An experimental study on the effects of the use of multi-walled carbon nanotubes in ethylene glycol/water-based fluid with indirect heaters in gas pressure reducing stations

•Design and construction of the experimental indirect gas heater.•Use of MWCNTs in an experimental device.•Obtaining experimental data for different volume fractions and temperatures of nanofluid.•Increasing Nusselt number of gas at volume fraction of 0.05 and temperature of 70 °C.•Increasing outlet temperature difference of gas (48%) at volume fraction of 0.05. Heaters that work with indirect fire and water heating have a variety of applications, especially in the gas industry and in gas processing. In the present study, an experimental device is first constructed to enhance heat transfer in indirect heaters in gas pressure reducing stations in Iran, and then its efficiency is examined by adding multi-walled carbon nanotubes (MWCNTs) to ethylene glycol/water-based fluids. The efficiency of the experimental device was tested with MWCNTs at volume fractions of 0.025, 0.05, 0.1, 0.2 and 0.3 and diameters of 20–30 nm to enhance heat transfer. The results showed that the viscosity of the nanofluid was enhanced by increasing the volume fraction of their nanoparticles while an increase in the temperature reduces the viscosity and density of the nanofluid. Besides, the specific heat coefficient of the nanofluid is increased with temperature, but did not show significant changes with the increase in volume fraction. Increasing the volume fraction, however, increased the thermal conductivity coefficient and viscosity ratios, and increasing the Nusselt number also increased the convective heat transfer coefficient. Furthermore, results show a 34.5 °C increase in the outlet gas temperature difference and a 48% growth in efficiency at volume fraction of 0.05 and temperature of 70 °C. These findings are relatively consistent with the theoretical assumptions.