Experimental Study On Forced Convection Heat Transfer In Concentric Annular Channels

The flow and heat transfer in annular channels have been paid more and more attention for their wide application in engineering, such as heat exchanger and nuclear power. However, the previous research in this aspect is deficient, and there are many problems to be solved.In this study, using air as working media, under the condition of inner wall adiabatic and outer wall with uniform heat fluxes, the experimental research and numerical simulation of forced convection heat transfer in circular tube and horizontal concentric annular channels(the sizes of annular gap are 12.5mm, 9mm and 6mm) are carried out, the Reynolds number ranges from 10000 to 60000. The experimental data are analyzed using hydraulic diameter and heat diameter in the study and the effect of mass flow rate, heat fluxes and the size of annular gap on heat transfer is also discussed. The results are as follows:Firstly, the heat transfer coefficient is increased as Re increases in annular channels, the same as that in circular tube. It shows that annular channels may not enhance heat transfer. In this experiment, the annular channel of 6mm gap can enhance heat transfer, but it is not for annular channels of 9mm and 12.5mm gaps. Secondly, using heat diameter is more reasonable than using hydraulic diameter. Thirdly, the heat transfer coefficient is increased with the increase of mass flow rate. On the contrary, the heat transfer coefficient is increased as the annular gap decreases. The heat fluxes change has hardly influenced on the heat transfer coefficient.Fourthly, the friction factors for single phase flow in annuli are smaller than that in circular tube at the same condition, and they are increased as the annular gap decreases. Finally, the simulation value is compared with experimental result. Although there is some deviation, the overall trend is of the same. In addition, the temperature and velocity field are obtained.