Numerical simulation of influence of Langmuir adsorption constant on gas drainage radius of drilling in coal seam

To determine reasonable distance of gas pre-drainage drillings in coal seams, a solid–gas coupling model that takes gas adsorption effect into account was constructed. In view of different adsorption constants,the paper conducted the numerical simulation of pre-drainage gas in drillings along coal seam, studied the relationship of adsorption constants and permeability, gas pressure, and effective drainage radius of coal seams, and applied the approach to the layout of pre-drainage gas drillings in coal seams. The results show that the permeability of coal seams is on the gradual increase with time, which is divided into three sections according to the increase rate: the drainage time 0–30 d is the sharp increase section;30–220 d is the gradual increase section; and the time above 200 d is the stable section. The permeability of coal seams is in negative linear and positive exponent relation with volume adsorption constant VLand pressure adsorption constant PL, respectively. The effective drainage radius is in negative linear relation with VLand in positive exponent relation with PL. Compared with the former design scheme, the engineering quantity of drilling could be reduced by 25%.

Experimental study of evaporation of sessile water droplet on PDMS surfaces

Evaporation of sessile water droplet on polydimethylsiloxane （PDMS） surfaces with three different curing ratios （5：1, 10：1, and 20：1） was experimentally investigated in this paper. We show that the constant contact radius （CCR） evaporation on surface with high curing ratio lasts longer than that with low curing ratio. We also measured Young＇s moduli of PDMS films by using atomic force microscopy （AFM） and simulated surface deformation of PDMS films induced by sessile water droplet. With increasing curing ratio of PDMS film, Young＇s modulus of PDMS film is getting lower, and then there will be larger surface deformation and more elastic stored energy. Since such energy acts as a barrier to keep the three-phase contact line pinned, thus it will result in longer CCR evaporation on PDMS surface with higher curing ratio.

Effect of substrate elasticity on evaporation kinetics and evaporative deposition of aqueous polystyrene nanoparticles droplets

Evaporation of aqueous polystyrene(PS)nanoparticles droplets on silicon and polydimethylsiloxane(PDMS)surfaces was studied.Experimental results showed that softer PDMS surfaces yielded a longer constant contact radius(CCR)stage,which could be ascribed to surface deformation of PDMS induced by the vertical component of liquid-vapor interfacial tension.Ringlike depositions of nanoparticles with different crack patterns were found on both silicon and PDMS surfaces.In-situ observation of crack formation showed that nanoparticle movement on the silicon surface was impeded,resulting in radial cracks with periodic distribution.In contrast,nanoparticles were shown to move easily on the PDMS surface.This observation indicated the difference in crack patterns on surfaces could be attributed to the friction force between nanoparticles and the substrate.A large friction force between nanoparticles and the substrate prevented cracks from moving,resulting in a radial crack pattern with periodic distribution,while a small friction force produced multiple large cracks.