Thermal Fractionation Research Articles

Numerical study of thermal radiation and suction effects on copper and silver water nanofluids past a vertical Riga plate

PurposeThe purpose of this paper is to explore the flow of Cu-water and Ag-water nanofluids past a vertical Riga plate. The plate is infinite in height and has zero normal wall flux through its surface. Influence of thermal radiation, slip, suction and chemical reaction on the flow characteristics are reported.Design/methodology/approachNon-dimensional forms of the flow governing equations are obtained by means of a set of similarity transformations. Numerical solution is obtained with the help of fourth-fifth-order Runge–Kutta–Fehlberg method with shooting procedure. Comparison of solution profiles of Cu-water and Ag-water nanofluids are presented graphically and with the help of tables. Influence of pertinent parameters on skin friction and heat transfer rate is also reported.FindingsResults reveal that the skin friction coefficient is more prominent in the case of Ag-water nanofluid for an increase in thermal radiation and volume fraction. The role of suction and slip is to increase velocity but decrease the temperature in both nanofluids. Temperature and velocity of both nanofluids increase as volume fraction and thermal radiation values are augmented. Heat transport increases with thermal radiation. Region near the plate experiences rise in nanoparticle concentration with an increase in chemical reaction parameter.Originality/valueA complete investigation of the modeled problem is addressed and the results of this paper are original.

Investigation of the void fraction–quality correlations for two-phase hydrogen flow based on the capacitive void fraction measurement

The void fraction and vapor quality are important parameters for characterizing the gas–liquid two-phase flow. However, neither an established void fraction measurement method nor a verified void fraction – vapor quality interconversion model is available for the two-phase hydrogen flow. The object of this study is the development of a void fraction measurement technique and the investigation of the void fraction–quality correlations. A capacitive void fraction sensor was developed using the electric field analysis (EFA) and design of experiment (DOE), and it was applied in a boiling hydrogen experimental facility. The experimental conditions were as follows: the inner diameter of the heating pipe was 15 mm, the mass flux was ranged from 50 to 110 kg/m2s, and the static pressure was ranged from 250 to 300 kPaA. Further, the correlation between the thermal equilibrium quality (χac=− 0.03–0.14) and void fraction (α = 0–70%) was compared with that obtained in previously proposed models, and the void fraction – actual quality – thermal equilibrium quality interconversion models applicable to the boiling hydrogen flow were investigated. It was observed that the combination of the Sekoguchi model for thermal equilibrium quality – actual quality conversion and the Steiner drift-flux model for actual quality – void fraction conversion agreed well with the experimental results.

Lignin Valorizations with Ni Catalysts for Renewable Chemicals and Fuels Productions

Energy and fuels derived from biomass pose lesser impact on the environmental carbon footprint than those derived from fossil fuels. In order for the biomass-to-energy and biomass-to-chemicals processes to play their important role in the loop of the circular economy, highly active, selective, and stable catalysts and the related efficient chemical processes are urgently needed. Lignin is the most thermal stable fraction of biomass and a particularly important resource for the production of chemicals and fuels. This mini review mainly focuses on lignin valorizations for renewable chemicals and fuels production and summarizes the recent interest in the lignin valorization over Ni and relevant bimetallic metal catalysts on various supports. Particular attention will be paid to those strategies to convert lignin to chemicals and fuels components, such as pyrolysis, hydrodeoxygenation, and hydrogenolysis. The review is written in a simple and elaborated way in order to draw chemists and engineers’ attention to Ni-based catalysts in lignin valorizations and guide them in designing innovative catalytic materials based on the lignin conversion reaction.

Performance analysis of hybrid photovoltaic thermal solar system in Iraq climate condition

In this paper, the hybrid photovoltaic/thermal solar domestic hot water (PVT-SDHW) has been numerically investigated to determine its thermal and electrical performance of a house consists of 5 persons in Iraq climate environment. Detailed mathematical formulation of the PVT-SDHW system have been developed. To validate the feasibility of the developed numerical code, the present results have been compared with the experimental and numerical results and the comparison shows a good agreement between them. The PVT-SDHW system has been tested using the solar radiation data of Mosul city/Iraq that was estimated from ASHRAE Clear Sky Model. The auxiliary heater power, electrical power generation, storage tank water temperature, thermal solar fraction and demand electrical fraction have been analysed. The packing factor (rc) has been considered in this study as a key parameter. The results show that the minimum auxiliary heater power required and the maximum thermal solar fraction occurred when rc=0. Most importantly, the results also indicated that the electricity production has been increased by increment in rc. For rc=1, it has been found that the PVT-SDHW provides hot water between 61.7% and 83% and electricity generation between 24.5% and 43.9% needed by a family of five persons for various months.

Heat transfer and nanofluid flow over a porous plate with radiation and slip boundary conditions

Presence of different terms with various values can alter the thermal behavior of the nanofluids flow over porous surfaces. The aim of this research is to study the influence of nanoparticles volume fraction, nanoparticles type, suction or injection, the heat generation or absorption, the Eckert number, thermal and velocity slip parameters, and radiation on the velocity and temperature fields on the flow and heat transfer over a porous flat plate. Four different types of nanoparticles including metal nanoparticles (Cu), metal oxide nanoparticles (Al2O3) and carbon-based nanomaterials (MWCNTs and SWCNTs) which were dispersed in the water (as based fluid) are studied. The governing equations are converted into the ordinary differential equations using similarity solution and solved numerically by the RKF45 algorithm. The results of the simulations showed a contradiction with the results of other researchers who expressed that using nanoparticles with higher thermal conductivity and volume fraction led to increasing heat transfer rate in nanofluids; this study proves that, in some cases, boosting the volume fraction of nanoparticles has a potential to decrease the heat transfer rate due to significant changes in values of some parameters including radiation, heat generation, and viscous dissipation.

On Simulation of Sheet Electron Beams with Regard to the Initial Transverse Thermal Velocities of Electrons

A technique to take into account the initial transverse electron thermal velocities in converged sheet electron beams has been developed. This determines the main integral characteristics of a thermal beam in a gun and transportation region of the paraxial approximation via chosen characteristic electron trajectories. We have equations of characteristic electrons motion, initial conditions to solve equations, and formulas for the current density distribution in the thermal beam cross-section and current fraction in conventional boundary. The derived equations and formulas may be used in modeling electron-optical systems and choosing parameters in which the effect of heat electron motion on beam characteristics will lie within tolerable limits.

CVFEM approach for EHD flow of nanofluid through porous medium within a wavy chamber under the impacts of radiation and moving walls

In current investigation, ferrofluid circulation and energy transport inside a wavy-walled porous enclosure are modeled considering radiation and EHD effects. The finite volume method is employing for simulation of EHD circulation structures and thermal transmission. Properties of working fluid depend on the electric field and nanosized solid particles concentration. Impacts of thermal radiation, nanoparticles shape, and volume fraction are considered in governing equations. Distributions of unknown functions are received for various voltage, permeability, radiation parameters, nanoparticles’ shape and concentration. Results have shown that platelet form leads to the strongest convective circulation. An amplification of electric force characterizes a diminution of the boundary layer thickness. Greater permeability of the porous medium characterizes the strongest convective circulation and thermal transmission.

Effects of different sizes and dispatch strategies of thermal energy storage on solar energy usage ability of solar thermal power plant

The solar energy usage ability is mainly considered in the construction of solar thermal power plant (STPP) which is affected by factors of design direct normal irradiance (DNI), solar multiple (SM), thermal energy storage (TES) size and dispatch fraction (DF). In this paper, a general model is developed in order to obtain the relationship among these factors, the electricity output and the solar energy usage efficiency of STPP. Based on the modeling method, a critical design of DNI is derived and some suggestions for improvement in the design of DNI are presented in order to improve the efficiency, which can result in the reduction of waste solar energy. The effects of SM, TES size and DF on the critical design of DNI are also investigated. It is found that the solar energy usage ability will be only dependent on the TES size when TES size is below 6 h and the solar energy usage ability will be dependent on both TES size and DF when TES size is above 6 h. The increase of TES size and the decrease of DF beyond their corresponding critical design DNI will reduce the solar energy usage ability of STPP. The results obtained can provide an important basis for studying the solar energy utilization capacity of STPP and determine the design parameters of STPP.

Thermal driven flows inside a square enclosure saturated with nanofluids: Convection heat functions and transfer rate revisions from a homogenous model

In former theoretical researches of nanofluid flows, numerical investigations could not agree with experimental observations, particularly regarding whether the mixing nanoparticles will enhance or deteriorate the heat transfer. In the present work, thermal driven buoyancy flows of nanofluids in a square enclosure were modeled by the use of homogeneous assumptions and the effective kinematic viscosity and thermal conductivity formulas. Thoroughly developed heat transfer coefficient is subsequently proposed, aiming to critically evaluate the performance of nanofluid heat transport. Numerical results are presented over a wide range of thermal Rayleigh number (103 ≤ Ra ≤ 106) and nanoparticles volume fraction (0.001 ≤ φ ≤ 0.04). Present modeling results accurately predict both the enhancement and deterioration of the natural convection heat transfer, fully validated by former experimental observations. Overall, mathematical models and Nusselt number definitions proposed in the present work effectively enhance the reliability of numerical modeling researches on the nanofluid heat transfer. Present clarification research on the Nusselt unifications could benefit future development of thermal carrier fluid enhanced by nano-particles.

An experimental investigation of the use of gasoline-acetylene mixtures at different excess air ratios in an SI engine

Abstract This study presents experimental results of engine performance, combustion analyzes and emissions values in an SI engine fueled by gasoline-acetylene blends. The experiments were carried out at 1500 rpm engine speed, different loads (25% and 50%) and optimum spark timing under different mixture conditions. Engine was operated up to 1.70 and 2.12 excess air ratios for 500 g/h and 1000 g/h acetylene flow rate at 25% load, respectively. For 50% load, engine was operated up to 1.82 excess air ratios for 1000 g/h acetylene flow rate. Engine parameters such as brake thermal efficiency, cylinder pressure, mass fraction and emission values (CO, UHC and NOX) were analyzed for each fuel blends. Results were shown that due to decreased ignition timing to prevent knocking, the addition of acetylene to gasoline decreased brake thermal efficiency at rich and stoichiometric conditions and increased the CO emissions. Acetylene adding at lean mixtures caused an increase in brake thermal efficiency and a decrease in CO emissions, because of proper ignition advance. Furthermore, adding of acetylene increased combustion limits, significantly reduced UHC emissions but increased NOX emissions. Moreover, NOX emissions obtained from mixture with acetylene were measured quite low at high excess air ratios.

Chain structure comparison of two low density polyethylene resins fractionated by temperature rising elution fractionation and thermal fractionation

Two low-density polyethylene resins were fractionated into 11 fractions using the temperature rising elution fractionation technique. The resins were of injection molding grade with similar densities but different melt indexes and mechanical properties. High-temperature gel permeation chromatography (HT-GPC), 13C-nuclear magnetic resonance (13C-NMR) spectroscopy, differential scanning calorimetry (DSC), and successive self-nucleation/annealing (SSA) thermal fractionation were employed to characterize the original resins and their fractions. Resin A had a higher molecular weight and broader molecular weight distribution than resin B did. The highest contents were found for the 80 °C and 75 °C fractions of resins A and B, respectively. In addition, the highest molecular weights for resins A and B at 2.14 × 105 and 1.42 × 105 g/mol, respectively, were attained for the fractions eluted at 80 °C. According to the results of 13C-NMR, the total branching contents of resins A and B, including short- and long-chain branching, were 3.63 mol% and 4.89 mol%, respectively. DSC analysis revealed that the crystallinity of fractions 3–10 of resin A was lower than that of resin B. We noted the presence of approximately eight multiple melting peaks in the original sample and fractions from the results of SSA. These peaks indicated the inhomogeneity of the molecular chain. Lw and Ln of resin A were longer than those of resin B. Lastly, the relationship between chain structure and property was also discussed.

(Micro)structure, thermal behavior and mechanical properties of ethylene–propylene–1-octadecene terpolymers from chain-walking polymerization of 1-octadecene

This paper reports the polymerization of 1-octadecene catalyzed by a series of α-diimine Ni(II) complex, with methyl ligand backbone and different substituents in the ortho and para aryl positions, in combination with Et2AlCl. We obtained semicrystalline ethylene–propylene–1-octadecene terpolymers with high molecular weight and narrow molecular weight distribution. The formation of such terpolymers is due to the numerous combinations of insertion and chain-walking pathways. The effect of the type of ligand and monomer feedstock concentration on the activity, regioselectivity, polymers (micro)structure, and structure/properties is thoroughly investigated by NMR, DSC, WAXD and SAXS. The thermal behavior and the crystal structure of the polymers are strongly influenced by the level of incorporation of methyl and longer alkyl branches. The chain heterogeneity of the polymers is investigated by successive self-nucleation and annealing thermal fractionation evaluating the crystallizable sequence length, and the lamellar thickness.

Temporal constraints on lateral organic matter transport along a coastal mud belt

Constraints on timescales of lateral transport of sedimentary organic carbon (OC) over continental shelves and associated influences on the distribution and abundance of OC remain sparse. Preferential degradation of labile, young OC during lateral transport results in apparent “diagenetic aging” of OC. Additionally, sediment translocation can also result in “transport time-associated aging” of associated organic matter (OM) as a function of the lateral transport time (LTT). Here, we use a coupled thermal decomposition and radiocarbon (14C) approach to constrain timescales of lateral transport and concomitant loss of OC associated with different grain size fractions of sediments collected from two locations ∼275 km apart along a dispersal pathway on the inner shelf of the East China Sea. The 14C age contrasts between corresponding thermal fractions are used to distinguish these two components of sedimentary OM “aging”. To minimize interferences from hydrodynamic sorting and diagenetic aging of OC accompanying lateral transport, we assess 14C age differences of decomposition products from the most thermally-refractory OC components associated with specific grain size fractions between locations. We show that LTTs vary among different grain size fractions, and examine relationships between LTTs and sedimentary OC loss in order to assess the decomposition of OC as a consequence of lateral transport. We suggest that the decomposition of OC associated with protracted lateral transport exerts a strong influence on OC burial efficiency, with broad implications for carbon cycling over continental shelves.

Fundamental solution of steady oscillations for porous materials with dual-phase-lag model in micropolar thermoelasticity

This article deals with the study of propagation of plane waves in an isotropic thermoelastic medium for porous materials with the linear theory of micropolar thermoelasticity. The problem is treated in the context of dual-phase-lag model of thermoelasticity. It is found that, for one-dimensional model, there exists three longitudinal waves, namely elastic (E-mode), thermal (T-mode), and volume fraction (V-mode) in addition to transverse waves which get decoupled from rest of the motion and not affected by thermal and volume fraction fields. In case of steady oscillations, the fundamental solution of the system of differential equations in terms of elementary functions has been constructed. The phase velocity and attenuation coefficient of these waves are computed numerically and presented graphically.

Effect of Strain Induced Martensite Reversal on the Degree of Sensitization of Metastable Austenitic Stainless Steel

Effect of reversion of strain induced martensite on degree of sensitization (DOS) of Cr-Mn Austenitic stainless steel (ASS) have been examined. The martensite reversion is known to be effective in refining the grain size of metastable ASS. However, martensitic reversal takes place only after severe cold rolling reductions. In this study, the effect of degree of cold rolling and subsequent thermal ageing on the microstructure, mechanical, and sensitization properties of a metastable Cr-Mn ASS was investigated. Samples were cold worked (25% and 45%) and then thermal aged at different temperature of 700°C and 900°C for 2 hrs. Microstructures were subjected to optical microscopy. Microstructural study shows that with increasing thermal ageing temperature, strain induced martensite undergoes reversal to austenite and is associated with grain refinement. XRD analysis has revealed that at 25% cold work, volume fraction of martensite was 24%, and as cold work was increased to 45%, the volume fraction of martensite was 42%. Whereas after thermal ageing at 700°C, part of strain induced martensite undergo reversal to austenite and only 18% martensite is left in the matrix. On thermal ageing at 900°C, only 2% strain induced martensite was left in the matrix. Hardness also follows the same trend as observed for volume fraction of martensite during cold work and subsequent thermal ageing. As the cold work percentage increases, hardness and volume fraction increases but as thermal ageing temperature increases, both hardness and volume fraction of martensite decrease rapidly. Degree of sensitization (DOS) decreases with increasing thermal ageing temperature.

Application of Multidimensional Analysis Methods to Dead Oil Characterization on the Basis of Data on Thermal Field-Flow Fractionation of Native Asphaltene Nanoparticles

Molecular-mass distribution curves of native nanoasphaltenes in the form of fractograms for a significant sample of crude oils have been obtained using the thermal field-flow fractionation of asphaltenes, and a multidimensional analysis of the fractionation data has been carried out in order to construct calibration models for predicting the physicochemical properties of the studied oils.

Liquefaction of thermal extracts from co-thermal dissolution of a sub-bituminous coal with lignin and reusability of Ni-Mo-S/Al2O3 catalyst

Four thermal dissolution soluble fractions (TDSFs) with different thermal dissolution soluble yields (TDSYs) obtained from thermal and co-thermal dissolutions (CTDs) of a Chinese sub-bituminous Shenfu (SF) coal and lignin were characterized by elemental analysis, FT-IR and synchronous ?uorescence spectrum measurements. The hydro-liquefaction properties of the four TDSFs and SF raw coal with and without catalyst were compared and the recycled use property of the catalyst in hydro-liquefaction of the TDSF from CTD of SF coal and lignin was further probed. The results suggests that the TDSF from the thermal dissolution (TD) of SF coal contained much more amount of aromatic components and polyaromatic hydrocarbons (PAHs) with 4 and more rings than those from the CTD of SF coal and lignin at the same temperature. TDSFs gave much higher liquefaction conversions and oil yields than SF raw coal in hydro-liquefaction with or without catalyst. Almost all TDSF was converted with much high yield of oil and the TDSF from CTD of SF coal and lignin gave higher yield of oil than that from the TD of SF coal in hydro-liquefaction with Ni-Mo-S/Al2O3 catalyst which demonstrated a good reusability in the hydro-liquefaction of TDSF from the CTD of SF coal and lignin. Carbon deposition was hardly observed in the 4 times recycle used catalyst.

Study of the speed of flame distribution in the combustion of methane-hydrogen fractions

At present, natural gas of the Urengoyskoye field is burned in boilers of thermal power plants (TPP) to generate electricity. At the same time, refineries and petrochemical plants deepen the processing of fossil liquid hydrocarbons. The final product of processing is not only motor fuels, ethylene glycols, plastics, accompanying inert gases such as argon, but also a large amount of combustible secondary gaseous mixtures of the methane series. These mixtures contain a wide array of combustible components. Among them there is the methane-hydrogen fraction, which is characterized by a fairly high hydrogen content. A distinctive feature of the use of hydrogen as a fuel is the high rate of flame propagation and the relatively low heat of combustion [1, p.6-8]. The methane-hydrogen fraction due to the volatility of the composition and a wide range of changes in the heat of combustion was recently used in refineries for their own needs as an insignificant additive to combusted natural gas in process furnaces [2-5]. If the methane-hydrogen fraction was not utilized as a fuel in these furnaces, it was burned in flares. Due to the increase in oil refining volumes and the increase in the amount of methane-hydrogen fraction produced, it became realistic to use this gaseous fraction as the main fuel for power boilers of thermal power plants located near petrochemical plants. In the near future, it is planned to use the methane-hydrogen fraction as an additive to the natural gas for 20 power steam boilers of the Nizhnekamsk CHP-1 with a total thermal capacity of 6000 MW. The supplier of the methane-hydrogen fraction is the TAIF NK oil refineries. Depending on the technology of oil refining, the hydrogen content in the methane-hydrogen fraction ranges from 10 to 27% (by weight). The concentration limits of hydrogen ignition in a mixture with air have been experimentally studied by many researchers [6–8] mainly during bench testing or inside laboratories. A feature of the oxidation of hydrogen by air oxygen is the fact that there is a difference between the spread of the flame in limited volumes and in large volumes of the furnace space of energy boilers [9]. In small volumes, when the flame front collides with the wall, oxidation reactions are interrupted, and this does not occur in large volumes. Therefore, the study of flame propagation speed and concentration limits of ignition of methanehydrogen fractions mixed with air in relation to the conditions of furnace volumes of power boilers is relevant. In this work using the in-house software [2-5] calculations were made to determine the burning rate for various compositions of mixtures of methane-hydrogen fractions (MHF) with Urengoi natural gas. It was found that the flame propagation rate of the MHF, compared with hydrogen (see Table 2), decreases 1.76 times. For a mixture of the MHF with Urengoi gas with thermal fractions of the MHF of 12% and 25%, the flame propagation rate increases, respectively, 1.4 times and 1.78 times compared with burning pure Urengoi gas.

Fundamental solution of steady oscillations in thermoelastic medium with voids

ABSTRACT The article deals with the study of plane wave propagation in the thermoelastic medium in the presence of voids. The problem is considered in the context of three-phase-lag model of generalized thermoelasticity. There exists three longitudinal waves, namely elastic (E-mode), thermal (T-mode) and volume fraction (V-mode) in addition to transverse waves which get decoupled from the rest of motion and not affected by thermal and volume fraction fields. The fundamental solution of the system of differential equations in case of steady oscillations in terms of the elementary functions has been constructed. The phase velocity and attenuation coefficient of these waves are computed numerically and presented graphically.

Online coupling of thermal field-flow fractionation and Fourier transform infrared spectroscopy as a powerful tool for polymer characterization

The rapid growth and increasing importance of complex polymers has accelerated the need for advancement in characterization techniques. The analysis of such materials is challenging and the determination of different molecular parameters requires the combination of different advanced analytical techniques. Preferably, coupled and hyphenated techniques are used that provide different molecular parameters simultaneously in one experiment.Complementary to column-based fractionation techniques, channel-based methods such as thermal field-flow fractionation (ThFFF) are attractive as they can address different molecular parameters for a variety of analytes ranging from single macromolecules to macromolecular assemblies and nanoparticles. In the past, ThFFF has been coupled to a variety of size (molar mass) sensitive detectors such as multiangle laser light scattering and dynamic light scattering. Now, for the first time, the online coupling of ThFFF to Fourier transform infrared (FTIR) spectroscopy is presented. Different from standard single- or dual-wavelength IR detectors, this detector provides full spectra over the complete mid infrared range that can be used for concentration detection as well as chemical composition information. The applicability of online multidetector ThFFF-FTIR is demonstrated for selected polymer blends and copolymers comprising styrene and methyl methacrylate.