MWCNT in PEG-400 nanofluids for thermal applications: A chemical, physical and thermal approach Marco A. Marcos a , Nikita E. Podolsky b , David Cabaleiro a,c , Luis Lugo a , Alexey O. Zakharov b , Viktor N. Postnov b,f , Nikolay A. Charykov d , Sergei V. Ageev b , Konstantin N. Semenov e,b,f, ⁎ a Departamento de Física Aplicada, Universidade de Vigo, Vigo E-36310, Spain b Saint Petersburg State University, Universitetskii pr. 26, Petergof, 198504 Saint Petersburg, Russia c Université Rennes 1, LGCGM, EA3913, F-35704 Rennes, France d Saint Petersburg State Technological Institute (Technical University), Moskovskii pr. 26, 190013 Saint Petersburg, Russia e Pavlov First Saint Petersburg State Medical University, L'va Tolstogo str. 6-8, 197022 Saint Petersburg, Russia f Almazov National Medical Research Centre, Akkuratova str. 2, 197341 Saint Petersburg, Russia abstract article info Article history: Received 27 May 2019 Received in revised form 25 July 2019 Accepted 22 August 2019 Available online 23 August 2019 The paper presents novel data on synthesis, identification and physicochemical investigation of MWCNT/PEG- 400 nanofluids as potential nano-enhanced heat transfer and storage media. In the framework of our research, we studied the influence of temperature and nanoparticle concentration on thermal conductivity (k), viscosity (η), density (ρ) and isobaric heat capacity (C p ), using different techniques such as transient hot wire, rheology, oscillating U-tube, and Temperature-Modulated Differential Scanning Calorimetry (TMDSC), respectively. In order to characterize the new nano-enhanced phase change materials, several dispersions of MWCNT in PEG- 400 were studied, of which the highest concentration presents enhancements in thermal conductivity and ther- mal diffusivity up to 12.7% and 13.5%, respectively. Different approaches were used to theoretically describe those experimental thermophysical properties as functions of temperature and MWCNT concentration. Thus, nanopar- ticle volume fraction dependence of relative viscosity was correlated based on Einstein, Brinkman, Batchelor, Krieger-Dougherty, Maron-Pierce and Brenner-Condiff models, while Hamilton-Crosser, Xue and Murshed models were applied for the description of thermal conductivity behaviour. © 2019 Elsevier B.V. All rights reserved. Keywords: MWCNT PEG-400 Nanofluid Thermal conductivity Viscosity Density 1. Introduction The modification of thermofluids with nanostructured materials has emerged as an interesting strategy to enhance heat transfer perfor- mance in cooling applications. Unlike colloidal suspensions based on particles with micro- or macrometric sizes, nanoparticle dispersions are expected to exhibit good temporal stabilities, as well as lower dy- namic viscosities and clogging issues. The interest in nanofluids as new coolants is proved by the large research developed in this field dur- ing recent years [1–5]. In this sense, it is important to highlight the ex- istence of different studies in which nanofluids based on ceramic or metal oxides, boron nitrides, metal nanoparticles (aluminium, copper or gold), metal carbides, graphite, graphene or other carbon allotropes such as single-walled (SWCNT) or multi-walled carbon nanotubes (MWCNT) were investigated as potential heat transfer media [6,7]. A re- vision of literature shows as nanofluid effective properties can be prop- erly tuned by modifying different affecting to the nanoadditives such as shape, size, solid concentration and nature. In the case of carbon-based nanofluids, authors observed that such characteristics strongly depend on different parameters of the approach used to stabilize the disper- sions, such as the (non-)functionalization of nanomaterials or the addi- tion of surfactants [8–11]. A brief summary of previous investigations on synthesis and thermophysical characterization of single and multi-walled nanotubes nanofluids is presented as follows. Halelfadl et al. [12] experimentally studied thermophysical properties of aqueous dispersions based on MWCNT (diameter of 9.2 nm and length of 1.5 μm) stabilized with so- dium dodecylbenzenesulfonate (SDBS). A Newtonian behaviour was observed in the temperature range T = 273–313 K for all concentrations lower than 0.55 wt.%. The viscosity of Newtonian nanofluids was de- scribed as a function of concentration by using different models (such as Einstein, Brinkman, Brenner, Condiff or Maron-Pierce equations), and values provided by Maron-Pierce model were the most consistent with experimental results (mean-square deviations b5%). Hung et al. [13] studied MWCNT (diameter of 20–30 nm and length of 10 μm) sus- pensions in water with chitosan working both as dispersant and stabi- lizer. Authors found that the sample prepared at 1.5 wt.% of MWCNT and 0.4 wt.% of chitosan showed an improvement in thermal Journal of Molecular Liquids 294 (2019) 111616 ⁎ Corresponding author at: Pavlov First Saint Petersburg State Medical University, L'va Tolstogo str. 6-8, 197022 Saint Petersburg, Russia. E-mail address: knsemenov@gmail.com (K.N. Semenov). https://doi.org/10.1016/j.molliq.2019.111616 0167-7322/© 2019 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq