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This paper presents an experimental investigation aimed at studying the influence of nano-CuO coating on the pool boiling heat transfer enhancement of SS 316 LN stainless steel. The coating was developed using the sol-gel dip coating technique. The Scanning Electron Microscopic and X-Ray Diffraction apparatus were used to analyze morphological and structural characteristics of the coating. The complex interaction of coating process parameters on the boiling heat transfer coefficient was studied using the concept of design of experiment. The results reveal as much as 30% increase in the boiling heat transfer coefficient for the sol-gel derived CuO coated boiling surface compared to its uncoated counterpart. The coating was found to tailor the porosity, roughness and wettability of the surface. The heat transfer coefficient increased with an increase in porosity, roughness and decrease in wettability of the boiling surface. Analysis of variance results revealed that the molar concentration of the CuO sol was the most significant parameter influencing the heat transfer coefficient while sintering temperature was the least significant parameter.

In this study, we investigated self-propelled sessile droplet evaporation on superheated surfaces with mixed wetting patterns. The primary reason for droplet motion was an increase in surface temperature and the difference in surface energy, which affected the moving contact line and moved droplets close to the wetting regions and then out to the heating surface. In this study, we observed that increases in temperature significantly influenced the changes in surface adhesion force. The force balance equation was used to demonstrate the existence of a moment of droplet movement. In addition, temperature data demonstrated energy conservation behaviour. The heterogeneous wetting surface exhibited greater differences in energy because of the energy expended during liquid–vapour phase transition and droplet movement.

This paper discusses the synthesis and characterization of a novel hybrid nanofluid and its performance analysis on a parabolic trough direct absorption solar collector. Broadening the absorption spectra of working fluid using nanoparticles is the new research revolution for increasing the volumetric solar absorption efficiency. It is reported that plasmonic silver nanoparticles have higher absorption in visible spectra while antimony doped tin oxide has an absorption peak in the near-infrared region. Hence, antimony tin oxide/silver hybrid nanoparticle with broad spectral absorptivity was synthesized. Optimization of the nanofluid composition performed using response surface methodology yielded an optimized mass fraction of antimony tin oxide and surfactant, sodium dodecyl sulfate, as 0.1% each. The solar weighted absorption fraction of optimized nanofluid was obtained as 90.12%. Performance evaluation of the solar collector was based on ASHRAE standards 93–2010. The optical efficiency of the parabolic collector was calculated to be 75%. The maximum thermal efficiency obtained by the optimized nanofluid applied parabolic trough direct absorption solar collector was 63.5% at a flow rate of 0.022 kgs−1 and the highest exergy efficiency obtained was 5.6%. Thermal and exergy efficiency was observed to increase with increase in flow rate.

Experiments are conducted to assess the heat transfer benefits of the hydrophilic coating on a rectangular minichannel. The spray pyrolysis technique is used to obtain the surfactant added ZnO–Al 2 O 3 coatings. The effect of surfactant weight percentage on hydrophilicity has been investigated using the static contact angle meter. An appreciable enhancement in the critical heat flux (CHF) and the average heat transfer coefficient (HTC) are observed on surfactant added ZnO–Al 2 O 3 coatings compared to pure ZnO coatings. A maximum enhancement of 44.6% in CHF and 29.7% in HTC are observed for the 4 wt.% surfactant added ZnO–Al 2 O 3 composite coating, for a mass flux of 88 kg/m 2 s.

Augmenting thermal and optical properties of working fluids used in solar thermal conversion systems using hybrid nanomaterials is gaining prominence. In the present study photo-thermal analysis and thermal conductivity investigations were performed on SiO2/Ag–CuO binary water based nanofluid. The influence of particle concentration and surfactant concentration on thermo-optical properties were investigated using the design of experiment concept. Analysis of variance (ANOVA) was employed to study the significance of the process parameters on thermal conductivity and solar weighted absorption fraction of nanofluid. The statistical optimisation of the process parameters was done using the desirability function. The optimum combination of nanoparticles and surfactant that yield good thermal conductivity and solar absorption was found to be SiO2/Ag: 206.3 mg/L, CuO: 864.7 mg/L, and SDS (surfactant): 1996.2 mg/L. The optimum mass fraction of constituents yielded a relative thermal conductivity of 1.234 and solar weighted absorption fraction of 82.82%.