Working Fluid Fill Control for Low-Temperature Waste Heat Engines
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Solution Overview
Problem
Current waste heat recovery systems are inefficient in utilizing low-temperature and low-flow rate waste heat sources, as they require high-temperature steam-based Rankine cycles, which are costly and impractical for small-scale operations.
Innovation Solution
A thermodynamic cycle-based waste heat recovery system using a working fluid circuit with a high pressure side and a low pressure side, incorporating a waste heat exchanger, expander, recuperator, cooler, pump, and mass management system, which includes a fill system to manage working fluid mass and pressure, allowing for efficient energy conversion from a wide range of thermal sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If steam-based Rankine cycle is used, then high temperature waste heat can be converted to power, but it requires high temperature (600°F or greater) and large heat content, making it impractical for small flow rate and low temperature sources
Solution Approach 1:
The patent changes the working fluid from water/steam to organic fluids with lower boiling points (such as R-134a, R-123, or other organic compounds). This parameter change allows the system to operate effectively with waste heat sources at temperatures as low as 200-400°F, expanding adaptability to various waste heat sources including low temperature and small flow rate sources.
Solution Approach 2:
The patent introduces an organic working fluid as an intermediary substance between the waste heat source and the turbine. This intermediary fluid absorbs heat from diverse waste heat sources (including low temperature sources) and transfers energy to the turbine, enabling power generation from sources that cannot directly drive steam-based systems.
2Power
If steam-based Rankine cycle is used, then power generation from waste heat is achieved, but equipment cost and operating labor are high due to complexity of boiling water at multiple pressures/temperatures
Solution Approach 1:
The patent extracts the phase change process from the water/steam system and applies it to organic working fluids that operate at lower temperatures and pressures. This simplifies the system by eliminating the need for complex high-pressure steam generation equipment, multiple boilers, and associated safety systems required for steam-based Rankine cycles.
Solution Approach 2:
The patent employs organic working fluids that can be used in simpler, less expensive equipment compared to steam systems. The system uses standard heat exchangers and turbines designed for lower pressure applications, reducing both equipment cost and operating complexity while maintaining power generation capability.
3Ease of operation
If waste heat is discharged directly into the environment, then simple operation is maintained, but thermal energy is lost without utilization
Solution Approach 1:
The patent creates a self-service system where waste heat automatically drives the organic working fluid through the thermodynamic cycle, producing power without requiring complex control systems or additional energy input. The system utilizes the temperature differential between the waste heat source and the environment to self-generate electricity, maintaining operational simplicity while capturing energy.
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 system effectively converts thermal energy into mechanical energy, enabling efficient power generation from waste heat sources, including those with low temperatures and small flow rates, by utilizing a carbon dioxide working fluid in a supercritical or subcritical state, thereby overcoming the limitations of traditional Rankine cycles.
Implementation Method 1
a waste heat exchanger in thermal communication with a waste heat source also connected to the working fluid circuit, whereby thermal energy is transferred from the waste heat source to the working fluid in the working fluid circuit
Implementation Method 2
an expander located between the high pressure side and the low pressure side of the working fluid circuit, the expander operative to convert a pressure/enthalpy drop in the working fluid to mechanical energy
Implementation Method 3
a recuperator in the working fluid circuit operative to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit
Implementation Method 4
a cooler in thermal communication with the low pressure side of the working fluid circuit operative to control temperature of the working fluid in the low side of the working fluid circuit
Implementation Method 5
a pump in the working fluid circuit and connected to the low pressure side and to the high pressure side of the working fluid circuit and operative to move the working fluid through the working fluid circuit
Data Source
AI summary
Embodiments provide a heat engine system containing working fluid (e.g., sc-CO2) within high and low pressure sides of a working fluid circuit and a heat exchanger configured to transfer thermal energy from a heat source to the working fluid. The heat engine system further contains an expander for converting a pressure drop in the working fluid to mechanical energy, a shaft coupled to the expander and configured to drive a device (e.g., generator or pump) with the mechanical energy, a recuperator for transferring thermal energy between the high and low pressure sides, and a cooler for removing thermal energy from the working fluid in the low pressure side. The heat engine system also contains a pump for circulating the working fluid, a mass management system (MMS) fluidly connected to the working fluid circuit, and a supply tank fluidly connected to the MMS by a supply line.