Internal Blast II: Gas-Mixing Effect in Large Scale (62 cubic meter) Chamber

The previous paper described how incomplete mixing of detonation product gases with the existing atmosphere could theoretically reduce internal blast quasi-static pressure by a factor of two, without considering fuel-air reactions (1). Extent of gas mixing was inferred in small-scale experiments by measuring pressure and temperature at two locations within a 3-liter chamber; unmixed product gases and atmosphere will be hot and cold, respectively. In this paper the study is extended to large scale, with 1 kg pentolite charges in a 62 cubic meter chamber. Fine-wire thermocouples are fast enough for the expanded time scale of events in the larger chamber, about 5 - 10 ms thermocouple response time compared to about 100 ms rise time to peak pressure, and showed significant unmixed regions of gas. Losses in peak quasi-static pressures of up to 11 percent can be attributed to this mixing effect for pentolite charges in the simple geometries tested. --footnote-- (1) Granholm, R.H. and Sandusky, H.W., ``Factors Affecting Internal Blast,'' Shock Compression of Condensed Matter, Proceedings of the 15th A.P.S. Topical Conference on, June 2007.