Numerical study of helical tape inserts for air to oil double pipe heat exchanger

This work has been studying the thermo hydraulic performance of stainless-steel double pipe heat exchanger, inner and outer diameters are (114.3 and168.3mm) with 3.05 mm thickness and 1500 mm length numerically by using Solid Works 2016 package. The recycle wasted energy in the exhaust gases for the purpose of heating the heavy fuel oil and helical tape with different pitches (11, 14, 17) cm is inserted in the inner side of the inner tube as an enhancement heat transfer device. Reynolds number is varied between (25148 and 64883) for air side (inner tube), oil flow rate in the outer tube is 0.1 kg/s. The numerical results are first verified for helical tape with different pitches, then they are compared with the previous study that conducted on the same heat exchanger with twisted tape inserted with four twisted ratios under the same boundary condition and then the both results compared with plain heat exchanger. The result show that as compared with plain tube, using helical tape with smaller pitch (11) cm and inlet air velocity (34) m/s the enhancement percentage in heat transfer rate, Nusselt number and convection heat transfer increased up to 62.51%, 159.45 %, and 148.16% respectively, while the result for twisted tape at lower twisted ratio (1.5) from previous study is 23.68%, 86.92% and 76.31% to same parameters above. The higher-pressure drop is obtained when using minimum pitch for helical tape and higher Reynolds number.