Evolution Of Temperature Distribution Research Articles

Temperature distribution evolution in zero-gap alkaline water electrolyzer: Experimental and modeling

Alkaline water electrolysis technology is currently the most prospective commercial choice for producing green hydrogen, however, accurately modeling the temperature distribution evolution inside the alkaline water electrolyzer is still a challenge, since the existence of strong coupling multi-physical fields among gas–liquid flow, electrochemistry and heat transfer. In this article, 3D simulation models of the zero-gap alkaline water electrolyzer are established considering the mutual coupling relationship among two-phase flow, electrochemistry and heat transfer as well as the bypass current effect to study the heat transfer property and temperature profiles under different electrolysis conditions. The simulation study is conducted for the electrolyzer consisting of five electrolysis cells. The voltage, temperature difference and gas production rate were measured experimentally and simulated well using the established models. It indicates that the average relative error is respectively 0.45% for the estimated cell voltage, 13% for the estimated outlet-inlet temperature difference of the cathode flow channel, and 1.18% for the estimated hydrogen production rate. The characteristics of temperature distribution evolution in the zero-gap alkaline water electrolyzer have been disclosed, accordingly the suitable heat management strategy has been suggested for the stable operation. The results would provide a useful guide on the optimization and design of large-scale alkaline water electrolyzer to implement long-term stable operation with low cost.

The Study of Hydrogen Volume Fraction Effects on the Flame Temperature of Turbulence Diffusion Propane Jet Flames

This paper studies the influence of hydrogen volume fraction effects on the temperature distribution of diffusion turbulent propane jet flames. Numbers of experimental scenarios have been carried out to investigate the evolution of temperature distribution under different hydrogen volume fractions. In the continuous region, these experimental results show that the temperature distribution and the maximum temperature of diffusion of turbulent jet flames are proportional to the hydrogen volume fraction under the same heat release rate of propane. Considering the model of virtual point source and the three-stage model, the theoretical model between the hydrogen volume fraction and flame temperature has been analyzed. The relationship among the temperature distribution, hydrogen volume fraction, and heat release rate has been modified. It can provide some important references for the fire risk assessment of turbulent diffusion jet flames.

Standard Cooling of Rapidly Rotating Isolated Neutron Stars in 2D

We study the long-term thermal evolution of axisymmetric rotating neutron stars in full general relativity. To this aim, we develop NSCool 2D Rot, a major upgrade to the 1D neutron stars thermal evolution code NSCool by Page. As a first application of our new code, we address the standard cooling of isolated neutron stars with rotation frequencies up to the mass shedding limit. We investigate the effects of the equation of state (EOS) by considering different combinations of core and crust EOSs. The results indicate complex time-dependent evolution of temperature distribution throughout the whole volume of the star, and in particular, in the crust. We show that most of that complexity can be attributed to the formation of a heat blob in the crust and the latitude dependence of the heat diffusion timescale through the crust.

Variable duty cycle heating strategy based online two-dimensional model for self-heating lithium-ion battery

It is a challenge to online obtain the time-varying temperature distribution of self-heating lithium-ion battery (SHLB), which results in a lack of theoretical basis for heating strategies to optimize heating time and temperature distribution uniformity. To reveal the evolution of temperature distribution and improve the temperature distribution uniformity of SHLB during heating, a variable duty cycle heating strategy with online two-dimensional model is proposed. Distributed thermal equivalent circuit model coupled with electrical model can obtain the two-dimensional temperature distribution of battery in real-time. The results show that the maximum temperature gap between the proposed model and the finite element model (FEM) is only 1.2 °C, while 90 % of the calculation time is saved. The proposed model can calculate the temperature distribution almost as accurately as FEM under different conditions. Based on the proposed model, heating currents of different values and duty cycles are applied to investigate their effects on the temperature distribution evolution of SHLB. Finally, we propose a variable duty cycle heating strategy that can automatically switch the duty cycle of the heating current according to the heating uniformity requirements in order to consider both heating time and the temperature distribution uniformity. The results show that compared with constant duty cycle heating, the variable duty cycle heating strategy can reduce the temperature difference by 35 % and limit the temperature difference to the pre-set boundary. The proposed strategy and method have considerable potential for use as improved temperature uniformity in battery management system.

Dieless drawing wire with a given end geometry by realizing temperature distribution evolution

Dieless drawing that has been widely used to produce metal tubes, wires, and rods has more potential for the future, especially in manufacturing high performance screws and nails with specific points. Because there are no dies but heating and cooling system along with drawing platform needed, it is highly flexible and meets the requirements of the steadily asked manufacturing on-demand. Under this trend, this study attempts to propose a heat transfer model that can achieve the required temperature evolution for dieless drawing a wire to form a specific end geometry as a nail point by obtaining the required evolution of heat transfer coefficient and the correspondingly approximated cooling fluid rate. After it is validated with tests on a dieless drawing platform implemented with a cooling system, whose cooling flow rate is controllable, the results show that for a linear end geometry of a stainless steel wire, there is no significant difference between the temperature distribution evolution required and obtained from the experiment. Furthermore, the end geometry of the drawn wire falls within the current industry standard tolerances as well.

Low-speed performance compensation of a turbocharged natural gas engine by intake strategy optimization

Power output at the low engine speed is limited for natural gas engines, even though the turbocharging technology is used. In this paper, the intake system of a turbocharged spark-ignition natural gas engine with 4 valves (2 intake valves and 2 exhaust valves) was optimized by considering the intake strategy effects on the engine torque output and fuel economy improvement. Firstly, a 1D numerical model with hierarchical 1D/3D approach based on GT-SUITE was developed and validated against the experimental data of engine torque and fuel consumption rate. This approach combined detailed analysis of in-cylinder flow, charge movement and combustion. Secondly, different intake strategies were designed and their effects on the intake mass flow rate and in-cylinder mass during the intake process, the swirl flow, tumble ratio and the turbulent kinetic energy during the compression process, the flame propagation and temperature distribution evolution after the spark ignition, and the pressure and heat release rate were numerically investigated. The results showed that compared with the original intake strategy, the asynchronized intake strategy (the intake valves close earlier and the intake valve lifts are reduced, while two intake valves have different intake strategy) reduces the backflow in the end of intake stroke, improves the in-cylinder swirl flow, increases the maximum heat release rate and shortens the combustion duration, and it is believed to be the optimized intake strategy. Finally, different cam profiles corresponding to the numerically designed intake strategies were applied to the bench test engine and the dyno experiments showed that the optimized intake strategy improves the torque and reduces the brake specific fuel consumption by 41.42% and 8.1% respectively at a low engine speed of 1200 rpm.

Spatially and temporally heterothermic kinetic model of hydrogen absorption and desorption in metals with heat transport

Numerical modelling of hydrogen transport is effective for designing and optimizing various energy systems, including hydrogen storage devices, fuel cells, and nuclear fusion reactors. In the present study, we propose and demonstrate a spatiotemporally heterothermic, autonomous kinetic model of hydrogen absorption and desorption in metals for precise simulations. Our bidirectional transport model comprises elementary mass transfer processes of surface adsorption and desorption, subsurface transport, and bulk diffusion. Also implemented are heat generation and conduction stemming from the absorption enthalpy, to determine the evolution of temperature distribution in the metal body, as well as the hydrogen concentration profile. Simulations by our transport model reproduce experimental hydrogen absorption and desorption curves for various temperature levels and metal scales with a single identical set of numerical equations and kinetic parameters, to thus verify the validity of the model.

Experimental and numerical studies on the formability of AA5754 and AA6082 thin sheets in nonisothermal warm redrawing process

The present work demonstrates a comparative investigation of the nonisothermal warm forward redrawing behavior of AA5754-H22 and AA6082-O sheets. The design and development of a new warm forward redrawing process was demonstrated. The complete redrawing was obtained by keeping the redrawing die and binder at 200 °C and cooling punch near to room temperature using water circulation. This process improved the thickness and surface strain distribution in redrawn cups without the onset of strain localization at the bottom corner. A thermomechanical finite element (FE) model of the nonisothermal warm redrawing process was developed applying the temperature-dependent Barlat-89 yield criterion and the Cowper–Symonds strain rate sensitive hardening model. The FE model reasonably predicted the part depth, earing development, thickness distribution, and surface strain evolution of the redrawn cups. The evolution of temperature distribution within the redrawing cup during the process was captured from FE simulations, and its role in the improvement in redrawing depth was demonstrated. Furthermore, the post-forming characterization of redrawn cup wall was also evaluated by microhardness and ring hoop tensile tests. It was found that the hardness, hoop tensile strength, and energy absorption capacity of AA5754-H22 cups were better than AA6082-O cups.

Investigation of ablation efficiency during the pulsed laser ablation of a zinc metal target in a distilled water environment

In this study, the effect of Nd:YAG laser energy with a 9 ns time duration as one of the important parameters on the laser ablation of a zinc metal target in a distilled water environment has been investigated both experimentally and theoretically. The influence of plasma shielding on the ablation rate for 100–600 mJ energies is also considered. After investigating XRD, SEM, and UV-Vis results of each sample, it is determined that synthesized nanostructures are ZnO nanoparticles, and also the morphologies of the synthesized nanostructures are formed in two forms of hexagonal crystals and amorphous nanosheets. By increasing the laser energy to 400 mJ, the ablation rate on the zinc target increases. However, with increasing energy up to 600 mJ, the plasma shielding effect is evident and the ablation rate is reduced. Also, the theoretical two-fluid heat transfer model of nanosecond pulsed laser ablation is developed to visualize the evolution of temperature distributions, crater profile, and ablation depth.

Measurement of thermal conductivity and thermal diffusivity of one-dimensional-system material by scanning electron microscopy and infrared thermography

A novel measurement system consisting of scanning electron microscopy and infrared (IR) thermography has been constructed to measure the thermal conductivity and the thermal diffusivity on a micro-/nanometer scale. In this study, we measured them for a stainless-steel wire with a diameter of 50 μm to demonstrate the validity of our system. The time evolution of temperature distribution on the whole of the stainless-steel wire was recorded by the IR thermograph when the wire was irradiated by the electron beam (EB). A time response of the wire temperature corresponding to the on/off of the EB irradiation was clearly observed, indicating that local EB heating was realized. In addition, the experimental time evolution of temperature at its transient phenomena was in good agreement with the theoretical calculation based on a one-dimensional (1D) equivalent-circuit model of heat flow coupled with electric current, where the thermal parameters, such as thermal conductivity and heat capacitance, were set to bulk values. Therefore, it can be concluded that our system is valid to evaluate the thermal conductivity of the 1D wire sample. For evaluating the thermal diffusivity of the wire sample, we applied a periodic EB irradiation by a rectangular wave with a frequency of 0.25 Hz. The thermal diffusivity was evaluated to be (2.8 ± 0.6) × 10−5 m2 s−1, which was seven times as large as that of bulk stainless steel. Our system can be applied to an AC calorimetry method for a 1D system sample after the analysis procedure is further modified.

Laser ablation of lanthanum phosphate for pulsed laser deposition

AbstractA theoretical model has been used to simulate pulsed laser ablation of Lanthanum Phosphate (LaPO4) by nanosecond Nd:YAG laser irradiation. Material ablation rate per laser pulse was experimentally measured as a function of average incident laser fluence up to 12J/cm2. Calculations were performed by solving the heat conduction equation by an explicit finite‐difference technique to generate time evolution of temperature distribution, melt depth and ablation rate from the target during and after irradiation with a nanosecond laser pulse. Good agreement between our experimental and calculated ablation rates validates our theoretical model. The calculated maximum surface temperature of the LaPO4 target indicated that for laser fluence levels, up to 20J/cm2 material ejection from LaPO4 target is expected to occur via normal boiling and evaporation successfully avoiding explosive boiling. Our calculations confirm that operating with laser fluence at near ablation threshold levels for LaPO4 also restricts dissociation of the LaPO4 target to oxides with loss of gaseous products. Therefore, our study of pulsed laser ablation of LaPO4 target helps in making judicious selection of laser parameters for Pulsed Laser Deposition (PLD) of LaPO4 coatings and films of desired stoichiometric purity and homogeneity, while successfully ensuring phase stability of the target.

Modeling unsteady heat and mass transfer with prediction of mechanical stresses in wood drying

This work presents a predictive transient two-dimensional model describing the evolution of heat, mass and mechanical stresses during wood dehydration inside an experimental drying chamber. The history of the distributions of moisture content and temperature and the effects produced by its gradients on the stresses were simultaneously modeled. The non-linear coupled differential equations of heat, mass and stresses were integrated by the Control Volume Finite Element method using triangular elements with linear interpolation functions for the dependent variables. Variation of the physical and mechanical properties with the moisture content and temperature in the wet wood were included in the analysis. Experimental results of Pinus radiata being dried inside a conditioned chamber at constant air velocity equal to 1.6 m/s, 44 °C dry-bulb and 36 °C wet-bulb temperatures were used for validation purposes. The mathematical model allows an accurate prediction of the relevant industrial information, such as: drying curves, evolution of temperature distribution, history of moisture content distribution and mass/thermal stresses.

Experimental Evaluation of Using Silica Aerogels as the Thermal Insulator for Combustor Liners

An experimental study was conducted for evaluating the feasibility of using silica aerogel as thermal insulator for combustor liners. Aerogels are a superior material for minimizing heat flux to the metal structure of the combustion liner due to their low thermal conductivity. In this study, a conical natural gas fired swirling-flame combustor was utilized for reproducing the combustion environment. The silica aerogel blanket was attached to the inner side of a perforated combustor liner. Temperature distribution on the outer side of the combustion liner was measured using a calibrated IR camera. To create a protective cooling film over the aerogel surface, cooling air was supplied from the back side of the perforated metal liner and was allowed to penetrate the silica aerogel blanket to be discharged to the combustor. As the combustor was operated at a fixed equivalence ratio of 0.83, cooling air flow rates were varied to evaluate the effectiveness of transpiration cooling on the aerogel blanket as various cooling flow rates. The measured evolution of temperature distribution confirmed thermal equilibriums for every test condition with transpiration cooling. The measured temperature distribution of metal liner demonstrated superior thermal insulation of aerogel blanket under the protection of cooling film with a temperature difference as high as 1580 K between combustion products temperature and the metal liner temperature on the back side. In addition, silica aerogel samples were examined before and after the combustion tests to understand their material degradation exposing to a typical gas turbine combustor environment using high-resolution scanning electron microscope (SEM). Test results suggest multiple degradation mechanisms to the silica aerogel blanket samples from the combustion tests. Improvements can be made to the silica aerogel blankets for a more resilient thermal insulator, for example, by replacing glass fibers in silica aerogels.

Thermal field and tissue damage analysis of moving laser in cancer thermal therapy.

In this paper, a closed-form analytical solution of hyperbolic Pennes bioheat equation is obtained for spatial evolution of temperature distributions during moving laser thermotherapy of the skin and kidney tissues. The three-dimensional cubic homogeneous perfused biological tissue is adopted as a media and the Gaussian distributed function in surface and exponentially distributed in depth is used for modeling of laser moving heat source. The solution procedure is Eigen value method which leads to a closed form solution. The effect of moving velocity, perfusion rate, laser intensity, absorption and scattering coefficients, and thermal relaxation time on temperature profiles and tissue thermal damage are investigated. Results are illustrated that the moving velocity and the perfusion rate of the tissues are the main important parameters in produced temperatures under moving heat source. The higher perfusion rate of kidney compared with skin may lead to lower induced temperature amplitude in moving path of laser due to the convective role of the perfusion term. Furthermore, the analytical solution can be a powerful tool for analysis and optimization of practical treatment in the clinical setting and laser procedure therapeutic applications and can be used for verification of other numerical heating models.

Pore-scale investigation on effects of void cavity distribution on melting of composite phase change materials

Composite Phase Change Materials (PCMs) incorporated with metal foams are promising candidates for thermal management for space exploration. However, void cavities are generated as a result of the volume change of PCM during the melting process, introducing a resistance to heat transfer due to the low thermal conductivity of the void. In this work, the effects of void cavity distribution on the conduction-dominated melting of composite PCMs under microgravity conditions are studied by a two-dimensional pore-scale lattice Boltzmann method, in which a microstructural description of the metal foam is experimentally characterized with the help of X-ray micro-Computed Tomography. Two typical distribution patterns of void cavities are analsed and computed performance is compared (1) a near-wall void cavity, and (2) randomly distributed void cavities. The evolutions of temperature distributions and melting interfaces are compared, and the average liquid fraction and energy stored per width are deduced to describe the energy storage performance. Moreover, the influence of the volume fraction of void cavities is investigated by comparing temperature distributions and energy storage performances of composite PCMs with four different volume fractions of void cavities (0%, 3.7%, 7.6%, 15.2%). After introducing void cavities, the energy stored per width is reduced by 5.7%, 12.3% and 20.2% for randomly distributed void cavities when volume fraction of void cavities is 3.7%, 7.6%, and 15.2%, respectively, and reduced by 42.2%, 64.1% and 79.7% for the near-wall void cavity, respectively. This work initiates the study of the effects of void cavity distribution on composite PCMs, which will stimulate work on structural optimization of thermal management systems.

THEORETICAL STUDY OF HEAT CONDUCTION IN MULTI-LAYER SPHERICAL BODY WITH PHASE TRANSFORMATION IN LAYERS

The objective of the study is to build a simple yet informative mathematical model that describes the heat conduction in a spherical multi-layer body with phase transformation in the layers. The numerical scheme based on the theory of Markov chains is proposed to solve this problem numerically. The radial sector of the body is divided into finite number of spherical perfectly mixed cells of different volume, which form a chain of cells. The heat exchange between the cells is described with the heat conduction matrix, the entries of which depend on the local thermo-physical properties of material in the cells (heat conduction coefficient, density, specific heat capacity). These properties can vary from one cell to another and with time. The outer cell of the chain can exchange with heat with outside environment, the temperature of which can vary with time. The state of the process is observed in discrete moments of time separated by small but finite transition duration. If the temperature of a cell reaches the value, the phase transformation begins at which, the evolution of the cell thermal and phase state is described with the corresponding kinetic equation of the phase transformation. The process of melting and solidification is used as the example to verify the qualitative predictability of the model. The graphs of temperature distribution evolution and diagrams of phase content distribution in a multi-layer spherical body are presented. The obtained results on the evolution of the thermal and phase state of the ball have no contradiction to the physical sense of the process. The proposed algorithm has very low computational time (1-3 min for one regime). The other processes of the phase transformation can be easily implemented in the model, for instance, drying, exothermic and endothermic chemical reactions, etc.

A Novel 2D Model for Freezing Phase Change Simulation during Cryogenic Fracturing Considering Nucleation Characteristics

A 2D computational fluid dynamics (CFD) model in consideration of nucleation characteristics (homogeneous/heterogeneous nucleation) using the volume of fluid (VOF) method and Lee model was proposed. The model was used to predict the process of a multiphase flow accompanied by freezing phase change during cryogenic fracturing. In this model, nucleation characteristic (homogeneous and heterogeneous nucleation) during the freezing process and the influence of the formed ice phase on the flowing behavior was considered. Validation of the model was done by comparing its simulation results to Neumann solutions for classical Stefan problem. The comparison results show that the numerical results are well consistent with the theoretical solution. The maximum relative differences are less than 7%. The process of multiphase flow accompanied by the freezing of water was then simulated with the proposed model. Furthermore, the transient formation and growth of ice as well as the evolution of temperature distribution in the computational domain was studied. Results show that the proposed method can better consider the difference between homogeneous nucleation in the fluid domain and heterogeneous nucleation on the wall boundary. Finally, the main influence factors such as the flow velocity and initial distribution of ice phase on the fracturing process were discussed. It indicates that the method enable to simulate the growth of ice on the wall and its effect on the flow of multiphase fluid.

Estimation of Combustion Temperature Field From the Electrical Admittivity Distribution Obtained by Electrical Tomography

Measurement of combustion temperature field is essential for combustion diagnosis. As intrusive devices for temperature measurement interfere the flow field of flame, nonintrusive thermometry techniques are highly desired. Electrical tomography, which is a noncontact technique and can reconstruct the complex admittivity distribution in the flame, is promising for combustion diagnosis. However, the admittivity distribution needs to be mapped to temperature field in practical applications. In this article, an ion current probe and a thermocouple measured the electrical admittivity and temperature in the flame, served as calibration devices for establishing the mapping model from the reconstructed admittivity to temperature. Polynomial, exponential, and eXtreme Gradient Boosting (XGBoost) regression modeling methods were used to fit the mapping model. Accuracies of training and test data sets of the XGBoost mapping model were the highest, and their mean relative error were only 0.69% and 16.69%, respectively. An alcohol lamp flame was monitored by using the dual-modality electrical tomography. Reconstructed images of conductivity and permittivity were mapped to temperature distributions with the established mapping model. The estimated highest temperature was ring-shaped distributed, and it was verified by the longitudinal image of temperature reconstructed from a flame photo of 432-nm radiation. The proposed method was also used to monitor the temperature variations during the ignition and blowout processes of the alcohol lamp flame. The experimental results showed that the proposed method was effective to capture the evolution of temperature distributions in highly dynamic combustion field.

Minimization of the sample temperature deviation and the effect of current during high-temperature compressive creep testing by the spark plasma sintering apparatus

Recently, spark plasma sintering (SPS) systems have been used as high-temperature compressive creep testing devices. However, SPS systems can have complex temperature distributions within the experimental configuration that might lead to inaccuracies in the creep test results. For example, sample temperature profiles have been found to deviate from the initial temperature distribution as the sample is deformed during the creep test. Therefore, finite element analysis has been carried out on the SPS creep test mold configuration to evaluate the temperature distribution within an electrically conducting sample in three cases. Then, a multi-step thermal-electrical analysis was conducted to confirm the existence of and quantify a temperature deviation present during sample deformation. Thereafter, a systematic parametric investigation was performed to assess the effect of several geometrical parameters on the deviation in the sample temperature during deformation. Based on its results, recommendations for an optimal mold design that minimizes the sample temperature deviation during creep testing are provided. Finally, it is proposed that the thickness of the graphite felt used on the upper part of the die should be modified to further minimize the sample temperature deviation. The results of this study contribute to the overall understanding of the temperature distribution evolution and the effect of current during creep testing with an SPS apparatus and also provide practical geometrical recommendations for the use of SPS creep testing to achieve minimal sample temperature deviation.

Numerical simulation of cryosurgery in biological tissue with developed circulatory system

This paper is devoted to the modeling of the cryogenic impact on biological tissue with a developed circulatory system: large blood vessels, dense distributed small vessels and capillaries penetrating the tissue. The case of cryogenic destruction of a cancer tumor localized near a large artery is considered. The paper presents a direct numerical simulation of the temperature distribution evolution in biological tissue including the calculation of blood flow parameters in a vessel. The mathematical model is based on the Pennes bioheat transfer model with enthalpy modification and the quasi-one-dimensional hemodynamic model of blood flow in arteries, taking into account local changes in the elastic properties of the vessel walls due to strong cooling of adjacent tissue. A numerical algorithm based on explicit finite-volume approximation of the heat transfer model and the hybrid characteristic scheme (after splitting the equation with respect to physical processes) for numerical solution of hyperbolic systems is developed in order to simulate cryosurgery for the tumor near the artery. The main focus of the paper is a numerical study of the circulatory system parameters’ influence on the shape of the final distribution of the cellular necrosis zone. We study the dependence of the necrosis front penetration depth on the perfusion power which characterizes the density of capillary distribution, the peak and background rates of blood flow in the artery, the diameter of the blood vessel and the thickness of its walls.