Liquid-Coupled Indirect-Transfer Exchanger Application to the Diesel Engine

The efficiency of turbocharged diesel engines can be increased by cooling the charge air. This paper presents a design approach for liquid-coupled indirect-transfer heat exchanger systems to perform the air-cooling function. The two advantages most commonly cited for this approach to charge-air cooling are (1) the heat exchangers involved are easily packaged so that their shapes can be controlled by judicious design, and (2) simple gas ducting allows for compact machinery arrangements and relatively low charge-air pressure drop. An analytical approach to the design of liquid-coupled indirect-transfer heat exchanger systems is presented. Performance curves are constructed on the basis of this analysis. Four important design conditions are evident from the observation of these performance curves including (1) the relative capacity rate combination of the three fluids (ambient air, coupling liquid, and engine charge-air) which yields the highest overall effectiveness, (2) an optimum coupling-liquid flow rate, (3) the relative effectiveness distribution for each of the two component heat exchangers (hot and cold components), and (4) a broad design range for the optimum area distribution between the hot and cold exchangers. These performance curves serve as a guide for the design of a liquid-coupled charge-air cooling system.