A 212-mm-square, 15-mm-thick tile has the thermo-physical properties of Pyrex (ϵ = 0.83) and emerges from a curing process at an initial temperature of Ti = 145°C. The backside of the tile is insulated while the upper surface is exposed to ambient air and surroundings at 25°C. (a) Estimate the time required for the tile to cool to a final, safe-to-touch temperature of Tf = 42°C. Use an average tile surface temperature of T¯=(Ti+Tf)/2 to estimate the average free convection coefficient and the linearized radiation coefficient. How sensitive is your estimate to the assumed value for T¯? (b) Estimate the required cooling time if ambient air is blown in parallel flow over the tile with a velocity of 10 m/s

A 212-mm-square, 15-mm-thick tile has the thermo-physical properties of Pyrex (ϵ = 0.83) and emerges from a curing process at an initial temperature of Ti = 145°C. The backside of the tile is insulated while the upper surface is exposed to ambient air and surroundings at 25°C. (a) Estimate the time required for the tile to cool to a final, safe-to-touch temperature of Tf = 42°C. Use an average tile surface temperature of T¯=(Ti+Tf)/2 to estimate the average free convection coefficient and the linearized radiation coefficient. How sensitive is your estimate to the assumed value for T¯? (b) Estimate the required cooling time if ambient air is blown in parallel flow over the tile with a velocity of 10 m/s

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 3.10P: 3.10 A spherical shell satellite (3-m-OD, 1.25-cm-thick stainless steel walls) re-enters the...

See similar textbooks

Similar questions

Partially-frozen ice cream is being placed in a package before completion of the freezing process. The package has dimensions of 8 cm by 10 cm by 20 cm and is placed in air- blast freezing with convective heat coefficient of 50 W/(m2 K) for freezing. The product temperature is -5°C when placed in the package, and the air temperature is -25°C. The product density is 700 kg/m3, the thermal conductivity (frozen) is 1.2 W/(m K), and the specific heat of the frozen product is 1.9 kJ/(kg K). If the latent heat to be removed during blast freezing is 100 kJ/kg, estimate the freezing time.
(a) If the cost of producing the hot water is $0.10 per kWh, what is the representative daily costof heat loss from an uninsulated pipe to the air per meter of pipe length? The convectionresistance associated with water flow in the pipe may be neglected.(b) Determine the savings associated with application of a 10-mm-thick coating of urethaneinsulation (k = 0.026 W/m-K) to the outer surface of the pipe.
The author and his then 6-year-old son have conducted the following experiment to determine the thermal conductivity of a hot dog. They first boiled water in a large pan and measured the temperature of the boiling water to be 94°C, which is not surprising, since they live at an elevation of about 1650 m in Reno, Nevada. They then took a hot dog that is 12.5 cm long and 2.2 cm in diameter and inserted a thermocouple into the midpoint of the hot dog and another thermocouple just under the skin. They waited until both thermocouples read 20°C, which is the ambient temperature. They then dropped the hot dog into boiling water and observed the changes in both temperatures. Exactly 2 min after the hot dog was dropped into the boiling water, they recorded the center and the surface temperatures to be 59°C and 88°C, respectively. The density of the hot dog can be taken to be 980 kg/m3, which is slightly less than the density of water, since the hot dog was observed to be floating in water while…
A well-insulated inside room, 6 m wide and 9 m long with a 3 m ceiling height, is to be heated by means of a ceiling panel installation. It is desired to maintain the surface of the floor at a temperature of 27 oC. Determine the necessary ceiling surface temperature to meet this requirement if the floor is to be planed oak, the ceiling is to be painted with an oil paint, and it is estimated that the portion of the heating requirement to be supplied by radiation is 2 500 W. Assume the walls to be nonconducting but reradiating.
A rectangular slab of butter which is 46.2 mm thick at a temperature of 277.6 K in a cooler is removed and placed in an environment at 297.1 K. The sides and bottom of the butter container can be considered to be insulated by the container sidewalls. The flat top surface of the butter is exposed to the environment. The convective coefficient is constant at 8.52 W/m2 K. Calculate the temperature in the butter at the surface, at 25.4 mm below the surface, and at 46.2 mm below the surface at the insulated bottom after 5 h exposure. k = 0.197 W/m-K, Cp = 2.30 kJ/kg-K and ρ = 998 kg/m3. Ans: T= 292.2 K , 288.3
Juice in cans 150 mm long and 60 mm in diameter is initially at 27°C and is to be cooled by placement in a refrigerator compartment at 4°C. In the interest of maximizing the cooling rate, should the cans be laid horizontally or vertically in the compartment?
An electrical heater 114 mm long and 7 mm in diameter is inserted into a hole drilled normal to the surface of a large block of material having a thermal conductivity of 9 W/m · K. Estimate the temperature reached by the heater when dissipating 54 W with the surface of the block at a temperature of 27°C.
During hot summer weather, many people put “koozies” around their beverages to keep the drinks cold. In addition to preventing a warm hand from heating the container through conduction, what other mechanisms slow the process of warming beverages?
The emissivity of galvanized steel sheet, a common roofing material, is ε = 0.13 at temperatures around 300 K, while its absorptivity for solar irradiation is αS = 0.65. Would the neighborhood cat be comfortable walking on a roof constructed of the material on a day when GS = 750 W/m2, T∞ = 16°C, and h = 7 W/m2 · K? Assume the bottom surface of the steel is insulated.
Steam at a temperature of 723 K is flowing through a pipe with an outer diameter of 100 mm. The pipe is insulated with 30-mm thick mineral wool, the average thermal conductivity of which is 0.065 W/m.K. Determine the outside surface temperature of mineral wool if the ambient air temperature is 300 Assume the hot-surface temperature of the mineral wool is the same as that of the flowing steam and the value of the surface coefficient of the insulating material is 33 W/m2.K.
1. A composite furnace wall is made up of a 12-in. lining of magnesite refractory brick, a 5-in.thickness of 85% magnesia, and a steel casing 0.10-in. thick. Flue gas temperature is 2200 F andthe boiler room is at 80 F. Gas side film coefficient is 15 Btu/hr-sq.ft-F and air side is 4.0.Determine:a. The thermal current Q/Ab. Interface temperaturesc. Effect on thermal current and inside refractory wall temperature if the magnesia insulation weredoubled.
You are interested in analyzing the rate at which a spherical ice ball melts. What heat equation should you use for the ice? List all assumptions.