Explain the NTU-effectiveness method for heat exchanger design.

The NTU-effectiveness method is used when outlet temperatures are unknown. NTU (Number of Transfer Units) = UA/Cmin, where Cmin is the smaller heat capacity rate. Effectiveness (epsilon) = actual heat transfer / maximum possible = Q/(Cmin*(Th,in - Tc,in)). Relationships between NTU, effectiveness, and capacity ratio (Cr = Cmin/Cmax) exist for each flow configuration. This method is preferred for rating problems (determining performance of existing exchangers) and when iterative LMTD calculations are inconvenient.