Hydraulic Calculation And Optimization Design Of Compressed Air Foam System

Compressed air class A foam has better fire extinguishing and heat insulation performance,and it has been widely used in fire fighting in petrochemical field in recent years.In this paper,the hydraulic calculation of compressed air class A foam conveying in pipeline is studied,and the foam mixer and combined elbow are optimized,which purpose is to provide technical support for the application of compressed air type A foam in petrochemical engineering.The structure of the foam mixer was optimized.The results show that: 20 screen-type mixing units installed inside the foam mixer can basically achieve the foam expansion multiple required by the project;According to the spacing of the three mixing elements studied in this paper,it is found that the mixer has the best mixing effect when the spacing is 30 mm;Under the premise of meeting the foaming multiple and flow rate,the smaller the gas-liquid two-phase velocity difference is,the easier the two-phase mixing is.The flow of compressed air class A foam in pipelines with internal diameters of 15 mm,25 mm and 80 mm was studied by hydraulic calculation.The results show that: In the laminar flow condition,the relative errors of the simulated and experimental flow resistance losses of the foam in the horizontal bend pipe and the vertical rise pipe are both less than 10%,and the relationship between the two kinds of pipeline resistance coefficients and Reynolds number is obtained;The flow pressure and density of foam in vertical riser pipe are obtained;The resistance along the pipe dominates the resistance loss of foam flowing through the elbow.In the turbulent state,the spalart-allmaras model was used to conduct numerical simulation of foam transportation over long distances in horizontal straight pipe and bend pipe.The relative error between the simulated value and the experimental value of the resistance loss was within 10%,and the relationship between the resistance coefficient in horizontal straight pipe and bend pipe and the Reynolds number was obtained;Rabinowitsch-mooney equation can accurately calculate the viscosity of foam in horizontal straight pipe with high shear rate;The model of homogeneous flow is used to calculate the resistance loss at the elbow,the relative error between the calculated result and the simulated value of resistance loss is within 15%;The velocity field and pressure field at the elbow were analyzed,and it was found that the velocity field recovered to the state before passing the elbow at 8 diameters downstream of the elbow,and the secondary flow phenomenon at the elbow was analyzed.The numerical simulation of combined bend was studied.The results show that: The greater inlet velocity of the foam,the greater the influence area of the elbow on the downstream flow field;at the given inlet velocity,the optimal solution exists for the length between the two elbows.A method for calculating resistance coefficient of combined bend is presented.