Capillary performance analysis of copper powder-fiber composite wick for ultra-thin heat pipe
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ORIGINAL
Capillary performance analysis of copper powder-fiber composite wick for ultra-thin heat pipe Junyi Niu 1 & Ning Xie 1 & Xuenong Gao 1,2 & Yutang Fang 1,2 & Zhengguo Zhang 1,2 Received: 4 July 2020 / Accepted: 20 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Excellent ultra-thin heat pipes (UTHP) require a wick with high capillary force (ΔPc) and a good permeability performance (K). In this work, a copper powder-fiber composite wick was fabricated by sintering of the copper powder and fiber mixture. Effects of the copper powder particle size, copper powder volume ratio, as well as the super-hydrophilic treatment were investigated, and the results indicate that the copper powder volume ratio is the most significant factor by orthogonal experiments. Moreover, sensitivity analysis shows that super-hydrophilic treatment contributes the lower capillary force and higher permeability, except when copper powder particle size is high to 80 mesh and powder ratio is low to 20%. Interestingly, the overall capillary performance (ΔPc·K) of the super-hydrophilic treated wicks is significantly improved. Besides, for the super-hydrophilic treated wicks, both the smaller copper powder particle size and volume ratio contribute the higher permeability and better comprehensive performance, even though a worse capillary force. Nomenclature ΔPc ΔPr ΔPg σ θ rpr recr µ dh/dt ρ g ε K ΔPc·K Kji
Capillary pressure, kPa Flow resistance loss, kPa Gravity loss, kPa Water surface tension,N/m Contact Angle between water and the wick Pore radius of the wick, m Effective capillary radius,m Viscosity of water, Pa·s Capillary rising rate, m/s Density of water at 25 , kg/m3 Acceleration of gravity in water at 25 , m/s2 Porosity of the wick Permeability of the wick, m2 Capillary parameter, N Sum of the evaluation index of the level i for factor j
* Xuenong Gao [email protected] 1
Key Laboratory of Enhanced Heat Transfer and Energy Conservation, The Ministry of Education, School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China
2
Guangdong Engineering Technology Research Center of Efficient Heat Storage and Application, South China University of Technology, 510640 Guangzhou, China
Kji Rj j i yji Ni A1, t1, A2, t2, y0
Average value of Kji for factor j Range between the maximum and mini mum values of Kji Factor notation (A, B, C) Level number Result value for factor j at level i Total level number for factor Constant values for the fitted curve
1 Introduction As an efficient passive heat transfer device, heat pipe (HP) has been widely used in high-density and high-integration electronics without extra energy to drive [1–3]. In the past two decades, miniaturization and lightweight of electronics, such as business laptop and mobile phone, have turned out to be the significant demands of consumers. Hence, ultra-thin heat pipe (UTHP) with a better heat transfer performance and a smaller volume, has become the main research hotspot in HP technology[4,
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