Vacuum Pump Exhaust Purge Control for Accurate Rotor Temperature Sensing
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Solution Overview
Problem
Existing vacuum pump exhaust systems face challenges in accurately measuring the temperature of rotating portions due to low gas flow rates and pressure, leading to measurement errors and potential creep issues, as conventional methods fail to prevent backflow of process gas and ensure sufficient heat transfer.
Innovation Solution
A vacuum pump exhaust system with a purge gas supply unit that controls the flow rate and pressure of purge gas to ensure a higher flow velocity and intermediate or viscous flow around the temperature sensor, preventing backflow and enhancing heat transfer, while using a constricted portion to increase flow velocity and a mass-flow controller to manage flow rates during temperature measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If low gas flow rate is used for purge gas, then purge gas consumption is reduced, but measurement accuracy deteriorates due to insufficient heat transfer
Solution Approach 1:
The patent changes the pressure parameter of purge gas to achieve intermediate flow or viscous flow regime, which enhances heat transfer capability compared to molecular flow. By controlling gas pressure rather than just flow rate, sufficient heat quantity is transmitted to the temperature sensor even with reduced purge gas consumption
Solution Approach 2:
The patent utilizes gas flow dynamics and pressure control mechanisms to optimize heat transfer. By regulating purge gas pressure to achieve specific flow regimes (intermediate or viscous flow), the system ensures adequate thermal conduction to the sensor while minimizing gas consumption
2Quantity of substance
If low purge gas flow rate is used, then gas pressure around temperature sensor is reduced, but heat transfer becomes insufficient leading to measurement errors
Solution Approach 1:
The patent changes the pressure parameter to transform the flow regime from molecular flow to intermediate or viscous flow. This parameter change enables effective heat transfer through thermal conduction and convection mechanisms that are absent or weak in molecular flow, ensuring accurate temperature measurement with reduced gas amounts
3Productivity
If high speed rotation is continued at high temperature, then productivity is maintained, but creep occurs reducing durability
Solution Approach 1:
The patent implements a feedback mechanism where the temperature sensor continuously monitors the rotating portion temperature, and this information is used to control the rotation speed. When temperature reaches a predetermined threshold, the rotation speed is reduced or stopped, preventing creep while allowing high-speed operation during normal conditions to maintain productivity
Solution Approach 2:
The temperature sensor is positioned to detect temperature changes in advance before creep occurs. By monitoring temperature trends and taking preliminary action to reduce rotation speed when thresholds are approached, the system prevents durability damage while maximizing operational efficiency
4Measurement precision
If process gas flows backward due to low purge gas velocity, then measurement accuracy deteriorates, but increasing purge gas flow rate increases gas consumption
Solution Approach 1:
The patent changes the pressure parameter to achieve intermediate or viscous flow regime, where gas molecules have sufficient mean free path and collision frequency to effectively counteract backflow. This pressure-based approach prevents process gas intrusion and maintains measurement accuracy without requiring high flow rates that would increase consumption
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
Accurate temperature measurement of the rotating portion is achieved, preventing measurement errors and creep, while reducing the consumption of purge gas and minimizing the risk of corrosion and deposition, thereby ensuring the durability of the rotating portion.
Implementation Method 1
a mean velocity of purge gas is quite low, e.g., about 4 cm per second. Thus, if low-thermal-conductivity process gas for a semiconductor manufacturing device or the like flows backward, the purge gas cannot wash off (press back) the process gas.
Implementation Method 2
the velocity (flow rate) of purge gas is low... a heat quantity may be insufficiently transmitted so as to increase errors of measurement by the temperature sensor
Implementation Method 3
The rotating portion rotates at high speed and thus it is necessary to measure the temperature by using a non-contact temperature sensor (temperature sensor unit)... Japanese Patent Application Publication No. H11-37087 describes a technique of increasing radiation factors of a rotor blade, a target of measurement, and a heat receiving portion
Data Source
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AI summary
A vacuum pump exhaust system, a vacuum pump provided for the vacuum pump exhaust system, a purge gas supply unit, a temperature sensor unit, and an exhausting method of the vacuum pump are achieved, by which a temperature of a rotating portion can be accurately measured. In the vacuum pump exhaust system according to the present embodiment, at least when the temperature of the rotating portion is measured, the vacuum pump supplies the purge gas to the vacuum pump such that an amount of the purge gas satisfies one of following conditions: an amount of the purge gas flowing at a higher velocity than a backflow velocity of gas exhausted by the vacuum pump on at least a part of a downstream side of the temperature sensor unit, and an amount of the purge gas having a pressure of one of an intermediate flow and a viscous flow around the temperature sensor unit. The exhaust system of the present embodiment further includes a purge gas supply unit capable of controlling a flow rate of purge gas introduced into the vacuum pump. This configuration can prevent process gas from flowing backward so as to change the composition around the temperature sensor unit, thereby accurately measuring the temperature of the rotating portion.