To cool an omelet, which has a radius of 10 cm, from 90 C to room...
To cool an omelet, which has a radius of 10 cm, from 90 C to room temperature of 68 F, you need to remove 100 W of heat energy from it. What is the convection heat transfer coefficient between the omelet and the air? Assume emissivity of omelet to be 0.90. Hint: Which types of heat transfers among conduction, convection and radiation are possible between omelet and air?
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To cool an omelet, which has a radius of 10 cm, from 90 C to
room...
(13) A brewery fermentation tank 12 m in diameter is situated in a room, which has...
(13) A brewery fermentation tank 12 m in diameter is situated in a room, which has a temperature of 15°C. The tank is constructed of 10-mm welded steel plate with 12-mm glass lining. The temperature at the inner surface of the glass lining is 50°C. Assume that the convective resistance offered by the air film on the outside of the tank equals the combined resistance of the glass and steel. The thermal conductivity of glass is 0.80 W/mK and that...
1.23 Under conditions for which the same room tempera- ture is maintained by a heating or...
1.23 Under conditions for which the same room tempera- ture is maintained by a heating or cooling system, it is not uncommon for a person to feel chilled in the win- ter but comfortable in the summer. Provide a plausible explanation for this situation (with supporting calcu- lations) by considering a room whose air temperature is maintained at 20°C throughout the year, while the walls of the room are nominally at 27°C and 14°C in the summer and winter, respectively....
Problem 2 (50 Points A flat, isothermal vertical heating panel, 0.5 m wide by 1 m...
Problem 2 (50 Points A flat, isothermal vertical heating panel, 0.5 m wide by 1 m high is mounted inside a large room. The surface of the panel has an emissivity of 0.90 and is maintained at 400 K If the walls and air of the room are at 300 K, calculate: a) The Rayleigh number of the free convection boundary layer. b) Selecting a suitable equation for Nusselt number, calculate the heat transfer coefficient of the flow c) The...
A rod of 10-mm diameter and 250-mm length has one end maintained at 100°C
A rod of 10-mm diameter and 250-mm length has one end maintained at 100°C. The surface of the rod experiences free convection with the ambient air at 25°C and a convection coefficient that depends on the difference between the temperature of the surface and the ambient air. Specifically, the coefficient is prescribed by a correlation of the form, hfc = 2.89[0.6 +0.624(T - T∞)1/6]2, where the units are hfc (W/m².K) and T (K). The surface of the rod has an...
Homework 7 heat transfer 2018-20 1) A horizontal tube of 12.5-mm dimeter with an outer srface temperature of 240°C is placed in a room with an air temperature of 20°C. Estimate the heat transfer rate...
Homework 7 heat transfer 2018-20 1) A horizontal tube of 12.5-mm dimeter with an outer srface temperature of 240°C is placed in a room with an air temperature of 20°C. Estimate the heat transfer rate per unit length of the tube due to free convection. 2) Air at -10°C flows at 10 m/s over the roof plate of two 5m length rooms whose air is at Too-200C. The roof plate is 0.20-m thick concrete (k = 0.6 w/ m. K)....
4. Mixed-Mode Heat Transfer - A transistor capsule is roughly spherical with a 1 cm diameter,...
4. Mixed-Mode Heat Transfer - A transistor capsule is roughly spherical with a 1 cm diameter, covered by a very thin dielectric coating with radiation emissivity E 0.85 The transistor surface is at 60 °C and the surrounding air is at 30°C. The transistor is contained by the black walls of a spherical case with temperature 35 °C, where the case walls are located at a distance H 10 cm from the transistor capsule wall. a) Find the rate of...
III. A composite walled window separates oven cavity from room air. The composite is to consist...
III. A composite walled window separates oven cavity from room air. The composite is to consist of two high temperature plastics of thickness L. = 2L. and thermal conductivities k = 0.15 W/(m·K) and k, = 0.08 W/( m K). During the self-cleaning process, the oven w and oven air temperatures are at 400°C, while the room air temperature is at 25°C. The insid convection coefficient, outside convection coefficient, and radiation heat transfer coefficient to be confused with Stefan Boltzmann...
3. A spherical ball having a diameter of 5 mm and at a temperature of 90°C...
3. A spherical ball having a diameter of 5 mm and at a temperature of 90°C is covered by a 3 mm thick plastic insulation. The ball is exposed to air at 24°C, with a combined convection and radiation heat transfer coefficient of 35 W/m² °C. Determine if the plastic insulation on the ball will help or hurt heat transfer from the ball.
Cold conditioned air at 10°C is flowing inside a 1.5 cm thick square aluminum (k = 240 w/mK) duct...
Cold conditioned air at 10°C is flowing inside a 1.5 cm thick square aluminum (k = 240 w/mK) duct of inner cross section of 25x25cm at a mass flow rate of 1.0 kg/s. The duct is exposed to air at 35°C with a combined convection-radiation heat transfer coefficient of 15 W/m2K. The convection heat transfer coefficient at the inner surface is 75 W/.m2.K. If the air temperature in the duct should not increase by more than 1°C determine the maximum...
3) Consider a spherical solid object that is at temperature Tobject=60∘C, placed in a room of...
3) Consider a spherical solid object that is at temperature Tobject=60∘C, placed in a room of temperature Troom=20∘C. The object, which has emissivity e = 1, is transferring heat by radiation at a rate of -230 W. What would be the net radiative heat transfer rate, if the temperature of the spherical object was doubled and everything else (radius, emissivity and room temperature) remained the same?
(13) A brewery fermentation tank 12 m in diameter is situated in a room, which has a temperature of 15°C. The tank is constructed of 10-mm welded steel plate with 12-mm glass lining. The temperature at the inner surface of the glass lining is 50°C. Assume that the convective resistance offered by the air film on the outside of the tank equals the combined resistance of the glass and steel. The thermal conductivity of glass is 0.80 W/mK and that...
1.23 Under conditions for which the same room tempera- ture is maintained by a heating or cooling system, it is not uncommon for a person to feel chilled in the win- ter but comfortable in the summer. Provide a plausible explanation for this situation (with supporting calcu- lations) by considering a room whose air temperature is maintained at 20°C throughout the year, while the walls of the room are nominally at 27°C and 14°C in the summer and winter, respectively....
Problem 2 (50 Points A flat, isothermal vertical heating panel, 0.5 m wide by 1 m high is mounted inside a large room. The surface of the panel has an emissivity of 0.90 and is maintained at 400 K If the walls and air of the room are at 300 K, calculate: a) The Rayleigh number of the free convection boundary layer. b) Selecting a suitable equation for Nusselt number, calculate the heat transfer coefficient of the flow c) The...
Homework 7 heat transfer 2018-20 1) A horizontal tube of 12.5-mm dimeter with an outer srface temperature of 240°C is placed in a room with an air temperature of 20°C. Estimate the heat transfer rate per unit length of the tube due to free convection. 2) Air at -10°C flows at 10 m/s over the roof plate of two 5m length rooms whose air is at Too-200C. The roof plate is 0.20-m thick concrete (k = 0.6 w/ m. K)....
4. Mixed-Mode Heat Transfer - A transistor capsule is roughly spherical with a 1 cm diameter, covered by a very thin dielectric coating with radiation emissivity E 0.85 The transistor surface is at 60 °C and the surrounding air is at 30°C. The transistor is contained by the black walls of a spherical case with temperature 35 °C, where the case walls are located at a distance H 10 cm from the transistor capsule wall. a) Find the rate of...
III. A composite walled window separates oven cavity from room air. The composite is to consist of two high temperature plastics of thickness L. = 2L. and thermal conductivities k = 0.15 W/(m·K) and k, = 0.08 W/( m K). During the self-cleaning process, the oven w and oven air temperatures are at 400°C, while the room air temperature is at 25°C. The insid convection coefficient, outside convection coefficient, and radiation heat transfer coefficient to be confused with Stefan Boltzmann...
3. A spherical ball having a diameter of 5 mm and at a temperature of 90°C is covered by a 3 mm thick plastic insulation. The ball is exposed to air at 24°C, with a combined convection and radiation heat transfer coefficient of 35 W/m² °C. Determine if the plastic insulation on the ball will help or hurt heat transfer from the ball.
Cold conditioned air at 10°C is flowing inside a 1.5 cm thick square aluminum (k = 240 w/mK) duct of inner cross section of 25x25cm at a mass flow rate of 1.0 kg/s. The duct is exposed to air at 35°C with a combined convection-radiation heat transfer coefficient of 15 W/m2K. The convection heat transfer coefficient at the inner surface is 75 W/.m2.K. If the air temperature in the duct should not increase by more than 1°C determine the maximum...
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