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Purpose Increasing heat transfer rate in spiral heat exchangers is possible by using conventional methods such as increasing number of fluid passes and counter flowing. In addition, newer ideas such as using pillows as baffles in the path of cold and hot fluids and using nanofluids can increase heat transfer rate. The purpose of this study is to simulate turbulent flow and heat transfer of two-phase water-silver nanofluid with 0-6 Vol.% nanoparticle concentration in a 180° path of spiral heat exchanger with elliptic pillows. Design/methodology/approach In this simulation, the finite volume method and two-phase mixture model are used. The walls are subjected to constant heat flux of q″ = 150,000 Wm−2. The inlet fluid enters curves path of spiral heat exchanger with uniform temperature Tin = 300 K. After flowing past the pillows and traversing the curved route, the working fluid exchanges heat with hot walls and then exits from the section. In this study, the effect of radiation is disregarded because of low temperature range. Also, temperature jump and velocity slipping are disregarded. The effects of thermophoresis and turbulent diffusion on nanofluid heat transfer are disregarded. By using finite volume method and two-phase mixture model, simulations are performed. Findings The results show that the flow and heat transfer characteristics are dependent on the height of pillows, nanoparticle concentration and Reynolds number. Increasing Reynolds number, nanoparticle concentration and pillow height causes an increase in Nusselt number, pressure drop and pumping power. Originality/value Turbulent flow and heat transfer of two-phase water-silver nanofluid of 0-6 per cent volume fraction in a 180° path of spiral heat exchanger with elliptic pillows is simulated.

In this presentation, flow physics and natural heat transfer of water/Ag nanofluid are implemented by utilizing finite volume method (FVM) considering 0–6% of solid nanoparticles in volume fraction in an elliptical‐shaped enclosure affected by different attack angles range from 45° to 135°. This survey's foremost objective is to find the optimum attack angle for the highest heat transfer performance in the studied geometry. The attained results demonstrated that the Rayleigh number's augmentation leads to buoyancy force amplification and intensification of velocity components in the enclosure. Hence, the shapes of streamlines for each attack angle are different from the other states. The enhancement of the Rayleigh number causes better temperature distribution between cold and hot sources. The attack angle changes are the other factor for creating and intensity of the temperature gradients. By increasing the attack angle when the heat is transferred from the hot source to the top of the enclosure, the thermal distribution effects come with high gradients due to the flow balance disturbance and the changes in two sources' location. As the fluid moves, velocity components always change. In Rayleigh number of Ra = 1 × 103 due to a decrease of buoyancy force and negligible density changes in the enclosure, the average friction coefficient (Cfave) is not considerable, and for everyone studied attack angles, these changes are negligible. By augmenting attack angle (attack angles of 90° and 135°), because the tangential velocity component is weakened by gravity force, the values of created surface stress and fluid adhesion to the hot surface are less.

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