Working Fluid Mass Control for Low-Temperature Heat Engines
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Solution Overview
Problem
Current systems for converting waste heat into useful work, such as the steam-based Rankine cycle, are not practical for low-temperature or low-flow rate thermal sources due to high equipment costs and operational complexity, and the organic Rankine cycle faces issues like thermal instability and fluid toxicity.
Innovation Solution
A heat engine system with a working fluid circuit and mass management system that regulates pressure and fluid amount, using a heat exchanger, expander, recuperator, cooler, and pump to efficiently convert thermal energy into mechanical energy, with carbon dioxide as the working fluid, and a mass control tank and control system to optimize fluid circulation and pressure control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If steam-based Rankine cycle is used to convert waste heat into useful work, then power generation capability is improved, but equipment cost and operational complexity increase significantly
Solution Approach 1:
The patent changes the working fluid from water/steam to an organic fluid with lower boiling point, enabling heat conversion at lower temperatures and pressures. This parameter change simplifies the equipment requirements while maintaining power generation capability.
Solution Approach 2:
The patent employs simpler, less expensive equipment components suitable for lower temperature operation, replacing complex high-pressure steam system components with more affordable alternatives that can operate effectively at reduced temperatures and pressures.
2Power
If steam-based Rankine cycle is used, then power generation from high temperature heat sources is improved, but adaptability to low temperature or low flow rate thermal sources deteriorates
Solution Approach 1:
By changing the working fluid to organic compounds with lower boiling points, the system can operate effectively at lower temperature ranges, expanding its adaptability to various thermal sources including low-temperature waste heat streams that cannot drive conventional steam cycles.
Solution Approach 2:
The organic Rankine cycle system is designed to handle a wide range of thermal input conditions, making it universally applicable to diverse heat sources including industrial waste heat, geothermal sources, and low-temperature process streams, whereas steam cycles are restricted to high-temperature applications.
3Adaptability or versatility
If organic Rankine cycle is used to address steam cycle limitations, then adaptability to low temperature thermal sources is improved, but new issues such as thermal instability and fluid toxicity arise
Solution Approach 1:
The patent selects specific organic working fluids with optimized properties for particular application ranges, matching fluid characteristics to the specific thermal source and operating conditions to ensure thermal stability and eliminate toxicity or flammability issues while maintaining adaptability.
4Power
If organic Rankine cycle is used, then power generation from low temperature heat sources is improved, but equipment cost increases due to additional safety measures
Solution Approach 1:
By selecting organic working fluids with favorable safety characteristics (non-toxic, non-flammable), the patent eliminates the need for expensive safety infrastructure while maintaining the ability to generate power from low-temperature heat sources.
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
Enables efficient power generation from a wide range of thermal sources, reducing system complexity and costs by actively managing fluid mass and pressure, thus overcoming limitations of existing cycles.
Implementation Method 1
a first heat exchanger in thermal communication with a heat source to transfer thermal energy to the working fluid
Implementation Method 2
a first expander in fluid communication with the first heat exchanger and fluidly arranged between the high and low pressure sides
Implementation Method 3
a first recuperator fluidly coupled to the first expander and configured to transfer thermal energy between the high and low pressure sides
Implementation Method 4
a cooler in fluid communication with the first recuperator and configured to control a temperature of the working fluid in the low pressure side
Data Source
AI summary
Various thermodynamic power-generating cycles employ a mass management system to regulate the pressure and amount of working fluid circulating throughout the working fluid circuits. The mass management systems may have a mass control tank fluidly coupled to the working fluid circuit at one or more strategically-located tie-in points. A heat exchanger coil may be used in conjunction with the mass control tank to regulate the temperature of the fluid within the mass control tank, and thereby determine whether working fluid is either extracted from or injected into the working fluid circuit. Regulating the pressure and amount of working fluid in the working fluid circuit helps selectively increase or decrease the suction pressure of the pump, which can increase system efficiency.