Air heated by the arc moves upward because it is less dense than the cooler air around it, and it moves at a speed for which the buoyant force and the drag force are equal.
The heat exchanging surface is arched or is inclined upward at the middle part and consists of a plurality of heat exchanging pipes which are arc-shaped or inclined upward at the middle parts.
所述换热面为拱形或向中间上方倾斜的换热面，由多根弧 形或向中间上方倾斜的换热管组成。
3
She spun around in circles, her chin tilted upward, her arms outspread in an arc, until she collapsed dizzy with laughter on the lawn.