Buffer Tank Mixing for Stable Ultrapure Water Resistivity
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Solution Overview
Problem
The existing resistivity regulating apparatuses for ultrapure water used in semiconductor and liquid crystal production face issues with resistivity deviations and fluctuations due to gradual gas dissociation and uneven ion concentrations, leading to challenges in maintaining consistent resistivity values, especially as the regulated resistivity increases, and require lengthy pipes that incur pressure drops and space constraints.
Innovation Solution
A resistivity regulating apparatus that includes a gas dissolving device to generate treated liquid with dissolved gas and a buffer tank to promote convection and uniform ion concentration, reducing deviations and fluctuations while minimizing apparatus scale and pressure drop, by using a cylindrical buffer tank with strategically positioned feed and discharge ports to enhance turbulent flow and convection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a long pipe is disposed downstream of the resistivity regulating apparatus to allow natural mixing and dissociation, then the deviations and fluctuations in resistivity are reduced, but the pressure drop increases, space requirements increase, and the pipe length is limited
Solution Approach 1:
The invention divides the mixing and dissociation function into two separate components: the gas dissolving device performs gas dissolution and initial ionization, while the buffer tank provides the environment for complete dissociation and uniform mixing. This segmentation eliminates the need for long pipes while achieving reliable resistivity stability.
Solution Approach 2:
The buffer tank acts as an intermediary between the gas dissolving device and the treatment process. It receives the gas-added ultrapure water, allows complete dissociation and mixing within its volume, and then supplies uniformly mixed treated water, eliminating the need for long downstream pipes.
2Reliability
If gas is dissolved in ultrapure water using a hollow fiber membrane module, then the resistivity is reduced through ion generation, but the ionization is incomplete and takes time, causing deviations in resistivity measurements at different locations
Solution Approach 1:
The gas dissolving device performs preliminary gas dissolution and initial ionization (first dissociation step) before the water enters the buffer tank. This preliminary action allows the second dissociation step to complete in the buffer tank, ensuring complete ionization and consistent resistivity measurements downstream.
Solution Approach 2:
The invention extracts the mixing and dissociation function from the flow path and places it in a dedicated buffer tank. This separation allows complete dissociation to occur without requiring long pipes in the treatment flow path, eliminating resistivity deviations at different measurement locations.
3Reliability
If ultrapure water merges with gas-added ultrapure water, then the resistivity is regulated, but the ion concentration becomes uneven depending on the mixed state, causing fluctuations in resistivity
Solution Approach 1:
The buffer tank serves as an intermediary mixing chamber where gas-added ultrapure water and ultrapure water are thoroughly mixed before being supplied to the treatment process. This ensures uniform ion concentration and eliminates resistivity fluctuations caused by uneven mixing.
Solution Approach 2:
The buffer tank provides a volume sufficient to achieve homogeneous mixing of gas-added and regular ultrapure water. The tank's design ensures complete mixing and uniform distribution of ions, resulting in consistent resistivity values without fluctuations.
4Reliability
If the resistivity regulated value is increased, then the quality of treated water is improved, but the deviations and fluctuations in resistivity become more apparent
Solution Approach 1:
The invention extracts the mixing and dissociation process from the flow path and places it in a dedicated buffer tank. This ensures complete and uniform dissociation before measurement, eliminating deviations and fluctuations that become apparent at higher resistivity values, thereby improving measurement accuracy.
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 apparatus effectively reduces resistivity deviations and fluctuations, stabilizes resistivity, and reduces apparatus size and pressure drop, achieving consistent ion concentration and efficient resistivity regulation without the need for lengthy pipes.
Implementation Method 1
the gas dissolved in ultrapure water is dissociated (ionized) in two steps provided by the following equation (1) and equation (2)... Ions are generated due to dissociation equilibrium, and the generated ions reduce the resistivity of ultrapure water
Implementation Method 2
the flow path of the treated liquid widens rapidly, and the flow rate of the treated liquid thus drops rapidly. This causes the treated liquid fed to the buffer tank to undergo convection in the buffer tank, which promotes dissociation of the treated liquid
Implementation Method 3
The treated liquid fed to the buffer tank is stirred in the form of turbulent flow in the buffer tank, which promotes uniformization of ion concentration
Data Source
AI summary
A resistivity regulating apparatus includes: a gas dissolving device that causes a regulating gas to dissolve in a liquid targeted for resistivity regulation to generate a treated liquid in which the regulating gas is dissolved in the liquid, the regulating gas being used to regulate a resistivity of the liquid; and a buffer tank to which the treated liquid discharged from the gas dissolving device is fed.