Mass Transfer Characteristics Research Articles

A new trend in combustion engine’s deep waste heat recovery by application of condensing economizers in exhaust boilers

Waste heat recovery technologies to remove heat and harmful pollution from exhaust gas–vapor mixtures remain a general trend in enhancing the efficiency of power plants. The exhaust gases from combustion engines when water-fuel emulsion (WFE) combustion contain a large amount of solid particles, deposition of which on the heating surfaces of the exhaust gas boilers (EGB) can degrade their heat transfer performance and shorten the service life. The processes of pollution deposition from exhaust gases on the economizer condensing heat exchange surface (CHES) of the EGB were studied, and their effect on the CHES heat and mass transfer characteristics was assessed. It is found that increasing the water content in the WFE to 30 % enhances the intensity of acid mass transfer due to decreasing the low-temperature corrosion rate with reaching the maximum-intensity at wall temperatures of 110…120 °C against 140…150 °C in conventional practice, which allows deeper exhaust heat utilization and increasing boiler heat productivity by about 30 %. At a water content of 30 % the sulfuric acid concentration was 57 %, which confirms the hypothesis about the passage of the nitrous mechanism of sulfuric acid formation in the condensate on CHES. The optimized CHES cleaning periodicity values corresponding to the smallest fouling coefficient and the highest heat transfer were determined. The correlations for determining the fouling, heat transfer and thermal efficiency coefficients for the CHES of the EGB when WFE combustion are provided. They are helpful for designing the economizer CHES of EGB.

Exploration of Arrhenius activation energy and thermal radiation on MHD double-diffusive convection of ternary hybrid nanofluid flow over a vertical annulus with discrete heating

The primary objective of this article is to examine the effect of discrete heating on MHD double-diffusive convection and thermal radiation of ternary hybrid nanofluid flow heat and mass transfer in a vertical cylindrical annulus along with Arrhenius activation energy and chemical reaction. In this study, the cavity inner wall has two distinct flush-mounted heat sources, while the outer wall is isothermally cooled at a lower temperature. The top and bottom walls are thermally insulated. The ensuing equations that govern the physical framework are solved using the implicit Crank-Nicholson finite difference technique. As the heater advances upward, the flow intensity decreases, leaving a part of the fluid static at the bottom of the cylinder. Because more heat induces high buoyant flow in the annulus, the absolute value of axial velocity and wall temperature rises as the length of the heat source rises. Enhancing the activation energy parameter values drops the Arrhenius energy function, elevating the pace of the generative chemical process and hence the concentration. Increasing the thermal radiation parameter lowers the surface heat flux while enhancing the nanofluid temperature. The Brownian motion parameter corresponds to the random motion of nanoparticles in a fluid, and this irregular movement augments the collision of nanoparticles with fluid particles, causing the particle's kinetic energy which leads to thermal energy and hence increases temperature, a 10% increment in Brownian motion parameter leads to 26% rise in the temperature. Also, the heat and mass transfer characteristics are forecasted and analyzed by considering the Levenberg–Marquardt backpropagating artificial neural network technique.

Heat and Mass Transfer in Unsteady MHD Casson Fluid Flow Over a Semi-Infinite Vertical Plate Through Porous Medium with Dissipative and Radiative Effects

Nowadays, Casson fluid and its diverse applications are highly effective across a vast array of industrial, biological and environmental sectors, due to its unique flow properties. This study focuses on the numerical investigation of the heat and mass transfer characteristics of an unsteady incompressible Casson fluid flow over a semi-infinite vertical flat plate by considering free convection effects. The fluid is conducting the electrical current as it moves through the porous medium. The formulation of the governing equation is based on the use of this phenomenon. In the model, the formulated governing equations are converted into non-dimensional form first, and the MHD mathematical model is analyzed using the boundary conditions. The scheme of finite difference method is implemented to solve the model, where concentration profiles are also discussed. Stability and convergence criteria are applied for the accuracy of numerical techniques, and the effects of various parameters on skin friction, rate of heat and mass transfer have been examined significantly. The results indicate that the temperature of the plate increases with the increase in the value of the magnetic parameter for the Casson fluid but the reverse is observed in its limiting case. The present results are compared and checked with previously published results and a remarkable conclusion is given at the end of the study.

Numerical analysis of Nano-encapsulated PCM magnetohydrodynamics double-diffusive convection and entropy generation in vertical enclosures with porous layer

This study investigates the effects of Nano-Encapsulated Phase Change Materials (NEPCMs) on double diffusive free convection in a partially porous cavity, considering Soret-Dufour effects and magnetohydrodynamics. The problem is modeled using non-dimensional governing equations, solved numerically through a Galerkin finite element method. The research examines the influence of key parameters including Rayleigh number (Ra: 103–105), Darcy number (Da: 10–4 -10–1), Hartmann number (Ha:0−80), NEPCM volume fraction (ϕ:0−0.04), Lewis number (Le:0.1−10), fusion temperature (θf:0.1−0.9), and Stefan number (Ste:0.1−0.9) on heat and mass transfer characteristics and entropy generation. Results show that increasing Ra significantly enhances heat and mass transfer, with Nusselt and Sherwood numbers rising by 424.8 % and 547.3 % respectively as Ra increases from 103 to 105. Higher Da and ϕ improve heat transfer, while stronger magnetic fields suppress both heat and mass transfer. An optimal fusion temperature (θf=0.5) is identified for maximum heat transfer enhancement. Total entropy generation, considering thermal diffusion, nanofluid friction, magnetic effects, porous medium, and mass diffusion contributions, increases by 15,957 % with Ra and decreases by 42.5 % with increasing Ha. The Bejan number analysis reveals that non-thermal irreversibilities become increasingly dominant at higher Ra and Ha values. The study concludes that NEPCMs can effectively enhance heat transfer in partially porous cavities, with their performance strongly influenced by Ra, Da, and Ha. The findings provide valuable insights for optimizing thermal management systems incorporating NEPCMs, particularly in applications involving porous media and magnetic fields.

Chemical Reaction and Cross Diffusion Effects on Heat and Mass Transfer Characteristics of Viscoelastic Oil-Based Nanofluid Over a Porous Nonlinear Stretching Surface

The impact of chemical reaction and cross diffusion on heat and mass transport characteristics of viscoelastic flow of Al2O3 and CuO oil-based nanofluids past a porous nonlinear stretching surface has been examined. Similarity transformation was used to transform the governing partial differential equations into coupled nonlinear ordinary differential equations and solved numerically by employing the fourth order Runge-Kutta algorithm with a shooting method. Results for the entrenched parameters controlling the flow dynamics have been tabulated and illustrated graphically. The results foundCuO-oil based nanofluid to exhibit higher mass transfer rate and lower heat transfer rate and skin friction coefficient than Al2O3-oil based nanofluid under the same viscoelastic condition. This indicates that CuO-oil based nanofluid can be used as the working fluid in mechanical dampers.

Effect of Photolithographic Biomimetic Surface Microstructure on Wettability and Droplet Evaporation Process

In nature, engineering technology and daily life, wetting phenomena are widespread and have essential roles and significance. Bionics is becoming increasingly important nowadays and exploring the mechanism that influences biomimetic surface microstructure on droplet wetting process and heat and mass transfer characteristics is becoming more meaningful. In this paper, based on photolithography technology, SU-8 photoresist was used as raw material to prepare biomimetic surfaces with microstructures in various arrangements. The research results show that the wettability of biomimetic functional surfaces can be regulated by regulating the shape and arrangement of photoresist micro-pillars. At the same time, the effects of surface microstructure configuration and roughness on the heat and mass transfer processes within the droplets were also comprehensively studied. The results show that a biomimetic surface with cylindrical micro-pillars can effectively inhibit the evaporative cooling effect of the liquid–vapour interface. This effect becomes more evident with the increase in roughness, and the interface temperature difference can be reduced by up to 18%. Similarly, the biomimetic surface with cylindrical micro-pillars can also effectively promote the evaporation rate of sessile droplets, which can be increased by about 13%. In addition, the research also shows that regardless of the structure, substrate temperature changes will significantly impact the wetting phenomenon of the biomimetic surface. This study aims to guide the optimal design of biomimetic surfaces prepared based on photoresistance.

Achieving High Performance with Less Energy Consumption: Intermittent Ultrasonic-Mediated Operation Mode for Fe/V Non-Aqueous Redox Flow Battery

Deep eutectic solvents (DESs) have attracted much attention as sustainable electrolytes for redox flow batteries. Despite the tremendous advantages of DES-based electrolytes, their high viscosity property has a negative effect on their mass transfer, limiting current density and power density. The ultrasonic effect has been demonstrated as an efficient strategy to improve mass transfer characteristics. Incorporating ultrasonic waves into a deep eutectic solvent (DES) electrolyte enhances the mobility of redox-active ions, thereby accelerating the reaction dynamics of the Fe(III)/Fe(II) redox pair. This enhancement makes it suitable for use in non-aqueous electrolyte-based redox flow batteries. However, it is necessary to consider the loss of ultrasonic on the internal structure of the battery, as well as the loss of battery component materials and ultrasonic energy consumption in practical applications. Moreover, the continuous extension of the duration of ultrasonic action not only hardly leads to a more significant improvement of the battery performance, but is also detrimental to the energy and economic savings. Herein, intermittent ultrasound is used to overcome the quality transfer problem and reduce the operating cost. Good electrochemical performance enhancement is maintained with a roughly 50% reduction in energy consumption values. The mechanism as well as the visualization of the pulsed ultrasonic field on each half cell has been envisaged through fundamental characterization. Finally, the feasibility of interrupted ultrasonic activation applied to Fe/V RFB using DES electrolytes has been demonstrated, demonstrating similar behavior with continuous ultrasonic operation. Therefore, the interrupted ultrasonic field has been found to be a more effective operation mode in terms of energy cost, avoiding alternative undesirable effects like overheating or corrosion of materials.

A transient source-function-based embedded discrete fracture model for simulation of multiscale-fractured reservoir: Application in coalbed methane extraction

The classic embedded discrete fracture model (EDFM) may cause certain errors when simulating the transient flow process within the multi-scale fractured system. In this study, the transient transmissibility was derived by using the point (matrix-fracture) and line (fracture-fracture) source functions. The transient source-function-based EDFM (tSEDFM) is established via this method. Then, based on the dual criteria that dNNC is less than a certain distance and its projection point is within the corresponding fracture domain, a 3D fracture meshing method for arbitrary fracture geometry and orientation is established. The finite volume method is used to discrete the fluid flow equations for matrix and fracture systems, considering the multi-deformation-induced permeability evolution. Consequently, the numerical simulation framework of FVM-tSEDFM is proposed to investigate the transient mass transfer characteristics. Compared with the current pEDFM, the pressure drop near fractures of the proposed model is higher and the gap narrows as pressure wave further spreads. Compared with AEDFM, the Tmf of tSEDFM is almost the same, but AEDFM's Tff is substantially higher in the initial stage and the attenuation rate is slower, resulting in an error of nearly 15% at the hydraulic fracture location. As fracture density increases, more transient flow makes AEDFM- and EDFM-calculated BHP values deviate from tSEDFM. History matching using the tSEDFM with only 10000 meshes shows better results where the mismatching rate is larger than 90%. Simulation of CBM extraction indicate that sharp pressure decline occurs near the fractures, resulting in gas desorption enhancement and rapid productivity increment. The tSEDFM demonstrates good practicality in calculating the production and long-term permeability evolution. Results also show that the tSEDFM can correct the underestimation of mass exchange in the early stage and overestimation since the pseudo-steady stage, and can be better applied to the numerical simulation of multi-scale fractured reservoirs. As the dominant factor for gas extraction, sensitivity analyses of fracture properties are also documented.

Numerical Investigation of Heat and Mass Transfer Characteristics in MHD Boundary Layer Flow of a Nanofluid over a Stretching Sheet

Nanofluids, which are simply suspensions of nanoparticles in a base fluid, have greater mass and heat transfer capabilities compared to regular fluids. Nanofluids are distinguished by their ability to transmit heat and mass. The potential applications of nanofluids in the scientific community have seen a spike in attention as a result of this. Simulations of the mass and heat transport parameters in magneto hydrodynamic boundary layer flow of a nanofluid across a stretched sheet are presented in this paper. These simulations were carried out using numerical methods. This investigation is going to look at a lot of important aspects, such as thermophoresis, Brownian motion, and the presence of a magnetic field that is applied. Continuity, momentum, energy, and concentration are the equations that are responsible for controlling the problem. The momentum equation takes into account the opposing magnetic field by means of the Lorentz force component. On the other hand, the energy and concentration equations take into account the mobility of the nanoparticles in the nanofluid as a result of Brownian motion and thermophoresis. Because of similarity transformations, the controlling partial differential equations are reduced to a set of ordinary differential equations. This action is taken in order to make the numerical application of the solution more straightforward. Calculating numerical solutions to these modified equations using any common technique, such as the Runge-Kutta-Fehlberg algorithm, is the next step that has to be taken. Utilizing this method, which is not only accurate but also time-saving, it is possible to solve issues that are associated with nonlinear boundary layers.

Uncertainty analysis of MHD oscillatory flow of ternary nanofluids through a diverging channel: a comparative study of nanofluid composites

Purpose This study aims to investigate the heat and mass transfer characteristics of a temperature-sensitive ternary nanofluid in a porous medium with magnetic field and the Soret–Dufour effect through a tapered asymmetric channel. The ternary nanofluid consists of Boron Nitride Nanotubes (BNNT), silver (Ag) and copper (Cu) nanoparticles, with a focus on understanding the thermal behaviour and performance across mono, hybrid and tri-hybrid nanofluids. This paper also examines the thermal behaviour of MHD oscillatory nanofluid flow and carries out an uncertainty analysis of the model using the Taguchi method. Design/methodology/approach The governing equations for this system are transformed into coupled linear partial differential equations using non-similarity transformations and solved numerically with the Crank–Nicolson scheme. The impact of temperature sensitivity at three distinct temperatures (5°C, 20°C and 60°C) is incorporated to analyse variations in viscosity and Prandtl number. The study also examines the combined effects of Soret–Dufour numbers and thermal radiation on heat and mass transfer within the nanofluid. Findings The results demonstrate that the inclusion of BNNT, Ag and Cu nanoparticles significantly enhances heat and mass transfer rate, with copper nanoparticles showing superior performance in terms of skin friction and heat transfer rates. The Soret and Dufour effects play critical roles in modulating heat and mass diffusion within tri-hybrid nanofluids. The study reveals that temperature sensitivity alters heat and mass transfer characteristics depending on the temperature range, with pronounced variations at elevated temperatures. The influence of thermal radiation and the Peclet number is found to significantly impact temperature distribution and overall heat transfer performance within the asymmetric channel. Originality/value To the best of the authors’ knowledge, this study is the first to analyse the heat and mass diffusion in a ternary nanofluid composed of BNNT, Ag and Cu nanoparticles, considering porous media, oscillatory flow and thermal radiation within a tapered asymmetric channel. The research extends to a novel examination of temperature sensitivity in mono, hybrid and tri-hybrid nanofluids at varying temperature gradients. Furthermore, a comparative analysis of skin friction and heat transfer rates between copper, alumina and ferro composites is presented for optimising the nanofluid performance.

Effects of increased rainfall on heat and mass transfer and deformation of sulfate saline soil: An experimental investigation

To study the effect of increased rainfall on the heat and mass transfer and deformation characteristics of sulfate saline soil, a geometric similarity ratio model (1:6) of the natural site was created inside the self-developed indoor baseplate-atmospheric dual-temperature control model box. For the first time, combined with the characteristics of the surface energy change, the characteristics of water-heat-salt-mechanical coupling changes within sulfate saline soil under normal rainfall and twice the increase in rainfall were studied. The results show that the increased rainfall leads to a more significant decrease in upward shortwave radiation and downward longwave radiation, as well as a more significant increase in the surface net radiation and surface evaporation rate. Additionally, the increase in rainfall leads to an obvious cooling trend in the surface temperature. Compared with normal rainfall, an increase in rainfall leads to a significant increase in soil water content and conductivity, while soil heat flux and temperature significantly decrease. The increased rainfall caused a temperature drop of 1.6 °C at 5 cm of saline soil. Moreover, the increased rainfall leads to an increase in the heat release time of sulfate saline soil. Meanwhile, the impact of increased rainfall on the soil water content, conductivity, and temperature gradually weakens with increasing depth. The increased rainfall can exacerbate thawing settlement deformation and alleviate salt frost heave deformation. Compared with normal rainfall, twice the increase in rainfall results in a 0.9 mm increase in thawing settlement deformation and a 2.5 mm decrease in salt frost heave deformation.

Influence of laminated porous cathode structure on the performance and mass transfer of Li[sbnd]O2 batteries

The porous cathode is a crucial component of LiO2 batteries, and its porous structure significantly impacts the battery's performance. In this study, a stacked porous cathode was fabricated via roller pressing. The influence of the cathode structure on the battery performance and mass transfer characteristics were examined using experimental and simulation methods. The structural characteristics, electrochemical properties, and overall battery performance of the stacked porous cathode were analyzed. Furthermore, the effects of the cathode structure on mass transfer within the cathode and battery performance were explored through numerical simulation. The results indicate that when the mass ratio of CNTs to ACET on the diaphragm side is 5:1, the cathode exhibits optimal structural parameters, with an average pore size of 24 nm and a maximum pore volume of 0.85564 cm3/g. Concurrently, the battery demonstrates an exceptionally high area specific capacity of 30.35 mAh/cm2. Integrating the simulation findings, it was observed that adjusting the structural parameters of the cathode enhances material transfer efficiency, thereby improving battery performance.

Dynamic modeling of air–metal plasma mixture of single-turn coil with erosion at megaGauss magnetic field

Single-turn coil (STC) is a destructive pulsed magnet aiming at 100–300 T magnetic field. Due to the high discharge current, the conductor of STC is heated rapidly and undergoes melting and vaporization, leading to the generation of supersonic air–metal vapor mixed plasma jet and the magneto-fluid effect. In this study, the mixed plasma mass-transfer and fluid dynamic characteristics are modeled at megaGauss magnetic field, high temperature, high pressure, and supersonic conductor shock deformation. The collision integral method is employed to calculate the fluid transport properties. In addition, a boundary constraint model of fluid–structure interaction (FSI) compatible with both fluid wall boundary condition and plasma jet entrance condition and a model to simultaneously solve the thermal ionization and high electric field ionization of the mixed vapor are proposed. As the result, the distributions of plasma electrical conductivity, current density, electron, heavy particles, temperature, air body load, and velocity are derived. Especially, the region of highest electrical conductivity is not the air domain near the inner surface of the conductor with the highest electron density and the highest magnetic field, but the air domain near the outer surface of the conductor with the relatively higher electron density and lower magnetic field.

Study on solid powder fuel transport characteristics and mixing degree in scramjet combustor

Abstract The powder scramjet engine is considered the best engine for hypersonic weapons because of its advantages of easy adjustment, flame stability, and high efficiency. However, due to the extremely short residence time of particle fuel in the combustion chamber under high Mach conditions, there is a risk of fuel mixing. Based on the existing combustion chamber models of scramjet engines, this paper proposes a new solid fuel blending enhancement structure by combining shock generator structure and transverse jet and compares the performance and mass transfer characteristics of different shock generators. The CFD method is used to solve the RANS formula to simulate the particle transfer process, and the SST k-ω model is used to calculate the complex turbulence. It was found that when the reverse shock generator was used, the mixing degree of solid particles was higher.

A novel leaf bionic flow field with structured multi-level channel based on Murray's law in proton exchange membrane fuel cell for enhanced mass transfer

The design of flow field has a significant impact on the performance of proton exchange membrane fuel cells (PEMFCs). In this study, a novel leaf bionic flow field is designed and optimized based on Murray's law. The power consumption ratio is first used in the bionic PEMFC. Additionally, an evaluation criterion, the mass transfer efficiency evaluation criterion (MTEEC), is proposed to characterize mass transfer efficiency, and field synergy theory is used to analyze performance differences in mass transfer among various flow fields. The results demonstrate that adding multi-level channel and obstacles in the flow field significantly enhances cell output performance and reduces voltage losses in mass transfer regions. Applying Murray's law to distribute multi-level channel improves the uniformity of oxygen concentration distribution in the flow field and alleviates under-rib water accumulation. Compared to the secondary stream flow field (SSFF), the structure mesh of leaf bionic flow field (SMLBFF) demonstrates a nearly 19% increase in current density output at 0.45 V. SMLBFF exhibits an 81.51% increase in convective mass transfer rate compared to SSFF at 0.4 V. Moreover, the MTEEC of SMLBFF shows improvements of 179.68% at 0.5 A/cm2 and 135.43% at 1.0 A/cm2, compared to SSFF.

Performance Investigation of a Novel Staggered Round Table Channel for Proton Exchange Membrane Fuel Cells

Based on the internal mass transfer of a proton exchange membrane fuel cell (PEMFC), a novel staggered round table channel is proposed, namely, round table stoppers are arranged on both sides of the channel and in the direction of gas flow. The study systematically investigates the effects of various structural parameters on the PEMFC performance, including the arrangement of round tables on both sides of the channel, radius, degree of sparseness, and number. It is found that the staggered arrangement can improve the cell performance more significantly, and the current density can be increased by 5.0% compared with the direct channel. With the proper increase of the radius and number of round tables, the round table stopper forces the reactant to diffuse downward and improves the uniformity of reactant distribution. Compared with other sparsity, the equidistant arrangement of stoppers in the channel is conductive to accelerating the convective mass transfer and drainage characteristics of the cell. As shown by numerical analysis results, the performance and dewatering efficiency of PEMFC are the best when the round tables on both sides are staggered, the radius is 0.65 mm, the number is 10, and the round table in the channel is arranged equidistantly.

Real Case Study of 600 m3 Bubble Column Fermentations: Spatially Resolved Simulations Unveil Optimization Potentials for l-Phenylalanine Production With Escherichia coli.

Large-scale fermentations (»100 m³) often encounter concentration gradients which may significantly affect microbial activities and production performance. Reliably investigating such scenarios in silico would allow to optimize bioproduction. But related simulations are very rare in particular for large bubble columns. Here, we pioneer the spatially resolved investigation of a 600 m³ bubble column operating for Escherichia coli based l-phenylalanine fed-batch production. Microbial kinetics are derived from experimental data. Advanced Euler-Lagrange (EL) computational fluid dynamics (CFD) simulations are applied to track individual bubble dynamics that result from a recently developed bubble breakage model. Thereon, the complex nonlinear characteristics of hydrodynamics, mass transfer, and microbial activities are simulated for large scale and compared with real data. As a key characteristic, zones for upriser, downcomer, and circulation cells were identified that dominate mixing and mass transfer. This results in complex gradients of glucose, dissolved oxygen, and microbial rates dividing the bioreactor into sections. Consequently, alternate feed designs are evaluated splitting real feed rates in two feeds at different locations. The opposite reversed installation of feed spots and spargers improved the product synthesis by 6.24% while alternate scenarios increased the growth rate by 11.05%. The results demonstrate how sophisticated, spatially resolved simulations of hydrodynamics, mass transfer, and microbial kinetics help to optimize bioreactors in silico.

Heat and mass transfer and deformation during chiffon cake baking

The structural transformation from a foam liquid to a porous solid during cake baking involves pore development and solidification, resulting in complex coupled heat transfer, mass transfer, and deformation processes. Studying the mechanisms can provide important references for understanding the physical processes of numerous foods containing gas pores. We constructed a multiphase flow-deformation model for chiffon cake baking, and validated its accuracy by comparing the experimental results of temperature and height. Based on the model, the heat transfer, mass transfer, and deformation characteristics were investigated. In the pore-closed region, the evaporation-diffusion-condensation process of water vapor enhances heat transfer, and its contribution to heat transfer has an equivalent thermal conductivity of up to 0.64 W/(m·K), which increases the heating rate. In the pore-opening region, the water vapor evaporates from the high-temperature, high-water activity region and is transported towards the lower-temperature region and external environment. This process enhances heat transfer and induces an evaporative cooling effect, resulting in a uniform temperature distribution that remains below 100 °C across the majority of the region. Cake expansion occurs in the low-viscosity, pore-closed region, and the water vapor generated at high temperatures serves as the primary driving force source, contributing up to 84.6%.

Microscale heat and mass transfer characteristics of CO2 flooding in nanotubes of tight oil reservoirs

AbstractThe mechanism of heat and mass transfer in tight oil reservoirs after CO2 injection is complex. In this paper, first, a CO2 transfer model within microscale adjacent nanotubes in tight oil reservoirs is established. Then, the typical heat and mass transfer characteristics of microscale CO2 in tight oil reservoirs is analyzed, and the influence of grid density on the calculation results is discussed. Finally, the influence of thermal conductivity of tight oil reservoirs on CO2 physical properties parameters is revealed. Results show that: (a) From the inlet end of the thick nanotube to the outlet of the nanotube, the pressure of CO2 drops from 3.5 to 3.3697 MPa. (b) When the mesh length is equal to 5 nm, the CO2 pressure in the thin nanotube drops from 3.5 to 3.3329 MPa, and the CO2 pressure in the thick nanotube drops from 3.5 to 3.2018 MPa. (c) Organic amines react with CO2 to form salts, which can seal high permeability layers and cracks, but there is a risk of environmental pollution.

Theoretical analysis of heat and mass transfer characteristics of a counter-flow packing tower with different heating modes

Mass extraction/injection and multi-stage system have been proven to be effective approaches to improve the performance of humidification and dehumidification (HDH) desalination system. However, these two optimization schemes cause that the flow ratios of water to air at different positions of humidifier or that of different humidifiers have great difference. A single heating mode is inapplicable to all flow ratios of water to air. Hence, it is necessary to reveal the relationship among mass flow ratio, heating mode and thermal efficiency of humidifier for the selection of appropriate heating mode. A theoretical model of packing tower (typical kind of humidifier) which agrees well with experimental results was established in this paper, and the average relative errors of outlet air temperature, humidity and thermal efficiency are 2.3 %, 4.9 % and 5.8 %, respectively. A comparison among the thermal efficiencies of a counter-flow packing tower with different heating modes (I: solution heated, II: air heated, III: solution-air heated) was conducted. It is found that there exist two values of mass flow ratio (FRI-II and FRII-III) at which the thermal efficiencies of air heated and solution-air heated are equal and that of solution heated and solution-air heated are equal, respectively. However, the thermal efficiency of solution heated is always higher than that of solution-air heated (FRI-III does not exist). It seems clear that there is a relationship between FR and thermal efficiency (η) as follows: FR < FRI-II, ηI > ηIII > ηII; FRI-II < FR < FRII-III, ηI > ηII > ηIII; FR > FRI-II, ηII > ηI > ηIII. Additionally, the effects of inlet parameters on the FRI-II and FRII-III are also evaluated. The results show that the maximum temperature, inlet solution concentration and ambient temperature have positive effects on FRI-II and FRII-III, but ambient relative humidity has negative effect. In the final part, the selection of the heating mode of a counter-flow packing tower is taken as example to introduce the application of FRI-II and FRII-III proposed in this paper.