The study provides a numerical analysis of laminar forced convective heat transfer of graphene oxide nanosheets suspended in the mixture of water and ethylene glycol in laminar flow regime using single phase approach in a circular horizontal tube under constant heat flux conditions. The length and diameter of the simulation domain for numerical investigation are 2 m and 4.5 mm respectively. The effect of various flow conditions and weight concentrations have been investigated on local heat transfer coefficient, average heat transfer coefficient, friction factor, pressure drop and thermal performance factor of the nanofluids. The range of weight concentration and Reynolds number used in this study are 0.01–0.1 wt.% and 400–2000 respectively. The maximum percentage enhancement in average heat transfer coefficient was 13.04% for weight concentration and Reynolds number of 0.1 wt.% and 2000 respectively. The maximum pressure drop enhancement ratio was 2.12 at Reynolds number and weight concentration of 400 and 0.10 wt.%. The enhancement in heat transfer coefficient was found lower as compared to corresponding enhanced pressure drop for all weight concentrations. The thermal performance factor of nanofluids is less than one for all weight concentrations and nanofluids showed no advantage over base fluid as heat transfer fluid in laminar flow regime.

Thermal-hydraulic characteristics of water based ZrO2 nanofluids has been investigated in a segmental baffled shell and tube heat exchanger in turbulent flow regime. The effect of Reynolds number, nanoparticle loading, mass-flow rate, and tube lay-out has been analysed on overall heat transfer coefficient. The effect of Reynolds number on the tube side pressure drop and convective heat coefficient have also been discussed. The effect of shell side mass-flow rate was also investigated on shell side heat transfer coefficient determined using Bell-Delaware method. The nanoparticle volume concentration is taken very low i. e. 0.2%, 0.4%, and 0.8%, respectively. The improvement in both tube side convective heat transfer coefficient and overall heat transfer coefficient has been observed. The maximum improvement in the convective heat transfer coefficient is found to be 14.1% for 0.8% ZrO2 nanofluids. However, the percentage enhancement in tube side pressure drop was higher than the percentage increment in the tube side heat transfer coefficient.

Passive solar desalination with no discharge promises great potential for sustainable desalination. Herein, we provide a comprehensive modelling scheme for the investigation of coupled heat and mass transport in passive desalination devices. Our modelling approach integrates mass, momentum, species, and energy transport models to study the coupled phenomena of wicking, solar-driven evaporation, and salt precipitation. Our numerical model can predict the impact of spatiotemporal variation in temperature, salt concentration, and wicking velocity on the evaporation flux and thermal efficiency of solar evaporators. The impact of the evaporator’s shape, solar flux, salt concentration, and light reflection by salt crystals has been studied on the evaporator’s performance. We observed a two-fold increase in evaporation flux when solar irradiance increases from 1000 W/m² to 2500 W/m². A reduction in the thermal efficiency of the evaporators is predicted at higher solar fluxes. The modelled evaporator can achieve an evaporation flux of over 0.5 kg/m²h under 1000 W/m² for 3.5 wt.% saline water. The salt concentration along the z-position of the evaporator exhibited a double arch-shaped profile, which influences its evaporation performance. These findings provide vital guidelines for the design of high-throughput solar desalination systems.