Research On Flow Characteristics Of Compressed Air Foam In Pipe Of Elevating Fire Truck

Fire extinguishing technology using compressed air foam is a new way to extinguish fire.which has been developed rapidly in recent years at home and abroad and has been successfully applied in fire fighting for petrochemical industries,etc.With the demand for obstacle-crossing and high-altitude fire extinguishing,the influence of rheological characteristics,pressure gradient changes,and flow characteristics and patterns of the compressed air foam flow in long fire fighting pipes on piping systems is the problem that restricts the effective delivery of fire-fighting materials in the pipe of towers fire trucks.Therefore,this thesis researches the rheological characteristics of compressed air foam in the pipe by means of theoretical research,numerical analysis,and experimental results to provide the theoretical and experimental basis for the flow law of compressed air foam,pressure drop and vibration characteristics of flow pipe,flow law in long pipe and other flow characteristics such as foam spray trajectory.In order to reveal the morphological distribution of compressed air foam and grasp the morphological and microstructural diagrams of foam,the evolution of foam is recorded and analyzed by microscope to get the conditions for the formation of uniform foam structure with high foaming multiples;based on the energy conservation equation,the pseudoplastic power law model,and the influence of Reynolds number on the friction coefficient,the constitutive equation and the pressure loss model applicable to compressed air foam are derived;based on the vibration equation of single-phase fluid conveying pipe and considering the linear velocity and mean flow velocity of foam,the vibration equation of pinned-pinned pipe conveying foam flow is studied and the fundamental natural frequency solutions for first two orders are obtained,providing a theoretical method to reduce the instability caused by resonance for engineering applications.In order to optimize the design of the foaming device that fits the test bench and the compressed air foam system,the CFD-FLUENT numerical simulation method is used to compare the characteristics of the spiral foaming device and the baffle foaming device from the gas-liquid content ratio,the velocity and the pressure distribution,and to optimize the design of the foaming device.The PID closed-loop feedback control is adopted to design and realize real-time matching display,automatic deployment and self-control.The foam control system with self-control and precise proportioning is designed to clean up the foam generating system with stable flow rate and stable pressure fluctuation.It can achieve precise control of different proportions and lay the foundation for experimental research.In order to obtain the flow distribution for different mixture proportions and gas-liquid proportions,a high-speed image particle acquisition system is used to study the foam flow distribution in the straight pipe.And observe the foam with different proportions,measure the foam multiplier and foam viscosity and find a model suitable for describing the flow characteristics of compressed air foam through test regression.Based on the consistency coefficient,rheological index and power-law fluid model,this thesis analyzes the pressure loss model of compressed air foam and the interrelationship of main parameters through experimental regression to provide a theoretical method for effectively revealing the rheological characteristics and pressure loss law of compressed air foam.In order to realize the experimental research of fire fighting pipe on a large scale,we independently researched and developed the vehicle-mounted compressed air foam system and studied the flow characteristics of different proportions of formed foam;this thesis studies the pressure loss of compressed air foam in heterogeneous flow pipe and the pipe vibration caused by gas-liquid mixed foam and got the local resistance pressure loss calculated by homogeneous flow method.The local resistance coefficient of the tested control valve is obtained by experimental data regression to provide the theoretical basis for component selection and provide the basic vibration test data and the basis for pipe selection in the pratical engineering.In order to accurately calculate the energy loss of the piping system and conveying characteristics,this thesis introduced the numerical simulation method for fluid dynamics and proposed the lightweight calculation method under multi-factor and multi-boundary constraints of piping pressure loss,strength and stability;against the difficult problem of accurate positioning of compressed air foam in fire fighting,the mathematical model of the jet flow trajectory considering the external environment is established and then the mathematical solution method of Longue Coulter is used to obtain the theoretical prediction model of compressed air foam jet trajectory.The test combined with theory is used to verify the jet trajectory model as well as the fire extinguishing of the tower fire truck to provide a theoretical basis for the practical application of compressed air foam in the tower fire truck.The thesis contains 152 figures,38 tables and 146 references.