Overall heat transfer coefficients and axial temperature distribution in a triple tube heat exchanger

Computation of overall heat transfer coefficients in a triple tube heat exchanger (TTHE) is more complicated than in the case of a double tube heat exchanger (DTHE) as the two overall heat transfer coefficients are not independent of one other. A new procedure was developed to calculate these overall heat transfer coefficients and an effective overall heat transfer coefficient value for known inlet and outlet temperatures, and heat capacities of the fluids (product and heating/cooling medium). In this study, this newly developed procedure was utilized and the overall heat transfer coefficients and axial temperature distribution of fluids were computed for a cooling process for different flow rates and inlet temperatures of the fluid streams. The effectiveness of the TTHE was compared to that of a DTHE of identical length. It was observed that when the fluids were flowing in a cocurrent manner, the temperature of the cooling medium with lower heat capacity exceeded the temperature of the product before the fluids exit the TTHE, which caused a decrease in the effectiveness of the TTHE.