Experimental And Theoretical Study On Heat Transfer Enhanced Tube Of The Inside And Outside Triangle Finned Tube With Small Spiral Angles (IOSF Tube) For Improving The Performance Of The High-Pressure Preheater In The Power Station.

A new heat transfer enhanced tube of the inside and outer triangle finned tube with small spiral angles (IOSF tube ) was introduced and manufactured for improving the performance of the high-pressure preheater in the power station.Based on the laboratory experiments, the total heat transfer coefficient of the vertical IOSF tube was 63%-95% larger than that of the smooth tube, with the outer surface heat transfer coefficient being 3.5-4 times that of the smooth tube and the inside surface heat transfer coefficient being 18% larger than that of the smooth tube. Compared with the spirally fluted tube, the IOSF tube obtained a 4-27% larger total heat transfer coefficient but had a only 40-80% pressure drop of the inside flowing fluid. In the mean time, this type of enhanced tube was also applied into a high-pressure preheater with the same heat transfer area. The field experimental results showed that the total heat transfer coefficient of the high-pressure preheater with the IOSF tubes was 43% larger than that of the previous. When the temperature of the heating water vapor in the shell side was 159℃ and the temperature of the water into the tubes was 101℃, the temperature of the water out of the tubes could be increased from 150℃ to 156℃. So a nice result of energy conservation could be obtained.In this paper, the heat transfer surface of the outer side was divided into the film condensation zone and the drainage zone. The equations describing these two zones were formulated respectively. Then a coupled equation based on the equilibrium between the amount of the condensate and the drainage was induced to solve these equations. So a three dimensional simulation model was set up. The model don't involve any experimental coefficient and the simulation results compared the experimental and other researchers' results showed high accuracy. So it can be widely applied to design and optimize the condenser with IOSF tubes and vertical grooved tubes.As seen from the simulation, Though the drainage ability of the IOSF tube with the spiral angle of fins on the outer side β<27° is slightly lower than the vertical grooved tube, but the effective heat transfer surface has a slightly increase. As a result, the heat transfer ability of the IOSF tube is almost equal to the vertical grooved tube. The angle φ of the groove among the fins and the starts N of the fins are the main parameters that play an important role on the condensation. The height H of the fins is a function of φ and N. For the IOSF tube with the outer diameter Do of 0.016m, the length L of 0.7m, the spiral angle β of 18° ,the height H of 0.001m, 76° for the φ and 32 for the N are the optimum...