Q3. Consider a sealed 20-cm-high electronic box whose base dimensions are 40 cm x 40 cm placed in a vacuum chamber (Figure 3). 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 60°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. - 40 cm. 40 cm 100 W e = 0.95 T,- 60°C Electronic ' box 20 cm Štand Figure 3

Q3. Consider a sealed 20-cm-high electronic box whose base dimensions are 40 cm x 40 cm placed in a vacuum chamber (Figure 3). 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 60°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. - 40 cm. 40 cm 100 W e = 0.95 T,- 60°C Electronic ' box 20 cm Štand Figure 3

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 1.29P: 1.29 A spherical interplanetary probe with a 30-cm diameter contains electronic equipment that...

See similar textbooks

Similar questions

2.55 A long, 1-cm-diameter electric copper cable is embedded in the center of a 25-cm-square concrete block. If the outside temperature of the concrete is 25oC and the rate of electrical energy dissipation in the cable is 150 W per meter length, determine temperatures at the outer surface and at the center of the cable.
Q3: Consider a (15cm x 20cm) printed circuit board (PCB) that has electronic components on one side as shown in the figure. The board is placed in a room at 20°C. The heat loss from the back surface of the board is negligible. The surface temperature of circuit board is 46°C. Determine the total heat loss by convection and radiation if the board is vertical, Take the emissivity of the surface of the board to be 0.8 and assume the surrounding surfaces to be at the same temperature as the air in the room. (Answers: 8W) Hint: The properties of the air at latm. are as follow: k = 0.02607 W/m. C v =1.631x10 m³/s Pr = 0.7275 Insulation PCB, T, 8W L= 0.2 mh Air T = 20°C
Q3: Consider a (15cm x 20cm) printed circuit board (PCB) that has electronic components on one side as shown in the figure. The board is placed in a room at 20°C. The heat loss from the back surface of the board is negligible. The surface temperature of circuit board is 46°C. Determine the total heat loss by convection and radiation if the board is vertical, Take the emissivity of the surface of the board to be 0.8 and assume surrounding surfaces to be at the same temperature as the air in the room. the (Answers: 8W) Hint: The properties of the air at latm. are as follow: k = 0.02607 W/m.°C v = 1.631×10$ m²/s Pr = 0.7275 Insulation РСВ, Т, 8 W L= 0.2 m Air T, = 20°C
(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
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?
A radiator plate of 0.2-m (wide) x 0.4-m (height) is in a room of 22°C. One side (the hot side facing the room) of the radiator plate is maintained at a temperature of 80°C, the other sides are assumed to be insulated, as shown in Figure 1. If the following assumptions can be made: 1) steady operating conditions exist; 2) the air an ideal gas; 3) the local' atmospheric pressure is 1.00 atm: (a) Briefly and qualitatively analyze the four different locations for the radiators marked A), B), C) and D), as shown in Figure 1, and rank them in terms of heat transfer efficiency by natural convection. (b) Determine the rate of heat transfer from the radiator plate by natural convection if the plate is A) vertical and C) horizontal with the hot surface facing down. Compare the two and provide a brief discussion of the findings. wall A 0.4 mi C 0.4 m 0.4 m B floor ceiling 0.4 m wall Nu Nu=0.59Ra Nu-0.1 Raa 0.387Ral Nu- - {0.825 + 11 + (0.492/Pr)162) (complex but more accurate) Use vertical plate…
A 50 cm x 50 cm square circuit board with chips on one side at 25 °C by vertical convection and radiation in a room at room temperature will be cooled. Each chip emits 5900 W of power and the chip The emissivity of their surfaces is known as 0.59. of chips the back side of the surface on which it is placed is insulated and the temperature of the surrounding surfaces It is 20 °C. Cooling of the surface where the chips are located to 35 °C If desired, calculate the number of chips that can be placed on this plate.
(a) Calculate the rate of heat transfer by radiation from a car radiator at 110°C into a 50.0ºC environment, if the radiator has an emissivity of 0.750 and a 1.20-m^2 surface area. (b) Is this a significant fraction of the heat transfer by an automobile engine? To answer this, assume a horsepower of 200hp (1.5kW) and the efficiency of automobile engines as 25%.
Consider steady heat transfer between two large parallel plates at constant temperatures T1 = 300 K and T2 = 200 K that are L = 1 cm apart, as shown below. Assuming the surface to be black, determine the rate of heat transfer between the plates per unit surface area assuming the gap between the plates is a) filled with still air with k = 0.0219 W/moC, b) free-flowing air with h = 7.5 W/m2oC, c) evacuated, d) filled with urethane insulation with k = 0.026 W/moC, and e) filled with superinsulation that has an apparent thermal conductivity k = 0.00002 W/moC
Consider steady heat transfer between two large parallel plates at constant temperatures T1 = 300 K and T2 = 200 K that are L = 1 cm apart, as shown below. Assuming the surface to be black, determine the rate of heat transfer between the plates per unit surface area assuming the gap between the plates is a) filled with still air with k = 0.0219 W/m°C, b) free flowing air with h = 7.5 W/m2°C, c) evacuated, d) filled with urethane insulation with k = 0.026 W/m°C, and e) filled with superinsulation that has an apparent thermal conductivity k = 0.00002 W/m°C PLEASE ANSWER LETTER D AND E, THANK YOU
2. Consider steady heat transfer between two large parallel plates at constant temperatures of T1 = 295 K and T2 = 155 K that are L = 2 cm apart. Assuming the surfaces to be black, determine the rate of heat transfer between the plates per unit surface area assuming the gap between the plates is (a) filled with atmospheric air,(k = 0.01979 W/m- o C) (b) evacuated,(c) filled with superinsulation having an apparent thermal conductivity of 0.00015 W/m · °C.
Question Consider heat loss through the two walls of a house on a winter night. The walls are identical, except that one of them has a tightly fit glass window. Through which wall will the house lose more heat? Explain.