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An analysis of low flow for solar thermal system for water heating
摘要： The mass flow rate in the collector loop of a solar domestic hot water system (SDHW) affects its thermal performance. The initial investment and the operation cost are also affected by the selection of the primary flow. Common design rules state a standard specific flow rate of 50 l/hm2 for most collector models. However, the emergence of electronically commuted motors recommends reviewing the interest of the low flow alternative (7–14 l/hm2) for solar thermal systems. In this paper, the thermal performance of a typical serpentine collector has been measured for different mass flow rates. The resulting performance curves and associated measurement uncertainty bands show only a moderate improvement in performance as the flow rate increases. Once the collector thermal behaviour has been characterized, the whole system is modelled, and the initial investment and operating cost are calculated for two design options: high flow (80 l/hm2) and low flow (20 l/hm2). As expected, the solar fraction is slightly higher for the high flow system (4.6% higher) and the number of hours of operation is lower for this system (4.4% less hours of operation). Considering the lower investment cost of the low flow system, the best thermal behaviour of the high flow system requires near 18 years to amortize the largest investment. If other considerations like embodied energy are accounted for, the common practice in designing SDHW systems should promote low flow.
关键词： Solar thermal simulation,Flat plate collector,Low flow,Variable flow
更新于2025-09-23 15:22:29
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A scan-wise adaptive remeshing framework for thermal simulation of the selective laser melting process
摘要： Physics-based thermal simulation of laser powder bed fusion can greatly help understanding the process and reducing time and cost associated with experimental approaches. Numerical methods including the finite element method have been widely used to predict parts thermal-structural history during the build process. However, the simulation has scalability issues because both layer thickness and laser spot diameter are too tiny compared to the part-scale. Therefore, it is only feasible to run these simulations with massive computational resources or if the boundary conditions are simplified, which inevitably reduces the prediction accuracy. This paper proposes a tetrahedral element-based scan-wise adaptive remeshing framework for thermal simulation of the selective laser melting (SLM) process. Results show that a significant reduction of the computational time and resources can be achieved due to the reduction of the number of nodes. The proposed framework enables part-scale thermal modeling of the SLM process with detailed thermal history without sacrificing the accuracy. The effectiveness of the proposed framework is demonstrated through a large size cantilever problem.
关键词： Selective laser melting,Melt pool,Adaptive remeshing,Thermal simulation
更新于2025-09-23 15:19:57
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Thermal Design Considerations for III-N Vertical-Cavity Surface-Emitting Lasers Using Electro-Opto-Thermal Numerical Simulations
摘要： III-N VCSELs undergo severe self-heating which limits the output optical power. This makes thermal management a critical design consideration. The three most common VCSEL structures (hybrid VCSELs, flip-chip VCSELs and ELOG VCSELs) have been studied using advanced self-consistent electro-opto-thermal numerical simulations. The key geometric and material parameters affecting the thermal resistance of these devices have been identified. Our simulations suggest that some of the proposed solutions and design modifications can increase the maximum optical output power by as much 100%. This manuscript also describes the correct method of using numerical simulation in device design—to predict trends and isolate the key factors affecting device performance.
关键词： electro-opto-thermal simulation,thermal resistance,VCSEL,III-Nitride,laser diode,device modeling
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Structured Auxiliary Mesh (SAM) Algorithm for Opto-Thermal Simulation of Laser-Based Lighting Systems
摘要： Laser-based lighting systems are an emerging technology, the next step in solid state lighting that revolutionized the way artificial light is generated. The configuration of interest here is the laser-excited remote phosphor (LRP) scheme that consists of a laser diode as the excitation source of an appropriately chosen phosphor sheet. The phosphor is employed for the down-conversion of the incident laser light and broadening of the output spectrum. Although some commercial applications have already been developed, the optimization of LRP systems has yet to be achieved. A bottleneck in their performance is the thermal dependency of the phosphor’s emission characteristics, a phenomenon also known as thermal quenching. As a result, the need for an opto-thermal simulation strategy arises that will enable the study and optimization of LRP systems [1]. The opto-thermal simulation model discussed here is based on Monte Carlo simulations for the optical part, where the absorbed radiant flux is calculated. These optical thermal losses are subsequently used as a volume heat source to solve the transient heat equation by applying the finite element method (FEM) [2]. As thermal quenching is a time-dependent phenomenon in nature, this is an iterative procedure, where the absorbed flux must be calculated for most of the time steps. Typical Monte Carlo ray tracing algorithms use voxel-based meshes to store any calculated properties / attributes. The problem that arises here is that the computational cost for converting the voxel-based mesh to an FEM mesh would be prohibiting for time-dependent analysis. The solution is to directly store the absorbed flux to the FEM mesh. However, the issue that now emerges is locating the interpolating point, namely the point in space where the absorption occurs, within the unstructured FEM mesh. The processing time of a brute force search would be too long, so more sophisticated solutions must be found. SAM algorithms, which were first introduced in [3], are part of a class of algorithms known as geometric search algorithms [4, 5] that deal with point location in unstructured meshes. We propose here a modified SAM algorithm that uses the optical voxel-based mesh as the auxiliary structured mesh for geometric searching. The two meshes, optical and FEM, are superimposed. As point location in voxel-based meshes is trivial, by mapping which elements of the FEM mesh belong to each voxel, we can easily narrow down the number of searches required. To this end, two maps, implemented as binary search trees, are implemented. The first map, maps the voxel number to the nodes of the FEM mesh that lie within it, while the second map, maps the elements of the unstructured mesh that these nodes belong to. The set-up times of these maps heavily depend on the density of the FEM mesh and the order of the elements used. The use of higher-order elements results in considerable set-up times. As higher order elements are not necessary for thermal analysis, this is not a critical issue here. On the other hand, the denser the optical mesh, the fewer FEM elements are mapped to each voxel. However, the size of voxels should be appropriately chosen, since too small voxels may lead to degenerative cases where there are voxels without any nodes lying in them. A distinct advantage of this method is that once the maps are assembled, the search time of elements is O(1). Simulation plays an increasingly crucial role in the study and optimization of optical systems. Due to the increase in computational capabilities, modelling of more complex phenomena can be included and the need of multi-physics approaches rises. The optical properties of materials often shift to temperature above tolerance levels that may render a particular optical design ineffective. In other cases, structural loads may be the critical issue as they can lead to misalignment of optical elements. The proposed SAM algorithm that enables a more efficient coupling of optical and FEM analysis is a valuable tool to such approaches of optical problems.
关键词： Laser-based lighting systems,opto-thermal simulation,Monte Carlo simulations,SAM algorithm,finite element method,thermal quenching
更新于2025-09-16 10:30:52
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris, France (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Design and Modelling of a Shunt for Current Measurements at 10 a and up to 1 MHz: A Theoretical Approach
摘要： Electrical current shunts used as resistance standards in metrology laboratories are characterized by a broadband operating frequency bandwidth and are commonly calibrated up to 100 kHz. The use of a current shunt requires the preliminary knowledge of its magnitude deviation from DC and phase angle according to the frequency. The best magnitude performances published so far are limited to 2 μΩ/Ω at 100 kHz. In this paper, we present an innovative shunt design for current measurements at 10 A up to 1 MHz. The relative deviation from DC is less than 0.2 μΩ/Ω and 20 μΩ/Ω in magnitude at 100 kHz and 1 MHz respectively.
关键词： calibration,AC–DC transfer,Current shunts,3D thermal simulation,current measurement,3D electromagnetic simulation,uncertainty,AC current,modeling
更新于2025-09-10 09:29:36
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Accurate and efficient analysis of the upward heat flow in InGaP/GaAs HBTs through an automated FEM-based tool and Design of Experiments
摘要： This paper presents an extensive analysis aimed at quantifying the impact of all the key technology parameters on the upward heat flow in state‐of‐the‐art InGaP/GaAs heterojunction bipolar transistors (HBTs) for various emitter areas and shapes. Extremely accurate thermal simulations are conducted in a relatively short time with a tool relying on a commercial 3‐D finite‐element method (FEM) solver and an in‐house routine for automated geometry construction, optimized mesh generation, sequential solution, and data storing/processing. Design of Experiments is used to define a thermal resistance model as a function of the aforementioned parameters on the basis of a few FEM data.
关键词： finite‐element method (FEM),gallium arsenide (GaAs),Design of Experiments (DOE),thermal simulation,thermal resistance,heterojunction bipolar transistor (HBT)
更新于2025-09-04 15:30:14
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Enhanced Sensing Performance of Integrated Gas Sensor Devices
摘要： Semiconducting metal oxide (SMO) gas sensors, dedicated to wearable devices were designed, fabricated, and characterized in terms of power consumption, thermal distribution, and sensing capability. The sensors demonstrate a sensitivity down to ppb-level VOC concentrations at a low power consumption of 10.5 mW. To further enhance the baseline stability and sensing response characteristics at low power consumption, a new sensor structure is proposed. The design implements novel aspects in terms of fabrication and microheater geometry, leading to improved sensor performance which enables new applications for SMO gas sensors. In this work, two designs were analyzed using experimental characterization and simulation. The results of the analyses of the two sensors are comparatively reported.
关键词： microheater,electo-thermal simulation,gas sensor,semiconducting metal oxide
更新于2025-09-04 15:30:14