Experimental and numerical study on heat transfer performance of single-phase water in a horizontal mini-annular channel

Based on the author's knowledge, the heat transfer characteristic of water in a horizontal annular channel with annular width of 3.0 mm was investigated using Fluent for the first time. The simulated method is verified using an experimental device and by comparing the results with correlations from the literature. The maximum experimental relative error for Nusselt number was less than 21.03 %. The effects of inlet Reynolds number, heat flux and inlet temperature on the heat transfer performance were studied. Results showed that the flow with the studied inlet Reynolds number range of 1100-1729 in the annular channel is turbulent, indicating that the transition from laminar to turbulent flow occurs early compared to macro channel and thus the annular channel with annular width of 3.0 mm is a mini-channel. Compared to the macro channel, the temperature and velocity fields of mini-annular channel at cross section are more uniform. As the inlet Reynolds number, heat flux and inlet temperature increase, the Nusselt number increases. As the inlet temperature and inlet Reynolds number rise, the heat transfer performance increases while it decreases as the heat flux increases. The increase of Nusselt number is between 144 % and 209 %. The heat transfer performance is also evaluated by the entropy generation rate. Compared to the macro channel, the mini-annular channel exhibits better heat transfer entropy generation rate. As the inlet temperature and inlet Reynolds number increase, and as the heat flux decreases, the heat transfer entropy generation rate decreases.