Analysis of the model of tube-in-tube heat exchangers

The operation of a tube-in-tube heat exchanger with cocurrent and countercurrent flows of heat-transfer agents is analyzed in the steady state mode on the basis of the traditional model. The characteristics of the given flow modes of heat-transfer agents are compared. A number of inequalities, whose proof have not been developed in the literature or containing errors, are proven for the parameters characterizing the operation of a heat exchanger in the cocurrent and countercurrent modes.