EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER IN INTERFIN CHANNELS OF PUNCHED SPIRAL TUBE FINNING

Abstract

To reduce the metal consumption of boilers of steam-turbine power units and waste-heat boilers of gas-steam turbine units, the spiral-tape finning of low-temperature convection heating surfaces is applied. However, the heat transfer in the bundles of such tubes has not been studied sufficiently, the influence of the geometric dimensions of the cut portion of the fins has not been experimentally investigated. In most heat exchange calculation methods, based on the generalization of the results of experimental studies, this influence is also not taken into account. It is proposed to take into account the influence of the finning geometry on heat transfer by introducing correction coefficients in the generalizing equations, determined from the results of a numerical research. To evaluate the validity of the introduction of the results of numerical research into generalizing equations, an experimental investigation of heat exchange in the interfin channels of the punched spiral finning of the tubes is carried out. A research method is developed based on the results of measurements of the surface temperatures of the fins and air in different zones of the interfin channel along its height, as well as the air temperature in front of the bundle and the air flow through the bundle. The study is carried out by placing the calorimeter tubes in the transverse rows of the chess and corridor bundles of tubes at different Reynolds numbers. The results of the investigation of one of the bundle. The calorimeter is installed in the fifth row of a six-row tube bundle with fin interval of Sf = 6 mm and tube steps in the bundle S1 = 85 mm, Ś2 = 85 mm. At the Reynolds number, Red = 10042: the heat flux in the interfin channels Q = 711.0 W, the same according to electrical measurements - 731.0 W; discrepancy - 2.73 %; the heat transfer coefficient in the blade zone is αifcb = 162.0 W/m2°C; discrepancy – 2.88 %. The average surface heat transfer coefficient in the interfin channel is ͞ αifc = 132.35 W/m2°C; by numerical calculation - 122.6; discrepancy is 7.31 %. The average surface heat transfer coefficient of a single transverse row of tubes, taking into account the flow of a part of the air through the intertubular channels, is ͞ αc = 83.05 W/m2°C; the discrepancy is 5.12 %. In the remaining experiments, the difference in the values of the heat transfer coefficients is 3.19 ... 15.7 %. The results of the investigation confirm the validity of the use of the results of numerical investigation in generalizing equations for calculating the heat transfer of bundles of tubes with a spiral finning