| Jet impingement cooling is a heat transfer and flow engineering problem widely studied by researchers and plays an important role in industrial applications and basic research.Among the heat transfer methods of single-phase heat transfer enhancement,jet impingent heat transfer can not only have higher heat transfer capacity,but also conveniently control the geometrical structure and flow parameters of jet flow field.In this paper,a new flower-sharped swirl nozzle was proposed to build an experimental platform for swirl jet impact heat transfer.The flow and heat transfer characteristics of swirl jet impact heat transfer were studied by using deionized water as the jet working medium through numerical simulation and experiments.The main work was as follows:(1)The physical model and mathematical model of swirl jet impinging heat exchange plate were established.Boundary conditions were defined and structured mesh was divided.Based on the experiments of Martin[40]et al,different turbulence models were used to predict impingent jet cooling,and SST k-co was selected as the turbulence model of impingent jet cooling in this paper.(2)The basic flow characteristics and heat transfer characteristics of swirling jet cooling were studied.The flow and heat transfer characteristics were analyzed by flow parameters such as velocity,turbulent kinetic energy and heat transfer parameters such as local Nusselt number and temperature.The flow characteristics of the swirl jet were as follows:the swirl jet has a low velocity at the swirl groove,and the turbulent kinetic energy at the junction of the central hole area and the peripheral swirl groove was high;The heat transfer characteristics of swirl jet were as follows:the coupling surface would form a dark blue annular "cold spot" region(namely the peak region of Nusselt number).The local Nusselt number decreased with the increase of radial distance.The distribution of velocity and turbulent kinetic energy in the free jet area approximately formed an "L" type distribution.The effects of different nozzles number,swirl nozzle section shape and hydraulic parameters on heat transfer were investigated.The swirling jet has faster propagation speed and wider range than the traditional circular jet.For the swirl nozzle,the more the number of nozzles,the better the heat transfer uniformity.Flower shape can make jet nozzle working medium gain more turbulent kinetic energy,The smaller the swirl angle was,the higher the flow impact velocity was,the swirl angle of rotational flow impingement cooling influence on the target board of r/dj<8 or less range.The influence of Re and H on heat transfer was investigated.The local Nusselt number of the target surface decreased gradually with the increase of H.Increasing Re could effectively improve the heat transfer efficiency.(3)The experimental platform of swirl jet impingement finned target plate test system with water as cooling medium was set up.The composition of the test system was introduced,including heating system,temperature measurement system,water supply system,pressure measurement system and flow measurement system.The swirl nozzle physical parts were made by 3D printing.Experimental data processing method was introduced.The specific steps of the experiment were introduced.Analysis ways of experimental were introduced which including instrument errors,environmental error,human error,device error and experimental uncertainty analysis.(4)In order to study the influence of the shape of the impact heat transfer target plate on the heat transfer effect,a 30° flower-shaped nozzle obtained by numerical simulation was used to study the heat dissipation of the finned target plate.The general circular nozzle was selected as the research object to verify the reliability of the simulation and experimental results.The effects of the arrangement of fins,types of fins and hydraulics parameters on the heat transfer effect of the finned plate cooling by swirl jet were studied.The results showed that the temperatures distribution in the target plate obviously were affected by the fin angle.With the increased of fin angle,the temperature field distribution was approximately annular.Compared with the smooth target board,10° oblique 4×4 mm2 type continuous fin in the x=5 mm of the location of temperature was reduced by 25%.Increasing fin could not only increase the cooling effect of stagnation area,but also could improve the efficiency of the heat transfer surface.The heat transfer effect of 10° fin plate was more uniform among three different fin plates with different inclination angles.The heat dissipation effect of discontinuous fin was better than that of continuous fin plate.The impact stagnation point and the Nusselt number of the wall jet area decreased with the increase of the jet distance H,and the effect of swirl on the heat transfer of the target surface woke with the increase of the jet distance H.With the decreased of Re,local Nu changed gently in the region of x<2 mm.When the Re between from 80000 to 120000,Nu in the area of 1<x≤5 mm was high and the change was obviously,indicating that the main area of cyclone shock heat transfer was concentrated in this area.Proposing a new swirl nozzle and finned target,the numerical simulation and experimental study showed that swirl nozzle could effectively improve the heat transfer efficiency and expand the heat transfer area.It is innovative.There is practical engineering application value in direction of heat transfer enhancement in the future.Figure[51]table[9]reference[38]... |
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