A design for a parallel, finless, flat-tube heat exchanger is proposed and assessed for high performance in air conditioners. In this design, a longitudinal vortex generator (LVG) plate consisting of thousands of LVGs is placed in front of the finless heat exchanger in the airflow path, thus resulting in improved heat transfer. The LVG was installed in front of the finless heat exchanger with a gap of about 1 mm, which ensured that under wet and frost/defrost conditions, the condensed or defrosted water would not drip onto the LVG. Therefore, the drain and defrosting performance was not affected by the LVG. A novel, double-triangular shape was developed for the LVG using a numerical method, and some parameters which significantly affect the performance of LVG were numerically analyzed. (C) 2018 Elsevier Ltd. All rights reserved.