Cryogenic Milling Supercooling Liquid Nitrogen Heat Transfer
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Solution Overview
Problem
Existing cold grinding methods using cryogenic refrigerants face challenges with heat transfer inefficiencies and uncontrollable cooling due to gas refrigerants, leading to particle agglomeration and increased energy expenditure, especially when grinding materials with rubber-elastic or plastic properties.
Innovation Solution
Supercooling the cryogenic refrigerant below its boiling point before feeding it to the grinding device ensures it remains largely in a liquid state, enhancing heat transfer and allowing for precise control of the cooling process, thereby preventing agglomeration and reducing energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If gas refrigerant is used for cooling the feed material, then cooling coverage is improved, but heat transfer efficiency deteriorates
Solution Approach 1:
The patent changes the physical state parameter of the refrigerant from gas to liquid by supercooling it below its boiling point. This parameter change transforms the heat transfer mechanism from convection (gas) to conduction and phase change (liquid), dramatically improving heat transfer efficiency while maintaining good cooling coverage
Solution Approach 2:
The patent utilizes the phase transition of the refrigerant from liquid to gas during evaporation on the particle surface. This phase change absorbs large amounts of heat (latent heat of vaporization), providing highly efficient cooling. The refrigerant is supercooled below its boiling point and then allowed to evaporate on the particle surfaces, creating an effective heat transfer mechanism
2Loss of energy
If liquid cryogenic refrigerant is used for cooling, then heat transfer efficiency is improved, but control reliability deteriorates due to gas bubble formation
Solution Approach 1:
The patent applies preliminary action by supercooling the refrigerant below its boiling point before it enters the grinding chamber. This pre-cooling prevents premature evaporation and gas bubble formation in the supply lines, ensuring reliable liquid flow control. The refrigerant is cooled to a temperature where it remains liquid even when exposed to ambient heat, eliminating the gas bubble problem
Solution Approach 2:
The patent changes the temperature parameter of the refrigerant to a supercooled state (below boiling point). This parameter change increases the refrigerant's stability and prevents unwanted phase transitions in the supply system, improving control reliability while maintaining high heat transfer efficiency upon contact with the feed material
3Device complexity
If grinding is performed without supercooling, then process simplicity is maintained, but cooling control precision deteriorates
Solution Approach 1:
The patent changes the temperature parameter of the refrigerant to a supercooled state, which provides precise control over the cooling process. The supercooled refrigerant remains liquid until it contacts the feed material, ensuring consistent cooling performance and preventing premature evaporation that would compromise cooling precision
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 method enables efficient grinding of materials to particle sizes below 500 μm with reduced equipment needs and prevents reagglomeration, achieving reliable and economical cold grinding of difficult-to-process materials.
Implementation Method 1
the cryogenic refrigerant is supercooled to a temperature below its boiling point before it is fed to the grinding device
Implementation Method 2
the heat transfer is so good here that within the particles of the feed material there is a large temperature difference between the quickly cooled outer surface and the still warm core
Implementation Method 3
The refrigerant, which is at least predominantly in the solid or liquid state, evaporates when it comes into thermal contact with the feed material or the grinding media
Implementation Method 4
A part of the refrigerant will therefore already evaporate when it is fed to the grinding device due to the unavoidable heat input via the walls of the feed lines and thus impair the cooling effect
Data Source
Figure 1
AI summary
The method involves milling the feedstock in a milling unit (2) and cooling the feedstock with a liquid cryogenic cooling agent before or during the milling process. The liquid cryogenic cooling agent is undercooled to a temperature below its boiling point before its delivery to the milling unit. The liquid nitrogen is used as a cryogenic cooling agent. An independent claim is also included for a device for fine milling of the mill material.