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Enhanced Evaporation Strength through Fast Water Permeation in Graphene-Oxide Deposition.

Tong WL, Ong WJ, Chai SP, Tan MK, Hung YM - Sci Rep (2015)

Bottom Line: The capillary force attributed to the frictionless interaction between the atomically smooth, hydrophobic carbon structures and the well-ordered hydrogen bonds of water molecules is sufficiently strong to overcome the gravitational force.As a result, a thin water film is formed on the GO deposited layers, inducing filmwise evaporation which is more effective than its interfacial counterpart, appreciably enhanced the overall performance of TPCT.This study paves the way for a promising start of employing the fast water permeation property of GO in thermal applications.

View Article: PubMed Central - PubMed

Affiliation: Mechanical Engineering Discipline, School of Engineering, Monash University, 47500 Bandar Sunway, Malaysia.

ABSTRACT
The unique characteristic of fast water permeation in laminated graphene oxide (GO) sheets has facilitated the development of ultrathin and ultrafast nanofiltration membranes. Here we report the application of fast water permeation property of immersed GO deposition for enhancing the performance of a GO/water nanofluid charged two-phase closed thermosyphon (TPCT). By benchmarking its performance against a silver oxide/water nanofluid charged TPCT, the enhancement of evaporation strength is found to be essentially attributed to the fast water permeation property of GO deposition instead of the enhanced surface wettability of the deposited layer. The expansion of interlayer distance between the graphitic planes of GO deposited layer enables intercalation of bilayer water for fast water permeation. The capillary force attributed to the frictionless interaction between the atomically smooth, hydrophobic carbon structures and the well-ordered hydrogen bonds of water molecules is sufficiently strong to overcome the gravitational force. As a result, a thin water film is formed on the GO deposited layers, inducing filmwise evaporation which is more effective than its interfacial counterpart, appreciably enhanced the overall performance of TPCT. This study paves the way for a promising start of employing the fast water permeation property of GO in thermal applications.

No MeSH data available.


Related in: MedlinePlus

(a) Thermal conductance of uncharged TPCTs coated with thin GO and SO nanoparticles depositions as a function of  during the heat conduction experiments. (b) The evaporator heat transfer coefficient augmentation ratio, η, as a function of  with nanoparticles weight ratio as a parameter. Two distinct regimes –  and  can be clearly identified.
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f5: (a) Thermal conductance of uncharged TPCTs coated with thin GO and SO nanoparticles depositions as a function of during the heat conduction experiments. (b) The evaporator heat transfer coefficient augmentation ratio, η, as a function of with nanoparticles weight ratio as a parameter. Two distinct regimes – and can be clearly identified.

Mentions: To exclusively elucidate the role of thermal conductivity of nanoparticles deposition on the evaporator wall surface, we first examine the effective thermal conductance of uncharged TPCTs that had been coated with GO and SO during the experiments. The working fluids were evacuated from the TPCTs to exclude the two-phase heat transfer process. Simple heat conduction experiments were conducted. The primary objective is to examine the heat conduction contribution of the nanoparticle deposited layer. Except for the specimens, the experimental setup is identical to that in Fig. 1(b). The thermal conductance which can be considered as the effective thermal conductivity of specimen is calculated as , where L is the distance between the two measured temperatures, Ac is the cross section area of the evacuated glass tube and ΔT = Tevap − Tcond is the temperature difference. Figure 5(a) depicts the results of the heat conduction experiments. Although the thermal conductance of GO deposition is slightly higher than that of SO deposition, they are only marginally higher (with a maximum of 6%) than that of the uncoated surface. This is not surprising as GO intrinsically has significantly lower thermal conductivity as compared to the pristine graphene with high in-plane thermal conductivity nature743. Due to the introduction of oxygenated functional groups and defects in GO during vigorous oxidation process, in-plane heat transfer through lattice vibrations is impeded744. High in-plane thermal conductivity of graphene is attributed to the covalent sp2 bonding between the carbon atoms and the heat flow is anisotropic7. On the other hand, the layered structure of GO is governed by the cross-plane van der Waals force and the repulsive electrostatic force which is induced by the negatively charged functional groups645. As a result, the cross-plane heat transfer is ineffective as compared to the in-plane heat transfer. In fact, based on non-equilibrium molecular dynamics simulations, the thermal conductivity of GO with an oxygen coverage of 20% was estimated to be 8.8 W/m·K which is three orders of magnitude lower than the thermal conductivity of pristine graphene43. In addition, at the interface between the glass substrate and the adjacent GO sheets, poor van der Waals coupling limits the heat transfer6 and a high thermal resistance (hence a low thermal conduction) is induced between the GO sheets and the glass substrate. This shows the insignificant contribution of thermal conductivity of the GO deposition, which is essentially associated with heat conduction, to the thermal performance enhancement of TPCT. Hence we postulate that the performance enhancement and the effects of GO deposition are entailed by the two-phase heat transfer process.


Enhanced Evaporation Strength through Fast Water Permeation in Graphene-Oxide Deposition.

Tong WL, Ong WJ, Chai SP, Tan MK, Hung YM - Sci Rep (2015)

(a) Thermal conductance of uncharged TPCTs coated with thin GO and SO nanoparticles depositions as a function of  during the heat conduction experiments. (b) The evaporator heat transfer coefficient augmentation ratio, η, as a function of  with nanoparticles weight ratio as a parameter. Two distinct regimes –  and  can be clearly identified.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4477327&req=5

f5: (a) Thermal conductance of uncharged TPCTs coated with thin GO and SO nanoparticles depositions as a function of during the heat conduction experiments. (b) The evaporator heat transfer coefficient augmentation ratio, η, as a function of with nanoparticles weight ratio as a parameter. Two distinct regimes – and can be clearly identified.
Mentions: To exclusively elucidate the role of thermal conductivity of nanoparticles deposition on the evaporator wall surface, we first examine the effective thermal conductance of uncharged TPCTs that had been coated with GO and SO during the experiments. The working fluids were evacuated from the TPCTs to exclude the two-phase heat transfer process. Simple heat conduction experiments were conducted. The primary objective is to examine the heat conduction contribution of the nanoparticle deposited layer. Except for the specimens, the experimental setup is identical to that in Fig. 1(b). The thermal conductance which can be considered as the effective thermal conductivity of specimen is calculated as , where L is the distance between the two measured temperatures, Ac is the cross section area of the evacuated glass tube and ΔT = Tevap − Tcond is the temperature difference. Figure 5(a) depicts the results of the heat conduction experiments. Although the thermal conductance of GO deposition is slightly higher than that of SO deposition, they are only marginally higher (with a maximum of 6%) than that of the uncoated surface. This is not surprising as GO intrinsically has significantly lower thermal conductivity as compared to the pristine graphene with high in-plane thermal conductivity nature743. Due to the introduction of oxygenated functional groups and defects in GO during vigorous oxidation process, in-plane heat transfer through lattice vibrations is impeded744. High in-plane thermal conductivity of graphene is attributed to the covalent sp2 bonding between the carbon atoms and the heat flow is anisotropic7. On the other hand, the layered structure of GO is governed by the cross-plane van der Waals force and the repulsive electrostatic force which is induced by the negatively charged functional groups645. As a result, the cross-plane heat transfer is ineffective as compared to the in-plane heat transfer. In fact, based on non-equilibrium molecular dynamics simulations, the thermal conductivity of GO with an oxygen coverage of 20% was estimated to be 8.8 W/m·K which is three orders of magnitude lower than the thermal conductivity of pristine graphene43. In addition, at the interface between the glass substrate and the adjacent GO sheets, poor van der Waals coupling limits the heat transfer6 and a high thermal resistance (hence a low thermal conduction) is induced between the GO sheets and the glass substrate. This shows the insignificant contribution of thermal conductivity of the GO deposition, which is essentially associated with heat conduction, to the thermal performance enhancement of TPCT. Hence we postulate that the performance enhancement and the effects of GO deposition are entailed by the two-phase heat transfer process.

Bottom Line: The capillary force attributed to the frictionless interaction between the atomically smooth, hydrophobic carbon structures and the well-ordered hydrogen bonds of water molecules is sufficiently strong to overcome the gravitational force.As a result, a thin water film is formed on the GO deposited layers, inducing filmwise evaporation which is more effective than its interfacial counterpart, appreciably enhanced the overall performance of TPCT.This study paves the way for a promising start of employing the fast water permeation property of GO in thermal applications.

View Article: PubMed Central - PubMed

Affiliation: Mechanical Engineering Discipline, School of Engineering, Monash University, 47500 Bandar Sunway, Malaysia.

ABSTRACT
The unique characteristic of fast water permeation in laminated graphene oxide (GO) sheets has facilitated the development of ultrathin and ultrafast nanofiltration membranes. Here we report the application of fast water permeation property of immersed GO deposition for enhancing the performance of a GO/water nanofluid charged two-phase closed thermosyphon (TPCT). By benchmarking its performance against a silver oxide/water nanofluid charged TPCT, the enhancement of evaporation strength is found to be essentially attributed to the fast water permeation property of GO deposition instead of the enhanced surface wettability of the deposited layer. The expansion of interlayer distance between the graphitic planes of GO deposited layer enables intercalation of bilayer water for fast water permeation. The capillary force attributed to the frictionless interaction between the atomically smooth, hydrophobic carbon structures and the well-ordered hydrogen bonds of water molecules is sufficiently strong to overcome the gravitational force. As a result, a thin water film is formed on the GO deposited layers, inducing filmwise evaporation which is more effective than its interfacial counterpart, appreciably enhanced the overall performance of TPCT. This study paves the way for a promising start of employing the fast water permeation property of GO in thermal applications.

No MeSH data available.


Related in: MedlinePlus