Droplet evaporation and boiling for different mixing ratios of the silver-graphene hybrid nanofluid over heated surfaces

Abstract Droplet evaporation is a complex phase change process with a wide range of cooling applications, such as spray cooling and dropwise hotspot cooling in microelectronics, to name a few. The hybrid nanofluid droplet evaporation and its residue effects on evaporation of the subsequent hybrid nanofluid droplet is investigated in this research. Silver-graphene (Ag-GNP) hybrid nanofluid exhibiting synergistic thermal properties is investigated and prepared by dispersing silver nanoparticles along with graphene nanoplatelets in water at 0.1% volume fraction and with different mixing ratios, followed by ultrasonication. The evaporation rate and wetting characteristics of a 3 μl volume of Ag-GNP hybrid nanofluid droplet on a copper surface were studied using an optical tensiometer. Once dried, the nanoporous structure of the residue surface was examined using a scanning electron microscope, while the surface roughness was measured using an optical profiler. Experiments were continued to further investigate the evaporation rate and wetting effects of the subsequent Ag-GNP hybrid nanofluid droplet over the residue surface. The results showed improved wetting characteristics, with 88% reduction in initial static contact angle and 163–196% enhancement in evaporation rate of the subsequent Ag-GNP hybrid nanofluid droplets over the residue surfaces as compared to the copper surface.

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Investigation of the Thermal Conductivity, Viscosity, and Thermal Performance of Graphene Nanoplatelet-Alumina Hybrid Nanofluid in a Differentially Heated Cavity

Frontiers in Energy Research ◽

10.3389/fenrg.2021.737915 ◽

2021 ◽

Vol 9 ◽

Author(s):

Adeola O. Borode ◽

Noor A. Ahmed ◽

Peter A. Olubambi ◽

Mohsen Sharifpur ◽

Josua P. Meyer

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Heat Transfer Performance ◽

Temperature Gradients ◽

Hybrid Nanofluid ◽

Mixing Ratio ◽

Graphene Nanoplatelet ◽

Hybrid Nanomaterial ◽

Mixing Ratios ◽

Hybrid Nanofluids

This paper investigates the thermophysical properties and heat transfer performance of graphene nanoplatelet (GNP) and alumina hybrid nanofluids at different mixing ratios. The electrical conductivity and viscosity of the nanofluids were obtained at temperatures between 15–55°C. The thermal conductivity was measured at temperatures between 20–40°C. The natural convection properties, including Nusselt number, Rayleigh number, and heat transfer coefficient, were experimentally obtained at different temperature gradients (20, 25, 30, and 35°C) in a rectangular cavity. The Mouromtseff number was used to theoretically estimate all the nanofluids’ forced convective performance at temperatures between 20–40°C. The results indicated that the thermal conductivity and viscosity of water are increased with the hybrid nanomaterial. On the other hand, the viscosity and thermal conductivity of the hybrid nanofluids are lesser than that of mono-GNP nanofluids. Notwithstanding, of all the hybrid nanofluids, GNP-alumina hybrid nanofluid with a mixing ratio of 50:50 and 75:25 were found to have the highest thermal conductivity and viscosity, enhancing thermal conductivity by 4.23% and increasing viscosity by 15.79%, compared to water. Further, the addition of the hybrid nanomaterials improved the natural convective performance of water while it deteriorates with mono-GNP. The maximum augmentation of 6.44 and 10.48% were obtained for Nuaverage and haverage of GNP-Alumina (50:50) hybrid nanofluid compared to water, respectively. This study shows that hybrid nanofluids are more effective for heat transfer than water and mono-GNP nanofluid.

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Evaporation of Silver-Graphene Hybrid Nanofluid Droplet on its Nanostructured Residue and Plain Copper Surfaces at Elevated Temperatures

ASME 2020 Heat Transfer Summer Conference ◽

10.1115/ht2020-8922 ◽

2020 ◽

Author(s):

Farooq Riaz Siddiqui ◽

Chi Yan Tso ◽

Sau Chung Fu ◽

Huihe Qiu ◽

Christopher Yu Hang Chao

Keyword(s):

Substrate Temperature ◽

Evaporation Rate ◽

Elevated Temperatures ◽

Droplet Evaporation ◽

Copper Surface ◽

Copper Plate ◽

Hybrid Nanofluid ◽

Copper Surfaces ◽

Latent Energy ◽

Droplet Sizes

Abstract Droplet evaporation is an efficient process as it removes a large amount of heat by using the latent energy, making it suitable for heat transfer applications. In this research, evaporation of the silver-graphene hybrid nanofluid (SGHF) droplet, because of its synergistic thermal conductivity, is investigated for substrate temperature in a range of 25–100 °C. The experiments for droplet evaporation were performed in an environmental facility for two droplet sizes, 3 μL and 30 μL volume, on a copper plate. A 100 W silicone heater mat was used to heat the copper plate from the underside, while two T-type thermocouples were used to monitor its surface temperature. As droplet evaporation ended, a porous residue was formed on the copper surface. Subsequently, a 3 μL volume of the SGHF droplet was dispensed on the porous residue surface. The results showed a tremendous rise in the evaporation rate (up to 160%) for the subsequent SGHF droplet sitting on the porous residue as compared to the non-wetted copper surface. Moreover, the evaporation rate of the SGHF droplet on the copper surface increased up to 56% as compared to the water droplet for a substrate temperature range of 25–100 °C.

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Droplet Evaporation of Cu–Al2O3 Hybrid Nanofluid Over Its Residue and Copper Surfaces: Toward Developing a New Analytical Model

Journal of Heat Transfer ◽

10.1115/1.4048970 ◽

2020 ◽

Vol 143 (2) ◽

Author(s):

Farooq Riaz Siddiqui ◽

Chi Yan Tso ◽

Sau Chung Fu ◽

Huihe Qiu ◽

Christopher Y. H. Chao

Keyword(s):

Analytical Model ◽

Evaporation Rate ◽

Heat Dissipation ◽

High Heat ◽

Droplet Evaporation ◽

Copper Surface ◽

Hybrid Nanofluid ◽

High Heat Flux ◽

High Heat Transfer ◽

Critical Residue

Abstract Droplet evaporation-based cooling techniques, such as the spray cooling, give high heat transfer rates by utilizing latent energy and are usually preferred in thermal applications. However, with the significant rise in heat dissipation levels for high heat flux devices, these devices cannot be thermally managed due to the limited cooling capacity of existing thermal fluids. In this paper, we report the evaporation of the Cu–Al2O3 hybrid nanofluid (HNF) droplet on a copper surface as well as its own residue surface, developed from the evaporation of the first Cu–Al2O3 HNF droplet. As the main novelty, we identify the critical residue size and investigate the residue size effect, above and below the critical residue size, on evaporation rate of the succeeding Cu–Al2O3 HNF droplet resting over a residue surface. We also develop a new analytical model to estimate the Cu–Al2O3 HNF droplet evaporation rate and compare our results with other existing models. The results show that the Cu–Al2O3 HNF droplet gives 17% higher evaporation rate than a water droplet on a copper surface. Also, the evaporation rate of the Cu–Al2O3 HNF droplet on a residue surface sharply increases by 106% with increasing residue size up to the critical residue size. However, further increasing the residue size above its critical value has a negligible effect on the droplet evaporation rate. Moreover, the evaporation rate of the Cu–Al2O3 HNF droplet on its residue surface is enhanced up to 104% when compared to a copper surface.

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