Numerical study of using perforated conical turbulators and added nanoparticles to enhance heat transfer performance in heat exchangers

The current study investigates the two-phase turbulentnanofluid flow insidein a heat exchanger tube equipped with a novel type of conical turbulators having two parallel rows of holes, for first time.The range of Reynolds number was between 4000and20000 under turbulent flow regime and uniform wall temperature condition.Water is considered as the base fluid and TiO2 nanoparticles with volume fractions of0–2.5% are added as the second phase to the base fluid.The effect of number of the conical insert turbulators, number of the holes and volume fraction of the nanoparticles on flow field,average Nusselt number,friction factor and performance evaluation criterion(PEC) have been numerically investigated.The results show that the proposed turbulators create vortices and recirculating currents that have significant effect on heat transfer.As number ofthe turbulators increases,Nusselt number increases obviously.However,the presence of holes also reduces the friction factor andpressure drop that is related to lower resistance in the flow path.In general,the use of perforated conical turbulators improves PEC by creating controlled turbulent flows.Onthe otherhand,the useof added nanoparticles also enhances heat transfer.The presented turbulators increase PEC up to43% compared to the smooth tube,if the parameters are determined properly.The maximum PEC of1.43 is obtained at M=8,N=4 and Re=4100,which shows good performance compared to othertypes of turbulators.