JP-2022518487-A5 -

Dates

Publication Date

20221222

Application Date

20200117

Description

Many industrial processes require the accurate and precise measurement and control of various process fluids. For certain processes, such as measuring incompressible fluids (e.g., liquids), only volumetric flow rate (e.g., liters/minute (lpm), standard cubic centimeters/minute (sccm), or cubic meters/second ( m³ /s)) needs to be measured. However, other processes, such as measuring compressible fluids (e.g., gases), often require mass flow rate measurement (e.g., milligrams/minute (mg/m) or kilograms/second (kg/s)). Therefore, for compressible fluids, the discussion of the fluid's volumetric mass density (also simply called mass density herein) can be considered a function of absolute pressure and temperature. For example, in the semiconductor and related industries, mass flow meters and mass flow controllers are used to accurately and precisely measure and control the mass of process fluids introduced into process chambers. A wide variety of technologies can be used to measure flow rates within devices such as thermal devices, ultrasonic time-of-flight devices, Coriolis devices, and pressure-based devices. Referring now to Figure 2, a cross-sectional view of one embodiment of a differential pressure-based flow meter 200 according to the subject matter of this disclosure is shown. The differential pressure-based flow meter 200 is shown to include a fluid inlet 201 and a fluid outlet 203 for the fluid to flow through a flow path 205. Figure 2 is also shown to include a flow sensor 207 having a first side 207A and a second side 207B, as well as a flow limiting element 211 and a flow meter body 215. Since the fluid flowing through the flow path 205 is in direct hydrostatic or pneumatic communication with the flow sensor 207, there is no need for the first and second pressure ports 105A, 105B in Figure 1 to relay pressure to the first and second cavities 103A, 103B, as required by differential pressure-based flow meters of the prior art. As a result, since the pressure ports 105A, 105B and cavities 103A, 103B are not required in various embodiments of the subject matter of this disclosure, there is no dead volume that could capture contaminants and release them later. Furthermore, because the flow path is continuous, the differential pressure-based flow meter 200 is continuously flushed during operation. Continuing to refer to Figure 2, the first bend 209 and the second bend 213 are located on opposite sides of the flow limiting element 211. However, for a given embodiment of the differential pressure-based flowmeter 200, if it is desirable that the fluid flow be a laminar flow regime, at least one of the first bend 209 and the second bend 213 may be located upstream and downstream of the flow limiting element 211, respectively, for at least 5 to 7 diameters (based on internal dimensions and assuming that the cross-section of the flow path is circular). Alternatively, in addition to the length of the path increased to at least 5 to 7 diameters, various rectifier devices known in the art may also be used within the flow path 205. Based on the fundamental principles of fluid dynamics, those skilled in the art will recognize how to position and size the flow path 205 to accommodate the flow of a laminar fluid. For example, if the flow path 205 does not have a circular cross-sectional area, other relevant internal characteristic length dimensions, such as the hydraulic diameter in the case of a flow path having a rectangular cross-section, or the lengths of the channels upstream and downstream of the bends 209 and 213, may be selected to restore laminar flow. Based on reading and understanding the subject matter of this disclosure, those skilled in the art will recognize how to determine the length of the flow path (e.g., before or after the bends) to produce laminar flow for a given fluid flow rate, fluid density, and fluid kinematic viscosity.