Pressure-Type Flow Rate Control Device for Mixed Gas Accuracy
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Solution Overview
Problem
Existing pressure-type flow rate control devices are unable to accurately calculate and control the flow rate of mixed gases, as they rely on characteristics specific to individual gases, leading to significant discrepancies between calculated and actual measurements.
Innovation Solution
A pressure-type flow rate control device calculates the average density, specific heat ratio, and gas constant of a mixed gas to determine its flow factor, allowing for accurate flow rate calculation and control by using processors to adjust the supply of the mixed gas through an orifice, ensuring the flow rate meets a predetermined target.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the flow factor of each gas type is weighted by mixing ratio to calculate mixed gas flow factor, then the calculation can be performed for mixed gases, but the calculation accuracy deteriorates significantly
Solution Approach 1:
The patent changes the parameters used for calculation from individual gas flow factors to averaged physical properties (density, specific heat ratio, gas constant) of the mixed gas. By calculating these average parameters based on mixing ratios and using them in the flow factor formula, the method achieves both mixed gas applicability and high calculation accuracy.
Solution Approach 2:
The patent treats the mixed gas as a composite system by calculating effective average parameters that represent the combined properties of multiple gas types. This composite approach allows the system to handle mixed gases while maintaining calculation precision by considering the contribution of each component gas.
2Device complexity
If pressure-type flow rate control is used instead of thermal mass flow control, then device complexity is reduced, but the ability to control mixed gas flow rate accurately is lost
Solution Approach 1:
The patent modifies the calculation parameters to use averaged physical properties of the mixed gas (density, specific heat ratio, gas constant) rather than flow factors of individual gases. This parameter transformation enables the simple pressure-type control device to accurately calculate and control mixed gas flow rates.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device achieves high accuracy in calculating and controlling the flow rate of mixed gases, ensuring it meets the desired value, thereby improving the precision of gas supply in semiconductor manufacturing and chemical plants.
Implementation Method 1
when the relationship between the upstream pressure P1 and a downstream pressure P2 of the orifice satisfies a critical expansion condition P1/P2≥approx. 2, the flow rate Q is expressed as Q=FF·S·P1(1/T1)1/2
Implementation Method 2
Assuming that the flow velocity of the gas when flowing out of the orifice reaches sound velocity at the gas temperature
Implementation Method 3
calculating an average density ρAV, an average specific heat ratio κAV, and an average gas constant RAV of the mixed gas, respectively, by: ρAV=X·ρ(A)+(1−X)·ρ(B), κAV=X·κ(A)+(1−X)·κ(B), and RAV=X·R(A)+(1−X)·R(B)
Implementation Method 4
a controller controlling the supply amount adjusted by the adjuster such that the flow rate Q of the mixed gas that is calculated becomes a predetermined target flow rate Q0
Data Source
AI summary
A pressure-type flow rate control device 1, while maintaining an upstream pressure P1 of an orifice 5 at approximately at least twice a downstream pressure P2, calculates a flow factor FF of a mixed gas consisting of two types of gases mixed at a mixture ratio of X:(1−X) by FF=(k/ρ){2/(κ+1)}1/(κ−1)[κ/{(κ+1)R}]1/2 using an average density ρ, an average specific heat ratio κ, and an average gas constant R of the mixed gas that are calculated by weighting the densities, specific heat ratios, and gas constants of the two types of gases at the mixture ratio, and calculates a flow rate Q of the mixed gas passing through the orifice by Q=FF·S·P1(1/T1)1/2, where S is the orifice cross section, and P1 and T1 are respectively the pressure and temperature of the mixed gas on the upstream side of the orifice.