ORC Working Fluid Composition for Thermal Stability and Lubrication
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Solution Overview
Problem
The existing steam cycle processes, particularly in organic Rankine cycles, face challenges in achieving thermal stability and long-term durability of the working fluid when used in conjunction with internal combustion engines, especially in high-temperature applications like heat exchangers in motor vehicles, due to the requirements for a lubricant that is thermally stable and largely immiscible with the working medium.
Innovation Solution
A working fluid composition comprising a C1 to C4 alcohol or C3 to C4 ketone as the working medium, mixed with a hydrocarbon lubricant and optionally an emulsifier, where the lubricant has a specific viscosity range and is not soluble in the working medium, ensuring adequate lubrication and thermal stability, and the addition of optional components like antiwear agents and antioxidants for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lubricant is added to the working medium to ensure adequate lubrication of the expander, then the lubrication performance is improved, but the thermal stability and chemical resistance of the working fluid deteriorates due to miscibility and degradation at high temperatures
Solution Approach 1:
The patent divides the working fluid into two distinct phases: a working medium phase (organic liquid) and a lubricant phase (hydrocarbon). The lubricant is not completely miscible but forms a separate phase that can be distributed through the system, providing lubrication while maintaining thermal stability of each component in its own phase.
Solution Approach 2:
The patent creates a composite working fluid system combining an organic working medium (such as refrigerants R134a, R125, R12) with a hydrocarbon lubricant (such as HFC oils). This composite system leverages the low boiling point and working efficiency of the organic medium while utilizing the thermal stability and lubrication properties of the hydrocarbon lubricant.
2Reliability
If an organic lubricant such as glycol or polyglycol ether is used to ensure solubility in the working medium, then the lubricant becomes completely soluble, but the viscosity of the working medium increases
Solution Approach 1:
The patent changes the solubility parameter by selecting a hydrocarbon lubricant with specific molecular weight and structure that has limited solubility in the organic working medium. This partial immiscibility prevents excessive viscosity increase while still allowing sufficient lubricant distribution through the system via phase separation and re-mixing cycles.
3Temperature
If the lubricant is evaporated and condensed first in the expander to meet high temperature requirements, then the thermal stability is improved, but the lubricant must have a condensation temperature above the steam outlet temperature which limits lubricant selection
Solution Approach 1:
The patent adjusts the condensation temperature parameter of the lubricant by selecting hydrocarbons with specific boiling points higher than the working medium. This ensures the lubricant condenses after the working medium in the expander, allowing the system to operate at high temperatures while maintaining adequate lubrication, and provides flexibility in selecting from various hydrocarbon options.
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 proposed working fluid composition provides thermal and chemical stability, ensuring the organic Rankine cycle's durability and efficiency in utilizing waste heat from internal combustion engines, with the lubricant being evenly transported and maintaining mechanical energy production over time, even in thermally stressed conditions.
Implementation Method 1
The circuit includes moving parts and requires lubrication
Implementation Method 2
the working medium is heated and evaporated in the evaporator by supplying heat from outside
Implementation Method 3
the working medium is heated and evaporated in the evaporator
Implementation Method 4
By the expansion of the steam, an expander is operated and mechanical energy is produced
Implementation Method 5
an organic Rankine cycle
Implementation Method 6
the working medium is cooled, liquefied in the condenser
Implementation Method 7
the working medium is cooled, liquefied in the condenser
Data Source
AI summary
The present invention relates to a working fluid for a steam-turbine cycle process, said fluid comprising a working medium, a lubricant and preferably an emulsifier. The working medium is a C1 to C4 alcohol and/or a C3 to C5 ketone, optionally mixed with water. The invention also relates to a device for a steam cycle process, which device contains the working fluid, and to the use of the working fluid in an organic Rankine cycle. The lubricant is a hydrocarbon and the emulsifier is a surface-active substance.