| In the ventilation and air conditioning system,the purpose of air volume measurement is to test whether the air volume of the air conditioning and ventilation system in each area of engineering construction can meet the requirements of design and use.The air volume measurement at the air inlet can directly reflect the ventilation situation in the actual control area.The accurate measurement of the air volume at the air outlet can realize the efficient and energy-saving operation of the system and achieve the purpose of precisely controlling the indoor environment.In this paper,aiming at the ventilation and air conditioning system with spherical nozzle as the air inlet,in order to improve the measurement accuracy of air volume at spherical nozzle,the measurement of air volume hood was studied by numerical simulation and its structure was optimized.The main research work and conclusions of this paper are as follows:(1)Based on the actual size of the existing air volume cap and spherical nozzle,the physical model of the air volume measurement at the air outlet was established.According to the flow characteristics during the measurement process,the appropriate turbulence model and boundary conditions were selected,and the correctness of the numerical simulation model was verified by experiments.(2)Based on the verified numerical simulation calculation model,the process of measuring the air volume of the spherical nozzle with the existing air volume hood was numerically simulated,the distribution characteristics of the flow field and the measurement errors in the hood were obtained,and the causes of the relative errors in air volume measurement were analyzed.It is found that the main reason for the error in measuring the air volume of the spherical nozzle by the air volume hood is the unreasonable structure of the existing air volume hood,which leads to the uneven velocity distribution of the measured section of the base section,the measurement point cannot express the actual measurement value accurately,resulting in a large measurement error.(3)Through the method of combining orthogonal test and numerical simulation,the air volume measurement of the spherical nozzle was carried out the orthogonal test of the structural parameters of the air volume cap,and the weight of the influence of each structural parameter on the measurement error of the spherical nozzle was studied.The research shows that the weight of the influence of different structural parameters on the air volume measurement accuracy of the spherical nozzle is the base diameter > cover length > cover diameter,and the design of the appropriate base diameter of the air volume cover is the key to accurately measure the air volume of the spherical nozzle.(4)According to hood structure parameters which affect measurement error of the spherical vents weighted order,and the structural parameters of air volume hood was optimized based on improving the measurement accuracy of air volume,through different spherical vents in the numerical simulation under different structural parameters of hood,According to the change rule of relative error index and velocity uniformity index of each measuring point,the design requirements of air volume hood structure parameters to improve the air volume measurement accuracy of spherical nozzle were studied.It is found that when the velocity uniformity index of the designed air volume hood is greater than 0.8,the relative error index of air volume measurement tends to [-3%,3%],and the accuracy of the measurement results is high.The air volume hood under this structure can accurately measure the air volume of the spherical nozzle. |
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