Estimating the longitudinal maximum gas temperature attenuation of ceiling jet flows generated by strong fire plumes in an urban utility tunnel

Abstract

This study is centred on longitudinal maximum gas temperature attenuation of ceiling jet flows generated by strong fire plumes in a utility tunnel. A theoretical correlation is derived by incorporating the approximate boundary layer thickness. To obtain related coefficients, a series of full-scale fire tests are also conducted in a utility tunnel under construction. Four Existing models for the estimation of longitudinal temperature decay are compared and analysed in detail. It is seen that none of them are applicable to make satisfactory predictions in current situations, while good agreement is observed between our theory and test data. Additionally, impinging conditions of strong plumes under different ceiling clearances above fuel are divided into three states. We find Stanton numbers in temperature attenuation were overestimated by Delichatsios, and they are reassessed under these states. In these one-dead-end cases, it is also found the end wall has a great impact not only on the upstream flow pattern, but also on the characteristics of downstream flow. As the fire moves away from the dead end, the downstream gas temperature decays more slowly and Stanton number becomes smaller. In an enclosed case, a new expression has also been provided following the same derivation procedure. The present work positively provides a tool for the assessment of thermal environment, heat exposure and estimation of fire detection time in engineering practice.