Experimental study of natural convection from an array of square fins

In this research, we experimentally investigate natural convection heat transfer of three finned-tube exchangers with an array of square fins and a fin spacing of 5, 9, and 14 mm. The exchangers are in a 5.8m×4m×3m control room where temperature and humidity are automatically controlled with heating, cooling, humidifying, and dehumidifying equipment. We changed the surface temperature of the center tube by varying the input power of the heating element from 8.4 to 56.7 Watts. To measure the temperature of various points on each exchanger, we used ten T-type thermocouples and conduct four experiments for each exchanger and measured its temperature under the steady-state condition. We also calculated average natural heat transfer coefficient. The results show that amount of radiation heat transfer to the surroundings is about 10%, and the contribution of natural convection is approximately 80% of the total input power to the heating element for all experiments. In addition, average natural heat transfer coefficient increases to a certain value and then decreases when fin spacing increases. Finally, from the results of experiments, we established an empirical relationship in an equation for predicting Nusselt number when the Rayleigh number is between 6.5 and 1335, based on the fin spacing.