7-128 To defrost ice accumulated on the outer surface of an automobile windshield, warm air is blown over the inner surface of the windshield. Consider an automobile windshield (k = 1.4 W/m.K) with an overall height of 0.5 m and thick- ness of 5 mm. The outside air (1 atm) ambient temperature is -20°C, and the average airflow velocity over the outer windshield surface is 80 km/h, while the ambient temperature inside the automobile is 25°C. Determine the value of the con- vection heat transfer coefficient for the warm air blowing over the inner surface of the windshield that is needed to cause the accumulated ice to begin melting. Assume the windshield sur- face can be treated as a flat plate surface.

7-128 To defrost ice accumulated on the outer surface of an automobile windshield, warm air is blown over the inner surface of the windshield. Consider an automobile windshield (k = 1.4 W/m.K) with an overall height of 0.5 m and thick- ness of 5 mm. The outside air (1 atm) ambient temperature is -20°C, and the average airflow velocity over the outer windshield surface is 80 km/h, while the ambient temperature inside the automobile is 25°C. Determine the value of the con- vection heat transfer coefficient for the warm air blowing over the inner surface of the windshield that is needed to cause the accumulated ice to begin melting. Assume the windshield sur- face can be treated as a flat plate surface.

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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Required information Air flows in a pipe under fully developed conditions with an average velocity of 1.25 m/s and a temperature of 24°C. The pipe's inner diameter is 4 cm, and its length is 4 m. The first half of the pipe is kept at a constant wall temperature of 100°C. The second half of the pipe is subjected to a constant heat flux of 200 W. The properties of air at 80°C are p = 0.9994 kg/m³, k = 0.02953 W/m-K, v= 2.097 x 10-5 m²/s, cp=1008 J/kg-K, and Pr = 0.7154. NOTE: This is a multi-part question. Once an answer is submitted, you will be unable to return to this part. Air 1.25 m/s 2m T, = 100°C D = 4 cm 2 m g, = 200 W Determine the wall temperature at the exit of the tube. The wall temperature at the exit of the tube is 282 * °C.
7. Air at 600 K, 1 atm is flowing across a flat plate kept at 300 K with a convection coefficient of 91 W/m2 K. If the Stanton number at this condition of flow is 0.039. what is the velocity of the air? Express your answer in m/s.
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Air is flowing in parallel over the upper surface of aflat plate with a length of 4 m. The first half of the plate length,from the leading edge, has a constant surface temperatureof 50°C. The second half of the plate length is subjected toa uniform heat flux of 86 W/m2. The air has a free streamvelocity and temperature of 2 m/s and 10°C, respectively.Determine the local convection heat transfer coefficients at1 m and 3 m from the leading edge. Evaluate the air propertiesat a film temperature of 30°C. Is the film temperatureTf = 30°C applicable at x = 3 m?
A food product with 73% moisture content in a 7 cm diameter can wants to be frozen. The density of the product is 970 kg / m³, the thermal conductivity is 1.2 W / (m K), and the initial freezing temperature is -2 ° C. After 11 hours in the freezing medium -30 ° C, the product temperature becomes -10 ° C. Estimate the convection heat transfer coefficient of the freezing medium. Assume the can as an infinite cylinder. h = W / (m² K).
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Partially-frozen ice cream is being placed in a package before completion of the freezing process. The package has dimensions of 8 cm by 10 cm by 20 cm and is placed in air- blast freezing with convective heat coefficient of 50 W/(m2 K) for freezing. The product temperature is -5°C when placed in the package, and the air temperature is -25°C. The product density is 700 kg/m3, the thermal conductivity (frozen) is 1.2 W/(m K), and the specific heat of the frozen product is 1.9 kJ/(kg K). If the latent heat to be removed during blast freezing is 100 kJ/kg, estimate the freezing time.
Air at 20 °C blows over a hot plate 50 by 75 cm maintained at 250 °C. The convection heat-transfer coefficient is 30 W/m2·K. Find:Calculate the convective heat transfer rate.Assuming that the plate is made of carbon steel (1% C) 2 cm thick and that additional 300 W is lost from the plate surface by radiation besides convection heat transfer, calculate the plate temperature on the other side.(Note: the thermal conductivity of carbon steel (1% C) is about 43 W/m·K)
Hot water is flowing though the center of a AISI 304 stainless steel pipe with a diameter of 300mm, a wall thickness of 10mm and a length of 5m. The pipe is coated with a 2.5mm thick layer of Teflon and covered with a 30mm thick layer of insulation. The water is flowing at a velocity of 0.0015 m/s. Assume the velocity profile to be fully developed. The water is at a temperature of 92°C and the air surrounding the pipe is at 22°C. Some transport properties and dimensions are shown in the table below. 1. What is the heat transfer rate through the pipe and insulation? 2. What is the heat flux at the inner pipe surface and the outer surface of the insulation? 3. What is the temperature of the outer surface of the insulation? Insulation Pipe Too water Uwater Teflon Tm air hair Pipe inner diameter: 300mm Pipe wall thickness: 10mm Teflon Layer thickness: 2.5mm Insulation thickness: 30mm Length: 5m To, water: 92°C Lair: 22°C hair: 75 W/m2/K k30455: 15.2 W/m/K kTeflon: 0.38 W/m/K kinsulation:…
0.809 and 0.795 3-176 The overall heat transfer coefficient of a wan s determined to be U= 0,425 W/m-°C under the condi- tions of still air inside and winds of 12 km/h outside. What will the U-factor be when the wind velocity outside is doubled? Answer: 0.428 W/m-°C ransler olls of
2. Consider airflow over a plate surface maintained at a temperature of 215°C. The temperature profile of the airflow is given as T(y) = Too (Too - T,) exp (- V fluid The airflow at 1 atm has a free stream velocity and temperature of 5 cm/s and 25°C, respectively. Determine the heat flux on the plate surface and the convection heat transfer coefficient of the airflow.