Experimental Investigation of Heating Element Performance with Bypass Tubes

Abstract

This study presents an investigation of the thermo-hydraulic performance of a rotary air preheater heating element utilizing bypass tubes and wire coiled coil matrix turbulators. The work purpose is to improve heat transfer efficiency and minimize flow resistance while considering the practical problems observed in failed heating elements utilized in industrial units such as the Al-Hartha Thermal Power Station in southern Iraq. The experimental setup is intended for simulating working conditions of an air preheater under cyclic charging and discharging of hot and cold air flows. Air from a single matrix is switched between the two directions of flow using a valve-controlled system driven by an automated control panel. Three different types of bypass layout are tested in order to determine the best positioning and number of the tubes. Additionally, bypass tubes with various diameters (10, 15 and 20 mm) and shapes (circular and squared section) are tested. Also, three turbulators with different pitches are inserted into the bypass tubes to increase turbulence and enhance convective heat transfer. The results clarify the interlinked influences of bypass flow control and turbulent augmentation on the overall performance of stack heat recovery elements. The thermo-hydraulic performance for inline-tube arrangement rises on the order of 7.58% over the conventional element, while the 15 mm tubes deliver improvement of 15.47%. The cylindrical section outperformed the square section over examined Re range, with an improvement 23.49%, while the 5 mm pitch turbulator achieved an improvement of 23.92%.