The Variables U and A of Heat Exchangers

\[Q = U A\; \Delta T_{m}\]

  • Increasing \(U\) leads to the requirement of increased \(h\) of the fluids. This leads to increasing the power required for pumping. This leads to increasing the operating cost.

  • Increasing \(A\) leads to the requirement of increasing the length and diameter of exchanger. This leads to increasing the fixed cost.

  • Optimizing \(U\) and \(A\), so as minimize the total cost (= fixed cost + operating cost) is the task of engineer.