Evaluation of simplified calculation methods for determining heat transfer between a smoke flow and a sprinkler spray: Fid-Bau Portal

Evaluation of simplified calculation methods for determining heat transfer between a smoke flow and a sprinkler spray

Li, Kai Yuan / Spearpoint, Mike J.

Empirical equations determining heat transfer between a smoke layer and a sprinkler spray have been assessed by using data from several experiments available in the literature. The comparison of the heat loss and temperature of the smoke layer under sprinkler spray shows that the equations developed by Williams for 15 mm pendent conventional sprinklers agree reasonably well with the experimental results. Equations from Spearpoint et al. (Spearpoint MJ, Williams C and Morgan HP. Engineering relationships for calculating the heat transfer from a horizontally-moving Buoyant smoke layer to a sprinkler spray, Fire Research Station, Borehamwood, Herts, UK, 1993 (unpublished)) perform fairly well compared to upright sprinkler experiments especially for a spray sprinkler case but need more validation due to the lack of experimental data. Predictions from the equation given by Heselden are close to the values for a pendent conventional sprinkler with a depth below ceiling less than 0.3 m but values are lower than those given by Williams (Williams C. The Downward Movement of Smoke due to a Sprinkler Spray, PhD dissertation, South Bank University, London, UK, 1993) and by Li et al. (Li SC, Chen Y, Wei D, Yang D, Sun XQ, Huo R and Hu LH. A Mathematical Model for Cooling Effect of Sprinkler on Smoke Layer. In: Proceeding ASME 2009 Heat Transfer Summer Conference, San Francisco, California, USA, Vol. 3, 2009, pp. 7–13). If the effect of smoke downdrag is taken into account, then the Heselden equation performs well whereas the other equations give relatively higher predictions. For a conservative assessment, the predictions from the equation given by Li et al. multiplied by a factor of 1½ are sufficiently in excess of the maximum heat loss values predicted by other equations. However, the heat loss must be compared to the total convective heat flow to avoid getting unreasonable results. The study has been limited by data regarding smoke temperature, layer depth, sprinkler types, and operating pressures. As a result, the conclusions should only be applied to 15-mm nominal sprinklers for a smoke flow with an average temperature of less than 100°C, a depth less than 1.6 m, and water flow rates below 133 L/min. The equations should be used with care for any other conditions.