A review on fluid flow and heat transfer in helical channel

Abstract

As an important structure to improve the efficiency of heat transfer and mass transfer, helical channel has been widely used in the application fields of power generation, refrigeration, chemical reaction, heat recovery, food processing and material mixing because of its compact structure and easy processing. Different from the straight channel, helical channel can produce the secondary flow perpendicular to the axial flow direction, which can increase the disturbance of the fluid flowing in the channel, and then reduce the thickness of the boundary layer, and enhance the heat transfer characteristics. The flowing state of the liquid in helical channel becomes relatively complicated because of the curvature and torsion of helical channel, the centrifugal force and centripetal force cause the fluid to flow toward the wall and form the Dean vortex, and then flow field and velocity field will be changed. In addition to the use of helical channel instead of straight channel to improve the heat transfer efficiency of the passive heat transfer technology, the use of efficient heat exchange quality can further improve the performance of heat transfer equipment. For example, the nanofluid is prepared by adding nanoparticles and dispersing agent in the base liquid, because of higher thermal conductivity of nanoparticles and the Brown movement, it is widely used in the heat exchanger. The flow and heat transfer characteristics of the fluid in the helical channel have become a hot research topic in recent years, and they are of crucial guiding significance for practical applications. At present, the essential reason for the secondary flow is that the centrifugal force produced by the curvature and torsion of the helical channel can affect the fluid, however, with the secondary flow, the flow resistance will increase with the increase of heat transfer. On the other hand, the addition of nanoparticles in the base fluid not only has a significant improvement on the heat transfer coefficient, but also has higher flow resistance compared with the base fluid. The results show that the flow resistance increases with the increase of heat transfer characteristics under the two conditions of heat transfer enhancement. At the same time, how to reduce the increase of flow resistance is the key to optimize the heat transfer characteristics of helical channel. The research focused on the structural parameters of helical channel and the working fluid, and the research progress of fluid flow and heat transfer in helical channel was reviewed. The influence of different structures and working fluid on the characters of fluid flow and heat transfer in helical channel were summarized. The effect of structure parameters such as coiled curvature radius, coil diameter, coil pitch, cross-section shape and physical property parameters such as their kinds and concentrations on heat transfer and flow resistance were analyzed. The conclusions of experiments and simulations in laminar and turbulent flows were compared. Reference for structure optimization and working fluid selection of helical channel were provided, and the development directions of fluid flow and heat transfer characteristics in helical channel were also proposed.