Investigation Of Experiment And Numerical Simulation For Heat Transfer Enhancement Of Spiral-gear Inserts In A Tube

Tube-insert heat transfer enhancement technology, which can improve efficiencyof heat exchanger significantly and have the function of preventing and cleaning fouling,has been attracted attention to by experts and scholars in the heat transfer field. Manyheat exchanger tubes have serious fouling problem, which leads to economic loss andeven influences normal operation, so heat transfer enhancement technology for inserts isdeveloped rapidly. Lots of tube-insert heat transfer enhancement technologies have beenapplied widely, but there is a common problem in these technologies, most of themhave unsatisfactory heat transfer effect and limited ability of preventing and cleaningfouling. In order to solve these problems, this paper proposed a new technology of tubeinsert heat transfer enhancement: asymmetric spiral-gear inserted tube heat transferenhancement technology.For study mechanism of heat transfer enhancement of the spiral-gear inserted neartube, fluid flow law in the annular clearance between the insert and the tube is analyzedin theory. Theoretical computation formula of spiral gear self-rotating kinetic moment isconducted through fluid dynamics analysis, which is important to the spiral gearself-rotating and optimization design of tube structural parameters.According to the numerical simulation results, heat transfer enhancementsimulation experiment of spiral gear inserted tube was done. The results show thatstable heat transfer coefficients of tube with spiral gear inserts is increased about85%compared with that of smooth tube on the different velocities in vertical device and theheat transfer enhancement is very remarkable. While stable heat transfer coefficients oftubes with two kinds of enhanced laterality spiral gear inserts are increased by89%(thenumerical simulation result is86%) and112%separately compared with that of smoothtube on the same velocity in horizontal device and its the heat transfer enhancement isalso very remarkable. On the same condition, ordinary laterality of spiral gear insertedtube has abilities of heat transfer enhancement and fouling cleaning. At last, the stableheat transfer coefficient of tube with spiral gear inserts is increased by95%and89%separately compared that of coiled-wire inserted tube and another tube fitted withtwisted-tape elements on the same condition in horizontal device and its heat transferenhancement effect is more significant, but it has the advantage of good ability inpreventing and removing hard scale and tube wall has no excessive cleaning sign after experiment. Therefore, spiral-gear heat transfer enhancement technology is more efficient andenergy saving.Finally, for comparison of the two kinds of tubes, regular smooth tube and tubewith spiral gears inserted, the numerical simulations about heat transfer and fluid flowwere done. The results show that stream lines of the spiral-gear inserted tube arethree-dimensional spiral lines. The axial, radial and tangential velocities near inner nearwall are increased greatly in comparison with that without inserts in tubes and heattransfer is enhanced. Fluid turbulence intensity and average surface convection heattransfer coefficient wall are improved significantly compared with that of smooth tubeand the pressure drop caused by spiral-gear inserts is in the permissible range ofengineering application. This heat transfer enhancement technique of spiral gearinserted tube has a broad prospect of engineering application.