Abstract: An airflow supply duct for use in a transportation refrigeration trailer is provided including an inlet portion adjacent a first end and an outlet portion adjacent a second opposite end. A generally curvilinear central portion is disposed between the inlet portion and the outlet portion. The inlet portion, the central portion, and the outlet portion form an interior flow path. The airflow supply duct has a rectangular cross-section having an approximately uniform cross-sectional area along a length of the airflow duct. A height and width of the airflow supply duct vary along the length of the airflow supply duct such that a ration of the width to the height at the second end is greater than the ration of the width to the height at the first end.