Enhancing Heat Recovery Efficiency in Double‐Pipe Heat Exchangers: An Experimental Comparative Study of Different Shapes of Wavy‐Edge Tapes With the Plain Pipe Case

ABSTRACT This study tests how using three kinds of wavy‐edge tapes, wavy‐edge tape (WET), perforated wavy‐edge twisted tape (PWETT), and perforated wavy‐edge twisted tape with semicircular cut shape (PWETTc), with a semicircular cut, affects how well a dual‐pipe heat exchanger (DPHE) works and compares it with the smooth one. The HE was selected as a heat renewal apparatus in the brick plant to reclaim heat from exhaust gases for the preheating of the heavy fuel oil (HFO). Air was used as a hot gas as a replacement for furnace exhaust gases because it possesses analogous thermal characteristics, flowing through the inner pipe at different speeds (13, 20, and 27 m/s) and temperatures (200°C and 250°C). In contrast, HFO enters the shell side in the opposite direction at mass flow rates (0.06, 0.08, and 0.1 kg/s) with a steady temperature of 40°C. Both the pipes and tapes are composed of stainless steel. The trial outcomes show that when the Reynolds number increased from 90,440 to 187,837, the heat transfer rate, oil outlet temperature, and effectiveness of the HE improved, with the PWETTc having a semicircular‐cut shape showing increases of 45%, 21%, and 23%, respectively. Conversely, an augmentation in the oil flow rate from 0.06 to 0.1 kg/s led to a reduction in the oil outlet temperature by 8.5% for the WET pipe at 250°C, and by 8.6%, 12.6%, and 17% for the smooth pipe at 200°C, 225°C, and 250°C, respectively. The outcomes indicate that the DPHE with PWETTc form boosts the Nusselt number and the enhancement in heat transport by about 26%–28% and 50%, respectively, compared with a smooth dual pipe. The results show that using a twin pipe with PWETTc inserts to preheat HFO at an exhaust air temperature of 250°C and a speed of 27 m/s can lower viscosity, diminish the needed electric power, and save 2.3 MW of energy for one factory each year.