| The horizontal tube falling film evaporator is a key equipment in the low-temperature multi-effect seawater desalination technology,and the centrifugal solid cone nozzle is commonly used to distribute the liquid for the evaporator.The uniformity of the liquid distribution is directly related to the efficiency and stability of the evaporator.In this paper,the internal and external flow field of a swirl solid cone nozzle is experimentally studied.The corresponding relation between inlet pressure and the flow parameters and flow characteristics,the interaction between the internal and external flow field as well as the distribution characteristics of the spray density under the interference of double nozzles are explored.The main research work includes the following aspects:(1)On the basis of consulting a large number of domestic and foreign literatures,a basic understanding of the contents and progress of the experimental research on the centrifugal nozzle is obtained.Following the principle of innovation and practical engineering application,the experimental scheme of is determined to both satisfy the current research content and to leave space for further improvement in the future.(2)A transparent solid cone nozzle is made according to the similarity principle.The flow rate,spray cone angle,spray density and other parameters are experimentally studied to set up a uniform law between the internal and external flow fields and to analyze the influence of the nozzle structure and inlet pressure on the spray characteristics.The experimental results show that when the inlet pressure increases,the flow rate increases,but the growth rate tends to be slow down.The spray cone angle increases at first,and then it remains unchanged which is limited by the angle of the expansion section.A higher inlet pressure corresponds to a shorter time for the nozzle to reach the spray stability.The spatial-dependent spray density increases with the increase of inlet pressure,and the increase amplitude also varies in different positions.The spray density is low in the center and the marginal area,but is higher in the vicinity of the off-center area.The nozzle will entrain air and air flow field with different shape characteristics will be formed under different pressures.There is a certain relationship between the uneven distribution of spray density and the air cone flow field.(3)According to the principle of peak-load shifting,the experimental study and theoretical analysis are carried out focusing on the spray density distribution of double nozzles at two different distances and under multiple inlet pressure conditions.It is found that the spray inhomogeneity caused a single nozzle can be greatly improved by the nozzle interference.Under the interference of two nozzles,the distribution of the spray density is well symmetrical along the center which is very different from that of a single nozzle.Increasing the inlet pressure can enhance the spray uniformity,and changing the distance between the two nozzles will also change the uniformity of spray.To sum up,the experimental research and theoretical analysis of swirl solid nozzles have been carried out in this paper.The relation between the nozzle characteristic parameters is obtained.The effects of the nozzle geometry and inlet pressure on the spray characteristics are understood,and the shape characteristics of the gas-liquid two phase flow field and the distribution of the external spray density are also captured.The distribution of the spray density with double nozzles interference under different working conditions provides a certain data support and theoretical guidance for the rational arrangement of the multi nozzle distributor as well as the improvement of the working performance and stability of the horizontal tube falling film evaporator. |
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