Chapter 8, Problem 8.56P

One way to cool chips mounted on the circuit boards ofa computer is to encapsulate the boards in metal framesthat provide efficient pathways for conduction to supporting cold plates. Heat generated by the chips is thendissipated by transfer to water flowing through passages drilled in the plates. Because the plates are madefrom a metal of large thermal conductivity (typicallyaluminium or copper), they may he assumed to be at atemperature, $T_{s,cp}$ .

(a) Consider circuit hoards attached to cold plates ofheight $H=\text{75}0\text{ mm}$ and width $L=\text{ 6}00\text{ mm}$ . eachwith N = 10 holes of diameter $D=\text{ l}0\text{ mm}$ . Ifoperating conditions maintain plate temperatures of $T_{s,cp}=32°\text{C}$ with water flow at $m_1=0.2\text{Kg/s}$ perpassage and $T_{m,i}=7°\text{C}$ , how much heat may he dissipated by the Circuit boards?

(b) To enhance cooling, thereby allowing increased power generation without an attendant increase insystem temperatures, a hybrid cooling scheme maybe used. The scheme involves forced airflow over theencapsulated circuit boards, as well as water flowthrough the cold plates. Consider conditions forwhich $N_{cb}=10$ circuit hoards of width $W=\text{35}0\text{ mm}$ are attached to the cold plates and their average surface temperature is $T_{s,cb}=47°\text{C}$ when $T_{s,cp}=32°\text{C}$ . Ifair is in parallel flow over the plates with $u_{\infty }=10$ m/sand $T_{\infty }=7°\text{C}$ , how much of the heat generated bythe circuit hoards is transferred to the air?