Experimental Investigation of Thermohydraulic Performance of Three-Fluid Tubular Heat Exchanger with Al2O3-water Nanofluid

Abstract

The thermohydraulic performance of Al ₂ O ₃ -water nanofluid operating in a three-fluid tubular heat exchanger under turbulent flow conditions is studied experimentally. Water-based Al ₂ O ₃ nanofluids were prepared at three volume fraction levels (1%, 2%, and 3%) by dispersing Al₂O₃ nanoparticles in pure deionized water. Nanoparticles with an average particle size of 50nm and volume concentration of 0% − 3% have been employed. Turbulent flow (Re: 2500-10,000) of nanofluids through the inner annulus of the three-fluid tubular heat exchanger has been considered. The hot fluid flows through the inner tube, the intermediate temperature fluid flows through the outer annulus, and the cold nanofluid flows through the inner annulus. Experiments were conducted for four possible flow arrangements of three-fluid parallel flow heat exchangers: parallel, parallel-counter, counter-parallel, and counter-flow. Two-thermal communication has been considered as the cold nanofluid simultaneously receives heat from the hot and intermediate-temperature fluids. Before applying nanofluids, initial experiments were conducted using pure water to validate the experimental facility. The uncertainty analysis has been carried out, and the maximum was found to be 2.65%, 10.54%, and 11.87%, respectively, for the Reynolds number, Nusselt number, and friction factor at Re = 10,000. For a particular flow arrangement, it has been found that Nu is augmented with the increase in nanofluid flow rate (Re) and nanoparticle volume concentration (ϕ). A maximum enhancement in the Nusselt number has been obtained for the pure water case (ϕ = 0%) in all the flow arrangements. An increase in Nu by 95.31%, 71.83%, 63.04%, and 62.92% has been found for parallel, parallel-counter, counter-parallel, and counter flow arrangements, respectively, with the increase in Re from 2500 to 10,000.