Variation Of Temperature Distribution Research Articles

RESIDUAL - STRESS AND TEMPERATURE FIELDS IN SURFACE TESTING: FINITE-ELEMENT ANALYSIS

Numerous advancements have been made to treat part surfacing, however, the presence of surface imperfections resulting from finishing processes has raised concerns about their potential to serve as stress concentrators. To address this concern, the present study utilized the power of the finite element method and cutting-edge software applications. The main aim of the study is to evaluate the stress-strain condition of material surfaces post-finishing, leveraging the comprehensive capabilities offered by these software systems. A significant component of the investigation centered on the influence of non-stationary temperature fields, as monitored by dynamic thermoelements, on the stress-strain dynamics within material surfaces. Visualization techniques were employed to depict the specified field functions, revealing notable variations in temperature distribution. The findings demonstrated that the standard function identified the highest temperature area within the 3-7-4 node segment, while the alternative function pinpointed it within the 4-node segment, indicated by the red area. These outcomes highlight the valuable role of non-stationary temperature fields in balancing the mechanical and physical aspects of the finishing process. This study contributes significant insights into the post-finishing stress-strain state of material surfaces, emphasizing the potential advantages of using modern software systems for in-depth exploration.

Computational Fluid Dynamics Analysis of Temperature Distribution in Solar Distillation Panel with Various Flat Plate Materials

As the world population continues to grow, the demand for clean water is increasing daily, making it a crucial resource to access. However, there are ways to harness abundant resources like solar energy and seawater to produce clean water. The present studies have conducted experimental investigations to convert seawater into freshwater using solar stills, where solar energy is utilized as the primary heat source for evaporation. The temperature distribution inside the solar stills was analyzed using a flat plate made of three different materials: copper, stainless steel, and aluminum. To examine the temperature distribution and performance of the solar stills, researchers employed computational fluid dynamics simulations (Ansys R15.0). The results showed variations in temperature distribution among the three plate materials. Copper flat plates achieved the highest temperature, approximately 44.5 Celsius, followed by aluminum at 43.91 Celsius, while stainless steel exhibited the lowest temperature at around 42.01 Celsius. The average heat flux across the three materials was approximately 581 W/m2. Additionally, observations indicated that the amount of convection occurring in copper flat plates was 121.108 Watts; in aluminum, it was 118.517 Watts; and in stainless steel, it was 105.05 Watts. The radiation energy for stainless steel flat plates was 29.93 W; for copper, 16.14 W; and for aluminum, 13.49 W.

In-situ optimization of lateral film uniformity in PVD system by using Fiber Bragg grating temperature sensors

Fiber Bragg grating (FBG) based temperature sensing method has been employed in this work for measuring the lateral temperature distribution on substrate plane during pulse DC magnetron sputtering deposition for optimization of lateral film uniformity. The evolution of temperature distribution with the variation of important process parameters like pulse width (496–1616 ns), deposition pressure (3.1 × 10−3–1.9 × 10–2 mbar) and sputtering power (25–250 W) have been measured over 40 mm radial distance on glass substrate horizon. To investigate the effect of substrate height on the temperature distribution, the later has been measured at two different substrate heights (60 mm and 90 mm) for varying sputtering power. Finally, the effect of variation in temperature distribution on uniformity of thickness and optical, morphological and structural properties have been investigated by separately depositing two HfO2 thin films at two representative extreme deposition powers (75 W and 200 W). The correlation of film non-uniformity of the above properties with the temperature distribution suggests that FBG based multipoint temperature sensing can be possibly used as an indicative tool for in situ optimization of the lateral film uniformity. In addition, the fast response and workability in plasma environment of FBG sensors enables precise in situ mapping of temperature distribution in sputtering process.

Comparing Influence of Thermal Effects in Experimental Models - Thermotherapy in Medical Rehabilitation

Introduction: The subject of thermometry and impact of thermal effect on the human body is still a topic known and discussed in medical care. One of the basic methods in clinical diagnosis is the measurement of body temperature. In biological tissues, there are two main types of reactions caused by optical radiation: photochemical and thermal. The effects of radiation exposure depend on its properties and physical parameters, including the amount of absorbed dose and the duration of exposure. In the case of thermotherapy as a therapeutic method, the appropriate choice of radiation type and the selection of physical parameters is a necessary condition for obtaining desired, beneficial therapeutic effects. The aim of the study is to investigate the thermal effect of non-ionizing radiation: infrared (IR), ultraviolet (UV) and electromagnetic field (EMF) induced in short-wave diathermy (MD), measured with classical thermometers and a thermal imaging camera. The thermal effect, as a result of overheating with three different factors: IR, UV, MD; and under the same conditions, is studied. The variation in temperature distribution in different phantoms is evaluated in order to delve into the subject of thermal effect regarding each radiation separately and to consider its suitability for medical diagnosis and therapy.Material and methods: The thermal effect study was carried out on two phantoms. The first phantom F1 - a wooden cuboid (27.0 x 7.0 x 7.5cm) with five holes drilled at 5-cm intervals, into which thermometers were inserted (depth 5 cm). The second phantom - F2 was a biological tissue, the lower part of pork ham cut off along with the bone with fat covering and skin. Phantoms F1 and F2 were treated with an infrared heater (P1), a lamp emitting ultraviolet radiation (P2) and short-wave diathermy (P3); C and irradiation - 20 minutes, temperature measurements at intervals of 5 minutes, i.e. 5, 10, 15 and 20 minutes for the examined factors. During the experiment, temperature measurements were periodically made with the IR Thermal Radiometric Camera MobIR M3. For obtaining reliability of the measurements, the whole trial was repeated 10 times. Before the thermograms were made, two-hour intervals were applied between successive measurements, maintaining a constant ambient temperature of 23C.Results: With regard to UV radiation, there was an increase in the average temperature among the thermometers. This was particularly noticeable in the first thermometer with a 1.9% increase (up to 25.110.29C) above the ambient temperature (24.650.34C) after 15 minutes of measurements. After 20 minutes, the average temperature increase in thermometer 1 was 2.2% (up to 25.180.23C). A temperature increase in subsequent thermometers may be related to thermal conductivity and an increase of ambient temperature. In turn, for IR, an average 1.7% (to 25.160.87C) temperature increase of all thermometers was observed at 15 minutes and at 20 minutes, by 2.9% (to 25.481.35C) compared to baseline temperature (24.750.47\C). Comparing the average temperature of thermometer 1 with the ambient temperature (24.750.49C), the highest increase of 12.8% (to 27.930.69C) was noted after 20 minutes of measurements. In diathermy, after 10 minutes, an increase in the average temperature in thermometer 1 was observed by 2.8% (to 25.690.46C) above the ambient temperature. The highest increase in average temperature was recorded in thermometers 1 and 5 in the 20thminute of measurements.Conclusions: All of the applied methods caused temperature increases in the used phantoms. The temperature distribution in the wooden phantom corresponds to that in the biological tissue for the interaction of infrared radiation (IR) and short-wave diathermy (MD), which was confirmed by thermovision. The increase in the internal temperature of the superheated biological structure corresponds to the increase in the distribution of the phantom’s internal temperature.

Numerical Investigation of Thermohydraulic Characteristics in Supercritical CO2 Natural Circulation Loop with Spatially Varying Temperature

Investigation of thermohydraulic characteristics is highly significant for any natural circulation loop (NCL) applications. The physical properties of supercritical fluids are highly sensitive to temperature when they cross pseudo-critical points. In the current study, steady state thermohydraulic characteristics of NCL with a spatially varying temperature distribution on the source along with different orientations of the source and sink are numerically investigated. A three-dimensional rectangular NCL with a uniform diameter and constant length of source and sink is modeled. The temperature of the sink is held constant, while the temperature of the source varies spatially with local maximum and minimum temperatures. The system performance is investigated for four different operating pressures ranging from 8 to 12 MPa. The mass flow rate is observed to increase with increasing operating pressure for all orientations and heat load distribution at the source. The results also indicate that heat transfer degrades when the fluid crosses the pseudo-critical point. It has been noticed that spatially varying temperature distribution has a maximum of 48% heat transfer variation compared to the constant temperature distribution. Furthermore, a source or sink located in the horizontal leg performs better than the vertical leg.

Analysis of Fluid Flow Characteristic with Different Temperature and Different Methods in T-junction Pipe

Thermal fatigue is a material deterioration caused by temperature. Thermal fatigue or commonly referred to as Thermal Fatigue is a potential risk in the piping system, it can occur in the mixing flow at the T-junction. Thermal fatigue depends on the magnitude of the frequency, location, temperature attenuation, and the ratio of the angular flow velocity of the branch pipe to the main pipe. T-joint pipe is the most common piping system structure and is widely used in industrial fields such as petrochemical, marine, nuclear and so on. The research method used is experimentation and simulation using the Ansys student 2021 software with the Realizable method. The results showed that the experimental and simulation results were different but had a graphical tendency. The experimental results showed that the highest temperature was found at a speed of 0.8 m/s at the inlet hot was 35°C, while the simulation results showed a flow velocity of 0.8 m/s at the inlet hot reaches a temperature of 41°C at the right side of the thermocouple 250mm from the lip of the outlet. Flow characteristics with maximum variable temperature distribution, resulting from the ratio of the difference in velocity of cold inlet flow of 0.2 m/s with a diameter of 56mm and hot inlet flow of 0.8 m/s with a pipe diameter of 19mm.

Geometric nonlinear transient analysis of mechanically and thermally shocked functionally graded shell panels

The present paper investigates the von-Karman geometrically nonlinear structural responses of ceramic-metal functionally graded shell panels under the effect of the cases of mechanical and thermal shocks on their ceramic-rich surface. The constituents in the FGM are temperature-dependent and are graded as per the recently proposed four-parameter power laws while their effective properties in the shells are obtained using the Mori-Tanaka homogenization scheme. The transient thermoelastic problem is solved by importing the temporally varying temperature distribution from the nonlinear 1D heat equation as thermal loads into the FE code developed for thin and moderately thick shells based on higher-order shear deformation theory. The nonlinearity in the heat equation is linearized using Picard method in each Crank-Nicholson time-step while the linearization step in the geometric nonlinear problem uses Newton-Raphson method in each Newmark time-step. The new results presented in the manuscript study the effect of geometric nonlinearity on the responses of FG shell panels and the effect of different parameters of four-parameter FG laws. It was observed that including geometric nonlinearity significantly affects the responses of the shell panel structures when the loading direction, either mechanical or thermal, along with the gradation direction is reversed.

Nonlinear vibration analysis of FGM sandwich structure under thermal loadings

The geometrically nonlinear thermal frequencies of the functionally graded (FG) sandwich structures are predicted numerically in the current work considering the variable temperature distributions (linear and nonlinear). For numerical analysis of the FG sandwich structure, an in-house finite element code has been developed in MATLAB using the higher-order shear deformation theory (HSDT) and Green–Lagrange nonlinear strain kinematics. The governing equation of motion for the graded sandwich structure is obtained using Hamilton’s principles, and the direct iterative method is used to predict the nonlinear vibration response of the sandwich structure. The temperature distributions along the thickness of the sandwich structure are considered. Temperature dependent material properties are considered in the present work for computation of frequency responses under thermal environment. The material properties are described in accordance with the power-law distribution. The current models are initially validated with the published results. The influence of various input parameters, i.e. the curvature ratio (CRO), thickness ratio (TRO), aspect ratio (ARO), boundary conditions, and power-law indices on the nonlinear vibration behaviours of FG sandwich structure have been studied.

Modelling the influence of marine ice on the dynamics of an idealised ice shelf

AbstractUnderstanding the dynamic behaviour of ice shelves, specifically the controls on their ability to buttress the flow of ice into the ocean, is critical for predicting future ice-sheet contributions to sea level rise. Many large ice shelves, which are predominantly composed of meteoric ice, have a basal layer of marine ice (formed from accumulated platelets at the ice–ocean interface), comprising up to 40% of their thickness locally. Differences in temperature, chemistry and microstructure between marine and meteoric ice mean the rheological properties of the ice vary throughout the ice shelf. These differences are not explicitly accounted for in ice-sheet modelling applications, and may have an important influence on ice shelf dynamics. We tested the sensitivity of a model of an idealised ice shelf to variations in temperature distribution and flow enhancement, and found that incorporating a realistic thermal profile (where the marine ice layer is isothermal) had an order of magnitude greater effect on ice mass flux and thinning than incorporating the mechanical properties of the marine ice. The presence of marine ice at the ice shelf base has the potential to significantly increase deviatoric stresses at the surface and ice mass flux across the front of an ice shelf.

Understanding the factors affecting the self-heating process of compost piles: Two-dimensional analysis

Industrial compost piles contain large volumes of bulk organic materials. Normally, there are two main heat generation processes—oxidation of cellulosic materials and biological activity within the compost pile. Biological heating occurs at a lower temperature range, but it may `kick-start' the oxidation reaction. Nevertheless, biological heating is desirable and is a key component in composting operations. However, there are cases when the temperature within the compost piles increases beyond the ignition temperature of cellulosic materials which can result in spontaneous ignition. This investigation considers the self-heating process that occurs in a compost pile using a two-dimensional spatially-dependent model incorporating terms that account for self-heating due to both biological and oxidative mechanisms. The variation of temperature distribution within different pile geometries is examined.

Doppler broadening using discrete cosine transform and kernel reconstruction for spatially variable media

Doppler broadening plays key roles in understanding the temperature dependence of materials’ particle reaction rates, which are vital for high fidelity nuclear reactor physics simulations. However, the treatment of spatially continuously variable temperature distribution is far from its maturity to reach the goal of routine high fidelity reactor whole core transport. This article made an attempt to move one step closer to the goal by proposing and verifying a solution package innovative in three aspects. First, we present the DCT-DB Doppler broadening method, efficient in computation and compact for storage, being based on discrete cosine transform by reformulating the Doppler broadening problem as solving a heat equation. The total, elastic, absorption, capture and fission resonance plus background cross sections (if needed) of 512 nuclides from the most recent ENDF/B-VIII.0 data library are studied in the temperature ranging from 200 K to 3,000 K. The maximum relative errors achieve the 0.001 target (in the meaningful range) after validated against NJOY 2016. The new method is computationally efficient, where for the nuclides with maximum intermediate energy grid size of 226 (more than 67 millions), GPU delivers a computing power equivalent to 1 to 2 orders of magnitudes of CPU cores running with the NJOY Doppler broadening method, while generating cross sections at 1 to 2 orders of magnitudes lower errors. The storage of coefficients for all 512 nuclides compresses in an almost numerically lossless way to be 715 MB. Second, we combine the kernel reconstruction method with improved Monte Carlo delta tracking and track length (as track integral) estimators to perform on-the-fly Doppler broadening in media with spatially continuously variable properties, where the algorithm takes into consideration all of the temperature variance, the coolant density variance and the atomic density variance from such as depletion together. The on-the-fly Doppler broadening runtime data is 3.69 GB, attainable by taking as lower as minutes with the DCT-DB processing code on GPU. Numerical simulations of homogeneous pincell problems, homogeneous 3x3 assemblies mini reactor problems, and pincell problems with variable temperature distributions are validated against the ENDF point-wise cross sections, where the new method costs only 3 to 5 times more computational time than reference problems with uniform temperature valued at the single ENDF point-wise cross section table used, which is competitive with existing methods. The new method's competitiveness over windowed multipole for spatially variable media is justified for on-the-fly Doppler broadening for problems with depleted fuel on GPU devices as well. The widely adopted approach of using average temperatures in fuel, gap, clad and moderator of a pincell could underestimate fission power by 0.04% and k-effective by 45 pcm. In fair comparisons, Apple M1 Pro CPU is 3–6 times more energy efficient than mainstream AMD64 CPUs. The new method is also in favor of current and coming exascale HPC systems with large memory bandwidth. Third, we found a closed form of relationship between multipole parameters and DCT coefficients, which brings a broader picture to existing Doppler broadening methods.

Unsupervised deep learning based approach to temperature monitoring in focused ultrasound treatment

Temperature monitoring in ultrasound (US) imaging is important for various medical treatments, such as high-intensity focused US (HIFU) therapy or hyperthermia. In this work, we present a deep learning based approach to temperature monitoring based on radio-frequency (RF) US data. We used Siamese neural networks in an unsupervised way to spatially compare RF data collected at different time points of the heating process. The Siamese model consisted of two identical networks initially trained on a large set of simulated RF data to assess tissue backscattering properties. To illustrate our approach, we experimented with a tissue-mimicking phantom and an ex-vivo tissue sample, which were both heated with a HIFU transducer. During the experiments, we collected RF data with a regular US scanner. To determine spatiotemporal variations in temperature distribution within the samples, we extracted small 2D patches of RF data and compared them with the Siamese network. Our method achieved good performance in determining the spatiotemporal distribution of temperature during heating. Compared with the temperature monitoring based on the change in radio-frequency signal backscattered energy parameter, our method provided more smooth spatial parametric maps and did not generate ripple artifacts. The proposed approach, when fully developed, might be used for US based temperature monitoring of tissues.

Simulation of Variable Magnetic Field Effect on Natural Convection Heat Transfer of Fe3O4/Graphite Slurry based on Experimental Properties of Slurries

Natural convective heat transfer of Fe3O4/graphite slurry in a square cavity is numerically examined. The slurry is assumed to be a non-Newtonian ferrofluid under a variable external magnetic field. The left and right walls of the cavity are assumed to be at a relatively low temperature (Tc), while the horizontal walls are thermally insulated. A heat source with a variable temperature distribution is located at the bottom of the enclosure. The non-Newtonian behavior of the graphite slurry (a mixture of ethylene glycol and graphite powder) has been modelled using experimental results. The control volume method and the SIMPLE algorithm were used to discretize and solve the governing equations considering the Ferro-hydrodynamics (FHD), the Magnetohydrodynamics (MHD) and the non-Newtonian fluid behavior. The heat transfer and fluid flow properties are determined for different locations of the magnetic field source, and different values of the magnetic number (Kelvin force), and the Hartmann number (Lorentz force). The results show that when the magnetic field source is located below the enclosure and near the heat source, the vortices are strengthened resulting in an increased heat transfer. The heat transfer rate is affected by FHD and MHD. When the magnetic field source is located at the corner points, the heat transfer rate is not significantly affected by the magnetic and Hartmann numbers. However, once the magnetic field source is located near the central point of the lower wall of the enclosure, the heat transfer rate is influenced by the increase of the magnetic number.

Unsteady analysis of the cold energy storage heat exchanger in a liquid air energy storage system

Liquid air energy storage (LAES) is promising in the large scale energy storage field. The heat exchanger (Hex) in a LAES system using liquid phase working mediums for cold energy storage (CES) works discontinuously for the intermittent characteristic of the LAES. Variable temperature distribution exists in the Hex for CES (Hex-CES) in the intermittent process, and degrades the performance of the CES unit. In this paper, a computational model is constructed for the unsteady process in the Hex-CES of a 100 kW LAES system using liquid phase working mediums for CES to study the unsteady effect. The established steady temperature gradient is decreased gradually in the static process during which the LAES stops working and basically turns to zero gradient 12 h later. In the next operation cycle, it takes 34.8 min to reestablish the steady temperature gradient in the Hex-CES. Two methods to reduce the unsteady effect are proposed, the influence of key parameters on weakening the unsteady effect is investigated, and the optimal operation parameters in the static process are obtained. The results obtained in this paper are expected to provide the basis for the application of CES using liquid phase mediums and enhance the performance of LAES.

Design of microwave hot-airflow vibrating drying equipment for initial drying and enzymatic inactivation of fresh fruits and vegetables

We developed and optimized microwave hot-airflow vibrating drying (MHAVD) equipment to improve drying efficiency and control the quality of dried agricultural products such as fruits and vegetables. Through three-dimensional modeling and finite element analysis, we simulated and demonstrated microwave source distribution modes and field intensity uniformity. We proposed two flow diversion modes, parallel deflection mode and V-shaped deflection mode, for the hot air distribution system, and we used finite element modeling to analyze them and determine the most optimal modes for use with the dryer. The microwave field strength that achieved the greatest uniformity on the surface of the material tray was used with feeding ports at X = 60 mm, Y = 80 mm, and H = 70 mm. The V-shaped deflector reduced the difference in the wind speeds on the material from 1.1 m/s to 0.36 m/s, thereby significantly increasing the uniformity, although no significant improvement in the local uniformity was noted when the parallel deflector was used. We used fresh balsam pear slices as a representative raw material to measure temperature distribution variations, moisture states, and distribution variations, and we also measured the polyphenol oxidase (PPO) enzymatic activity of the material during the primary drying with MHAVD. The results showed that balsam pear slices could be uniformly and efficiently dried in an environment below 70 °C, and the dry basis moisture content can be reduced from 15.82 to 12.35 in 12 minutes. The NMR/MRI results indicate that mainly free water in the balsam pear slices was decreased in the MHAVD process, with good moisture reduction uniformity. The PPO enzymatic activity decreased from 15.92 U/g to 0 U/g after drying. MHAVD provides a feasible method of enzyme killing, which also has the function of pre-drying for fruits and vegetables. Highlights A microwave hot-airflow vibrating drying experimental apparatus was designed Hot-air and vibrated can improve the uniformity of microwave drying There is a perfect correlation between moisture content and signal amplitude Free water can transform into immobilized water and combined water Microwave pretreatment can inactivate PPO enzyme

Numerical solution for a porous fin thermal performance problem by application of Sinc collocation method

Heat transfer can be enhanced in various equipment by utilizing fins that have pores in their media. Efforts have been made to solve the porous fins problem by numerical, semianalytical, and analytical methods. In this paper, after the extraction of equations and the expression of boundary conditions, the Sinc collocation method is employed for problem solving the first time. By using the properties of the Sinc collocation method, the nonlinear problem is discritized into a nonlinear system of equations. The results support the accuracy and speed of the solution. The effects of effective physical parameters such as fins porosity, thermal conductivity of fin, Raley's number, and Darcy parameter have been considered in solving the problem. Also, the variations in temperature distribution, efficiency, and performance of fins are investigated. Therefore, changes in the parameters of the solving method indicate the convergence of the problem in the domain of many issues. In general, the results show that the proposed method can be considered as a powerful method for solving different types of fines.

Effect of Linearly Varying Heating Inside a Square Cavity under Natural Convection

Telecommunication devices such as ADSL Modems or Wi-Fi routers are being widely used around the globe. Thermal management of such equipments are of critical importance as the increased power consumptions caused by technological upgrades results in increased heat generation within these systems. The heat transfer process inside such sealed and passively cooled equipments can be simplified as natural convection inside enclosures. Studying actual conditions inside electronic enclosure are necessary for their effective thermal management. This study aims at investigating the effect of non-isothermal heating inside such enclosures with linearly varying temperature distribution on free convection inside square enclosure. The issue of free convection of air interior of a square chamber with linearly varying temperature distributions on the left partition is studied numerically. The effect of change of Rayleigh number, temperature distributions, on flow and temperature field and rate of transfer of heat are analysed. Rayleigh number is chosen to vary in between 103 and 106. Four different cases of linearly varying temperature distributions are considered. The outcomes are presented as stream line plot, isotherm contour and average Nusselt number. The outcomes depicted that case of linearly increasing temperature along the height gives higher Nusselt number than other cases.

Temperature-Dependent Electromagnetic Design of Inhomogeneous Planar Layer Variable Thickness Radome for Power Transmission Enhancement

A novel inhomogeneous planar layer variable thickness radome (VTR) is presented in this letter. To improve the performance of the radome, the effect of thermal coefficient of expansion on radome wall thickness is incorporated in the design stage. The proposed radome exhibits superior power transmission compared to the conventional monolithic constant thickness radome and the monolithic VTR. A Geometrical optics based 3-D ray tracing with aperture integration technique is used for the performance prediction of the radome. The designed radome exhibits an insertion loss as low as 0.006 dB and a maximum boresight error of 2.4 mrad. A time lapse study on the radome performance due to varying temperature distribution as the radome mounted vehicle attains hypersonic velocity is also presented. Superior performance at hypersonic environment makes this radome an attractive choice for airborne applications.

Geometric optimization of segmented thermoelectric generators for waste heat recovery systems using genetic algorithm

Recently, kinds of thermoelectric (TE) materials have been applied in the waste heat recovery system. This paper further presents a geometric optimization for segmented thermoelectric generator (STEG) modules to improve the energy harvesting performance. Sixteen length ratios of two TE materials are optimized to achieve the maximum output power. In the optimization procedure, the genetic algorithm is employed to find the optimal solution, while thermal, flow, and electric fields are fully coupled and solved by the finite element method. The optimization results indicate that the maximum output power of optimal STEGs is 24.39% (parallel-flow) and 24.33% (counter-flow) higher than that of non-segmented TEGs. Besides, the STEG under parallel-flow has better electrical performances due to the increase of temperature difference and the variation of temperature distribution. The interface temperatures are just fluctuating around the turning point of ZT values, despite of the significant variations of end temperatures. The performances of each TE legs are also investigated, which shows that some TE materials have little contribution to the whole TE module. Subsequently, hybrid TEG modules are proposed to reduce the manufacturing difficulty, which are further ranked by a multiple criteria decision-making technique. Compared with optimal STEGs, two best compromise solutions decrease the maximum output power only about 1.5%, but reduce the proportion of segmented TE legs by 56.25% and 50%, respectively.

3D numerical investigation of the heat and flow transfer through cold protective clothing based on CFD

A three-dimensional (3D) model solving the heat and flow transfer through cold protective clothing under various ambient conditions was developed based on the torso thermal manikin in the present work. The conjugate problem of conduction, convection and radiation was simultaneously solved by the proposed model. The air in the computation domain was treated as a uniform turbulent flow, but it was considered as a slow air movement when the air was in the clothing modeled as a homogenous porous structure. Ideal contact between skin and clothing ensemble was assumed to eliminate the effect caused by the air layer enclosed at the gap. Validation study was performed by comparing the numerical results with experimental results obtained from the torso thermal manikin in a climate chamber. A good agreement was found with the maximum difference in heat flux and thermal resistance below 7.4% and 7.8%, respectively. The dependence of various parameters such as ambient temperature, air velocity and clothing thickness on clothing thermal insulation was further clarified by extensive parametric study. The local variations in temperature distribution, radiative and convective heat flux along the clothing outer surface were found to be significant, indicating that a space-average method would withhold the variation between different local positions. The global relative contribution of conduction, convection and radiation under different temperature and windy conditions were also evaluated. Besides, the lowest comfort temperature at activity level 2 met and 4 met was investigated for clothing with different thickness, and the effect exerted from wind was pronounced.