The rear window of a car is defrosted by the passage of warm air on the internal surface. If the warm air is at 40 °C and the internal convection transfer coefficient is 30 W/m²°C, what are the temperatures of the internal and external surfaces of the glass (4 mm thick) if the external air temperature is -10 °C and the convection coefficient is 65 W/m²°C?

The rear window of a car is defrosted by the passage of warm air on the internal surface. If the warm air is at 40 °C and the internal convection transfer coefficient is 30 W/m²°C, what are the temperatures of the internal and external surfaces of the glass (4 mm thick) if the external air temperature is -10 °C and the convection coefficient is 65 W/m²°C?

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 2.40P: One end of a 0.3-m-long steel rod is connected to a wall at 204C. The other end is connected to a...

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1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10-cm thickness is . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in Appendix 2, Table 11.
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.
One end of a 0.3-m-long steel rod is connected to a wall at 204C. The other end is connected to a wall that is maintained at 93C. Air is blown across the rod so that a heat transfer coefficient of 17W/m2 K is maintained over the entire surface. If the diameter of the rod is 5 cm and the temperature of the air is 38C, what is the net rate of heat loss to the air?
As a designer working for a major electric appliance manufacturer, you are required to estimate the amount of fiberglass insulation packing (k = 0.035 W/m K) that is needed for a kitchen oven shown in the figure below. The fiberglass layer is to be sandwiched between a 2-mm-thick aluminum cladding plate on the outside and a 5-mm-thick stainless steel plate on the inside that forms the core of the oven. The insulation thickness is such that the outside cladding temperature does not exceed 40C when the temperature at the inside surface of the oven is 300C. Also, the air temperature in the kitchen varies from 15Cto33C, and the average heat transfer coefficient between the outer surface of the oven and air is estimated to be 12.0W/m2K. Determine the thickness of the fiberglass insulation that is required for these conditions. What would be the outer surface temperature when the inside surface of the oven is at 475C?
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.
20-m pipe has an outside diameter of 50 mm. Pipe is insulated with a layer of asbestos, then followed by a layer of cork. Inside and outside diameter of the cork is 77 mm and 80 mm, respectively. If the temperature drop from pipe to cork is 1165°C, calculate the inside diameter of the pipe (mm). The rate of the heat transfer is 8778 W. The thermal conductivity of steam pipe, asbestos and cork are 0.045 kW/m-K, 0.058 W/m-K and 0.043 W/m-K respectively.
The ceiling area of 100 square meters consists of four materials. The thermal insulation value of these materials from top to bottom is 1, 50, 0.6 and 0.45 square meters per watt per degree, respectively. If the outside temperature is O degrees and the internal temperature is 25 degrees, what is the speed Heat transfer through the wall?
Convection heat transfer from a plate (2 m x 2 m) is 450 W. If surface temperature of plate is 450 K and surrounding temperature is 300 K, what will be value of heat transfer coefficient?
In a solid sphere of 0.2 m diameter, heat is generated at the rate of 1.2 x 106 W/m3. The center temperature is 300°C. Conductivity is 50 W/m-K. What is the surface temperature?
Convection - Heat Transfer Coefficient (HTC) (1) The temperature of inner surface of insulation wall is t,=100°C, while the outer surface releases the heat by convection to surroundings air with temperature of -20°C. The thickness of the insulating layer is 5 cm and its thermal conductivity of 0,05 W/(m-K). What is the value of heat transfer coefficient on the outside this wall if its surface temperature t, is of 0°C.
A homeowner wants to reduce their monthly heating bill and carbon footprint and is considering replacing a 20cm x 40cm x .50cm single pane window with a double pane to help in this endeavor. The double pane glass window is advertised to reduce thermal energy loss by 67%. The thermal conductivity of glass is .84 W/(m*K). Find the heat lost every minute by the single paned window if the temperature difference between inside and outside of the house is 14C.
A metal cube of 0.1 m sides is being cooled down uniformly from 300°C to 30°C by placing it in cold water at 10°C. The convection coefficient of water around the cube is 40 W/m².K. The properties of the cube material are as follows - thermal conductivity: 137 W/m-K, density: 1600 kg/m³; specific heat: 800 J/kg.K. Neglect radiation. Find the time required for coo cooling. 1426-2