Characteristics of heat transfer and flow of Al2O3/water nanofluid in a spiral-coil tube for turbulent pulsating flow

Abstract

K Thermal conductivity (W/m K) L Length of tube (m) m Mass flow rate (kg/s) N Revolution per minute of the rotating valve spindle (rpm) Pe Peclet number Pr Prandtl number Q Heat transfer rate (W) r Inner radius of tube (m) R Radius of spiral coil (m) Re Reynolds number T Temperature (K) U Average overall heat transfer coefficient (W/m 2 K) V Average velocity of mean flow (m/s) Wo Womersly number, Wo = D i 2 υ ω Greek letters α Thermal diffusivity (m 2 /s) µ Dynamic viscosity (kg/m s) ρ Density (kg/m 3 ) υ Kinematic viscosity (m 2 /s) ω Angular pulsation frequency (1/s) ∞ Ambient medium ϕ Nanoparticle volumetric fraction Superscript -Average Subscripts ave Average i Inlet m Mean o Outlet pu Pulsated st SteadyAbstract In the past two decades, enhancement of heat transfer characteristics of original fluid using nanofluids has been proposed by a large number of researchers. In this paper, an experimental study was carried out to investigate effect of pulsation on heat transfer of fluid flow inside a spiral-coil tube. In order to perform the experiments, a hot water reservoir tank was prepared and the spiral-coil was immersed horizontally inside the tank. Average temperature of the hot water bath was kept constant at 60 °C to establish a quiescent region of uniform temperature. The experiments were conducted in turbulent flow regime using distilled water and Al 2 O 3 /water nanofluid at 0.5, 1, and 1.5 % particle volume concentration. Results showed that overall heat transfer coefficient of the base fluid flow increases by using nanofluid or pulsation into the base fluid flow up to 14 %. Heat transfer results also indicated that combination of the nanofluid and the pulsation into the fluid flow can increase significantly the overall heat transfer coefficient up to 23 %. List of symbolsA Inside heat transfer area (m 2 ) C p Specific heat capacity (J/kg K) D i Inner diameter of tube (m) f Frequency (Hz)

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