Investigation On Enhanced Heat Transfer Mechanism And Cleaning Dynamics Of The Rotating Twisted Tape

The question of the low efficiency and fouling deposit for heat exchangers has been a worldwide difficult problem all the time. The cleaning technology of a self-rotating twisted tape has been developed, which has double functions of heat transfer enhancement and online cleaning fouling. Heat exchangers, which are made and transformed with rotating cleaning twisted tapes, can keep running with the high efficiency.The purpose of this paper is to investigate the heat transfer enhancement mechanism and cleaning dynamics of a rotating twisted tape. The investigation is focused on the following aspects.(1) Experimental investigation of the flow and turbulent characteristics in the tube with a self-rotating twisted tape insertThe flow and turbulent characteristics in the tube with and without a self-rotating twisted tape insert are investigated experimentally by using Laser Doppler Velocimeter.The results show the flow flied of the axial velocity, the tangential velocity, the axial turbulence intensity and the tangential turbulence intensity in the tube with and without a self-rotating twisted tape insert are obviously different. The axial flow velocity near the tube wall area in the tube with a self-rotating twisted tape insert is higher than that of the smooth tube. There are distinct tangential motions in the tube with a self-rotating twisted tape insert, but there are only random tangential motions in the smooth tube. The turbulence intensity in the tube with a self-rotating twisted tape insert is higher than that of the smooth tube. According to experimental results of the velocity and turbulence intensity flied in the tube with a self-rotating twisted tape insert, the heat transfer enhancement mechanisms are initially analyzed.(2) Numerical simulation of the fluid flow and heat transfer in the tube with a twisted tape insertThe fluid flow in the tube with a self-rotating twisted tape insert is analyzed. According to the tangential motion characteristic of the swirl flow field in the tube with a self-rotating twisted tape insert, a conception of a self-rotating twisted tape being dummied as an equivalent still twisted-tape is put forward, which shows that the helix motion of the fluid in the tube with a self-rotating twisted tape insert can be dummied as the helix motion in the tube with a still twisted tape insert, which the twist ratios of the still twisted tape is augmented.