83 Heat Transfer Characteristics of CNT-Heat Transfer Oil Nanofluid Flow Inside Helically Coiled Tubes under Uniform Wall Tempoerature Condition

In the present work, an experimental investigation is carried out to study the heat transfer characteristics of a temperature dependent nanofluid, CNT-heat transfer oil, inside inclined helically coiled tubes. The investigation has covered the range of Reynolds number (Re) from 10 to 1900, pitch to tube-diameter ratio (P/d) from 1.6 to 6.1, coil to tube diameter ratio (⁠D_c/d⁠) from 14.1 to 20.5, and coil-length to tube-diameter ratio between 167.4 and 251.3. The nanofluid was prepared by dispersion of carbon nano tube (CNT) nanoparticles in heat transfer oil and stabilized by means of an ultrasonic device. Data was acquired for thermal entrance region under laminar flow regime and uniform wall temperature condition while the applied viscous nanofuid flow was assumed to be hydrodynamically fully developed. The uniform wall temperature condition was achieved by locating helical coiled tubes in the reservoir full of saturated steam. Thermal performance of the coiled tubes has been assessed for CNT-Heat transfer oil nanofluid with different particle weight fraction from 0.1% to 0.4%. In addition to considerable heat transfer enhancement due to the utilization of helically coiled tubes instead of straight ones, substantial heat transfer augmentation was observed due to the nanofluids application instead of pure base fluids.