Enhanced Heat Transfer Surface Development for Exterior Tube Surfaces

Enhanced heat transfer surfaces are produced by modifying a process surface. New tube and process designs are necessary in order to increase heat transfer, minimize operating costs and save energy. In a comparison of first generation Vipertex enhanced heat transfer tubes with smooth tubes, an increase of performance in excess of sixty percent was determined for the enhanced tubes. This study was undertaken to further enhance heat transfer on the outer surface of these heat transfer tubes. Through the use of computational fluid dynamic (CFD) methods, a flow optimization study of the characters that are used to build the enhanced surface was performed. This study evaluates the effect of character pattern and character geometry on the fluid flow and heat transfer of the process surface. As a result, new process surface designs were developed that produce performance enhancement on the outside of a tube for Reynolds numbers to 215,000. For this range, the minimum increase in heat transfer was experimentally determined at low flows to be 125 %; an increase of heat transfer in excess of 200 % was found for high flows. Modest increases of the friction factor accompany these increases in heat transfer.Heat transfer enhancement is important in the development of high performance thermal systems. Many industrial processes involve the transfer of heat energy and most employ old technology; if improved process performance is desired, these processes should be considered for redesign using enhanced surfaces. Enhanced heat transfer performance is the result of a combination of surface variations that are a result from this detailed surface study. Enhanced performance characteristics include: increased fluid turbulence, secondary fluid flow patterns enhancement, disruption of the thermal boundary layer and increased process surface area. These enhanced factors lead to an increase in the heat transfer coefficient; the ability to produce a unit with a smaller unit footprint; systems that are more economic to operate and have a prolonged product life. This provides a very important and exciting advancement in the design of processes that utilize heat transfer tubes and surfaces.