Temperature and velocity distributions of a ceiling jet along an inclined ceiling – Part 1: Approximation with exponential function

• Temperature and velocity distributions of a ceiling jet were presented.
• Correlations were developed by applying an exponential function.
• Coefficients were represented as a function of the inclination angle of ceiling.
• The reproducibility of the apex position of the distribution was improved.

It is important to understand velocity and temperature distributions within a ceiling jet, because fire detectors operate within this region. Many researchers have worked positively to clarify ceiling jet properties by means of experimental and theoretical approaches, and sophisticated correlations have been developed to represent temperature and velocity distributions within the ceiling jet that flows under an unconfined, horizontal ceiling with smooth surface. Few studies focus on the ceiling jet that flows under an inclined ceiling. A series of pool fire tests are conducted using a smooth, unconfined model ceiling with varying inclination angles of up to 40°. Temperature distributions are measured using thermocouple rakes consisting of chromel–alumel with a strand wire diameter of 0.2 mm. Velocity distributions are also obtained using particle image velocimetry.On the basis of the measured data, empirical formulae to represent temperature and velocity distributions are developed by applying an exponential function that decays monotonically with the distance from the ceiling surface, and coefficients included in these formulae are represented as a function of the inclination angle of the ceiling. To verify the applicability of the developed formulae to an actual fire, they are compared with the full-scale test data and show a good agreement.