Combined experimental and numerical investigations on heat transfer augmentation in truncated ribbed channels designed by adopting fractal theory

摘要

This work experimentally tests and numerically investigates the heat transfer augmentation, the flow characteristics and the overall thermal performance of truncated ribs in a rectangular channel with an aspect ratio of 1∶4 designed by using the fractal theory. The liquid crystal thermography (LCT) method in steady-state is adopted and the three-dimensional CFD numerical simulations with an established transition k-kl-ω model are conducted to reveal the underlying thermo-fluid mechanisms. Seven cases with novel truncated ribs designed by using fractal theory are designed to improve the heat transfer performances compared with the case with continuous ribs. Among them, ribs with different cross sections, different arrangements and different cut-off angles are studied, based on which, two ways to improve the heat transfer performances with respect to the truncated ribs are given. In addition, two indexes, i.e., Nu/Nu_0/(f/f_0) and Nu/Nu_0/(f/f_0)~(1/3), are considered to study the overall thermal performance of the considered cases. Results show that with respect to the factor Nu/Nu_0/(f/f_0), the designed cases can improve the overall thermal performance up to 38.21%, and with respect to the factor Nu/ Nu_0/(f/f_0)~(1/3), the designed cases can improve the overall thermal performance up to 12.16%. By analyzing the flow characteristics, the underlying mechanisms about such thermal performance enhancements of the designed cases are revealed.