Applied Temperature Profile Research Articles

Thermophoretic microfluidic cells for evaluating Soret coefficient of colloidal particles

Thermodiffusion or thermophoresis gained much interest in bio, chemical, and energy engineering. Although there are several methods to measure thermophoresis, they consume large sample volumes, are limited to binary mixtures, and give only indirect access to the applied temperature profile. Herein, we propose a thermophoretic microfluidic cell for quantitative measurements of the Soret coefficient of colloids. The actual microscale measuring channel lies between cooling and heating channels to achieve a one-dimensional temperature gradient. Fluorescence lifetime imaging microscopy with Rhodamine B is utilized to measure the spatial temperature profile in the channel. The fluorescence intensity of fluorescently labeled polystyrene particles with a diameter of 25 nm is used to monitor the concentration profile. The observed temperature and concentration profiles are one-dimensional, as gradients in the longitudinal and height directions can be neglected. In the investigated temperature range, the averaged difference between the measured Soret coefficients with the cell and determined with the Thermal Diffusion Forced Rayleigh Scattering set-up is less than 8%.

The effect of emulsifier by-products and storage conditions on the techno-functional properties of model aerosol whipping cream

Model aerosol whipping cream (AWC) with a medium-chain saturated monoacylglyceride (me-sMAG) emulsifier and different emulsifier by-products was stored either at 20 °C, 30 °C, or with a temperature profile for 16 weeks (w). Techno-functional properties were analysed and the MAG content was determined by high-performance thin-layer chromatography with fluorescence detection during the storage time. After 8 w, the MAG content of the me-sMAG emulsifier in the product decreased by about 20%, independent of the applied emulsifier by-products and storage temperatures. No effect of the emulsifier by-products on the techno-functional properties of model AWC was found. Although storage at 20 °C had no effect on the techno-functional properties, storage at 30 °C and at the applied temperature profile led to emulsion instabilities with ongoing storage. At 30 °C and short storage times, the foam stability of the model AWC increased, while the foaming capacity decreased and emulsion destabilisation was not observed.

Estimation of the Entropy Coefficient of Lithium-Ion Batteries Via a Temperature and Open-Circuit Voltage Kernel Function

Lithium-ion battery temperature is driven by two key heat source terms – irreversible and reversible heat. The reversible heat generation term is often neglected when characterising and simulating battery temperature. This is primarily due to the long experimental time (~20 hours) associated with the widely followed potentiometric technique used to quantify reversible heat. Reversible heat can however contribute to around 70% of the total heat generation, when a battery is subjected to low charge and discharge currents, and it is quantified via a coefficient termed as the entropy coefficient.Robust techniques are therefore required that can significantly reduce the experimental time and quantify the entropy coefficient to improve battery temperature prediction and subsequent design of battery pack thermal management systems. In this abstract a bespoke experimental rig using a Peltier element is built that allows a user-defined thermal profile to be applied on to the surface of a coin cell (Figure 1). The applied temperature profile is designed in a manner that perturbs the cell open-circuit-voltage (OCV) to identify the underlying dynamics between the measured OCV response (at a given state-of-charge, SoC) and applied cell surface temperature profile. This dynamic relationship is characterised by a kernel function relating temperature and OCV. Using system identification techniques, the temperature profile can be designed to minimise the experimental time required to estimate the underlying open-circuit voltage and temperature kernel function and robustly determine the entropy coefficient at the particular cell SoC.The approach is applied on a coin cell consisting of Kokam 5 Ah electrodes and the entropy coefficient, is estimated as -0.57 ± 0.02 mV/K (when at 30% SoC) within an experimental time interval of 8 hours. The initial results are encouraging and further work is in progress to compare and validate the procedure against the default potentiometric technique.Figure 1: Experimental rig design for the thermal excitation and open-circuit voltage (OCV) measurement of the coin cell under test. Figure 1

Effect of Rotating Magnetic Field on Thermal Convection and Dopant Transport in Floating-Zone Crystal Growth

A three-dimensional numerical study was carried out to understand the effects of rotating magnetic field on thermocapillary convection and impurity concentration distribution in a floating full zone growth process of doped Si crystals under zero gravity. Even though the applied temperature profile was axisymmetric, the simulation results showed that the flow structures and concentration distribution in the molten zone exhibited three-dimensional disordered patterns in the absence of a rotating magnetic field. For the application of rotating magnetic field, Lorentz force forced convection to rotate in the same direction of the magnetic field and made the tangential velocity in the melt increase with the growing radial distance. Under a relatively low magnetic field, the thermocapillary flow became an oscillatory three-dimensional convection. However, two dimensional axisymmetric distributions of both the melt flow and the impurity concentration were presented under the magnetic field with sufficiently strong intensity. Meanwhile, the thermocapillary convection in the molten zone formed a back flow region with flow in the direction from the high temperature to low temperature along the free surface and through intermediate section. The concentration contours became uniform, and thus the isolines of concentration formed a series of concentric circles in the growth interface. Therefore, the rotating magnetic field was effective for ameliorating the stability of the melt flow and the uniformity of the concentration distribution which was beneficial to the growth of crystals with a radial uniform crystal.

Thermomechanical Behavior of Superalloy Thermal Protection System Under Aerodynamic Heating

This study investigated the thermomechanical behavior of a superalloy thermal protection system panel using a combination of experiments and numerical simulation. A superalloy thermal protection system panel was created by sandwiching a thermal insulation material and two superalloy plates with the support of spacer structures. The applied temperature profile was calculated from aerodynamic heating data. The thermal protection system panel was tested for three thermal cycles (approximately three missions). Thermal deformation of the thermal protection system panel was measured using a three-dimensional digital image correlation method. The results indicate that the presented thermal protection system panel provided good thermal protective performance under a thermal loading of 1023 K (750°C) with a heat-shielding index of 78% in the steady-state condition. The crucial finding is the permanent deformation of the thermal protection system panel after the first thermal cycle test. The thermomechanical coupled simulation results reveal the occurrence of a permanent deformation due to the plastic deformation of the spacer supporting structure, which was also observed in this Paper’s experiment. This study offers an indispensable understanding of the thermomechanical response of the thermal protection system panel, which is crucial for preventing damage to the thermal protection system panel and for modifying the structural design of the supporting structure in the thermal protection system panel.

Exactness of measured/predicted temperature distributions for heat generation in arbitrary non-variable cross-section bar using entropy generation method

• A novel application of second law of thermodynamics. • Usable for validation purposes in every study which involves heat transfer. • Presenting a unique value of non-dimensional total entropy generation rate. • Investigating the effect of cross sectional geometry on lost work. The purpose of the present study is to introduce the entropy generation method as a new validation tool of numerical and experimental studies in the heat transfer field where there exist no similar solutions with which to compare results. Analysis of temperature profiles has been conducted in bars with internal thermal energy generation, constant temperature boundary condition and arbitrary non-variable cross section. The bars have steady state Fourier heat conduction and uniform thermal energy generation. The total rate of entropy generation can be calculated using two different methods: The 1st method is based on integrating local entropy generation rate on the solution domain, and the 2nd one is based on the thermodynamic definition of entropy and the Clausius theorem. The equality of these two results depends on the exactness of the applied temperature profile. The closer the entropy generation rates in the control volume (EGRCVs), the more accurate the predicted temperature profile would be and thus, the obtained results are more reliable. Seven different geometries have been examined for the bar cross section and a correlation between error of temperature distribution and error of entropy generation has been obtained. Moreover, the effect of the cross section geometry on entropy generation has been studied and the distribution of local entropy generation rate for the selected geometries was plotted.

Numerical study on thermal stresses of a planar solid oxide fuel cell

A three-dimensional (3D) finite element model consists of positive electrode–electrolyte–negative electrode (PEN) and metallic interconnect (MIC) assembly is constructed by using commercial finite element software Abaqus. With the simulated temperature profile in the planar solid oxide fuel cell (SOFC), the finite element method is employed to calculate the thermal stress distribution in a planar SOFC. The effects of temperature profile, electrodes and electrolyte thickness, and coefficients of thermal expansion (CTEs) mismatch between components are characterized. The value and distribution of thermal stress are the functions of the applied materials CTEs, applied temperature profiles and thickness of anode and electrolyte. The calculated results can be applied as the guide for SOFC materials selection and SOFC structure design. The anode is subjected to large tensile stresses and the electrolyte is subjected to large compressive stresses during the first cooling from the sintering temperature. The chemical reduction of NiO to Ni in the porous anode lowers the absolute stress level in the PEN structure by 20%. The large tensile stresses in the anode and the large compressive stresses in the electrolyte relax partly when the SOFC operates at high temperature. Cracks could probably appear in the anode structure when the PEN structure is cooling to room temperature after the sintering.

Interaction between Al–Si melt and dielectric layers during formation of local Al‐alloyed contacts for rear‐passivated Si solar cells

AbstractThe alloy formation between physical vapor deposited Al and Si at the rear side of the industrially applicable passivated emitter and rear solar cell has been investigated. New insights of sequential phases and phenomena like escape of gaseous bubbles from the melt and reduced surface wetting as a function of the applied temperature profile are documented by in situ light‐microscopic observation. A cross‐sectional analysis of the local contact formation is performed using scanning spreading resistance microscopy. During the melting phase, the interaction of Al and Si at locally opened areas in a dielectric layer stack, as well as the interaction between Al–Si melt and the dielectric layers is recorded with a video camera and analyzed. It was found out that the SiOx layer reacts with the Al–Si melt and that SiNy layer plays a fundamental role for the correct isolation of the solar cells.magnified imageTypical shape of a locally alloyed Al–Si/Al‐BSF (back surface field) point contact in an i‐PERL Si solar cell with laser‐ablated openings in a dielectric stack that separates the Al cover layer from the Si bulk of the wafer.

Multi-layer thermoelectric-temperature-mapping microbial incubator designed for geo-biochemistry applications

We demonstrate a novel, vertical temperature-mapping incubator utilizing eight layers of thermoelectric (TE) modules mounted around a test tube. The temperature at each layer of the TE module is individually controlled to simulate the vertical temperature profile of geo-temperature variations with depth. Owing to the constraint of non-intrusion to the filled geo-samples, the temperature on the tube wall is adopted for measurement feedback. The design considerations for the incubator include spatial arrangement of the energy transfer mechanism, heating capacity of the TE modules, minimum required sample amount for follow-up instrumental or chemical analysis, and the constraint of non-intrusion to the geo-samples during incubation. The performance of the incubator is experimentally evaluated with two tube conditions and under four preset temperature profiles. Test tubes are either empty or filled with quartz sand, which has comparable thermal properties to the materials in the geo-environment. The applied temperature profiles include uniform, constant temperature gradient, monotonic-increasing parabolic, and parabolic. The temperature on the tube wall can be controlled between 20 °C and 90 °C with an averaged root mean squared error of 1 °C.

Carbon/metal nanotubes with tailored order and configuration by direct carbonization of inverse block copolymer micelles inside nanoporous alumina

Carbonaceous nanotubes decorated with metal nanoparticles were obtained by heating inverse block copolymer micelles loaded with metal precursors inside nanoporous alumina. Simple changes in the applied temperature profile allowed tailoring of the wall morphology of the nanotubes and the spatial arrangement of the metal nanoparticles.

Optimal cooling strategies in polymer crystallization

An optimal control problem for cooling strategies in polymer crystallization processes described by a deterministic model is solved in the framework of a free boundary problem. The strategy of cooling both sides of a one dimensional sample is introduced for the first time in this model, and is shown to be well approximated by the sum of the solutions of two one-phase Stefan problems, even for arbitrary applied temperature profiles. This result is then used to show that cooling both sides is always more effective in polymer production than injecting the same amount of cold through only one side. The optimal cooling strategy, focused in avoiding low temperatures and in shortening cooling times, is derived, and consists in applying the same constant temperature at both sides. Explicit expressions of the optimal controls in terms of the parameters of the material are also obtained.

Flexible temperature sensors on fibers.

The aim of this paper is to present research dedicated to the elaboration of novel, miniaturized flexible temperature sensors for textronic applications. Examined sensors were manufactured on a single yarn, which ensures their high flexibility and good compatibility with textiles. Stable and linear characteristics were obtained by special technological process and applied temperature profiles. As a thermo-sensitive materials the innovative polymer compositions filled with multiwalled carbon nanotubes were used. Elaborated material was adapted to printing and dip-coating techniques to produce NTC composites. Nanotube sensors were free from tensometric effect typical for other carbon-polymer sensor, and demonstrated TCR of 0.13%/K. Obtained temperature sensors, compatible with textile structure, can be applied in rapidly developing smart textiles and be used for health and protections purposes.

Improved thermal design of a compression mold

AbstractAn analysis of the heat transfer in a tool for producing neat resin disks was conducted to determine how to bring about a better agreement between the tool temperature and the applied temperature profile. Using the commercial code FLUENT to investigate the relative effects of heat conduction into the tool and heat loss from the tool by convection, it was shown that convective heat transfer appears more important than conduction in controlling the tool performance. Decreasing the height of the tool was predicted to decrease the heat losses by convection. Redesigning of the tool based on this analysis resulted in the tool experiencing the applied temperature profile. © 2007 Wiley Periodicals, Inc. Adv Polym Techn 26:86–99, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20091

Bridgman growth of detached GeSi crystals

Ge 1− x Si x (0< x<0.12) has been grown by the vertical Bridgman technique using adjustments in the applied temperature profile to control the pressure difference between the bottom and top of the melt. Using this technique, a pressure difference is created by decreasing the temperature in the gas volume above the melt while the sample is molten but prior to growth. A maximum pressure difference approximately equal to the hydrostatic pressure of the molten sample can thus be obtained. Several GeSi crystals were grown in pyrolitic boron nitride ampoules. When a pressure difference was applied, samples were reproducibly grown mostly detached. For comparison, samples were also grown in a configuration in which gas could flow freely between the gap below the melt and the volume above the melt and no pressure difference could be established. These samples were initially attached. Existence of detachment was determined both by measuring the surface roughness of the samples with a profilometer and by observations of the sample surfaces with optical and electron microscopy.

Synthesis of polystyrene with mixtures of mono- and bifunctional initiators

This work studies the bulk and nonisothermic polymerization of styrene (S) using mixtures of mono- and bifunctional initiators. The effects on polymerization rate and on molecular weight averages after changes in the global initiator concentration and in the nature of the initiator mixtures were experimentally and theoretically analyzed. The mathematical model was adapted from the literature to admit initiator mixtures and to simulate the applied temperature profiles. Compared to the standard use of monofunctional initiators, the use of initiator mixtures that include bifunctional initiators presents the advantage of reducing the polymerization time, while not deteriorating the final polymer quality. The simulation program accurately describes the evolution of conversion, but exhibits some deviations with the average molecular weights. © 1996 John Wiley & Sons, Inc.

On convection in the earth's core driven by lateral temperature variations in the lower mantle

Lateral variations in heat flux or temperature in the lowermost mantle, associated with mantle convection, will drive fluid flow in the liquid core. The effect is modelled by a rotating spherical shell with uniform lower boundary temperature and a laterally varying upper surface temperature and the solutions found by numerical calculation, some for a density-stratified fluid. The problem depends upon two dimensionless numbers, a horizontal Rayleigh number and a stratification parameter. The calculations are restricted to surface temperatures which are symmetric about the equator and steady solutions are found. Induced toroidal flows near the surface are closely linked with the applied temperature profile through the thermal wind equation and Coriolis forces make the convection penetrate into the shell. Stratification acts mainly to suppress radial flow but the surface toroidal flow is relatively unaffected. The results illustrate the powerful influence exerted by the surface temperature but are difficult to apply directly to the earth's core because molecular values of the thermal diffusivity entail a very long time-scale. Assuming a turbulent thermal diffusivity equal to the magnetic diffusivity gives a more realistic time-scale and it is possible to recover, for specific simple imposed temperature profiles, flows similar to those found in the earth's core from inversion of geomagnetic secular change.