HEAT TRANSFER OF FLAT-OVAL TUBE BUNDLES IN CROSS FLOW

The goal of this work was to create generalized relationships for calculating the convective heat transfer coefficients of staggered bundles of flat oval tubes based on the obtained experimental data for recuperative heat exchangers of the “gas-gas” type in a wide range of changes in the geometric characteristics of tubes, bundles and flow regime parameters. An analysis of the known literature data by the authors shows that no systematic studies of the influence of geometric and step characteristics of tubes on heat transfer and aerodynamic drag of flat-oval tube bundles during transverse air flow in a wide range of Reynolds numbers were carried out. The results of numerical modeling are not experimentally confirmed. The published works contain fragmentary data, which are usually of carried a private character. Presented experimental studies of convective heat transfer of staggered bundles of flat oval tubes with transverse air flow around them were carried out in the range of Reynolds numbers 2000 < Red1 <30000 with a variation in the relative elongation of the profile of the flat oval tube d2 / d1 from 2 to 5, and the ratio of the transverse tube pitch to the longitudinal S1 / S2 ranged from 0,4 to 1,45. The influence of geometric and operational parameters on the heat transfer of bundles is established. The heat transfer rate of staggered bundles of flat-oval tubes when varying the elongation of the tubes profile d2 / d1 in the range from 2 to 5 changes by (10-25) %, and when varying the step characteristics of the tubes at d2 / d1 = const by (8-12) %. Evaluation of the accuracy of the generalizing formulas, which was carried out on the basis of an array of experimental data for the 49 studied bundles, indicates that the difference between the experimental and calculated values of the Nusselt numbers does not exceed ± 10%. Design relationships are proposed for determining the heat transfer coefficients of staggered bundles of flat-oval tubes, taking into account the influence of the operating parameters on the heat transfer, the geometric characteristics of flat-oval tubes and bundles and can be used in calculating the heat transfer of air heaters of boiler units, gas turbine plant regenerators