Radial Flow Packed-Bed Thermal Energy Storage (TES)
Radial flow packed-bed thermal energy storage (TES) differs from traditional axial flow designs primarily in flow direction and associated performance characteristics. Here is a detailed comparison:
Flow Configuration
- Axial flow TES: Fluid flows longitudinally from one end of the cylindrical packed bed to the other (along the axis).
- Radial flow TES: Fluid flows radially, typically from the center outwards toward the vessel wall or vice versa through perforated pipes.
Thermal Efficiency
- Axial flow systems generally exhibit slightly higher thermal efficiency, reported in the range of 85-94% during thermal charging and discharging cycles.
- Radial flow configurations show comparable but slightly lower thermal efficiencies, usually between 83-91%.
Pressure Drop and Pumping Losses
- Radial flow designs tend to have lower pressure drops compared to axial flow systems, which reduces pumping power requirements and operational costs.
- Axial flow systems typically exhibit higher pressure drops, which can result in greater parasitic energy consumption.
Net System Efficiency (Including Pressure Losses)
- When considering both thermal efficiency and pressure drop, axial flow systems show net efficiencies around 80-87%, whereas radial flow systems range from 74-82% on average. However, certain radial flow designs with optimized aspect ratios can outperform axial flow in net efficiency.
Thermocline Behavior and Thermal Front Spread
- Radial flow packed beds tend to experience a wider thermal front spread (thermocline), which can negatively affect thermal efficiency by causing less sharp separation between hot and cold zones.
- Axial flow designs maintain a narrower thermocline, supporting higher thermal efficiencies but at the cost of greater pressure drop.
Capital Costs and Volume
- Radial flow TES may require additional volume for bypass flow paths, potentially increasing capital costs compared to axial flow systems.
Experimental and Prototype Results
- Laboratory-scale radial flow prototypes have demonstrated improvements in charging efficiency (up to 80%) compared to axial flow counterparts (around 75%), indicating potential practical advantages in some settings.
Summary Table
| Feature | Radial Flow Packed-Bed TES | Axial Flow Packed-Bed TES |
|---|---|---|
| Flow direction | Radial (center to wall or reverse) | Axial (end-to-end) |
| Thermal efficiency | 83-91% | 85-94% |
| Pressure drop | Lower | Higher |
| Net system efficiency (thermal + pressure losses) | 74-82% (some optimized cases higher) | 80-87% |
| Thermocline sharpness | Wider thermal front (less sharp) | Narrower thermal front (sharper) |
| Capital cost implications | Potentially higher due to bypass volume | Lower relative capital cost |
| Prototype results | Improved charging efficiency shown | Established performance |
Conclusion
Radial flow packed-bed TES offers competitive thermal performance with the advantage of lower pressure drops and potential efficiency improvements in some configurations, especially at shorter cycle times or optimized aspect ratios. However, axial flow systems traditionally provide higher thermal efficiency and simpler vessel designs with potentially lower capital expenditure. The choice between radial and axial flow TES depends on trade-offs among thermal efficiency, pressure losses, capital cost, and operational conditions. Ongoing research and prototype testing indicate radial flow TES could achieve high exergetic efficiencies (>95%) with proper design.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/how-does-the-radial-flow-packed-bed-thermal-energy-storage-compare-to-traditional-axial-types/
