Local Temperature Distribution Research Articles

Comparison of direct numerical simulation with volume-averaged method on composite phase change materials for thermal energy storage

Melting heat transfer in open-cell metal foams embedded in phase-change materials (PCMS) predicted by the volume-averaged method (VAM) was systematically compared with that calculated using direct numerical simulation (DNS), with particular attention placed upon the contribution of natural convection in the melt region to overall phase change heat transfer. The two-temperature model based on the assumption of local thermal non-equilibrium was employed to account for the large difference of thermal conductivity between metallic ligaments and PCM (paraffin). The Forchheimer extended Darcy model was employed to describe the additional flow resistance induced by metal foam. For the DNS, a geometric model of metal foam based on tetrakaidehedron cells was reconstructed. The DNS results demonstrated significant temperature difference between ligament surface and PCM, thus confirming the feasibility of local thermal non-equilibrium employed in VAM simulations. Relative to the DNS results, the VAM combined with the two-temperature model could satisfactorily predict transient solid-liquid interface evolution and local temperature distribution, although pore-scale features of phase change were lost. The presence of natural convection affected significantly the melting front shape, temperature distribution and full melting. The contribution of natural convection to overall phase change heat transfer should be qualitatively and quantitatively given sufficient consideration from both macroscopic (VAM) and microscopic (DNS) point of views. Besides, practical significance and economic prospective using metal foam in TES unit for WHR system to provide residential heating or hot water is discussed and analyzed.

Influence of ageing on human body blood flow and heat transfer: A detailed computational modelling study.

Ageing plays a fundamental role in arterial blood transport and heat transfer within a human body. The aim of this work is to provide a comprehensive methodology, based on biomechanical considerations, for modelling arterial flow and energy exchange mechanisms in the body accounting for age‐induced changes. The study outlines a framework for age‐related modifications within several interlinked subsystems, which include arterial stiffening, heart contractility variations, tissue volume and property changes, and thermoregulatory system deterioration. Some of the proposed age‐dependent governing equations are directly extrapolated from experimental data sets. The computational framework is demonstrated through numerical experiments, which show the impact of such age‐related changes on arterial blood pressure, local temperature distribution, and global body thermal response. The proposed numerical experiments show that the age‐related changes in arterial convection do not significantly affect the tissue temperature distribution. Results also highlight age‐related effects on the sweating mechanism, which lead to a significant reduction in heat dissipation and a subsequent rise in skin and core temperatures.

Modeling of Temperature Distribution in a Proton-Conductive Ceramic Fuel Cell

Proton-conductive Ceramic Fuel Cells (PCFCs) have potential to achieve higher energy efficiency compared with conventional SOFCs, since protons react with oxygen to generate water at cathode side and the fuel at anode side does not diluted. However, some part of generated electrons reacts with transferred electron holes, and the total numbers of electrons in external circuit decrease. The generation and extinction of holes result in loss of energy and excessive heat generation. Then, the hole current should be carefully examined and controlled. The conductivity of holes strongly depending on local temperature, thickness of electrolyte, partial pressure of oxygen etc.. Therefore, for optimizing the performances of a given PCFCs, coupled analysis considering local temperature, partial pressures, ionic current density is mandatory. Especially, the temperature is one of the strongest factors of the conductivity. Then, the temperature distribution was discussed with results from coupled numerical model considering local temperature distributions, partial pressures, geometries of a cell, and overpotentials. Figure 1

Drying Uniformity Analysis in a Tray Dryer: An Experimental and Simulation Approach

This study aimed to use a Computational Fluid Dynamics (CFD) simulation of a tray dryer to investigate the possible causes of non-uniformity in the absolute final product humidity after the drying process in an empirically constructed tray dryer. In the experimental part, turmeric, which is the rhizome of a perennial herbaceous plant with interesting properties for the cosmetic and food industries, was dried. Pieces of turmeric with identical dimensions were placed in different zones of the dryer and their initial and final humidity values were empirically measured. In the simulations, the momentum and energy equations were solved with ANSYS software (Student v.17.2). The K-epsilon model was used to model the turbulence and the boundary and process conditions were identical to those used in the experiment. Although the steady-state CFD simulations show a homogenous local temperature distribution in the dryer, the local turbulence intensity profiles display dead zones with low turbulence values. Furthermore, these dead zones are consistent with areas where the product exhibits higher humidity. Low local turbulence values can negatively affect the local mass transfer coefficient, which may explain the experimental results of this study.

Performance analysis of industrial PCM heat storage lab prototype

A 140 l lab scale shell-and-tube PCM heat storage was built and tested, and the experimental results were compared to a numerical model. Natural convection in the PCM was found to significantly influence the local temperature distribution in the storage vessel, which could not be predicted well by the model, since the model assumes only conductive heat transport in the PCM. Nevertheless, the overall thermal power output of the storage could be predicted fairly well, if a correction term was used in the model to compensate for the enhanced heat transfer in the molten PCM. Experimentally, a horizontal orientation was found to be beneficial due to increased heat exchange during charging (melting). Comparing the two PCMs used in the testing (RT70 and MgCl2·6H2O), it was found that the RT70 had stable performance while the salt hydrate showed a reduced melting enthalpy which was ascribed to phase separation. For the RT70, a thermal power of 5 kW is obtained during phase change in the charging phase, and 3.5–2 kW during phase change in the discharging phase, while for MgCl2·6H2O this was 3.5 kW and 3–2 kW respectively.

A thermo-frictional tyre model including the effect of flash temperature

ABSTRACTA new tyre model is developed that can predict the influence of both macroscopic and local flash temperature on tyre force generation. The model comprises two heat-transfer solvers. A macroscopic solver calculates the 3D temperature distribution across the tread and sidewall at a resolution of a few millimetres. A separate flash-temperature solver calculates the local hot-spot temperature distribution at the macro-asperity tyre-road contact interface at a resolution of micrometres. The two heat-transfer solvers are coupled with a structural model for the calculation of tyre forces and the sliding speed distribution along the contact patch. The sliding speed distribution feeds into the flash-temperature model and the local coefficient of friction is found as a function of sliding speed, flash temperature, normal pressure, road roughness and the complex modulus of rubber. The proposed tyre model is the first to include the effect of a changing macroscopic temperature distribution on the build-up of the local flash temperature, and to account for road-tread conduction at the macro-asperity contact interface. The model is applicable for identifying the friction envelope and optimum temperature range for tyres on roads with known roughness. This is important in motorsport where knowledge of grip offers a competitive advantage.

Fluctuations of conformational mobility of macromolecules around the glass transition.

The heterogeneity of local dynamics in disordered systems is behind some key features of glass transition. In order to improve our understanding of the molecular dynamics in disordered systems in the vicinity of the glass transition, different parameters have been proposed to quantitatively describe dynamical heterogeneity. In the case of polymers, free volume models relate the macromolecular mobility to the free or accessible volume. The relationship between dynamic heterogeneity and fluctuations of accessible volume seems straightforward. In the present work, the heterogeneity of local dynamics in polymeric systems is analyzed by computer simulation with the bond fluctuation model. The value of the accessible volume around each polymer chain is evaluated from a snapshot or static structure at each system state, resulting in a distribution of accessible volume that reflects system heterogeneity. The relationship between the average value and the standard deviation of free volume distributions at different temperatures fits a master curve for different systems, regardless of the specific inter- and intramolecular interaction potentials that define each material. The dynamic slowdown around the glass transition is accompanied by a clear evolution of the mean value and shape of the accessible free volume distribution. The relative fluctuation of the dynamically accessible volume has been used as a parameter to quantitatively describe heterogeneity. The fluctuation varies with temperature with remarkable differences between the liquid and glassy states of the systems studied, presenting a peak at the glass transition temperature, which can be interpreted as a reflection of the distribution of local glass transition temperatures.

Electrothermally actuated moving contact line dynamics over chemically patterned surfaces with resistive heaters

In this paper, we explore the moving contact line dynamics of two Newtonian immiscible fluids over substrates patterned with two different alternative chemical patches. The bulk fluid motion is actuated using electrothermal kinetics where the thermal field is generated by incorporating resistive heaters on the substrate. The electrothermal forces, which arise from the local gradient in electrical conductivity and permittivity, strongly depend on the local temperature and potential distributions. The thermal field and the potential distribution can be modulated by altering the heater characteristics and electrode patterning. The contact line motion and its intricate physics can be effectively tuned by altering the geometrical parameters of the heaters and electrode arrangement. Further, a comparison is executed between conventional electrothermal and heater-assisted electrothermal processes. The interfacial dynamics of the immiscible binary fluids is greatly affected by the present electrothermal mechanism and shows advantages over the conventional electrothermal process. The results presented here are effective for developing various smart devices involving multiphase flow dynamics within an electrokinetic paradigm.

Conjugate heat transfer in artificial ground freezing using enthalpy-porosity method: Experiments and model validation

Artificial ground freezing (AGF) system is a temporary excavation-support method that is used in underground mines and tunneling projects to improve and stabilize ground structure, and to control groundwater seepage. The conjugate heat transfer between the bayonet freeze pipes and the ground plays a vital role in determining ice wall formation, heat extraction rate and closure time. In this study, a controlled laboratory scale AGF experimental rig is conceived and developed at Mine Multiphysics laboratory, McGill University. It is equipped with more than 80 temperature readings, thorough properties characterization, and an advanced instrumentation system to quantify the conjugate heat transfer process. We also developed a three-dimensional conjugate mathematical and numerical model of the bayonet freeze pipes and porous ground structure using enthalpy-porosity method. The model is further validated against global heat balance and local temperature distributions from our experiments at various operating conditions. Good agreement between model predictions and experimental data was achieved with R2=0.972. The results indicate that higher coolant Reynolds number gives rise to a higher Nusselt number and, thus, higher heat extraction rate which is mirrored by a shorter closure time. Coolant Reynolds number is found to have a higher effect on the heat transfer performance as compared to coolant temperature and grounds initial temperature. Finally, the model is a reliable tool that can be extended and employed for design and optimization of industrial AGF system.

Current and Temperature Distribution Measurement in a Polymer Electrolyte Membrane Water Electrolyzer Cell

The uniform distribution of the current and temperature under the normal operating conditions of the polymer electrolyte membrane water electrolyzer (PEMWE) cell is important to ensure its high efficiency and durability. In this work, a segmented sensor plate S++ is inserted between the flow field plate and current distributor plate at the cathode side of a single PEMWE cell to measure the local current and temperature distribution under different water flow configurations of the anode and cathode side and various current loads of PEMWE. The active area of the single PEMWE cell is 50 cm2. One hundred segments in the segmented sensor plate provide high resolution in the current and temperature distribution measurement. The current and temperature distribution are measured under co-flow and counter-flow of water recirculation between anode and cathode and under different current loads from 10A to 70A. Besides, the polarization curve and electrometrical impedance spectrum are measured under different water flow configurations. Initial results reveal that when operated with co-flow of water re-circulation in anode and cathode, the cell shows better performance. With co-flow configuration, the charge transfer for hydrogen evolution and oxygen evolution reaction is larger compared with counter-flow configuration. The current shows similar distribution pattern under different water flow configuration and different current loads. However, uniformity in current distribution becomes better with lower current. The temperature distribution is not significantly influenced by the current load, while the counter-flow of water re-circulation results in more uniform temperature distribution. Figure 1

Direct and inverse approaches for analysis and optimization of fins under sensible and latent heat load

An inverse methodology is introduced by differential evolution (DE) search algorithm to determine optimal dimensions of a wet fin for a given volume for to maximize heat transfer rate. The DE optimization method is first employed to explore multiple combinations of geometrical fin parameters satisfying a constraint volume. The pertinent rates of heat transfer are computed using a forward analysis based on the differential transform method. In this study for a fixed fin volume, a same value of heat transfer rate in wet fins can be acquired for multiple values of surface areas, and also, even a given surface area can yield multiple values of heat transfer rates. Hence, the local temperature distribution acts as an important factor in selecting a unique set of fin dimensions towards maximizing the rate of heat transfer. The evaluation of sensitivity coefficients reveals that among various geometric parameters, the fin thickness plays an influential role significantly to govern the heat transfer rate.

CONVECTION HEAT TRANSFER IN A CHANNEL OF DIFFERENT CROSS SECTION FILLED WITH POROUS MEDIA

A forced convection heat transfer in ducts (circular, triangular, rectangular) cross sections and (1m) length with hydraulic diameter (0.1m) filled with porous media (glass spheres 12 mm diameter) is investigated experimentally at constant heat flux from the wall (1070W/m²) with Reynolds number range of (12461-2500). Comparison was made between three ducts for local temperature distribution and local Nusselt number). The experimental results showed the effect of Reynolds number and cross section on the temperature profile and local Nusselt number,also empirical correlations for average Nusselt number and Peclet number were obtained for three ducts.

The feasibility of desorption on Zeolite-water pair using dry gas

The increase in temperature, reduction in partial pressure, reduction in concentration, purging with an inert fluid, and displacement with a more strongly adsorbing species are the basic things that occur in the practical method of desorption. In this study, dry gas at constant temperature and pressure was employed as the aid to reduce the partial pressure in the water desorption on the zeolite 13X. The objective of this study is to confirm the feasibility of desorption using dry gas experimentally and numerically. The implication of heat and mass transfers were numerically investigated to find the most influential. The results of numerical simulation agree with the experimental ones for the distribution of local temperature and average water adsorbed in the packed bed.

Factors affecting overall and local temperature distribution in aircraft cabins

Temperature is an important factor that influences the comfort of passengers during journeys in an aircraft. The aim of this paper is to investigate the characteristics of mean temperature inside an aircraft cabin mockup in different fresh air supply ways (ceiling air supply and ceiling and side air supply). The intake air temperature and ambient temperature (1200 ± 50 m3/h, 22 ± 0.2 °C and 25 ± 0.5 °C) are the same. What's more, both the local temperature distribution in front of a real person and that in front of an unheated manikin are tested under the same intake air condition. The results indicate that the equilibrium mean cabin temperature is lower when the ceiling and side air supply ways are used. In the case of intake air temperature changes, a smaller mean temperature fluctuation is observed when the fresh air is supplied from ceiling ducts. However, the temperature around the manikin fluctuates more greatly, and that around the person is relatively steady when the intake air changes. The mean local temperature around the person is higher than that around the manikin. The temperature difference between the right and left sides of the chair shows little difference in both cases.

Heat flux and temperature determination in a cylindrical element with the use of Finite Volume Finite Element Method

This paper presents a method to determine the local heat flux and temperature distribution on a thick cylindrical surface through the solution of an inverse heat conduction problem (IHCP). In particular, the method is developed for cases when traditional measurements cannot be performed due to difficulties in accessing the surface; a common situation in engineering and research practice. In particular, inverse methods are sensitive to measurement errors, for example, those caused by a mispositioned temperature sensor on a solid body. Hence, this paper proposes a method that is insensitive to, and can accurately be used, even in presence of these errors. The proposed method lowers the error in the local heat flux and temperature determination hence making the inverse methods more reliable.The proposed method is based on the finite element-finite volume method (FEMFVM) approach. It is tested using measurement data obtained on a laboratory stand. The measurements are performed using thermocouples installed inside a solid cylindrical wall.The method is tested and compared to other numerical methods, including the finite volume method (FVM) and the finite element method (FEM). Extensive additional calculations are carried out to evaluate the impact of random measurement errors on the accuracy of the proposed method.The calculation results prove that the new method is suitable and useful in the case of complex geometrical shapes and enables accurate determination of parameters such as the heat flux, and the outer surface temperature.

Electronic Griffiths phase and quantum interference in disordered heavy-fermion systems

We investigated the specific heat and electrical resistivity of disordered heavy-fermion systems ${\mathrm{Ce}}_{2}{\mathrm{Co}}_{0.8}{\mathrm{Si}}_{3.2}$ and ${\mathrm{Ce}}_{2}{\mathrm{Co}}_{0.4}{\mathrm{Rh}}_{0.4}{\mathrm{Si}}_{3.2}$. Results show that pronounced non-Fermi-liquid behavior in these Kondo disordered compounds originates from approaching metal-insulator transition rather than from proximity to magnetic instability. Power-law divergence of the local Kondo temperature distribution, $P({T}_{K})$, in the limit of ${T}_{K}\ensuremath{\rightarrow}0$, and clear signature of the quantum interference corrections in the resistivity detected deep below the onset of Kondo coherent state, point to electronic Griffiths phase formation in the studied compounds.

Effect of Thermal Conductivity on Nozzle Guide Vane Internal Surface Temperature Distribution

Abstract Conjugate heat transfer analysis is carried out in a cascade domain for a nozzle guide vane. The nozzle guide vane is internally cooled by jet impingement cooling, and the external surface is cooled by film cooling. A computational study was carried out with three different materials, having conductivity values of 0.0048, 0.2 and 1.1 W/m.K. Distribution of local surface temperature along the leading edge, pressure and suction surface is reported. The leading edge region showed the maximum increase in internal surface temperature as the conductivity increased among the different regions of the vane internal surface. However, the pressure and suction surfaces showed relatively less increase in the surface temperature distribution. In order to validate the computational result, the obtained temperature data were compared with experimentally obtained surface temperature data. The flow phenomena like jet lift-off and self-induced cross-flow affect the local temperature distribution differently in the three materials. For a constant mainstream and coolant flow, the surface temperature gradient is higher for the lower conductivity material, and the gradient decreases as conductivity increases. Hence, a material with higher conductivity is desired in a combined impingement and film cooled nozzle guide vane, to increase the durability of the vane.

Effects of surface roughness on local friction and temperature distributions in a steel-on-steel fretting contact

It has generally been assumed that initial surface roughness has significant influences on local frictional shear stresses and flash temperatures in fretting contacts. However, since these hypotheses are difficult to directly measure, the frictional shear stress and temperature rise distributions in a steel-on-steel fretting contact are investigated by finite element method. The rough contacting surfaces were modelled as fractal surfaces by the Weierstrass-Mandelbrot function. The simulation results show that the frictional shear stress distribution resulted from the rough contact model is discrete, and the local stresses are highly concentrated which result in higher peak temperature rise than that from the smooth contact model. The influences of the plasticity of materials, load and frequency on the temperature rise are also discussed.

Experimental study of natural convection heat transfer from a nonuniformly heated flat plate simulating PV panel

In view of the characteristic of Photovoltaic (PV) conversion, an experimental study has been conducted to investigate the natural convection heat transfer from a flat plate. In order to simulate the real PV cells, three electrical heating circuits were employed to achieve a linear nonuniform heat flux boundary condition. The major parameters, such as the gradient parameter of heat flux k, tilt angle θ and heat flux qw were introduced to analyze their influence on heat transfer ability. Both the local temperature distribution and the overall trend of Nusselt number have been presented. Comparing with the uniform thermal boundary condition, the results show that the local convection heat transfer coefficient is fluctuated at the positions where heat flux has changed. When gradient parameter of heat flux increases, the difference of local convection heat transfer coefficient at the top of the plate between tilt angle θ = 0° and 90° becomes smaller. Moreover, it is observed that the gradient parameter of heat flux has a promotion effect on average convection Nusselt number at larger tilt angle, but the effect becomes complex as tilt angle is smaller. Finally, a correlation combining all significant factors has been put forward to estimate the natural convection heat transfer.

An Experimental Approach to Characterizing the Channel Local Temperature Induced by Self-Heating Effect in FinFET

In this paper, we have developed a methodology of a lateral profiling technique of the channel local temperature in 14 nm FinFET, incurred by the self-heating effect (SHE). As SHE happens, the thermal source generated near the drain will dissipate toward the source side. Since the interaction between RTN trap and channel carriers is very sensitive to the temperature, the channel local temperature can be extracted through this interaction process between random-telegraph-noise (RTN) trap and carriers, and the position of the channel local temperature can be obtained from the RTN trap position. The results show that the highest temperature happens at the drain edge during SHE and pFinFET exhibits a much higher temperature than that of nFinFET. Furthermore, the distribution of channel local temperature can be described by the Fourier’s law of thermal conduction. Averaged channel temperature can be used to extract the thermal resistance, $R_{\mathrm{ th}}$ , which increases rapidly as the channel length is scaled down to 20 nm, further degrading the SHE, in terms of a significant short channel effect. We also found that the incremental channel resistance is proportional to the incremental channel local temperature, whose slope indicates the degree of SHE, and the slope of pFinFET is larger than that of nFinFET. Finally, SHE will cause 10% and 14% degradation of $I_{\mathrm{ d}} V_{\mathrm{ ds}}$ for n- and pFinFET respectively. This can be reasonably explained by the decay of saturation velocity in high temperature. The results obtained based on this methodology will help us on the understanding of the SHE impact on a nano-scaled FinFET device.