CO2-Based Working Fluid Mixtures for High-Temperature Thermodynamic Cycles
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Solution Overview
Problem
Existing thermodynamic cycles using CO2 as a working fluid face limitations in achieving high temperatures due to its low critical temperature and thermal instability, making them inefficient for applications above 400°C, and alternative mixtures with improved critical temperatures suffer from poor thermal stability or carcinogenicity issues.
Innovation Solution
A mixture comprising CO2 as the main component with additives such as TiCl4, TiBr4, SnCl4, SnBr4, VCl4, VBr4, GeCl4, or metal carbonyls like Ni(CO)4, which increases the critical temperature and provides high thermal stability, allowing efficient operation at temperatures up to 700°C without significant degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If CO2 is used as working fluid in thermodynamic cycles, then the cycle can operate at high pressures, but the critical temperature remains low (about 31°C) limiting efficiency at temperatures above 400°C
Solution Approach 1:
The patent applies composite materials by creating a working fluid mixture composed of CO2 combined with specific organic compounds (perfluorocarbons, polyethers perfluorates, ketones perfluorates). This composite fluid combines the high pressure operability of CO2 with the elevated critical temperature properties of the organic additives, enabling efficient thermodynamic cycle operation at temperatures above 400°C while maintaining the benefits of CO2-based systems.
2Temperature
If organic fluids are used to raise critical temperature, then the critical temperature increases, but thermal stability deteriorates making use above 350-400°C impossible
Solution Approach 1:
The patent applies parameter changes by carefully selecting and optimizing the chemical composition parameters of the organic fluid components. Specifically, it uses perfluorinated compounds and polyethers perfluorates whose molecular structures provide both elevated critical temperature and enhanced thermal stability. The invention changes the chemical parameters of the working fluid to achieve simultaneous improvement in both critical temperature and thermal stability, allowing operation above 400°C.
3Temperature
If CO2 mixtures with propane, butane, or cyclopropane are used to improve critical temperature, then the critical temperature is raised, but thermal stability deteriorates due to poor stability of additional components
Solution Approach 1:
The patent applies this principle by replacing unstable hydrocarbon components (propane, butane, cyclopropane) with more stable perfluorinated compounds and polyethers perfluorates. These alternative components, while achieving the same critical temperature improvement, provide superior thermal stability and can withstand high temperatures above 400°C without degradation, effectively creating a durable long-term working fluid solution.
4Stress or pressure
If compressors are used to increase CO2 pressure in gaseous phase, then pressure increases, but energy consumption increases making use at limited maximum temperatures unfavorable
Solution Approach 1:
The patent applies parameter changes by modifying the critical temperature parameter of the working fluid through the addition of organic compounds. This fundamental parameter change allows the system to achieve higher operating temperatures without proportionally increasing pressure requirements, thereby reducing the energy consumption of compression equipment while maintaining thermodynamic cycle efficiency.
Data Source
AI summary
Described herein is a working fluid for a thermodynamic cycle that includes CO2 as main component and one or more of the compounds selected from the group including: TiCl4, TiBr4, SnCl4, SnBr4, VCl4, VBr4, GeCl4, metal carbonyls, by way of example Ni(CO)4.