Heat Dissipation Process Research Articles

Influence of varying the Ethylene-Vinyl Acetate layer thicknesses on the performance of a polycrystalline silicon solar cell integrated with a microchannel heat sink

Modifying the polycrystalline silicon solar cell by reducing the thermal resistance of the ethylene–vinyl acetate (EVA) layer is essential to enhance the thermal management process. This modification will improve the heat dissipation process from the silicon wafer especially at a higher solar concentration ratio (CR) and in return enhance the solar cell performance and output power. Thus, a modified design of a solar cell integrated with a microchannel heat sink is developed. In this new design, variations of the Ethylene-Vinyl Acetate (EVA) upper- and lower-layer thickness along with the interval width between the two consecutive silicon layers are investigated. To determine the effect of varying the design parameters on the cell temperature at various solar concentration ratios and coolant mass rates, a three-dimensional comprehensive model for the solar cell integrated with a heat sink is developed. The model is simulated and validated with numerical results and measurements. Results indicate that reducing the EVA lower layer thickness has a remarkable effect on the solar cell temperature. At a solar concentration ratio of 20, varying the EVA lower layer thickness from 1.0 mm to 0.2 mm results in decreasing the maximum cell temperature from 102.3 °C to 69.3 °C. With further increase of the concentration ratio up to 30, the maximum cell temperature reduces from 138.3 °C to 87.4 °C. It is found that at a coolant rate of 2000 gm/min, and a concentration ratio of 20, maximum temperature in the modified and conventional solar cell with a lower EVA thickness of 0.2 mm and 0.5 mm, reaches 69.3 °C and 81.5 °C, respectively. Furthermore, the conventional cell efficiency is about 8.90%, while the modified one achieves 9.6%. At a CR = 30, the maximum temperature of the modified cell is 87.4 °C, while it is beyond the permissible temperature for the conventional cell. However, the solar cell temperature was not affected by varying the EVA upper layer and the interval width between the silicon layers. The finding of the current results provides another direction for researchers to utilize a higher concentration ratio with polycrystalline silicon solar cells.

Analysis of Recovery Time of HTS Tapes With Electrical Insulation Layers for Superconducting Fault Current Limiters Under Load Conditions

The implementation of superconducting fault current limiters (SFCL) in the electrical power system requires the coordination of its parameters with the installed power system protection (PSP), in particular when using automatic reclosing (AR). The crucial parameter for AR is the recovery time of the SFCL, understood as the SFCL return time to the superconducting state after its operation. This time will depend mainly on the efficiency of the cooling system and the heat dissipation processes in the electrical insulation system. This article presents the results of experimental research on the return time to the superconducting state of superconducting tapes with layers of electrical insulation of various thicknesses. The tests were carried out in conditions in which the density of energy generated during the surge current flow correspond to the operating conditions of superconducting material in SFCL. Also, the transfer of this energy to liquid nitrogen corresponds to phenomena occurring in SFCL. The recovery time of several types of high temperature superconducting tapes in the zero current state and recovery under load were determined. The range of the load current at which it is possible return to the superconducting state was determined for tapes with and without electrical insulation. It has been shown that the analysis of these processes must take into account the strong dependence between the thermal energy transfer from the sample surface to liquid nitrogen and the type of nitrogen evaporation process on the surface of the sample. The presented research results are of particular importance for the functionality of SFCL and its cooperation with the PSP.

A Methodology for Predicting Temperature Distribution inside Concrete Pavement under A Pool Fire

ABSTRACT Understanding the internal temperature distribution of concrete is critical to further determine the variation characteristics of its thermo-mechanical properties. Due to the complexity of heat transfer during the combustion of pool fires, the internal temperature distribution of concrete under its influence is much different from that under uniform high-temperature field. In this work, a systematic mathematical model was proposed to predict the temperature distribution inside concrete pavement under the action of pool fire, and a series of corresponding experiments were conducted to validate the prediction results. Heat transfer process during pool fire combustion and heat dissipation process of high-temperature concrete after pool fire extinction were both analyzed in detail. A comprehensive heat transfer coefficient was used to predict the temperature distribution in combustible liquid. Temperature control discretization equations inside the concrete in both the processes of pool fire combustion and extinction were derived. The established mathematical model was implemented by MATLAB programming. Finally, corresponding experiments were conducted to verify the model prediction results, and the results showed that the two were in good agreement. The results obtained in this work can facilitate a better understanding of the design and maintenance of concrete pavement.

Marine NMEA 2000 Smart Sensors for Ship Batteries Supervision and Predictive Fault Diagnosis.

In this paper, an application for the management, supervision and failure forecast of a ship’s energy storage system is developed through a National Marine Electronics Association (NMEA) 2000 smart sensor network. Here, the NMEA 2000 network sensor devices for the measurement and supervision of the parameters inherent to energy storage and energy supply are reviewed. The importance of energy storage systems in ships, the causes and models of battery aging, types of failures, and predictive diagnosis techniques for valve-regulated lead-acid (VRLA) batteries used for assisted and safe navigation are discussed. In ships, battery banks are installed in chambers that normally do not have temperature regulation and therefore are significantly conditioned by the outside temperature. A specific method based on the analysis of the time-series data of random and seasonal factors is proposed for the comparative trend analyses of both the battery internal temperature and the battery installation chamber temperature. The objective is to apply predictive fault diagnosis to detect any undesirable increase in battery temperature using prior indicators of heat dissipation process failure—to avoid the development of the most frequent and dangerous failure modes of VRLA batteries such as dry out and thermal runaway. It is concluded that these failure modes can be conveniently diagnosed by easily recognized patterns, obtained by performing comparative trend analyses to the variables measured onboard by NMEA sensors.

The influence of infiltration angle on the identification effect of seepage with linear heat source method

The linear heat source (LHS) method is an effective way to realize large-range and distributed monitoring of seepage. Research on this method, however, fails to consider the influence of seepage direction. Based on the seepage mechanics and heat transfer theory, this article sets up a mathematical model to describe the heat dissipation process of LHS in porous media. On such basis, the finite element method was adopted to study the influence of seepage velocity and seepage direction on the law of heat dissipation of LHS. The results showed that the heat dissipation process of LHS meet well with Newton’s Law of Cooling. Its cooling velocity was in positive correlation with the seepage velocity and infiltration angle. Hence, when the seepage direction is unknown, adopting this method for seepage identification is uncertain, may leads to misjudgment. At the end of the paper, the authors discuss a solution to this problem.

Flexible Films for Smart Thermal Management: Influence of Structure Construction of a Two-Dimensional Graphene Network on Active Heat Dissipation Response Behavior.

In recent years, the development and wide application of micro-electronic technology brings forward high demands for active thermal management systems. However, such systems are not only costly, but also usually tethered, and need constant power to operate. To avoid such a limitation, smart thermal management systems have been developed to achieve active thermal management. Here, inspired by the temperature control principle of a butterfly, a shape memory polymer was used to endow the thermally conductive graphene-polymer hybrid film with intelligence. As the device temperature reaches 60 °C, the bud-shaped hybrid film started to bloom, which is a visually active heat dissipation process. As a result, this active process promoted the thermal management capacity of the hybrid film and increased the temperature-raising time of the light-emitting diode. Through the construction of a bilayer structure, the transmission channel for phonon transfer was optimized, which lead the hybrid film to attain a remarkable thermal conductivity of 21.83 W·m-1·K-1 with 30 wt % graphene. This graphene-polymer hybrid film shows potential application in the smart thermal management field.

The transpiration characteristics and heat dissipation analysis of natural leaves grown in different climatic environments

Because vegetation is one of the typical backgrounds on land, it is necessary to investigate the transpiration characteristics and heat dissipation processes of the leaves grown in different natural environments to optimize the thermal infrared camouflage performance of the bionic materials for countering the thermal infrared detection. Considering ambient temperature and relative air humidity as the dominant environmental factors, daily transpiration rates of various kinds of leaves grown in Wuxi (summer and winter, moderate relative air humidity) and Xishuangbanna (summer, high relative air humidity) were measured respectively, and a thermophysical model was established to investigate the heat dissipation processes of the leaves. Results show that the average daily transpiration rates of the leaves are 1.42, 0.42 and 0.92 kg/m2∙day in Wuxi summer, Wuxi winter and Xishuangbanna summer respectively, indicating that the daily transpiration rates vary significantly with different environments. In Wuxi summer and winter, the daily transpirative heat flow accounts for approximately 55.8% and 24.3% of the total heat dissipation of the Cinnamomum camphora leaves respectively, revealing the significant effect of the transpirative heat transfer on the temperature of the leaves grown in the environment of high ambient temperature and the weakened effect in the environment of low ambient temperature. In Xishuangbanna summer, the daily transpirative heat flow accounts for approximately 37.3% of the total heat dissipation of the Ailanthus leaf, which is significantly lower than that in Wuxi summer, indicating that relative air humidity also dominates the effect of transpirative heat transfer on the temperature of the leaves.

The effect of fatigue crack rate on the heat dissipation in metals under mixed-mode loading

The monitoring of a heat dissipation process can give an important information about kinetics of deformation process and current crack propagation rate. The work is devoted to the theoretical and experimental study of the problem. The estimation of the heat sources during the mechanical test was carried out based on infrared temperature measurements combined with an additional system for direct monitoring of a heat flow. To propose the phenomenological description of evolution of plastic work (energy dissipation) at the crack tip under arbitrary loading conditions we used a relations introduced by Dixon in 1965. To illustrate the abilities of the proposed approximation we compare the derived equation with the results of fatigue crack propagation test in flat titanium Grade 2 specimens. The theoretical and experimental results give a good quantitative agreement.

Photosynthesis in Arabidopsis Is Unaffected by the Function of the Vacuolar K+ Channel TPK3.

Photosynthesis is limited by the slow relaxation of nonphotochemical quenching, which primarily dissipates excess absorbed light energy as heat. Because the heat dissipation process is proportional to light-driven thylakoid lumen acidification, manipulating thylakoid ion and proton flux via transport proteins could improve photosynthesis. However, an important aspect of the current understanding of the thylakoid ion transportome is inaccurate. Using fluorescent protein fusions, we show that the Arabidopsis (Arabidopsis thaliana) two-pore K+ channel TPK3, which had been reported to mediate thylakoid K+ flux, localizes to the tonoplast, not the thylakoid. The localization of TPK3 outside of the thylakoids is further supported by the absence of TPK3 in isolated thylakoids as well as the inability of isolated chloroplasts to import TPK3 protein. In line with the subcellular localization of TPK3 in the vacuole, we observed that photosynthesis in the Arabidopsis null mutant tpk3-1, which carries a transfer DNA insertion in the first exon, remains unaffected. To gain a comprehensive understanding of how thylakoid ion flux impacts photosynthetic efficiency under dynamic growth light regimes, we performed long-term photosynthesis imaging of established and newly isolated transthylakoid K+- and Cl--flux mutants. Our results underpin the importance of the thylakoid ion transport proteins potassium cation efflux antiporter KEA3 and voltage-dependent chloride channel VCCN1 and suggest that the activity of yet unknown K+ channel(s), but not TPK3, is critical for optimal photosynthesis in dynamic light environments.

Semi-analytical flash temperature model for thermoplastic polymer spur gears with consideration of linear thermo-mechanical material characteristics

AbstractThe temperature increase that occurs during running of a polymer gear pair can be divided into two components: the nominal and flash temperatures. The latter denotes the short-term temperature increase that takes place during a gear meshing cycle. A thorough analysis of the flash temperature yields an insight into the heat dissipation process, which also determines the nominal temperature increase. We focus here on the flash component using numerical and analytical computation tools, with which we can obtain realistic predictions of the temperature increase during a gear meshing cycle. The analysis is performed using a decoupled procedure that involves a mechanical finite element analysis, followed by a semi-analytical temperature evaluation method based on the computed mechanical response of the system. With it, we obtain an improved flash temperature model that offers an accurate representation of the real life thermo-mechanical processes taking place at the gear teeth contact interfaces.Highlights Sliding friction during polymer gear meshing generates dominant part of heat losses. The developed flash temperature model is based on numerical and analytical tools. Meshing kinematics influence considerably the frictional losses and temperature rise. Flash temperature model applicable to any type of spur gear geometry. The model provides necessary groundwork for long term nominal temperature analysis.

Features of the estimation of the intensity of heat exchange in self-ventilated disk-shoe brakes of vehicles

Analysis of the energy load of a cargo vehicle self-ventilated disk-brake system, which significantly affects the operational parameters of its friction pairs is made. Plastic deformation of the disk friction belts can be observed under cyclic loading of the brake friction pairs, and the deformation process is aggravated by the fact that the yield strength of the material drops in their local zones. Due to plastic friction during compression of the disk friction belts heated zones, therefore they bulge, further leading to the formation of microcracks.The research is based on the fact that during the vehicle braking moment, the intensity of heat transfer from the outer and inner, matte and polished surfaces of the self-ventilating braking disk by convection is much lower than the intensity of heat dissipation processes in the right and left body of the half-disks under heat conduction. This is explained by the fact that the rate of heating is ten times higher than the rate of forced air cooling.As a result of the research, the regularities of the thermal conductivity change in the half-disk side surface, the inverse of which is the thermal resistance of the half-disk were revealed. The design and heat transfer processes in the self-ventilated disk-shoe brake of the vehicle are considered. The intensity of heat transfer of a vehicle's self-ventilated brake disk is investigated in relation to speed and with account of heat transfer coefficients from external and internal surfaces of the disk. The influence on the intensity of the heat transfer process on the surface areas through the disk thickness is established

Optimum Methods of Thermal-Fluid Numerical Simulation for Switchgear

Thermal-fluid coupled calculation is an effective way to simulate the temperature rise and heat dissipation process of switchgear. But there are still problems such as huge calculation and low accuracy need to be solved. This paper discusses the optimization methods of the thermal-fluid coupled field for the switchgear from grid controlling, boundary conditions, and heat source calculation. First, the mesh adaption method based on posterior error estimation is proposed to achieve efficient mesh refinement with less redundancy. The final mesh size is only 32.3% of that obtained with the traditional global-refining method. Then, an external flow model is built to obtain the convective heat transfer coefficient of the enclosure, replacing the process of artificial choosing. The results show that the convective heat transfer coefficient at the enclosure under natural convection is 0.4 W/(m 2 ·°C) ~1.4 W/(m 2 ·°C). Afterwards the eddy current field is used to solve the heat generation in the switchgear. The heat sources are coupled to the thermal-fluid calculation so that the influence of current non-uniformity, contact heat, and eddy loss is considered. At last, the methods are applied to the steady-state temperature rise simulation of KYN28A-12kV/630A switchgear and the results are compared with the test data. The maximum relative error between simulation and experimental results is 3.43%, which proves the validity of the mentioned methods.

Thermal and mechanical properties of micro Cu doped Sn58Bi solder paste for attaching LED lamps

The junction temperature is a key factor in determining the reliability of light emitting diode (LED) package, which can be lowered using high thermal conductive soldering material. The effects of Cu micro particles on the thermal and mechanical properties as well as microstructures of Sn58Bi solder paste were investigated in this paper. The results indicated that the thermal conductivity of Sn58Bi-5 wt% Cu solder layer is 26.60 W/(m·K), which is much higher than the Sn58Bi solder layer of 18.89 W/(m·K). According to the thermal simulation analysis, the temperature on chip is the highest area inside the whole LED package. The maximum junction temperature of soldered LED package decreases with 5 wt% Cu particles addition and then increases. The maximum junction temperature of LED package increases as the input power increases from 1 to 3 W. The lowest junction temperature is obtained in Sn58Bi-5 wt% Cu soldered package. There is no significant degradation in shear strength of 5 wt% Cu micro particles doped Sn58Bi solder joint when comparing with the pure Sn58Bi soldered ones. The shear strength of solder joint decreases approximately 50% when the content of added Cu micro particles increases from 5 to 15 wt%, and weak bonding presents in 20 wt% Cu doped solder joint. Comparing with the Sn58Bi solder, the solder layer with 5 wt% Cu micro particles exhibited more uniform microstructure and the number of coarse Bi-rich phases is reduced. The Cu micro particles facilitate the heat dissipation process of Sn58Bi solder layer by adding highly conductive cores in the layer. The 5 wt% Cu micro particles doped Sn58Bi solder exhibits remarkable thermal and mechanical performance in attaching LED packages.

Modeling and Simulation of Dynamic Heat Dissipation Based on S-Function under MATLAB Simulink Environment

This paper discusses a model implementation of dynamic heat dissipation simulation based on S-Function under MATLAB Simulink Environment. The subtle changes in heat dissipation process can be simulated through this model and the model can be easily used to build thermal control system. A multiloop thermal system, including two payloads and fluid loop system, has been built to test this model. From the simulation results we can analyze the efficiency of heat dissipation in different payload distributions and different flow rate allocations. This model is possibly used for high accuracy temperature control and complex multiloop thermal system analysis.

Numerical investigation of heat transfer from multi-bulges pins

This paper presents an attempt to improve the thermal performance of the absorber plate in photovoltaic solar systems by introducing novel configurations of pin fins. The cross-sectional area of these pins varies along the pin length producing small bulges with regular geometric shapes. The objective of changing the pin profile is to increase the heat transfer area and to produce a better mixing effect in the passages of the cooling fluid. Three shapes of bulges (diamond, cylinder and circular rings) have been employed to produce three forms of multi-bulges pin. The novel pins have been investigated under the influence of steady laminar forced convection flow. The effect of fin design on the absorber heat dissipation behavior has been studied and reported. The numerical model has been carried out by using CFD Fluent software. Finite volume technique is used and SIMPLE algorithm is applied. The thermal performance is presented in terms of surface temperatures of fin and plate, thermal efficiency of the absorber and average Nusselt number. In comparison with conventional pin fins, the results showed that the proposed pin fins indicate a good insight in the heat dissipation process and more effective in thermal performance.

Optoelectronic performance enhancement in pulsed laser deposited gallium-doped zinc oxide (GZO) films after UV laser crystallization

This study investigates the process–microstructure–property relationship during a UV laser crystallization of a transparent conductive layer—gallium doped zinc oxide (GZO) films after pulsed laser deposition (PLD). UV laser induced crystallization technique is able to apply ultra-fast post-treatment to modify GZO films with better structural and optoelectronics properties, suggesting a potential for large-scale manufacturing. A physical simulation model coupled laser–matter interaction and heat-transfer was utilized to study pulse laser heating and heat dissipation process. The laser crystallized GZO film exhibits low resistivity of ~ 3.2 × 10−4 Ω cm, high-Hall mobility of 22 cm2/V s, and low sheet resistance of 22 Ω/sq. High-transmittance (T) over 90% at 550 nm is obtained (with glass substrate). The optoelectronic performance improved mainly attributes to grain boundary modification in the polycrystalline film, e.g., decrease of grain boundary density and passivation of electron trap at grain boundaries.

A lumped thermal model of lithium-ion battery cells considering radiative heat transfer

Thermal management plays a critical role in battery operations to improve safety and prolong battery life, especially in high power applications such as electric vehicles. A lumped parameter (LP) battery thermal model (BTM) is usually preferred for real-time thermal management due to its simple structure and ease of implementation. Considering the time-varying model parameters (e.g., the varying convective heat dissipation coefficient under different cooling conditions), an online parameter estimation scheme is needed to improve modelling accuracy. In this paper, a new formulation of adaptive LP BTM is proposed. Unlike the conventional LP BTMs that only consider convection heat transfer, the radiative heat transfer is also considered in the proposed model to better approximate the physical heat dissipation process, which leads to an improved modelling accuracy. On the other hand, the radiative heat transfer introduces nonlinearity to the BTM and poses challenge to online parameter estimation. To tackle this problem, the simplified refined instrumental variable approach is proposed for real-time parameter estimation by reformulating the nonlinear model equations into a linear-in-the-parameter manner. Finally, test data are collected using a Li ion battery. The experimental results have verified the accuracy of the proposed BTM and the effectiveness of the proposed online parameter estimation algorithm.

Evaluation of the quality of layers applied by LDT laser metal deposition

The article presents the results of a study of C45 carbon steel hardfacing using laser metal deposition with Stellit Co-21 powder. The microstructure of the cross-section of samples prepared with different scanning speed and the amount of used powder at constant laser power was observed. Analyzing the cross-sectional areas of the samples, it was found that, at specific production parameters, cracks occur in weld overlay, which should be associated with the amount of heat supplied and discharged, especially at the unheated basis.This may be confirmed by the presence of deposits of weakly branched dendrites in the microstructure, which should be related to the directional heat dissipation process and rapid directional crystallization. It is possible to regulate these phenomena by selecting appropriate processing parameters. The microstructure analysis of cross-sectional areas of samples after hardfacing using LDT technique indicates good metallurgical quality of the deposit with a small heat affected zone of about 660÷760m. The microhardness measurements on the sample cross-sections indicated a wide micohardness distribution ranging from 510HV1 in the weld overlay, about 410HV1 in the heat affected zone, to 270HV1 in the C45 steel base.

Process development of bottle gourd sweetmeat by microwave heating: Changes in rheological, textural, sensory and morphological parameters

Abstract The effect of replacement of khoa-sugar mixture in bottle gourd sweetmeat (BGSM) with varying proportions of bottle gourd pomace (BGP) was studied. Rheology of preliminary mix, used for preparation of bottle gourd sweetmeat, was studied in order to predict the behaviour of final product under different processing conditions. Results showed that increase in temperature beyond 30 °C caused increase in elasticity (G′) of mix whereas decrease in temperature showed increase in viscosity (G″). Microwave heat dissipation process revealed that samples microwaved at low power (700 W) caused increase in temperature from 80 °C in 1 min to 112 °C in 5 min. Sweetmeat was heated until total solid content reached 85%. Heating time varied as a function of BGP and highest heating time of 5.32 min was required for BGSM containing highest BGP concentration (40%). Significant (p

Experimental investigation of a solar thermal storage heater assembled with finned heat pipe and collective vacuum tubes

A novel solar thermal storage heating equipment that is integrated with several highly efficient solar collecting heat storage units (HSU) that filled with phase-change material (PCM) and combined with finned heat pipe to enhance the heat dissipation process was developed and experimentally studied. Due to its advantages such as compactness, easy integrity, intelligent operation, rapid heat storage and dissipation rates, and higher overall utilization efficiency, it may has extensive applications in near future in green heating of residential or commercial buildings, agricultural greenhouse heating, drying and other temperature control system. The solar radiation intensity, elevation angle of the equipment, ambient air temperature and flow-rate were considered experimentally as operating parameters. And the characteristics of the temperature distribution in different sections of the PCM in the HSUs were analyzed. The heat storage performance was studied at different solar radiation flux and elevation angle and the heat dissipation performance was conducted by changing ambient air temperatures and convective velocities. Experimental results showed that the optimum elevation angle of the apparatus was 60° (when used in July/August in the western part of Inner Mongolia). The more extensive the solar radiation, the higher heat storage capacity and rate of the STHSE were achieved. Higher ambient air velocity and lower temperature could significantly improve the overall heat dissipation performance and efficiency. At ambient air temperature of 18 °C and velocity of 6.0 m/s through the wind tunnel, the overall heat dissipation rate reached 414 W and the overall efficiency of heat dissipation was obtained as high as 97%.