Consider the base plate of a 1200-W household iron that has a thickness of L 0.5 cm, base area of A 300 cm2, and thermal conductivity of k 15 W/m · °C. The inner surface of the base plate is subjected to uniform heat flux generated by the resistance heaters inside, and the outer surface loses heat to the surroundings at T 20°C by convection. Taking the convection heat transfer coefficient to be h 80 W/m2 · °C and disregarding heat loss by radiation. Evaluate the temperatures at the inner and the outer surfaces. Resistance heater 1200 W Base plate Insulation 300 cm? T = 20°C h

Consider the base plate of a 1200-W household iron that has a thickness of L 0.5 cm, base area of A 300 cm2, and thermal conductivity of k 15 W/m · °C. The inner surface of the base plate is subjected to uniform heat flux generated by the resistance heaters inside, and the outer surface loses heat to the surroundings at T 20°C by convection. Taking the convection heat transfer coefficient to be h 80 W/m2 · °C and disregarding heat loss by radiation. Evaluate the temperatures at the inner and the outer surfaces. Resistance heater 1200 W Base plate Insulation 300 cm? T = 20°C h

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

See similar textbooks

Similar questions

A 5-cm-external-diameter, 10-m-long hot water pipe at 80°C is losing heat to the surrounding air at 5°C by natural convection at a rate of 1175 W. Determine the rate at which the work potential is wasted during this process as a result of this heat loss.
A 90-hp (shaft output) electric car is powered by an electric motor mounted in the engine compartment. If the motor has an average efficiency of 91 percent, determine the rate of heat supply by the motor to the engine compartment at full load.
A 300-ft-long section of a steam pipe whose outer diameter is 4 in passes through an open space at 50°F. The average temperature of the outer surface of the pipe is measured to be 280°F, and the average heat transfer coefficient on that surface is determined to be 6 Btu/h·ft2·°F. Determine (a) the rate of heat loss from the steam pipe and (b) the annual cost of this energy loss if steam is generated in a natural gas furnace having an efficiency of 86 percent, and the price of natural gas is $1.10/therm (1 therm = 100,000 Btu).
A hot water pipe at 80°C is losing heat to the surrounding air at 5°C by natural convection with a convection heat transfer coefficient of 25 W/ m2.°C. The rate of heat loss from the pipe by convection is to be determined.
A building with an internal volume of 400 m3 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°C, and the local atmospheric pressure is 95 kPa. The building is losing heat to the surroundings at a steady rate of 450 kJ/min. Air is forced to flow through the duct and the heater steadily by a 250-W fan, and it experiences a temperature rise of 5°C each time it passes through the duct, which may be assumed to be adiabatic. How long will it take for the air inside the building to reach an average temperature of 24°C?
A building with an internal volume of 400 m3 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°C, and the local atmospheric pressure is 95 kPa. The building is losing heat to the surroundings at a steady rate of 450 kJ/min. Air is forced to flow through the duct and the heater steadily by a 250-W fan, and it experiences a temperature rise of 5°C each time it passes through the duct, which may be assumed to be adiabatic. Determine the average mass flow rate of air through the duct.
Heat is transferred steadily through a 0.2-m-thick, 8 m × 4 m wall at a rate of 2.4 kW. The inner and outer surface temperatures of the wall are measured to be 15°C and 5°C. The average thermal conductivity of the wall is (a) 0.002 W/m·°C (b) 0.75 W/m·°C (c) 1.0 W/m·°C (d) 1.5 W/m·°C (e) 3.0 W/m·°C
An exercise room has 6 weight-lifting machines that have no motors and 7 treadmills each equipped with a 2.5-hp (shaft output) motor. The motors operate at an average load factor of 0.7, at which their efficiency is 0.77. During peak evening hours, all 12 pieces of exercising equipment are used continuously, and there are also two people doing light exercises while waiting in line for one piece of the equipment. Assuming the average rate of heat dissipation from people in an exercise room is 600 W, determine the rate of heat gain of the exercise room from people and the equipment at peak load conditions.
A gas enclosed in a container that has a piston with a cross-sectional area of 0.15 m2 has a vacuum pressure of 40 kPa and a temperature of 200 °C when the piston moves 20 cm compressing the gas. Determine the work done if the atmospheric pressure of the place is 100 kPa. a) 1.8 kJb) 1.2 kJc) 9.0 kJd) 3.0 kJ
On a hot summer day, the air in a well-sealed room is circulated by a 0.50-hp fan driven by a 65 percent efficient motor. (Note that the motor delivers 0.50 hp of net shaft power to the fan.) The rate of energy supply from the fan–motor assembly to the room is (a) 0.769 kJ/s (b) 0.325 kJ/s (c) 0.574 kJ/s (d) 0.373 kJ/s (e) 0.242 kJ/s
A heat engine receives heat from a source at 1100 K at a rate of 400 kJ/s, and it rejects the waste heat to a medium at 320 K. The measured power output of the heat engine is 120 kW, and the environment temperature is 25°C.Determine the rate of irreversibility.
If the container is placed in a colder environment, how will it affect the actual heat transfer and the irreversibility of the system?