The 3-layer wall consists of glass-air-glass and the thickness is 2 cm, 5 cm, and 2 cm, respectively. These walls separate the rooms at 100°C and 30°C. Wall area 1200 cm² while the conductivity of glass and air are 0.84 and 0.02 J/s.m.K, respectively. Determine (a) heat flowing through the wall every second, (b) the temperature of the boundary between the air-glass and between the air-glass.

The 3-layer wall consists of glass-air-glass and the thickness is 2 cm, 5 cm, and 2 cm, respectively. These walls separate the rooms at 100°C and 30°C. Wall area 1200 cm² while the conductivity of glass and air are 0.84 and 0.02 J/s.m.K, respectively. Determine (a) heat flowing through the wall every second, (b) the temperature of the boundary between the air-glass and between the air-glass.

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 1.56P: A pipe carrying superheated steam in a basement at 10C has a surface temperature of 150C. Heat loss...

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A pipe carrying superheated steam in a basement at 10C has a surface temperature of 150C. Heat loss from the pipe occurs by radiation (=0.6) and natural convection (hc=25W/m2K). Determine the percentage of the total heat loss by these two mechanisms.
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.
The heat transfer rate from hot air by convection at 100C flowing over one side of a flat plate with dimensions 0.1m0.5m is determined to be 125 W when the surface of the plate is kept at 30C. What is the average convection heat transfer coefficient between the plate and the air?
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.
2.55 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.
It is designed in such a way that the internal temperature of a commercial heat treatment furnace can reach up to 165 oC. All surfaces of the furnace consist of firebrick (10 cm), insulation material and sheet metal (3mm) from the inside out. Given that the outdoor temperature is 22 oC, the outer sheet will be allowed to go up to 35 oC, which is a temperature that will not disturb in contact with hands. In this case, determine the insulation material thickness to be used. The thermal conductivity coefficient of the insulation material is insulation 0.066 W / m oC, 60 W / m oC for sheet metal and 115 W / m oC for firebrick. Indoor heat transfer coefficient will be accepted as 25 W / m2 oC and 12 W / m2 oC for outdoor environment.
It is designed in such a way that the internal temperature of a commercial heat treatment furnace can reach up to 165 oC. All surfaces of the furnace consist of firebrick (10 cm), insulation material and sheet metal (3mm) from the inside out. Given that the outdoor temperature is 22 oC, the outer sheet will be allowed to go up to 35 oC, which is a temperature that will not be disturbed by hand contact. In this case, determine the insulation material thickness to be used. Insulation material thermal conductivity coefficient is 0.066 insulation W / m oC, 60 W / m oC for sheet metal and 115 W / m oC for firebrick. Indoor heat transfer coefficient will be accepted as 25 W / m2 oC and 12 W / m2 oC for outdoor environment.
A 2x2-m glass window, 1 cm thick is subjected to 10°C and 3°C inner and outer temperatures respectively. If the thermal conductivity of the glass is 0.78 W/m-°C, what is the amount of heat loss, in kl, through the glass over a period of 5 hours?
1. A 1000-W iron is left on the iron board with its base exposed to the air at 20°C. The convection heat transfer coefficient between the base surface and the surrounding air is 35 W/m². °C. If the base has an emissivity of 0.6 and a surface area of 0.02 m², determine the temperature of the base of the iron. 2. The inner and outer surfaces of a 5-m x 6-m brick wall of thickness 30 cm and thermal conductivity 0.69 W/m °C are maintained at temperatures of 20°C and 5°C, respectively. Determine the rate of heat transfer through the wall, in W.
The inner and outer surfaces of a cylindrical shell with radii of 1 cm and 2 cm are 300 °C and 100 °C, respectively. If the thermal conductivity of the shell is 2 W/m-K, determine the heat transfer through the shell per unit length of the cylinder.
A square thermal window is constructed of two sheets of flat glass, each 4.00 mm thick, separated by 5.00 mm of stationary air. If the inside of the window is at 20.0 oC, the external one at -30.0 oC and the cross-sectional area of the window is 6.00 m2, determine for the steady state: kglass= 0,80 W/(m*K); kair= 0,024 W(m*K) a) The temperatures between the air layer ?1 and ?2 indicated in the figure.b) The flow of heat through the window
3) The two sides of a large plan wall are maintained at constant temperatures of T₁ = 120°C and T₂ = 50°C, respectively. If you know that the wall thickness L = 0.2 m, thermal conductivity k = 1.2 W/m.K, and surface area A= 15 m². Determine (a) the variation of temperature within the wall and the value of temperature at x = 0.1 m and (b) the rate of heat conduction through the wall under steady conditions. -02-1