Search

Thermal engineering experiments were carried out with laboratory water-to-water tube-in-tube heat exchangers of the same design parameters with smooth and profiled inner tubes. The tubes were profiled by confuser–diffuser constrictions of the flow section of the inner channel, which were formed by the deformation of their walls and placed along the length at a step that was constant and equal for all profiled tubes. The obtained results showed a dependence of the heat transfer enhancement in the tube channel on the Reynolds and Prandtl numbers, with the dependence on the latter being much stronger than that on the former, at least in cases where the heat carrier is water. [ABSTRACT FROM AUTHOR]

The results of thermal engineering experiments on a water–water tubular heat exchanger of the tube-in-tube type with heat transfer intensified by periodic confuser–diffuser elements arranged along the channel length at a step equal to the doubled inner diameter of the inner tube are compared with the results of experiments on a similar smooth-tube heat exchanger and the results of calculations by the criterial models of B.S. Petukhov, S.S. Kutateladze, W. Nusselt, and M.A. Mikheev. The comparison showed that the ratio of heat transfers in the tube channels of the intensified and smooth-tube heat exchangers, being a function of the Reynolds and Prandtl numbers, depends on the latter to a much higher extent. As a consequence, at least for water as a medium where the Prandtl number depends on temperature, the intensification of heat transfer is determined not only by the profiling parameters, but also by the parameters of the heat transfer process itself. In addition, the comparison demonstrated that the replacement of experimental data on smooth-tube heat exchangers by the results of calculation by the criterial models worsens the accuracy of estimates and leads to an increase in deviations with an increase in the Reynolds number Re. [ABSTRACT FROM AUTHOR]

It is known that the results of calculations for various criterial models of convective heat transfer may differ from each other, which, according to existing ideas, is usually associated with different operating conditions of the heat exchangers under study. In the work, thermal engineering experiments are carried out with a laboratory water-to-water tubular heat exchanger of the "pipe-in-pipe" type with smooth tubes at normal pressure and moderate temperatures at various inlet temperatures of the heat carriers and their flow rates. The results of the experiment are compared with the results of calculations based on the models of B.S. Petukhova, S.S. Kutateladze, Nusselt, and M.A. Mikheev. The comparison shows that the discrepancies between the experiment and the models, as well as between the models themselves, stem not only from experimental inaccuracies, but also from inaccuracies in the models themselves. [ABSTRACT FROM AUTHOR]

Since it is known that the results of calculations for various criterial models of convective heat transfer may differ from each other, we compare the experimental data on heat transfer obtained in experiments on laboratory water-to-water tubular heat exchangers with smooth tubes of three different diameters at normal pressure and moderate temperatures with the results of calculations for the criterial models of B.S. Petukhova, S.S. Kutateladze, Nusselt, and M.A. Mikheev. The experiments are carried out on a two-dimensional flow grid of a tube and inter-tube channel, which makes it possible, in accordance with the previously developed method, to construct the longitudinal profiles of the heat-exchange parameters. The results of processing of the experimental data using the method of average values and the longitudinal profiles demonstrate good agreement when compared with each other. It is found that the deviations of the experimental data from the results of calculations using criterial models are systematic in nature; depend on the range of the defining parameters, i.e., the Reynolds and Prandtl numbers Re–Pr in which they are compared; increase with increasing Re number; and, depending on the Pr numbers, have an extremum. [ABSTRACT FROM AUTHOR]