Heat loss rates from Hydrogen-Air turbulent flames in tubes

Experiments were performed to study heat fluxes to tube walls caused by propagating turbulent flames and detonations. Tests were made in cylindrical explosion tubes of 174- and 520-mm i.d. with obstacles using hydrogen-air mixtures (10%, 11.5%, and 13% H 2 ) and stoichiometric hydrogen-oxygen mixtures diluted with nitrogen (dilution coefficient g in the range from 0.5 to 5.7). Three different flame-propagation regimes were studied: slow (subsonic) combustion, sonic flames, and detonations. Fast thermal gauges (time resolution <4 ms) were constructed and thoroughly calibrated for the tests. The rate of energy loss from the combustion products was shown to depend significantly on the speed of the flame propagation. The tube diameter did not influence the values of heat fluxes, while the characteristic duration of the process, in addition to the total energy absorbed by the tube walls, differed greatly at two different scales. The main mechanism for the heat losses in the present tests was shown to be the convective heat transfer. Results suggest that qualitative and quantitative accounting for heat losses from the combustion products are necessary for turbulent combustion models to increase the reliability of their predictions.