The side surfaces of a 3-m-high cubic industrial furnace burning natural gas are not insulated, and the temperature at the outer surface of this section is measured to be 110°C. The temperature of the furnace room, including its surfaces, is 30°C, and the emissivity of the outer surface of the furnace is 0.7. It is proposed that this section of the furnace wall be insulated with glass wool insulation (k = 0.038 W/m·K) wrapped by a reflective sheet (« = 0.2) in order to reduce the heat loss by 90 percent. Assuming the outer surface temperature of the metal section still remains at about 110°C, determine the thickness of the insulation that needs to be used. The furnace operates continuously throughout the year and has an efficiency of 78 percent. The price of the natural gas is $1.10/therm (1 therm = 105,500 kJ of energy content). If the installation of the insulation will cost $550 for materials and labor, determine how long it will take for the insulation to pay for itself from the energy it saves.
Energy transfer
The flow of energy from one region to another region is referred to as energy transfer. Since energy is quantitative; it must be transferred to a body or a material to work or to heat the system.
Molar Specific Heat
Heat capacity is the amount of heat energy absorbed or released by a chemical substance per the change in temperature of that substance. The change in heat is also called enthalpy. The SI unit of heat capacity is Joules per Kelvin, which is (J K-1)
Thermal Properties of Matter
Thermal energy is described as one of the form of heat energy which flows from one body of higher temperature to the other with the lower temperature when these two bodies are placed in contact to each other. Heat is described as the form of energy which is transferred between the two systems or in between the systems and their surrounding by the virtue of difference in temperature. Calorimetry is that branch of science which helps in measuring the changes which are taking place in the heat energy of a given body.
The side surfaces of a 3-m-high cubic industrial
furnace burning natural gas are not insulated, and the temperature
at the outer surface of this section is measured to
be 110°C. The temperature of the furnace room, including
its surfaces, is 30°C, and the emissivity of the outer surface
of the furnace is 0.7. It is proposed that this section of the
furnace wall be insulated with glass wool insulation (k =
0.038 W/m·K) wrapped by a reflective sheet (« = 0.2) in
order to reduce the heat loss by 90 percent. Assuming the
outer surface temperature of the metal section still remains
at about 110°C, determine the thickness of the insulation that
needs to be used.
The furnace operates continuously throughout the year
and has an efficiency of 78 percent. The price of the natural
gas is $1.10/therm (1 therm = 105,500 kJ of energy content).
If the installation of the insulation will cost $550 for materials
and labor, determine how long it will take for the insulation
to pay for itself from the energy it saves.
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