Reverse heat transfer

The temperature crossing and reverse heat transfer for heat exchangers were investigated,which are often met in the heat exchanger design and are easily neglected in the practice. The faults of the reverse heat transfer were also pointed out. By the rigorous simulation for a hydrocarbon-water heat exchanger,and to achieve the specified heat duty,the exchanger area needs 229 m2 with 6.5 ℃ temperature crossing if a single heat exchanger is used; the area is reduced to 78 m2 without any reverse heat transfer if two heat exchangers in series are adopted. It concludes through the analysis of three types of normal heat exchangers that the temperature crossing is not allowed for one-pass shell side and two-pass tube side heat exchangers due to the risk of reverse heat transfer and much lower correction factor of logarithm mean temperature difference; the temperature crossing is allowed and no risk is existed for heat exchangers either in one-pass shell side and one-pass tube side heat exchanger or in two-pass shell side and two-pass tube side heat exchanger. One of the methods to solve the reverse heat transfer was pointed out.