Temperature Gradient Profiles Research Articles

Impact of variable viscosity, thermal conductivity, and Soret–Dufour effects on MHD radiative heat transfer in thin reactive liquid films past an unsteady permeable expandable sheet

AbstractSignificance of magnetohydrodynamic effect on a viscous (temperature‐dependent) and chemically reactive thin fluid film flow past an unsteady permeable stretchable plate with Soret–Dufour effects, nonlinear thermal radiative, and suction under the action of a convective type of boundary condition is analyzed. The problem consists of nonlinear governing basic equations that are highly nonlinear due to the existence of nonlinear thermal radiative terms in the energy equation. Analytical solutions are challenging to achieve for such types of problems, so a numerical scheme adopts the numerical solution. Computed solutions indicate that decreasing the Dufour number (and simultaneously increasing the Soret number) enhances heat flux, whereas the reverse trend is estimated for the concentration gradient field. The influence of magnetization indicates a decrement in the thin liquid film velocity distribution, whereas an increment is observed in temperature and solutal gradient profiles. Further, an enhancement in thermoradiative values focuses on decreasing the heat flux profiles, whereas a decreasing trend is determined in the solutal gradient by incrementing the Schmidt number. The variations of the velocity field, temperature, and concentration gradients are shown for the unsteady parameter lying in the range [0.8, 1.4]. Similarly, the range of different parameters utilized are [0.0, 1.0], [0.0, 2.0], [0.8, 1.5], [0.5, 2.0], [0.0, 1.0], [0.2, 3.0], [1.0, 2.0], [0.0, 3.0], [0.4, 1.0], and [0.4, 1.0]. The novelty of the present study lies in its analysis of complex fluid dynamics phenomena and their implications for various industrial processes and engineering applications, including coating processes, heat exchangers, microfluidics, and biomedical engineering. The insights gained from the study can contribute to developing more efficient and innovative research in these areas. Further, we have compared the present results with those available in the literature under some special cases and found them to be in excellent agreement.

Insights Into Viscosity/Thermal Conductivity of a Micropolar Nanofluid Flow Near a Horizontal Cylinder

The purpose of this study is examining the changes in viscosity and thermal conductivity of a micropolar nanofluid on a horizontal cylinder, specifically on the axisymmetric stagnation inflow. Nanofluid viscosity is known to exhibit an exponential change with temperature, while thermal conductivity was found as a linear with temperature to enhance the heat transfer rates of nanofluid flow by numerical calculations. A horizontal circular cylinder with an axisymmetric stationary point was the subject of the mathematical model, which described an incompressible, constant micropolar nanofluid flow over it. The importance of predicting heat and mass transfer for a horizontal cylinder are common in many applications, including refrigerator condensers and flat-plate solar collectors. For this reason, it is imperative to study heat and mass transfer in horizontal cylinder geometries. Furthermore, taken into account were fluid temperature factors like nanofluid viscosity and micro-rotation viscosity. It introduced aluminum oxide nanoparticles to two common fluids: pure water and ethylene glycol. It was capable of to estimate the pressure gradient profiles, temperature gradient profiles, shear stress, Nusselt number, angular and azimuthal velocities, and curvature parameters for various numerical values of micropolar, variable viscosity/thermal conductivity, and curvature. An exact match is found in a table that contrasts the current numerical computation with the published data. Based on our simulation results, it seems that the temperature profile variation for both pure water with alumina nanoparticles and ethylene glycol is significantly influenced by the Reynolds number and the viscosity/thermal conductivity characteristics of the nanofluid. Nevertheless, the micropolar parameter barely makes a difference. Furthermore, the concavity of the pressure profiles is pushed upwards, and it appears that the pressure biographies for ethylene glycol are more pressure-intensive than those for pure water. By increasing the value of the variable viscosity parameter of the nanofluids, it can be achieved to discern clearly between the angular velocity profiles in the two scenarios. Engineers and researchers working on propulsion technology for missiles, airplanes, and spacecraft can especially benefit from these perceptions.

Fabrication of gradient hydrogels using a thermophoretic approach in microfluidics

The extracellular matrix presents spatially varying physical cues that can influence cell behavior in many processes. Physical gradients within hydrogels that mimic the heterogenous mechanical microenvironment are useful to study the impact of these cues on cellular responses. Therefore, simple and reliable techniques to create such gradient hydrogels are highly desirable. This work demonstrates the fabrication of stiffness gradient Gellan gum (GG) hydrogels by applying a temperature gradient across a microchannel containing hydrogel precursor solution. Thermophoretic migration of components within the precursor solution generates a concentration gradient that mirrors the temperature gradient profile, which translates into mechanical gradients upon crosslinking. Using this technique, GG hydrogels with stiffness gradients ranging from 20 to 90 kPa over 600 µm are created, covering the elastic moduli typical of moderately hard to hard tissues. MC3T3 osteoblast cells are then cultured on these gradient substrates, which exhibit preferential migration and enhanced osteogenic potential toward the stiffest region on the gradient. Overall, the thermophoretic approach provides a non-toxic and effective method to create hydrogels with defined mechanical gradients at the micron scale suitable for in vitro biological studies and potentially tissue engineering applications.

Thermal boundary layer modelling for heat flux prediction of bubbles at saturation: A priori analysis based on fully-resolved simulations

This study presents and investigates uni-directional thermal sub-layer enhancement techniques within the context of an interface tracking method for simulating bubbly flows at saturation. Current discretisation methods on structured and fixed Cartesian grids tend to spread the bubbles' interface region, creating a trade-off between the freely moving nature of the bubble to the detriment of accurately capturing the discontinuous aspect of the interface and variations of properties and fluxes crossing it. Although robust techniques have been described in the literature to ensure energy conservation, less research has been undertaken to develop a methodology to retrieve the non-linear behaviour of quantities in the interface vicinity at a reasonable computational cost. In this study, the discretised bubble surface is used as a basis for addressing several quasi-static radial sub-problems that are bounded by an interfacial constant saturation temperature and a CFD temperature field value. A first approach, based on an analytical solution fitted at each time step using underlying Eulerian field values, has been developed to incorporate near-interface physics. This includes the tangential effect, incoming fluid velocity, and local mean curvature (first order surface approximation). A semi-analytical approach needs to meet certain assumptions to be valid. This is due to its derivation from a simplified plane boundary-layer development or from a spherical diffusion problem which limits its applicability range. Therefore, a second approach based on a uni-directional sub-resolution fed carefully by interpolated velocity and tangential source terms demonstrates promising results as it aligns with the principal variations of the solution. Both methodologies have been applied onto DNS data of a steady rising bubble configuration at low and moderate Reynolds {3.6;62.5} and Prandtl {1;2.5;5} numbers with a constant interfacial temperature after an extensive analysis of the advection-diffusion terms hierarchy. The key aspects to maximise the effectiveness of the sub-resolution method have been clearly identified and discussed. The Sub-resolution shows better applicability to our case study on moderately large thermal layers. The newly predicted interfacial temperature gradient and temperature profile could be re-employed for Eulerian fluxes correction.

Effect of radiation and viscous dissipation using the Galerkin method over a vertical porous plate with variation in temperature

AbstractIn the presence of viscous dissipation and radiation effects, a numerical analysis is performed for an unsteady‐free convective, radiative, chemically reactive, radiation absorption, viscous, incompressible, and electrically conducting fluid passing through an exponentially accelerating vertical porous plate. Numerical methods are used to solve the collection of nondimensional governing equations and their boundary conditions. Graphs are used to study the effects of different physical characteristics on flow quantities. Tables are used to study the differences in skin friction, the Sherwood number, and the Nusselt number for the physical interest. The analysis and explanation of the fluctuation in radiation and flow parameters on velocity and temperature gradient profiles through graphs using the Galerkin technique is the novelty of this work. For the magnetic, Prandtl, heat sink, radiation, Schmidt, and chemical reaction parameters, skin friction is significantly higher; however, for the Grashof, modified Grashof, permeability, radiation absorption, Dufour, and Soret numbers, skin friction has the opposite tendency.

Single crystal growth and physical properties of La, Co doped (Eu,Ca)FeAs2

We report the growth of La and Co doped (Eu,Ca)FeAs2 ((Eu0.5Ca0.4La0.1)(Fe0.97Co0.03)As2, La,Co-(Eu,Ca)112) single crystals via high temperature sintering method and their superconducting properties were investigated. Unlike other iron-based superconductors, single crystals of this compound were relatively easy to obtain by sintering at high temperatures from stoichiometric compositions. Using small amounts of precursor (0.5 g) and optimization of the isothermal temperature and temperature gradient profiles, relatively large (up to 2.8 mm2) 112 single crystals were obtained. X-ray diffraction measurements on the 112 single crystals indicated only (0 0 l) Bragg peaks. Energy dispersive X-ray spectroscopy analysis indicated the composition of the grown 112 single crystals to be (Eu0.54, Ca0.38, La0.09)(Fe0.96, Co0.037)As2. The coexistence of superconductivity and Eu2+ magnetism, as reported in EuFeAs2, was confirmed. The onset of superconducting transition temperature of 30 K (magnetic susceptibility) and 31.8 K (electrical resistivity) was observed in the La,Co-(Eu,Ca)112 single crystal grown by thermal gradient method. Our present results indicating further optimization of Co doping may enhance the superconductivity in these compounds. The La,Co-(Eu,Ca)112 iron-based superconductor, which have unique physical properties and are relatively easy to grow as single crystals, may bring an interesting playground in the field of superconducting materials.

Magneto-Thermo Heat Transfer of a Chemically Reactive and Viscous Dissipative Casson Nanofluid Thin Film Over an Unsteady Stretching Surface with Variable Thermal Conductivity

This paper addressed unsteady magnetohydrodynamic flow and heat transfer of an incompressible Casson nanofluid thin film past a stretching sheet by considering the features of thermal radiation, chemical reaction, and viscous dissipation. The problem is modeled mathematically, and the governing basic equations are brought into nonlinear ordinary differential equations by utilizing appropriate similarity transformations. Then the transformed equations are then solved numerically by using the bvp4c solver. The influences of pertinent physical variables are performed on velocity, temperature gradient, and nanoparticle concentration gradient profiles. It is seen that the profile of the nanoparticle concentration gradient enhances by increasing the values of the Schmidt number, whereas the opposite trends are observed by increasing the values of the thermophoresis parameter. It is also analyzed that by increasing the values of the thermophoresis parameter, there is an increase in the profiles of the temperature and concentration distributions. The computed results are obtained by giving main consideration to the convergence process and comparing them with the results existing in the literature.

Flexible combinatorial ionic/electronic thermoelectric converters to efficiently harvest heat from both temperature gradient and temperature fluctuation

It is of great significance to develop novel heat-harvesting technology due to abundant waste heat on earth. Although thermoelectric generators (TEGs) based on the Seebeck effect under temperature gradient has been studied for more than 200 years, their thermoelectric (TE) performance is still not good enough for large-scale practical application. Ionic TE materials can exhibit much higher thermovoltage than electronic conductors, but they can be used to harvest heat merely from temperature fluctuation. In order to take the advantages of these two types of TE materials, we developed flexible combinatorial TE converters (CTECs) with an ionic TE capacitor (ITEC) made of an ionogel and a TEG consisted of poly (3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), which were connected in parallel, that is, the electrodes of the ITEC and TEG at the hot end are wired together, while those at the cold end are connected. These CTECs can harvest heat from both temperature gradient by the TEG and temperature fluctuation by the ITEC. Their TE performances are sensitive to the factors like heating/cooling rates, temperature gradient profile and internal resistance of the TEG. The specific average power supplied by the CTEC can be up to 4.7 times as that of the control TEG with PEDOT:PSS. Moreover, the TE performance can be further improved by combining an ITEC with a TEG consisted of both p- and n-type legs in series, which can generate a specific average power as 5.8 times as the CTECs with the TEG of only one p-type leg.

Die dimensions impact on fibrous plant protein formation during high moisture extrusion

Plant-based meat analogues that mimic the structure and texture of meat are becoming very popular. They can be produced using high moisture extrusion (HSE). . High protein materials first undergo intense thermomechanical treatment in the extruder barrel and then are textured and simultaneously cooled in the die. The mechanisms underlying this structuring process are not sufficiently understood and depend on numerous and interconnected factors, including raw materials composition and process parameters. This study focuses on the effects of die height and die length on extruder responses (torque, pressure), textural properties and fibration of soy concentrate extrudate obtained at high moisture (60% w/w). In order to evaluation the quality of fibration, and to complete texture analysis, a visual method base on angle of fibration was developed. By comparing extrudate obtained with die of 2 mm and 5 mm height, this study shows that a minimum height is necessary for temperature gradient and velocity profile creation in the die. In order to study die length higher than the one observed in the literature, a modular die with different lengths was specially developed for this study, going from 150 to 600 mm for a extrusion barrel length of 640 mm. Results show a linear correlation between fibration and die length: the longer is the die, the more elongated is the internal flow pattern. This change in flow pattern leads to an improvement in the quality of the extrudate fibration.It confirms that die length is one of the main influencing factor for fiber formation, and that a minimum length is required to obtain extrudats which structure really mimics meat fibres.

Multi-objective integrated BES-CFD co-simulation approach towards pandemic proof buildings

COVID-19 has posed an extraordinary burden to those professionals responsible for properly operating and safely maintaining facilities throughout this disaster. Considering this global pandemic, the common spaces in buildings must be reconsidered to accommodate a future in-presence existence. Governments address human health and safety as the most vital considerations worldwide; thus, Heating, Ventilation, and Air Conditioning (HVAC) designs, airflow patterns, and temperature distribution must all be reconsidered to achieve such healthy circumstances. Based on this, a Building Energy Simulation-Computational Fluid Dynamics (BES-CFD) validated model has been analysed in terms of various HVAC designs. The simulations assessed the proposed solutions in terms of energy-saving, operational CO2 emissions, thermal comfort enhancement, and infection control. The results were closely examined and showed that the Underfloor Air Distribution (UFAD) system generates approximately laminar vertical airflow, reducing the likelihood of indoor infections and viral transmission. Supply air is delivered to the inhabitants’ zone without sacrificing mixing efficiency, ensuring long-term indoor environmental quality. Moreover, the UFAD model proved to be more cost-efficient compared to the Conventional Overhead Distribution (COHD) and has a lower carbon footprint and energy consumption. In terms of thermal comfort, the dynamic simulations showed a noticeable enhancement in PMV. Additionally, the UFAD provides a vertical temperature gradient profile that is sufficiently uniform. Moreover, the integrated DOAS-UFAD systems’ effectiveness was proved through a techno-economic analysis with a Return on Investment of 8.25% and a Payback period of 7.3 years.

Core transport barriers induced by fast ions in global gyrokinetic GENE simulations

A novel type of internal transport barrier called F-ATB (fast ion-induced anomalous transport barrier) has been recently observed in state-of-the-art global gyrokinetic simulations on a properly optimized ASDEX Upgrade experiment and presented in Di Siena et al (2021 Phys. Rev. Lett. 127 025002). Unlike the transport barriers previously reported in the literature, the trigger mechanism for the F-ATB has been shown to be a wave-particle resonant interaction between supra-thermal particles—generated via ion cyclotron resonance heating—and ion scale plasma turbulence. This resonant mechanism strongly depends on the particular shape of the fast ion temperature and density profiles. Therefore, to further improve our theoretical understanding of this transport barrier, we present results exploring the parameter space and physical conditions for the F-ATB generation by performing a systematic study with global GENE simulations. Particular emphasis is given to the transport barrier width and its localization by scanning over different energetic particle temperature profiles. The latter are varied in amplitude, half-width, and radial localization of an ad-hoc Gaussian-like energetic particle logarithmic temperature gradient profile. For the reference parameters at hand, a threshold in the ratio between the fast ion and electron temperature and the amplitude of the fast ion logarithmic temperature gradient is identified to trigger the transport barrier effectively. The role of q = 1 rational surface to the transport barrier formation is investigated as well by retaining electromagnetic effects and its impact found to be negligible for this particular barrier formation mechanism.

Effect of chemical reaction on mixing transition and turbulent statistics of cylindrical Richtmyer–Meshkov instability

Direct numerical simulations of a three-dimensional cylindrical Richtmyer–Meshkov instability with and without chemical reactions are carried out to explore the chemical reaction effects on the statistical characteristics of transition and turbulent mixing. We adopt 9-species and 19-reaction models of non-premixed hydrogen and oxygen separated by a multimode perturbed cylindrical interface. A new definition of mixing width suitable for a chemical reaction is introduced, and we investigate the spatio-temporal evolution of typical flow parameters within the mixing regions. After reshock with a fuller mixing of fuels and oxygen, the chemical reaction becomes sufficiently apparent at affecting the evolution of the flow fields. Because of the generation of a combustion wave within the combustion regions and propagation, the growth of the mixing width with a chemical reaction is accelerated, especially around the outer radius with large temperature gradient profiles. However, the viscous dissipation rate in the early stage of the chemical reaction is greater because of heat release, which results in weakened turbulent mixing within the mixing regions. We confirm that small-scale structures begin to develop after reshock and then decay over time. During the developing process, helicity also begins to develop, in addition to kinetic energy, viscous dissipation rate, enstrophy, etc. In the present numerical simulations with cylindrical geometry, the fluctuating flow fields evolve from quasi-two-dimensional perturbations, and the generations of helicity can capture this transition process. The weakened fluctuations during shock compression can be explained as the inverse energy cascade, and the chemical reaction can promote this inverse energy cascade process.

Effect of Briquette Thickness on Iron Nugget Formation in Fluxless Processing of Iron Sand Concentrate under Isothermal – Temperature Gradient Profiles

Currently, electric furnaces and blast furnaces are used to process iron sand concentrate or titanomagnetite to produce pig iron and titanium slag. The titania content in the slag ranges from 10 to 25 mass% of blast furnaces and 30 to 35 mass% of electric furnaces. The low titania content in the slag is due to the addition of flux, some iron oxide must be retained in the slag to adjust the viscosity of the slag and the mixing of iron sand concentrate with ordinary iron ore. The low titania content in the slag makes titania extraction economically unattractive. One method to achieve high titania slag is the carbothermic reduction process without flux addition. A series of experiments have been carried out on the carbothermic reduction of cylindrical briquettes consisting of iron sand concentrate and coal under an isothermal – temperature gradient profile up to 1380°C to produce iron nuggets separated from slag. The briquettes have a diameter of 13 mm, and the thickness varied from 2 to 18 mm. The results showed that the thickness of the briquettes significantly affected the iron recovery in the nuggets. The briquettes with 2 mm thickness showed higher iron recovery in the nugget. The study also found that the sulfur content in coal may have contributed to the formation of iron nuggets.

Impact of Stratification Mechanisms on Turbulent Characteristics of Stable Open-Channel Flows

Abstract Flow over a surface can be stratified by imposing a fixed mean vertical temperature (density) gradient profile throughout or via cooling at the surface. These distinct mechanisms can act simultaneously to establish a stable stratification in a flow. Here, we perform a series of direct numerical simulations of open-channel flows to study adaptation of a neutrally stratified turbulent flow under the combined or independent action of the aforementioned mechanisms. We force the fully developed flow with a constant mass flow rate. This flow forcing technique enables us to keep the bulk Reynolds number constant throughout our investigation and avoid complications arising from the acceleration of the bulk flow if a constant pressure gradient approach were to be adopted to force the flow instead. When both stratification mechanisms are active, the dimensionless stratification perturbation number emerges as an external flow control parameter, in addition to the Reynolds, Froude, and Prandtl numbers. We demonstrate that significant deviations from the Monin–Obukhov similarity formulation are possible when both types of stratification mechanisms are active within an otherwise weakly stable flow, even when the flux Richardson number is well below 0.2. An extended version of the similarity theory due to Zilitinkevich and Calanca shows promise in predicting the dimensionless shear for cases where both types of stratification mechanisms are active, but the extended theory is less accurate for gradients of scalar. The degree of deviation from neutral dimensionless shear as a function of the vertical coordinate emerges as a qualitative measure of the strength of stable stratification for all the cases investigated in this study.

Numerical simulation of evaporation phenomena and heat transfer of liquid Hydrocarbon in a microtube

Evaporation and heat transfer is the key process that affects the performance of the portable liquid fuel system. The flow boiling of liquid n-heptane is studied numerically in a 0.2 mm microtube under non-uniform boundary conditions. At low fuel flow rate (5 μl/min) and low thermal gradient, the average value of heat transfer coefficient was 4000 W/m2-K, mean evaporation efficiency was 0.80, and low pressure drop oscillations of magnitude 600 Pa were observed. In addition, the flow pattern was stable with a dynamic liquid-vapor interface. At high flow rate (70 μl/min), the average value of heat transfer coefficient and pressure drop oscillations magnitude increases to 16000 W/m2-K and 2500 Pa respectively, whereas mean evaporation efficiency decreases to 0.65. The diameter and intensity of the nucleate bubble and the liquid droplets depends on flow rate and thermal gradients. At low fuel flow rate, high frequency low magnitude pressure drop fluctuation was obtained while at high low frequency high magnitude pressure drop fluctuation was obtained. Numerical calculations are also performed under several wall temperature profiles of the same temperature gradients that have shown smaller effect on evaporation efficiency.

Experimental and numerical modelling of solid and hollow biomass pellets high-temperature rapid oxy-steam combustion: The effect of integrated CO2/H2O concentration

Oxy-steam combustion behaviour of rice straw (RS) pellets was studied at high temperatures experimentally in a new plasma combustion system and numerically using an upgraded one-dimensional unsteady-state single particle combustion model with a new homogeneous devolatilization volatile combustion and heterogeneous char oxidation sub-models under different O2/H2O/CO2/N2 gas compositions. Experimental results showed that the temperature gradient profiles for both the surface and center decreased significantly when the steam was added to the gas mixture at 20 and 40%. At 30% H2O, the heat consumption of the gasification reaction decreased which resulted in a higher particle temperature and a higher char oxidation reaction rate. Combustion characteristics for heating, ignition, devolatization, and combustion stages were obtained and confirmed through the time of recorded pictures by high-speed camera. The obtained experimental results were validated through fitting the measured values of surface and center temperature-time profiles, ignition time, final pellet diameter, and time for the maximum amount of released volatiles, under different H2O and CO2 concentrations, with those predicted from the model solution. Also, the mass of the released volatiles and pellet diameter history were predicted from the model solution. Results of the model solution proved the reality and credibility of the measured and calculated experimental findings.

Probing the temperature gradient in the core boundary layer of stars with gravito-inertial modes

Aims. We investigated the thermal and chemical structure in the near-core region of stars with a convective core by means of gravito-inertial modes. We determined the probing power of different asteroseismic observables and fitting methodologies. We focus on the case of the B-type star KIC 7760680, rotating at a quarter of its critical rotation velocity. Methods. We computed grids of 1D stellar structure and evolution models for two different prescriptions of the temperature gradient and mixing profile in the near-core region. We determined which of these prescriptions is preferred according to the prograde dipole modes detected in 4 yr Kepler photometry of KIC 7760680. We considered different sets of asteroseismic observables and compared the outcomes of the regression problem for a χ2 and a Mahalanobis distance merit function, where the latter takes into account realistic uncertainties for the theoretical predictions and the former does not. Results. Period spacings of modes with consecutive radial order offer a better diagnostic than mode periods or mode frequencies for asteroseismic modelling of stars revealing only high-order gravito-inertial modes. We find KIC 7760680 to reveal a radiative temperature gradient in models with convective boundary mixing, but less complex models without such mixing are statistically preferred for this rotating star, revealing extremely low vertical envelope mixing. Conclusions. Our results strongly suggest the use of measured individual period spacing values for modes of consecutive radial order as an asteroseismic diagnostic for stellar modelling of B-type pulsators with gravito-inertial modes.

Analysis of unsteady magnetohydrodynamic radiative thin liquid film flow, heat and mass transfer over a stretching sheet with variable viscosity and thermal conductivity

The present article is related to the study of magnetohydrodynamic (MHD) heat and mass transfer in a thin liquid film over a permeable unsteady stretching surface in the presence of chemical reaction, applied magnetic field, viscous dissipation, and thermal radiation with variable viscosity and thermal conductivity. Computed results for unsteadiness parameter, temperature ratio parameter, radiation parameter in the presence/absence of the viscous dissipation and Ohmic heating are analyzed and discussed. The computed results reveal that the viscous and Ohmic dissipations reduce the temperature gradient profiles in the thin liquid film. Further, the thermal radiation decreases the cooling rate of the thin liquid film but the reverse effect is seen by increasing the Prandtl number.

Post-gel polymerisation shrinkage profiling of polymer biomaterials using a chirped fibre Bragg grating

A strain profile measurement technique using a chirped fibre Bragg grating (CFBG) sensor by implementing an integration of differences (IOD) method is reported in this paper. Using the IOD method the spatial distribution of strain along the length of the CFBG is extracted from its power reflectance spectra. As a proof of concept demonstration, the developed technique is applied to measure the polymerisation shrinkage strain profile of a photo-cured polymer dental composite which exhibits a non-uniform strain distribution attributed to the curing lamp characteristics. The result from the CFBG technique is compared with that of an FBG array embedded in the dental composite and is correlated with the degree of conversion of the material which also depends on the curing lamp intensity distribution. This technology will have significant impact and applications in a range of medical, materials and engineering areas where strain or temperature gradient profile measurement is required in smaller scales.

Experimental investigation of burning characteristics of porous combustible soaked in liquid oxidizer

Experimental investigations of burning characteristics of a tested specimen consisting of a polyethylene foam soaked in 100 wt% hydrogen peroxide are made. All experiments are carried out in a large volume chamber, which newly introduced in our previous work at an initial pressure range from p = 0.1 to p = 0.35 MPa in absolute with various fuel porosity range from ε = 0.6 to ε = 0.9, which corresponds to global equivalence ratios from φ = 0.51 to φ = 3.8. Temperature measurements using an R-type thermocouple embedded into the specimen are then conducted to investigate thermal structure (e.g., profiles of temperature and temperature gradients and burning surface temperature) of the burning specimen for deep understandings of the burning process. Following forced ignition at top surface of the specimen, steady successive-burning process is successfully observed for all conditions studied in this work. Burning rates (a rate at which the top surface moves downward) are measured by carefully tracking the top surface of the specimen by adopting an image processing software. Findings show that overall burning rates at the rate from 1 to 3.2 mm/s are obtained and influenced by pressure and the fuel porosity. Additionally, results of the direct temperature measurements reveal that the temperature gradient in the gas-phase layer near the top surface (burning surface) of the specimen increases as pressure increases, resulting in an increase in the overall burning rate. The top surface temperature and its pressure dependency, and a global activation energy at the top surface temperature of the specimen are experimentally measured accordingly.