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# Consider a $15-\mathrm{cm} \times 20-\mathrm{cm}$ printed circuit board $\mathrm{(PCB)}$ that has electronic components on one side. The board is placed in a room at $20^{\circ} \mathrm{C}$. The heat loss from the back surface of the board is negligible. If the circuit board is dissipating $8 \mathrm{~W}$ of power in steady operation, Find the average temperature of the hot surface of the board, assuming the board is $(a)$ vertical; $(b)$ horizontal with hot surface facing up; and $(c)$ horizontal with hot surface facing down. 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.

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$\textbf{Given:}$

• Dimensions of the printed circuit board: $15-\text{cm} \times 20-\text{cm}$;

• Ambient temperature: $T_\infty = 20 \text{\textdegree} \text{CF}$;

• Dissipated power from the board: $\dot Q = 8 \text{ W}$;

• Emissivity of the board surface: $\varepsilon = 0.8$;

• Temperature of the surrounding surfaces: $T_\text{surr} = 20 \text{\textdegree} \text{C}$;

$\textbf{Required:}$

• The average temperature of the hot surface of the board if:

a) board is vertical;

b) board is horizontal with hot surface facing up;

c) board is horizontal with hot surface facing down;

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