Cryopump Baffle Plate Differential Conductance Gas Flow
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Solution Overview
Problem
The evacuation capability of cryopumps is compromised due to increased heat input when the heat shield is formed by multiple cylindrical members, leading to inefficient gas evacuation.
Innovation Solution
A cryopump design featuring a baffle plate with a first portion at the center and a second portion at the edge, where the second portion has greater conductance than the first, allowing gas to flow more efficiently into the main body and promoting uniform deposition of condensed gas on the cryopanels, thereby enhancing evacuation capability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the heat shield is formed by multiple cylindrical members (first shield and second shield), then the evacuation capability is improved by evacuating gas through the flow passage between shields, but the heat input to the flow passage is increased which lowers the evacuation capability
Solution Approach 1:
The baffle plate is designed with non-uniform hole distribution, creating different conductance characteristics in different regions. The first region (central area) has a first conductance and the second region (outer area) has a second conductance that is different from the first, allowing localized control of gas flow to optimize both evacuation capability and heat input management
2Productivity
If gas flows through the baffle plate into the main body, then evacuation is achieved, but condensed gas deposits unevenly on the cryopanel with concentration at the central portion
Solution Approach 1:
The baffle plate employs region-specific hole patterns where the first region (central area) and second region (outer area) have different conductances. This local differentiation directs gas flow to achieve more uniform condensed gas deposition across the cryopanel surface, preventing excessive concentration at the central portion while maintaining effective evacuation
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 design improves the uniformity of condensed gas deposition on cryopanels, expanding the deposition region and enhancing the overall evacuation capability of the cryopump without increasing the baffle plate's thickness, thus maintaining the main body's volume.
Implementation Method 1
The baffle plate includes a first portion and a second portion. The first portion includes a center of the baffle plate and first holes extending through the baffle plate. The second portion includes an edge of the baffle plate and second holes extending through the baffle plate. The second portion has a greater conductance than the first portion.
Implementation Method 2
the cryopanel is connected to a refrigerator... condensed gas is readily deposited on the circumferential portion (portion including the edge) of the cryopanel
Data Source
AI summary
A cryopump includes a cryopanel, a main body, and a baffle plate. The cryopanel is connected to a refrigerator. The main body accommodates the cryopanel. The baffle plate is located in a gas inlet of the main body. The baffle plate includes a first portion and a second portion. The first portion includes a center of the baffle plate and a first hole extending through the baffle plate. The second portion includes an edge of the baffle plate and a second hole extending through the baffle plate. The second portion has a greater conductance than the first portion.