THERMOHYDRAULIC PERFORMANCE OF THREE-FLUID TUBULAR HEAT EXCHANGER USING NANOFLUIDS: EXPERIMENTAL AND NUMERICAL INVESTIGATIONS

Abstract

Improving thermal and hydraulic performance of heat transfer devices has been a main area of interest in recent research and investigations. Replacing conventional heat exchangers with three fluid heat exchangers could play a big role in supporting the growing needs of higher efficiencies in these devices. In the present study, numerical and experimental investigation of a three-fluid tubular heat exchanger with nanofluid has been carried out. The study addresses the heat transfer and pressure drop performance of the selected heat exchanger using nanofluid. The effects of Reynolds number, volume concentration of nanoparticles, and flow arrangements on heat transfer and pressure drop has been conducted. Reynolds numbers ranging from 2500-10,000 and particle concentrations at 0% (for pure water), 1, 2, and 3% have been used as operational parameters for both the approaches. For numerical simulation, single-phase as well as multi-phase approaches have been implemented for further understanding of nanofluid behavior. Furthermore, optimization of operational parameters has also been done to determine optimal working conditions. For experimental investigation, water-based Al2O3 nanofluids were prepared at three levels (1%, 2%, and 3%) of volume concentration. The nanofluid used in the present study is Al2O3-water with 50 nm nanoparticle size. Turbulent flow (Re: 2500-10,000) of nanofluids through the inner annulus of the three-fluid tubular heat exchanger has been considered. Experiments were conducted for four flow arrangements: parallel, parallel-counter, counter-parallel, and counter flow. Two-thermal communication was considered as the cold nanofluid receives heat from the hot and intermediate temperature fluids simultaneously. The uncertainty analysis has been carried out and the maximum was found to be 2.65%, 10.54%, and 11.87%, respectively for Reynolds number, Nusselt number and friction factor. Numerical and experimental results displayed non-monotonic variation of thermal performance factor with Reynolds number. However, thermal performance factor increased with the increase in volume concentration of nanoparticles for all the flow arrangements. Furthermore, the overall effectiveness of three-fluid tubular heat exchanger increases with the increase in nanofluid flow rate and volume concentration of nanoparticles. Effectiveness was found the highest for counter flow arrangement and lowest for parallel flow arrangement, with counter-parallel and parallel-counter ranking in between. The results of the investigation revealed that the use of nanofluids provides an enhancement in thermal and hydraulic performance.