方慧, 程瑞锋, 仝宇欣, 李琨. 基于CFD的植物工厂圆形锯齿状水冷LED灯管降温效果模拟[J]. 农业工程学报, 2021, 37(7): 212-217. DOI: 10.11975/j.issn.1002-6819.2021.07.026
    引用本文: 方慧, 程瑞锋, 仝宇欣, 李琨. 基于CFD的植物工厂圆形锯齿状水冷LED灯管降温效果模拟[J]. 农业工程学报, 2021, 37(7): 212-217. DOI: 10.11975/j.issn.1002-6819.2021.07.026
    Fang Hui, Cheng Ruifeng, Tong Yuxin, Li Kun. Numerical simulation of the cooling efficiency of circular serrated water-cooled LEDs using CFD in plant factory[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2021, 37(7): 212-217. DOI: 10.11975/j.issn.1002-6819.2021.07.026
    Citation: Fang Hui, Cheng Ruifeng, Tong Yuxin, Li Kun. Numerical simulation of the cooling efficiency of circular serrated water-cooled LEDs using CFD in plant factory[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2021, 37(7): 212-217. DOI: 10.11975/j.issn.1002-6819.2021.07.026

    基于CFD的植物工厂圆形锯齿状水冷LED灯管降温效果模拟

    Numerical simulation of the cooling efficiency of circular serrated water-cooled LEDs using CFD in plant factory

    • 摘要: 为及时将LED灯管芯片产生的热量传导出去,提升LED灯的性能,延长其使用寿命,设计了一种圆形锯齿状水冷LED灯管,并通过计算流体力学(Computational Fluid Dynamics, CFD)软件构建水冷LED灯管模型,对其降温效果进行研究。在模型中将LED灯珠芯片设置为内热源,热流密度根据灯珠的数量和电光转化效率计算,其值为1.7×107 W/m3。验证试验表明,模拟值与实测值吻合较好,最大误差为16.4%,构建的CFD模型能准确模拟灯管各结构的温度分布。利用验证的模型模拟不同水流速度对水冷LED灯管温度分布及水流压降的影响。结果表明:不同流速下水冷LED灯管的金属散热灯罩、灯珠芯片和水流的温度分布比较均匀,表明该灯管的结构设计合理,灯珠芯片释放的热量能很快传导到水流中并被带走;当灯管入口水流速度从0.10 m/s增加到0.25 m/s时,进出水温差从1.4 ℃下降到0.5 ℃。因此,在对水冷LED灯管进行串联时,可根据进水温度和环境温度的差来计算可串接灯管数量;入口水流速度的增加亦会增加水流阻力,根据模拟得到灯管进出水压差计算出灯管对水流的阻力系数为2.2,为水泵选型提供了依据。

       

      Abstract: LEDs are more commonly used than fluorescent lamps in plant factories with artificial light for energy savings. But the LEDs cannot convert the input power to light at 100 % efficiency. Part of energy can be converted into heat, and then be transferred to the ambient environment, in terms of heat conduction, radiation, and convection. However, heat dissipation of LEDs has become a great challenge, as the power increased while the volume of LEDs reduced. In this study, a circular serrated water-cooled LED was designed to transmit the heat generated by LEDs in time for a longer service life. A three-dimensional Computational Fluid Dynamic (CFD) model was developed to assess the design, where the LED bubbles were set as the internal heat source. The electrical efficiency was assumed to be 32% and 49% in the red and blue LEDs, respectively. The heat flux of 1.7×107 W/m3 was calculated, according to the number of lamp beads and the electrical to light conversion efficiency. The constructed grids were approximately 1 162 800 for each case, including 220 881 nodes with a minimum element size of 2 mm. Much finer meshes were automatically imposed near the bubbles with proximity and curvature size functions in meshing. The SIMPLE was selected for the pressure-velocity coupling. A least-square cell-based scheme was used for the gradient term in spatial discretization. The second-order scheme was applied for the pressure term. The second-order upwind discretization schemes were used for momentum and energy equations, whereas, the first-order upwind discretization schemes were used for turbulence equations, mainly for higher accuracy. The convergence criterion was set as 10-6 on energy and 10-3 on continuity, momentum and viscous terms. Inlet and outlet boundary conditions were set for the numerical solution using the velocity-inlet and pressure-outlet. The inlet water velocity and water temperature were set as 0.2 m/s and 24 ℃, respectively. The simulated value of the LED water-cooled lamp was close to the measured value, with the maximum error of 16.4%, indicating that the CFD model could accurately simulate the temperature distribution of each structure of the lamp. The validated model was used to simulate the influence of different water flow velocities on the temperature distribution and water flow pressure drop in a water-cooled LED lamp. The results showed that the temperature distribution of bubbles and water flow was relatively uniform, and the structure of the lamp was reasonable. The heat released by the bead chip was quickly transferred into the water flow; when the inlet velocity of the lamp increased from 0.10 to 0.25 m/s, and the difference of water temperature between the inlet and outlet dropped from 1.4 ℃ to 0.5 ℃. Therefore, a series of connected lamps were calculated, according to the temperature difference between the inlet water and the ambient air, when the water-cooled LED lamps were connected in series. The inlet flow velocity also improved the flow resistance, where the resistance coefficient of lamps to the water flow was 2.2.

       

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