Siloxane mixtures
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Solution Overview
Problem
Siloxane mixtures used as heat transfer fluids in solar thermal power plants experience significant changes in physical properties over time due to temperature-dependent rearrangement processes, leading to increased vapor pressure and operational challenges, which are not effectively addressed by the addition of metallic stabilizers due to cost and material constraints.
Innovation Solution
A mixture of methylpolysiloxanes comprising linear and cyclic compounds with specific molecular ratios and proportions, allowing for nearly constant physical properties over time under thermal stress, even if the chemical composition has not reached equilibrium, by controlling the molar mass distribution and composition to maintain properties like viscosity and vapor pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If metallic stabilizers and hydrogen-containing silicon compounds are added to noncyclic methylpolysiloxanes to suppress rearrangement processes, then the composition stability is improved, but the material costs increase and vapor pressure still rises over time
Solution Approach 1:
The invention extracts and eliminates the need for metallic stabilizers and hydrogen-containing silicon compounds from the siloxane mixture. By formulating a specific mixture of noncyclic and cyclic methylpolysiloxanes with controlled composition, the patent achieves long-term stability without requiring additional stabilizing additives, thereby reducing material costs while maintaining composition stability.
Solution Approach 2:
The invention creates a composite siloxane mixture system combining noncyclic methylpolysiloxanes (60-95 wt%) and cyclic methylpolysiloxanes (5-40 wt%) in specific proportions. This composite formulation leverages the complementary properties of both components to achieve inherent stability without requiring external stabilizers, resolving the contradiction between composition stability and material cost.
2Duration of action of moving object
If siloxane mixtures are used as heat transfer fluids at high temperatures for extended periods, then the operational duration is improved, but the physical properties change due to rearrangement processes
Solution Approach 1:
The invention performs preliminary action by pre-equilibrating the siloxane mixture composition before use. The specific formulation of noncyclic and cyclic methylpolysiloxanes is designed to reach equilibrium composition rapidly and maintain stable physical properties throughout the operational period, preventing significant changes in viscosity and vapor pressure during extended high-temperature service.
Solution Approach 2:
The invention controls the composition parameters of the siloxane mixture by specifying precise weight percentage ranges of noncyclic (60-95 wt%) and cyclic (5-40 wt%) methylpolysiloxanes. This parameter control ensures that the mixture maintains stable physical properties during prolonged operation, resolving the contradiction between operational duration and physical property stability.
3Stability of the object's composition
If the composition of siloxane mixtures is allowed to reach equilibrium state at operating temperature, then the chemical stability is improved, but the vapor pressure increases considerably
Solution Approach 1:
The invention applies local quality by creating a non-uniform distribution of siloxane components with different volatilities. The specific mixture of noncyclic and cyclic methylpolysiloxanes in controlled proportions ensures that the less volatile cyclic components dominate the equilibrium composition, thereby achieving chemical stability while suppressing the increase in vapor pressure that would occur with complete equilibration of more volatile components.
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 siloxane mixture maintains constant physical properties such as density, vapor pressure, viscosity, and thermal conductivity over time, reducing the need for additional control measures and extending the operational lifespan of solar thermal devices without substantial increases in material costs.
Implementation Method 1
The composition of siloxane mixtures is temperature-dependent by virtue of rearrangement processes, and as a result is also time-dependent until attainment of the equilibrium state at the chosen temperature
Implementation Method 2
The siloxane mixture maintains constant physical properties such as density, vapor pressure, viscosity, and thermal conductivity over time
Data Source
AI summary
The invention provides mixtures, liquid at 25° C., of methylpolysiloxanes comprising at least two methylpolysiloxanes selected from linear compounds of the general formula I Me3SiO-(Me2SiO)x-SiMe3 (I), and cyclic compounds of the general formula II (Me2SiO)y (II), wherein the mixture comprises at least one linear methylpolysiloxane of the general formula I and at least one cyclic methylpolysiloxane of the general formula II, Me means methyl radical, x has values greater than or equal to zero and the arithmetic mean of x, weighted by the molar proportions, over all linear methylpolysiloxanes is between 3 and 20, y has values greater than or equal to 3 and the arithmetic mean of y, weighted by the molar proportions, over all cyclic methylpolysiloxanes is between 3 and 6, the numerical ratio of the Me3Si— chain ends groups in the compounds of the general formula I to the sum of the Me2SiO— units in the compounds of the general formulae I and II is at least 1:2 and at most 1:10, and further definitions are described in claim 1, and the use of the mixtures as heat carrier fluids.