There are some models [1-4] to study about thermal conductivity of nanofluids, where
$$ k_{\rm eff} = k_{\rm eff}(k_0, k_1, \phi) $$
is the general form with $k_0$, $k_1$, and $\phi$ are thermal conductivity of base fluid and dispersed particle, and volume fraction of the solid particle.
- Ji-Hwan Lee, Seung-Hyun Lee, Chul Choi, Seok Jang, Stephen Choi, “A Review of Thermal Conductivity Data, Mechanisms and Models for Nanofluids”, International Journal of Micro-Nano Scale Transport [Int J Micronano Scale Transp], vol 1, no 4, p 269-322, Dec 2010, url http://dx.doi.org/10.1260/1759-3093.1.4.269.
- Periyasamy Mukesh Kumar, Jegadeesan Kumar, Rengasamy Tamilarasan, Seshachalam Sendhilnathan, Sivan Suresh, “Review on Nanofluids Theoretical Thermal Conductivity Models”, Modern Engineering Technology [Mod Eng Technol], vol 19, no 1, p 67-83, Jan 2015, url https://doi.org/10.4186/ej.2015.19.1.67.
- Inês Gonçalves, Reinaldo Souza, Gonçalo Coutinho, João Miranda, Ana Moita, José Eduardo Pereira, António Moreira, Rui Lima 2, “Thermal Conductivity of Nanofluids: A Review on Prediction Models, Controversies and Challenges”, Applied Sciences [Appl Sci], vol 11, no 6, p 2525, Mar 2021, url https://doi.org/10.3390/app11062525.
- Gianluca Coccia, Sebastiano Tomassetti, Giovanni Di Nicola, “Thermal conductivity of nanofluids: A review of the existing correlations and a scaled semi-empirical equation”, Renewable and Sustainable Energy Reviews [Renew Sust Energ Rev], vol 151, no, p 111573, Nov 2021, url https://doi.org/10.1016/j.rser.2021.111573.