Development of the heat transfer surfaces on the tube inside makes it very
difficult or even impossible to determine the heat transfer coefficient
analytically. This paper presents the experimental determination of the
coefficient in an internally rifled tube with spiral ribs. The tests are
carried out on a laboratory stand constructed at the Institute of Thermal
Power Engineering of the Cracow University of Technology. The tube under
analysis has found application in a supercritical circulating fluidized bed
boiler. The heat transfer coefficient local values are determined for the
Reynolds numbers included in the range of ~6000 to ~50000 and for three
ranges of the heating elements power. As the medium flows through internally
rifled tubes with spiral ribs, the heat transfer process gets intensified
compared to similar processes taking place in smooth tubes. Based on the
obtained experimental data, a correlation is developed enabling
determination of the dimensionless Chilton-Colburn j factor. The equation
form is selected so that a comparison with existing results of tests
performed on rifled tubes can be made. Comparing the Nusselt number values
calculated based on the developed correlation with those obtained using
other correlations described in the literature, it can be observed that the
criterial number is about twice higher. The research results confirm the
thesis that the element internal geometry has a sub-stantial impact on the
heat transfer process.