In a new study published in Scientific Reports, scientists investigated the use of perforated annular inserts to enhance heat transfer in water-cooled tubes. Combining CFD analysis with experimental testing, the team showed that an optimized element geometry increased the thermo-hydraulic performance factor (THPF) by 77.1%. The authors note that the developed passive method is particularly promising for efficient cooling of absorber tubes in photovoltaic-thermal (PVT) systems.
The work was led by Rasha Abdulrazzaq Jasim, Adnan Ibrahim, and Mohammad Alkhader. In the paper published on September 5, 2026, they describe how the inserts modify the flow structure inside the tube, intensifying convective heat transfer while maintaining acceptable hydraulic losses. The researchers varied parameters to find the optimal combination:
- hole shape
- number of holes per ring
- inner diameter
- number of rings
CFD calculations were carried out at a constant heat flux of 1000 W/m² and Reynolds numbers from 897 to 6505. The best performance was demonstrated by the configuration:
- 🔹 six circular holes per ring
- 🔹 inner diameter of 7.1 mm
- 🔹 five rings
A physical prototype of this design was fabricated and tested on a bench rig; the discrepancy between numerical and experimental data did not exceed ±3%.
The result is important specifically because of the comprehensive evaluation using THPF, which accounts not only for the increase in heat transfer, but also for the rise in hydraulic resistance. This approach makes it possible to improve heat-transfer efficiency in PVT system absorber tubes without a significant increase in energy consumption for heat-transfer-fluid circulation.