Natural convection heat transfer around horizontal tube in vertical slot

An experimental and numerical study of natural convection around horizontal tube placed between two isothermal walls of different temperature is presented. Two experimental set-ups are built for visualizing the flow and to measure the temperature around the tube and walls confined in the close cavity. An FEM computer code has been applied for analysing the influence of various parameters on the flow structure and heat transfer. The fluid in slot is air (Pr = 0.71). The measurement are taken for Rayleigh number: for slot Ras=2×107–1×109; for tube Rar=6×102–9×102. On analysing the heat transfer from the tube, it has been found that the intensity decreased and increased unexpectedly. The explanation can be given after visualisation. It is observed that the hot air near the heated wall aspirated the layers of hot air from the horizontal tube. The uplift pressure and the tendency of the system to reach balance causes the air layers of the similar temperature and density to merge. However, this effect (similar to the movement of the hot air in a chimney) also found to be dependent on the intensity of the heat transfer.