Heat Transfer and hydrodynamics in Annular Chromatography：CFD—Simulation and Experiments

IntrotctiouAImular chrDmatography Provides the POssibility ofseparating multicomponent fixtures continuously inone single unit. The rotating annulus of thechromatotw can be filled with arbitw stationalsPhases depending on the existing separation Problem.The feed is introduced at a fixed and stationary sechonat the top of the unit, while the eluent is distributedeverywhere else around the upper circumference. At thebottom the separated Products can be collected atcendn stationals exit angle…     

Experiments and Modelling of Coal Devolatilization

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Numerical Modeling of Biomass Pyrolysis—Heat and Mass Transport Models

We consider the pyrolysis of robinia pseudoacacia, which is a common material for biomass gasifiers. We formulate three models of the process, with increasingly detailed physics, best suited for different spatial scales from large to small. For each model, we perform numerical simulations of adaptable complexity and compare the results with the thermogravimetric analysis (TGA) experiments.     

Modeling Heat Transfer and Skin Friction Frequency Responses of a Cylinder in Cross-Flow—a Unifying Perspective

The dynamic behavior of skin friction and heat transfer of a cylinder in pulsating cross-flow is investigated. Existing analytical solutions are presented as transfer functions versus frequency, known from control theory. New results for Reynolds number ranges where no appropriate model exists until now are derived. These results are obtained by the combination of computational fluid dynamics and system identification (CFD/SI). In the CFD/SI approach, time series for fluctuations of skin friction and the rate of heat transfer are generated by imposing broad-band inlet velocity fluctuations in a CFD simulation of laminar flow across a cylinder. Direct numerical simulations are conducted for mean flow Reynolds numbers between 0.1 and 40, solving the incompressible Navier–Stokes equations in a two-dimensional domain using a finite volume approach. The SI framework allows to estimate transfer functions for the response of skin friction and heat transfer to velocity fluctuations from time series data. Available analytical models for the dynamic behavior of skin friction and heat transfer usually match the simulated data up to a point, but do not give any dependence on Reynolds number. This shortcoming is addressed in this work. The identified models especially excel at Reynolds numbers of order 10.     

Fabrication,permeation, and corrosion stability measurements of silica membranes for HI decomposition in the thermochemical iodine–sulfur process

In this study, a corrosion-stable silica membrane was developed to be used in H₂ purification during the hydrogen iodide decomposition (2HI → H₂ + I₂), which is a new application of the silica membranes. From a practical perspective, the membrane separation length was enlarged up to 400 mm and one end of the membrane tubes was closed to avoid any thermal variation along the membrane length and sealing issues. The silica membranes consisted of a three-layer structure comprising a porous α-Al₂O₃ ceramic support, an intermediate layer, and a top silica layer. The intermediate layer was composed of γ-Al₂O₃ or silica, and the top silica layer that is H₂ selective was prepared via counter-diffusion chemical vapor deposition of a hexyltrimethoxysilane.To the best of our knowledge, this is the first report of 400-mm-long closed-end silica membranes supported on Si-formed α-Al₂O₃ tubes produced via chemical vapor deposition method. A 400-mm-long closed-end membrane using a Si-formed α-Al₂O₃ tube exhibited a higher H₂/SF₆ selectivity of 1240 but lower H₂ permeance of 1.4 × 10⁻⁷ mol Pa⁻¹ m⁻² s⁻¹ with compared with the membrane using a γ-Al₂O₃-formed α-Al₂O₃ tube (907 and 5.6 × 10⁻⁷ mol Pa⁻¹ m⁻² s⁻¹, respectively). The membrane using the Si-formed α-Al₂O₃ tube was more stable in corrosive HI gas than a membrane with a γ-Al₂O₃-formed α-Al₂O₃ tube after 300 h of stability tests. In conclusion, the developed silica membranes using the Si-formed α-Al₂O₃ tubes seem suitable for membrane reactors that produce H₂ on large scale using HI decomposition in the thermochemical iodine–sulfur process.     

Experimental and Modeling Investigation of Coal Gasification in a Fluidized Bed Reactor

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Modeling Yin—Yang Balance in Tai—Chi Diagram with a Melting—Freezing Rotating Device

InttoductionTai-chi diW is a symboI of wisdom in theChinese history, and is a very influential diagram in theWhole Chinese civilization. However, there is littlescientific research wOrk available in the literatUre thatprovides a physical model that can describe and interprethe yin-yang balance in the tai-chi diagram.The Presen stUdy is in an atteInPt to interpret theyin-yang balance in the tai--chi dign with a stwleNcal 1angUage through the Physical Processes ofmelhng and freezing in a r…     

Evaluation of Single Phase Flow in Microchannels for High Heat Flux Chip Cooling—Thermohydraulic Performance Enhancement and Fabrication Technology

The increased circuit density on today's computer chips is reaching the heat dissipation limits for air-cooling technology. The direct liquid cooling of chips is being considered as a viable alternative. This paper reviews liquid cooling with internal flow channels in terms of technological options and challenges. The possibilities presented herein indicate a four- to ten-fold increase in heat flux over the air-cooled systems. The roadmap for single-phase cooling technology is presented to identify research opportunities in meeting the cooling demands of future IC chips. The use of three-dimensional microchannels that incorporate either microstructures in the channel or grooves in the channel surfaces may lead to significant enhancements in single-phase cooling. A simplified and well-established fabrication process is described to fabricate both classes of three-dimensional microchannels. Proof-of-concept microchannels are presented to demonstrate the efficacy of the fabrication process in fabricating complex microstructures within a microchannel.     

Fabrication and thermo-physical properties characterization of ethylene glycol—MoS2 heat exchange fluids

This study reports on the fabrication and thermo-physical properties evaluation of ethylene glycol (EG) based heat exchange fluids containing molybdenum disulfide nanoparticles (MoS₂ NPs) and micrometer sized particles (MPs). For this purpose, MoS₂ NPs and MPs (with average size of 90 nm and 1.2 μm; respectively) were dispersed and stabilized in EG with particle loading of 0.25, 0.5, 1 wt%. To study the real effect of MoS₂ NP/MP the use of surfactants was avoided and ultrasonic agitation was used for dispersion and preparation of stable MoS₂ NFs/MFs. The objectives were investigation of impact of MoS₂ particle size (including NP/MP) and particle loading on thermo-physical properties of EG based MoS₂ NFs/MFs including thermal conductivity (TC) and viscosity of NFs/MFs at 20 °C. All suspensions (NFs/MFs) exhibited a higher TC than the EG as base liquid and NFs showed higher TC enhancement values than the MFs. A TC enhancement of 16.4% was observed for NFs containing 1 wt% MoS₂ NPs while the maximum increase in viscosity of 9.7% was obtained for the same NF at 20 °C. It indicates this NF system may have some potential to be utilized in heat transfer applications.     

Numerical Computations of Confined Swirl Flows in Augmentor of Jet Engines and Comparisons with Experiments

This paper describes the design of four types of swirlers which produce different velocity profiles.The dataof confined turbulent swirling flowfields are obtained from experiments and numerical calculations.The actualflow profiles at the swirler exit basically agree with the desired profiles.Two kinds of turbulence models,k-ε model and DDC model,are used to predict the flowfields producedby swirl augmentors.The results show that the DDC model,based on interaction between dissipation anddispersion,can overcome the defect of k-ε model and predict the swirling flowfields more accurately than k-εmodel.     

Heat Transfer,Fluid Mechanics,and Thermodynamics in Our Environment—HEFAT2012

This editorial provides an overview of a special issue dedicated to the 9th International Conference on Heat Transfer, Fluid Mechanics, and Thermodynamics—HEFAT2012—hosted on Malta. All papers for this conference were peer reviewed and 270 papers were accepted. Of these, 10 of the best papers were selected for this issue and peer reviewed for a second time according to journal standards. The 10 papers focus on the characteristics of oxyfuel and air-fuel combustion in an industrial water tube boiler, numerical and optical analysis of a weather-adaptable solar reactor, the mitigation of crystallization fouling using projectiles in tubular heat exchangers, the mitigation of crystallization fouling in a single heated tube using projectiles of different sizes and hardness, a framework for the analysis of thermal losses in reciprocating compressors and expanders, an annular impinging jet controlled by radial synthetic jets, multi-effect plants and ionic liquids for improved absorption chillers, the effect of climatic parameters on the heat transfer mechanisms in a solar distillation still, empirical correlations for slightly decaying grid turbulence, and pool boiling on modified surfaces using R-123. The current issue of Heat Transfer Engineering is the ninth special journal issue dedicated to selected papers from the HEFAT conferences.     

Experiments and Simulations of Laminar Forced Convection With Water–Alumina Nanofluids in Circular Tubes

This work reports fundamental experimental-theoretical research related to heat transfer enhancement in laminar channel flow with nanofluids, which are essentially modifications of the base fluid with the dispersion of metal oxide nanoparticles. The nanofluids were synthesized by a two-step approach, using a dispersant and an ultrasound probe or a ball mill for alumina nanoparticles dispersion within the aqueous media. The theoretical work involves the proposition of an extension of the thermally developing flow model that accounts for the temperature variation of all the thermophysical properties, including viscosity and the consequent variation of the velocity profiles along the thermal entry region. The simulation was performed by making use of mixed symbolic-numerical computation on the Mathematica 7.0 platform and a hybrid numerical-analytical methodology (generalized integral transform technique, GITT) in accurately handling the governing partial differential equations for the heat and fluid flow problem formulation with temperature dependency in the thermophysical properties. Experimental work was also undertaken based on a thermohydraulic circuit built for this purpose, and sample results are presented to verify the proposed model. The aim is to confirm that both the constant properties and temperature-dependent properties models, besides available correlations previously established for ordinary fluids, provide adequate prediction of the heat transfer enhancement observed in laminar forced convection with such nanofluids and within the experimented Reynolds number range.     

Modeling and Measurements of Heat Transfer Phenomena in Two-Phase PbSn Alloy Solidification in an External Magnetic Field

The main aim of this work is to study numerically the influence of an external magnetic field on the solidification processes of two-component materials. Based on the continuum model of two-phase flow a mathematical model for the directional solidification of a binary alloy in a magnetic field is presented. The model includes mass, momentum, energy and species mass conservation equations written in compressible form and additional relationships describing the temperature-solute coupling. The geometry under study is a cylindrical mold with adiabatic walls and cooled bottom. The macroscale transport in the solidification of alloys is governed by the progress of the two-phase mushy zone, which is treated by means of a porous medium approach. The volume fraction of liquid and solid phases, respectively, is calculated from a 2D approximation of the phase diagram. The results of calculation are compared with experimental data.     

Forests,fuelwood and livelihoods—energy transition patterns in eastern Indonesia

The central thesis of the energy ladder model is a unidirectional transition from primitive to advance fuel with increased affluence of households. Although now largely discredited, this assumption remains a foundation of laissez-faire policies that anticipate energy transition resulting spontaneous forest recovery with economic development. Our results suggest that such policies can undermine broader policy objectives and actually worsen forest conditions in rural Indonesia. Based on a case study of forest margin communities in eastern Indonesia, we demonstrate that fuel subsidy reform did little to reduce rural household demand for fuelwood, while dramatically increasing fuelwood demand for processing agricultural products. Our results show how household decisions related to fuel sources are affected by non-economic considerations and external factors, such as opportunities to sell fuelwood. We argue that policy interventions that encourage energy transition of households do not necessarily improve forest conditions, as household fuelwood use may be a symptom, rather than a driver of deforestation and forest degradation. Thus policies to improve forest conditions should focus more on addressing the market environment of forest-margin communities, providing energy alternatives to small industries that are often the larger consumers of fuelwood.     

Modeling and prediction of NOx emission in an LPG–diesel dual-fuel CI engine

Different alternative fuels have been proposed by various researchers in diesel engines in view of increased NO_x and particulate emissions. Out of the various methods proposed, dual fueling is one of the most important techniques that helps solve the different operational problems related to diesel engine combustion and emission. In the current study, modeling and predicting the formation of NO_x emission in a duel fuel liquefied petroleum gas (LPG)–diesel engine has been undertaken. Simulations have been conducted for various LPG flow rates at different engine loads and the predicted NO_x values are compared with the experimental values. The results found that there is a decent agreement between the forecasted and the investigational results, where the average difference is within 13.7%. Furthermore, it is found that minimum NO_x emission was observed for an LPG flow rate in the range of 0.4–0.6 kg/h and when the engine is running with 75% loading.     

Efficient Equipment with Special Heat Exchanger for Thermal Treatment of Polluted Air—Experiments,Computations, Applications

A quite new and unique piece of equipment for the thermal treatment of gas wastes (i.e., the incineration of volatile organic compounds contained in polluted air) has been developed. This compact equipment is characterized by a cylindrical combustion chamber placed inside a heat exchanger—a polluted air preheater. This cylindrical preheater consists of several concentric stainless sheets. Both flue gas from the combustion chamber and polluted air heated by flue gas flow in the spaces between the cylindrical sheets. Narrow distance strips placed between the sheets form helical rectangular ducts, through which we can achieve a counter-current flow of process fluids. A mathematical model for the calculation and/or simulation of the equipment consists of submodels of a heat exchanger and combustion chamber and the annular space between them. Based on the results of measurements on an industrial scale experimental facility, new correlations for the thermal and hydraulic calculations of the heat exchanger were developed. Some industrial applications are briefly mentioned.     

Analysis of chemical,electrochemical reactions and thermo-fluid flow in methane-feed internal reforming SOFCs: Part I – Modeling and effect of gas concentrations

Direct internal reforming solid oxide fuel cells (DIR SOFCs) have complicated distributions of temperature and species concentrations due to various chemical and electrochemical reactions. The details of these properties are studied by a 3-D numerical simulation in this work. The simulation modeling used governing equations (mass, momentum, energy and species balance equations) generally suitable to porous medium with porosity variable of zero (solid), 0.3 (porous medium) and 1.0 (fluid). Chemical kinetics equations for the internal reforming and shift reactions based on the Langmuir–Hinshelwood model were incorporated. Hydrogen and carbon monoxide oxidations were considered both participating in electrochemical reactions. The experimentally measured current density–potential curves were compared with the simulation data to validate the code, which revealed that the simulation model was able to predict the dilution effect of nitrogen and the mass transfer under high current densities. It is found that the temperature dramatically declined near the fuel inlet with strong endothermic reactions, but it increased along the fluid flow with electrochemically exothermic reactions. A low steam-to-carbon ratio (SCR) led to high steam reforming and water gas shift reaction rates, which generated a greater amount of hydrogen. Therefore, current density increased with low SCR. The average current density due to carbon monoxide electrochemical oxidation varies from 205.3 A/m² under an SCR of 2.0 to 47.6 A/m² under an SCR of 4.0. The average current density due to hydrogen electrochemical oxidation was 5535.4 A/m² under an SCR of 2.0, which was 27 times higher than that of carbon monoxide. The total current density ranged from 5740.8 A/m² under an SCR of 2.0 to 2268.9 A/m² under an SCR of 4.0.     

Theoretical Analysis of the Pressure Oscillation Phenomena in Capillary Pumped Loop

INTRoDUCTIONCaPillaryPumpedLoop(CPL)isakindofheat-transferdevicewithhighefficiencyandhighreliabilityItcanmeettherequlrmellts0fthefuturelargespace-craftandisconsideredtobeoneofthemostpromisingthermal-Controlequlpmentinthefuturel1'2'3].Inthec0nventi0nalCPLanalysism0del,itiscon-sideredthattheheat-transfercapabilityofCPLisoalydetendnedbythecaPinarYf0rceofthewickintheeVaPor8tor.Thelo0PwinoperatenormallywhenPc@ishigherthantheresistanceofthewholel00pAPont,i.e.,Pc@>APont.However,sincethe…