Research On Characteristics Of Fluid Heat Transfer Enhancement And Anti-fouling In The Tubes Inserted With Twisted Tapes

As a kind of effective element for heat transfer augmentation and continuous swirl flow, twisted tape is widely used in many areas of chemical equipment such as heat transfer enhancement, anti-fouling, fluid mixing etc. Lots of researches on twisted tapes have been carried out by many scholars both home and abroad. Still, the heat transfer performance of twisted tape need to be developed further.Aimed at the issues of lack of researches on flow conditions of tubes inserted in twisted tapes, poor thermal performances and incomplete structures optimization of tubes inserted with typical twisted tapes etc., the 3-edge twisted tape were developed and simulated using Fluent15.0 in the condition of turbulent(Re=5000~30000) and laminar flow(Re=400~1500). As a comparison, the circular tube, typical twisted tape and grid spiral tape were also simulated. The results showed that the thermal performance of 3-edge twisted tape is better than the other types of twisted tapes, and the optimization work of twisted tape is carried out from different aspects:edge number n, twist ratio y, edge length m. The anti-fouling performance of the tube inserted with twisted tape is simulated and compared with that of the plain tube. The conclusions are as follows:The simulation results showed that tubes inserted with twisted tapes can generate a swirl flow, which induce a radial flow and a tangential flow deviating from axial direction, to exacerbate the mixing of the boundary flow and mainstream flow, and make the velocity and thermal boundary layer thinner. The velocity of heat transfer from the tube wall to the main fluid is accelerated, and the heat transfer coefficient of the fluid near the tube wall is improved.The heat transfer and resistance characteristics of plain tube and tubes inserted with twisted tapes in the turbulent flow condition showed that:the Nu of the tube with 3-edge twisted tape is the largest, the smallest and roughly equal Nu had been achieved by both heat transfer of the tubes with grid spiral tape and typical twisted tape. The friction factors of tubes inserted with twisted tapes from low to high are: grid spiral tape, 3-edge twisted tape and typical twisted tape. The best thermal performance coefficient is for the tube inserted with 3-edge twisted tape, which is better than other twisted tapes.The results of the optimization work showed that: the Nu and f increase with increasing edge number n, decrease with the increasing twist ratio y and increase with the increase edge length m. By comparing the tubes inserted with different parameters of twisted tapes, the best thermal performance coefficient η of 1.33 is achieved by the tube inserted with 3-edge twisted tape with the parameters of y=2.0, m=9mm, which is 11.9%~33.2% and 5.47%~5.98% higher than those of the plain tube and the tube inserted with typical twisted tape respectively.The results of the simulation of the twisted tapes in the laminar flow condition showed that: Nu increases with the edge number, except the 5-edge twisted tape. Also Nu and f increases with the increasing edge number and edge length, and decreases with the increasing twisted ratio. Friction factor f increases with the increasing edge number, decrease of twist ratio and the increase of edge length. The best thermal performance coefficient η reaches 4.96 for the tube inserted with 3-edge twisted tape with the parameters of y=2.0, m=9mm.The anti-fouling characteristics of the plain tube and tube inserted with twisted tapes were studied. The results show that the swirl flow generated in the tube with twisted tapes can scour the tube wall, and the volume friction of Ca Co3 in radial direction is well-distributed, making it uneasy for the anti-fouling to deposit, which means that the anti-fouling characteristic of the tubes inserted with twisted tape is superior than that of the plain tube. The coefficients of variation(CV)of plain tube, typical twisted tube, 3-edge twisted tape are 8.72%, 3.71% and 3.22% respectively.The smaller the CV is, the better anti-fouling performance has been achieved. The anti-fouling performance of particle with different diameters(5um, 10 um, 20um)has been researched. The diameter influences the distribution of particle. Within the scope of diameters been studied, the bigger the diameter is, the easier the fouling happens to heat transfer tube.