 \mathrm{kJ} / \mathrm{kg}\) and a velocity of \(50 \mathrm{m} / \mathrm{s}\). The rate of work done on the refrigerant is measured to be \(132.4 \mathrm{kW}\). If the elevation change between the compressor inlet and exit is negligible, determine the rate of heat transfer associated with this process, in \(\mathrm{kW}\).
Liquid water at \(300 \mathrm{kPa}\) and \(20^{\circ} \mathrm{C}\) is heated in a chamber by mixing it with superheated steam at \(300 \mathrm{kPa}\) and \(300^{\circ} \mathrm{C}\). Cold water enters the chamber at a rate of \(1.8 \mathrm{kg} / \mathrm{s} .\) If the mixture leaves the mixing chamber at \(60^{\circ} \mathrm{C}\) determine the mass flow rate of the superheated steam required. Answer: \(0.107 \mathrm{kg} / \mathrm{s}\)
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.
What do you think about this solution?
We value your feedback to improve our textbook solutions.
