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• New theory for heat transfer via microbubble mediated solvent phase change. • Prediction for heat transfer coefficient/microbubble phase fraction correlation. • Consistent with analysis of freezing onset for boiled water placed in a freezer. • Inferred HTCs are inversely correlated related to oxygen solubility at onset temp. • Supports assertion that microbubble phase fraction is controlled by initial temp. Microbubbles dispersions in aqueous solutions can be long lived. For instance, 20micron size microbubbles take on the order of a day to rise one meter. Consequently, any currents in a reasonably sized vessel would be expected to entrain such a microbubble dispersion as the buoyant force is exceeded by the inertial force of liquid currents. This paper argues for the advantages of a microbubble dispersion mediated condenser with two benefits. The obvious advantage over fine bubble direct contact heating or cooling is that the microbubble phase, which can be engineered with a throughput of approximately a hectare per second of interfacial area flux per cubic meter of solution volume, should not be limited by heat transfer to and from the liquid and microbubble phase. Rather the limitation will be on the wetted area for heat transfer of the vessel to its heat exchange configuration. The second potential advantage follows from the theory proposed in this paper. Arranging the condenser in the microbubble mediated airlift configuration will introduce additional heat transfer from microbubbles vaporizing hotter water near the central plume and convecting that additional latent heat to the cold wall, which condenses the water vapor and releases the latent heat. This additional convection of latent heat is proposed as an additional source term for heat transport equation, and the magnitude of the effect is shown to be proportional to the phase fraction of microbubbles. This theory is shown to be consistent with analysis of observations of freezing times measured by Mpemba and Osborne [Phys. Educ. 4:172-5, 1969], that infer heat transfer coefficients from fitting Newton's law of cooling. The inferred heat transfer coefficient ratio from the presumed highest microbubble phase fraction to the lowest is ~7.4:1. Whether or not that enhancement level persists to a microbubble condenser in an airlift vessel, the promise of additional heat transfer should be explored. [ABSTRACT FROM AUTHOR]

• A mass transfer rate relaxation method for the distillation is proposed. • The proposed method relaxes the integer stage number into the continuous variable. • The penalty extent of non-integer stage can be manipulated effectively. • Better optimization result is obtained with higher probability due to its characteristic. Determining the optimal state number in distillation column design is a mixed-integer nonlinear programming (MINLP) problem, which is difficult to solve. One strategy to solve this problem is relaxing integer stage numbers into continuous variables and solving an easier nonlinear programming (NLP) problem. However, the existing relaxation model often converges to non-integer stage numbers or poor local optima in practical applications, which motivates this paper to develop a new relaxation model. The proposed relaxation model employs an interpolation function to relax the discrete decision on the existence of a stage by varying interphase mass and heat transfer rate between zero and equilibrium state. By adjusting a shape parameter in the interpolation function, the interpolation function shape and its penalty extent of non-integer stage can be manipulated. The results of three distillation column optimization cases show that the proposed model can effectively avoid converges to non-integer stage numbers or poor optima. [ABSTRACT FROM AUTHOR]

• Flow patterns in helically coiled tubes (HCTs) are classified by visual observation. • Flow-regime map is proposed and mechanisms of flow transitions are presented. • Void fraction for the entire tube cross-section is measured by WMS technique. • New correlations of distribution parameter and drift velocity are proposed. Helically coiled tubes (HCTs) are widely used in industries owing to their compact structure and excellent heat and mass transfer efficiency. Due to the complexity of three-dimensional flow in HCTs, profound knowledge on the flow pattern characteristics is not well documented in existing literature. In this paper, we employ the wire-mesh sensor (WMS) and image tomography technique to measure a series of essential parameters (e.g. flow structures, phase fraction) to explore the flow pattern transition mechanism. According to our observation, bubbly, plug, slug, wavy and annular flow are recognized, and the mechanisms of flow pattern transitions are carefully discussed based on the analysis of the forces. In addition, the variation of void fraction in both temporal and spatial dimensions is discussed in detail. By introducing the drift flux analysis, new correlations of distribution parameter and drift velocity are proposed taking both HCTs structure and flow condition into account. [ABSTRACT FROM AUTHOR]

In this paper, the study of the heat exchange effect on the dynamic behaviour of single-phase natural circulation with internal heat generation is presented. In order to predict natural circulation instabilities, two different methods of analysis are developed and compared. The first approach is a linear analysis in which the governing equations are firstly linearized around a steady-state solution of the system and then treated by means of the Fourier transform. This strategy is adopted to compute, in a semi-analytical way, dimensionless stability maps for different system configurations, highlighting the heat exchange effect on the system dynamics. The second approach consists in numerically solving the nonlinear governing equations and allows investigating some transients of interest. For this purpose, an object-oriented one-dimensional model of natural circulation loops has been developed, and the corresponding results have been compared with RELAP5 and Computational Fluid-Dynamics (CFD) time-dependent simulations. The developed models have been applied to investigate the dynamic behaviour of two loop configurations characterized by large instability regions, namely the Horizontal Heater–Horizontal Cooler (HHHC) and the Vertical Heater–Horizontal Cooler (VHHC). [ABSTRACT FROM AUTHOR]

In this paper, the interfacial heat transfer in spherical and distorted fluid particles, flowing at Re numbers up to 80.0, is studied through the Volume-of-Fluid approach, aiming the development of closure relations for the interfacial heat and mass transfer, in the context of the Two-Fluid model. The Nusselt numbers of spherical particles are compared with the usual correlations presented in the literature to validate the numerical model. From the approach adopted in this work, based on the detailed modeling of the interfacial heat transfer process, it is possible to analyze the local flow structure and thermal field around the fluid particles, providing a better understanding of the effect of the particle deformation on the global heat transfer coefficients. It is shown that the interfacial heat flux distribution is affected by the particles shape, which substantially affects the flow and thermal fields around the fluid particles and, consequently, the total heat transfer rate. In addition, the effect of the increase of the interfacial area density, due to the particle deformation, on the total interfacial heat transfer is analysed. New correlations are proposed for the interfacial Nu or Sh numbers, in single rising fluid particles, which become dependent on the Eötvös ( Eo ) number, and for the correction of the interfacial area density, which should be included in the closure of the interfacial heat or mass transfer terms in the Two-Fluid model equations. It is shown that, as the particles become distorted, the transfer coefficient decreases, but the interfacial area increases, compensating the effect on the total interfacial flow. Nonetheless, for highly distorted particles, the effect of the interfacial area increase becomes dominant and the resulting total interfacial transfer is higher than the case of spherical particles. [ABSTRACT FROM AUTHOR]

The unique properties of ceramic foams make them well suited to a range of applications in science and engineering such as heat transfer, reaction catalysis, flow stabilization, and filtration. Consequently, a detailed understanding of the transport properties (i.e. permeability, pressure drop) of these foams is essential. This paper presents the results of both numerical and experimental investigations of the morphology and pressure drop in 10 ppi (pores per inch), 20 ppi and 30 ppi ceramic foam specimens with porosity in the range of 75–79%. The numerical simulations were carried out using a GPU implementation of the three-dimensional, multiple-relaxation-time lattice Boltzmann method (MRT-LBM) on geometries of up to 360 million nodes in size. The experiments were undertaken using a water channel. Foam morphology (porosity and specific surface area) was studied on post-processed, computed tomography (CT) images, and the sensitivity of these results to CT image thresholding was also investigated. Comparison of the numerical and experimental data for pressure drop exhibited very good agreement. Additionally, the results of this study were verified against other researchers׳ data and correlations, with varying outcomes. [ABSTRACT FROM AUTHOR]

Two-phase flows are regularly involved in the heat and mass transfer in industrial processes. To ensure the safety and efficiency of such processes, an accurate prediction of the flow field and phase distribution by means of Computational Fluid Dynamics (CFD) is required. Nowadays, Direct Numerical Simulations (DNS) of large-scale two-phase flow problems are not feasible due to the computational costs involved. Therefore, the Euler–Euler framework is often employed for large-scale simulations, which involves macro-scale modelling of turbulence, mass and momentum transfer. The research activities at Helmholtz–Zentrum Dresden–Rossendorf (HZDR) focus on general closure models for multiphase flows that are closer to physics and include less empiricism. As part of this effort, an Algebraic Interfacial Area Density model (AIAD) is developed for the morphology detection in the two-fluid Euler–Euler approach. Drag models for free surface flows are often based on experimental correlations, their applicability thus being limited to certain flow regimes. In this paper, a modified free-surface drag model based on local shear stress is investigated that avoids this limitation. For this purpose, the algebraic morphology detection mechanism of the AIAD model is revised. In DNS of free surface flow a dampening of the gas side turbulent fluctuations in the near surface region was found by previous investigators. This effect has also been accounted for in Euler–Euler simulations by means of dampening functions. In this work, the significance of turbulence dampening, in case of free surface flows, is examined quantitatively for the k – ω turbulence model. Model validation is performed with the commercial CFD code ANSYS CFX by means of experimental data of countercurrent, supercritical stratified air–water flow. The revised morphology detection mechanism is seen as an improvement with respect to the detection of sharp interfaces. Satisfactory quantitative agreement is achieved for the modified free surface drag model based on experimental pressure difference, liquid levels and interfacial shear stress. Furthermore, it is demonstrated that turbulence dampening has to be accounted for in the k – ω model to qualitatively reproduce the mean flow and turbulence quantities from the experiment. More CFD grade experimental data is required for further model validation. [ABSTRACT FROM AUTHOR]

• Alternating spout deflection shows satisfactory gas-solid hydrodynamics homogeneity. • Alternating spout deflection shows satisfactory gas-solid heat transfer efficiency and homogeneity. • Spout fluidization has heat core in annulus region due to spout incoherence. Spout deflection has long been regarded as a threat to efficient gas-solid interactions in spout fluidised beds, as it may break the stable symmetrical particle circulation in the spout-fluidisation flow pattern. In this paper, the so-called alternating spout deflection (ASD) is evaluated and compared with the spout-fluidisation (SF) flow pattern in terms of gas-solid hydrodynamics, mixing and heat transfer performance at particle scale by means of a Computer Fluid Dynamic-Discrete Element Method (CFD-DEM) model. The comparisons show in the SF over ~40% particles are in a densely packed state, whereas in the ASD the proportion of particles in a packing state is less than 20%; Then their mixing performance are compared using the improved Lacy index, indicating that the mixing speed and final state of the mixing process are similar. Further, the two patterns are compared in terms of heat transfer. It is indicated that in the ASD flow pattern, the mean particle temperature drops quicker; moreover, the homogeneity of the heat transfer is also better in terms of mean square error of particle temperature, compared to the SF. The underlying mechanism is also explored: in the ASD the hot particle cores can be mitigated due to the spout incoherence phenomena, which is however unavoidable in the SF. This paper corrects the negative view that the alternating spout deflection is not as effective as the spout-fluidisation pattern in terms of gas-solid mixing and heat transfer performance. [ABSTRACT FROM AUTHOR]

• Effect of heat transfer processes on mass transfer during extraction reported. • Conventional and microwave extraction heating rate incrementally effects yield. • Step changes in microwave extraction time only for high dielectric loss biomasses. • Step changes in mass transfer rates achieved above a threshold microwave power. • Temperature-Induced Diffusion experimentally confirmed to drive mass transfer. Solvent extraction is a mass transfer process. In this paper, we investigate the role of heat transfer in solvent extraction: in particular, how the heat transfer properties of the solid and the heating method (conventional heating and microwave heating) drive this mass transfer process. Water-based solvent extraction of pectin from orange peel, apple pomace, mango peel and carrot pulp was carried out. The thermal conductivity and dielectric loss were shown as good predictors of extraction performance, with step change increases in mass transfer rates when microwave processing was applied to biomass with dielectric loss significantly higher than water (e.g. 120 mins reduced to 45 mins for optimal pectin extraction from apple pomace). When the loss factor was lower there was no difference in extraction performance between the two technologies (e.g. carrot pulp extraction time was 60 mins in both cases). Further investigations were carried out at different heating rates for both conventional and microwave extraction in order to decouple the effects of microwave volumetric and selective heating. It was shown that below a certain power threshold (within the range of 100–120 W in these experiments), microwave and conventional extraction are equivalent, while above the threshold, microwaves achieved a step-change in extraction time. These findings are the first experimental confirmation of recent theoretical advances in microwave biomass processing, in which Temperature-Induced Diffusion drives mass transfer. It is also the first paper to allow identification of biomass characteristics that will be most amenable to microwave extraction. [ABSTRACT FROM AUTHOR]

The absorption of steam bubbles in a hot aqueous solution of Lithium Bromide is a key process that occurs in the absorber vessel of a heat transformer system. During the condensation process, their size and shape changes dynamically with time as they rise up through the column of liquid. An understanding of the factors that control the vertical upwards motion of the bubbles is necessary to enable proper design of such units. However, the exact vertical displacement of a bubble moving through a liquid is difficult to predict and becomes much more complex if the bubble is simultaneously collapsing. In this paper, the displacement of steam bubbles collapsing in a concentrated aqueous lithium bromide solution (LiBr–H 2 O) has been quantified experimentally. A simple kinetic model predicting the vertical displacement as a function of time was then developed from elementary force–balance considerations. A key feature of the system is the large variability in the motion of the bubbles arising from extreme fluctuations in their size and shape. Bubble dynamic morphology was modelled with stochastic techniques and the output from this was used in the kinetic model to predict dispersion in bubble displacement with time. While the uncertainty predicted by the stochastic model is shown to be less than that observed experimentally, it nonetheless highlights the importance of this random behaviour during the design of such an absorption column. [ABSTRACT FROM AUTHOR]

Two-phase flow without phase change can radically increase the heat transfer rate in microchannels due to the internal recirculation of the fluids. In this paper, both numerical and experimental studies on the hydrodynamics and heat transfer of two-phase flow without phase change in small channels and tubes are reviewed. These two-phase flows are either made up of gas–liquid or immiscible liquid–liquid slug flows. This review includes a general introduction of the hydrodynamics of two-phase flow in microchannels and shows that there is little agreement between measured and predicted pressure drop. Furthermore heat transfer rates are examined in the form of Nusselt number ( Nu ) correlations based on different flow parameters. Values are compared using a standard flow regimes for two-phase slug flow indicating huge variability (over 500%) in the Nu values obtained from reported correlations. We attribute this to insufficient description and consideration of the flow conditions. Finally a perspective on future research directions in the field is suggested, including control through wettability and the use of novel liquids. [ABSTRACT FROM AUTHOR]

This paper presents a constitutive equation for the thermal heat transfer associated by mass transfer, applicable to both Eulerian–Eulerian and Eulerian–Lagrangian multiphase computational fluid dynamic models. The proposed equation was incorporated into the open-source multiphase CFD code MFIX ( https://mfix.netl.doe.gov ) to demonstrate that the numerical predictions match experimental data for the limiting cases of evaporation and condensation. The application of the proposed equation to two cases of a reacting carbon particle yields physically consistent expressions for the heats of reaction. [ABSTRACT FROM AUTHOR]

This paper examines the convective heat transfer in the turbulent bubbly flow between two parallel walls under a constant heat flux condition with a Reynolds number of up to Re=5600 based on the channel width and the average velocity. Direct numerical simulation is used to fully resolve the turbulent flow and the motion of bubbles. The channel is vertical and the flow is directed upward so that nearly spherical bubbles accumulate at the wall but deformable bubbles remain in the middle. The results show that the presence of bubbles enhances the mixing and consequently the heat transfer for both nearly spherical and deformable bubbles, as compared with results for single-phase flows. [ABSTRACT FROM AUTHOR]

This paper presents a transient model of internal catalytic combustion suitable for isolated channels and monolith reactors. Due to time-scales in the problem, the model considers a quasi-steady gas phase with a transient solid. The gas is described by axially varying bulk temperature and species. The gas includes lateral diffusion via transfer coefficients and the specification of a gas-phase species concentration at the wall; axial diffusion is neglected. The solid phase is a thermally thin shell with axially varying temperature, surface species, and surface species concentrations. The solid includes axial heat conduction and external heat loss by convection and radiation. The combustion process utilizes detailed gas and surface reaction models. The gas-phase model becomes a system of stiff ordinary differential equations with respect to axial position; the upstream (inlet) boundary conditions are specified and the axially varying solid properties are parameters in integration. The solid phase discretizes into a system of stiff ordinary differential-algebraic equations with respect to time. The time evolution of the system comes from alternating integrations of the quasi-steady gas phase and transient solid. The model is compared to two experimental cases using CO fuel: (1) steady-state conversion in an isothermal platinum tube and (2) transient propagation of a catalytic reaction inside a small platinum tube and includes external tube temperature measurements. This work presents sensitivity studies on important parameters including internal transfer coefficients, catalytic surface site density, external heat-loss, and others. Under mass-transfer limited conditions, global transfer coefficients are adequate to predict fuel conversion. Near light-off, the model predictions improve for the first case after adjusting the surface kinetics such that the net rate of CO adsorption increases compared to O 2 . For the second case, predictions of transient propagation speeds are good for equivalence ratios near unity and greater but require adjustment of external heat loss or kinetics to match under lean conditions. [ABSTRACT FROM AUTHOR]

This paper reviews the use of direct numerical simulation (DNS) models for the study of mass, momentum and heat transfer phenomena prevailing in dense gas-solid flows. In particular, we consider the DNS models as the first important step in a multiscale modeling strategy. Both the merits and the limitations of different DNS methods are discussed, in particular for the field of fluidized bed modeling. The importance of the closures for interfacial transfer of mass, momentum and heat, obtained from DNS and applied in coarser scale models, is demonstrated with illustrative examples. Finally, we present our view on required future developments of DNS models for the investigation of various chemical engineering problems. [ABSTRACT FROM AUTHOR]

In this paper we report the extension of an earlier reported DNS method (Deen et al., 2012; Deen and Kuipers, 2013) based on a novel Immersed Boundary Method (IBM) which incorporates the fluid-solid coupling at the level of the discrete field equations. The extended method is used to study coupled mass and heat transport in dense fluid-particle systems where the coupling arises as a consequence of an exothermal chemical reaction proceeding at the exterior surface of the particles. Following a detailed verification (using an independent numerical technique) and validation (using established empirical correlations) we apply our DNS technique to study coupled mass and heat transfer in a dense fluid-particle system. In addition a comparison is made with results obtained from a simple one-dimensional (1D) heterogeneous reactor model which uses empirical closures for the fluid-particle mass and heat transfer coefficients. The main features of the complex transient temperature profiles obtained from our DNS agree quite well with the corresponding profiles obtained from the 1D heterogeneous reactor model. [ABSTRACT FROM AUTHOR]

Abstract: The optimal integration of work and its interaction with heat can represent large energy savings in industrial plants. This paper introduces a new optimization model for the simultaneous synthesis of work exchange networks (WENs), with heat integration for the optimal pressure recovery of process gaseous streams. The proposed approach for the WEN synthesis is analogous to the well-known problem of synthesis of heat exchanger networks (HENs). Thus, there is work exchange between high-pressure (HP) and low-pressure (LP) streams, achieved by pressure manipulation equipment running on common axes. The model allows the use of several units of single-shaft-turbine-compressor (SSTC), as well as stand-alone compressors, turbines and valves. Helper motors and generators are used to respond to any demand and excess of energy. Moreover, between the WEN stages the streams are sent to the HEN to promote thermal recovery, aiming to enhance the work integration. A multi-stage superstructure is proposed to represent the process. The WEN superstructure is optimized in a mixed-integer nonlinear programming (MINLP) formulation and solved with the GAMS software, with the goal of minimizing the total annualized cost. Three examples are conducted to verify the accuracy of the proposed method. In all case studies, the heat integration between WEN stages is essential to improve the pressure recovery, and to reduce the total costs involved in the process. [Copyright &y& Elsevier]

Abstract: Conventional network structure modifications for retrofitting heat exchanger networks (HENs) usually require a large network superstructure, which might lead to very large scale retrofit models, and thus increases the computational difficulties of optimization, especially for industrial applications. This paper presents a novel optimization approach of retrofitting HENs for both small scale and industrial scale problems. To overcome the drawback of the existing retrofit research, a simple but efficient method is proposed to determine the network retrofit superstructure based on the concept of pinching match. Then two optimization stages (network structure optimization and investment optimization) are solved with the MILP-based iteration method that has been developed. The proposed approach has many benefits for solving HEN retrofit problems. First, smaller size of retrofit superstructure is provided based on the pinching match analysis. Second, the MILP-based iteration method developed converts conventional a mixed integer non-linear programming (MINLP) to a mixed integer linear programming (MILP), and significantly reduce the computational difficulties of nonlinear programming associated with configurational changes or structural modifications for existing heat exchanging arrangements, which is upgraded based on the MILP-based iterative method proposed by Pan et al. (2012a) for retrofitting HENs with heat transfer intensifications, as the earlier work was only applicable to the cases without network topology modification. In case studies, the new proposed approach is compared with the existing methods in two literature examples and one industrial problem, demonstrating that the new proposed approach is able to obtain better and more realistic solutions for HEN retrofitting considering the economic trade-offs between energy savings and investments. [Copyright &y& Elsevier]

This paper demonstrates the capacity of dense suspensions of solid particles to transfer concentrated solar power from a tubular receiver to an energy conversion process by acting as a heat transfer fluid. Contrary to a circulating fluidized bed, the dense suspension of particles’ flows operates at low gas velocity and large solid fraction. A single-tube solar receiver was tested with 64µm mean diameter silicon carbide particles for solar flux densities in the range 200–250kW/m2, resulting in a solid particle temperature increase ranging between 50°C and 150°C. The mean wall-to-suspension heat transfer coefficient was calculated from experimental data. It is very sensitive to the particle volume fraction of the suspension, which was varied from 26 to 35%, and to the mean particle velocity. Heat transfer coefficients ranging from 140W/m2 K to 500W/m2 K have been obtained, thus corresponding to a 400W/m2 K mean value for standard operating conditions (high solid fraction) at low temperature. A higher heat transfer coefficient may be expected at high temperatures because the wall-to-suspension heat transfer coefficient increases drastically with temperature. The suspension has a heat capacity similar to a liquid heat transfer fluid, with no temperature limitation but the working temperature limit of the receiver tube. Suspension temperatures of up to 750°C are expected for metallic tubes, thus opening new opportunities for high efficiency thermodynamic cycles such as supercritical steam and supercritical carbon dioxide. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the mathematical modeling of the ice crystallization process occurring during the freezing of sorbet in a continuous scraped surface heat exchanger (SSHE). Two different modeling approaches have been used, both of which include the nucleation, growth and breakage phenomena of the ice crystals. For both models, the rate of ice crystal nucleation and growth were determined by the subcooling degree. The first model combines heat transfer and population balance equations (PBE), assuming plug flow. The evolution of the values of product temperature, mean chord length, ice volume fraction and apparent viscosity were determined as a function of the residence time. The second model is a coupled model of heat transfer and PBE combined with an empirical model of residence time distribution (RTD), which makes it possible to take into account the fact that the fluid fractions flowing throughout the SSHE do not have the same time–temperature history. The values of the variables (product temperature and mean chord length) were determined for each fraction of fluid exiting the SSHE, and the bulk values were then calculated using the RTD. Simulation results were compared to a set of experimental data obtained during the ice crystallization process of sorbet in a continuous SSHE at the laboratory pilot scale. With a first estimated set of model parameters, it has been shown that the experimental tendencies are represented very satisfactorily by the two models within a 10% error limit. These modeling approaches can then be considered as a promising tool for the understanding and the prediction of the ice crystallization process in SSHEs so as to identify new ways to improve the performance of the process. [Copyright &y& Elsevier]

Abstract: In this paper a simulation model is presented for the direct numerical simulation (DNS) of wall-to-liquid heat transfer in dispersed gas–liquid two-phase flow using a volume of fluid (VOF) approach. Our model extends the VOF model developed by van Sint Annaland et al. (2005) to non-isothermal conditions. Our VOF method involves an interface reconstruction technique based on piecewise linear interface representation. The surface tension is incorporated using a three-dimensional version of the continuous surface force (CSF) model of Brackbill et al. (1992). The model is applied to predict the heat exchange rate between the liquid and a hot wall kept at a fixed temperature. It is found that, due to bubble induced agitation in the liquid phase, the heat transfer rate between the wall and the liquid is considerably enhanced especially when bubble coalescence prevails in the vicinity of the hot wall. Although this finding is obvious from an intuitive point here we present quantitative results to describe this phenomenon. [Copyright &y& Elsevier]

Abstract: Until recently, generating clouds of microbubbles was a relatively expensive proposition, with the smallest bubbles requiring high energy density from either the saturation–nucleation mechanism or Venturi effect. Due to the expense of processing with microbubbles, exploration of the acceleration effects of microbubbles for physico-chemical processes are largely unstudied, particularly those that are combined effects. In this paper, the trade-off between heat transfer and evaporation on the microbubble interface are explored, largely by computational modelling but supported by some experimental evidence. The hypothesis is that both processes are inherently transient, but that during short residence times, vaporization is favoured, while at longer residence times, sensible heat transfer dominates and results in re-condensation of the initially vaporized liquid. The computational model address how thin a layer thickness will result in the maximum absolute vaporization, after which sensible heat transfer condenses the vapour as the bubble cools. This maximum vaporization layer thickness is estimated to be a few hundred microns, on the order of a few microbubble diameters at most. If the maximum vaporization estimate and the contact time necessary to achieve it are accurately estimated, these are engineering design features needed to design a vaporizing system to achieve maximum removal of vapour with minimum heat transfer. The modelling work presented here should be considered in light of the humidification experiments also conducted which showed the exit air at 100% saturation, but increasing gas temperature with decreasing layer height, and decreasing water temperature with decreasing layer height, all of which are consistent with the predictions of the computational model. [Copyright &y& Elsevier]

Abstract: A method for the modeling of a seepage catalytic packing internal (SCPI) in a catalytic distillation column was developed and applied to the simulation of a catalytic distillation (CD) process. Based on the structure of the internal, rigorous mathematical models consisting of differential algebraic equations were developed to predict the temperature and composition profiles in the CD column. Based on the gPROMS platform, the gPROMS language was used to compile three modules, one for the reaction and the other two modules for hydrodynamic calculations and heat and mass transport calculations. In addition, a graphical user interface (GUI) design and the corresponding port design were implemented for each unit module to clearly represent the flow-sheet of the catalytic distillation process. According to the characteristics of the model, a new approach was proposed to avoid convergence difficulties and to improve the stability of the calculations. This approach was demonstrated to be an efficient method, which can reduce the simulation time and still accurately predict the results. Mathematical models and corresponding programs of reaction, separation, and the flow-sheet of CD process were validated. The simulated results were in good agreement with the experimental results, indicating that the simulation methods established in this paper are feasible. Furthermore, the gPROMS is a reliable and suitable technique for studying the catalytic distillation process of SCPI. [Copyright &y& Elsevier]

Abstract: Accurate predictions of the sulfuric acid condensation behavior on the surfaces of heat exchangers are crucial for understanding the local low-temperature corrosion characteristics of heat exchangers and designing them. In this paper, a new numerical model has been developed to predict the condensation rate of sulfuric acid and condensate acidic solution concentration on heat exchanger surfaces. By correlating the vapor–liquid equilibrium (VLE) data of H2SO4–H2O solutions from experiments and in conjunction with multi-component diffusion theory, the proposed model obtains numerical solutions of condensation heat transfer under the conditions of a coupled wall and fluid boundary condition and a multi-component mixture of flue gas and the sulfuric acid solution (saturated partial pressure of sulfuric acid and water vapor). The numerical model has been validated by a comparison of the simulation results with available experimental data, and applied to an analysis of the H-type finned tube heat exchanger, which has been widely used in the field of waste heat recovery. The distributions of the condensation rate and condensate concentration on the fin surface are also calculated. The results show that the three dimensional distribution of acid solution concentration is consistent with the fin temperature. An increase in water vapor could result in a sharp reduction of the acid solution concentration and an increase in deposition, which may indicate a serious risk for low-temperature corrosion. In contrast, increasing the flue gas temperature will reduce the corrosion risk by reducing the condensation rate and increasing the acid concentration. [Copyright &y& Elsevier]

Abstract: Direct contact heat transfer via injection of volatile liquid is an effective strategy for removing heat from a viscous liquid pool. The rapid evaporation effectively removes heat and the generated bubbles move quickly to the top surface. In this paper, we present an experimental and phenomenological analysis of the evaporation of a drop in a slightly miscible liquid. The phenomenon was visualized using a two-dimensional transparent experimental set-up with a single inlet at the bottom. The videos were used to estimate bubble dimensions, its rise velocity, distance from the detachment point, and fraction of vapor and the liquid phases in the evaporating drop. The initial drop size, temperature difference between the hot fluid and the low boiling solvent and the nucleation rate governed the rate of change of the drobble (combined entity of drop and bubble) diameter and its rise velocity. A phenomenological model describing transient behavior of drobble (motion and heat transfer) is developed. The transient variation in the interfacial areas for heat transfer and the projected area were found to have effect on the predictions. The model and results will also provide useful basis for extending the work towards better understanding of direct contact heat transfer in viscous systems like polymerization reactors. [Copyright &y& Elsevier]

• New theory: coupled heat transfer, dissolved gases & microbubble phase change. • Consistent with analysis of endogeneous microbubbles from saturation/nucleation. • Theory agrees with analysis of onset of freezing for (un)boiled water. • Propositions to explain why sometimes the Mpemba effects (un)observed. Zimmerman [Chem.Eng.Sci. 238: 116618, 2021] developed a theory for additional convection of latent heat by microbubbles from regions of hot water to regions of cold water, a modified heat transport equation that incorporates this convective effect, and a scaling analysis that gives a rough prediction for how this additional heat transfer is proportional to the phase fraction of microbubbles. This theory is supported by arguing that Mpemba and Osborne (1969) had such microbubbles dispersed, resulting in a strong correlation between the dissolved gas solubility at saturation, dependent on the sole controlled variable – the initial temperature of the freezing experiment – and the inferred heat transfer coefficient. The argument was made that the source of the microbubbles was exogeneous due to vigorous boiling. In this paper, a range of systematic errors and uncertainties concerning the Mpemba effect is explored. The two largest uncontrolled variables are the level of vigorous boiling and the level of dissolved gases in tap water. Using the same approach for estimation of the heat transfer coefficients, the experiments of Bregovic (2012) which had no boiling are analyzed. The resulting heat transfer coefficients are shown to pass the accepted Mpemba line criteria for the occurrence of a Mpemba effect. Employing the scaling analysis for additional heat transfer shows reasonable agreement with the hypothesis that source of microbubbles in Bregovic's experiments is endogeneous: the saturation-nucleation mechanism for spontaneous growth of microbubbles in supersaturated water. The parallel analysis applied to the experiments of Mpemba and Osborne show consistency with predictions of endogenous microbubble generation, too. [ABSTRACT FROM AUTHOR]

Abstract: This paper analyses reaction and thermal front development in porous reservoirs with reacting flows, such as those encountered in oil shale upgrading. A set of dimensionless groups and a 1D code are developed in order to investigate the important physical and chemical variables of such reservoirs when heated by in situ methods. Theory necessary for this study is presented, namely shale decomposition chemical mechanisms, governing equations for multiphase flow in porous media and necessary closure models. Plotting the ratio of the thermal front speed to the fluid speed allows one to infer that the reaction front ends where this ratio is at a minimum. The reaction front follows the thermal front closely, thus allowing assumptions to be made about the extent of decomposition solely by looking at thermal front progression. Furthermore, this sensitivity analysis showed that a certain minimum permeability is required in order to ensure the formation of a traveling thermal front. Compared to varying deposit porosities and kerogen activations energies, varying temperature, pressure and permeability are more important. [Copyright &y& Elsevier]

Abstract: Multiphase heat and mass transfer in microscale devices is a growing field of research due to the potential of these devices for use in various engineering applications. Before the heat and mass transport phenomena in such systems can be modeled, the hydrodynamics of adiabatic multiphase flow, in the absence of specie transport across interfaces, must be accurately predicted. In the present paper, a finite element implementation of the phase field method is applied to simulate Taylor flow in mini/microchannels. Channels with characteristic dimensions ranging from 100 to 500μm are modeled and criteria present in the literature for domain discretization are assessed. The effects of phase field parameters, namely mobility and interface thickness, on the predicted flow features are discussed. The predicted Taylor bubble lengths are compared against empirical correlations as well as available experimental data in the literature. The predicted gas void fraction data for different channel dimensions are compared with numerous experimental studies. The present results indicate a linear variation of gas void fraction with respect to volumetric flow ratio for all channel sizes. [Copyright &y& Elsevier]

Abstract: The formation of gas bubbles in a liquid is of both academic and industrial interest, and sets the initial conditions for the hydrodynamics, heat and mass transfer as well as chemical reactions from a dispersed gaseous phase to the liquid phase in industrial processes. The literature on bubble formation from a single submerged orifice is large in both Newtonian and non-Newtonian fluids. Despite the numerous theoretical and experimental investigations, the mechanisms of bubble growth and detachment remain far from fully understood. The study of bubble formation at micro-scale and especially in the presence of a lateral liquid flow field is still very limited. This is the topic for consideration in the present paper. In particular, this study compares both qualitatively and quantitatively the formation of bubbles at micro- and macro-scales. A high-speed digital camera (up to 10,000 imagess−1), a micro-Particle Image Velocimetry (μ-PIV) system and also a macro-PIV (PIV) were employed in this work, to measure the velocity flow field at micro- and macro-scales. At macro-scale, experiments were conducted in a square Altuglas column of 0.1m filled with water or viscous Emkarox solutions using different orifice sizes and various gas flowrates. A rotating device above the orifice in the column was used to impose a shear flow on the forming bubble at the orifice. At micro-scale, different sizes of micro-reactors (600 and 1000μm) and different micro-devices were employed to compare the mechanism of bubble formation. A correlation based on dimensionless numbers was proposed to estimate the formed bubble volume at micro- and macro-scales in order to reveal the main factors governing the formation mechanisms. [Copyright &y& Elsevier]

Abstract: The deposition of calcium carbonate on solid surfaces under certain conditions poses a serious problem to many industries. This scaling may lead to a lowering of heat transfer efficiency, increased energy consumption and unscheduled equipment shutdown. In order to prevent potential scaling problems it is, therefore, important to understand the mechanism of calcium carbonate deposition. This paper is an extension of previous work on the understanding of calcium carbonate crystal formation, aggregation and deposition. It describes the application of an inline technique based on Focused Beam Reflectance Measurement (FBRM) to determine the rate of calcium carbonate formation. FBRM provides a real time measurement of the dimension and number of crystals and this technique has proven to be a sensitive method with which to monitor the initial stages of the scale formation process. The effect of initial calcium ion concentration and temperature on the scaling rate has been determined, and these inline results validated from complementary offline scale measurement techniques. [Copyright &y& Elsevier]

Abstract: Supersonic quenching of magnesium vapour plays a pivotal role in the carbothermal reduction process for magnesium and the production of fine magnesium powders. Modelling of this process has previously been based on Classical Nucleation Theory in a one-dimensional flow expansion without considerations of background gas turbulence and the associated heat and mass transfers. This paper presents a single-velocity field, multi-component fluid model that overcomes the above shortcomings. The model has been validated using steam condensation data and applied to study supersonic quenching of magnesium vapour in a laboratory-scale Laval nozzle. Modelling results indicate a strong dependence of the vapour condensation characteristics on parameters such as vapour concentration and choice of carrier gas. The model is potentially a useful tool for designing and up-scaling processes that utilise supersonic quenching of metallic vapours. [Copyright &y& Elsevier]

Abstract: Sufficient downhole steam equality is important for the success of steam injection performance. In this paper, a system model is developed to predict steam quality with variable (T, P) fields in steam injection wells. In particular, the formation temperature, which changes over time, was examined. A hybrid algorithm for solving the model is used, along with the fourth-order Runge–Kutta method and the finite difference method. Data from a Chinese X Well is used as a case history to verify the calculations and a trend and sensitivity analysis was also done for the model. The effect of the process variables such as injection rate, injection pressure, pipe diameter and heat insulation thickness were put into test for the sensitivity of the model. The results provide technical reliability when designing well tests in deviated wells. [Copyright &y& Elsevier]

Abstract: This paper is devoted to the heat and mass transfer characteristics of the magnetohydrodynamic nanofluids flow over a permeable stretching/shrinking surface. The hydrodynamic as well as thermal slip conditions are accounted for. The novelty is that derivation of exact analytical solutions are aimed for different water-based nanofluids containing Cu, Ag, CuO, , and TiO2. Results of the present analysis in the absence of hydrodynamic and thermal slip for the stretching sheet are in excellent agreement with those available in the literature. The velocity and temperature profiles, skin friction coefficient and Nusselt number are easily examined and discussed via the closed forms obtained. A rescaling of the governing equations is also proposed, which enables one to interpret the physical coefficients in terms of the published data. [Copyright &y& Elsevier]

Abstract: Sorption enhanced methane reforming (SER), employing a CaO-based solid as a high temperature CO2 sorbent, is generally considered to be a promising route for H2 production. In this paper we present a dynamic pseudo-homogeneous model to describe the operation of a packed bed reactor in which the SER reaction is carried out under adiabatic conditions. This reactor can be implemented according to several process schemes, including a novel Ca/Cu looping process for hydrogen generation with inherent CO2 capture. The proposed SER model is based on the well-established principles of gas–solid contact and heat transfer in fixed-bed reactors and on the kinetic expressions published in the literature that describe the main reactions involved in the process. The resulting model describes the transient performance of the SER reaction and confirms the theoretical viability of this critical reaction stage in a large scale H2 production facility. It is demonstrated that the SER process can yield a CH4 conversion and H2 purity of up to 85% and 95%, respectively, under operating conditions of 923K, 3.5MPa, a steam/carbon ratio of 5 and a space velocity of 3.5kg/m2 s. [Copyright &y& Elsevier]

Abstract: In this paper a novel simulation technique is presented to perform Direct Numerical Simulation (DNS) of fluid flow and heat transfer in dense fluid–particle systems. The unique feature of our fluid–solid coupling technique is the direct (i.e., implicit) incorporation of the boundary condition (with a second-order method) at the surface of the particles at the level of the discrete momentum and thermal energy equations of the fluid. Contrary to lattice Boltzmann or other commonly used immersed boundary implementations, our method does not require using any effective diameter. A fixed (Eulerian) grid is utilized to solve the Navier–Stokes equations for the entire computational domain. Dissipative particle–particle and/or particle-wall collisions are accounted via a hard sphere discrete particle approach using a three-parameter particle–particle interaction model accounting for normal and tangential restitution and tangential friction. Following the detailed verification of the method several dense multi-particle systems are studied in detail involving stationary arrays of particles and fluidized particles. [Copyright &y& Elsevier]

Abstract: This paper presents a CFD modeling of hydrodynamics, heat transfer and cracking reaction in a heavy oil riser together with a bottom airlift loop mixer. By extending a validated gas–solid flow model to incorporate feedstock vaporization and 12-lump kinetic model, a three-phase flow and reaction model is established. CFD analysis is performed, and the effects of operating parameters are thus evaluated. The results indicate that the bottom airlift loop mixer causes the hot and the cool catalyst well mix and obtains a uniform catalyst temperature at riser inlet. There exists optimal product distribution, with a maximum light liquid yield at about 30.0m of up the riser. Product yields are more sensitive to injection angle than to feedstock droplet size and reaction temperature. A catalyst-to-oil ratio in the range of 7–8 and a shorter reaction time of 3.02s are preferable for a higher light liquid yield. [Copyright &y& Elsevier]

Abstract: In this paper, a new analytical method named DTM-BF is proposed and applied to study the MHD mixed convective flow and heat transfer of an incompressible, viscous and electrically conducting fluid over a stretching permeable wedge in the presence of thermal radiation and ohmic heating. The boundary layer governing equations of PDES are transformed into highly nonlinear coupled ODES and the approximate solutions are derived by the new proposed analytical technique—the differential transformation and basis functions method (DTM-BF) on unbounded domains. The effects of the velocity ratio parameter, magnetic field parameter, the wedge angle parameter, the mixed convection parameter, suction/injection parameter, thermal radiation parameter, Eckert number and Prandtl number are presented. Moreover, the reliability and effectiveness of the DTM-BF have been verified by comparing analytical results with numerical solutions. Some new characteristics of the mixed convective flow and heat transfer over a wedge are investigated and discussed. [Copyright &y& Elsevier]

Abstract: This paper considers a new approach of improving the efficiency of adsorption–catalytic removal of volatile organic compounds (VOCs) from waste gases based on the use of a combined structured fixed bed consisting of a coarse-grained adsorbent–catalyst and a microfiber catalyst. Numerical mathematical modeling showed that during high-temperature oxidative regeneration of the adsorbent–catalyst, the microfiber catalyst (∼0.01mm in diameter) is heated much faster than large pellets (∼2–20mm in diameter) of the adsorbent–catalyst due to the significantly higher external specific surface area (∼500–5000 times greater). This allows one to efficiently oxidize unoxidized VOCs desorbed from the surface of the adsorbent–catalyst, thus minimizing the desorption losses and significantly increasing the degree of gas purification (up to 99%). [Copyright &y& Elsevier]

Abstract: In gas–solid riser flows, meso-scale structures have significant effects on the flow, mass/heat transfer as well as reaction behavior. To be consistent with these structures, this paper reformulates the Energy-Minimization Multi-Scale (EMMS) model in terms of its structure-dependent conservation equations. These conservation equations (namely the Structure-dependent multi-Fluid Model, SFM) may reduce to the Two-Fluid Model (TFM) if homogeneous distribution is assumed within each grid, and restore to the balance equations of the original EMMS model if they are used to describe steady-state, global behavior. The closure of the structure-dependent parameters in SFM requires the stability condition defined in the original EMMS model. Thus, the EMMS-based multi-Fluid Model (EFM) can be defined with the stability-constrained SFM. Our previous practice in Multi-Scale Computational Fluid Dynamics (MSCFD), which is characterized by coupling of TFM and EMMS drag coefficient, can then be viewed as a simplified realization of EFM. Finally, simulation with this simplified version of EFM was performed and compared to experimental data for verification. [Copyright &y& Elsevier]

Abstract: Followed by the numerical study of , the macroscopic hydrodynamic and heat transfer characteristics in some novel structured packed beds are experimentally studied in this paper, where the packings of ellipsoidal or non-uniform spherical particles are investigated for the first time with experiments and some important results are obtained. For present experiments, the interstitial heat transfer coefficient in the packed bed is determined using an inverse method of transient single-blow technique. The effects of packing form and particle shape are carefully investigated and the experimental and numerical results () are also compared in detail. Firstly, it is discovered that, the computational method reported by might be appropriate for heat transfer predictions in structured packings, while it might underestimate the friction factors, especially when the porosity is relatively low. Secondly, it is found that, the traditional Ergun''s and Wakao''s equations might overpredict the friction factors and Nusselt numbers for the structured packings, respectively, and some experimental modified correlations are obtained. Furthermore, it is also revealed that, both the effects of packing form and particle shape are significant to the macroscopic hydrodynamic and heat transfer characteristics in structured packed beds. With proper selection of packing form, such as simple cubic packing (SC) and particle shape, such as ellipsoidal particle, the pressure drops in the structured packed beds can be greatly reduced and the overall heat transfer performances will be improved. These experimental results would be reliable and useful for the optimum design in industry applications. [Copyright &y& Elsevier]

Abstract: Equation of power consumption in the flow process of micro-fluid elements has been deduced in this paper by analyzing the mechanical energy equilibrium equation of microelement based on the stress relation of Newtonian fluid. By setting minimum power consumption as optimization objective and entransy consumption as constraint condition, optimization flow field equation for convective heat transfer on the basis of energy conservation equation and continuity equation are constructed. Numerical investigations of forced convective heat transfer in a circular tube based on the optimized controlling equations are conducted, and the results show that there are multi-longitude-vortexes existing in velocity field, which leads to an enhancement of heat transfer. The analysis for the heat transfer and flow resistance shows that this kind of flow field accommodates a far greater heat transfer increase than flow resistance increase, which proves that the proposed optimization theory is effective in designing high efficient heat transfer enhancement unit. [Copyright &y& Elsevier]

Abstract: The paper deals with thermosolutal Marangoni convection, which can be formed with an electrically conducting fluid along a vertical surface in the presence of a magnetic field, heat generation and a first-order chemical reaction. In conformity to actuality, it is assumed that the surface tension varies linearly with both the temperature and concentration and that both interface temperature and concentration are quadratic functions of the interface arc length x. The general governing partial differential equations are converted into nonlinear ordinary differential equations using unique similarity transformations. The analytical approximate solutions of similarity equations are firstly obtained by double-parameter transformation perturbation expansion method and Padé approximants technique. The effects of Hartmann number, heat generation coefficient and the chemical reaction coefficient on the velocity, temperature and concentration profiles as well as the wall velocity are presented and discussed. [Copyright &y& Elsevier]

Abstract: In this paper, linear programming formulations, complemented by concept based pinch analysis results, are developed to target the minimum energy requirements in a heat integrated fixed flow rate water allocation networks. These formulations can be applied for the cases of heat integration through isothermal and non-isothermal mixing in water allocation networks involving single as well as multiple contaminants. The earlier reported approaches are based on linear programming formulation for the case of isothermal mixing and either mixed integer non-linear programming or discontinuous non-linear programming formulations for the case of non-isothermal mixing. It has been observed that the earlier reported methodologies produce sub-optimal results for the case of non-isothermal mixing. However, the proposed methodologies produce the optimum results because of the rigorously proved linear formulation. Utility requirements for isothermal as well as for non-isothermal mixing cases are compared over a range of minimum approach temperatures, to evaluate the energy performance using illustrative examples. [Copyright &y& Elsevier]

Abstract: The paper presents a model-based investigation of a metal hydride reactor applied as a solid state hydrogen storage device. The elements of a metal hydride reactor are hydrogen supply duct, internal hydrogen distribution, hydride bed, reactor shell and the flow domain of the heat transfer fluid. Internal hydrogen distribution and hydride bed are porous media. Therefore, hydrogen flows through non-porous and porous regions during its reversible exothermic absorption and endothermic desorption, respectively. The interface between porous and non-porous regions is a discontinuity with respect to energy transport mechanisms. Hence, Danckwerts-type boundary conditions for the energy balance equation are introduced. Application of the first and second law of thermodynamics to the interface reveals that temperature jumps may occur at the hydrogen inlet but are not allowed at the hydrogen outlet. Exemplarily the loading behavior of a metal hydride storage tank based on sodium alanate is analyzed. It is demonstrated and experimentally validated that only Danckwerts-type boundary conditions predict the important cooling effect of the inlet hydrogen on the exothermic absorption process correctly. [Copyright &y& Elsevier]

Abstract: In this paper, the regulation problem of convection governed dynamical processes described by linear distributed parameter models with position-independent inputs is addressed by combining the method of characteristics (MC) and the Malek-Zavarei and Jamshidi theorem. In this approach, the MC is used to transform the first order partial differential equations model of such processes into a set of time-delayed ordinary differential equations whose elements are used to generate certain matrices that satisfy linear matrix inequalities that render the proportional integral (PI) control parameters that guarantee the process stability. The performance of the proposed PI controller is tested via numerical simulations in the temperature regulation of a linear heat exchanger and compared to a tightly tuned classical PI controller. The application of the proposed controller is extended to regulate the outlet concentration in a nonlinear non-isothermal plug flow reactor. It is shown that the proposed controller is able to handle the infinite dimensional nature of the process model yielding smooth and unsaturated responses around the predetermined set-point trajectory in the face of load changes, time varying boundary conditions and set-point changes. [Copyright &y& Elsevier]

Abstract: Nuclear magnetic resonance (NMR) is used to non-destructively measure the moisture and dehydration profiles in gypsum during one sided heating to temperatures of 400°C reflecting the conditions during fire. The temperature and moisture profiles are recorded simultaneously. The gypsum used in the experiments was extensively characterised using TGA, DSC, MIP, and NMR. The influence of the initial moisture content on the drying and dehydration processes was tested by varying the moisture content of the samples: capillary saturated, 50% RH, and 0% RH. By calibrating the NMR signal with moisture content we have shown that it is possible to not only measure free or absorbed water with NMR, but also measure the degree of hydration of the gypsum. Furthermore, by comparing the NMR signal decays it is possible to distinguish between these two water populations. The measured water profiles reveal that during one sided heating of a gypsum sample the dehydration inside is taking place in a two-step reaction. Furthermore, the profiles indicate that the vapour produce by the dehydration reactions condensates and thereby increases the local moisture content. The condensated water forms a so-called moisture peak behind the dehydration front. To our knowledge the measurements described in this article are the first quantitative in-situ evidence for the existence of two dehydration fronts in gypsum during one sided heating. Furthermore, the built up of a moisture peak in gypsum behind the dehydration front has not been reported in the literature to our knowledge. The NMR heating experiments presented in this paper can be used to evaluate and validate hygro-thermal models in the field of fire research on building materials. [Copyright &y& Elsevier]

Abstract: In this paper a methodology for thermodynamic analysis and distillation column ‘targeting’ is presented, with emphasis on the use of side condensers and side reboilers. Research in the past has been towards the establishment of a heat distribution curve, showing the way in which heat can be added or extracted across the different column sections. One major disadvantage of these profiles is that they refer to reversible columns, and cannot be used effectively to target for modifications in a real column. The main feature of the proposed methodology is the introduction of a minimum driving force, defined in terms of exergy loss distribution of the existing column, to set realisable targets for side reboiling/condensing in real columns, resulting in considerable energy savings. In addition to providing realisable targets, the new approach also provides the design engineer with information about the best location to place a side exchanger, and the required additional column modifications. The methodology can be applied using conventional column models in commercial process simulation programs, but can be significantly simplified by using reboiled and refluxed absorber models in a bespoke program. Simulation results for modified designs set by the new approach, for binary and multicomponent separations, verify the feasibility of the targets. This contrasts with previous approaches, which result in temperature shifts and heat load penalties after placing side reboilers/condensers, thus requiring additional simulation time and experienced judgement. [Copyright &y& Elsevier]

Abstract: With the study object of an 100kt/a SL-II ethylene cracking furnace, this paper used Computational Fluid Dynamics (CFD) method to carry out coupled simulation studies on the flow, combustion, radiative heat transfer and thermal cracking reaction processes in the cracking furnace. The standard k–ε two-equation model was applied to turbulence simulation. The finite-rate/eddy-dissipation model was used for modeling of non-premixed combustion of the bottom burners and premixed combustion of the sidewall burners. The Discrete Ordinates (DO) model was applied to the simulation of radiative heat transfer of furnace. The simulation results show the detailed information about velocity, temperature and concentration fields in the furnace and heat flux distribution on the reactor tubes skin. This work will provide a theoretical basis for the optimization of the geometrical structure and operational parameters of the cracking furnace. [Copyright &y& Elsevier]

Abstract: Single-phase microreactors and micro-heat-exchangers have been widely used in industrial and scientific applications over the last decade. In several cases, operation of microreactors has shown that their expected efficiency cannot be reached either due to non-uniform distribution of reactants between different channels or due to flow maldistribution between individual microreactors working in parallel. The latter problem can result in substantial temperature deviations between different microreactors resulting in thermal runaway which could arise from an exothermic reaction. Thus advances in the understanding of heat transfer and fluid flow distribution continue to be crucial in achieving improved performance, efficiency and safety in microstructured reactors used for different applications. This paper presents a review of the experimental and numerical results on fluid flow distribution, heat transfer and combination thereof, available in the open literature. Heat transfer in microchannels can be suitably described by standard theory and correlations, but scaling effects (entrance effects, conjugate heat transfer, viscous heating, and temperature-dependent properties) have often to be accounted for in microsystems. Experiments with single channels are in good agreement with predictions from the published correlations. The accuracy of multichannel experiments is lower due to flow maldistribution. Special attention is devoted to theoretical and experimental studies on the effect of a flow maldistribution on the thermal and conversion response of catalytic microreactors. The review concludes with a set of design recommendations aimed at improving the reactor performance. [Copyright &y& Elsevier]

Abstract: Complete elimination of fouling in heat transfer equipment is rarely achieved in practice, so cleaning of fouled units is a regular task in the process industries. Algorithms for scheduling cleaning have, to date, minimized the net losses due to fouling by focusing on when and which units to clean. In contrast, this paper focuses on when and how to clean a unit, when more than one cleaning method is available. The model formulation is approached by idealizing a foulant deposit as consisting of two layers, soft (fresh) and hard (aged). The hard material is formed through the ageing of the soft material. Hard deposits are more difficult to remove and require time- and cost-intensive cleaning methods (such as mechanical cleaning). Soft deposits are removed through less time- and cost-intensive methods such as chemical cleaning by recirculation of solvents. The hard deposit usually consists of more thermally conductive material and hence, for a given thickness, has a lower thermal resistance compared to the soft deposit. This work introduces a new methodology to identify optimum cleaning cycles (OCCs) under the presence of both soft and hard deposit, when two cleaning methods (solvent and mechanical cleaning) are available. The analysis of OCCs is extended and a new concept called the ‘cleaning supercycle’ is elaborated, which can be related to the optimal time between plant shutdowns. [ABSTRACT FROM AUTHOR]