Comparison between single- and two-phase heat transfer in a thermally stratified enclosure

• Dimensionless variables can be used to assess thermal enhancement or de-enhancement for single- and dual-phase flow.
• When ΔTBath = 10 °C for particle size, d1 = 134 µm, there was a thermal enhancement compared to when ΔTBath = 20 °C.
• When ΔTBath = 20 °C for particle size, d2 = 230 µm there was a de-enhancement similar to when ΔTBath = 10 °C.

The ratio of local Nusselt number of two-phase natural convection, Nuy, two, to local Nusselt, Nuy, single, number of single-phase natural convection was empirically determined. Gelatin particles were immersed in a custom-built rectangular enclosure. With one end maintained at a thermal high, the particles settling and thermal enhancement characteristics were analyzed. The value of η (η = Nuy, two/Nuy, single) decreased significantly at y/H (dimensionless height) = 0.03 for all cases. The laminar-to-turbulent transition was in the range of 0.136 ≤ y/H ≤ 0.538 for ΔTBath = 10 °C, and 0.136 ≤ y/H ≤ 0.335 for ΔTBath = 20 °C. In general, for dual-phase flow, when ΔTBath = 10 °C for particle size of 134 μm, there was a thermal enhancement as compared to when ΔTBath = 20 °C, where there was a de-enhancement.