Fluid hydrodynamics and thermal transports in nanofluids pulsating heat pipes applied for building energy Exploitations: Experimental investigations and full numerical simulations

•Surface tensions on thermal performance were fully investigated for pulsating heat pipe (PHP) with GO (Graphene Oxide) nanofluids;•Thermal performance for modified nanofluid was enhanced compared with traditional nanofluids;•Representative flow patterns from CFD methodology were obtained for PHP with nanofluids;•Nucleate boiling and oscillation of PHP were enhanced at lower surface tension of nanofluids;•PHP with GO nanofluids could be widely applied for built energy conversion and exploitation. Pulsating heat pipe (PHP), as a potential low-grade energy conversion system, has been drawn great attentions in recent years. GO (Graphene Oxide) nanoparticle with SDS (Sodium Dodecyl Sulphate) surfactant based-fluid, as a modified working fluid, was introduced here to enhance thermal performance of PHP. Firstly, an experimental investigation on PHP charged with novel nanofluid has been fully conducted to determine the influence of heat powers and nanoparticle mass concentrations on the thermo-hydrodynamic behavior. Our experimental results indicated that the pumping active and pulsation motions were strengthened for the PHP filled with proposed GO-SDS nanofluid. Average enhancement rates of thermal performance 27 % and 7 % were successfully achieved in optimum concentration 0.1 wt% and filling ratio 60 % of modified nanofluid corresponding to deionized water and GO nanofluid (without SDS solution), respectively. Subsequently, numerical modelling of fluid flow and heat transfer process in PHP with novel nanofluids was established by utilizing CFD/VOF phase interface tracking methodology. The flow behaviors including bubble growth, compression and merging in the process and oscillation heat transfer performance inside PHP were subsequently observed and analyzed. The mechanism of heat transfer enhancement of GO nanofluid PHP with the change of surface tension was further discussed. CFD results demonstrated that lower surface tension of nanofluid causes a 5.11 % reduction in liquid phase fraction of original GO nanofluid, and the activation of nuclear boiling at a lower temperature and the reduction of contact angle. Thereby it promotes the evaporation heat transfer intensity of PHP, then effectively decaying the temperature peak of evaporation section. The modified nanofluid (σ = 42.6 mN/m) was further numerically confirmed a much better heat transfer performance 13 % comparing with that of GO nanofluid without SDS solution (σ = 72.8 mN/m). Present research results