the composite wall of a refrigerator has a thermal conductivity of 0.05 W/m-K and a wall thickness of 50 mm. In a room of 25 °C, the refrigerated cold space inside the refrigerator is maintained at 4 °C. Assume the inner and outer convection heat transfer coefficients are 5 W/m² K and 10 W/m².K, respectively. Neglect radiation heat transfer. Determine the rate of heat leaking into the refrigerator per unit surface area.

the composite wall of a refrigerator has a thermal conductivity of 0.05 W/m-K and a wall thickness of 50 mm. In a room of 25 °C, the refrigerated cold space inside the refrigerator is maintained at 4 °C. Assume the inner and outer convection heat transfer coefficients are 5 W/m² K and 10 W/m².K, respectively. Neglect radiation heat transfer. Determine the rate of heat leaking into the refrigerator per unit surface area.

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 1.19P: 1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the...

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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.
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.
The heat transfer coefficient between a surface and a liquid is 57 W/(m2K). How many watts per square meter will be transferred in this system if the temperature difference is 10C?
Consider a large plane wall of thickness L=0.4 m, thermal conductivity k =1.8 W/m.K, and surface area A=30 m2. The left side of the wall is maintained at a constant temperature of T1= 900C while the right side loses heat by convection to the surrounding air at T∞= 250C with a heat transfer coefficient of h = 24 W/m2.K. Assuming constant thermal conductivity and no heat generation in the wall, (a) express the differential equation and the boundary conditions for steady one-dimensional heat conduction through the wall. (b) Obtain a relation for the variation of temperature in the wall by solving the differential equation and (c) evaluate the rate of heat transfer through the wall. Heat transfer course
Q2/ Consider a 1.2-m-high and 2-m-wide glass window whose thickness is 6 mm and thermal conductivity is k = 0.78 W/m. °C. Determine the steady rate of heat transfer through this glass window and the temperature of its inner surface for a day during which the room is maintained at 24°C while the temperature of the outdoors is 5°C. Take the convection heat transfer coefficients on the inner and outer surfaces of the window to be h1 = 10 W/m2 °C and h2= 25 W/m2 °C, and disregard any heat transfer by radiation.
The brick wall of a house measures 4 x 7 m and has a thickness of 0.3 m. The thermal conductivity of the brick is 0.69 W/m.K. If the inner and outer temperatures of the wall are 26oC and 8oC respectively, determine the rate of heat transfer through the wall.
Consider a solid sphere of radius r=50 cm. The heat is generated steadily inside the sphere at a rate of (15000) W/m³. The conductivity of the sphere is 10 W/m.K. Surface of the sphere is cooled by cooling water whose temperature and convection heat transfer coefficient are 10°C and 125 W/m2.K. Determine the temperatures at the center and surface of the sphere. Find the total heat transfer rate from the surface of the sphere. To=10 °C h=125 W/m2.K r-50 cm egen=(15000)W/m³ To=10 °C h=125 W/m2.K
Consider a solid sphere of radius r=50 cm. The heat is generated steadily inside the sphere at a rate of (15000) W/m3. The conductivity of the sphere is 10 W/m.K. Surface of the sphere is cooled by cooling water whose temperature and convection heat transfer coefficient are 10oC and 125 W/m2.K. Determine the temperatures at the center and surface of the sphere. Find the total heat transfer rate from the surface of the sphere.
0.3MW / m3 heat is generated in a 6 cm thick flat wall. One surface of the wall is insulated and the other surface is exposed to an environment of 93C. The convection heat coefficient between the wall and the environment is 570 W / m2C and the heat conduction coefficient for the wall is 21 W / Since it is mC, calculate the maximum temperature (T0) inside the wall (C).
A plane wall 3.5 cm thick generates heat internally. The wall is made of a material with thermal conductivity of 44 W/m K. Both faces of the wall are maintained at 50.30°C. If the maximum temperature inside the wall is 61°C, what is the rate of internal heat generation in the wall per unit volume? Express your answer in W/m³.
A steel tube with a thermal conductivity of 45 W/m.K carries a fluid at 200°C, with a convection heat transfer coefficient of 210 W/m2./K. The tube has an external diameter of 5 cm, a wall thickness of 1 cm and a length of 2 m. The ambient air and surroundings are at 25°C, with a convection heat transfer coefficient of 25 W/m2.K. Neglecting the effects of radiation, determine: 1) The total resistance considering the effects of radiation only on the outside, with the coefficient hr = 2W/m2.K 2) The new heat transfer rate, considering the effects of radiation, if an additional layer of 15 mm thick foam with a conductivity of 0.03 W/m.K is added to the system. 3) The critical insulation radius of the system after adding this insulating layer.
I just took a water bottle out of my refrigerator (0₁ = 3°C) and placed it on the kitchen counter. The environment is at 0₂ = 20 °C. The overall heat transfer coefficient between the bottle and the environment is 2 W/K and the heat capacity of the bottle and its contents is 3 kJ/K. Over what time periods would you consider the bottle to be an adiabatic system? A diather- Colar mal system?