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The 5-mm-thick bottom of a 200-mm-diameter pan may be made from aluminum
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EBK INTRODUCTION TO HEAT TRANSFER
- The inside of a hollow cylinder is maintained at a temperature ??, and the outside is at a lower temperature, ??. The wall of the cylinder has a thermal conductivity ?. Ignoring end effects, show that the rate of energy conduction from the inner surface to the outer surface in the radial direction is ??/?? = 2??? [?? − ??/ ln(?/?)]The passenger section of a jet airliner is in the shape of a cylindrical tube with a length of 35.0 m and an inner radius of 2.50 m. Its walls are lined with an insulating material 6.00cm in thickness and having a thermal conductivity of 4.00 × 10−5cal/s ⋅ cm ⋅ °C. A heater must maintain the interior temperature at 25.0°C while the outside temperature is −35.0°C. What power must be supplied to the heater?arrow_forward3. A lumped system with a volume of 0.003 m³ and a surface area of 0.08 m² is made of a material with density of 3800 kg/m³, thermal conductivity of 300 W/m K, and specific heat of 200 J/kg K. If the system is exposed to a convection environment with h = 60 W/m2 K, what is the approximate time it will take for this system to reach equilibrium with the environment? Express your answer in minutes.arrow_forwardThe resistance of a copper wire used to make a motor is 0.5 Ω at 250C and 0.8 Ω at the motor’s operating temperature. Determine the operating temperature and the rise in temperature of the motor, given that copper has a temperature constant of 234.50Carrow_forward
- A steel rod, which is free to move, has a length of 200 mm and a diameter of 20 mm at a temperature of 15oC. If the rod is heated uniformly to 115oC, determine the length and diameter of this rod to the nearest micron at the new temperature if the linear coefficient of thermal expansion of steel is 12.5 x 10-6 m/m/C. Is there a stress on the rod at 115oC?arrow_forwarda. What is the heat flux, q"1 [in W/m2], at the left-hand side of layer B? Express your answer as a negative number if the heat flux goes to the left, and as a positive number if the heat flux goes to the right. b.What is the heat flux, q"2 ( in W/m2) at the right-hand side of layer B? Express your answer as a negative number if the heat flux goes to the left, and as a positive number if the heat flux goes to the right. c. What is the temperature, T1, on the left-hand side of layer B, in Celsius? d. What is the temperature, T2, on the right-hand side of layer B, in Celsius?arrow_forwardA spherical container with an inner radius r1 = 1 m and an outer radius r2 = 1.05 m has its inner surface subjected to a uniform heat flux of q1=7kw/m^2. The outer surface of the container has a temperature T2 = 25°C, and the container wall thermal conductivity is k = 1.5 W/m·K. Show that the variation of temperature in the container wall can be expressed as and determine the temperature of the inner surface of the container at r = r1.arrow_forward
- The pump of a water distribution system is powered by a 15-kW electric motor whose efficiency is 90 percent. The water flow rate through the pump is 50 L/s. The diameters of the inlet and outlet pipes are the same, and the elevation difference across the pump is negligible. If the absolute pressures at the inlet and outlet of the pump are measured to be 100 kPa and 300 kPa, respectively, determine (a) the mechanical efficiency of the pump and (b) the temperature rise of water as it flows through the pump due to mechanical inefficiencies.arrow_forwardAn inventor claims to have developed a resistance heater that supplies 1.2 kWh of energy to a room for each kWh of electricity it consumes. Is this a reasonable claim, or has the inventor developed a perpetual-motion machine? Explain.arrow_forwardA classroom that normally contains 40 people is to be air-conditioned with window air-conditioning units of 5-kW cooling capacity. A person at rest may be assumed to dissipate heat at a rate of about 360kJ/h. There are 10 light bulbs in the room, each with a rating of 100W. The rate of heat transfer to the classroom through the walls and the windows is estimated to be 15,000kJ/h. If the room air is to be maintained at a constant temperature of 21°C, determine the number of window air-conditioning units required.arrow_forward
- Q#01: Write a short note on the following: What are the best possible solutions to increase the heat transfer rate of a body? Which material will transfer more heat? Either a material with thermal conductivity ? = 121 or ? = 22 . Justify your answer.arrow_forwardAn exercise room has 6 weight-lifting machines that have no motors and 7 treadmills each equipped with a 2.5-hp (shaft output) motor. The motors operate at an average load factor of 0.7, at which their efficiency is 0.77. During peak evening hours, all 12 pieces of exercising equipment are used continuously, and there are also two people doing light exercises while waiting in line for one piece of the equipment. Assuming the average rate of heat dissipation from people in an exercise room is 600 W, determine the rate of heat gain of the exercise room from people and the equipment at peak load conditions.arrow_forwardIs the heat transfer in the metal rod transient considering that its temperature varies along its length?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning