Experimental Analysis of Heat Transfer Enhancement in Double-Pipe Heat Exchangers Using Nanofluids

Abstract

This paper presents a reproducible experimental methodology for evaluating heat-transfer enhancement in a counter-flow double-pipe heat exchanger using Al₂O₃/water nanofluids. The study is designed to isolate the effects of nanoparticle volume concentration and flow rate on heat-transfer coefficient, Nusselt number, exchanger effectiveness and pressure drop. Stable nanofluids at 0.25–1.00 vol.% are prepared by a two-step dispersion method and circulated through the inner tube while hot water flows through the annulus. Inlet, outlet and wall temperatures, volumetric flow rate and differential pressure are recorded after steady state is achieved. The thermal performance is evaluated from an energy balance, logarithmic mean temperature difference (LMTD), overall heat-transfer coefficient, Reynolds number, Nusselt number and effectiveness. The experimental sequence includes a distilled-water baseline and uncertainty analysis so that enhancement can be distinguished from measurement scatter. Literature up to 2018 indicates that nanofluids can improve convective heat transfer in double-tube exchangers, but increasing concentration may also increase viscosity and pumping losses [5–12]. The proposed design therefore evaluates thermal gain together with hydraulic penalty and identifies a practical concentration range rather than maximizing heat transfer alone. An illustrative result set shows the expected monotonic rise in heat-transfer coefficient with Reynolds number and nanoparticle concentration, with a moderate pressure-drop penalty.