Thermodynamics: An Engineering Approach
8th Edition
ISBN: 9780073398174
Author: Yunus A. Cengel Dr., Michael A. Boles
Publisher: McGraw-Hill Education
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Chapter 2.8, Problem 124RP
The pump of a water distribution system is powered by a 15-kW electric motor whose efficiency is 90 percent. The water flow rate through the pump is 50 L/s. The diameters of the inlet and outlet pipes are the same, and the elevation difference across the pump is negligible. If the pressures at the inlet and outlet of the pump are measured to be 100 kPa and 300 kPa (absolute), respectively, determine the
FIGURE P2–123
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The pump of a water distribution system is powered by a 15-kW electric motor whose efficiency is 95 percent. The water flow rate
through the pump is 50 L/s. The diameters of the inlet and outlet pipes are the same, and the elevation difference across the pump
is negligible. If the pressures at the inlet and outlet of the pump are measured to be 100 kPa and 300 kPa (absolute), respectively,
determine the mechanical efficiency of the pump.
Water
300 kPa
100 kPa
150 Ls
motor
Motor
15 kW
The mechanical efficiency of the pump is
%.
2. An air-conditioning system requires air flow at the main supply duct at a rate of 180 m³/min. The average velocity of
air in the circular duct is not to exceed 10 m/s to avoid excessive vibration and pressure drops. Assuming the fan
converts 70 percent of the electrical energy it consumes into kinetic energy of air, determine the size of the electric
motor needed to drive the fan and the diameter of the main duct. Take the density of air to be 1.20 kg/m3.
Note that Air Power of the fan is give by: AP = Qy Ah
Where: Q = volume flow rate of air m3/s, y = specific weight of air, kN/m³, Ah = pressure head, m
Ans: 618 mm
180 m/min
10 m/s
A water pump delivers 6 hp of shaft power when operating. If the pressure differential between the outlet and the inlet of the pump is measured to be 1.2 psi when the flow rate is 15 ft^3/s the changes in velocity and elevation are negligible, determine the mechanical efficiency of this pump. Show the energy diagram and label it accordingly
Chapter 2 Solutions
Thermodynamics: An Engineering Approach
Ch. 2.8 - What is total energy? Identify the different forms...Ch. 2.8 - List the forms of energy that contribute to the...Ch. 2.8 - How are heat, internal energy, and thermal energy...Ch. 2.8 - What is mechanical energy? How does it differ from...Ch. 2.8 - Natural gas, which is mostly methane CH4, is a...Ch. 2.8 - Portable electric heaters are commonly used to...Ch. 2.8 - Prob. 7PCh. 2.8 - Prob. 8PCh. 2.8 - 2–9E Calculate the total potential energy, in Btu,...Ch. 2.8 - Prob. 10P
Ch. 2.8 - Prob. 11PCh. 2.8 - At a certain location, wind is blowing steadily at...Ch. 2.8 - A water jet that leaves a nozzle at 60 m/s at a...Ch. 2.8 - Prob. 14PCh. 2.8 - Prob. 15PCh. 2.8 - Consider a river flowing toward a lake at an...Ch. 2.8 - When is the energy crossing the boundaries of a...Ch. 2.8 - Consider an automobile traveling at a constant...Ch. 2.8 - A gas in a pistoncylinder device is compressed,...Ch. 2.8 - A room is heated by an iron that is left plugged...Ch. 2.8 - A room is heated as a result of solar radiation...Ch. 2.8 - Prob. 23PCh. 2.8 - A small electrical motor produces 5 W of...Ch. 2.8 - Prob. 25PCh. 2.8 - 2–26C Lifting a weight to a height of 20 m takes...Ch. 2.8 - Prob. 27PCh. 2.8 - Prob. 28PCh. 2.8 - Prob. 29PCh. 2.8 - Prob. 30PCh. 2.8 - Prob. 31PCh. 2.8 - Prob. 32PCh. 2.8 - Prob. 33PCh. 2.8 - A ski lift has a one-way length of 1 km and a...Ch. 2.8 - The engine of a 1500-kg automobile has a power...Ch. 2.8 - Prob. 36PCh. 2.8 - What are the different mechanisms for transferring...Ch. 2.8 - On a hot summer day, a student turns his fan on...Ch. 2.8 - Prob. 39PCh. 2.8 - A vertical pistoncylinder device contains water...Ch. 2.8 - At winter design conditions, a house is projected...Ch. 2.8 - A water pump increases the water pressure from 15...Ch. 2.8 - Prob. 43PCh. 2.8 - Prob. 44PCh. 2.8 - A university campus has 200 classrooms and 400...Ch. 2.8 - Prob. 46PCh. 2.8 - Consider a room that is initially at the outdoor...Ch. 2.8 - Prob. 48PCh. 2.8 - 2-49 The 60-W fan of a central heating system is...Ch. 2.8 - Prob. 50PCh. 2.8 - An escalator in a shopping center is designed to...Ch. 2.8 - Prob. 52PCh. 2.8 - How is the combined pumpmotor efficiency of a pump...Ch. 2.8 - Prob. 54PCh. 2.8 - Can the combined turbinegenerator efficiency be...Ch. 2.8 - Consider a 2.4-kW hooded electric open burner in...Ch. 2.8 - Prob. 57PCh. 2.8 - Prob. 58PCh. 2.8 - Prob. 59PCh. 2.8 - A geothermal pump is used to pump brine whose...Ch. 2.8 - Prob. 62PCh. 2.8 - Prob. 63PCh. 2.8 - The water in a large lake is to be used to...Ch. 2.8 - A 7-hp (shaft) pump is used to raise water to an...Ch. 2.8 - At a certain location, wind is blowing steadily at...Ch. 2.8 - Reconsider Prob. 265. Using appropriate software,...Ch. 2.8 - Water is pumped from a lake to a storage tank 15 m...Ch. 2.8 - Prob. 69PCh. 2.8 - A hydraulic turbine has 85 m of elevation...Ch. 2.8 - Prob. 71PCh. 2.8 - Water is pumped from a lower reservoir to a higher...Ch. 2.8 - Prob. 73PCh. 2.8 - An oil pump is drawing 44 kW of electric power...Ch. 2.8 - How does energy conversion affect the environment?...Ch. 2.8 - What is acid rain? Why is it called a rain? How do...Ch. 2.8 - Why is carbon monoxide a dangerous air pollutant?...Ch. 2.8 - What is the greenhouse effect? How does the excess...Ch. 2.8 - What is smog? What does it consist of? How does...Ch. 2.8 - Prob. 80PCh. 2.8 - Consider a household that uses 14,000 kWh of...Ch. 2.8 - When a hydrocarbon fuel is burned, almost all of...Ch. 2.8 - Prob. 83PCh. 2.8 - A typical car driven 20,000 km a year emits to the...Ch. 2.8 - What are the mechanisms of heat transfer?Ch. 2.8 - Which is a better heat conductor, diamond or...Ch. 2.8 - How does forced convection differ from natural...Ch. 2.8 - What is a blackbody? How do real bodies differ...Ch. 2.8 - Define emissivity and absorptivity. What is...Ch. 2.8 - Does any of the energy of the sun reach the earth...Ch. 2.8 - The inner and outer surfaces of a 5-m 6-m brick...Ch. 2.8 - The inner and outer surfaces of a 0.5-cm-thick 2-m...Ch. 2.8 - Reconsider Prob. 292. Using appropriate software,...Ch. 2.8 - Prob. 94PCh. 2.8 - Prob. 95PCh. 2.8 - Prob. 96PCh. 2.8 - Prob. 97PCh. 2.8 - For heat transfer purposes, a standing man can be...Ch. 2.8 - Prob. 99PCh. 2.8 - Prob. 100PCh. 2.8 - A 1000-W iron is left on the ironing board with...Ch. 2.8 - A 7-cm-external-diameter, 18-m-long hot-water pipe...Ch. 2.8 - A thin metal plate is insulated on the back and...Ch. 2.8 - Reconsider Prob. 2103. Using appropriate software,...Ch. 2.8 - The outer surface of a spacecraft in space has an...Ch. 2.8 - Prob. 106PCh. 2.8 - A hollow spherical iron container whose outer...Ch. 2.8 - Consider a vertical elevator whose cabin has a...Ch. 2.8 - Consider a homeowner who is replacing his...Ch. 2.8 - Prob. 110RPCh. 2.8 - Prob. 111RPCh. 2.8 - Prob. 112RPCh. 2.8 - 2–113 The U.S. Department of Energy estimates that...Ch. 2.8 - Prob. 114RPCh. 2.8 - Prob. 115RPCh. 2.8 - Prob. 116RPCh. 2.8 - Prob. 117RPCh. 2.8 - Consider a TV set that consumes 120 W of electric...Ch. 2.8 - Water is pumped from a 200-ft-deep well into a...Ch. 2.8 - Prob. 120RPCh. 2.8 - Prob. 121RPCh. 2.8 - In a hydroelectric power plant, 65 m3/s of water...Ch. 2.8 - The demand for electric power is usually much...Ch. 2.8 - The pump of a water distribution system is powered...Ch. 2.8 - On a hot summer day, the air in a well-sealed room...Ch. 2.8 - Prob. 126FEPCh. 2.8 - A 2-kW electric resistance heater in a room is...Ch. 2.8 - A 900-kg car cruising at a constant speed of 60...Ch. 2.8 - Prob. 129FEPCh. 2.8 - Prob. 130FEPCh. 2.8 - Prob. 131FEPCh. 2.8 - A 2-kW pump is used to pump kerosene ( = 0.820...Ch. 2.8 - Prob. 133FEPCh. 2.8 - Prob. 134FEPCh. 2.8 - Prob. 135FEPCh. 2.8 - Prob. 136FEPCh. 2.8 - Prob. 137FEPCh. 2.8 - Heat is transferred steadily through a...Ch. 2.8 - The roof of an electrically heated house is 7 m...
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