•Quantitative analysis of key factors influencing surface tension modeling.•Liquid density is more important at low pressures.•Gradient theory can effectively predict mixture surface tensions.The surface tension plays a major role in interfacial transport and reaction processes in many combustion processes. Since the surface tension is related to differences between the vapor and liquid phases, the saturated vapor pressure, vapor composition and liquid density are three of the key factors influencing the surface tension. However, there are few quantitative analyses of the effects of these factors on the surface tension. This study uses gradient theory combined with cubic equation of state (EOS) and van der Waals mixing rule to make a quantitative study of the influence of the saturated vapor pressure, vapor composition and liquid density on surface tension calculation. The effects of the saturated vapor pressure and vapor composition are analyzed by comparing the results of setting the binary interaction parameter kij in the van der Waals mixing rule to zero and the correlated value. The effect of the liquid density is investigated by comparing the results of using Peng–Robinson (PR) EOS and Volume Translation Peng–Robinson (VTPR) EOS. The results show that, for the binary hydrocarbon mixtures investigated, the liquid density has much more influence on surface tension compared with the saturated vapor pressure and vapor composition. And the gradient theory combined with VTPR EOS and the van der Waals mixing rule can accurately predict the surface tension with an average error of ±1% for the binary hydrocarbon mixtures.

Foulants with low concentration in effluent are generally considered minor for determining resistance to membrane filtration. This study probed spatial distribution of proteins, nucleic acids and α- and β-d-glucopyranose polysaccharides in fouling layer using multiple staining technique and confocal laser scanning microscope (CLSM) imaging and clarify their individual contributions to the overall permeate flow resistance. In the present case, the β-d-glucopyranose polysaccharides occupied over 80% of the volume of the fouling layer and were the major foulant. The other three components (proteins, nucleic acids and α-d-glucopyranose polysaccharides) were minor foulants. The computational fluid dynamics calculations revealed that the β-d-glucopyranose polysaccharides contributed much greater to cake resistance than did the other three foulants; however, its contribution could only count 12–15% of the overall resistance of filter cake. Marked reduction in cake permeability is yielded by blockage of large pore in fouling layer by minor pollutants.Highlights► We probed spatial distribution of EPS in fouling layer on membrane after filtration. ► The contributions of filtration resistances by individual foulants were identified. ► The β-d-glucopyranose polysaccharides occupied over 80% volume of the fouling layer. ► Blockage of large pore by minor pollutants determined the cake resistance in filtration.

•A condensation pressure determination method for ORC with zeotropic mixture is given.•The effects of condensation temperature glide on the ORC performance are analyzed.•Mixture mole fractions for the maximum power output of a geothermal ORC are identified.•The biomass ORC performance with part of the latent heat transferred in the IHE is analyzed.The organic Rankine cycle (ORC) has been widely used to convert low-grade (<300 °C) thermal energy to electricity. Use of zeotropic mixtures as the working fluids improves the thermodynamic performance of ORC systems due to better matches of the temperature profiles of the working fluid and the heat source/sink. This paper presents a method to determine the optimal ORC condensation pressure when using a zeotropic mixture. This study also investigates the effects of the condensation temperature glide of the zeotropic mixture on the ORC thermodynamic performance. Geothermal water and biomass are used as the heat sources. Zeotropic mixtures of butane/pentane (R600/R601), butane/isopentane (R600/R601a), isobutane/pentane (R600a/R601) and isobutane/isopentane (R600a/R601a) were selected as the working fluids for the geothermal ORC with octane/decane, nonane/decane and octamethyltrisiloxane/decamethyltetrasiloxane (MDM/MD2M) selected as working fluids for the cogenerative ORC driven by the biomass energy. Two optimal working fluid mole fractions maximize the cycle efficiency, exergy efficiency and net power output for cooling water temperature increases less than the maximum condensation temperature glide, while the highest net power output appears at the higher mole fraction of the more volatile component for the geothermal ORC when the condensation temperature glide of the working fluid mixture matches the cooling water temperature increase. Higher condensation temperature glides result in large thermal loss to the heat sink and exergy destruction in the condenser. There is only one optimal working fluid mole fraction that maximizes the thermal efficiency, exergy efficiency and net power output when the cooling water temperature increase is greater than the condensation temperature glide.