6. A ceramic teapot with emissivity 0.70 and a shiny teapot with emissivity 0.10 each hold...
6. A ceramic teapot with emissivity 0.70 and a shiny teapot with emissivity 0.10 each hold 0.55 L of tea at 95˚C. (a) Estimate the rate of heat loss from each and (b) estimate the temperature drop after 30 minutes for each. Consider only radiation and assume the surroundings are at 20˚C.
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6. A ceramic teapot with emissivity 0.70 and a shiny teapot with
emissivity 0.10 each hold...
The dark surface of a ceramic stove top may be approximated as a blackbody. The “burners”,...
The dark surface of a ceramic stove top may be approximated as a blackbody. The “burners”, which are integral with the stove top, are heated from below by electric resistance heaters. (A) Consider a burner of a diameter D = 200 mm operating at a uniform surface temperature of Ts = 200?C in ambient air at T? = 20?C. Without a pot or pan on the burner, what are the rates of heat loss by radiation (i.e. qrad) and convection...
In this problem you will consider the balance of thermal energy radiated and absorbed by a...
In this problem you will consider the balance of thermal energy radiated and absorbed by a person in a room. The rate of heat transfer from radiation is: ΔQΔt=eσA(T42−T41)=eσAT42−eσAT41. This equation has two terms which represent the rate of absorption from the room (a gain) and the rate of radiation into the room (a loss). In this problem, we will consider these two terms separately. Assume that the area of a human body may be considered to be that of...
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)....
hair dryer may be idealized as a circular duct through which a small fan draws ambient...
hair dryer may be idealized as a circular duct through which a
small fan draws ambient air and within which the air is heated as
it flows over a coiled electric resistance wire.
(1) If a dryer is designed to operate with an electric power
consumption of Pelec= 1500 W and to heat air from an ambient
temperature of Ti= 20°C to a discharge temperature of To= 45°C, at
what volumetric flow rate ∀˙ should the fan operate? Heat loss...
Problem 3 (30): Steam at Too,1 340 °C flows in a cast iron pipe [k- 80 W/m.°C] whose inner and outer diameter are Di 6 cm and D2 -8 cm, respectively. The pipe is covered with a 4-cm thick glass wool...
Problem 3 (30): Steam at Too,1 340 °C flows in a cast iron pipe [k- 80 W/m.°C] whose inner and outer diameter are Di 6 cm and D2 -8 cm, respectively. The pipe is covered with a 4-cm thick glass wool insulation [k-0.05 W/ m°C]. Heat is lost to the surroundings at Too,2 - 21°C by natural convection and radiation, with a combined heat transfer coefficient of h- 18 W/m2 °C. Taking the heat transfer coefficient inside the pipe to...
1) 2) 3) PROJECT #1 (2.5 Marks): The heat that is conducted through a body must...
1)
2)
3)
PROJECT #1 (2.5 Marks): The heat that is conducted through a body must frequently be removed by other heat transter processes. For example, the heat generated in an electronic device must be dissipated to the surroundings through convection by means of fins. Consider the one-dimensional aluminum fin (thickness t 3.0 mm, width Z 20 cm, length L) shown in Figure 1, that is exposed to a surrounding fluid at a temperature 1. The conductivity of the aluminum...
You just made a cup (0.3 liters) of coffee, but it is too hot to drink....
You just made a cup (0.3 liters) of coffee, but it is too hot to drink. You wish to decrease the temperature of the tea from 72°C down to 64"C by submerging a numoer or aluminusp hcffefthe snd owever, instead o temperature (25°C), then how many spoons will be required to decrease the coffee to the optimum temperature? 5 spoons Assume: Cp for coffee 4184 Cp for aluminum 921 density of coffee= 1000 kg/m no heat loss from the cup...
Problems 4, 5 & 6 15) A heat-conducting rod, 0.90 m long and wrapped in insulation,...
Problems 4, 5 & 6
15) A heat-conducting rod, 0.90 m long and wrapped in insulation, is made of an aluminum section that is 0.20 m long and a copper section that is 0.20m long. Both sections have a cross- sectional area of 0.00040 m2, The aluminum end and the copper end are maintained at temperatures of 30 C and 230 C respectively. The thermal conductivities of aluminum and copper are 205 W/m K (aluminum) and 385 W/m K (copper)....
MULTIPLE CHOICE |18 pt-3 pt each): In this section, you are expected to select the best...
MULTIPLE CHOICE |18 pt-3 pt each): In this section, you are expected to select the best answer out of the optionsgiven. No partial credit will be given. Only one answer may be chosen ifthe answer is not obvious it will be considered incomplete. When heating a solution, a scientist detects a temperature increase in the solution overtime. Which of the following statements accurately characterizes the solution during this period? 1. The solution is at its boiling point The velocity of...
What would happen to you if you fell out of a spaceship, naked? Hollywood has given us many portrayals of this event, wi...
What would happen to you if you fell out of a spaceship, naked? Hollywood has given us many portrayals of this event, with the skin boiling or instantly freezing; but what actually happens, and what effect is most severe? The lack of oxygen is one: we know that humans can only survive a number of minutes without breathing. But there are a number of other factors to consider. (A) Assume a human is a 2 m tall cylinder of 75...
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)....
hair dryer may be idealized as a circular duct through which a
small fan draws ambient air and within which the air is heated as
it flows over a coiled electric resistance wire.
(1) If a dryer is designed to operate with an electric power
consumption of Pelec= 1500 W and to heat air from an ambient
temperature of Ti= 20°C to a discharge temperature of To= 45°C, at
what volumetric flow rate ∀˙ should the fan operate? Heat loss...
Problem 3 (30): Steam at Too,1 340 °C flows in a cast iron pipe [k- 80 W/m.°C] whose inner and outer diameter are Di 6 cm and D2 -8 cm, respectively. The pipe is covered with a 4-cm thick glass wool insulation [k-0.05 W/ m°C]. Heat is lost to the surroundings at Too,2 - 21°C by natural convection and radiation, with a combined heat transfer coefficient of h- 18 W/m2 °C. Taking the heat transfer coefficient inside the pipe to...
1)
2)
3)
PROJECT #1 (2.5 Marks): The heat that is conducted through a body must frequently be removed by other heat transter processes. For example, the heat generated in an electronic device must be dissipated to the surroundings through convection by means of fins. Consider the one-dimensional aluminum fin (thickness t 3.0 mm, width Z 20 cm, length L) shown in Figure 1, that is exposed to a surrounding fluid at a temperature 1. The conductivity of the aluminum...
You just made a cup (0.3 liters) of coffee, but it is too hot to drink. You wish to decrease the temperature of the tea from 72°C down to 64"C by submerging a numoer or aluminusp hcffefthe snd owever, instead o temperature (25°C), then how many spoons will be required to decrease the coffee to the optimum temperature? 5 spoons Assume: Cp for coffee 4184 Cp for aluminum 921 density of coffee= 1000 kg/m no heat loss from the cup...
Problems 4, 5 & 6
15) A heat-conducting rod, 0.90 m long and wrapped in insulation, is made of an aluminum section that is 0.20 m long and a copper section that is 0.20m long. Both sections have a cross- sectional area of 0.00040 m2, The aluminum end and the copper end are maintained at temperatures of 30 C and 230 C respectively. The thermal conductivities of aluminum and copper are 205 W/m K (aluminum) and 385 W/m K (copper)....
MULTIPLE CHOICE |18 pt-3 pt each): In this section, you are expected to select the best answer out of the optionsgiven. No partial credit will be given. Only one answer may be chosen ifthe answer is not obvious it will be considered incomplete. When heating a solution, a scientist detects a temperature increase in the solution overtime. Which of the following statements accurately characterizes the solution during this period? 1. The solution is at its boiling point The velocity of...
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