Heat Transfer Enhancement in Continuous Helical Baffled Shell-and-Tube Heat Exchangers Regarding Local Thermal Resistance Analysis

This study introduces the local thermal resistance analysis method to figure out the priority of helical plug flow and heat transfer characteristics in continuous helical baffled shell-and-tube heat exchangers (CHB-STHX). The effect of helix angle on the flow behavior and heat transfer performance is numerically investigated, while the double-layer CHB-STHX is proposed for further improving the local heat transfer. Meanwhile, the performance evaluation criterion (PEC) and the thermal resistance evaluation factor (TEF) are regarded as the performance evaluation criteria in comparison to traditional segmental baffed shell-and-tube heat exchangers. Results show that the highest TEF for CHB-STHXs reaches 0.33 W/K with a helix angle of 5.35°. When both flow and heat transfer characteristics are considered, the 7.12°-helix angle CHB-STHX displays much better comprehensive performance. Based on the results of local thermal resistance analysis, the high thermal resistance region near the center tube needs to be improved. As a result, a double-layer CHB-STHX and a non-uniform double-layer CHB-STHX is proposed. The overall PEC improvement reaches 9.4%.