| 摘要 |
A laminar flow element for use in thermal mass flow sensors and flow controllers is designed to provide a high degree of precision. The precision laminar flow element includes a laminar flow element having a generally pointed entry end for maintaining a pure laminar flow path around the laminar flow element. The generally pointed entry end serves to direct an incoming gas flow stream equally about an outer surface of the laminar flow element. In this way, the laminar flow path is uniform so as to maintain a desired flow accuracy. The laminar flow element provides a plurality of standoff pins protruding from the outer surface of the laminar flow element to maintain a substantially equal radial clearance around the outer surface. By maintaining a substantially equal radial clearance from one laminar flow element to another, the laminar flow element is highly interchangeable. The laminar flow element may also provide a plurality of slots formed in the laminar flow element to accept a relatively high incoming gas flow stream. The precision laminar flow element preserves a linear flow ratio for low and high flow rates. The laminar flow element may be incorporated into a thermal mass flow sensor or flow controller such that the laminar flow element is substantially concentric with a borehole of a flow block. Various laminar flow elements with different annular clearances may be inserted in the same borehole of the flow block to provide a variety of flow rate ranges. |
