Novec gas is a clean fire extinguishing agent that causes no harm to the human body and is used in ships and marine structures.
This study was performed to develop a design technique for a Novec fire extinguishing system to control the thermal runaway of lithium-ion batteries.
Gas-based fire extinguishing systems pressurize fire extinguishing agents into a storage container and keep them in it before discharging them through the pressure of the container, which means that the time it takes to discharge the entire or some of the fire extinguishing agents is the most important factor in the design process. Since fire extinguishing agents are discharged through the pressure of the storage container, the discharge pressure continues to drop from the point when the discharge starts. It is realistically impossible to take all of these into consideration in the design process.
Gas-based fire extinguishing systems are designed with a predetermined level of average discharge pressure based on the pressure of their storage container. In the present study, the average discharge pressure was set at 42 bars since the pressure of a Novec gas container was 50 bars.
The discharge time of gas-based fire extinguishing systems varies according to the length and size of a pipe and the discharge characteristics of a nozzle. Since the material properties of Novec gas were not revealed, the Fanning coefficients widely used in gas-based piping systems were applied in the study.
The study developed a design technique for Novec gas-based fire extinguishing systems based on the piping network analysis technique, applied it to a Novec gas-based fire extinguishing system designed arbitrarily, and found that its fire extinguishing agents could be discharged within ten seconds.
In addition to the design technique for Novec gas-based fire extinguishing systems, the study analyzed flows to develop a nozzle and conducted an experiment with Novec gas.
A nozzle was designed with a row of orifices based on the nozzles used in CO2 fire extinguishing devices, which are gas-based fire extinguishing systems representing nozzles for Novec gas-based fire extinguishing systems. The single-row nozzle was interpreted for its flows, and the results show that it did not meet the 0.63kg/s recommended by Novec gas-based fire extinguishing system manufacturers. A four-row nozzle was redesigned and interpreted for its flows, and the results met the 0.63kg/s standard and confirmed the discharge characteristics of the nozzle.
A discharge experiment was conducted with Novec gas to further examine the characteristics of Novec gas-based fire extinguishing systems. Since gas-based fire extinguishing systems discharge their fire extinguishing agents in a very short time, the investigator used a precise measuring instrument to measure temperature and pressure.
The experiment discharged CO2 and Novec gas with the same pipe and nozzle to closely observe the discharge characteristics of Novec gas and compare them with those of CO2 whose discharge characteristics were known well. The experiment outcomes demonstrate that Novec gas had excellent cooling effects.