Citation: Induranga, A.; Galpaya, C.; Vithanage, V.; Koswattage, K.R. Thermal Properties of TiO 2 Nanoparticle-Treated Transformer Oil and Coconut Oil. Energies 2024, 17, 49. https://doi.org/10.3390/ en17010049 Academic Editor: Gianpiero Colangelo Received: 24 September 2023 Revised: 8 October 2023 Accepted: 9 October 2023 Published: 21 December 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Thermal Properties of TiO 2 Nanoparticle-Treated Transformer Oil and Coconut Oil Ashan Induranga 1,2,3 , Chanaka Galpaya 1,3 , Vimukthi Vithanage 1,2,3 and Kaveenga Rasika Koswattage 2,3, * 1 Faculty of Graduate Studies, Sabaragamuwa University of Sri Lanka, Belihuloya 70140, Sri Lanka; ashaninduranga@tech.sab.ac.lk (A.I.); chanakagalpaya@gmail.com (C.G.); vimukkthi@tech.sab.ac.lk (V.V.) 2 Department of Engineering Technology, Faculty of Technology, Sabaragamuwa University of Sri Lanka, Belihuloya 70140, Sri Lanka 3 Center for Nano Device Fabrication and Characterization (CNFC), Faculty of Technology, Sabaragamuwa University of Sri Lanka, Belihuloya 70140, Sri Lanka * Correspondence: koswattagekr@appsc.sab.ac.lk Abstract: This study investigates the impact of incorporating TiO 2 nanoparticles into two types of oils at different temperatures and with varying volume fractions: transformer oil (NYTRO LIBRA) and virgin coconut oil (manufactured by Govi Aruna Pvt. Ltd., Gampaha, Sri Lanka). The nanofluids were prepared using a two-step method by adding CTAB (cetyltrimethylammonium bromide) surfactant. To minimize nanoparticle agglomeration, this study employed relatively low-volume fractions. Ther- mal properties by means of thermal conductivity, thermal diffusivity, and volumetric heat capacity were measured in accordance with ASTM (American Society for Testing and Materials) standard methods using a multifunctional thermal conductivity meter (LAMBDA thermal conductivity meter). The measured thermal conductivity values were compared with theoretical models and previous research findings. It was confirmed that the modification of thermal properties was enhanced by doping TiO 2 nanoparticles with different volume fractions. Keywords: transformer oil; coconut oil; TiO 2 nanoparticles; nanofluids; thermal properties 1. Introduction ‘Nanofluid’ has been a developing topic in the engineering and scientific community since the beginning of the 21st century for various applications in engineering fields ever since its initial introduction by Choi in 1995 [1,2]. The term nanofluid is used to describe a solid–liquid mixture containing nanoscale particles with an average size of less than 100 nm with any kind of a base fluid. Numerous productive research efforts have been carried out using nanoparticles, particularly in the context of thermal conductivity across various fields. These nanoparticle- based fluids, termed nanofluids, have various applications in industrial areas. A rapid increase in the amount of research efforts related to nanofluids over the past two decades can be observed. This literature has investigated several factors that influence the thermal properties of nanofluids, such as nanoparticle concentration, particle size, particle shape, the thermal resistivity of interfacial layers, and Brownian motion [3–5]. It has been reported that nanofluids can be applied in various industrial cooling applications, such as electrical power systems, electronic cooling applications, biomedical systems, and the automobile industry [6–8]. Apart from experimental works, several studies have been carried out to model the thermal conductivity of nanofluids, considering both macroscopic and microscopic properties. However, widening the scope of empirical studies to apply nanofluids in real-time applications and build theoretical models is essential for advancing future heat transfer studies. Researchers have explained numerous mechanisms related to nanofluids that ex- plain the enhancement in the thermal properties of nanofluids, such as Brownian motion, Energies 2024, 17, 49. https://doi.org/10.3390/en17010049 https://www.mdpi.com/journal/energies