To ensure effective heat transfer from the food inside a freezer, the 2-mm thick layer of frost thatformed at its inside surface must be melted. If the compartment is in ambient air at 20°C and acoefficient of h = 2-Wcharacterizes heat transfer by natural convection from the exposed surface ofm2-Kthe layer, how long will it take for the entire layer of frost to melt in seconds if it is initially at 0°C? Thefrost has a density of 700 and a latent heat of fusion of 334m3kJkg'

Answered: Image /qna-images/answer/b173d2fe-5418-455d-91fc-7dd8b71df6cd.jpg

Answered: To ensure effective heat transfer from…

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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A food product with 73% moisture content is being frozen in a 7 cm-diameter can. The product density is 970 kg/m³, the thermal conductivity is 1.2 W/(m K), and the initial freezing temperature is -2.5°C. After 11 hour in the -40°C freezing medium, the product temperature is -10°C. Estimate the convective heat-transfer coefficient for the freezing medium. Assume the can has infinite height. a. h = ... W/m² K
A household oven door of 0.4 m height and 0.6 m width reaches an average surface temperature of 50°C during operation. Estimate the total heat loss to the room with ambient air at 22°C and convective heat transfer coefficient 5 W/m².K, if the door has an emissivity of 0.83 and the surroundings are also at 22°C.
A 200mm diameter spherical steel ball initially at 500°C is rapidly immersed in an oil bath that is at 20°C. The convection coefficient is h = 600W/m²-K, and the steel ball has the following properties: c= 500J/kg-K, p= 7000kg/m³, k=30W/m-K. Determine the time taken (min) for temperature at the surface of the ball to drop to 100°C.
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 20-cm diameter sphere has a surface temperature of 500 K. The sphere is suspended in 300 K still air. Find the heat transfer from the sphere. Neglect Radiation. (To find the heat transfer coefficient use Nusselt numbers) use properties of air at 300 K
In the arctic sea, the ice sheets are melting. Let's calculate the temperautre distribution in one such ice sheet. The sheet is 2 m thick. Under the sheet there is ice-water mixture and it can be assumed that the temperature of the bottom surface of the ice sheet is approximately 0°C. Air at -20°C is blowing above the sheet. The convection coefficient of air is 15 W/m².K. The thermal conductivity of ice is 2.2 W/m.K. What is the temperautre of icesheet at its center (i.e., at 1 m from the surface)?
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
An industrial cold room has four 200 mm thick walls made of concrete. The walls are insulated on the outside with a layer of foam 60 mm thick. Cladding with a thickness of 15 mm protects the foam on the outside from the elements. The composite wall surface temperatures are –3 °C on the inside and 18 °C on the outside of the room respectively. The thermal conductivities of concrete, foam and cladding are 0.75, 0.35 and 0.5 W/m K respectively. Assuming perfect thermal contact between the layers of the composite walls, draw the typical temperature distribution across the layers and determine the heat energy gained per hour through all 4 walls of the room with a total surface area of 20 m2. What does this heat energy represent in terms of the refrigeration system of the cold room?
The main body of plenum is a steel vessel of diameter 0.1meters has two semicircle domed ends. During operation is will contain mix of fuel and air at approximately 250OC. The wall of the vessel is 0.03meters thick and the plenum is 0.45meters long. Estimate the rate of heat loss from the vessel when the outside air temperature is 45OC. The thermal conductivity of steel is 45 W/m K and the surface heat transfer coefficient on the air side is 8 W/m2 . On the inside it is 65W/m2 . If it was possible to clad the plenum calculate the reduction in the rate of heat loss. Assume the lagging would be 5mm thick and has a thermal conductivity of 0.05 W/m.

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