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

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.

Figure 1

(a) Schematic diagram of a TPCT with temperature measurement points. (b) The experimental setup for the evaluation of performance of nanofluid charged TPCT.

Figure 2

(a) Effective thermal conductivity enhancement ratio, and (b) viscosity, of GO and SO nanofluids as a function of temperature for different nanofluid concentration.

Figure 3. Variations of ΔT reduction ratio, ψ = (ΔT_nf − ΔT_o)/ΔT_nf, of GO and SO nanofluids charged TPCTs as a function of , with the nanofluid concentration being a parameter.

Figure 4

Effective thermal resistance, R_eff, as a function of nanoparticles weight ratio, ϕ, of (a) GO nanofluids, and (b) SO nanofluids, charged TPCTs at different .

Figure 5

(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.

Figure 6

Time-lapse images of a 2 μl water droplet residing on (a) 0.1 wt% GO deposited layer, (b) 0.5 wt% SO deposited layer, and (c) uncoated glass surface, over a time span of 5 minutes. For each 60-s interval, the corresponding contact angle is recorded and depicted.

Figure 7

(a) Schematic illustration of evaporation process occurring at the effective region of a TPCT with (i) SO deposition, and (ii) GO deposition. In light of the fast water permeation effect, the effective evaporation region for TPCT with GO deposition is significantly extended across the evaporator wall surface (highlighted with red color) where filmwise evaporation is induced. (b) Relative deposition thicknesses of various GO nanofluid concentrations. The average thickness of 0.01 wt% GO deposition is used as a baseline for comparison.

Figure 8. FESEM images of SO nanoparticles and GO sheets deposited on the glass surface of the evaporator section of TPCT:

(a) 0.5 wt% SO nanoparticles, (b) 0.01 wt% GO sheets, (c) 0.05 wt% GO sheets and (d) 0.1 wt% GO sheets. The well distributed, closely-packed layered structure of GO sheets can be easily distinguished from the disorderly distributed spherical SO nanoparticles deposition. Higher concentration of GO sheets deposition is manifested in thicker strands.