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A 12-m-long and 5-m-high wall is constructed of two layers of 1 -cm-thick sheetrock
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HEAT+MASS TRANSFER:FUND...-CONNECTPLUS
- A 2-m x 1.8-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 radiation heat transfer coefficient at the surface of the outer furnace is 10 W/m² • °C. It is proposed to insulate this section of the furnace wall with expanded perlite insulation (k = 0.052 W/m • °C) in order to reduce the heat loss by 90%. Assuming the outer surface temperature of the metal section still remains at about 80°C, determine the thickness of the insulation that needs to be used. ANSWER:_______cmarrow_forwardA 4-m-high and 6-m-wide wall consists of a long 18-cm x 30-cm cross section of horizontal bricks (k = 0.72 W/mK) separated by 3-cm-thick plaster layers (k=0.22 W/mK). There are also 2-cm-thick plaster layers on each side of the wall, and a 2-cm-thick rigid foam (k=0.026 W/mK) on the inner side of the wall. The indoor and outdoor temperatures are 22°C and -4°C, and the convection heat transfer coefficients on the inner and the outer sides are h1= 10 W/m2K and h2= 20 W/m2K, respectively.Assuming one-dimensional heat transfer and disregarding radiation, determine the rate of heat transfer through the wall.arrow_forwardTwo pin fins are identical, except that the diameter of one of them is twice the diameter of the other. For which fin is the (a) fin effectiveness and (b) fin efficiency higher? Explain.arrow_forward
- A horizontal pipe having a surface temperature of 67 °C and diameter of 25 cm is buried at a depth of 1.2 m in the earth at a location where k = 1.8 W/m-°C. The earth surface temperature is 15 °C. Calculate the shape factor if the pipe length is 10 m.arrow_forwardA 2-m × 1.8-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 radiation heat transfer coefficient at the surface of the outer furnace is 10 W/m2·C. It is proposed to insulate this section of the furnace wall with perlite insulation (k = 0.052 W/m·C) in order to reduce the heat loss by 90 percent, Assuming the outer surface temperature of the metal section still remains at about 80°C, determine the thickness of the insulation that needs to be used.arrow_forwardA 2 m X 1.5 m section of wall of an industrial furnace burning gas is not insulated, and the temperature at the outer surface of this section is measured to be 80oC. The temperature of the furnace room is 30oC, and the combined convection and radiation heat transfer coefficient at the surface of the outer furnace is 10 w/oC. It is proposed to insulate this section of the furnace wall with glass wool insulation (K=0.038 W/moC) in order to reduce the heat loss by 90 percent. Assuming the outer surface temperature of the section remains at about 80oC, determine i) the thickness of the insulation that is needed and ii) the outer surface temperature of the insulation after installation.arrow_forward
- It is required to insulate a kitchen oven with cork board (k = 0.043 W/mK) so that the heat losses from the oven does not exceed 400 W/m2 when the inner surface of the oven is at 225°C and the outer surface of the oven is at 40°C. The thickness of insulation required is nearlyarrow_forwardBecause you forgot to let the pipes drip during a freezing night, a section of an outdoor pipe is now frozen. The frozen section is L = 1 m long and the inner pipe diameter is D = 1.8 cm. During the day, the pipe is exposed to the cold air, the Sun, and the radiating surroundings. The cold air temperature is T∞ = -10°C, and has convection heat transfer coefficient h = 20 W/m2·K. The Sun provides solar irradiance of Gsun = 1350 W/m2. The steel pipe surface has absorptivity α = 0.6 and emissivity ε= 0.1. The surroundings, such as vegetation, houses, ground, etc. can be assumed to be blackbody held at Tsur = 280 K. A) Using the energy conservation system illustrated below, establish an equation that describes the stored energy in the section of frozen water (Est). B) Determine the amount of time needed to melt the ice in the pipe. Ice has density ρ= 920 kg/m3, and latent heat of fusion hsf = 334 kJ/kg. The ice is Tw = 0°C. Ignore conduction through the pipe walls – assume the pipe…arrow_forwardA long stainless-steel (AISI 316) steam pipe, with an inside diameter of 6.00 cm and an outside diameter of 8.00 cm, is covered with a layer of asbestos insulation (k = 0.150 W/m-K) 1.00 cm thick, which in turn is covered with foam insulation (k = 0.044 W/m-K) 6.00 cm thick. The inside surface temperature of the stainless-steel steam pipe is measured to be 250.0°C, while the outside surface of the foam is exposed to convection, T_inf = 25.0°C, h_inf = 15.0 W/m^2-K. • Draw and label a sketch of this system. Include dimensions, known temperatures, etc. • Draw and completely label the corresponding 1-D steady-state conduction resistor diagram. • Determine the heat transfer rate through the pipe per unit length. • Calculate the temperature at the asbestos/foam interface.arrow_forward
- There are 3 windows in a room with a width of 100 cm and a height of 150 cm.There is a single glass (k=0. 9 W/mK) of 5 mm thickness in the windows initially. Instead of these glasses to save heatYou are considering replacing it with double glazing consisting of 5 mm glass and 12 mm air (k=0.022 W/mK). Indoor and outdoor environmenttemperatures are 20 0C and -10 0C, respectively, and the heat transfer coefficients are 7 W/m2 K and 25 W/m2 K. The total heat loss in the room is 3.5 kW.when switching to double glazing;a) Find the decrease in heat transfer. b) Considering that the heat given by the heaters remains 3.5 kW, what would the room temperature be?arrow_forwardA hot surface at 100°C is to be cooled by attaching 3-cm-long, 0.25-cm-diameter aluminum pin fins (k = 237 W/m·K) to it, with a center-to-center distance of 0.6 cm. The temperature of the surrounding medium is 30°C, and the heat transfer coefficient on the surfaces is 35 W/m2 ·K. Determine the rate of heat transfer from the surface for a 1-m x 1-m section of the plate. Also determine the overall effectiveness of the fins.arrow_forwardA 10-in-thick, 26-ft-long, and 10-ft-high wall is to be constructed using 9-in-long solid bricks (k = 0.40 Btu/h⋅ft⋅°F) of cross section 7 in × 7 in, or identical-size bricks with nine square air holes (k = 0.015 Btu/h⋅ft⋅°F) that are 9 in long and have a cross section of 1.5 in × 1.5 in. There is a 0.5-in-thick plaster layer (k = 0.10 Btu/h⋅ft⋅°F) between two adjacent bricks on all four sides and on both sides of the wall. The house is maintained at 80°F and the ambient temperature outside is 35°F. Take the heat transfer coefficients at the inner and outer surfaces of the wall to be 1.5 and 6 Btu/h⋅ft2⋅°F, respectively.arrow_forward
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