A 10-cm long, 10-cm diameter steel cylinder, whose thermal conductivity and thermal diffusivity are W 43 and 1.172 x 10 respectively, is taken out of a furnace with a uniform temperature of m-K 300°C. It is suddenly immersed in a cooling bath that is maintained at a constant temperature of 40°C and has a convection heat transfer coefficient of 280 m2-K Find the amount of heat loss from the cylinder after 2 minutes in kl. Express your answer as a positive value.

A 10-cm long, 10-cm diameter steel cylinder, whose thermal conductivity and thermal diffusivity are W 43 and 1.172 x 10 respectively, is taken out of a furnace with a uniform temperature of m-K 300°C. It is suddenly immersed in a cooling bath that is maintained at a constant temperature of 40°C and has a convection heat transfer coefficient of 280 m2-K Find the amount of heat loss from the cylinder after 2 minutes in kl. Express your answer as a positive value.

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 1.64P: The interior wall of a large, commercial walk-in type meat freezer is covered under normal operating...

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1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the convection heat transfer coefficient between the outer surface of the container and the air is 6.8 , the temperature of the air is 27°C, and the temperature of the surface of the sphere is –183°C, determine the rate of heat transfer by convection.
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.
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.
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.
1.39 On a cold winter day, the outside wall of a home is exposed to an air temperature of when the inside temperature of the room is at . As a result of this temperature gradient, there is heat loss through the wall to the outside. Consider the convective heat transfer coefficients for the air inside the room and at the outside wall surface to be, respectively, 12.0 and . If the composite room wall is modeled as a plane wall with a thermal resistance per unit area of , determine the temperature at the outer surface of the wall as well as the rate of heat flow through the wall per unit area. If the homeowner were to consider using a fiberglass insulation layer on the inside wall surface for reducing this heat loss by 50%, what is the required thickness of this layer and the outside wall temperature for this case?
2.55 A long, 1-cm-diameter electric copper cable is embedded in the center of a 25-cm-square concrete block. If the outside temperature of the concrete is 25oC and the rate of electrical energy dissipation in the cable is 150 W per meter length, determine temperatures at the outer surface and at the center of the cable.
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.
The interior wall of a large, commercial walk-in type meat freezer is covered under normal operating conditions with a 2-cm thick layer of ice. One day, a power outage cuts electricity to the refrigeration system of the freezer. Estimate the time required to melt this layer of ice if it has a mass density of 700kg/m3 and a latent heat of fusion of 334 kJ/kg. Consider the air temperature inside the freezer to be 20C with a heat transfer coefficient of 2W/m2K for convection from the freezer surface to air, and clearly state the assumptions made in your calculations.
1.29 A spherical interplanetary probe with a 30-cm diameter contains electronic equipment that dissipates 100 W. If the probe surface has an emissivity of 0.8, what is its surface temperature in outer space? State your assumptions in the calculations.
A person puts a few apples into the freezer at 15°C cool them quickly for guestswho are about to arrive. Initially, the apples are at a uniform temperature of 20°C,and the heat transfer coefficient on the surfaces is 8 W/m2·K. Treating the apples as9-cm-diameter spheres and taking their properties to be 840 kg/m3, Cp 3.81 kJ/kg·K, k = 0.418 W/m·K, and α =10-7 m2/s, determine the center and surface temperatures of the apples in 1 h. Also, determine the amount of heat transfer from each apple. Solve this problem using analytical one-term approximation method (notthe Heisler charts). Answer: Center: 11.2 ℃, Surface: 2.7 ℃, heat transfer: 17.2 kJ
A 2.2-mm-diameter and 10-m-long electric wire istightly wrapped with a 1-mm-thick plastic cover whose thermalconductivity is K = 0.15 W/m·K. Electrical measurementsindicate that a current of 13 A passes through the wire and there is a voltage drop of 8 V along the wire. If the insulatedwire is exposed to a medium at T` = 30°C with a heat transfercoefficient of h = 24 W/m2·K, determine the temperature at theinterface of the wire and the plastic cover in steady operation.Also determine if doubling the thickness of the plastic coverwill increase or decrease this interface temperature.
Refractory bricks are used as linings for furnaces, and they generally have low thermal conductivity to minimize heat loss through the furnace walls. Consider a thick furnace wall lining with refractory bricks (k = 1.0 W/m·K and a = 5.08 * 10-7 m2/s), where initially the wall has a uniform temperature of 15°C. If the wall surface is subjected to uniform heat flux of 20 kW/m2, determine the temperature at the depth of 10 cm from the surface after an hour of heating time.