Comparison of finned tube and plate-finned heat exchangers in waste heat recovery

Abstract

The use of waste heat recovery devices on mobile units (trucks and ships) is usually limited by the available space and the application of compact heat exchangers is recommended for such purposes. The performance of the heat exchanger is defined by the optimižed Rankine cycle (to achieve maximum power) and it depends on the mass flow and temperature of the flue gases and selection of the working fluid in Rankine cycle. An example of selection of the preheater performance (in case of water as the working fluid) is considered here, wherein the several surface types of finned tube and plate-finned heat exchangers are used, for which there are measured data of the heat transfer coefficient and friction factor. Heat exchangers are sižed according to the criteria of maximum allowed velocity of the flue gases and shapes of the heat exchanger frontal area. The sižed heat exchangers were compared with respect to the heat transfer coefficient, the area of the heat exchanger surface on the finned side, the volume of the heat exchanger and the pressure drop on both sides. From the comparison of the best plate-finned and the best finned tube heat exchangers it is concluded that in the recommended range of flue gases velocity (from 4 m/s to 6 m/s) the pressure drop at the gas side are similar (in the plate-finned heat exchanger it is in the range from 53.5 to 112 Pa and in the finned tube exchanger from 53.8 to 142.8 Pa), while the plate-finned exchanger has more than 50% smaller heat transfer area, compared to the finned tube one.