Success versus failure: Efficient heat devices in thermodynamics

Area of Science:

• Thermodynamics
• Energy Conversion
• Statistical Mechanics

Background:

• Classical thermodynamics defines upper performance limits (Carnot bounds) for energy converters.
• Establishing lower bounds for performance is complex, particularly with convenient definitions.
• Irreversibilities significantly influence device performance and stability.

Purpose of the Study:

• To investigate and unify the concept of lower performance bounds for heat engines, refrigerators, and heat pumps.
• To analyze the role of irreversibilities in device performance and stability.
• To provide a clearer understanding of optimization in finite-time and finite-size systems.

Main Methods:

• Utilizing thermodynamic distance between minimum energy and maximum entropy steady states to assess heat reservoir stability for irreversible engines.
• Applying majorization theory and Pareto front analysis to link stability coefficients with efficiency and entropy.
• Developing a general scheme to define regions of efficient and inefficient heat device operation.

Main Results:

• Identified stability coefficients related to majorization and Pareto fronts, connecting stability with efficiency and entropy.
• Defined a general region of efficient operation for heat devices, with inefficiency arising from dominant irreversibilities.
• Demonstrated the role of figures of merit in finite-time and finite-size optimization.

Conclusions:

• The study provides a unified framework for understanding lower performance bounds in energy converters.
• Irreversibilities are shown to be critical factors determining device efficiency and stability.
• The findings offer a clearer perspective on optimizing energy devices under practical constraints.