688 



MECHANICAL DESIGN AND PACKAGING 



Electronic Equipment 



Air to Air 

 Heat Exchanger 



(a) OPEN RAM AIR COOLING 



(b) PRESSURIZED AIR COOLING 



I Evaporation 

 Equipment Case. of piujd 



Cooling 



Air - 



Supply 



Electronic Equipment 



n rr 



Air-Cooled 

 Plate 



Ut 



Cooling 

 Air Exit 



na ^ 



Cooling Fluid 



Equipment 



(c) PRESSURIZED, CONDUCTION 

 OF HEAT TO AIR-COOLED PLATE 



(d) LIQUID COOLING 

 (evaporative) 



Fig. 13-3 Cooling Schemes for Electronic Equipment. 



maximum allowable component temperature, it will have to be cooled 

 before entering the equipment heat exchanger. Schemes b and c are more 

 critical than ^ in this respect. In Fig. 13-3d, which may also be pressurized, 

 the internal heat is conducted to an enclosed tank of liquid. The evapora- 

 tion of the liquid absorbs heat, preventing the sensitive components from 

 experiencing temperatures greatly above the boiling temperature of the 

 liquid. 



Cooling and temperature-control systems can operate in a transient or a 

 steady state. If the thermal environment and internal heating remain 

 constant for a sufficient time, a steady-state heat transfer condition is 

 reached. The flow of thermal energy for this condition may be indicated 

 as shown in Fig. 13-4. 



Cooling Fluid In 



Cooling Fluid Out 



Electronic 

 Equipment 



Fig. 13-4 Steady-State Cooling. 



