Development of heat exchanger with new mechanism of scraping temperature boundary layer

In recent years various approaches to reduce carbon dioxide emission from iron- and steelmaking industry have been made, and recovery of the waste heat is one of these approaches. Heat exchanger is one of key facilities to recover the waste heat released as sensible heat of fluids. In this study a new concept to raise efficiency of heat exchanger has been proposed. The temperature boundary layer is scraped from moving heat transfer surface by rigid blades to remove the heat transfer resistance of the boundary layer. Some prototypes of the heat exchangers of double-tube type with this concept were made. The inner tube of the heat exchanger rotates and the blades are set on both sides of the inner tube. The performance of the heat exchanger was examined in various combinations of working fluids. The results showed that the overall heat transfer coefficients, which is a key parameter to expresses heat exchanger performance, increased with increase in revolution of the inner tube regardless of working fluids. Thus the effectiveness of this new concept was confirmed. The effect of the boundary layer scraping is remarkable in the liquid-liquid or liquid-steam systems, and the heat transfer coefficient increased by about ten times in some cases. For the combination including gas, although this concept is useful, there still is a room to optimize the design of the heat exchangers to improve the performance. It is expected that practical use of this heat exchanger is great help to recover the waste heat from the industries.