부산대학교 도서관

This paper reports an experimental study on heat transfer enhancement in a heat exchanger equipped with a new structure of inserts. The proposed insert consists of the various number of self-rotating modules that rotate by moving gas over them. The insert was placed in the tube side of the water heater for heating natural gas. The thermal–hydraulic performance ratio was defined by considering both the favor increase in the heat transfer rate and the undesired increase in the pressure drop. The effects of the number of inserts (N), tank temperature (TR), and velocity of natural gas (u) were investigated on the thermal–hydraulic performance ratio, the friction coefficient, and the Nusselt number. Response surface methodology was applied to determine the optimal operating conditions. The optimum conditions of variables were found as follows: tank temperature of 40 °C, the gas velocity of 5 m s−1, and the number of inserts of 30. In these conditions, the value of the Nusselt number, the thermal–hydraulic performance ratio, and the coefficient of friction were obtained at 81.26, 1.37, and 0.55, respectively. The results revealed that increasing the number of insert modules enhanced the heat transfer rate and the Nusselt number. The thermal performance coefficient was reduced by increasing the velocity, meaning that the insert was more efficient at lower gas velocities. [ABSTRACT FROM AUTHOR]