International Journal of Advanced Thermofluid Research Vol. 5, No. 1, 2019 ISSN 2455-1368 (Online) Published by: International Research Establishment for Energy and Environment (IREEE), Kerala, India. (www.ijatr.org; www.ireee.net) 2 Effect of CuO-H20 and ZnO-H20 nanofluids on the Performance of Solar Flat Plate Collector Abdul Razak Kaladgi 1 *, G. Ramachandran 2 , Mohammed Aneeque 1 , Abdul Rajak Buradi 3 , Vishwanath K C 4 , Mohammed Avvad 1 , Mohammed Kareemulla 1 , Navaneeth .I.M 1 , Rayid Muneer 1 1 P. A. College of Engineering (affiliated to Visvesvaraya Technological University, Belgaum), Mangalore, India. 2 B Vinayaka Mission’s Kirupananda Variyar Engineering College, Vinayaka Mission’s Research Foundation (Deemed to be University), Salem, Tamil Nadu, India. 3 NITTE Meenakshi Institute of Technology, Bangalore, India. 4 Raja Rajeswari College of Engineering, Bangalore, India. * Corresponding Author: E-mail: arkmech9@gmail.com Received: 12 November 2019; Revised: 05 December; Accepted: 18 December; Published: 21 December 2019 Abstract: The solar flat plate collector is commonly used in low-temperature domestic applications for water heating. In this paper, copper oxide (CuO) and zinc oxide (ZnO) nanofluids were synthesized and prepared with water as base fluid, and its thermal efficiency is examined by conducting experiment on a solar flat plate collector. The experiment was conducted under forced flow conditions by varying the volume concentration and flow rates of both the nanofluids. For higher flow rates and volumetric fraction considered, substantial performance improvement was observed. The inclusion of EBT (eriochrome black T) and OA (olylamine surfactant, for CuO and ZnO nanofluid provided the best dispersion stability compared to pure water suspension. Keywords: Solar flat plate collector, Nanofluid, efficiency, forced convection. 1. Introduction The quest for efficient energy continues even today with scientists and engineers inventing new technologies and more efficient devices to harness energy (Abdul Razak et al., 2018; Afzal et al., 2017, 2019; Afzal, Kareemullah, et al., 2018; Afzal, Mohammed Samee, Abdul Razak, & Ramis, 2020; Afzal, Mohammed Samee, Abdul Razak, Khan, et al., 2020; Afzal, Samee, et al., 2018, 2020, 2020; Akthar et al., 2015; Kaladgi et al., 2020; Rahiman et al., 2014; Samee AD et al., 2018). To exemplify an innovative option, nanofluids have revolutionized energy extraction, transmission and storing systems over the years. As the substance transfers from micro to nano shape, different variables necessary to augment thermal efficiency dramatically changes. The variables are viscosity, thermal and electrical