| 摘要 |
<p>The fan comprises a rectangular housing with two large flat faces. A circular opening is cut in each of these faces, and a cylindrical cowl is attached to the sides of the opening. Inside the housing is a plate arranged to slide vertically, the plate sitting either in the lower closed part of the housing, or between the two circular opening. The plate has a small square box attached to it supporting an electric fan. Under the control of a servomotor turning a threaded shaft the plate may be lifted into a position so that the fan can withdraw fumes, or it may be lowered to leave the opening clear. The fan and servomotor are controlled according to the operating conditions inside the oven.</p> |
