ENHANCEMENT OF CONVECTIVE HEAT TRANSFER IN INTERNAL VISCOUS FLOWS BY INSERTING MOTIONLESS MIXERS

摘要

In chemical processing industries, heating, cooling and otherthermal processing of viscous fluids are an integral part of theunit operations. Enhancement of the natural and forcedconvection heat transfer rates has been the subject of numerousacademic and industrial studies. Motionless mixers, also knownas static mixers, are often used in continuous mixing, heattransfer, and chemical reactions applications. These mixershave low maintenance and operating costs, low spacerequirements, and have no moving parts. Heat exchangersequipped with mixing elements are especially well suited forheating or cooling highly viscous fluids. Shell and tube heatexchangers incorporate static mixing elements in the tubes toproduce a heat transfer rate significantly higher than that ofconventional heat exchangers. The mixing elementscontinuously create a new interface between the working fluidand tube wall, thereby producing a uniform heat history in thefluid. It is desired to employ motionless mixers in heat transferapplications to provide a high rate of heat transfer from athermally homogenous fluid with low pressure drop. In thepast, laboratory experimentation has been a fundamental part ofthe design process of a new static mixer for a given applicationas well as the selection of an existing static mixer. It is possibleto use powerful computational fluid dynamics (CFD) tools tostudy the performance of these mixers without resorting toexperimentation. In this paper, which is an extension to theprevious work of the authors, the enhancement of performanceof shell and tube heat exchangers by inserting motionlessmixers (SMX and helical) is studied for creeping, laminar, andlow-Re turbulent flows. It is shown that the studied mixersproduced similar flow histories for the working fluidconsidered. Both SMX and helical mixers are able to increasethermal performance of heat exchangers. The SMX mixermanifests a higher performance in temperature blending and in heat transfer enhancement compared to the helical mixer. However, the pressure drop created by SMX elements, and consequently the required energy to maintain the flow in tube, is significantly higher.