For heat transfer purposes, an egg can be considered to be a 4-cm diameter sphere having the properties of water. An egg that is initially at 8°C is dropped into boiling water at 100°C. The heat transfer coefficient at the surface of the egg is estimated to be 400 W/m2°C. 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? Assume negligible internal resistance i

For heat transfer purposes, an egg can be considered to be a 4-cm diameter sphere having the properties of water. An egg that is initially at 8°C is dropped into boiling water at 100°C. The heat transfer coefficient at the surface of the egg is estimated to be 400 W/m2°C. 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? Assume negligible internal resistance i

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.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.60P: 1.60 Two electric resistance heaters with a 20 cm length and a 2 cm diameter are inserted into a...

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1.60 Two electric resistance heaters with a 20 cm length and a 2 cm diameter are inserted into a well-insulated 40-L tank of water that is initially at 300 K. If each heater dissipates 500 W, what is the time required for bringing the water temperature in the tank to 340 K? State your assumption for your analysis.
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.
An ordinary egg can be approximated as a 5.5-cm-diameter sphere whose properties are roughly k=0.6 W/m.oC and a=0.14 x 10-6 m2/s. The egg is initially at a uniform temperature of 8 oC and is dropped into boiling water at 97 oC. Taking the convection heat transfer coefficient to be h=1400 W/m2.oC, determine how long it will take for the center of the egg to reach 70oC.
A long roll of 2-m-wide and 0.5-cm-thick 1-Mn manganesesteel plate (ρ = 7854 kg/m3 and cp = 0.434 kJ/kg·°C)coming off a furnace at 820°C is to be quenched in an oil bathat 45°C to a temperature of 51.1°C. If the metal sheet is movingat a steady velocity of 10 m/min, determine the requiredrate of heat removal from the oil to keep its temperature constantat 45°C.
Question -) Consider a stainless steel spoon (k = 15 W/m·K) partially immersed in boiling water at 95°C in a kitchen at 25°C. The handle of the spoon has a cross section of 0.2cm x 1.2 cm, and extends 18 cm in the air from the free surface of the water. If the heat transfer coefficient at the exposed surfaces of the spoon handle is 15 W/m2·°C, determine the temperature difference across the exposed surface of the spoon handle. State your assumptions.
Consider a stainless steel spoon (k = 15 W/m·K) partially immersed in boiling water at 95°C in a kitchen at 25°C. The handle of the spoon has a cross section of 0.2cm x 1.2 cm, and extends 18 cm in the air from the free surface of the water. If the heat transfer coefficient at the exposed surfaces of the spoon handle is 15 W/m2·°C, determine the temperature difference across the exposed surface of the spoon handle. State your assumptions.
Example 9: A 2-kW resistance heater wire whose thermal conductivity is k = 15 W/m ·°C has a diameter of D = 4 mm and a length of L = 0.5 m, and is used to boil water. If the outer surface temperature of the resistance wire is Ts = 105°C, determine the temperature at the center of the wire.
In a manufacturing facility, 2-in-diameter brassballs (k = 64.1 Btu/h·ft·°F, r = 532 lbm/ft3, and cp =0.092 Btu/lbm·°F) initially at 250°F are quenched in a waterbath at 120°F for a period of 2 min at a rate of 120 ballsper minute. If the convection heat transfer coefficient is42 Btu/h·ft2·°F, determine (a) the temperature of the balls afterquenching and (b) the rate at which heat needs to be removedfrom the water in order to keep its temperature constant at120°F.
An ordinary egg can be approximated as a 5.5-cm-diameter sphere. The egg is initially at a uniform temperature of 8°C and is dropped into boiling water at 97°C. Taking the properties of the egg to be ρ = 1020 kg/m3 and cp = 3.32 kJ/kg·°C, determine how much heat is transferred to the egg by the time the average temperature of the egg rises to 70°C.
THARMOFLUID A student living in a 3-m X 4-m X 4-m dormitory room turns on her 100-W fan before she leaves the room on a summer day, hoping that the room will be cooler when she comes back in the evening. Assuming all the doors and heat trans windows are tightly closed and disregarding any heat fer let through the walls and the windows, determine the temperature in the room when she comes back 8 h later. Use specific heat values at room temperature, and assume room to be at 100 kPa and 20°C in the morning she leaves.
The exhaust gases of an automotive engine leave the combustion chamber and enter a 8-ft-long and 3.5-in-diameter thin-walled steel exhaust pipe at 800°F and 15.5 psia at a rate of 0.05 lbm/s. The surrounding ambient air is at a temperature of 80°F, and the heat transfer coefficient on the outer surface of the exhaust pipe is 3 Btu/h?ft2?°F. Assuming the exhaust gases to have the properties of air, determine (a) the velocity of the exhaust gases at the inlet of the exhaust pipe and (b) the temperature at which the exhaust gases will leave the pipe and enter the air.
In a power plant, pipes transporting superheated vapor are very common. In a certain plant, superheated vapor is flowing at a rate of 0.3 kg/s inside a 5 cm diameter pipe of 10 m length. The air in the plant is maintained at 20oC while the surface temperature of the pipe is 100oC. If the temperature drop between the inlet and exit of the pipe is 30oC and the specific heat capacity of the vapor is 2190 kJ/kg.K, determine the convective heat transfer coefficient at the pipe surface. If necessary, how could this coefficient be increased?