Study On The Mixer And Piping System Of The Compressed Air Foam Fire Truck

Compressed air foam fire truck is an important rescue equipment for all kinds of fire rescue at home and abroad.It is very important to develop efficient compressed air foam mixer and pipeline system.The optimization of the mixer structure makes the gas-liquid mixing effect good,can spray foam with good stability and uniformity,and the optimization of the vehicle pipeline system structure can reduce the pressure loss,improve the fire engine injection flow and range,which has important research significance.In this thesis,the structure and performance of the mixer and pipeline system of compressed air foam fire truck are studied,and the research of the mixer structure and performance parameters on foam mixing characteristics and pressure loss analysis of pipeline system is explored,so as to clarify the gas-liquid mixing mechanism and pressure loss law and provide corresponding theoretical guidance for engineering application.The main research contents and conclusions of this thesis are as follows:（1）Study on structural optimization of compressed air foam mixer.The internal flow field of the mixer was analyzed by numerical calculation method,and the traditional mixer,concentric block mixer and block mixer were compared respectively.Thirdly,according to the gas-liquid two-phase flow law of different structural parameters,the influencing factors of the baffle on gas-liquid mixing mechanism are compared.The results show that: 1.The determinate block mixer is more suitable for compressed air foam mixing;2.The optimal structural parameters are determined as follows: 2 layers,15 mm distance between blocks,18°chamfer Angle of blocks and 45° clearance ratio of blocks.The optimized block mixer produces a high multiple,uniform foam fluid.（2）Performance parameter optimization and foam performance research of compressed air foam mixer.PBM group equilibrium model and bubble dynamics were used to analyze the particle size distribution.The uniformity and stability of gas-liquid mixture were taken as the main performance parameters to analyze the influence of different foam flow rate,the proportion of gap between the baffle（the cross-sectional area of the fluid flowing through）and the length of the pipe on the foam performance.The results show that the uniformity of foam increases with the increase of flow rate.In different clearance ratios,the foam particle size decreases with the decrease of fluid cross sectional area.The foam particle size decreases with the increase of pipe length.After optimized design of structure and performance parameters,combined with the test of foaming multiple and liquid out time,it is verified that the block mixer has better foam mixing effect and improves the foam performance.（3）Study on mechanical properties of fluid-structure interaction in compressed air foam mixer.The fluid-structure coupling analysis is carried out to analyze the influence of pipeline material strength,structural vibration characteristics and support stiffness through stress and deformation under different working conditions,constraints and structures.The results show that the block mixer is not suitable for high pressure conditions and semi-constraints.The change of block quantity layer from 1 layer to 2 layer is small.The vibration amplitude of pipeline structure increases with the increase of pipeline length.Under different structures and working conditions,better structures and constraints ensure excellent stability and reliability of the internal structure installed in the mixer and ensure the stability of the pipeline system.（4）Pressure loss analysis and optimization of compressed air foam mixer for piping system.By using computational fluid dynamics and flow field numerical calculation method,the relationship between the pressure loss of different mixers and the pipeline system was analyzed,and the pressure loss of the outlet pipe,the gun pipe and the self-protection pipe was analyzed respectively,and the law of the minimum pressure loss of the pipeline was found out.The results show that: 1.The influence of the baffle mixer on the pressure loss of the pipeline system: the pressure difference of the inlet and outlet of the foam mixture is greater than that of the inlet and outlet of the inlet and outlet of the outlet pipe and the gun pipe;In the pipeline of self-preservation system,the difference of pressure between them is very small.2.The law of reducing local pipeline energy loss: the pressure loss of different gun pipelines is related to pipeline distance,elbow number and elbow Angle;The pressure loss of the length of rightangle bend connecting reducing joint is inversely proportional to its length.The optimal pipe diameter ratio of step pipe diameter change is 2.5:1.25:1.Finally,combined with the hydraulic performance test of fire truck,the practicability of installing the block mixer is verified to reduce the energy loss of pipeline system and ensure the rationality of pipeline system design.