3- Pipes with inner and outer diameter of 50mm and 60mm, respectively, are used for transporting superheated vapor in a manufacturing plant. The pipes with thermal conductivity of 16 W/m.K are connected together by flanges with combined thickness of 20mm and outer diameter of 90mm. Air condition surrounding the pipes has a temperature of 25C and a convection heat transfer coefficient of 10 W/m².K. If the inner surface ww temperature of the pipe is maintained at a constant temperature of 150C, determine the temperature at the base of the flange and the rate if heat loss through the flange. Air, 25 °C h= 10 W/m2.°C D, = 50 mm T;= 150 °C 90 mm Pipe, k= 16 W/m-°C D = 60 mm t= 20 mm

3- Pipes with inner and outer diameter of 50mm and 60mm, respectively, are used for transporting superheated vapor in a manufacturing plant. The pipes with thermal conductivity of 16 W/m.K are connected together by flanges with combined thickness of 20mm and outer diameter of 90mm. Air condition surrounding the pipes has a temperature of 25C and a convection heat transfer coefficient of 10 W/m².K. If the inner surface ww temperature of the pipe is maintained at a constant temperature of 150C, determine the temperature at the base of the flange and the rate if heat loss through the flange. Air, 25 °C h= 10 W/m2.°C D, = 50 mm T;= 150 °C 90 mm Pipe, k= 16 W/m-°C D = 60 mm t= 20 mm

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.

Chapter2: Steady Heat Conduction

Section: Chapter Questions

Problem 2.38P: 2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from...

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2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.
3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer coefficient on one side is and on the other side is . If the temperature of both streams is suddenly changed from 38°C to 93°C, determine how long it takes for the copper plate to reach a temperature of 82°C.
Determine the rate of heat transfer per meter length from a 5-cm-OD pipe at 150C placed eccentrically within a larger cylinder of 85 magnesia wool as shown in the sketch. The outside diameter of the larger cylinder is 15 cm and the surface temperature is 50C.
Determine the rate of heat transfer per meter length to a light oil flowing through a 2.5-cm-ID, 60-cm-long copper tube at a velocity of 0.03 m/s. The oil enters the tube at 16C, and the tube is heated by steam condensing on its outer surface at atmospheric pressure with a heat transfer coefficient of 11.3 kW/m K. The properties of the oil at various temperatures are listed in the following table: Temperature, T(C) 15 30 40 65 100 (kg/m3) 912 912 896 880 864 c(kJ/kgK) 1.80 1.84 1.925 2.0 2.135 k(W/mK) 0.133 0.133 0.131 0.129 0.128 (kg/ms) 0.089 0.0414 0.023 0.00786 0.0033 Pr 1204 573 338 122 55
2.9 In a large chemical factory, hot gases at 2273 K are cooled by a liquid at 373 K with gas-side and liquid-side convection heat transfer coefficients of 50 and , respectively. The wall that separates the gas and liquid streams is composed of a 2-cm thick oxide layer on the gas side and a 4-cm thick slab of stainless steel on the liquid side. There is a contact resistance between the oxide layer and the steel of . Determine the rate of heat loss from hot gases through the composite wall to the liquid.
A mild-steel cylindrical billet 25 cm in diameter is to be raised to a minimum temperature of 760C by passing it through a 6-m long strip-type furnace. If the furnace gases are at 1538C and the overall heat transfer coefficient on the outside of the billet is 68W/m2K, determine the maximum speed at which a continuous billet entering at 204C can travel through the furnace.
Heat is transferred at a rate of 0.1 kW through glass wool insulation (density=100kg/m3) with a 5-cm thickness and 2-m2 area. If the hot surface is at 70C, determine the temperature of the cooler surface.
Estimate the rate of heat loss per unit length from a 5-cm ID, 6-cm OD steel pipe covered with high-temperature insulation having a thermal conductivity of 0.11 W/(m K) and a thickness of 1.2 cm. Steam flows in the pipe. It has a quality of 99% and is at 150C. The unit thermal resistance at the inner wall is 0.0026(m2K)/W the heat transfer coefficient at the outer surface is 17W/(m2K) and the ambient temperature is 16C.
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.
A transformer that is L=20cm long, 6.2 cm wide, and 5 cm high is to becooled by attaching a 10 cm × 6.2 cm wide polished aluminum heatsink (emissivity =0.03) to its top surface. The heat sink has seven fins,which are 5 mm high, 2 mm thick, and 10 cm long. A fan blows air at25°C parallel to the passages between the fins. The heat sink is todissipate 20 W of heat and the base temperature of the heat sink is notto exceed 60°C. Assuming the fins and the base plate to be nearlyisothermal and the radiation heat transfer to be negligible, determinethe minimum free-stream velocity the fan needs to supply to avoidoverheating. (k=0.02681W/m˚C, Pr=0.7248, V= 1.726×10-5 m2/s, )
To cool the hot oil, an engineer has suggested that the oil be pumped through a submerged pipe in a nearby lake. The pipe (external diameter = 20 cm) will be placed in the horizontal direction. The average pipe outer surface temperature is 130 °C. The temperature of the surrounding water is assumed to be constant at 10 °C. Pipe length 150 m. If it is assumed that there is no movement of water. a. Determine the convective heat transfer coefficient of the outer pipe surface to the water. =AnswerWatts/ (m² °C) b. Determine the rate of heat transfer from the pipe to the water. =AnswerkW
A hot surface at 100°C is to be cooled by attaching3-cm-long, 0.25-cm-diameter aluminum pin fins (k = 237 W/m·K) to it, with a center-to-center distance of 0.6 cm. Thetemperature of the surrounding medium is 30°C, and the heattransfer coefficient on the surfaces is 35 W/m2·K. Determine therate of heat transfer from the surface for a 1-m * 1-m sectionof the plate. Also determine the overall effectiveness of the fins.