Optimizing Organic Fluid Pairs for Waste Heat Recovery Systems Boosts Energy Efficiency

Why It Matters

This research provides a data-driven approach for designers to select the most effective working fluids for waste heat recovery systems. By understanding how different fluid pairs impact system performance, designers can improve the economic viability and environmental benefits of renewable energy integration.

Key Finding

The study found that using R245fa for both the heat pump and Organic Rankine Cycle (ORC) in a waste heat recovery system is the most efficient configuration. System performance is sensitive to operating temperatures, with higher evaporation temperatures being beneficial and higher storage temperatures detrimental to efficiency. The ORC evaporator is a significant area of energy loss.

Key Findings

• Increasing heat pump system evaporation temperature improves system power-to-power efficiency.
• Increasing hot storage tank temperature decreases the exergy efficiency of the TIPTES system.
• The working fluid pair R245fa + R245fa demonstrated the best performance.
• The ORC evaporator exhibited the largest exergy destruction (20.2% of total), while the ORC pump had the least (0.5%).
• Using the same working fluid for both heat pump and ORC cycles yields higher efficiency than using different fluids.

Research Evidence

Aim: To identify the optimal organic working fluid pair for a waste heat-driven thermally integrated pumped thermal energy storage system to maximize its power-to-power efficiency.

Method: Thermodynamic analysis and single-objective optimization

Procedure: A thermally integrated pumped thermal energy storage (TIPTES) system using waste flue gas was modeled. Sixteen different working fluid pairs composed of four organic fluids (R600, R245fa, R601a, R1336mzz(Z)) were thermodynamically analyzed. Key parameters like heat pump evaporation temperature and hot storage tank temperature were varied, and single-objective optimization was performed to determine the best performing fluid pair.

Context: Waste heat recovery and thermal energy storage systems

Design Principle

Maximize system efficiency by selecting a single, optimal working fluid and controlling operating parameters to minimize exergy destruction in thermal energy storage systems.

How to Apply

When designing or evaluating thermal energy storage systems for waste heat recovery, conduct a comparative thermodynamic analysis of various organic working fluid pairs, considering single-fluid versus dual-fluid approaches, and optimize operating temperatures.

Limitations

The analysis is based on a specific system model and may not be directly applicable to all TIPTES configurations. The study focused on thermodynamic performance and did not consider economic or environmental factors beyond energy efficiency.

Student Guide (IB Design Technology)

Simple Explanation: Choosing the right liquid (working fluid) for a system that stores and releases heat can make it much more efficient. Using the same liquid throughout the system is better than using two different ones. The best liquid found was R245fa.

Why This Matters: This research shows how a small design choice, like the type of fluid used, can have a big impact on how well a system works and how much energy it saves.

Critical Thinking: How might the cost and availability of different working fluids influence the practical application of these findings in a real-world design project?

IA-Ready Paragraph: This research highlights the critical role of working fluid selection in the performance of thermally integrated pumped thermal energy storage systems. The study found that using a single organic fluid, specifically R245fa, for both heat pump and Organic Rankine Cycle (ORC) components significantly improved power-to-power efficiency compared to using different fluids. This suggests that for design projects involving thermal energy storage and waste heat recovery, careful consideration and comparative analysis of working fluid pairs are essential to optimize energy utilization and system effectiveness.

Project Tips

• When researching working fluids, look for data on their thermodynamic properties and safety.
• Consider simulating different fluid pairs in your design to compare their theoretical performance.

How to Use in IA

• Reference this study when discussing the selection of working fluids for thermal energy storage or heat recovery systems in your design project.

Examiner Tips

• Demonstrate an understanding of how fluid properties influence system performance and efficiency.

Independent Variable: ["Type of working fluid pair","Heat pump evaporation temperature","Hot storage tank temperature"]

Dependent Variable: ["Power-to-power efficiency","Exergy efficiency","Exergy destruction"]

Controlled Variables: ["System configuration (TIPTES)","Heat source (waste flue gas)","Charging cycle (heat pump)","Discharging cycle (ORC)"]

Strengths

• Comprehensive thermodynamic analysis of multiple fluid pairs.
• Inclusion of optimization to identify the best performing configuration.

Critical Questions

• Were the environmental impacts of the tested working fluids considered?
• How sensitive are the results to variations in the waste flue gas temperature and flow rate?

Extended Essay Application

• Investigate the economic feasibility of implementing the optimal working fluid pair in a scaled-up waste heat recovery system, considering fluid cost, system complexity, and energy savings.

Source

Comparative study of thermally integrated pumped thermal energy storage based on the organic rankine cycle with different working fluid pairs · Frontiers in Energy Research · 2023 · 10.3389/fenrg.2023.1338391