Determination Of Temperature Profiles Research Articles

Combustion of waste solids in a fluidized bed to generate sustainable energy

Exploring alternative options to address the impending global energy crisis while taking into account environmental concerns and climate change mitigation and addressing the sky-rocketing energy demand has become urgently essential. This need is further highlighted by the significant reliance of the Republic of Serbia on imported energy sources so that the focus of its energy sector strategy is rational use of energy resources, use of renewable energy sources (RES), and waste management with satisfying environmental regulations. The use of low-calorific and waste materials in conjunction with fluidized bed combustion technology is a method to achieve all the above goals synergistically. This paper presents experimental results of combustion of several solid wastes (coal mining waste from the ?RB Kolubara? complex, Serbia, paper sludge and hazelnut shells), conducted in an industrial prototype and experimental bubbling FB boiler (capacity up to 500 kW). Burning these wastes has a variety of advantages, including recovering substantial energy remaining in the waste and minimizing the overall waste volumes. The work focused on determination of furnace temperature profiles, composition of the flue gas at the furnace outlet as well as fluidization air and fuel flowrates, the minimum fluidization rate, fluidization number, maximum heat output and the transferred heat of the tested fuels. Based on the obtained results, potentials of FBC of waste fuels and the possibility of utilization of their energy potential are evaluated.

Determination of temperature profile inside a PV module operating under specific conditions using a model coupling internal heating to optical absorption

In this study, the complex dynamics behind heat transfer within photovoltaic (PV) solar modules under spectral solar illumination are investigated. A new model coupling internal heating to optical absorption is derived from equations governing light-matter interaction throughout PV module multilayered structure. Reflection and transmission at each interface between two neighboring layers inside a PV module as well as absorption in each layer are taken into account. Dielectric properties of each interface are used to calculate its wavelength dependent reflectance and transmittance according TE and TM light polarization modes. Optical properties of each layer are utilized to determine its absorption coefficient and internal source of warming. Effects of incidence angle and light polarization modes on internal heat function are also analyzed. Heat equation is then solved in steady state limiting case and Temperature profiles inside a PV module under STC and NOCT conditions are determined.

A simple method for the quantitative assessment of soot production rate

Sooting tendency has been characterized with various empirical approaches such as smoke height and Threshold Sooting Index (TSI), that can be regarded as qualitative, as well as Yield Sooting Index (YSI), that is semiquantitative since it relies on the measurements of at least the peak soot volume fraction in the flame. All these techniques have the convenience of being easy to implement and of relying on inexpensive equipment. In the present work we present a comparatively easy but quantitative alternative to determine the soot production rate in counterflow flames. The approach is rooted in the use of: a) soot volume fraction measurements by pyrometry, b) the well established one-dimensional computational modeling of such flames for the determination of temperature and velocity profiles and c) the use of the soot governing equation. The technique is applied to several aliphatics, including methane, propane, ethylene, propene and acetylene. Soot production rate per unit flame area for the tested aliphatics ranges between 10−4 and 10−7 g/(cm2s) and, when normalized with respect to the carbon flux, between 10−5 and 10−2. On a logarithmic scale it correlates linealry with the peak temperature for all fuels. Soot yield scales as alkanes< alkenes < alkynes, with acetylene showing the highest sooting tendency even in flames at relatively low temperatures.

Heat transfer, vapour diffusion and Stefan flow around levitating droplets near a heated liquid surface

We consider a slowly condensing droplet levitating near the surface of an evaporating layer, and develop a mathematical model to describe diffusion, heat transfer and fluid flow in the system. The method of separation of variables in bipolar coordinates is used to obtain the series expansions for temperature, vapour concentration and the Stokes stream function. This framework allows us to determine temperature profiles and condensation rates at the surface of the droplet, and to calculate the upward force that allows the droplet to levitate. Somewhat counter-intuitively, condensation is found to be the strongest near the bottom of the droplet, which faces the hot liquid layer. The experimentally observed deviations from the classical law predicting the square of the radius to grow linearly in time are explained by the model. A spatially non-uniform phase change rate results in a contribution to the force not considered in previous studies, and comparable to droplet weight and the upward force calculated from the Stokes drag law. The levitation conditions are formulated accordingly, resulting in the prediction of levitation height as a function of droplet size without any fitting parameters. A simple criterion is formulated to define the parameter ranges in which levitation is possible. The results are in good agreement with the experimental data except that the model tends to slightly underpredict the levitation height.

An Efficient Reinforcement Learning Approach to Optimal Control with Application to Biodiesel Production

Optimal control problems are one of the most challenging problems in optimization. This paper presents a new and efficient Reinforcement Learning approach to optimal control problems based on the Batch Q-learning algorithm. To improve the convergence of the RL algorithm, we use k-dimensional uniformity of advanced sampling procedures, namely employing Hamersley sequences (HSS). HSS is used to randomly sample the state variables and discrete controls from the action space for the RL optimal control problem. The Neural-fitted Q-iterative algorithm is applied to solve an optimal control problem for a first-order state dynamical system. A real-world application of optimal temperature profile determination for biodiesel production in a batch reactor is presented. We present the comparison of our HSS-RL algorithm with that of the maximum principle.

Design and characterization of the polychromators for JT-60SA Thomson scattering systems

The Thomson scattering diagnostics are fundamental for a reliable determination of electron density and temperature profiles in Tokamak experiments. In JT-60SA, two systems are currently under development: one is dedicated to the core plasma region, the other to the edge region. They aim to measure the Te and ne profiles with a precision better than 10% and 5%, respectively, at an electron density of 1019 m−3 and with an electron temperature ranging from 10 eV up to 10 keV for the edge system and from 100 eV to 30 keV for the core one. The polychromators design, based on interference filters and APD detectors, is critical to achieve such performance. Each polychromator comprises 6 spectral channels measuring from 1064 nm down to 500 nm for the core system and to 660 nm for the edge one. The design aims at maximizing the efficiency and minimizing the noise under different plasma conditions. About 100 polychromators are manufactured by G.N.R.srl under an F4E contract. In this work, we present the polychromators design and performance. The key features of the optical design and of the mechanical structure are discussed. State of the art interference filters and APD detectors with custom electronics are described. Overall optical transmission measurements of the assembled polychromators and spectral channels calibration are then presented. More specific studies of the APD electrical noise and temperature dependence are discussed. The transmission functions are finally used to predict the error expected in the determination of the electron temperature and density under different levels of plasma light intensity.

Numerical simulation of thermal stratification in Lake Qiandaohu using an improved WRF-Lake model

Lake thermal stratification is important for regulating lake environments and ecosystems and is sensitive to climate change and human activity. However, numerical simulation of coupled hydrodynamics and heat transfer processes in deep lakes using one-dimensional lake models remains challenging because of the insufficient representation of key parameters. In this study, Lake Qiandaohu, a deep and warm monomictic reservoir, was used as an example to investigate thermal stratification via an improved parameterization scheme of the Weather Research and Forecast (WRF)-Lake. A comparison with in situ observations demonstrated that the default WRF-Lake model was able to simulate well the seasonal variation of the lake thermal structure. However, the simulations exhibited cold biases in lake surface water temperature (LSWT) throughout the year while generating weaker stratification in summer, thereby leading to an earlier cooling period in autumn. With an improved parameterization (i.e., via determination of initial lake water temperature profiles, light extinction coefficients, eddy diffusion coefficients and surface roughness lengths), the modified WRF-Lake model was able to better simulate LSWT and thermal stratification. Critically, employing realistic initial conditions for lake water temperature is essential for producing realistic hypolimnetic water temperatures. The use of time-dependent light extinction coefficients resulted in a deep thermocline and warm LSWT. Enlarging eddy diffusivity led to stronger mixing in summer and further influenced autumn cooling. The parameterized surface roughness lengths mitigated the excessive turbulent heat loss at the lake surface, improved the model performance in simulating LSWT, and generated a warm mixed layer. This study provides guidance on model parameterization for simulating the thermal structure of deep lakes and advances our understanding of the strength and revolution of lake thermal stratification under seasonal changes.

Thermocouple-based thermometry for laminar sooting flames: Implementation of a fast and simple methodology

This work reports the implementation and the validation of the extrapolation method for thermocouple temperature measurements corrected from the radiation losses in sooting flames. This simple method relies on the use of thermocouples having different size diameters and enables a fast and direct determination of the flame temperature by extrapolation to zero diameter. We propose here a detailed study of the possibilities and limitations offered by this method based on experimental measurements and comparison with well-established methods carried out in a laminar diffusion sooting flame. In details, a specific fast insertion setup using four different sized thermocouples has been implemented to record temperature values at different heights in the flame. From these data, we highlight that a linear calibration curve correlates the raw measured temperatures to the flame temperatures corrected of the radiation losses can be easily and rapidly obtained. The impact of soot deposition on the thermocouple on the temperature measurement is also discussed. To assess the reported thermocouple methodology, a direct comparison is made between the temperature profile determined along the vertical central axis of the flame by the extrapolation method with OH and NO LIF thermometry measurements as well as numerical simulation. Finally, we also report the comparison of experimental and simulated radial temperature profiles highlighting the adequate dynamic of the method for temperature profile determination in high temperature gradient conditions (500 K/mm). This work demonstrates that the extrapolation method is an efficient and fast method to determine accurate temperature profiles in flames, even in presence of soot particles up to a few hundred ppb, which can be useful for the development of fast and cheap sensors for either laboratory or larger-scale applications.

The evolution of temperature and density structures of OB cluster-forming molecular clumps

Context. OB star clusters originate from parsec-scale massive molecular clumps, while individual stars may form in ≲0.1 pc scale dense cores. The thermal properties of the clump gas are key factors governing the fragmentation process, and are closely affected by gas dynamics and feedback of forming stars. Aims. We aim to understand the evolution of temperature and density structures on the intermediate-scale (≲0.1–1 pc) extended gas of massive clumps. This gas mass reservoir is critical for the formation of OB clusters, due to their extended inflow activities and intense thermal feedback during and after formation. Methods. We performed ~0.1 pc resolution observations of multiple molecular line tracers (e.g., CH3CCH, H2CS, CH3CN, CH3OH) that cover a wide range of excitation conditions, toward a sample of eight massive clumps. The sample covers different stages of evolution, and includes infrared-weak clumps and sources that are already hosting an HII region, spanning a wide luminosity-to-mass ratio (L∕M) range from ~1 to ~100 (L⊙/M⊙). Based on various radiative transfer models, we constrain the gas temperature and density structures and establish an evolutionary picture, aided by a spatially dependent virial analysis and abundance ratios of multiple species. Results. We determine temperature profiles varying in the range 30–200 K over a continuous scale, from the center of the clumps out to 0.3–0.4 pc radii. The clumps’ radial gas density profiles, described by radial power laws with slopes between −0.6 and ~−1.5, are steeper for more evolved sources, as suggested by results based on dust continuum, representing the bulk of the gas (~104 cm−3), and on CH3OH lines probing the dense gas (≳106–108 cm−3) regime. The density contrast between the dense gas and the bulk gas increases with evolution, and may be indicative of spatially and temporally varying star formation efficiencies. The radial profiles of the virial parameter show a global variation toward a sub-virial state as the clump evolves. The linewidths probed by multiple tracers decline with increasing radius around the central core region and increase in the outer envelope, with a slope shallower than the case of the supersonic turbulence (σv ∝ r0.5) and the subsonic Kolmogorov scaling (σv ∝ r0.33). In the context of evolutionary indicators for massive clumps, we also find that the abundance ratios of [CCH]/[CH3OH] and [CH3CN]/[CH3OH] show correlations with clump L∕M.

Curie-supported accelerated curing by means of inductive heating – Part I: Model building

ABSTRACT Accelerating the polymerisation of adhesives has been a long-established field of research in context of adhesive bonding technology as long curing times – sometimes up to days – represent a decisive disadvantage in contrast to most mechanical joining techniques like riveting or screwing. In addition to, e.g., curing via UV, microwave or IR radiation, electromagnetic induction represents a promising solution for speeding up the cure of polymers. With this method, adhesively bonded components are subjected to an alternating electromagnetic field (EMF) that induces heat in EMF-sensitive materials, e.g., steel or aluminium. If intrinsic EMF-sensitivity of the materials to be bonded is not given, different types of susceptors like meshes, fibres or particles are added to the adhesive in order to be heated inductively and thus cure the adhesive from the inside. Recent research has focused on a special type of susceptors, so-called Curie particles (CP), which can only be heated inductively up to their specific Curie temperature (T c) at which CP-induced heating automatically stops. As a result, a curing process is created that eliminates the need for external temperature monitoring while simultaneously preventing overheating of the bond. As underlying curing kinetics – most importantly polymerisation enthalpy and curing time – significantly differ depending on the considered adhesive, induction times needed to achieve full cure must currently be determined through costly preliminary investigations on an experimental level. Thus, to contribute for a more efficient and controllable bonding process, the present study aimed at developing a numerical model based on the Finite Element Method (FEM) and capable of predicting the curing degree α in dependency of curing temperature profiles T Cure(t) and the CP content c cp. For this purpose, the curing kinetics of two fundamentally different 2K epoxy adhesives were linked to a transient heat flow simulation based upon experimentally determined heat loads. The validation of the developed FEA technique was successfully carried out using the example application of inductively cured large-scale Glued-in rod (GiR) specimens, whereby experimentally determined temperature profiles showed excellent agreement with the numerical predictions. The present paper focused on presenting preliminary experimental work as well as all analytical methods implemented for the numerical modelling.

Modified methodology for determining the temperature profiles of inverted u-tubes steam generators used in pwr power plants

The most common and reliable methodology for determining temperature profiles of Inverted U-tubes Steam Generators is using Computational Fluid Dynamics (CFD) programs. In this work, we developed a modified methodology, using the Wolfram Mathematica software, in order to determine, with good approximation, the temperature profiles of these kind of equipment. The first step was to determine expressions for the physical properties of the water in the operational conditions, like density, thermal conductivity, specific heat and dynamic viscosity. Geometrical parameters like tubes diameter and sub-channel flowing area, as well as the flow parameters like flow mass of primary and secondary fluid, were also considered for determining the numbers of Reynolds, Prandtl, Nusselt and, consequently, the variation of convective coefficients and the global heat transfer coefficient. With subroutines that use the method of the lines we were able to solve the partial differential equations applied to parallel and countercurrent heat exchangers with no phase change. The U-tubes SG were divided in two regions which the first one was calculated considering a parallel heat exchanger and the second one was calculated considering a countercurrent heat exchanger, depending on the flow direction of the primary and secondary circuit. During the phase change, a constant variation of the enthalpy was considered, making the primary fluid temperature decrease following a linear behavior. Using the developed methodology called “Enthalpy Ruler”, the encountered results were considered adequate, since the defined lengths are compatible with the constant variation of the enthalpy from the compressed liquid to saturated steam.

Design of thermomechanical treatment of high strength steels

Reducing the level of COx and NOx emissions from combustion engines is an important goal in the automotive industry. One way to reduce the emissions is to use lightweight parts in the car construction. High-strength steels are one of the successful choices for body parts. Their strengthening mechanisms provide them with better mechanical properties, which translates into thinner sheet metal blanks and ultimately reduced weight of parts. The main strengthening mechanisms include TRIP (TRansformed Induced Plasticity) and TWIP (TWinning induced plasticity). This paper outlines processing of high-strength steels, from forging to round bars and heat treatment to determination of phase transformations and temperature profiles for thermomechanical processing in an innovative tool. The experimental materials contained manganese, silicon and different aluminium levels. Their compositions were selected with a goal to observe the properties of advanced multiphase high strength steels during processing.

Accelerated curing of G-FRP rods glued into timber by means of inductive heating – Influences of curing kinetics

ABSTRACT Glued-in Rods (GiR) are nowadays widely established as an adhesively bonded connection type in timber engineering. The assemblies consist of rods, e.g. threaded rods or rebars, made of steel, or Fibre-Reinforced Polymers (FRP), which are bonded into wooden construction elements. In contrast to mechanical fastening, adhesive bonding often results in a better load transfer between the adherends, and consequently a reduction of local stress peaks in comparison to mechanical fasteners. Bonding of GiR is typically performed with 2 K polyurethanes (2 K-PUR) or 2 K epoxies (2 K-EPX), for which full curing can last up to several days. Consequently, before the connection can be stressed, or moved for further processing, components have to be maintained in fixed position. This process can be very time, and cost, consuming for contractors. In order to create a speedier, thus more efficient, bonding process, the present study investigated accelerated curing of large-scale GiR specimens with the help of inductively heated Curie particles (CP). The CP are added to the adhesives, and exposed to a high frequency (HF) electromagnetic field (EMF). The EMF heats the mix up until the Curie temperature (T C) is reached, at which point the heating automatically stops. Due to the generated heat, polymerisation is significantly accelerated in a process independent of external monitoring techniques that prevents adhesive overheating. In order to design this practitioner-friendly and controllable manufacturing process, kinetic models were developed, allowing the prediction of the degree of cure, α, in dependency of CP content. The kinetic models were applied to experimentally determined temperature profiles during inductive heating of large-scale GiR specimens, considering three commercially available 2 K-EPX, and one 2 K-PUR, all of which are widely used. The kinetic modelling allowed for a much better interpretation of the heating behaviour, highlighting, in particular, the contribution of enthalpy for adhesive curing, and by extension of the whole induction process.

Development of an endothermic electrode for electroporation-based therapies: A simulation study

Cell death mediated by non-thermal mechanisms is an essential characteristic of irreversible electroporation for tumor ablation. However, needle electrodes inherently promote thermal damage immediately adjacent to the electrode/tissue interface, especially in cases when intensive pulsed electric fields are applied to get a large ablation. In this study, we propose utilization of endothermic reactions in the core of clinically used needle electrodes to absorb the heat generated during electroporation, thereby accentuating the nonthermal aspect of irreversible electroporation. In this study, numerical models were developed to determine temperature profiles resulting from a typical irreversible electroporation (IRE) protocol in clinic using either conventional solid electrodes or hollow electrodes filled with NH4NO3 to facilitate an endothermic reaction in the electrode core. The results indicate that the endothermic electrodes can reduce the temperature rise and thermal damage during IRE treatment.

AlGaN/GaN HEMT channel temperature determination utilizing external heater

An improved method of average channel temperature and channel temperature profile determination is introduced in this paper applied to AlGaN/GaN HEMT using quasi-static I–V characterization and external heater. Particular HEMT resistances and threshold voltage were experimentally determined at different ambient temperatures from TLM measurements, HEMT output and transfer I–V characteristics. Negligible pinch-off area and leakage current dependence on drain voltage allows to obtain average temperature ∼77 °C for dissipated power 1.5 W using simple recurrent differential calculations. The HEMT channel temperature profile exhibiting maximum peripheral temperature ∼130 °C for dissipated power 1.5 W was simulated and verified utilizing the device electrical parameters variation.

Development of a three-dimensional surrogate geometry of the breast and its use in estimating the thermal conductivities of breast tissue and breast lesions based on infrared images

Due to the increase in life expectancy and the advances in techniques for detecting breast cancer, the number of women diagnosed with breast disorders has increased. The method commonly used for diagnosis is mammography, which has some limitations. Recent studies indicate that using infrared images has the potential to detect early neoplasms, since such images can detect changes in the surface temperature of the breast. This paper puts forward a methodology based on thermographic images for developing a reliable three-dimensional model of patients' breasts. By using this geometry, numerical simulations could be performed to determine temperature profiles, which were combined with data on temperatures measured by thermography, thus enabling thermophysical properties of mammary tissue and pathologies to be estimated. The model was developed using the breast profile curve obtained from the thermographic image and by adapting volumes of an Ortho Pauher external prosthesis. After sensitivity analyses, the Sequential Quadratic Programming (SQP) method was used to estimate the thermal conductivities of glandular and nodule tissues, using the maximum temperature in the lesion region as measured by the thermographic image. The results were compared with those of other authors and the values were measured by infrared camera, thereby validating the calculations reported.

Determination of temperature profile of the lithosphere between zero and 150 km penetration at Itagunmodi, Nigeria

In this work the temperature profile for the lithosphere was determined using data from radiogenic heat source and heat from other sources from 0 to 150 km depth was determined using a suitable mathematical expression. The temperature at the base of the lithosphere was given between 1200℃ to 1600℃. The Fourier’s law was applied and the results showed that the profile range from 27.0℃ to 1483.3℃. These results compared favourably well with existing literature values.Keywords: Temperature Profile; Lithosphere; Radiogenic Heat; Heat Flux

Rigorous channel temperature analysis verified for InAlN/AlN/GaN HEMT

This paper proposes a novel method of average channel temperature and channel temperature profile determination is discussed in theoretical part and subsequently applied to InAlN/AlN/GaN HEMT using quasi-static I–V characterization supported by thermal 3D FEM simulations. Experimentally was determined HEMT source resistance and threshold voltage from low-power output and transfer I–V characteristics at different thermal chuck temperatures. The HEMT channel average temperature nearly 88 °C for dissipated power 2 W was calculated taking advantage of the drain current change analysis applied in recurrent differential form. Additionally, the HEMT channel temperature profile was simulated utilizing the calculated channel dissipated power density.

Diffusion weighted magnetic resonance imaging for temperature measurements in catalyst supports with an axial gas flow

In situ thermometry of catalytic gas phase reactions allows to determine temperature profiles in catalyst beds. Diffusion weighted MRI is proposed as an alternative method for temperature measurements using capillaries filled with different liquids.

Improved velocity and temperature profiles for integral solution in the laminar boundary layer flow on a semi‐infinite flat plate

AbstractOne of the most important problems in Mechanical Engineering is the determination of laminar boundary layer thickness over a flat plate. Integral solution and similarity solutions are two well‐known methods for calculation of boundary layer thickness. However, integral solution method is a computational cost‐effective method rather than the similarity solution method. Velocity and temperature profiles must be determined for the integral solution method. Velocity boundary layer thickness can be determined by the velocity profile whereas for determination of thermal boundary layer thickness both velocity and temperature profiles must be used. Available velocity profiles do not give an exact value for velocity boundary layer thickness, while the Nusselt number is affected by these profiles. In this study, a new velocity profile is proposed which gives an exact value for laminar boundary layer thickness on a flat plate. In addition, two temperature profiles are proposed that give the exact values of the Nusselt number over a flat plate for uniform temperature and uniform heat flux boundary conditions. The calculated constants in the velocity boundary layer thickness equation and the Nusselt relations are validated with the results of the similarity solution method. Excellent agreement between the results of the two methods is observed.