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Supplemental material, sj-docx-1-pie-10.1177_09544089231151573 for Performance augmentation of a solar thermal desalination system using different floating absorber plates by Ashish Chandran K., Arun K. Raj and Sujith Kumar C.S. in Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering

This work deals with a multi-faceted objective of decreasing the heat leak to the compensation chamber (CC)/ reservoir of a Loop Heat Pipe (LHP) and simultaneously to utilize this heat to vaporize the liquid in contact with the evaporator by optimizing the fabricating parameters of the wick. In this study, the wick consists of three layers of equal thickness with different compositions of Nickel and Copper with naphthalene added as pore former (30% volume). The various parameters studied are sintering temperature (range of 700–800 °C), and composition gradient across different layers. The effect of these parameters on the wick properties – thermal diffusivity, porosity, permeability, pore radius and evaporation rate were studied. Five wicks with different composition gradient were cold-press sintered at 700 °C, 750 °C and 800 °C for 90 min in an inert atmosphere. The permeability of the wicks were determined using falling head permeater and an optimum value of permeability of 1.305 × 10-12 m2 was obtained for a sample of 36.4% mass of Cu. The porosity of the wicks were measured using the Archimede’s principle and the aforementioned wick has a porosity of 44.7% which was found to possess the lowest thermal diffusivity and subsequently highest evaporation rate.

Heat removal from a hot body is of vital importance for many industries like chemical, nuclear, and production industries. Cooling occurs in three stages: film boiling, nucleate boiling, and convective boiling. This study investigates the effect of surfactant on these three distinct stages of heat transfer with stainless steel (304). Contact angles are measured for deionized water and surfactant solutions (sodium dodecyl sulphate) and the critical micellar concentration of surfactant was determined. Vertical quenching tests were carried out in deionized water with and without the addition of surfactant under atmospheric pressure and temperature. The stainless-steel sample was heated to 480°C and then immersed into liquid tank. Type K thermocouple was used for measuring the centre temperature and cooling dynamics of the stainless-steel sample were studied. Added surfactant exhibits significant influence on the cooling behaviour. However, influence of surfactant largely governed by prevailing boiling regimes. In film boiling regime, deposition of surfactant stabilises the vapour layer, which prolonged the film boiling time. In nucleate boiling, surfactant facilitates enhanced cooling especially at the later stage of bubble incipience. Additionally, the temperature gradient in the film boiling is much lower than that of deionized water. A finite element model has been developed for determining the heat transfer coefficient.

The hydrothermal stability of titanium oxide (TiO2) made it a potential candidate in nanofilm (NF) coating on heating substrate for pool boiling enhancement ramified under passive technique. The objective is to conduct an experimental study on pool boiling of saturated water by the implementation of an annealed TiO2 micro-/nanostructured heating surface for the enhancement of heat transfer between the liquid and the heating surface envisioned as the corollary of annealing. Electron beam physical vapour deposition is employed to synthesize four TiO2 nanofilm-coated substrates of two different thicknesses (500 and 100 nm); among them, one from each thickness is annealed at an inert atmosphere. The test samples are characterized by transmission electron microscopy, scanning electron microscopy, and atomic force microscopy and contact angle metre (dynamic) to understand the morphology, topology and crystallinity and hydrophilicity of the surface. Experimental analysis of heating surfaces revealed that the annealed TiO2 1000 nm micro-/nanostructure-recorded maximum reduction in wall super heat (ΔT) of 52% and enhancement in heat transfer coefficient (h) of 74% than untreated copper substrate also exhibit superior structural stability after several runs rendering annealing a potential method for the amelioration of nucleation and structural stability of heating substrates. As hypothesized, annealing of nanofilm coating improved the structural stability of the NF rendering unwavering boiling performance evident from the results.

In this work we investigated the effects of surface modification on the capillary rise of the copper braids. The hydrophobic surfaces of the copper braids were modified to be hydrophilic. S...

Thermoelectric generators (TEGs) have become a notable topic for research in the last three decades. TEG is a promising element in the field of renewable energy in this age of ever-increasing energy demands. A TEG is a compact, quiet, highly reliable and environment friendly device with no moving parts. Although TEG finds its place in various applications, enhancing its efficiency is a focus in the field of thermoelectrics. Various solar thermal system configurations increase the efficiency of TEG for a given thermoelectric material. This review work predominantly focuses on these configurations for the solar applications of TEG as a vital tool in the field of solar energy. The paper thus, summarizes earlier literature works done to improve the efficiency of TEG through thermal system configurations, provides an outlook of present trends in the applications of TEG in a solar thermal system configuration with an outline of future research in TEG.

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.

Boiling heat transfer is a useful and efficient heat transfer process for high heat dissipating applications. Recent developments in altering the surface morphology by coating microscale and nanoscale structures have led to remarkable enhancement in two-phase heat transfer performance. This study reviews the recent experimental investigations performed on the boiling heat transfer enhancement using surface coatings and the mechanism behind the enhancement. Surface coatings will increase the critical heat flux (CHF) and the boiling heat transfer coefficient (HTC) by producing porous, finned, hydrophilic, and hybrid patterns over the surface. A comprehensive overview of recent investigations into the effects of surface coatings on bubble dynamics is also included in this paper.

In this work, pool boiling heat transfer experiments were conducted to investigate the effect of the heterogeneous wettable surfaces. Three different types of heterogeneous wettable surfaces were produced by printing the polymethyl methacrylate (PMMA) polymer on the plain copper and the hydrophobic polymer on the plain copper and superhydrophilic surface. The heat transfer experiments were conducted on a hollow copper cylinder of 25 mm outer diameter and 40 mm long, with de-ionized (DI) water as the working fluid. The effect of heterogeneous wettability on the boiling bubble dynamics, heat flux, surface temperatures and the average heat transfer coefficient (HTC) were investigated at the saturated conditions. An appreciable enhancement of 98.5% in the HTC was observed on the hydrophobic polymer printed plain copper sample as compared to the plain copper, at a lower heat flux of 15 kW/m 2 .

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.

In the present study, pool boiling heat transfer experiments are performed on a bare copper surface, a sandblasted copper surface, and carbon nanotube coated copper substrates. Experiments were conducted on the substrate surface area of 14 × 14 mm2 using de-mineralized water as the working fluid. The substrate is fixed tightly on the heater block, which is embedded with six cartridge heaters of total capacity 1500 W. Heat fluxes were measured using J-type thermocouples, which were aligned vertically along the heater block and also 1 mm from the top of the substrate. The pool boiling heat transfer experiments were conducted on bare, sandblasted and vertically aligned CNT coated copper substrates. The obtained results of sandblasted and CNT coated surfaces were compared with that of the bare copper surface. A remarkable enhancement of 38% in the CHF was observed on the CNT coated surface. The CNT coated surface was found to be effective in increasing the nucleate boiling and the CHF.

Laser texturing can effectively obtain the desired surface features on metals through melting and solidification, or through laser-based additive manufacturing techniques. In phase-change heat transfer applications, such modified surfaces can be both beneficial and durable. Surface modification by ultrafast processing lasers alters the heat transfer performances of boiling systems. This review summarizes the work leading to these technologies and their role in influencing the performance of boiling systems. It first discusses the types and material processing mechanism of lasers. Then, the applications of laser-textured surfaces in pool boiling and flow boiling are discussed in detail. Different types of surface patterns can be fabricated on boiling surfaces depending on experimental requirements. It is clearly evident that the design parameters and surface characteristics like surface roughness, surface wettability, and porosity can be easily controlled by controlling the laser parameters. Also, heat transfer performance of the textured surfaces changes as compared to the surfaces without any texturing. As surface features generated as a result of laser texturing are permanent, the durability of the structures can be increased with prolonged boiling performance. The review concludes with future recommendations for identifying the research gaps and improving the heat transfer processes by laser-textured surfaces.

Results showing the effects of varying the surface roughness on copper tubes in pool boiling of water are presented in this study. To obtain different surface roughness values of each sample, the copper tubes were rotated with an electric rotor and sanded using sandpaper of different grit sizes. The average surface roughness values of the plain copper tubes were in the range 0.032–0.544 µm. All experimental samples were horizontally oriented, and experiments were carried out in ambient conditions up to a moderate heat flux regime (450 kW/m2). Moreover, for a comparative analysis, a sample with a rough surface and hydrophobic patterns was included in this study. Compared with the smoothest surface, the aforementioned rough sample exhibited a heat transfer coefficient that was up to a factor 1.5 higher for the highest evaluated heat flux. These findings show that even small increments in the surface roughness along with the addition of hydrophobic patterns can significantly lower the wall superheat temperature and increase the heat transfer coefficient of copper tubes. Furthermore, supported by high-speed imaging of the experiment, it was observed that increasing the surface roughness caused bubbles to depart when their diameter was larger, and the nucleation site density and bubble departure frequency increased. In contrast, the rough surface with hydrophobic patterns exhibited the best overall enhancement, including the characteristics mentioned above of the rough surfaces along with a uniform distribution of the bubbles around the surface.

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.

Vertically aligned carbon nanotube (CNT)/diamond double-layered structure was synthesized on copper (Cu) substrate by hot-filament chemical vapor deposition. The structure was characterized by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The results show that the diamond layer has good adhesion to the Cu substrate and the CNTs have direct contact with the diamond layer. Field electron emission measurement shows that the double-layered structure on copper has very good emission stability and a much lower turn-on field than that on silicon (Si).

In this work, flow boiling heat transfer experiments were conducted to investigate the effect of a spray pyrolysed porous alumina coatings over a copper substrates. Two different porous alumina coatings were produced by varying the deposition temperature of the spray pyrolysis technique. The heat transfer experiments were conducted in a mini-channel of dimensions 30 × 20 × 0.4 mm, with de-mineralized water as the working fluid. The coated samples were tested repeatedly for three different mass fluxes and two subcooled temperatures, to investigate their effect on the heat flux, surface temperature and average heat transfer coefficient. An appreciable enhancement in heat flux was observed for the 300 °C spray pyrolysed alumina coated sample, when compared to the bare Cu and 350 °C spray pyrolysed alumina coated sample. An enhancement of 28.3% in the heat flux was observed for the 300 °C spray pyrolysed alumina coated sample compared to the bare Cu sample, for a lower mass flux of 88 kg/m 2 s.

In the present study, experiments are performed to understand the effect of carbon nanotubes (CNTs) and diamond coating over copper substrates on flow boiling heat transfer performance. Using de-mineralized water as the working fluid, heat transfer experiments were conducted in a mini-channel with an overall dimension of 25 × 20 × 0.4 mm. Each of the coated surfaces was tested repeatedly at different velocities to explore the dependence of heat transfer performance on parameters, especially the critical heat flux (CHF). The effect of wettability of the surface on flow boiling heat transfer was also studied. A remarkable increase in the critical heat flux was observed on CNT-coated surface when compared with bare Cu or diamond coated Cu substrate. An enhancement of 21.6% in the CHF was observed for a mass flux of 283 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%.