A long cylindrical rod has a 20-cm-diameter at a uniform temperature of 600°C. The rod is then allowed to cool slowly in a room at 200°C with a heat transfer coefficient of 80 W/m² °C. Calculate the temperature at the center of the rod 45 min after the start of the cooling process. Also, determine the heat transfer per unit length of the rod during this time period. Given: k=14.9 W/m.K, a = 3.95x10-6, m2/s p=7900 Kg/m3 Cp=0.477 KJ/Kg. °C %3D

A long cylindrical rod has a 20-cm-diameter at a uniform temperature of 600°C. The rod is then allowed to cool slowly in a room at 200°C with a heat transfer coefficient of 80 W/m² °C. Calculate the temperature at the center of the rod 45 min after the start of the cooling process. Also, determine the heat transfer per unit length of the rod during this time period. Given: k=14.9 W/m.K, a = 3.95x10-6, m2/s p=7900 Kg/m3 Cp=0.477 KJ/Kg. °C %3D

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.

Chapter3: Transient Heat Conduction

Section: Chapter Questions

Problem 3.16P: 3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer...

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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.
A slab of aluminium 10 cm thick is originally at a temperature of 500°C. It is suddenly immersed in a liquid at 100°C resulting it a heåt transfer coefficient of 1200. W/m2K. Determine the temperature at the center line and the surface 1 min after the immersion. Also the total thermal energy removal per unit area of slab during this period. The properties of aluminium for the given condition are, a = 8.4 x 10-5 m?/s, k =215 W/mK, p = 2700 kg/m3, C= 0.9.kJ/kgK.
Water hardening process of 2 m long and 0.05 m diameter steel bars will be carried out. The steel bar, which is heated up to 900 °C in the oven, is cooled to an average temperature of 100 °C in a water bath. The water bath is kept at a uniform temperature of 30 °C and the heat transfer coefficient between the water and the rod surface is 325 W/m2K. Accordingly, calculate the time required for the steel bar to cool to 100°C in the water bath. (Steel bar p=7832 kg/m3, cp=434 J/kgK, k=63.9 W/mK)
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A long cylindrical rod has a 20-cm-diameter at a uniform temperature of 600°C. The rod is then allowed to cool slowly in a room at 200°C with a heat transfer coefficient of 80 W/m² °C. Calculate the temperature at the center of the rod 45 min after the start of the cooling process. Also, determine the heat transfer per unit length of the rod during this time period.
For heat transfer purposes, an egg can be considered to be a 5.5-cm-diameter sphere having the properties of water. An egg that is initially at 8°C is dropped into the boiling water at 86°C. The heat transfer coefficient at the surface of the egg is estimated to be 800 W/m2-K. If the egg is considered cooked when its center temperature reaches 60°C, determine how long the egg should be kept in the boiling/water. Solve this problem using analytical one-term approximation method (not the Heisler charts). The length of/time for the egg to be kept in boiling water is determined to be min.
A thick concrete wall fairly large in size initially at 30 oC has its surface temperatureincreased to 600 oC by an intense fire which lasted for 25 minutes. The material maydisintegrate up to a depth where the temperature reaches 400 oC. Determine thethickness which may disintegrate and the heat flow at this depth and the total heatflow during that time. The thermal diffusivity is 4.92 x 19-7 m2/s and k = 1.28 W/m-K.
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A 6 cm diameter sphere is initially at a temperature of 100C. Later, this sphere was thrown into water at 800C. Calculate how long it will take for the center temperature of the sphere to reach 500C by taking the convection heat transfer coefficient as 80W / m2K.