Effect Of Temperature Gradient Research Articles

Colloidal deposit of an evaporating sessile droplet on a non-uniformly heated substrate

The pattern and profile of a dried colloidal deposit formed after evaporation of a sessile water droplet containing polystyrene particles on a non-uniformly heated glass are investigated experimentally. In particular, the effects of temperature gradient across the substrate and particles size are investigated. The temperature gradient was imposed using Peltier coolers, and side visualization, infrared thermography, optical microscopy, and optical profilometry were employed to collect the data. On a uniformly heated substrate, a ring with an inner deposit is obtained, which is attributed to axisymmetric Marangoni recirculation and is consistent with previous reports. However, the dimensions of the ring formed on a non-uniformly heated substrate are significantly different on the hot and cold side of the substrate and are found to be a function of the temperature gradient and particles size. In the case of smaller particle size, the contact line on hot side depins and together with twin asymmetric Marangoni recirculations, it results in a larger ring width on the cold side as compared to the hot side. In contrast, the contact line remains pinned in case of larger particles, and the twin asymmetric Marangoni recirculations advect more particles on the hot side, resulting in a larger ring width at the hot side. A mechanistic model is employed to explain why the depinning is dependent on the particle size. A larger temperature gradient significantly increases or decreases the ring width depending on the particle size, due to a stronger intensity recirculation. A regime map is proposed for the deposit patterns on temperature gradient-particle size plane to classify the deposits.

Effects of temperature gradient and particle size on self-ignition temperature of low-rank coal excavated from inner Mongolia, China.

This study investigates the effects of temperature gradient and coal particle size on the critical self-ignition temperature TCSIT of a coal pile packed with low-rank coal using the wire-mesh basket test to estimate TCSIT based on the Frank–Kamenetskii equation. The values of TCSIT, the temperature gradient and the apparent activation energy of different coal pile volumes packed with coal particles of different sizes are measured. The supercriticality or subcriticality of the coal is assessed using a non-dimensional index IHR based on the temperature gradient at the temperature cross-point between coal and ambient temperatures for coal piles with various volumes and particle sizes. The critical value IHRC at the boundary between supercriticality and subcriticality is determined as a function of pile volume. The coal status of supercritical or subcritical can be separated by critical value of IHR as a function of pile volume. Quantitative effects of coal particle size on TCSIT of coal piles are measured for constant pile volume. It can be concluded that a pile packed with smaller coal particles is more likely to undergo spontaneous combustion, while the chemical activation energy is not sensitive to coal particle size. Finally, the effect of coal particle size on TCSIT is represented by the inclusion of an extra term in the equation giving TCSIT for a coal pile.

Separate effects irradiation testing of miniature fuel specimens

Qualification of new nuclear fuels is necessary for their deployment and requires a thorough understanding of fuel behavior under irradiation. Traditionally, nuclear fuels have been qualified by performing exhaustive integral tests under a limited range of prototypic conditions designed for their specific reactor application. While some integral fuel testing is essential, basic data on behavior and property evolution under irradiation can be obtained from separate effects tests. These irradiations could offer reduced cost, reduced complexity, and in the case of accelerated testing, reduced time to achieve a given burnup. Furthermore, it may be desirable to design test irradiations capable of deconvoluting the myriad effects of burnup, temperature gradients, and other factors inherent to integral irradiation tests. Oak Ridge National Laboratory has developed an experimental capability to perform separate effects irradiation testing of miniature fuel specimens in the High Flux Isotope Reactor (HFIR): the “MiniFuel” irradiation vehicle. The small size (<4 mm3) of the fuel specimens simplifies the design, analysis, and post-irradiation examination. By reducing the fuel mass, the total heat generated inside the experiment vehicle can be dominated by gamma heating in the structural materials instead of fission heating in the fuel. This essentially decouples the fuel temperature from the fission rate, allowing for highly accelerated testing (3X−18X the burnup rate of a typical light water reactor for 235U enrichments varying from 0.22 wt% to 8 wt%) and an extremely flexible experiment design that can accommodate a wide range of fuel temperatures (∼100 °C to >1200 °C), compositions, enrichments, and even geometries without requiring detailed analyses for each fuel variant. This paper summarizes the experiment design concept, evaluates potential applications for specific fuel forms, and briefly describes the first set of experiments on uranium nitride kernels that have been assembled and are currently being irradiated in the HFIR.

Microstructure evolution and growth behavior of Cu/SAC105/Cu joints soldered by thermo-compression bonding

Purpose This paper used a novel technique, which is thermo-compression bonding, and Sn-1.0Ag-0.5Cu solder to form a full intermetallic compound (IMC) Cu3Sn joints (Cu/Cu3Sn/Cu joints). The purpose of the study is to form high-melting-point IMC joints for high-temperature power electronics applications. The study also investigated the effect of temperature gradient on the microstructure evolution and the growth behavior of IMCs. Design/methodology/approach In this paper, the thermo-compression bonding technique was used to form full Cu3Sn joints. Findings Experimental results indicated that full Cu/Cu3Sn/Cu solder joints with the thickness of about 5-6 µm are formed in a short time of 9.9 s and under a low pressure of 0.016 MPa at 450°C by thermo-compression bonding technique. During the bonding process, Cu6Sn5 grew with common scallop-like shape at Cu/SAC105 interfaces, which was followed by the growth of Cu3Sn with planar-like shape between Cu/Cu6Sn5 interfaces. Meanwhile, the morphology of Cu3Sn transformed from a planar-like shape to wave-like shape until full IMCs solder joints were eventually formed during thermo-compression bonding process. Asymmetrical growth behavior of the interfacial IMCs was also clearly observed at both ends of the Cu/SAC105 (Sn-1.0Ag-0.5Cu)/Cu solder joints. Detailed reasons for the asymmetrical growth behavior of the interfacial IMCs during thermo-compression bonding process are given. The compound of Ag element causes a reduction in Cu dissolution rate from the IMC into the solder solution at the hot end, inhibiting the growth of IMCs at the cold end. Originality/value This study used the thermo-compression bonding technique and Sn-1.0Ag-0.5Cu to form full Cu3Sn joints.

Visualization Analysis of Interrelationship between Temperature Profile and Water Distribution inside the PEFC

Introduction For more spread of Polymer Electrolyte Fuel Cells (PEFCs), water management inside it is very important. Water condensation and transportation modes are very difficult to reveal exactly, because there are many complicated phenomena inside Gas Diffusion Layer (GDL) which has fibrous structure and tiny pore diameter. Temperature profile largely affects on water distribution inside a PEFC. Therefore, we should understand interrelationship between temperature profile and water distribution inside a PEFC to optimize water distribution. There is a report [1] about interrelationship between them in which characteristics of heat transportation has been changed by changing type of GDL. However, in [1], they couldn’t clarify interrelationship because the change of heat transportation characteristics was too small. So in this report, by giving temperature gradient externally, temperature gradient inside cathode GDL of a PEFC was set. Then effects of temperature gradient in through-plane on water distribution in a PEFC is investigated. Experimental method X-ray CT X-ray CT machine, TDM1000-H-Ⅱ(2K)(Yamato Scientific Corp.) was used for visualizing water distribution inside a PEFC. By using this machine, 3-D image of a sample can be got. Total shooting time was about 15 minute. Tube voltage was 30 kV and voxel size was about 2.7 µm. Thin-Film Thermocouple (TFTC) For local temperature measurement, original sensor was fabricated using Micro Electro Mechanical Systems (MEMS) in our laboratory. The sensor was so fine and thin that it wouldn’t disturb a reaction inside a PEFC. The thermocouple was made from Au and Ni. Its measurement point had about 30 µm width and about 6 µm thickness. Cell Configuration An active area of 1 cm2 PEFC cell was used, and is has five 1mm width gas channels and five 1mm width ribs with parallel flow configuration. 15 µm thick reinforces type PEM was used. TGP-H-060 (with MPL 2.0 mg/cm2) was used and in both anode and cathode side. TFTC was inserted between interface of anode CL/MPL and cathode CL/MPL. Experimental proceed First, conditioning of CCM was performed at 0.1 V for 30 minute. Then target temperature was set by temperature controller, and steady waiting was performed for 10 minute. Then some information of a cell (cell voltage, some temperature, and so on) was recorded. Finally, visualization by X-ray CT was performed. Wet gas was supplied to a cell, and water temperature in bubblers was set to 55 ℃. Results and Discussion Two experiments were performed with different temperature gradient by controlling temperature of each separator. One case is that anode temperature is high (An_high) and the another is that cathode temperature is high (Ca_high). Figure.1 shows temperature profile and visualization images inside PEFC. In Fig.1(a), temperature at interface was measured by TFTC, and boundary temperature (An_S, Ca_S) means temperature of separators and was measured by K-type thermocouples. As you can see Fig.1(a), in two temperature profile, both cCL/MPL temperature are almost same and temperature gradients are almost against. And as you can see Fig.1(b), there are some difference in water distribution although both of cCL/MPL temperature are almost same. From these results, we assume it is temperature gradient that largely affects water distribution, not absolute temperature. Fig.1 Experimental results Reference [1] Sota H et al., ECS Trans., 80(8),143-153(2017) Figure 1

Xe gas bubbles evolution in UO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fuels&amp;ndash;A phase field simulation

Owing to the large formation energy of vacancies and inert gas atoms (Xe and Kr) in nuclear fuel (UO2), the thermodynamic equilibrium concentrations of these species are extremely low in the UO2 matrix, which makes it extremely difficult to conduct quantitative study of gas bubbles evolution by phase-field method (PFM). In this study, a more physics based quantitative phase-field model has been proposed. The free energy density of the system was derived according to the principles of thermodynamics and KKS model, the UO2 tri-vacancy, Xe gas atoms and gas bubbles were considered in the system. This model enables one to study the gas bubble growth with extremely low concentrations of vacancy and Xe gas atom in the UO2 matrix. The influence of temperature, vacancy and Xe gas atom generation rates on single and multi-gas bubbles evolution were studied. At high temperature and with high generation rates of vacancies and Xe gas atoms, the gas bubbles had higher growth rate. In addition, the effect of temperature gradient on gas bubble migration was also studied by adding a temperature gradient term in the Cahn-Hillard equations. The gas bubble preferred to migrate to high temperature area. Their shape changed from initial circular shape to a prolate shape along the direction of temperature gradient, which is consistent with the experimental results. The simulation results confirmed the formation of center cavity in the nuclear fuel pellet. The simulation results are consistent with the classical rate theory and experimental observations.

Modelling H3+ in planetary atmospheres: effects of vertical gradients on observed quantities.

Since its detection in the aurorae of Jupiter approximately 30 years ago, the H3+ ion has served as an invaluable probe of giant planet upper atmospheres. However, the vast majority of monitoring of planetary H3+ radiation has followed from observations that rely on deriving parameters from column-integrated paths through the emitting layer. Here, we investigate the effects of density and temperature gradients along such paths on the measured H3+ spectrum and its resulting interpretation. In a non-isothermal atmosphere, H3+ column densities retrieved from such observations are found to represent a lower limit, reduced by 20% or more from the true atmospheric value. Global simulations of Uranus' ionosphere reveal that measured H3+ temperature variations are often attributable to well-understood solar zenith angle effects rather than indications of real atmospheric variability. Finally, based on these insights, a preliminary method of deriving vertical temperature structure is demonstrated at Jupiter using model reproductions of electron density and H3+ measurements. The sheer diversity and uncertainty of conditions in planetary atmospheres prohibits this work from providing blanket quantitative correction factors; nonetheless, we illustrate a few simple ways in which the already formidable utility of H3+ observations in understanding planetary atmospheres can be enhanced. This article is part of a discussion meeting issue 'Advances in hydrogen molecular ions: H3+, H5+ and beyond'.

A magnetically-activated thermal switch without moving parts

With the ever increasing power dissipation in electrical devices, new thermal management solutions are in high demand to maintain an optimal operating temperature and efficient performance. In particular, recently developed magnetically-activated thermal switches (MATSs) provide an alternative to existing devices, using the magnetic and thermal properties of superparamagnetic nanofluids to dissipate heat in a controlled manner. However, the presence of moving parts is a major drawback in these systems that must still be addressed. Herein, we present a compact and automatized MATS composed by an encapsulated superparamagnetic nanofluid and an electromagnet allowing to activate the MATS without any moving part. We investigate the effect of different temperature gradients (10,26 and 40 °C) and powers applied to the coil (6.5, 15, 25 and 39 W) on the performance of this novel MATS. The results show that the highest (44.4%) and fastest (0.6 °C/s) temperature variation occur for the highest studied temperature gradient. On the other hand, with increasing power, there is also an increase in the efficiency of the heat exchange process between the two surfaces. These results remove one of the main barriers preventing the actual application of magnetic thermal switches and opens new venues for the design of efficient thermal management devices.

Analysis of the Thermomechanical Response of Structural Cables Subject to Fire

Cable-supported structures such as bridges and stadia are critical for the surrounding community and the consequences arising from a major fire event can be substantial. Previous computational studies into the thermal response of cables often employed simplistic heat transfer models that assumed lump capacitance or cross-sectional homogeneity without proof of validity. This paper proposes a methodology for calculating the thermal response of a cable cross-section allowing for heat transfer by conduction through each strand contact surface and radiation across inter-strand cavities. The methodology has been validated against two experiments of cables subjected to radiant heating and an input sensitivity analysis has been undertaken for the heat transfer and material parameters. The approach is compared against simple heat transfer lumped methods for a parallel-strand cable where it is shown that these lumped models are not always conservative. The model is then coupled with a two-dimensional generalised plain strain model to study the likely effect of the cross-sectional temperature gradients on the mechanical response. The study considers three qualitatively different hydrocarbon jet fire scenarios, both with and without external insulation for fire protection. It is shown that the proposed methodology can reproduce realistic cross-sectional temperature distributions with up to 50% temperature difference at the cable external surface and can capture the phenomenon of load shedding in a gradually heated cable. It is also shown that assuming a lumped thermal mass neglects the possibility of moment-inducing temperature gradients which are not considered in the ambient design of cables that is driven by tensile capacities. The proposed model and its predictions contribute towards an improved understanding and a more informed structural design of cable-supported structures in fire.

Towards a unified protocol for handling of CSF before \u03b2-amyloid measurements

BackgroundWidespread implementation of Alzheimer’s disease biomarkers in routine clinical practice requires the establishment of standard operating procedures for pre-analytical handling of cerebrospinal fluid (CSF).MethodsHere, CSF collection and storage protocols were optimized for measurements of β-amyloid (Aβ). We investigated the effects of (1) storage temperature, (2) storage time, (3) centrifugation, (4) sample mixing, (5) blood contamination, and (6) collection gradient on CSF levels of Aβ. For each study participant, we used fresh CSF directly collected into a protein low binding (LoB) tube that was analyzed within hours after lumbar puncture (LP) as standard of truth. Aβ42 and Aβ40 were measured in de-identified CSF samples using EUROIMMUN and Mesoscale discovery assays.ResultsCSF Aβ42 and Aβ40 were stable for at least 72 h at room temperature (RT), 1 week at 4 °C, and 2 weeks at − 20 °C and − 80 °C. Centrifugation of non-blood-contaminated CSF or mixing of samples before the analysis did not affect Aβ levels. Addition of 0.1–10% blood to CSF that was stored at RT without centrifugation led to a dose- and time-dependent decrease in Aβ42 and Aβ40, while Aβ42/Aβ40 did not change. The effects of blood contamination were mitigated by centrifugation and/or storage at 4 °C or − 20 °C. Aβ levels did not differ between the first to fourth 5-ml portions of CSF.ConclusionsCSF can be stored for up to 72 h at RT, 1 week at 4 °C, or at least 2 weeks at either − 20 °C or − 80 °C before Aβ measurements. Centrifugation of fresh non-blood-contaminated CSF after LP, or mixing before analysis, is not required. In case of visible blood contamination, centrifugation and storage at 4 °C or − 20 °C is recommended. After discarding the first 2 ml, any portion of up to 20 ml of CSF is suitable for Aβ analysis. These findings will be important for the development of a clinical routine protocol for pre-analytical handling of CSF.

The effect of temperature gradient on interfacial Cu6Sn5 growth during thermal compression bonding

The growth of Cu6Sn5 intermetallic compound (IMC) in Cu/Sn/Cu sandwich system is investigated by thermal compression bonding under a temperature gradient of 800 °C/cm at 400 °C on the hot end. The results show that the interfacial Cu6Sn5 layer shows symmetrical growth at both sides at initial stage, which means that the growth of the Cu6Sn5 layer is controlled by chemical potential gradient. The growth rate of interfacial Cu6Sn5 layer will gradually decrease with increasing Cu6Sn5 layer thickness, which means that the effect of chemical potential gradient on the growth of interfacial Cu6Sn5 layer is undermined and the effect of temperature gradient on the growth of interfacial Cu6Sn5 layer is enhanced. This is due to the fact that the Cu atoms migrate from hot end toward cold end during temperature gradient, the growth rate of Cu6Sn5 layer at cold end is faster than that at hot end. The consumption rate of Cu layer is 0.3 μm/s under temperature gradient of 800 °C/cm. By knowing the calculated consumption rate of Cu layer, the Cu layer thickness on SiC power device can be designed when evaluating the reliability of power device during thermal compression bonding.

Effect of temperature gradient on transient thermal creep of heated and stressed concrete in transient state tests

The stress-strain constitutive relation of concrete subjected to thermomechanical loads is extremely complicated since its deformation relies on the sequences in which the heat and loads are applied. Existing experiments demonstrated that the development of quasi-instantaneous transient thermal creep, generally referred to as TTC, was dependent on the virgin heating of a mechanically pre-loaded concrete specimen. However, the mechanism behind it is still not fully understood. In this paper, a numerical method is developed to analyze the stress fluctuation and corresponding plastic strain caused by the combination of pre-load and temperature gradient. The results show that the TTC calculated using existing semi-implicit methods is reasonable only at early stage but could be wrong at high temperatures. The sharp increase of TTC beyond around 500 °C observed in many tests could be attributed to the implicit inclusion of the extra plastic strain resulted from temperature gradient. By excluding the extra plastic strain generated at different temperature levels, a more accurate formula for calculating TTC is proposed.

Analysis of Turbulent Characteristics of Sheared Convective Boundary Layer under Different Shear and Potential Temperature Gradients

Effects of shear and potential temperature gradient on the formation mechanism and turbulence characteristics of the sheared convective boundary layer are studied through Large-Eddy Simulation (LES) experiments. Four cases with different velocity difference ΔU of 1.5ms−1 and 3.0ms−1 and different potential temperature gradient Γθ of 0.006Km−1 and 0.015Km−1 were conducted in the horizontal homogeneous atmospheric convective boundary layer of 6000m × 6000m × 2000m. The results show that the formation of the entrainment layer is affected integratedly by the horizontal shear effect and the vertical buoyancy effect, in which turbulence shows strong anisotropy and intermittent characteristics, wherein the mixed layer is dominated by stable small eddies, and the entrainment layer by strip-shaped large eddies. Compared with the pure buoyancy boundary layer, the entrainment flux ratio Af is 0.176∼0.385, and the height of the entrainment layer zi is shifted to the side with bigger velocity (U2). ΔU promotes entrainment and Γθ inhibits, especially for the upper limit of the entrainment layer h2. Obviously, the shear-shelter entrainment phenomenon appears under the weak shear and strong potential temperature gradient.

Characterization of Continuous Wave Laser-Induced Thermal Gradients in Magnetic Tunnel Junctions Integrated Into Microresonators via COMSOL Simulations

Spin caloritronics investigates static and dynamic effects on magnetic structures due to spin-currents generated by thermal gradients. Here, we present COMSOL simulation results using a 2-D heat transfer module applied to Co2FeAl/MgO/CoFeB magnetic tunnel junctions (MTJs) integrated into microcavity resonators. Microresonators are used in order to study the effects of temperature gradients on single micro-/nano-objects. We find that the thermal conductivity of the insulating barrier (MgO) plays a crucial role, influencing the overall temperature, as well as the thermal gradient over the barrier. Taking into account the microresonator structure around the MTJ, which is mainly made from copper, strongly affects the uniform heating of the overall stack. Nevertheless, the gradient over the barrier is relatively unaffected by the surrounding conditions. The simulation results provide insight into the temperature profile of the whole structure and show how modifying the structure of the surrounding materials may tune and optimize the thermal gradient magnitude and ultimately provide a path for quantifying spin-transfer torques induced by thermal gradients.

Characterizing ERA-Interim and ERA5 surface wind biases using ASCAT

Abstract. This paper analyzes the differences between ERA-Interim and ERA5 surface winds fields relative to Advanced Scatterometer (ASCAT) ocean vector wind observations, after adjustment for the effects of atmospheric stability and density, using stress-equivalent winds (U10S) and air–sea relative motion using ocean current velocities. In terms of instantaneous root mean square (rms) wind speed agreement, ERA5 winds show a 20 % improvement relative to ERA-Interim and a performance similar to that of currently operational ECMWF forecasts. ERA5 also performs better than ERA-Interim in terms of mean and transient wind errors, wind divergence and wind stress curl biases. Yet, both ERA products show systematic errors in the partition of the wind kinetic energy into zonal and meridional, mean and transient components. ERA winds are characterized by excessive mean zonal winds (westerlies) with too-weak mean poleward flows in the midlatitudes and too-weak mean meridional winds (trades) in the tropics. ERA stress curl is too cyclonic in midlatitudes and high latitudes, with implications for Ekman upwelling estimates, and lacks detail in the representation of sea surface temperature (SST) gradient effects (along the equatorial cold tongues and Western Boundary Current (WBC) jets) and mesoscale convective airflows (along the Intertropical Convergence Zone and the warm flanks for the WBC jets). It is conjectured that large-scale mean wind biases in ERA are related to their lack of high-frequency (transient wind) variability, which should be promoting residual meridional circulations in the Ferrel and Hadley cells.

Phase field simulation of dendrite sidebranching during directional solidification of Al-Si alloy

In this paper, the phase field method is used to study the multi control factors during directional solidification sidebranching growth of Al-Si alloy. The effects of primary dendritic spacing, pulling velocity, temperature gradient and thermal noise on the evolution of sidebranch are studied. As the primary dendritic spacing increases, the number of secondary branches symmetrically growing on both sides of the primary dendrites increases and the secondary branches are more developed; The increase of the pulling velocity and the temperature gradient can increase the instability of the sidebranch and the degree of solute enrichment in the secondary branches gap. Sidebranch remelting and coarsening will occur when the pulling velocity and temperature gradient are large; Without changing the tip morphology and steady-state behavior of the dendrite, appropriate thermal noise can trigger the sidebranching and make the sidebranch on both sides of the dendrite asymmetrically growth.

Free vibration of functionally graded sandwich shallow shells in thermal environments by a differential quadrature hierarchical finite element method

This paper presents a differential quadrature hierarchical finite element method (DQHFEM) for dynamic analyses of functionally graded material (FGM) sandwich shallow shells in thermal and non-thermal environments. A layer-wise theory based on the first-order shear deformation theory (FSDT) for each layer was adopted. Effective material properties of the FGM are estimated according to Voigt’s rule of mixture (ROM) and/or Mori–Tanaka (MT) scheme. For the shells in thermal environment, a nonlinear temperature distribution in thickness direction is considered and the elastic properties are assumed to be temperature dependent. The results obtained from the proposed formulation are validated with those available in literatures. Natural frequencies obtained from Sander’s, Love’s and Donnell’s shell theories for different geometric and boundary conditions are compared with each other first to assess the performance of different shell theories for FGM sandwich shells under non-thermal environment. Then the effects of volume fraction index, core thickness and temperature gradient on natural frequencies of FGM sandwich shells are investigated. The presented DQHFEM is much like the fixed interface mode synthesis method but does not need modal analysis and is of high accuracy. This work is the first application of the method to functionally graded sandwich shells in thermal environments.

Impurity effects on ion temperature gradient driven multiple modes in transport barriers

The impurity effects on ion temperature gradient (ITG) driven instability in transport barriers (TBs) are numerically investigated with the gyrokinetic integral eigenmode equations in tokamak plasmas. In particular, the effects of temperature and density gradients of the main ions ( and ) are analyzed independently to understand the physical mechanisms better, instead of keeping their ratio as carried out in previous works, when the parameters of impurity ions vary. It is found that the effect of impurity ions with outwardly peaked density profiles on ITG modes depends on the competition between the destabilizing effect of the impurity density gradient and the stabilizing effect induced by the dilution of main ions from impurity ions when is fixed, which is in significant contrast with the results for a fixed . The destabilizing effects include enhancement of ITG modes and coupling to the impurity mode (IM) in weak ITGs (big ) and strong impurity density gradient regimes. In addition, the stability boundaries for ITG modes, including high-order modes, are discussed in detail, and compared with previous works (Fröjdh et al 1992 Nucl. Fusion 32 419). Furthermore, the impurity ions with either inwardly or slightly outwardly peaked density profiles have weaker and stronger stabilizing effects on small and big poloidal wave vector modes, respectively. However, the impurity ions with steeper outwardly peaked density profiles have stronger stabilizing effects on big modes. Moreover, the inwardly peaked impurity ion density profiles are beneficial for main ion confinement and impurity decumulation, due to the main (impurity) ions flowing inwardly (outwardly). Finally, analyses of eigenmode structure and the quasi-linear particle flux are performed in detail. The results show that impurity ions have non-negligible effects, especially on higher-order ITG modes.

Effect of temperature gradient on competitive growth behavior of Si and YSi2 in a Si–Y eutectic alloy prepared by Bridgeman method

Abstract The Si–Y eutectic alloy has been prepared by Bridgeman method where the high temperature gradient (GE) can be obtained by means of double heating combining with liquid metal cooling. The microstructures of longitudinal section and cross section at different GE have been observed. It can be seen clearly that the YSi2 phase presents the evolution process of thick banded shape, island shape, reticular shape and fine strip shape as GE increases from 90 K/cm to 200 K/cm. Based on the interface growth temperature model, it can be concluded that the interface growth temperatures of Si phase and YSi2 phase both will decrease linearly with increasing GE while that of eutectic structure will keep a constant of 1485.6 K. Two critical temperature gradients GEC1 = 52 K/cm and GEC2 = 111 K/cm have been calculated. Eutectic coupling growth will take the dominant position when the actual GE is greater than GEC2. The primary Si phase will begin to form as GE is smaller than GEC2 and will be thicker as GE is smaller than GEC1. The coupling effect of withdrawal rate and GE on the microstructures of the Si–Y alloy also has been analyzed comprehensively.

Water desalination using a temperature gradient

A new concept for reverse osmosis is identified based on the use of a temperature gradient instead of pressure. When the temperature of the permeate-side of the membrane is higher than the feed-side then a significant driving force exists for water transport, which can overcome the osmotic pressure. The thermodynamics for this approach are developed within the paper, and as a result we have developed a single expression for driving force across a membrane for variable temperature, pressure and concentration. The thermodynamic predictions suggest for seawater a temperature difference of less than 1 °C is needed to overcome the osmotic pressure, and less than 3 °C to sustain a water flux equivalent to current reverse osmosis processes. Experimental investigation confirmed the temperature-dependence of water flux and the ability to carry out reverse osmosis at atmospheric pressure. The effect of temperature gradient and salinity on water flux was tested at ambient pressures and found to be in good agreement with the manufacturer-quoted permeability. The concept identified in this work has the potential to allow reverse osmosis to be carried out without the need for costly high pressure pumps and energy recovery systems, with energy requirements predicted to be lower than 2.0 kWh/m3.