An ordinary potato (k = 0.6 W/m.K and α = 0.13 × 10 -6 m2 /s)...
An ordinary potato (k = 0.6 W/m.K and α = 0.13 × 10 -6 m2 /s) can be approximated as a 6-cm diameter sphere. The potato is initially at a uniform temperature of 200 C and is to be baked in an oven with air temperature of 1800 C. The average convection coefficient between the potato and the air is experimentally determined to be 15 W/m2 .K. Determine how long it will take for the surface temperature of the potato to increase to 1600 C.
Homework Answers
4-79 White potatoes (k0.50 W/m-K and 0.13 X 10-6 m/s) that are initially at a uniform temperature of 25°C and have an a...
4-79 White potatoes (k0.50 W/m-K and 0.13 X 10-6 m/s) that are initially at a uniform temperature of 25°C and have an average diameter of 6 cm are to be cooled by refrigerated air at 2°C flowing at a velocity of 4 m/s. The average heat transfer coefficient between the potatoes and the air is experimentally determined to be 19 W/m2.K Determine how long t wl take for the center temperature of the potatoes to drop to 6°C. Also, determine...
In many cookbooks, it is stated that a slab of steak, roasted in a convection oven,...
In many cookbooks, it is stated that a slab of steak, roasted in a convection oven, is considered "well-done" when the center-line temperature of the slab reaches 80 °C. A slab of steak is initially at 6 °C before it is placed in the oven, in which the ambient air temperature is 175 °C. The mean convective heat transfer coefficient between the slab of steak and the air inside the oven 15 W/(m2.K) Approximate the slab of steak as a...
A large wall made of 10-cm-thick solid brick (k = 0.8 W/m.K, p 2000 kg/m3, and p 800 J/kg.K) is o...
Heat transfer question.
A large wall made of 10-cm-thick solid brick (k = 0.8 W/m.K, p 2000 kg/m3, and p 800 J/kg.K) is originally at a uniform temperature of 30°C. The wall is adiabatic (well insulated) on one side as shown in the figure. The other surface is suddenly exposed to convection air flow at 10°C, resulting in a heat transfer coefficient h=40W/m2.K. Fluid (4.1) Determine the temperature of both surfaces Gr 0 and x 10 cm) after 5 hr...
For such aircraft application (Figure 3), a wall is made from insulation material (k-0.030 W/m.K) and...
For such aircraft application (Figure 3), a wall is made from insulation material (k-0.030 W/m.K) and the insulation material is mounted between four layers of carbon steel (2 mm thickness), the carbon layers are separated by a 2 mm air gap (kair-0.025 W/mK). Figure 3, the thermal conductivity of the carbon steel is (k-15.5 W/m.K). The temperature inside the wall is maintained at 6 °C. The environmental temperature is 24°C. The engineer would like to avoid condensation occurring at outer...
7. (20 pts) A sphere with 30 mm in diameter initially at 800 K is quenched...
7. (20 pts) A sphere with 30 mm in diameter initially at 800 K is quenched in a large bath having a constant temperature of 320 K with a convection heat transfer of 75 W/m2.K. The thermophysical properties of the sphere material are: p=400 kg/mº, c=1600 J/kg-K, and k=1.7 W/mK. (Use characteristic length Lc=VIA to determine applicability of lumped method; Use radius of the sphere for one term approximation) a) Calculate the time required for the surface of the sphere...
A household oven door of 0.6-m height and 0.7-m width reaches an average surface temperature of...
A household oven door of 0.6-m height and 0.7-m width reaches an average surface temperature of 32°C during operation. The temperature of ambient air is 22°C. Assuming the door has an emissivity of 0.8 and the surroundings are also at 22°C, determine the heat transfer by free convection and the heat transfer by radiation. 1) What is the volumetric thermal expansion coefficient of air at the film temperature outside the oven door, in 1/K? 2) What is the Rayleigh number...
A plate (k = 10 W/m.K) is stiffened by a series of longitudinal ribs having a...
A plate (k = 10 W/m.K) is stiffened by a series of longitudinal ribs having a rectangular cross section with length L = 8 mm and width W = 4 mm. The base of the plate is maintained at a uniform temperature Tb = 75°C, while the rib surfaces are exposed to air at a temperature of T = 25°C and a convection coefficient of h = 600 W/m2.K. Using a finite-difference method with Ax = 4y = 2 mm...
The wall of a heat exchanger separates hot water at Tin 90 C with h." 80 w/m2.K from cold water a...
The wall of a heat exchanger separates hot water at Tin 90 C with h." 80 w/m2.K from cold water at Tout 10 C with h,ut 60 W/m2.K. The thermal conductivity of the heat exchanger is 180 W/m.K To extend the heat transfer area, two-dimensional ridges are machined on the cold side of the wall. This geometry causes non-uniform thermal stresses, which may become critical for crack initiation along the lines between two ridges. To predict thermal stresses, the temperature...
Solve quickly and carry units please rroblem I) A perfect sphere (Diameter-1 cm) of a gold...
Solve quickly and carry units please
rroblem I) A perfect sphere (Diameter-1 cm) of a gold alloy is placed in a special type o microwave oven. The sphere has a uniform initial temperature of 300 K. The microwave then turned on, which pr oduces u niform generation u-3,000,000 W/m2 within the sphere, and a fan produces convection heat transfer evenly over the surface of the sphere with convection coefficient h-6 W/m2 K and with air temperature Too- 300 K. Radiation...
Problem 2: A hot metal ball 0.00245 W/m°C; α-0151* 10-s m2/s; d 18 cm) initially at...
Problem 2: A hot metal ball 0.00245 W/m°C; α-0151* 10-s m2/s; d 18 cm) initially at a unifom temperature of 310°C is cooled by placing it in air at 29 C is flowing at a constant 4 m/s. In order to continue on in the manufacturing process, the temperature at the center of the ball must be 70°C. (μ. = 1.872*10-5 kg m-s). The air You mav assume that the properties of air may bem odeled as V = 1.608...
4-79 White potatoes (k0.50 W/m-K and 0.13 X 10-6 m/s) that are initially at a uniform temperature of 25°C and have an average diameter of 6 cm are to be cooled by refrigerated air at 2°C flowing at a velocity of 4 m/s. The average heat transfer coefficient between the potatoes and the air is experimentally determined to be 19 W/m2.K Determine how long t wl take for the center temperature of the potatoes to drop to 6°C. Also, determine...
In many cookbooks, it is stated that a slab of steak, roasted in a convection oven, is considered "well-done" when the center-line temperature of the slab reaches 80 °C. A slab of steak is initially at 6 °C before it is placed in the oven, in which the ambient air temperature is 175 °C. The mean convective heat transfer coefficient between the slab of steak and the air inside the oven 15 W/(m2.K) Approximate the slab of steak as a...
Heat transfer question.
A large wall made of 10-cm-thick solid brick (k = 0.8 W/m.K, p 2000 kg/m3, and p 800 J/kg.K) is originally at a uniform temperature of 30°C. The wall is adiabatic (well insulated) on one side as shown in the figure. The other surface is suddenly exposed to convection air flow at 10°C, resulting in a heat transfer coefficient h=40W/m2.K. Fluid (4.1) Determine the temperature of both surfaces Gr 0 and x 10 cm) after 5 hr...
For such aircraft application (Figure 3), a wall is made from insulation material (k-0.030 W/m.K) and the insulation material is mounted between four layers of carbon steel (2 mm thickness), the carbon layers are separated by a 2 mm air gap (kair-0.025 W/mK). Figure 3, the thermal conductivity of the carbon steel is (k-15.5 W/m.K). The temperature inside the wall is maintained at 6 °C. The environmental temperature is 24°C. The engineer would like to avoid condensation occurring at outer...
7. (20 pts) A sphere with 30 mm in diameter initially at 800 K is quenched in a large bath having a constant temperature of 320 K with a convection heat transfer of 75 W/m2.K. The thermophysical properties of the sphere material are: p=400 kg/mº, c=1600 J/kg-K, and k=1.7 W/mK. (Use characteristic length Lc=VIA to determine applicability of lumped method; Use radius of the sphere for one term approximation) a) Calculate the time required for the surface of the sphere...
A plate (k = 10 W/m.K) is stiffened by a series of longitudinal ribs having a rectangular cross section with length L = 8 mm and width W = 4 mm. The base of the plate is maintained at a uniform temperature Tb = 75°C, while the rib surfaces are exposed to air at a temperature of T = 25°C and a convection coefficient of h = 600 W/m2.K. Using a finite-difference method with Ax = 4y = 2 mm...
The wall of a heat exchanger separates hot water at Tin 90 C with h." 80 w/m2.K from cold water at Tout 10 C with h,ut 60 W/m2.K. The thermal conductivity of the heat exchanger is 180 W/m.K To extend the heat transfer area, two-dimensional ridges are machined on the cold side of the wall. This geometry causes non-uniform thermal stresses, which may become critical for crack initiation along the lines between two ridges. To predict thermal stresses, the temperature...
Solve quickly and carry units please
rroblem I) A perfect sphere (Diameter-1 cm) of a gold alloy is placed in a special type o microwave oven. The sphere has a uniform initial temperature of 300 K. The microwave then turned on, which pr oduces u niform generation u-3,000,000 W/m2 within the sphere, and a fan produces convection heat transfer evenly over the surface of the sphere with convection coefficient h-6 W/m2 K and with air temperature Too- 300 K. Radiation...
Problem 2: A hot metal ball 0.00245 W/m°C; α-0151* 10-s m2/s; d 18 cm) initially at a unifom temperature of 310°C is cooled by placing it in air at 29 C is flowing at a constant 4 m/s. In order to continue on in the manufacturing process, the temperature at the center of the ball must be 70°C. (μ. = 1.872*10-5 kg m-s). The air You mav assume that the properties of air may bem odeled as V = 1.608...
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