A 2-m * 1.5-m section of wall of an industrial furnaceburning natural gas is not insulated, and the temperatureat the outer surface of this section is measured to be 80°C.The temperature of the furnace room is 30°C, and the combinedconvection and radiation heat transfer coefficient at thesurface of the outer furnace is 10 W/m2·K. It is proposed toinsulate this section of the furnace wall with glass wool insulation(k = 0.038 W/m·K) in order to reduce the heat lossby 90 percent. Assuming the outer surface temperature ofthe metal section still remains at about 110°C, determine thethickness of the insulation that needs to be used.The furnace operates continuously and has an efficiency of78 percent. The price of the natural gas is $1.10/therm (1 therm =105,500 kJ of energy content). If the installation of the insulationwill cost $250 for materials and labor, determine how long it willtake 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.
A 2-m * 1.5-m section of wall of an industrial furnace
burning natural gas is not insulated, and the temperature
at the outer surface of this section is measured to be 80°C.
The temperature of the furnace room is 30°C, and the combined
convection and
surface of the outer furnace is 10 W/m2·K. It is proposed to
insulate this section of the furnace wall with glass wool insulation
(k = 0.038 W/m·K) 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 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 $250 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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