ORIGINAL Enhancement of convective heat transfer coefficient of ethylene glycol base cuprous oxide (Cu 2 O) nanofluids Ali Hassan 1 & Naveed Ramzan 2 & Asim Umer 1 & Ayyaz Ahmad 1 & Hina Muryam 1 Received: 21 February 2017 /Accepted: 13 July 2017 # Springer-Verlag GmbH Germany 2017 Abstract The enhancement in the convective heat transfer co- efficient of the ethylene glycol (EG) base cuprous oxide (Cu 2 O) nanofluids were investigated. The nanofluids of different volume concentrations i-e 1%, 2.5% and 4.5% were prepared by the two step method. Cuprous oxide (Cu 2 O) nanoparticles were ultrason- ically stirred for four hours in the ethylene glycol (EG). The experimental study has been performed through circular tube geometry in laminar flow regime at average Reynolds numbers 36, 71 and 116. The constant heat flux Q = 4000 (W/m 2 ) was maintained during this work. Substantial enhancement was ob- served in the convective heat transfer coefficient of ethylene glycol (EG) base cuprous oxide (Cu 2 O) nanofluids than the base fluid. The maximum 74% enhancement was observed in convec- tive heat transfer coefficient at 4.5 vol% concentration and Re = 116. Keywords Convective heat transfer coefficient . Ethylene glycol . Nanofluids . Cuprous oxide nanoparticles Nomenclature ρ nf Density of nanofluids(Kg/m 3 ) ρ bf Density of base fluids(Kg/m 3 ) ρ np Density of nanoparticles(Kg/m 3 ) μ Viscosity(kg/(m s)) C p, nf Heat capacity of nanofluids(W/(m 2 K)) C p, bf Heat capacity of base fluid(W/(m 2 K)) C p, np Heat capacity of nanoparticles(W/(m 2 K)) CHTC Convective heat transfer coefficient(W/(m 2 K)) D Diameter of the tube(m) EG Ethylene glycol K nf Thermal conductivity of nanofluids(W/(m K)) K np Thermal conductivity of nanoparticles(W/(m K)) K bf Thermal conductivity of base fluids(W/(m K)) L Length of the tube(m) l Variable length(m) NPs Nanoparticles NF Nanofluid Nu Nusselt number P Power supply(W) Pr Prandtl number Q Heat flux(W/m 2 ) Re Reynolds number 1 Introduction Nanotechnology is contributing in many areas of the science and technology. The heat exchanging equipment comprises a sub- stantial percentage of equipments installed in the process indus- tries. As the cost of the materials is going up, it is desired to have compact heat transfer equipment to reduce capital cost of equip- ment. To have the compact heat exchangers, different approaches are available. First approach is to have better designs of the heat exchangers using extended fins of different geometries. But this approach has limitations of pressure drop. Second approach is to use the fluids, which have better thermal properties. The conventional coolants that are generally used in the process industry as well as in the other applications are mostly water, the mixture of water and ethylene glycol of different * Ali Hassan ali.hassan@uet.edu.pk 1 Department of Chemical Engineering, Muhammad Nawaz Sharif University of Engineering and Technology, Multan, Pakistan 2 Department of Chemical Engineering, University of Engineering and Technology, Lahore, Pakistan Heat Mass Transfer DOI 10.1007/s00231-017-2113-5