Experimental investigation of the convection and radiation heat transfer in the tube with core-rod and multi-tube inserts

Abstract

Heat transfer and friction factor characteristics in a circular tube fitted with core-rod and multi-tube inserts at high temperature have been investigated experimentally. In the experiments, ambient air with Reynolds numbers in a range of 6000–20,000 is passed through a circular tube with uniform wall temperature and convection and radiation heat transfer phenomena are studied. Experiments have been performed at four constant wall temperatures in tubes with core-rod and multi-tube inserts. For each wall temperature considered, convection and radiation heat transfer coefficients have been determined. The experimental results show that at uniform wall temperature of 373, 473, 553 and 633 K, the average share of the radiation heat transfer coefficient to the total heat transfer coefficient is 13.9, 18.3, 24.7 and 28.7 % for core rod and 16.7, 19.1, 20.2 and 22.3 % for multi-tube insert, respectively. In addition it was noted that for the mentioned temperatures, the heat transfer coefficient increased by 227, 299, 327 and 369 % for core rod and 289, 407, 505 and 572 % for multi-tube insert, respectively in comparison to the plain tube.