curvature ratio and pitch spacing effect of helical coiled tube on pressure drop and heat transfer behavior of tio2/water nanofluid laminar flow

in the present study the effect of curvature ratio and coil pitch for tio2/water nanofluid laminar flow on heat transfer behavior and pressure drop through helical coils with different geometries was investigated experimentally. the tio2/water nanofluids at 0.25% to 2% particle volume concentrations have been prepared by using a two-step method. the experiments were performed for coils with curvature ratio of 10 and 20 and coil pitch of 24 and 42. based on the experimental data, it is found that the nusselt number as well as reynolds number improves while increasing particle volume concentration. this enhancement is due to the higher effective thermal conductivity of nanofluid and also intensification of nanoparticles. besides, increase in density and viscosity of nanofluid compared to the base fluid leads to a pressure drop increment for flow through helical coiled tube. furthermore, the heat transfer rate improves with the increase of pitch coils and decrease of curvature ratio. additionally, curvature ratio shows more significant effect on nusselt number and pressure drop than pitch spacing. 42.1% enhancement on nusselt number is obtained for the nanofluid with 2% volume concentarion in comparison to the base fluid. finally, it is shown that the experimental results and predicted results of nusselt number and pressure drop for nanofluid flow through helical coils hold reasonable agreement.