1. External storage pressure heptafluoropropane fire extinguishing system

The external storage heptafluoropropane fire extinguishing system is based on GB 50370-2005 "Code for Design of Gas Fire Extinguishing System" and GB 25972-2010 "Gas Fire Extinguishing System and Components", NFPA-2000, China Engineering Construction Standardization Association Standard CECS 386:2014 Technical Specification for External Storage Heptafluoropropane Fire Extinguishing System, etc., and the heptafluoropropane fire extinguishing agent is stored in a liquid state in a container, without nitrogen pressurization, and the storage pressure is only the saturated vapor pressure of the fire extinguishing agent. The power gas, which is used as the power for the extinguishing agent to be discharged, is stored in a separate container at a higher pressure. When the system is working, the high-pressure power gas is injected into the fire extinguishing agent storage bottle after depressurization through the pressure reducing device (at the same time, the bottle head valve of the chemical container is opened), and the power gas pushes the fire extinguishing agent (through the siphon and bottle head valve) to move forward along the pipe network system at high speed, and is sprayed out from the sprinkler head within the specified time to implement spray fire extinguishing.

2. Analysis of the differences between the external storage gas fire extinguishing system and the internal storage gas fire extinguishing system

The pushing pressure of the extinguishing agent, as well as the persistence of the pressure and the state of the extinguishing agent are the determinants of the delivery distance of the extinguishing agent. The greater and longer the pushing pressure of the fire extinguishing agent, the farther the conveying distance of the fire extinguishing agent, and the mass flow rate of the fire extinguishing agent in the pipeline is larger than that in the case of gas-liquid two-phase condition, and the larger the mass flow rate, the greater the flow rate per unit time. (Mass flow velocity is defined as the mass of the fluid flowing through the unit flow cross-sectional area per unit time, that is, the mass flow rate borne by the unit flow-through cross-sectional area, usually expressed in G, and the unit is Kg/(m2*s). Calculation of mass flow velocity: G=W/A, where W is the mass flow rate in Kg/s; A is the circulating area, and the unit is m2. ）

When the heptafluoropropane fire extinguishing agent is transported in the pipeline, with the continuous decrease of the pressure in the cylinder and the pipeline, the N2 dissolved in the heptafluoropropane is released along with the fire extinguishing agent vapor, which produces a large amount of gas, and produces the formation of air bags and duplex flow phenomena in the pipeline, which directly affects the fluidity performance of the fire extinguishing agent and the flow of the fire extinguishing agent.

The external pressure storage gas fire extinguishing system is to store the heptafluoropropane fire extinguishing agent and the high-pressure nitrogen as the propellant in different cylinders respectively, and only when the fire extinguishing agent needs to be sprayed, the nitrogen enters the fire extinguishing agent storage cylinder through the pressure reducing valve to promote the fire extinguishing agent spray. Therefore, in the external storage gas fire extinguishing system, because the contact time between high-pressure nitrogen and heptafluoropropane fire extinguishing agent is very short, there is almost no nitrogen dissolved in heptafluoropropane fire extinguishing agent, so that the degree of gas-liquid two-phase flow is greatly reduced, and the single-phase heptafluoropropane liquid can obtain a larger mass flow rate.

The external pressure storage gas fire extinguishing system can provide more power due to the separate storage of nitrogen driven by pressure, and the nitrogen of the external pressure storage gas fire extinguishing system can continue to provide and maintain a higher than the traditional heptafluoropropane chemical cylinder during the application of the agent