Rectangular in Twisted Tape Economizer Shell and Tube

Abstract

This paper presents the effects of insertion of twisted tape on heat transfer performance a shell-and tube heat exchanger recovering a waste heat from an once-through boiler. The heat exchanger consisted of tube of 0.033 m outside diameter and 34 m total length, corresponding to total heat transfer area of 3.55 m². The twisted-tape with rectangularshape hole with twist ratio (y/w) of 3 and total area of 0.09 m² was inserted in the heat exchange tube. As revealed by the experiential results, at exhaust gas speed of 5 m/s, the heats of 429 kW and 212.82 kW were found at outer and inner surfaces of tube, respectively, ensuring the heat transfer coefficients of 5,470 W/m²ºC  and 24.82 W/m²ºC and corresponding pressure drops were 28.77 Pa and 5.34 Pa. The performance of the heat exchange was 0.6. As a result, energy saving cost of 136,084 Baht/year was achievable, leading to quite short simple payback period of 1.1 year. These operating conditions were recommended/suitable for the once-though boiler generating steam at 500 kg/h at the maximum pressure of 7 kg/cm²