A spherical ball with a diameter of 11.5 cm, initially at uniform temperature of 170°C, is suddenly exposed to a convection environment at 44°C with convection coefficient of 380 W/m²K. What is the minimum thermal conductivity of the ball material such that the lumped capacity method is applicable? Express your answer in W/m K.

A spherical ball with a diameter of 11.5 cm, initially at uniform temperature of 170°C, is suddenly exposed to a convection environment at 44°C with convection coefficient of 380 W/m²K. What is the minimum thermal conductivity of the ball material such that the lumped capacity method is applicable? Express your answer in W/m K.

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.
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An isolating wall (made up of 2-10mm thick plywood with 5mm woven silica sheet in between) encloses a steam-room to prevent the outside area from having the same temperature as the inside of the room. If the total area of the wall is 100 sq.m. and coefficient of thermal conductivity (k) for plywood and silica sheets are 0.12 and 0.015 W/mK respectively, what is the rate of heat transfer if the inside temperature is 800 °C while the outside is 42°C? answer must be in Watts
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