Numerical study of heat transfer and thermal homogenization in a helical reactor

Abstract

A fast and accurate control of the flow temperature by heating or cooling through the wall is essential for many chemical applications, in particular to achieve optimal reaction intensification. A numerical study based on computational fluid dynamics (CFD) has been done to investigate thermal homogenization within a horizontally-coiled helical pipe. The main target is to examine and compare the flow and mixing characteristics when heating different axial parts of the coil. The entrance region and two other locations within the fully-developed flow region have been investigated for that purpose; the first, the third and the fifth turn of a ten-turn coil have been heated individually. In each case, temperature field and thermal homogenization were assessed. The performance was quantified in terms of the required axial length for the temperature profile to become uniform again after heating. The investigations were performed for water as a working fluid, and for a wide range of Reynolds numbers between 2000 and 16,000, covering both the laminar range and transition to turbulence in the helical pipe. The thermal mixing performance in the entrance region was found to be noticeably better than that in the fully-developed region, increasingly so at higher Reynolds numbers. Therefore, it is recommended to systematically use the entrance region of a coil reactor for a fast and efficient step rise of the flow temperature.