A furnace wall is made up of three layer of thickness 200 mm, 100 mm, and 125 mm with thermal conductivity of 1.65 W/m-K, k2, and 9.2 W/m-K respectively. The inside is exposed to gases at 1200°C with a convection coefficient of 25 W/m2 -K and the inside surface temperature is at 1000°C, the outside air temperature is at 30°C with convection coefficient of 12 W/m2 -K. Calculate: a. the unknown thermal conductivity;

A furnace wall is made up of three layer of thickness 200 mm, 100 mm, and 125 mm with thermal conductivity of 1.65 W/m-K, k2, and 9.2 W/m-K respectively. The inside is exposed to gases at 1200°C with a convection coefficient of 25 W/m2 -K and the inside surface temperature is at 1000°C, the outside air temperature is at 30°C with convection coefficient of 12 W/m2 -K. Calculate: a. the unknown thermal conductivity;

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 2.3P: 2.3 The shield of a nuclear reactor is idealized by a large 25-cm-thick flat plate having a thermal...

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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.
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.
2.3 The shield of a nuclear reactor is idealized by a large 25-cm-thick flat plate having a thermal conductivity of . Radiation from the interior of the reactor penetrates the shield and there produces heat generation that decreases exponentially from a value of at the inner surface to a value of at a distance of 12.5 cm from the interior surface. If the exterior surface is kept at 38°C by forced convection, determine the temperature at the inner surface of the field. Hint: First set up the differential equation for a system in which the heat generation rate varies according to .
An electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of 70C. It is to be cooled in 25C air by attaching aluminum fins with a total surface area of 12cm2. The convection heat transfer coefficient between the fins and the air is 20W/m2K. Estimate the operating temperature when the fins are attached in such a way that (a) there is a contact resistance of approximately 50 K/W between the surface of the device and the fin array and (b) there is no contact resistance (in this case, the construction of the device is more expensive). Comment on the design options.
A composite refrigerator wall is composed of 5 cm of corkboard sandwiched between a 1.2-cm-thick layer of oak and a 0.8-mm-thick layer of aluminum lining on the inner surface. The average convection heat transfer coefficients at the interior and exterior wall are 11 and 8.5W/(m2K) respectively. (a) Draw the thermal circuit. (b) Calculate the individual resistances of the components of this composite wall and the resistances at the surfaces. (c) Calculate the overall heat transfer coefficient through the wall. (d) For an air temperature of 1C inside the refrigerator and 32C outside, calculate the rate of heat transfer per unit area through the wall.
A cooling system is to be designed for a food storage warehouse for keeping perishable foods cool prior to transportation to grocery stores. The warehouse has an effective surface area of 1860 m2 exposed to an ambient air temperature of 32C. The warehouse wall insulation (k=0.17W/(mK)) is 7.5 cm thick. Determine the rate at which heat must be removed (W) from the warehouse to maintain the food at 4C.
1.4 To measure thermal conductivity, two similar 1-cm-thick specimens are placed in the apparatus shown in the accompanying sketch. Electric current is supplied to the guard heater, and a wattmeter shows that the power dissipation is 10 W. Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/m K. Problem 1.4
The wall of a furnace is made up of a material which has thermal conductivity of 2.65 W/m◦C and a thicknesses 300 mm. The inner side of the furnace wall is exposed to hot gases at 1200 ⁰C with a convection coefficient of 20 W/m2⁰C and the inside the surface is at 700 ⁰C. The air outside the furnace is at 20⁰C with a convection coefficient of 15 W/m2⁰C. Draw a clear diagram representing the system Determine the temperature of the outside surface of the furnace The rate of heat loss from the furnace.
A furnace wall is made up of three layer of thickness 150 mm, 110 mm, and 125mm with thermal conductivity of 1.65 W/m-K, k2, and 9.2 W/m-K respectively. Theinside is exposed to gases at 1050°C with a convection coefficient of 25 W/m2-Kand the inside surface temperature is at 900°C, the outside air temperature is at30°C with convection coefficient of 12 W/m2 -K. Calculate:a. the unknown thermal conductivity;b. the outside surface temperature and mid-plane temperatures in °F.
A cold storage room is constructed of an inner layer of 12.7mm of pine, a middle inner of 101.6mm of cork board, and an outer layer of 76.2mm of concrete. The wall surface temperature is 255.4 K inside the cold room and 297.1 k at the outside surface of the concrete. Thermal conductivity of pine is 0.151; corkboard 0.0433; concrete 0.762W/m-K. Calculate the heat loss in W for 1m^2 surface area.
1. (a) Consider a room with a 1.8-m-high and 2.0-m-wide double-pane window consisting of two 4-mm-thick layers of glass separated by a 10-mm-wide stagnant air space. The convection heat transfer coefficients on the inner and outer surfaces of the window are 12 W/m2 K and 25 W/m2 K, respectively, while the average thermal conductivity of glass is 0.78 W/m K; and the air, 0.026 W/m K. If the room is maintained at 22 oC, the outside temperature is -4 oC and heat transfer due to radiation can be neglected, determine: (i) Draw the sketch and thermal resistance network; (ii) the total thermal resistance; (iii) the steady rate of heat transfer through this double-pane window; (iv) the temperature of the inner surface of the window.…
A cold storage room is constructed of an inner layer of 12.7 mm of pine, a middle layer of 101.6 mm of cork board, and an outer layer of 76.2 mm of concrete. The wall surface temperature is 255.4 K inside the cold room and 297.1 K at the outside surface of the concrete. The conductivities for pine, for cork board and for concrete are 0.151 W/m.K, 0.0433 W/m.K, 0.762 W/m.K respectively. Calculate the heat loss in W for 1 m2 and the temperature at the interface between the wood and cork board.