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Two Phase Flow Phase Change and Numerical Modeling Part 16

Tham khảo tài liệu 'two phase flow phase change and numerical modeling part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 440 Two Phase Flow Phase Change and Numerical Modeling Peff 1 - fìpữ p c 1 pcp 0 flpcp p ef 1 - Po p 6 7 kf ko kp 2k0 2 kp - k0 kp 2k0 - kp - k0 for spherical particles by EMT 8 . As it was mentioned previously materials with higher thermal conductivity specific heat and density are beneficial for heat transfer. Besides the bulk material properties some specific to nanomaterials phenomena such as surface plasmon resonance effect 23 increased specific heat 64 and heat absorption 65 66 of nanoparticles can be translated to the advanced nanofluid properties in well-dispersed systems. Fig. 2. Interfacial effects in nanoparticle suspensions The size of nanoparticles defines the surface-to-volume ratio and for the same volume concentrations suspension of smaller particles have a higher area of the solid liquid interface Fig. 2 . Therefore the contribution of interfacial effects is stronger in such a suspension 15 34 35 67 . Interactions between the nanoparticles and the fluid are manifested through the interfacial thermal resistance also known as Kapitza resistance Rk Nanofluids for Heat Transfer - Potential and Engineering Strategies 441 that rises because interfaces act as an obstacle to heat flow and diminish the overall thermal conductivity of the system 11 . A more transparent definition can be obtained by defining the Kapitza length lk Rk0 9 where ko is the thermal conductivity of the matrix lk is simply the thickness of base fluid equivalent to the interface from a thermal point of view i.e. excluded from thermal transport Fig. 2 11 . The values of Kapitza resistance are constant for the particular solid liquid interface and defined by the strength of solid-liquid interaction and can be correlated to the wetting properties of the interface 11 . When the interactions between the nanoparticle surfaces and the fluid are weak non-wetting case the rates of energy transfer are small resulting in relatively large values of Rk. The overall contribution of the solid liquid