Non-uniform Temperature Profile Research Articles

Analysis of Fission Matrix Databases with Nonuniform Fuel Temperature Profiles for Static and Transient Calculations

Monte Carlo codes are the most accurate way to solve the neutronics in a reactor core but can be computationally expensive, especially for when feedback effects are considered or for transient calculations. In this paper, we use the fission matrix (FM) method to perform static and transient calculations with point-kinetics equations and a quasi-static model for an adiabatic transient with feedback. This was applied to a three-dimensional model of the Transient Reactor Test Facility (TREAT) experimental reactor using the Monte Carlo code Serpent for reference calculations and to generate fission matrix databases (FMDBs). In previous works, FMDBs were generated with uniform fuel temperature profiles. Here, we analyze the use of FMDBs with nonuniform temperature profiles, for static and transient calculations. For static calculations, comparison between Serpent and the FM method using nonuniform and uniform FMDBs showed maximum differences in multiplication factors of 57.0 and 77.9 pcm, respectively. For the fission source distribution, comparisons showed maximum root-mean-square differences of 1.10% and 4.89% for nonuniform and uniform FMDBs, respectively. Similar results were obtained when using homogenized databases. Therefore, using nonuniform FMDBs produces a better approximation than uniform databases. For transient calculations, comparisons between both database sets showed differences of 0.9% and −1.8% for the peak and final total power.

Impact of DC-DC Converters on the Energy Performance of a Dense Concentrator PV Array under Nonuniform Irradiance and Temperature Profiles

Efficiency losses resulting from electrical mismatching in densely packed photovoltaic arrays present a significant challenge, particularly exacerbated in nonuniformly illuminated receivers and under varying temperatures. Serial configurations are particularly susceptible to radiation nonuniformities, while parallel systems are negatively affected by temperature variations. Various authors have recommended the incorporation of electrical voltage and current sources to mitigate these losses. This study explores different electrical connection configurations utilizing concentrated photovoltaic (CPV) cells and DC-DC electrical current converters. A self-adaptive microfluidic cell matrix cooling system is employed to mitigate thermal dispersion caused by the highly nonuniform illumination profile. The obtained results for each configuration are compared with the total electrical power produced by individual cells, operating under identical radiation and temperature conditions to those of the entire array. The results reveal a noteworthy increase in production across all studied configurations, with the parallel–series arrangement demonstrating the most promising practical utility. This configuration exhibited a remarkable 50.75% increase in power production compared with the standard series connection.

Pattern-dependent resistivity variations in inkjet-printed conductors due to non-uniform ink drying

When fabricating inkjet-printed electronic devices and circuits, inkjet-printed conductive materials require drying and sintering to improve electrical conductivity. Electrical conductivity should be the same irrespective of pattern design, size, location, or density of adjacent patterns. However, we demonstrate that spatial variations in the drying process for inkjet-printed patterns with proximity to others cause resistivity variations. These resistivity variations are studied here experimentally for different circuit patterns and in arrays of inkjet-printed square electrodes. This variation depends not only on the location of each electrode in an array but also on the number of electrodes. This means that for the same drying temperature and duration, the array with a larger number of electrodes exhibits a larger resistivity variation. The sooner an electrode dries, the lower resistivity it achieves. The resistivity variation between an individual electrode and the center electrode in a 7 × 7 electrode array can be a factor of seven. This variation decreases for lower numbers of electrodes to a factor of three for a 3 × 3 array. Furthermore, x-ray photoelectron spectroscopy analyses provide evidence for the residual presence of carbon-based materials within electrodes after the drying process. These results confirm that the location of electrodes within an array significantly influences the amount of residual carbon-based materials, thereby contributing to resistivity variations. Although intense pulsed light sintering can decrease this variation, its optimal parameters depend on the printed designs, and our simulation results show a non-uniform temperature profile over the electrode arrays. Temperature increases more at the center of patterns than the corners, which can be useful in this case to improve resistivity uniformity. In this study, for the first time, we show how different printed shapes and designs can result in non-uniform resistivity after drying and sintering.

Insulation Resistance Degradation Models of Extruded Power Cables under Thermal Ageing

Insulation resistance (IR) is an essential metric indicating insulation conditions of extruded power cables. To deliver reliable IR simulation as a reference for practical cable inspection, in this paper, four IR degradation models for cross-linked polyethylene-insulated cables under thermal ageing are presented. In addition, the influences of methodologies and temperature profiles on IR simulation are evaluated. Cable cylindrical insulation is first divided into sufficiently small segments whose temperatures are simulated by jointly using a finite volume method and an artificial neural network to model the thermal ageing experiment conditions. The thermal degradation of IR is then simulated by dichotomy models that randomly sample fully degraded segments based on an overall insulation (layer) ageing condition estimation and discretization models that estimate the gradual degradation of individual segments, respectively. Furthermore, uniform and non-uniform temperature profiles are incorporated into dichotomy and discretization models, respectively, for a comparison. The IR simulation results are not only compared between different models, but also discussed around the sensitivity of IR simulation to segment sizes and degradation rates. This provides cable assessment engineers with insights into model behaviour as a reference for their selection of appropriate IR degradation models.

Numerical and Techno-Economic Analysis of Batch Annealing Performance Improvements in Tinplate Manufacturing

The present study examines the performance improvement in the batch annealing process used in tinplate manufacturing by enhancing the heat transfer towards the steel coils and altering annealing cycle parameters. Presently, the heat transfer in the furnace is non-uniform, resulting in non-uniform temperature profiles and recrystallisation inside the coils, affecting the final coated steel quality. This study modelled a current furnace and four improvement proposals utilising transient computational fluid dynamics, to produce coil temperature profiles and rank the cases by the highest coil temperature uniformity achieved at the end of soaking. By increasing the soaking temperature and time, as well as the coiling tension before annealing and altering the coil size, the aim was to achieve higher and more uniform coil temperatures that could ensure successful recrystallisation with less defects, especially at the cold spot area in the middle of the coil. Then, a techno-economic analysis compared the cost-effectiveness of the scenarios based on the associated costs and the improvement in the scratching defects of the batch-annealed steel. Overall, most cases exhibited positive results regarding temperature uniformity enhancement, but increasing the coiling tension was considered the most promising option, due to the combination of a large defect reduction potential and cost savings per cycle.

Impact of Non-Uniform Irradiance and Temperature Distribution on the Performance of Photovoltaic Generators

The use of photovoltaic (PV) panels has increased rapidly in the last few years and as a result has become one of the main sources of renewable energy. In this context, it is important to understand in detail how a PV panel reacts to different environmental conditions and how these affect total performance. An experiment has been designed to investigate the performance of a PV panel under various highly non-uniform temperature and irradiance profiles, generated by artificial lighting. Measurements of irradiance and temperature distribution are related to measured I–V curves and used as input to the five-parameter model. The results show the limitations of the model to emulate the PV response under such extreme conditions and provide useful insights about the effect of the temperature profile on the PV performance.

Carbon Dioxide Concentration Estimation in Nonuniform Temperature Fields Based on Single-Pass Tunable Diode Laser Absorption Spectroscopy.

We propose a novel technique to accurately predict carbon dioxide (CO2) concentrations even in flow fields with temperature gradients based on a single laser path absorption spectrum measurement and machine learning. Concentration measurements in typical tunable diode laser absorption spectroscopy are based on a ratio of two integrated absorbances, each from a spectral line with different temperature dependence. However, the inferred concentrations can deviate significantly from the actual concentrations in the presence of temperature gradients. Furthermore, it is also difficult to find an analytical expression to compensate for the effect of nonuniform temperature profiles on concentration measurements. In this study, the entire absorption feature was considered since its shape and peak intensities vary with temperature and concentration. Specifically, a predictive model is obtained in a data-driven manner that can identify and compensate for the effect of a nonuniform temperature field on the spectrum. Despite a very detailed understanding of the CO2 absorption spectrum, it is nearly impossible to collect sufficient spectra for model acquisition by varying all temperature gradient conditions. Therefore, the model was obtained using only simulated data, much like the concept of a "digital twin". Finally, the predictive performance of the acquired model was verified using experimental data. In all test cases, the predictive performance of the model was superior to that of the two-line method. Additionally, a gradient-weighted regression activation mapping analysis confirmed that the model utilizes both the peak intensities as well as the change in the shape of absorption lines for prediction.

Numerical thermal augmentation of ternary nanofluid in a tube with stent, torus-ring and surface-grooved twisted tapes under non-uniform wall temperature

This paper presents a numerical analysis of flow and thermal characteristics in a plain tube with various inserts, including a stent, torus ring, and surface-grooved twisted tape, using a ternary nanofluid consisting of SiO2, ZnO, and CaO nanoparticles as the working fluid. Computational fluid dynamics simulations were conducted using ANSYS Fluent commercial codes, focusing on laminar Reynolds numbers ranging from 500 to 2000 and a non-uniform wall temperature profile. The objective is to investigate the Nusselt number, pressure drop, thermal performance, and pumping power of the ternary nanofluid with nanoparticle concentrations ranging from 0.01 to 0.05%, considering various geometrical parameters of the grooved twisted tape insert, such as thickness ratio (0.019–0.033), width ratio (0.38–0.68), and pitch ratio (1.77–5.77). The results show that flow and thermal indicators such as Nusselt number, thermal performance factor, pressure drop and pumping power increased with thickness and width ratios. Conversely, an increase in pitch ratio results in lower flow and thermal indicators. For instance, in a plane tube without inserts, no noticeable difference in pressure drop is observed and the thermal performance factor is about 1.87-1.25 times that of pure water when nanoparticle concentration is increased from 0.01 to 0.05%. The width ratio 0.68, thickness ratio 0.033 and pitch ratio 1.77 yielded a maximum thermal performance factor of about 1.4, 1.7 and 2.3 more than smooth tube, respectively, and a maximum pumping power 0.000654 W, 0.000223 W and 0.00020 W, respectively. The findings emphasize significant improvements in heat transfer and flow properties, shedding light on the innovative configuration's potential application as an improved heat exchanger. This research advances understanding of ternary nanofluid behavior and provides useful information for enhancing heat transfer in a variety of engineering applications.

Potential application of electrical performance enhancement methods in PV/T module

Hybrid photovoltaic/thermal (PV/T) modules have been proposed to generate more electricity and heat, which can improve the solar energy conversion efficiency per unit area. However, the photovoltaic (PV) efficiency of PV/T modules decreases as the PV cell temperature increases, which significantly affects the solar energy conversion efficiency of PV/T modules. Here, four temperature profiles (uniform, single-Gaussian, double-Gaussian, multi-Gaussian) are proposed on the PV cell surface by adjusting the heat transfer arrangement for the PV cell cooling duct in the PV/T module. Compared with the uniform temperature profile, the multi-Gaussian temperature profile PV cell efficiency increased by 1.292%; the single-Gaussian temperature profile PV cell efficiency decreased by 4.308%. The results show that for PV cells in the PV/T module, different temperature profiles lead to great differences in electrical performance, and a nonuniform temperature profile can be set to improve their electrical performance.

Scale and shear investigation of the viability and consequences of controlling viscous heating for Argon flows in nano-channels

Molecular dynamics (MD) is used to investigate the combined effects of channel size and wall shear stress on force-driven Argon flows in nanochannels. The adaptive wall thermostat (AWT) is used to automatically adjust wall temperature refraining the viscous heating upsurge with the increased body force from increasing mean fluid temperature. AWT is functional up to “wall shear stress limit” (WSSL), classifying wall shear stress range into controllable and uncontrollable viscous heating ranges (CVH and UVH) before and beyond WSSL, respectively. With increasing wall shear stress in CVH, liquid Argon at ∼119.9 K exhibits more non-uniform temperature profile in larger channels. Consequently, further shear dependence of density profile and fluid molecular layering which leads to controversial size-dependent slip length. Within UVH, supercritical Argon emerges from the significant increase of temperature and pressure exceeding critical state; consequently, density profile and molecular layering decrease noticeably drifting toward walls which results in minor and proximate values of slip length in all channels approaching no-slip condition. The apparent viscosity is higher in larger channels with decreasing and increasing trends within CVH and UVH, respectively, associated with changing fluid state and phase. Finally, the continuum solution suggests the possibility of estimating the mass flow rate with reasonable accuracy relative to MD if implemented with appropriate properties and slip boundary condition.

Equivalent value of non-uniform temperature field for thermocouple measurement

The incoming flow is assumed to have a uniform temperature profile when the energy balance of a thermocouple bead is analyzed for the purpose of measurement corrections, which is hardly true in real applications. The incoming temperature is normally non-uniform and the temperature of the flow closer to the bead has a stronger influence on the bead temperature. Considering this, for the first time, a Gaussian probability density function is established to generate an equivalent temperature of the non-uniform temperature field, which can be used in the corrections. With the one-dimensional thermocouple heat transfer program, the bead temperatures are calculated with five non-uniform temperature profiles and compared with the bead temperatures with the uniform temperatures to find the variance correlation of the Gaussian function. The variance is correlated to the Nusselt number and the wire diameter and the bead diameter of the thermocouple. Many cases with different thermocouple sizes, velocities and temperature ranges and widths of the power function profile are simulated. For all the tested cases, the bead temperature differences between the real profiles and the equivalent profiles are less than 27K, demonstrating the good accuracy of the current method.

The Impact of Heat Source and Temperature Gradient on Brinkman–Bènard Triple-Diffusive Magneto-Marangoni Convection in a Two-Layer System

The effect of a heat source and temperature gradient on Brinkman–Bènard Triple-Diffusive magneto-Marangoni (BBTDMM) convection in a two-layer system is investigated. The two-layer system is horizontally infinite and is surrounded on all sides by adiabatic boundaries. It is exposed to basic uniform and non-uniform temperature profiles and heat sources. The appropriate eigenvalues and thermal Marangoni numbers (TMNs), which depend on temperature and concentration, are obtained for the temperature profiles (TPs) for lower rigid and higher free boundaries with surface tension. The transformed system of ordinary differential equations is solved by using an exact technique. For all three TPs, the impact of significant relevant parameters on these eigenvalues, and hence on BBTDMM convection, are investigated versus the thermal ratio. It is observed that, by increasing the values of the modified internal Rayleigh number for the fluid layer and the solute Marangoni numbers, the Darcy number, and the viscosity ratio for the set of physical parameters chosen in the study, one can postpone BBTDMM convection. Higher values of the modified internal Rayleigh numbers for the porous layer augment BBTDMM convection.

Aerothermal performances of a rotating turbine disk cavity with non-uniform wall temperature profiles in an aero-engine

Aerothermal performances of a rotating turbine disk cavity with non-uniform wall temperature profiles in an aero-engine

Triple diffusive Marangoni convection in a fluid-porous structure: Effects of a vertical magnetic field and temperature profiles

In this study, the triple diffusive Marangoni convection (TDMC) problem when a steady heat source is present in both layers and a vertical uniform magnetic field in a fluid-porous structure is investigated in closed form. The horizontally infinite fluid-porous structure, which is horizontally surrounded by adiabatic boundaries and subjected to basic uniform and non-uniform temperature profiles. For all three temperature profiles (TP), linear, parabolic and inverted parabolic, the eigenvalues, the thermal Marangoni numbers (TMNs) are determined in closed form for lower rigid and upper free boundaries with surface tension, depending on both temperature and concentrations. The effects of relevant parameters on the eigenvalues, hence on TDMC, against depth ratio are attempted for all TPs. It is noticed that, the inverted parabolic TP on TDMC in a composite layer is the most stable of all the three TPs, the linear TP is the most unstable one and the parabolic TP is the moderate one. The relevant physical parameters considered in the study are effective for porous layer dominant fluid-porous structures.

The Impact of the Temperature Control Strategy in Steady-State Virtual Vacuum Simulation on the Spontaneous Evaporation Rate and Corresponding Evaporation Coefficient

In the present paper, we propose a novel simulation approach that allows one to capture the steady-state evaporation into virtual vacuum state by maintaining a constant number of atoms within the liquid phase during the simulations. The proposed method was used to perform virtual vacuum simulations of argon at a temperature of 90 K in order to study the effects of the chosen simulation temperature control approach on the system’s temperature profiles, spontaneous evaporation rates, and the energetic characteristics of the evaporating atoms. The results show that the expected non-uniform temperature profile across the liquid phase can be flattened out by dividing the liquid phase into separately thermostated bins. However, the desired liquid surface temperature can be achieved only when the thermostat region boundary is placed outside the liquid phase. The obtained relationship between the surface temperature and the spontaneous evaporation rate show that the spontaneous evaporation rate and corresponding evaporation coefficient evaluation may change up to 21% when the surface temperature changes in a narrow temperature interval of 2.45 K. Furthermore, the results demonstrate that the thermostat region boundary position has no impact on the energetic characteristics of the evaporating argon atoms, even when the boundary is placed outside the liquid phase.

Outcomes of Uniform as well as Non-Uniform Temperature Profiles on the Onset of Double Diffusive Magneto-Darcy-Rayleigh-Benard Convection in a Two Layer set up in the presence of Local Thermal Non-Equilibrium

Outcomes of uniform as well as non-uniform temperature profiles that is linear, parabolic, inverted parabolic, Piecewise Linear Profile Heated from Below (PLHB), Piecewise Linear Profile Cooled from Above (PLCA) and Step Function (SF) temperature profile on the onset of Double Diffusive Magneto-Darcy-Rayleigh-Benard (DDMDRB) Convection in a two layer set up in the presence of Local Thermal Non-Equilibrium with incompressible fluid horizontally surrounded by adiabatic rigid boundaries. Analytical solution to the attained problem is accomplished by means of regular perturbation technique. The consequences of altering the parameters namely fluid phase thermal expansion ratio, solid phase thermal expansion ratio, solid phase thermal diffusivity ratio, inter-phase diffusivity ratio, solute Rayleigh number, Chandrasekhar number, thermal ratio and porous parameter have been elucidated graphically.

Effects of Uniform and Non-Uniform Temperature Gradients on Marangoni Convection in a Composite Layer with Variable Heat Sources

An investigation is carried out to determine the effect of uniform and non-uniform temperature profiles on single component Darcy-Benard Marangoni (DBM) convection in a composite layer system consisting of an incompressible fluid saturated porous layer on top of which is a layer of the same fluid with variable heat sources in both layers. The upper surface of the fluid layer is free with surface tension effects depending on temperature and the lower surface of the porous layer is rigid. The eigen value, thermal Marangoni number (TMN) is solved exactly for linear, parabolic and inverted parabolic temperature profiles for the adiabatic thermal boundary conditions at the horizontal boundaries of the composite layer. The influence of various dimensionless parameters on the eigen value against depth ratio is discussed in detail.

Influence of Fuel Temperature Distribution Dependence on Neutron-Physical Characteristics of Nuclear Core with WWER-1000 (1200)

This paper presents the results of the influence of reactivity on fuel temperature distribution for the neutron-physical characteristics of WWER 1000-1200 cores, which in turn affects the parameters of Xenon oscillation. The improved method for calculating Resonance Absorption in a 238 UO 2 (Doppler reactivity effect) with a Nonuniform Temperature Profile are developed. The parameters calculation results for Xenon oscillations have been calculated using complex program PROSTOR. The validation of the improved method was examined by comparing the calculated xenon parameters to measurement results obtained during commissioning tests of WWER-1000 reactor power units. Results showed a more accurate calculation for the Resonance Absorption in a 238 UO2, they significantly reduce the stabilization of Doppler Effect broadening, hence these facts, are vital importance in the case of load following mode accompanied by Xenon processes in the core. The improved method is implemented into the computer-software of the Full-Scale Simulator of the 3 rd Power Unit of the Rostov NPP and the Full-Scale Simulator of the 4 th Power Unit of the Kalinin NPP. The method was tested during acceptance tests of these Full-Scale Simulators.

Factors determining the flow erosion/part deformation of film insert molded thermoplastic products

Abstract Flow erosion and part deformation are unsolved molding problems that restrict the overall success of film insert molding. This work investigated, both experimentally and numerically, the factors that affect flow erosion and part deformation in film inset molded products. Three plate-with-thickness-variation geometries, namely flat, thin-to-thick, and thick-to thin, were molded for the products. Polystyrene films and polyethylene terephthalate (PET) resins were employed in the experiments. It was found that the thin-to-thick specimens exhibited the most severe flow erosion. Increasing the injection pressure or melt temperature worsened flow erosion. Meanwhile, for the processing parameters adopted in the experiments, part deformation generally increased with melt temperature and hold time, while it decreased with injection pressure and hold pressure. Additionally, a numerical software (Moldex® 3-D) was employed to simulate the temperature and shear stress distributions in molded products. The calculated results suggested that part deformation in insert molded products results mainly from the non-uniform temperature profile during the cooling stage, owing to the product configuration and the insert film, while flow erosion is induced by the high shear stress of the polymer melt in the filling stage.

Microwave-induced thermoacoustic signal characteristics in a dynamic temperature environment

We conduct a simulation-based study to investigate the impact of a dynamic temperature environment on the characteristics of microwave-induced thermoacoustic signals. We investigate thermoacoustic signals that are generated using an interstitial microwave ablation antenna powered by a microsecond pulsed microwave source. Two temperature regimes are examined: first, a spatially uniform temperature throughout the medium to experimentally validate the simulation model, and second, the realistic, spatially nonuniform temperature profiles that arise during microwave ablation. We employ a multi-physics model that considers electromagnetics, heat transfer, and acoustic physics to simulate the coupled processes of microwave absorption and heating of the medium and thermoacoustic signal generation and propagation. An interstitial coaxial antenna is used to generate microsecond microwave pulses that simultaneously induce microwave heating and excite thermoacoustic signals via microwave pulse absorption. We find that thermoacoustic signal characteristics are highly temperature-dependent and thus change significantly within an environment where temperature varies through space and time. Furthermore, the temperature-dependent properties within the active region of the antenna drive the evolution of thermoacoustic signal characteristics. Temperature-dependent thermoacoustic signal characteristics can be exploited to track the progress of microwave ablation. Consequently, microwave-induced thermoacoustic imaging is a promising method for monitoring microwave ablation in real-time.