A new method to determine the best units for breaking heat load loops of heat exchanger networks

For a heat exchanger network that contains more than the minimum number of units, it is often required to simplify the network by removing extra units . A new method is proposed to find the best units for breaking loops involv ed in the network. The energy penalty incurred by deleting a unit from a lo op depends not only on the heat loads of all units but; also on the structu re of the network. To take into account the effects of heat; loads and inte ractions of units on energy relaxation, the constrained units that cannot a bsorb any transferred energy and the redistribution of Delta t(min) are dis cussed. The constrained units make the evaluation of energy penalties of so me units simple and straightforward. When the redistribution of Delta t(min ) caused by deleting a unit is examined, the lower bound of the energy pena lty of the unit can be easily estimated. When the lower bound is compared w ith the heat loads of other units, it can be decided whether the unit shoul d be deleted or not. The proposed method is reliable and efficient. It cons iders effects of both the heat loads and the interactions of units and avoi ds calculations of the accurate energy penalties of all units. A common tes ting example is used to demonstrate the effectiveness of the proposed metho d.