Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN: 9781305387102
Author: Kreith, Frank; Manglik, Raj M.
Publisher: Cengage Learning
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37. A long and slender shaft of diameter 2R and length L1 + L2 is insulated overlength L1 and produces heat only in this section while over length L2, it is exposedto a convection boundary (h, Tf). Write the governing differential equations andthe associated boundary conditions from which temperatures in sections L1 and L2can be obtained. Both ends may be treated as adiabatic surfaces.
A 50-meter-long cast iron pipe with a 10-centimeter outside diameter goes through a 288 K temperature open environment. The temperature of the pipe's outer surface is 423 K, and the combined heat transfer coefficient on the pipe's outside surface is 25 W/m2 K.
Considering and stating the necessary assumptions determine, (5 marks)
(a) The rate of heat loss from the pipe
(b) The energy lost per year if the cost of the fuel is 0.52 $/therm ( 1 therm = 105,500 kJ)
c) The thickness of the insulation if 98% of the energy loss is planned to be saved. Consider the conduction coefficient of the insulation is 0.035 W/mK.
A 50-meter-long cast iron pipe with a 10-centimeter outside diameter goes through a 288 K temperature open environment. The temperature of the pipe's outer surface is 423 K, and the combined heat transfer coefficient on the pipe's outside surface is 25 W/m2 K.
Considering and stating the necessary assumptions determine,(a) The rate of heat loss from the pipe
(b) The energy lost per year if the cost of the fuel is 0.52 $/therm ( 1 therm = 105,500 kJ)
c) The thickness of the insulation if 98% of the energy loss is planned to be saved. Consider the conduction coefficient of the insulation is 0.035 W/mK.
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- 2.42 A circumferential fin of rectangular cross section, 3.7-cm OD and 0.3 cm thick, surrounds a 2.5-cm- diameter tube as shown below. The fin is constructed of mild steel. Air blowing over the fin produces a heat transfer coefficient of K. If the temperatures of the base of the fin and the air are and , respectively, calculate the heat transfer rate from the fin.arrow_forward3.5 In a ball-bearing production facility, steel balls that are each of 15 mm in diameter are annealed by first heating them to 870°C and then slowly cooling in air to 125°C. If the cooling air stream temperature is 60°C, and it has a convective heat transfer coefficient of , determine the time required for the cooling.arrow_forwardThe air-conditioning system in a Chevrolet van for use in desert climates is to be sized. The system is to maintain an interior temperature of 20C when the van travels at 100 km/h through dry air at 30C at night. If the top of the van is idealized as a flat plate 6 m long and 2 m wide and the sides as flat plates 3 m tall and 6 m long, estimate the rate at which heat must be removed from the interior to maintain the specifiedarrow_forward
- 3.10 A spherical shell satellite (3-m-OD, 1.25-cm-thick stainless steel walls) re-enters the atmosphere from outer space. If its original temperature is 38°C, the effective average temperature of the atmosphere is 1093°C, and the effective heat transfer coefficient is , estimate the temperature of the shell after reentry, assuming the time of reentry is 10 min and the interior of the shell is evacuated.arrow_forwardQuestion:- A cylindrical steel tank with a diameter of 3 m and height of 4.4 m is used to store chilled water (at 9.3 °C) as part of an air conditioning system for a building. The heat transfer (convection) co-efficient for the surface of the tank in contact with the water in this application is 15 W/(m2.K). Given the surface temperature of the metal tank is 40 °C. At what rate must heat energy be removed from the water just to maintain its temperature constant at 9.3 °C ? Assume the tank is an enclosed cylinder and that the tank is always full. Note - the thickness of the tank is not relevant to this problem. Work in base SI units.arrow_forwardConsider a closed cylindrical reactor vessel of diameter D= 1 ft, and length L= 1.5 ft. The surface temperature of the vessel, T1, and the surrounding temperature, T2, are 390 deg. F and 50 deg. F, respectively. The convective heat transfer coefficient, h, between the vessel wall and surrounding fluid is 4.0 Btu/h . ft . ⁰F. Calculate the thermal resistance in ⁰F .h/Btu.arrow_forward
- Hot water is to be cooled as it flows through the tubes exposed to atmospheric air. Fins are to be attached in order to enhance heat transfer. Would you recommend attaching the fins inside or outside the tubes? Why?arrow_forwardQuestion 3: A house has a composite wall of wood, fiberglass insulation, and plaster board, as indicated in the sketch. On a cold winter day the convection heat transfer coefficients are ho 60 W/m2 K and hi 30 W/m2 K. The total wall surface area is 350 m2. (a)Determine the total heat loss through the wall. (b) If the wind were blowing violently, raising ho to 300 W/m2 K, determine the percentage increase in the heat loss.arrow_forwardFins, or extended surfaces, commonly are used in a variety of engineering applications to enhance cooling. Common examples include a motorcycle engine head, a lawn mower engine head, extended surfaces used in electronic equipment, and finned tube heat exchangers in room heating and cooling applications. Consider aluminum fins of a rectangular profile, which are used to remove heat from a surface whose temperature is100° C . The temperature of the ambient air is 20° C. We are interested in determining how the temperature of the fin varies along its length and plotting this temperature variation. For long fins, the temperaturedistribution along the fin is given byarrow_forward
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