Gas-liquid Interface Temperature Research Articles

Superhydrophilic floral foam-based solar evaporator with excellent salt-resistance and cost advantages for high efficient desalination

Effective management of heat, outstanding water transport paths, and hydrophilicity are essential for porous solar-driven interfacial evaporators, but their development still faces many difficulties. Here, by cross-linking a carbon black (CB)/polyvinyl alcohol (PVA) slurry with three-dimensional super hydrophilic floral foam (FF) to form a CB/PVA functional film on the surface of FF, a CB/PVA-decorated floral foam based (FFCP) solar-driven water evaporator with low-cost was finally obtained. Owing to the super hydrophilicity, sufficient water supply, self-holding water capacity and the special porous structure of the FF, as well as efficient light absorption and photothermal conversion efficiency of the dispersed CB. The gas-liquid interface temperature of the optimized FFCP-1.0 evaporator reaches 41.2 °C under single solar irradiation, obtaining an evaporation rate of up to 1.69 kg m−2 h−1. In addition, the FFCP-1.0 evaporator had a great evaporation rate in highly concentrated salt solutions. Moreover, the FFCP-1.0 evaporator has remarkable purification effects on seawater, organic dye effluents and heavy metal ion solutions. The evaporator has low cost, excessive evaporation rate and excellent durability. Therefore, this work is of considerable scientific significance for promoting the practical application of porous-based solar evaporators and clean water production.

Investigation of carbon dioxide (CO2) capture in a falling film contactor by computer simulation

In this work, mathematical models of carbon dioxide (CO2) absorption by monoethanolamine amine (MEA) in a falling film contactor are developed. The proposed models aim to predict conversion of the gas–liquid reaction along the contactor, gas–liquid interface temperature profile (axial and radial), liquid film thickness along the contactor length, axial and radial concentration profiles of reactants in liquid film, and axial and radial profiles of velocity in the liquid film. A code written in MatLab was used to obtain these profiles based on multi grid method through programming of kinetic and thermodynamic equations and physical properties of the absorption system. The mathematical model is validated by an experimental measurement based on absorption of CO2 gas by MEA solution. Four parameters are studied as independent variables namely, mole fraction of carbon dioxide in gaseous mixture, molar concentration of absorbent (MEA, volumetric flow rate of MEA, and its temperature. It is found that the entrance effect of the falling film contactor is related to axial distance from the contactor entrance exponentially: E=B0exp(−B1y) An optimization technique based on minimization of the sum of the squared error between the experimental and predicted composition of absorption process is used to obtain B0 and B1. It is found that reaction between carbon dioxide and MEA is instantaneous, and the axial conversion of carbon dioxide in the gas phase varies exponentially with the contactor length.

Predictive Model of Supercooled Water Droplet Pinning/Repulsion Impacting a Superhydrophobic Surface: The Role of the Gas-Liquid Interface Temperature.

Dynamical analysis of an impacting liquid drop on superhydrophobic surfaces is mostly carried out by evaluating the droplet contact time and maximum spreading diameter. In this study, we present a general transient model of the droplet spreading diameter developed from the previously defined mass-spring model for bouncing drops. The effect of viscosity was also considered in the model by definition of a dash-pot term extracted from experiments on various viscous liquid droplets on a superhydrophobic surface. Furthermore, the resultant shear force of the stagnation air flow was also considered with the help of the classical Homann flow approach. It was clearly shown that the proposed model predicts the maximum spreading diameter and droplet contact time very well. On the other hand, where stagnation air flow is present in contradiction to the theoretical model, the droplet contact time was reduced as a function of both droplet Weber numbers and incoming air velocities. Indeed, the reduction in the droplet contact time (e.g., 35% at a droplet Weber number of up to 140) was justified by the presence of a formed thin air layer underneath the impacting drop on the superhydrophobic surface (i.e., full slip condition). Finally, the droplet wetting model was also further developed to account for low temperature through the incorporation of classical nucleation theory. Homogeneous ice nucleation was integrated into the model through the concept of the reduction of the supercooled water drop surface tension as a function of the gas-liquid interface temperature, which was directly correlated with the Nusselt number of incoming air flow. It was shown that the experimental results was qualitatively predicted by the proposed model under all supercooling conditions (i.e., from -10 to -30 °C).

Thermal Effects in Evaporation from Binary Liquid Mixtures

Thermal effects are considered assuming a volatile component evaporates from a binary liquid mixture in a very long tube. The work is an extension of the work of Chebbi and Selim (2006) (isothermal case) to include evaporative cooling. A similarity solution is provided for the gas–liquid interface temperature and the temperature profiles in the liquid and gas phases. The analysis accounts for the motion of the gas–liquid interface and shows evaporative cooling as expected. The magnitude of evaporative cooling is found significant when volatility of the volatile component is sufficiently high. The validity of the approximations used in the solution is addressed.

Convective Condensation of Oxy-Coal Combustion Flue Gas of Laminar Fow in a Vertical Pipe

The problem of the oxy-fuel combustion flue gas condensation is the condensation of vapor in the presence of high concentration non-condensable gas. The vapor condensing at dew point temperature releases heat and diffuses on to the surface of the pipe through a non-condensable gas film. Thus it is treated as combined heat and mass transfer problem governed by mass, momentum and energy balance equations for the vaporgas mixture and diffusion equation for the vapor species. The flow of the falling condensate film is governed by the momentum and energy balance equations. The temperature at the gas-to-liquid interface, at which the condensation takes place, is estimated with the help of the heat balance and mass balance equations at the interface. The local values of the condensation Nusselt number, condensate Reynolds number, gasliquid interface temperature and pressure drop are estimated from the numerical results for different values of the system parameters at inlet, such as vapor component, temperature of vaporgas mixture, gas phase Reynolds number and total pressure. The thermodynamic calculations were made and analyzed using numerical calculation method under different conditions.

Convective condensation of vapor in the presence of a non-condensable gas of high concentration in laminar flow in a vertical pipe

The problem of laminar film condensation of vapor in the presence of high concentration non-condensable gas such as humid air flowing in a vertical pipe under laminar forced convection conditions is formulated theoretically. The vapor condensing at dew point temperature releases both sensible and latent heats and diffuses on to the surface of the pipe through a non-condensable gas film. Thus it is treated as combined heat and mass transfer problem governed by mass, momentum and energy balance equations for the vapor–gas mixture and diffusion equation for the vapor species. The flow of the falling condensate film is governed by the momentum and energy balance equations. The temperature at the gas-to-liquid interface, at which the condensation takes place, is estimated with the help of the heat balance and mass balance equations at the interface. The local and average values of the condensation Nusselt number, condensate Reynolds number, gas–liquid interface temperature and pressure drop are estimated from the numerical results for different values of the system parameters at inlet, such as relative humidity, temperature of vapor–gas mixture, gas phase Reynolds number and total pressure. The gas phase convection Nusselt and Sherwood numbers are also computed from numerical results. The predictions of the present study are compared with the experimental data available in literature, and the agreement is found to be reasonably good. An implicit pressure correction method developed by the authors is used in solving the momentum balance equation for the gas phase.

A Theoretical Study on Convective Condensation of Water Vapor From Humid Air in Turbulent Flow in a Vertical Duct

The problem of condensation of water vapor from humid air flowing in a duct in turbulent flow is formulated theoretically. Vapor condensing at the dew-point temperature of the vapor-air mixture diffuses to the wall of the duct through an air film. The flow of the condensate is laminar. The condensing vapor releases both convection and latent heats to the wall of the duct. Thus, it is treated as a combined heat and mass transfer problem. The mass, momentum, and energy balance equations for the vapor-air mixture flowing in the duct and the diffusion equation for the vapor species are considered. Ti, the temperature at gas-to-liquid interface, at which condensation takes place, is estimated with the help of the heat balance and mass balance equations at interface. The local and average values of the condensation Nusselt number, condensate Reynolds number, gas-liquid interface temperature, and pressure drop are estimated from the numerical results for different values of the system parameters, such as relative humidity and temperature of air at inlet, gas phase Reynolds number, and total pressure at inlet. The gas phase convection Nusselt and Sherwood numbers are also computed. A comparison of the present work with experimental data, for the case of in-tube condensation of vapor from humid air, shows satisfactory agreement.

Condensation of Organic Binary Mixtures Flowing Downward inside a Vertical Tube.

Both heat and mass transfer in the gas phase and heat transfer in the liquid phase are examined experimentally for turbulent film condensation of organic binary mixtures flowing downward inside a vertical tube. For average heat flux, gas-liquid interface temperature and liquid phase Nusselt number, experimental results are compared with the analytical solutions based on stagnant film theory and heat transfer relationships for turbulent film condensation of pure vapors. The experimental results regarding heat transfer agree well with the analytical solutions, except that the liquid phase Nusselt number for ethanol and water mixtures is far higer in the experimental results than in the analytical solutions. This high liquid phase Nusselt number is considered to be caused by dropwise condensation in the liquid phase.

Condensation of Organic Binary Mixtures Flowing Horizontally in Horizontal Tube Bundle.

Both heat and mass transfer in the gas phase and heat transfer in the liquid phase are examined experimentally for film condensation of organic binary mixtures such as ethanol-water and methanol-water. Experimental results on average heat flux, gas-liquid interface temperature and liquid-phase Nusselt number are compared with the analytical solutions based on a stagnant film theory and heat transfer relationships for film condensation from a pure vapor. Experimental results on heat transfer agree well with the analytical solutions, except that the liquid-phase Nusselt number in experimental results in the condition of low mass fraction of water is considerably higher than that in analytical solutions. This high value of the liquid-phase Nusselt number is considered to be caused by dropwise condensation in liquid phase. However, its effect on the tube bundle is not so remarkable compared with that in gravity-controlled condensation on a vertical surface, This is considered to be caused by the condensate inundation effect.

Condensation of organic binary mixtures flowing downward inside a vertical tube

Both heat and mass transfer in the gas phase and heat transfer in the liquid phase are examined experimentally for turbulent film condensation of organic binary mixtures flowing downward inside a vertical tube. For an average heat flux, gas-liquid interface temperature and liquid-phase Nusselt number, experimental results are compared with analytical solutions based on stagnant film theory and heat transfer relationships for turbulent film condensation of pure vapors. The experimental results regarding heat transfer agree well with the analytical solutions, except that the liquid phase Nusselt number for ethanol and water mixtures is far higher for the experimental results than predicted by the analytical solutions. This high liquid phase Nusselt number is considered to be caused by dropwise condensation in the liquid phase. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(6): 362–381, 1996

Gas—liquid interface temperature rise for rapid absorption-reaction in a thin liquid film

Gas—liquid interface temperature rise for rapid absorption-reaction in a thin liquid film

Gas-liquid interface temperature rise in the case of temperature-dependent physical, transport and reaction properties

This paper anlyzes the problem of gas-liquid interface temperature rise for a first order gas-liquid reaction when the diffusion coefficient, solubility and reaction rate coefficient are dependent upon temperature. The analysis indicates that as long as the quantity ϵ eff, which is numerically equal to ϵ S − (ϵ + ϵ R /2 (wherein ϵ S , ϵ D and ϵ R are the dimensionless temperature-solubility, temperature-diffusion coefficient and temperature-reaction rate constant coefficients) is zero, Danckwerts' analysis [1–3] is useful for the calculations of large rise in gas-liquid interface temperature. For ϵ eff ≠ 0, the paper presents approximate empirical correlations for calculating gas-liquid interface temperature rise with the knowledge of Danckwerts' analysis and the magnitude of ϵ eff.

Gas absorption accompanied by two step complex chemical reactions: analytical solutions for penetration theory equations and gas—liquid interface temperature rise

Gas absorption accompanied by two step complex chemical reactions: analytical solutions for penetration theory equations and gas—liquid interface temperature rise