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A novel two-way coupling multi-scale model was proposed to investigate the catalytic distillation process. In the model, a microscopic model that focuses on the reactive performance of structure catalytic packing was used to calculate actual rate for catalytic distillation process, which is the basic parameter for process simulation. Furthermore, the traditional process simulation was used to provide proper boundary conditions for microscopic model. In order to validate the multi-scale model, heterogeneously catalyzed hydrolysis of methyl acetate was employed as a test system. The simulated final conversions of methyl acetate and catalyst layer efficiency factors were in good agreement with experimental results. The results indicated that as the equivalent diameter of catalyst layer decreases from 25.4 mm to 8.1 mm, the catalyst layer efficiency factor rises to 200% approximately. This study could provide a theoretical guide for the optimization of catalytic packing structure. [ABSTRACT FROM AUTHOR]

The upscaling process of multicomponent mass transfer and reaction in a rigid and homogeneous porous media was carried out using the method of volume averaging. The first-order reversible reaction which occurs at the solid-fluid interface was considered in this paper. The corresponding macroscopic governing equations were derived from the system dynamics at the pore scale. The effective coefficients were obtained by solving the associated closure problems. This study shows that if the backward reaction rate constant at the microscale is small enough, i.e. k - → 0 , the obtained upscaled model is in accordance with the macroscopic model derived from the first-order irreversible heterogeneous reaction case which was extensively investigated in the literature. The influence of reaction rates on the effective parameters in the macroscopic equations was also investigated. It has been found that both forward and backward reaction rates have significant influence on the effective diffusivities and effective reaction rates in the macroscopic equations. The established equations were successfully verified by the comparison of the direct numerical calculations. [ABSTRACT FROM AUTHOR]

• The efficiency factor that considers the catalyst layer structure was obtained. • A multi-scale and multi-objective model was proposed for catalytic distillation. • The parameters of column, and the structure of catalyst layer were optimized. This work aims to establishing a multi-scale and multi-objective optimization strategy for the catalytic distillation process. Firstly, the catalyst layer efficiency factor correlation that embraces the influence of the catalyst layer structure was obtained and then coupled with the process simulation to establish a multi-scale model for the catalytic distillation process. On this basis, genetic algorithm was employed to realize the multi-objective optimization. The hydrolysis process of methyl acetate in the reactive dividing wall column was investigated. The equipment parameters and operational conditions of the catalytic distillation column, and the structure parameters of the catalyst layer are optimized simultaneously. The results indicated that the minima of the total annual cost, the gas emission cost and the exergy loss decrease by 19.26%, 23.11% and 67.27%, respectively, by comparing with the counterparts obtained from the single-factor sensitivity analysis. Furthermore, the catalyst cost decreases by 30.88% per year. [ABSTRACT FROM AUTHOR]

In this paper, an attempt has been made to extend the modified Buongiorno model of nanofluids originally proposed by Yang et al. (2013a, J. Heat Transf. , 135, 054504) from the continuum flow regime to the slip flow regime, in consideration of the effects of both velocity slip and temperature jump near the wall. Since the use of velocity slip boundary condition has been extensively applied and well-understood in the literature, the focus of the present study is on the temperature jump boundary condition. Based on the theoretical results obtained using the Runge–Kutta–Gill method, one can conclude that the temperature jump near the wall has more significant influence on the dimensionless temperature than the dimensionless velocity and volume fraction of nanoparticles in the cross section of a channel. Moreover, the neglect of temperature jump leads to the overestimation of Nusselt number based on the bulk mean nanofluid thermal conductivity Nu B , especially in the slip flow regime. Subsequently, two key parameters of nanofluids, namely Knudsen number Kn and the ratio of Brownian and thermophoretic diffusivities N BT , were discussed in order to investigate their effects on the fluid flow and heat transfer characteristics of nanofluids. The results indicated that the increase of Kn not only enhances heat transfer performance, but also reduces pressure drop, demonstrating the promising prospect of nanofluids applications in micro and nano-scales devices. Furthermore, it is found that the maximum Nu B can be achieved when Kn is around 0.07 or when N BT is around 0.5, which is useful for optimizing nanoparticles for practical applications. [ABSTRACT FROM AUTHOR]

The present paper aims at an upscaled description of solute concentration transport processes in countercurrent dialyzer systems by means of a porous media approach based on the volume averaging theory. In consideration of solute diffusion and ultrafiltration processes, a general set of upscaled solute concentration transport equations has been derived for the three phases in a hollow fiber dialyzer, namely, the blood, membrane and dialysate phases. Moreover, the corresponding closure problems, which can be solved to obtain the effective properties in the upscaled model, are proposed. For the one-dimensional case, analytical expressions of solute concentrations in both blood and dialysate phases are achieved, so as to elucidate the influences of ultrafiltration flow rate and distribution coefficient on both clearance enhancement and solute concentration variations along the length of dialyzer. The results show that both ultrafiltration flow rate and distribution coefficient have no significant effects on solute concentration variations along the length of dialyzer. Nevertheless, the clearance enhancement are found to have linear relationship with both ultrafiltration flow rate and distribution coefficient. [ABSTRACT FROM AUTHOR]

• The rise of alkyl chain length led to different trend of mass transfer enhancement. • Biggest mass transfer enhancement by 36.8% was obtained under the C4H9 alkyl chain. • Interfacial mass transfer enhancement mechanisms by JNPs were elucidated. • Solute diffusion behaviors and molecule interaction energy are main mechanisms. Janus nanoparticles (JNPs) have drawn significant attention due to their unique surfaces with dual character. Herein, molecular dynamics simulation was conducted to investigate the molecular transfer characteristics across the hexane/water interface with amphiphilic JNPs, to elucidate the interfacial mass transfer enhancement mechanisms. The results manifested that the enhancement by JNPs first increases and then decreases with the rise of alkyl chain length, which is up to the biggest improvement under the C 4 H 9 alkyl chain (JNPs-4). The enhancement can be ascribed to the competitive balance between solute diffusion behaviors and molecule interaction energy. The self-diffusion coefficient of solute and the interaction between the solute and oil phases decreases, while the interaction between the solute and water phases increases with the rise of alky chain length. Moreover, maximum enhancement can be obtained by 5 vol% concentration JNPs-4 with 13.4 Å particle diameter, in which the mass transfer resistance is reduced by 36.8%. [ABSTRACT FROM AUTHOR]

• Vapor-liquid mass transfer layer performance was studied by the tracer method. • Mass transfer coefficients that consider four structure parameters were obtained. • The correlations of mass transfer coefficients exhibit good universality. • The correlations were used for the structure optimization of mass transfer layer. In order to implement the multi-scale model to optimize the structure of vapor-liquid mass transfer layer, vapor and liquid mass transfer coefficients that embrace the effects of structure parameters of mass transfer layer should be obtained in advance. In the study, the influences of four structure parameters on mass transfer performance were studied by the tracer method. Moreover, the corresponding mass transfer coefficients were correlated. By comparing with the experimental data of different types of structured catalytic packings, it has been found that the correlations exhibit good universality. Furthermore, the correlations were applied to the non-equilibrium model for the hydrolysis of methyl acetate (MA), so as to investigate the influences of four structure parameters on catalytic distillation process. The results indicated that wavy height and the area ratio of mass transfer layer to catalyst layer have more significant influences on the conversion of MA than inclined angle and base length. [ABSTRACT FROM AUTHOR]