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Rainbow schlieren-based direct visualization of thermal gradients around single vapor bubble during nucleate boiling phenomena of water
摘要： Real time non-intrusive diagnostics of thermal gradients around a single vapor bubble in isolated nucleate pool boiling with water as the working fluid have been presented. Direct visualization of transient evolution of temperature gradients in the vicinity of the heated substrate and around the single bubble as it undergoes various sub-processes has been performed using rainbow schlieren deflectometry. Boiling experiments have been conducted under saturated conditions. Results have been presented in the form of two-dimensional rainbow schlieren images wherein the degree of color re-distribution gives a direct measure of the strength of thermal gradients. Through the real time experimental images, various sub-processes/phenomena associated with boiling heat transfer such as development of superheat layer in the vicinity of the heated substrate, inception and further growth of the vapor bubble followed by scavenging of the superheat layer as the vapor bubble departs into the bulk fluid have been discussed. The profiles of hue distribution near the triple contact line brought out the presence of near stagnant fluid zone in which the heat transfer phenomenon was seen to be primarily diffusion-dominated. Beyond this narrow region, significant bulk fluid movement was observed on the basis of the spatial distributions of hue values recorded in the form of real time schlieren images. The experiments further revealed an instantaneous localized bending of the superheat layer as the bubble leaves the heater surface and subsequent shedding of the wake vortices from the edges of the departing bubble as it moves upwards in the bulk fluid.
关键词： Whole field temperature distribution,Heat transfer rates,Nucleate pool boiling,Rainbow schlieren deflectometry
更新于2025-09-23 15:22:29
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AIP Conference Proceedings [Author(s) SolarPACES 2017: International Conference on Concentrating Solar Power and Chemical Energy Systems - Santiago, Chile (26–29 September 2017)] - Design and performance analysis of volumetric solar receiver based on porous foam ceramics
摘要： Volumetric solar receiver is one of three main categories of solar receivers. It has great application prospect due to the simple structure, high thermal efficiency, and the air exit temperature can reach above more than 800℃. The porous material is used instead of tube as absorber in volumetric solar receiver to heat the working medium, and the incident radiation can be absorbed gradually from outside to inside. In this study, an one-dimensional volumetric solar receiver calculating model based on porous foam ceramics is constructed. The temperature distributions and radiation absorption efficiencies at different conditions are analyzed, and a kind of secondary heating volumetric solar receiver is put forward to further improve its thermal efficiency. The results show that both the outlet air temperature and the depth for the temperature of air and ceramic solid reaching to stability decreases apparently with decrease of porosity of ceramic foam, but the temperature of front surface of the receiver increases gradually. With decrease of porous ceramic diameter, the air exit temperature decreases gradually, and the depth for the temperature of air and ceramic solid reaching to stability is decreasing, while, the diameter change has little effect on the temperature of front surface. The air exit temperature increases apparently with decrease of air flow rate and rise of inlet air temperature, and increases with increase of incident radiation intensity. The energy absorbing efficiency is decreasing with decrease of air flow rate and rise of inlet air temperature, and decreases with increase of incident radiation intensity. The presented secondary heating type of receiver can improve the energy absorbing efficiency, although the feasibility and economy of this consideration need further verification in future.
关键词： volumetric solar receiver,porous foam ceramics,temperature distribution,radiation absorption efficiency,secondary heating
更新于2025-09-23 15:21:21
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Twoa??dimensional model of heat flow in edgea??emitting laser revisited: A new and more versatile approach
摘要： An analytical, two-dimensional, stationary model of heat flow in edge-emitting laser is revisited. In the work, we show how to use this approach to be able to calculate the temperature of the entire device including the most susceptible for thermal runaway region, namely the vicinity of the joint of mirrors and an active layer. Numerical tools based on our considerations are implemented in Matlab code and available at the software developer's web site. A procedure of investigation of surface recombination at facets with the help of our model combined with mirror temperature measurements is proposed. To get an insight in reasonableness of our theoretical research, we calculated temperature profiles and surface recombination velocities for example devices and successfully confronted them with results found in the literature.
关键词： temperature distribution,catastrophic optical damage,edge-emitting laser,heat conduction equation,thermal analysis,mirror temperature
更新于2025-09-23 15:19:57
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The effect of dynamic solar heat load on the greenhouse microclimate using CFD simulation
摘要： Indoor greenhouse temperature exceeds tolerable range for plants growth mostly during the summer in Ahvaz-Iran. Attempts for improving ventilation in summer was not adequate despite a huge energy consumption. Computational fluid dynamic models of a full scaled gable greenhouse covered by semitransparent materials among several adjacent greenhouses inside a greenhouse paradise for predicting the dynamics of its microclimate during a day as well as a year 2017-2018 were developed. The accuracy of the models was approved by comparing to the physical experiments and meteorological reports. The results approved the capability of the model for predicting variable solar heat load and higher indoor temperature than ambient in several hours of a day as well as surface heat transfer coefficient of the walls as affected by regional dominant wind profile. This study enhanced the understanding of required solar heat load removal during the hot months while the average temperature exceeds 40 °C for more than 11 hours a day. This finding also indicates the critical periods in which the fan assisted natural ventilation system can be applied to cool down the greenhouse from more than 40 °C to 25 to 35 °C.
关键词： Greenhouse,Temperature distribution,Modeling,Solar radiation,Dynamic microclimate,CFD
更新于2025-09-19 17:15:36
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Thermal characteristics of a compact LED luminaire with a cooling system based on heat pipes
摘要： To increase the compactness of a LED luminaire, in this work it has been suggested to use 8 radial thermal pipes as a heat sink from a COB (Chip-on-Board) matrix to the heat-transfer surface, while the latter should be rings of heat exchanger located concentrically around the light source. These rings are cooled utilizing natural convection of ambient air. The used computer modelling enabled us to evaluate the possibility of the suggested cooling system to provide the normal thermal regime for a power COB matrix. It has been shown that for the power 500 W, as the LED light source, provided that all electric power is converted into thermal power, the temperature of the luminaire base frame in the place of contact with the light source does not exceed 85.5 °С. When using the heat-conducting paste of Arctiс Silver 5 type with the heat conductivity coefficient 8.7 W/(m·°С) in the contact zone and the paste layer thickness 0.1·10-3 m, it corresponds to the temperature of the LED light source case 89.5 °С. With account of the thermal resistance inherent to the COB matrix, the temperature of its semiconductor crystals reaches 139.5 °С, which does not exceed the acceptable value of operation temperature for these crystals 140 °С. At lower values (from 50 to 80%) of the consumed electric power, which is converted into thermal energy, depending on the type of COB, the value of the working temperature of the semiconductor crystal is from 112.5 to 128.7 °C.
关键词： Velocity distribution,Temperature distribution,Heat pipe,Ring,LED luminaire,СОВ matrix
更新于2025-09-19 17:13:59
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[IEEE 2019 Smart Grid Conference (SGC) - Tehran, Iran (2019.12.18-2019.12.19)] 2019 Smart Grid Conference (SGC) - Introducing a novel method for improving the design of off-grid photovoltaic systems
摘要： Two-color pyrometric methods have been widely used in noncontact temperature measurement area. However, it is difficult to get synchronous monochromatic images for two-color pyrometric formula. Some researches use beam splitter to obtain two or more optical paths to capture the different monochromatic images, but the complex optical paths will bring spatiotemporal matching errors. Another method uses color camera to capture the Red, Green, Blue (RGB) channel images as the RGB monochromatic images, but substituting the Dirac delta function for spectral response function will result in the inaccuracy of the measurement results. In fact, the RGB monochromatic images can be obtained from the color image if the irradiance attenuations from color channel to single wavelength are calibrated. In this paper, a novel 3-D reconstruction method is proposed to measure the temperature distribution of combustion flame. First, the irradiance attenuations are calibrated to calculate the synchronous monochromatic images at R and G wavelengths. Second, the tomographic reconstruction of flame monochromatic emissive power is improved with visual hull restriction so that the energy distribution is more reasonable. Finally, the 3-D temperature distribution is calculated from the reconstructed monochromatic emissive power fields at R and G wavelengths using two-color pyrometric method. The alcohol and butane flames are tested in the laboratory-scale test rig. The experimental results indicate that our approach performs well in flame temperature field reconstruction.
关键词： irradiance,3-D reconstruction,two-color pyrometry,flame temperature distribution,temperature field measurement
更新于2025-09-19 17:13:59
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The effect of temperature distribution and cooling rate on microstructure and microhardness of laser re-melted and laser-borided carbon steels with various carbon concentrations
摘要： Laser heat treatment was arranged as a laser remelting and laser boriding. Materials with different carbon concentration were used. Three zones characterized the microstructure after laser treatment: re-melted zone (MZ), heat-affected zone (HAZ) and substrate material. The differences in carbon content and physical properties of used materials influenced the obtained microstructure, temperature distribution and hardness. In case of laser re-melted specimens, the limited martensite transformation proceeded only in C20, C45 and C90 steels. As a result of laser boriding the microstructure of MZ contained additionally iron borides. The specimens with higher dilution ratio value was characterized by higher hardness of re-melted zone. The aim of this study was to indicate the possibility of predicting the microstructure and depths of MZ and HAZ with the usage of Ashby and Esterling model. The influence of carbon concentration in steel on the thickness, dilution ratio and hardness of laser-borided layers was determined.
关键词： microhardness,laser remelting,temperature distribution,laser boriding,cooling rate,microstructure
更新于2025-09-19 17:13:59
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The effect of wind on the temperature distribution of photovoltaic modules
摘要： This paper discusses the thermal aspect of two different types of PV modules. The PV modules are categorised into two major groups: Frameless and Framed modules, and designing structure. Apart from the framed structure, thermal behaviour and its implicit effect on the system is also the key factor of the analysis. Two similar classes of modules are relatively examined and thereafter, are compared with differently manufactured (structure-wise) modules. Here, the framed modules, Solarex (pc-Si) and the RWE Schott Solar (pc-Si) are optically similar; whereas the Solar watt (c-Si) and the Duna Solar (a-Si) are frameless modules. A parallel dichotomy is established on the basis of the quality of the modules being used by the energy industry and the thermal response of the modules at the given conditions. The assessment of the PV modules is based upon the angular orientation of wind, thermal diffusivity of surface, thermal conductivity, heat transfer coefficient, inertial effect of surface, drag force, skin friction, and the thermal behaviour at vicinity of PV surface. The energy equation of the thermal boundary layer over the flat plate is used for thermal profiling of the different PV surfaces. From the experimental measurement, the ambience temperature, surface temperature and wind speed have been determined. The qualitative investigation of geometrically as well as structurally different solar modules is performed with the help of ODE45 application. The flow of air is laminar for all the modules and the drag force varies from 1.45 × 10?5 N to 2.10 × 10?5 N. Friction loss due to wind flow is found to be least for the Solar watt, while the wind orientation of 10° North of East keeps the temperature deviation of the surface from its ambience low for all the modules. The effect of the thermal boundary layer is relatively significant for the Solar watt and the RWE Schott solar modules. Hydrodynamic boundary layer formation has been demarcated from thermal boundary using Blasius and Pohlhausen’s solutions for momentum and energy equations of fluid past a flat surface.
关键词： Temperature distribution,Flow parameters,Thermal analysis,Skin friction,Windspeed,Photovoltaic modules
更新于2025-09-19 17:13:59
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Thermomechanical Stress Distribution Analysis of Junction Box on Silicon Photovoltaic Modules Based on Finite Element Analysis
摘要： The electrical failure associated with concentration of heat and thermomechanical stress inside junction boxes is one of the main failure modes of photovoltaic (PV) modules. Three types of potting junction boxes with partial 72 Si cells PV panel are modeled under a constant current steady-state condition. The temperature distribution results are veri?ed through thermal dissipation tests. It is found that when one diode is in the ON-state, the split kind of junction box shows the highest temperature distribution on the surface, which is nearly 15 ?C higher than the other two types under 25 ?C with 11 A current applied. When three diodes are working, the other two types of junction box with three diodes inside will be intensely heated. The internal temperature distribution shows that bigger size and more copper coverage can help improve the thermal dissipation. Thermomechanical stress analysis based on the steady-state conditions is then carried out. The results show stress concentration on the side wall of the type I junction box while the other two types having conspicuous impact to the backsheet.
关键词： thermomechanical stress,temperature distribution,junction box,photovoltaic (PV),Finite element analysis
更新于2025-09-12 10:27:22
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Optimizing on thermoelectric elements footprint of the photovoltaic-thermoelectric for maximum power generation
摘要： A finite element method (FEM) model for the hybrid PV-TE uni-couple is presented to determine the optimal geometry of the thermoelectric generator (TEG) element for the maximum efficiency. The three-dimensional (3D) governing equations of the thermoelectric for the heat transfer are solved using the FEM based on the temperature dependent properties of TEG materials. The geometric parameters of the TEG were anlyzed in the simulation include the ratio of the area of n- and p-type (An/Ap), the length and the area of the TEG. The result shows that for different areas and different lengths of TEG, the maximum power outputs of the PV-TE all occur with An/Ap = 1 which is different from the TEG solely optimization. This study will provide the valuable reference for PV-TE design.
关键词： finite element method,maximum efficiency,PV-TE,temperature distribution,footprint
更新于2025-09-12 10:27:22