Q. 3 A 50-cm x 50-cm circuit board that contains 121 square chips on one side is to be cooled by combined naturalconvection and radiation by mounting it on a vertical surface in a room at 25°C. Each chip dissipates 0.18 W of power,and the emissivity of the chip surfaces is 0.7. Assuming the heat transfer from the back side of the circuit board to benegligible, and the temperature of the surrounding surfaces to be the same as the air temperature of the room, determinethe surface temperature of the chips. Evaluate air properties at a film temperature of 30°C and 1atm pressure. Is this agood assumption?

Circuit board dimensions, 50cm×50cmTotal area of the circuit board, Atotal=0.5m×0.5m=0.25m2Number…

Answered: Q. 3 A 50-cm x 50-cm circuit board that…

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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7.Consider a person standing in a room maintained at 20°C at all times. The inner surfaces of the walls, floors, and ceiling of the house are observed to be at an average temperature of 12°C in winter and 23°C in summer. Determine the rates of radiation heat transfer between this person and the surrounding surfaces in both summer and winter if the exposed surface area, emissivity, and the average outer surface temperature of the person are 1.6 m2, 0.95, and 32°C, respectively.
(b) Consider a sealed 20-cm-high electronic box in Figure 1 whose base dimensions are 50 cm x 50 cm placed in a vacuum chamber. The emissivity of the outer surface of the box is 0.95. If the electronic components in the box dissipate a total of 120 W of power and the outer surface temperature of the box is not to exceed 55°C, determine the temperature at which the surrounding surfaces must be kept if this box is to be cooled by radiation alone. Assume the heat transfer from the bottom surface of the box to the stand to be negligible. 50 cm 120 W € = 0.95 T₁ = 55°C 20 cm Stand 50 cm. Figure 1 Electronic box
Consider a room whose door and windows are tightly closed, and whose walls are well-insulated so that heat loss or gain through the walls is negligible.
A 50-cm * 50-cm circuit board that contains 121 square chips on one side is to be cooled by combined natural convection and radiation by mounting it on a vertical surface in a room at 25°C. Each chip dissipates 0.18 W of power, and the emissivity of the chip surfaces is 0.7. Assuming the heat transfer from the back side of the circuit board to be negligible, and the temperature of the surrounding surfaces to be the same as the air temperature of the room, determine the surface temperature of the chips. Evaluate air properties at a film temperature of 30°C and 1 atm pressure. Is this a good assumption?
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Consider a sealed 20-cm-high electronic box whose base dimensions are 40 cm × 40 cm placed in a vacuum chamber. The emissivity of the outer surface of the box is 0.95. If the electronic components in the box dissipate a total of 100 W of power and the outer surface temperature of the box is not to exceed 55 °C, determine the (maximum) temperature (in °C) at which the surrounding surfaces must be kept if this box is to be cooled by radiation alone. Assume the heat transfer from the bottom surface of the box to the stand to be negligible. Round your answer to 2 decimal places.
A 50cm by 100 cm stainless steel plate with emissivity of 0.85 is maintained at 500°C. determine the heat produced by the plate in 30 minutes, and the power it dissipates
Consider a flat-plate solar collector placed horizontally on the flat roof of a house. The collector is 5 ft wide and 15 ft long, and the average temperature of the exposed surface of the collector is 94°F. The emissivity of the exposed surface of the collector Is 0.9. Determine the rate of heat loss from the collector by convection and radiation on a calm day when the ambient air temperature is 70 °F and the effective sky temperature for radiation exchange is 50°F. Take the convection heat transfer coefficient on the exposed surface as 2.5 Btu/h-ft2.°F. Tuky = 50°F 70°F Solar collector Given: a=0.1714 x 10-8 Btu/h-ft2.R4 4500 Btu/h
Determine the net heat transferred by radiation from a 9-ft square hot plate to a cold plate of equal size that are parallel to one another, and 20 ft apart if the hot plate is oxidized steel at 700°F and the cold plate is dull brass at 175°F.Ans: 2,863 Btu/hr
Consider a sealed 20-cm-high electronic box whose base dimensions are 40 cm x 40 cm placed in a vacuum chamber. The emissivity of the outer surface of the box is 0.95. If the electronic components in the box dissipate a total of 100 W of power and the outer surface temperature of the box is not to exceed 55°C, determine the temperature at which the surrounding surfaces must be kept if this box is to be cooled by radiation alone. Assume the heat transfer from the bottom surface of the box to the stand to be negligible.
Consider the rate of heat conduction through a double-paned window that has a 1.6-m2 area and is made of two panes of 0.76-cm-thick glass separated by a 0.75-cm air gap. You can ignore the increased heat transfer in the air gap due to convection. a. Calculate the rate of heat conduction through this window, in watts, given that the inside surface temperature is 15.0°C, while the outside temperature is -10.0°C. Make the assumption that the temperature differences across the two glass planes are equal. First find these and then the temperature drop across the air gap. b. For comparison, calculate the rate of heat conduction, in watts, through a single 1.67-cm-thick window of the same area and with the same temperatures as in part (a).
An asphalt playground is heated in the sun all day; by sundown it reaches a temperature of 45degC. If the asphalt has an emissivity of 0.8, what is the heat flux emitted off the asphalt at night?

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