The class includes 40 people. Heat loss from the walls of the class, including the glass windows, is negligible. A flow of cold air enters the classroom via the main entrance, flows in the classroom, and then leaves through an emergency exit door located at the back of the class. Both the entrance door and the emergency exit door have the same dimensions of 1.2 m length and 1.9 m height. Assuming steady-state heat transfer upon reaching the room temperature at a constant value: (a) If cold air enters the room at 20 °C, the heat generated due to the metabolism of a student/lecturer is 70 W, and air flow rate through both doors is 0.05 m/s, determine the room temperature. Assume that the changes in properties of air during the increase in room temperature may be safely ignored.

The class includes 40 people. Heat loss from the walls of the class, including the glass windows, is negligible. A flow of cold air enters the classroom via the main entrance, flows in the classroom, and then leaves through an emergency exit door located at the back of the class. Both the entrance door and the emergency exit door have the same dimensions of 1.2 m length and 1.9 m height. Assuming steady-state heat transfer upon reaching the room temperature at a constant value: (a) If cold air enters the room at 20 °C, the heat generated due to the metabolism of a student/lecturer is 70 W, and air flow rate through both doors is 0.05 m/s, determine the room temperature. Assume that the changes in properties of air during the increase in room temperature may be safely ignored.

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter5: Analysis Of Convection Heat Transfer

Section: Chapter Questions

Problem 5.3DP

See similar textbooks

Similar questions

1.3 A furnace wall is to be constructed of brick having standard dimensions of Two kinds of material are available. One has a maximum usable temperature of 1040°C and a thermal conductivity of 1.7 W/(m K), and the other has a maximum temperature limit of 870°C and a thermal conductivity of 0.85 W/(m K). The bricks have the same cost and are laid in any manner, but we wish to design the most economical wall for a furnace with a temperature of 1040°C on the hot side and 200°C on the cold side. If the maximum amount of heat transfer permissible is 950 , determine the most economical arrangement using the available bricks.
QUESTION FIVE (a) At a certain location, wind is blowing steadily at 10 m/s. Determine the mechanical energy of air per unit mass and the power generation potential of a wind turbine with 60-m-diameter blades at that location. Take the air density to be 1.25 kg/m3. (b) Consider an alcohol and a mercury thermometer that read exactly 0°C at the ice point and 100°C at the steam point. The distance between the two points is divided into 100 equal parts in both thermometers. Do you think these thermometers will give exactly the same reading at a temperature of, say, 60°C? Explain.(c) Determine the work required to deflect a linear spring with a spring constant of 70 kN/m by 20 cm from its rest position.
Box the final answer. Write legibly. An adiabatic room (with dimensions, LxWxH) with the smallest side equal to 5.25 meters initially contains air at 18.25ºC and 1.025 bar. A total of 52.5 KW of heat have been added to double its temperature. Calculate the total time elapsed in minutes to reach that final temperature if the dimensions of the room have a ratio of 3:2:1, respectively.
A woman informs an engineer that she frequently feels cooler in the summer when standing in front of an open refrigerator. The engineer tells her that she is only “imagining things” because there is no fan in the refrigerator to blow the cool air over her. A lively argument ensues. Whose side of the argument do you take? Why?
(assume certain values which are not provided to you ) The class includes 40 people. Heat loss from the walls of the class, including the glass windows, is negligible. A flow of cold air enters the classroom via the main entrance, flows in the classroom, and then leaves through an emergency exit door located at the back of the class. Both the entrance door and the emergency exit door have the same dimensions of 1.2 m length and 1.9 m height. Assuming steady-state heat transfer upon reaching the room temperature at a constant value: a-If cold air enters the room at 20 °C, the heat generated due to themetabolism of a student/lecturer is 70 W, and air flow rate through bothdoors is 0.05 m/s, determine the room temperature. Assume that thechanges in properties of air during the increase in room temperature maybe safely ignored. b-Why is volume not necessary to solve part (a)
What does it mean for an engineering device that has steady-flow? (choose 3 answers) 1- it has been operating for a long time. 2- the properties do not change with time. 3- the property values can be different at different location in the device. 4- the total energy content in the control volume remains unchanged. 5- the rate of energy coming into the system equals to the rate of energy exits the system.
Solve with thermal resistance and conduction/convection. Specifically account for the V= 9 ft/s The wall of a furnace has an inner temperature of 500 F. The wall has a thickness of 2 inches and has a thermal conductivity of 0.02 Btu/(h·ft·F). On the outside, air at 30 F flows over the 10 ft x 10 ft wall at a speed of 9 ft/s. Determine the rate of heat loss from the furnace to the environment.
Describe what happens to the system inside of a refrigerator or freezer in terms of heat transfer, work, and conservation of energy. Confine yourself to time periods in which the door is closed.
1 kg aluminum dumbbell initially held 2 meters above the floor is allowed to fall. This experiment is performed inside a room whose dimensions are 10m— 5m— 3m. Assuming that thewalls of the room do not conduct heat and that the room is empty (no other objects are present besides the dumbbell itself), estimate the change of the temperature inside the room as a result as a result of dropping the dumbbell.
In the United States, energy for household heating is generally sold using English units, e.g., therm, gal, and cord. A house in Wisconsin uses 1200 therms of thermal energy during the heating season. Calculate the cost of fuel if the furnace uses (a) natural gas with an efficiency of 70%; (b) No. 2 fuel oil, efficiency 65%; (c) kerosene, efficiency 99.9% (unvented); and (d) wood with l5% moisture with an efficiency of 50%. Use the data in Tables 2.2, 2.7, and 2.13. The efficiencies are based on the HHV. Assume the cost of natural gas is $8/MBtu, the cost of No. 2 fuel oil is $3/gal, the cost of kerosene is $3.50/gal, and the cost of wood is $100/cord. Assume the bulk density of cord wood is 30 lbm/ft3 .
5. A pot plant falls off the balcony of an apartment. The balcony is 20 m above the ground and the pot plant has a mass of 2 kg. After falling a distance of 2 m from the balcony, the pot plant has a velocity of 6,26 m·s-1. Ignore the effect of air resistance. * Your answer
According to the U.S. Geological survey, the volume of water in oceans, seas, and bays is 1.41 ✕ 1018 m3. The average concentration of naturally occurring uranium in seawater is 3.15 ✕ 10−6 kg/m3. If 0.670% of naturally occurring uranium is the fissionable isotope U-235 and each fission reaction yields 200 MeV, estimate the amount of time the uranium in the seawater on the planet could meet the planet's energy needs at an average usage of 1.94 ✕ 1013 J/s.