TY - JOUR
TI - Experimental determination of the heat transfer coefficient in internally rifled tubes
AU - Gradziel Slawomir
AU - Majewski Karol
AU - Majdak Marek
JN - Thermal Science
PY - 2019
VL - 23
IS - 14
SP - 1163
EP - 1174
PT - Article
AB - 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.