At present, the high pressure water mist fire extinguishing system has been paid attention to and applied in recent years. Water mist technology was first used in other fields, such as agricultural sprinkler irrigation, meteorological artificial fog and so on. After the 1990s, my country began the research on water mist in fire protection, and made breakthroughs, successfully developing a high-pressure water mist fire extinguishing system. It can generate fine water mist with a droplet size between 40 and 200µm through a fine water mist nozzle, which can be used for fire extinguishing in special places, replacing haloalkane fire extinguishing systems.
The high-pressure water mist fire extinguishing system is usually composed of water mist nozzles, connecting pipes, pressure storage cylinder units or continuous pressure pump units (devices). The cylinder system is composed of nozzles, connecting pipes and fittings, pneumatic control valves, check valves, collecting pipes, water storage containers, gas storage containers, detectors, alarm controllers and other components. The hardware and operation of the cylinder system is similar to that of a gas fire extinguishing system. However, the cylinder system is not as good as the pump system in the time and cost of water supply, and the use of a complete or independent cylinder device mainly depends on the number of cylinders required.
The water mist nozzle is a critical part of the system. The main ones used in fire fighting systems are spiral nozzles, impact nozzles, centrifugal atomizing nozzles, etc. The spray particle size of domestically produced water mist nozzles is generally greater than 400urn (Dv0.9>400um). small to limit its application.
The water mist nozzle is a spray component that physically atomizes the gas-water two-phase fluid through mechanical methods such as rotation, impact and jet under a certain working pressure. The control valve is the implementation of the system start, stop and circulation operations. part. The control valve activates various pneumatic cylinder devices, and the control cylinder then activates the driven cylinders of different configurations. The main functions of the control valve are: receiving the signal from the controller, controlling the air supply and water supply of the system, manual emergency operation, and feedback of the opening and closing status of the control valve and the pressure of the gas storage container.
1. Fire extinguishing mechanism and application of fine water mist:
The key to the success of a water mist fire extinguishing system is to increase the surface area of water particles per unit volume. After atomization of water particles, even the same volume of water can increase the total surface area. The increased surface area makes it easier to absorb heat and cool the combustion reaction. The water particles that absorb the heat easily vaporize and increase in volume by about 1700 times. Due to the generation of water vapor, it not only dilutes the concentration of oxygen near the flame, suffocates the combustion reaction, but also effectively controls the heat radiation. It can be considered that the water mist fire extinguishing is mainly through the dual effects of high-efficiency cooling and hypoxia asphyxiation.
2. Water mist nozzle:
A water mist nozzle is a device containing one or more orifices that can atomize water, and it is a key component in the system. The principle of water particles generated by the fine water mist nozzle is one of the following five ways. The liquid is released at a high speed relative to the surrounding air, and is shredded into water particles due to the speed difference between the liquid and the air; To a fixed surface, water particles are generated by collision; two streams of similar composition collide with each other, and each stream forms water particles: liquid vibrates or electrons smash into water particles (ultrasonic and electrostatic atomizers); liquid in a pressure vessel Heated above boiling point and suddenly released to atmospheric pressure (burst liquid sprayer)
The fire extinguishing ability of water mist depends more on the design of the water mist nozzle. At present, the fine water mist nozzles used in fire protection systems mainly include spiral nozzles, atomizing nozzles, impact nozzles, multi-head nozzles, and multi-hole nozzles. The key to improving the water mist system is the application of atomization technology and the development and design of new nozzles.
3. The principle of fine water mist forming:
The water mist nozzle is an important component to atomize the water flow and implement spray fire extinguishing, and it is also the key to the success or failure of the water mist system. The shapes of the nozzles of domestic manufacturers are different, but the fogging principles are similar. It is composed of eight parts such as the nozzle hole. Water with a certain pressure – nitrogen two-phase flow filter screen enters the nozzle, and rotates at high speed along the spiral space enclosed by the spring, nozzle and nozzle core under the action of pressure, and the water is completely removed after the two-phase flow of gas and water reaches the small hole of the nozzle. It is crushed and ejected along the nozzle outlet cone to form tiny mist droplets.
4. the water mist system fire extinguishing mechanism:
(1) Efficient heat absorption.
Since the particle size of the fine water mist is in the range of 40-200 μm, the specific surface area is 1700 times larger than that of ordinary water droplets, and it can be completely evaporated in the fire field. According to the latent heat of evaporation of 100 ℃ water is 2257kJ/kg, the heat absorption power of the water mist sprayed by each nozzle is about 300kW, which shows that its heat absorption efficiency is high and its cooling effect is strong.
After the water mist is sprayed into the fire field through the fine water mist nozzle, it evaporates rapidly to form steam, the volume expands rapidly, and the air is removed, forming a barrier around the combustion object to prevent the inhalation of fresh air. When the oxygen concentration around the combustion object is reduced to a certain level, the flame will be smothered and extinguished.
(3) Block radiant heat.
After the fine water mist is sprayed into the fire field, the steam formed by evaporation quickly covers the combustion material, flame and smoke plume, which has a good barrier to the radiant heat of the flame, and can effectively inhibit the radiant heat from igniting other objects around it, so as to prevent the spread of fire. Effect.
5. the application scope of the system:
The high pressure water mist fire extinguishing system has a wide range of applications. It can extinguish: Class A fires, Class B fires, Class C fires and live fires. Such as: electronic computer room, communication equipment, control room, tape library, library, archives, treasures library, power distribution room, generator room, oil-immersed transformer room, hydraulic equipment, dust removal equipment, painting production line, cable tunnel, subway station Fire protection in other places. However, it is not suitable for fighting fires that react with water and cause burning and explosion. As the use of haloalkane fire extinguishing agents is limited, the application scope of high-pressure water mist fire extinguishing systems is being studied and expanded. In civil buildings, it can be used in high and low voltage power distribution rooms, important electronic communication equipment rooms, oil and gas boiler rooms, diesel generator rooms and other places. In the communication room and the control room, it can be installed under the floor, in the room, on the ceiling, and its main purpose is to scrub the smoke, and the second is to extinguish the fire under the floor. It can also be installed in control rooms of power plants, gas turbines, etc. It is not limited by the place of use, whether it is ships, oceans, or land systems.