Liquid CO2 Supercooling with a Snow-Replenished Cold Bath
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Solution Overview
Problem
Existing methods for supercooling liquid carbon dioxide are limited by the inability to maintain a liquid cold bath below 5.18 bar, which restricts the temperature range for supercooling, leading to partial evaporation and disruptions in dosing systems.
Innovation Solution
A method involving a cold bath formed from a mixture of solid carbon dioxide and a liquid or pasty carrier medium, where a partial flow of liquid carbon dioxide is expanded to form carbon dioxide snow, which is then admixed to the carrier medium, allowing for a wide range of temperature setting and maintaining the cold bath in a liquid state for efficient heat transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the pressure of the cold bath is reduced below 5.18 bar to achieve lower temperatures, then the temperature range for supercooling is extended, but carbon dioxide changes into a mixture of gas and snow, making it impossible to maintain a liquid cold bath
Solution Approach 1:
The patent uses a composite cooling system consisting of liquid carbon dioxide as the primary coolant and solid carbon dioxide snow as an additive. The snow is introduced into the liquid cold bath to maintain the temperature and prevent the bath from transitioning to a gaseous state, allowing operation below the triple point pressure while maintaining a liquid cooling medium.
Solution Approach 2:
The patent exploits the phase transition of carbon dioxide from liquid to solid (snow) at pressures below 5.18 bar. By controlling the phase transition through controlled introduction of snow into the liquid bath, the system maintains a liquid cooling medium at temperatures that would normally cause complete vaporization, thus extending the supercooling temperature range.
2Reliability
If isobaric supercooling is used to achieve reliable liquid carbon dioxide for dosing, then reproducible dosing is achieved, but the aggregates required are very expensive to purchase and operate due to high power requirements
Solution Approach 1:
The system uses the cold bath to pre-cool the liquid carbon dioxide before it reaches the dosing element, reducing the energy burden on downstream components. The snow addition to the cold bath provides self-regulating cooling that reduces the need for high-power active cooling systems.
Solution Approach 2:
The liquid carbon dioxide is pre-cooled in the cold bath before dosing, which reduces the temperature differential that would otherwise need to be managed by high-power cooling aggregates during the dosing process itself, thereby reducing overall power requirements.
3Temperature
If a cooling coil surrounded by a bath of the same liquid cryogenic medium is used for supercooling, then the apparatus can supercool the cryogenic medium, but it is not possible to maintain a liquid cold bath when using carbon dioxide at pressures below 5.18 bar
Solution Approach 1:
Instead of using a simple liquid carbon dioxide bath, the patent creates a composite cooling system where solid carbon dioxide snow is introduced into the liquid carbon dioxide bath. This composite system allows the bath to remain liquid at temperatures and pressures where pure liquid carbon dioxide would vaporize, enabling supercooling below the triple point pressure.
Solution Approach 2:
The patent utilizes the phase transition properties of carbon dioxide by introducing solid snow into the liquid bath. The snow melts endothermically, providing cooling while maintaining the liquid phase of the bulk bath, thus enabling the cooling coil to supercool the passing liquid carbon dioxide even at pressures below 5.18 bar.
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
This approach enables efficient supercooling of liquid carbon dioxide over a broader temperature range, maintaining the cold bath in a liquid state and ensuring reliable dosing by continuously monitoring and adjusting the temperature and pressure to keep the carbon dioxide snow sublimated, thus maintaining a consistent cooling effect.
Implementation Method 1
As a result of the expansion, the temperature of the carbon dioxide drops drastically, for example to a value of -78°C at an internal container pressure of 1 bar
Implementation Method 2
a heat exchanger which is arranged in a thermally insulated container and is in heat exchange with a cold bath accommodated in the container
Implementation Method 3
the cold bath consisting of a mixture of a carrier medium with the carbon dioxide snow keeps its temperature constant until the supplied carbon dioxide snow has at least largely sublimated
Implementation Method 4
Endothermic effects resulting from the admixture and/or redemption can additionally lower the temperature of the cold bath and thus increase the cooling effect of the cold bath
Data Source
Figure 1
AI summary
According to the invention, the liquid carbon dioxide to be supercooled is brought into thermal contact with a cold bath (18) inside a container (2) in a heat exchanger (4). The cold bath (18) comprises a cold mixture of solid carbon dioxide (20) and a carrier medium. During heat exchange with the liquid carbon dioxide to be supercooled, part of the carbon dioxide in the cold bath (18) sublimates and is then discharged as carbon dioxide gas. The solid carbon dioxide sublimated from the cold bath (18) is replaced by removing a partial stream or a specified amount of the liquid carbon dioxide to be supercooled and expanding it at an expansion nozzle (12) arranged in the container and the carbon dioxide snow formed during the expansion is fed to the cold bath (18). is added. In this way, the cold bath (18) can be kept at a constant temperature for almost any length of time and used to supercool the liquid carbon dioxide.