Abstract：Using electrolytic dendritic copper powder with an average particle size of 55-112 μm as raw material and urea as pore forming agent, adding organic component binder, solvent and other organic matter to prepare slurry, using printing process to prepare capillary wick green, and then degreasing and sintering to prepare capillary wick with thickness of (0.2±0.02) mm. The effects of copper powder particle size, urea addition and slurry organic components on the pore structure and capillary performance of the capillary wick were studied. The results show that the addition of poreforming agent urea can increase the porosity, average pore size and permeability of the capillary wick structure, and reduce the capillary force and fractal dimension. As the particle size of copper powder decreases from 112 μm to 55 μm, the porosity, average pore size, average area, average perimeter, fractal dimension, permeability and capillary performanca parameters of the capillary wick all decrease, while the capillary force increases, its fractal dimension decreases from 1.39 to 1.20. The fractal dimension is related to the permeability, and as the permeability decreases, the fractal dimension decreases gradually. Its capillary performanca parameters are directly proportional to permeability and inversely proportional to capillary force. The capillary wick prepared by 112 μm copper powder has the best performance, the permeability is 2.02×10-10 m2, the capillary force (ΔPc) is 1.29 kPa, and the capillary performanca parameter (ΔPc·K) reaches 2.61×10-7 N.
[1] TANG Y, TANG H, LI J, et al.Experimental investigation of capillary force in a novel sintered copper mesh wick for ultra-thin heat pipes[J]. Applied Thermal Engineering, 2017, 115: 1020-1030. [2] POPOVA N, SCHAEFFER C, AVENAS Y, et al.Fabrication and thermal performance of a thin flat heat pipe with innovative sintered copper wick structure[C]// 41st IAS Annual Meeting, Conference Record of the 2006 IEEE. Tampa, Florida: USA, 2006: 791-796. [3] AOKI H, IKEDA M, KIMURA Y.Ultra-thin heat pipe and its application[J]. Frontiers in Heat Pipes, 2012, 2(4): 6-9. [4] LING W S, ZHOU W, LIU R L,et al.Thermal performance of loop heat pipe with porous copper fiber sintered sheet as wick structure[J]. Applied Thermal Engineering, 2016, 108: 251-260. [5] LI Y, HE J B, HE H F, et al.Investigation of ultra-thin flattened heat pipes with sintered wick structure[J]. Applied Thermal Engineering, 2015, 86: 106-18. [6] JIANG L L, TANG Y, PAN M Q, et al.Phase change flattening process for axial grooved heat pipe[J]. Journal of Materials Processing Technology , 2012, 212(1): 331-338. [7] YANG C, CHANG C, Song C Y, et al.Fabrication and performance evaluation of flexible heat pipes for potential thermal control of foldable electronics[J]. Applied Thermal Engineering, 2016, 95: 445-453. [8] LÜ L, LI J.Managing high heat flux up to 500 W/cm2 through an ultra-thin flat heat pipe with super hydrophilic wick[J]. Applied Thermal Engineering, 2017, 122: 593-600. [9] MANEEMUANG S, KAMMUANG-LUE N, TERDTOON P, et al.Effect of pipe flattening on pressure drop in vapor wick and thermal performanca of miniature round and flat-shape heat pipe with sintered fiber wick[J]. International Journal of Heat and Mass Transfer, 2021, 176: 121416. [10] HUANG G W, LIU W Y, LUO Y Q, et al.A novel ultra-thin vapor chamber for heat dissipation in ultra-thin portable electronic devices[J]. Applied Thermal Engineering, 2019, 167: 114726. [11] CAO Y W, WU D T, GUO C S, et al.Fabrication and capillary performance of bi-porous Ti3AlC2 wicks with controllable pore size proportion using dissolvable pore formers[J]. Journal of Materials Research and Technology, 2021, 15: 4370-4380. [12] 王德志, 王小鹰, 周盼, 等. 烧结工艺对环路热管用Ni多孔毛细芯性能的影响[J]. 粉末冶金材料科学与工程, 2014, 19(5): 687-694. WANG Dezhi, WANG Xiaoying, ZHOU Pan, et al.Effect of sintering process on the performance of Ni porous capillary core for loop heat pipe[J]. Powder Metallurgy Materials Science and Engineering, 2014, 19(5): 687-694. [13] 黄豆. 吸液芯毛细性能及均热板传热特性实验研究[D]. 北京: 北京交通大学, 2020. HUANG Dou.Experimental study on capillary performance of liquid suction core and heat transfer characteristics of vapor chamber[D]. Beijing: Beijing Jiaotong University, 2020. [14] ZHANG J, LIAN L X, LIU Y, et al.The heat transfer capability prediction of heat pipes based on capillary rise test of wicks[J]. International Journal of Heat and Mass Transfer, 2021, 164(10): 120536. [15] RU J M, KONG B, ZHU H, et al.Microstructure, capillary performance and gas permeability of bi-porous copper fabricated by tape casting[J]. Powder Technology, 2014, 256: 182-187. [16] RU J M, KONG B, FAN T X, et al.Porous copper with capillary performance and gas permeability prepared by two-step foaming method[J]. International Journal of Precision Engineering & Manufacturing, 2015, 16(7): 1461-1466. [17] RAK Z S, WALEER J.Porous titanium foil by tape casting technique[J]. Journal of Materials Processing Technology, 2006, 175(1/2/3): 358-363. [18] LIU W, CANFIELD N. Development of thin porous metal sheet as micro-filtration membrane and inorganic membrane support[J]. Journal of Membrane Science, 2012, 409/410: 113-126. [19] HOTZD, GREIL P.Review: aqueous tape casting of ceramic powders[J]. Materials Science and Engineering A, 1995, 202(1/2): 206-217. [20] 陈宁, 肖刚, 袁海, 等. LTCC丝网印刷细微线条技术研究[J]. 电子工艺技术, 2019, 40(2): 89-93. CHEN Ning, XIAO Gang, YUAN Hai, et al.Research on fine line technology of LTCC screen printing[J]. Electronic Process Technology, 2019, 40(2): 89-93. [21] 余芬芬. 高温共烧陶瓷(HTCC)用丝网印刷浆料的制备工艺与特性研究[D]. 武汉: 华中师范大学, 2014. YU Fenfen.Study on preparation process and characteristics of screen printing paste for high-temperature co-fired ceramics (HTCC)[D]. Wuhan: Central China Normal University, 2014. [22] 张世强, 李万河, 徐品烈. 硅太阳能电池的丝网印刷技术[J]. 电子工业专用设备, 2007, 36(5): 55-59. ZHANG Shiqiang, LI Wanhe, XU Pinlie.Screen printing technology of silicon solar cells[J]. Special Equipment for Electronics Industry, 2007, 36(5): 55-59. [23] CHEN Z S, LI Y, YU J, et al.Fabrication and characterization of ultra-thin vapour chambers with printed copper powder wick[J]. Applied Thermal Engineering, 2022, 201: 117734. [24] 王野, 纪献兵, 郑晓欢, 等. 环路热管烧结毛细芯的抽吸特性[J]. 高校化学工程学报, 2016, 30(3): 560-565. WANG Ye, JI Xianbing, ZHENG Xiaohuan, et al.Suction characteristics of sintered capillary core of loop heat pipe[J]. Journal of Chemical Engineering of Chinese Universities, 2016, 30(3): 560-565. [25] 刘培生, 马晓明. 多孔材料检测方法[M]. 北京: 冶金工业出版社, 2006: 100. LIU Peisheng, MA Xiaoming.Detection Method of Porous Materials[M]. Beijing: Metallurgical Industry Press, 2006: 100. [26] 吕泽坤. 图像分形维数的计盒方法改进[J]. 信息科技, 2020(11): 144-145. LÜ Zekun.Improvement of box counting method for image fractal dimension[J]. Information Technology, 2020(11): 144-145. [27] 顾怀章, 孙大方, 罗安智, 等. 激光熔覆多孔生物陶瓷涂层的分形维数分析[J]. 材料研究和发展, 2022, 1(2): 69-73. GU Huaizhang, SUN Dafang, LUO Anzhi, et al.Fractal dimension analysis of laser cladding porous bioceramic coating[J]. Materials Research and Development, 2022, 1(2): 69-73. [28] TANG Y, DENG D X, LU L, et al.Experimental investigation on capillary force of composite wick structure by IR thermal imaging camera[J]. Experimental Thermal and Fluid Science, 2010, 34(2): 190-196. [29] 胡钟元. 分形理论在材料学中的影响综述[J]. 化学工程与装备, 2016, 228(1): 177-179. HU Zhongyuan.A review of the influence of fractal theory in materials science[J]. Chemical Engineering and Equipment, 2016, 228(1): 177-179. [30] LI Q F, ZONG L, JIANG C, et al.Fabrication and capillary characterization of multi-scale micro-grooved wicks with sintered copper powder[J]. International Communications in Heat and Mass Transfer, 2021, 121: 105123. [31] DENG D X, LIANG D J, TANG Y, et al.Evaluation of capillary performance of sintered porous wicks for loop heat pipe[J]. Experimental Thermal and Fluid Science, 2013, 50: 1-9.
2023, Vol. 28 
