# Experimental Investigation on the Cooling and Inerting Effects of Liquid Nitrogen Injected into a Confined Space

^{1}

School of Engineering and Technology, China University of Geosciences (Beijing), Beijing 100083, China

^{2}

Key Laboratory of Deep Geodrilling Technology, Ministry of Land and Resources, China University of Geosciences (Beijing), Beijing 100083, China

^{*}

Author to whom correspondence should be addressed.

Received: 15 March 2019 / Revised: 16 April 2019 / Accepted: 17 April 2019 / Published: 22 April 2019

As a highly effective and environmentally benign suppression agent, liquid nitrogen (LN

_{2}) has been widely used for fire extinguishing in plants, dwellings, enclosed underground tunnels, and other confined spaces through cooling and inerting. It is of great significance to understand the cooling and inerting effects of LN_{2}injected into a confined space. A confined-space experimental platform was developed to study the injecting LN_{2}into the platform with different injection parameters, such as mass flux, pipe diameter, and inclination angle. In addition, a mathematical model of quantitatively assessing cooling and inerting effects was proposed by using heat transfer capacity, inerting coefficient, and cooling rate. Results showed that the inerting effect was gradually enhanced with a mass flux increasing from 0.014 to 0.026 kg/s and then tended to level off; an appropriate pipe diameter of 12 mm was optimal for the cooling and inerting effects in this experiment. In addition, a positively increasing inclination angle could contribute to the cooling and inerting effects. However, there was little effect on the cooling and inerting with an inclination angle less than 0°. This study can provide technical guidances for environmentally friendly fire extinguishing with LN_{2}in a confined space.