Experimental investigation on heat transfer characteristics of water flow in a narrow annulus

Experiments are carried out to investigate the convection heat transfer characteristics of water flow in a narrow annulus. The experiments include three flow directions, which are horizontal flow, upward flow and downward flow. Experimental results show that the heat transfer characteristics of single-phase water flow in the narrow annulus are different from those in circular tubes. The transition from the laminar to turbulent heat transfer in the narrow annulus is earlier than that in circular tubes. When the Reynolds number is lower than 150, the axial heat conduction has an important influence on the overall heat transfer and the heat transfer deteriorates here. Two techniques, i.e. measuring wall temperature and separating coefficient, were adopted in processing the experimental data. The results obtained by these two data processing techniques are different, especially when the Reynolds number is lower than 400. The differences between these two techniques are analyzed.