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Photovoltaic Roof Tiles: The Influence of Heat Recovery on Overall Performance
摘要： A photovoltaic (PV) roof tile serves both as a roofing material and as an electricity-producing surface. The main aim of the present study was to increase the overall system efficiency of PV tiles by using heat recovery. The chosen strategy was two-fold: determine the operational efficiency of PV tiles and optimize construction to increase the cooling effect when using air as the working medium. A detailed experimental study was undertaken to determine these effects. The results indicated that a combined electrical and thermal efficiency of 24% could be reached. This is promising and proves the potential for air to be the working medium in such systems. Moreover, this shows a direction for future system optimization.
关键词： experimental study,photovoltaic (PV) roof tiles,heat recovery,efficiency performance of electricity generation,solar light simulator
更新于2025-09-11 14:15:04
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Laser beam welding of DP980 dual phase steel at high temperatures
摘要： Dual phase steels have been used in safety components for the automotive industry and represents a standard in terms of energy absorbing steel alloys. After welding, these components present a martensitic transformation in the fusion and heat-a?ected zones with an intrinsic brittleness. The current contribution presents a procedure where the DP980 steel sheet is kept at a given temperature during and after the laser weld in order to generate bainite instead of martensite. The results using an isothermal treatment at 527 °C shown a microstructure composed by grain boundary and bainitic ferrite and retained austenite with a constant hardness in the base material and heat-a?ected and fusion zones of 280 HV. The room temperature welds present hardness values between 320 and 500 HV. The high-temperature welds also shown a decrease in the maximum residual stress at the weld centerline by 1/3, with a consequential reduction in the warp of the joined component.
关键词： Heat treatment,Hardness testing,Laser beam welding,Dual phase steels
更新于2025-09-11 14:15:04
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Development and optimization of the laser-assisted bonding process for a flip chip package
摘要： In a ?ne pitch ?ip chip package, a laser-assisted bonding (LAB) technology has recently been developed to overcome several reliability and throughput issues in the conventional mass re?ow (MR) and thermal compression bonding technology. This study investigated the LAB process for a ?ip chip package with a copper (Cu) pillar bump using numerical heat transfer and thermo-mechanical analysis. During the LAB process, the temperature of the silicon die was uniform across the entire surface and increased to 280 (cid:3)C within a few seconds; this was high enough to melt the solder. The heat in the die was quickly conducted to the substrate through the Cu pillar bumps. Meanwhile, the substrate temperature was low and remained constant. Therefore, a stable solder interconnection was quickly achieved with minimal stress and thermal damage to the package. The substrate thickness, the number of Cu bumps, and the bonding stage temperature were found to be important factors affecting the heat transfer behavior of the package. The temperature of the die decreased when a thinner substrate, a higher number of Cu bumps, and a lower bonding stage temperature were used. If the temperature of the die was not suf?ciently high, insuf?cient heat was transferred to the solder to melt it, resulting in incomplete solder joint formation. Thermo-mechanical analysis also showed that the LAB process produced lower warpage and thermo-mechanical strain than the conventional MR process. These results indicated that a LAB process using a selective local heating method would be bene?cial in reducing thermo-mechanical stress and increasing throughput for the ?ne pitch ?ip chip packages.
关键词： Laser-assisted bonding,Copper pillar bump,Thermo-mechanical analysis,Flip chip package,Heat transfer
更新于2025-09-11 14:15:04
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Heat-Recovery Solar Cell
摘要： Heat-recovery (HERC) solar cell—a concept of solar cells utilizing the heat for improving the power conversion e?ciency—is presented. HERC solar cell, characterized by an absorber hotter than electrodes, recovers heat as electricity to have high conversion e?ciency exceeding the detailed balance limit when carrier-energy ?ltering is employed. Being di?erent from hot-carrier solar cells, HERC solar cell does not require fast carrier extraction within the thermalization time, which largely improves its feasibility (feasible even with Si). An increment in the conversion e?ciency originates from thermoelectricity produced by the temperature di?erence. Requirements for materials of the ?ltering layers are also given based on a nonideal device simulation with the thermoelectric properties.
关键词： Si solar cells,Heat-recovery solar cell,carrier-energy filtering,thermoelectricity,power conversion efficiency
更新于2025-09-11 14:15:04
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Numerical Simulation on Laser Welding considering Surface Deformation and Convective Heat Transfer
摘要： Laser welding requires much capital investment comparing with generally employed arc welding. However, the laser welding enables to join very small objects with high accuracy because the laser has high energy density and high controllability. In addition, it is possible to suppress welding deformation due to low heat input. Therefore, the laser welding is employed for various joining processes. This study aims to clarify formation mechanism of weld pool in laser cladding in order to improve incomplete fusion through numerical simulation on laser welding considering deformation of weld pool surface and convective heat transfer in it. Consequently, it was found that the gas pressure plays important role for improve incomplete fusion in laser welding. The higher pressure of gas increases penetration depth by pushing away molten metal at center of the weld pool without changing direction of convection.
关键词： Laser Welding,Simulation,Convective Heat Transfer,Surface Deformation
更新于2025-09-11 14:15:04
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Improved banded method for spectral thermal radiation in participating media with spectrally dependent wall emittance
摘要： To develop an efficient and practical spectral radiation model for CFD simulations, a banded approach is proposed for a mixture of carbon dioxide and water vapor in varying thermodynamic states. Using a previously reported band dividing scheme, a statistical narrow band model is implemented to provide gray band absorption coefficient databases. The databases were then approximated by certain simple correlations, which can be readily used in CFD calculations of RTE solvers. The correlations were validated in several 1D and 3D benchmarks representing various combustion conditions. The accuracy and CPU cost of the proposed banded approach were studied and compared with those of other similar methods. The results demonstrated that the new approach is an efficient and accurate method that can be conveniently applied in a commercial CFD code for spectral radiation; moreover, it can handle non-gray walls. As a practical case study, the proposed approach was used to simulate radiative heat transfer within a back pass channel of a CFB boiler. The effect of combustion scenarios, i.e., air- and oxygen-fired, boiler load, inlet flow conditions, and wall material, was analyzed by the CFD model. The predictions of two different RTE solvers, i.e., P1 and DO, and the required CPU time were compared for gray and non-gray models.
关键词： Non-gray wall,Back pass channel,CFB boiler,Radiation heat transfer,Band absorption coefficient,Narrow band calculation,Non-gray gas modeling,Banded approach
更新于2025-09-11 14:15:04
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[Energy, Environment, and Sustainability] Advances in Solar Energy Research || Shell-and-Tube Latent Heat Thermal Energy Storage (ST-LHTES)
摘要： Thermal energy storage (TES) unit has become an integral part of thermal energy conservation. As the name implies, the device simply stores heat when energy from the source is available in excess, and releases the same when energy from the source falls short of the requirement. By doing so, such devices deliver heat energy across the temporal barrier, making thermal energy available for extended working hours of solar thermal power plants (STPP). High energy density and stable operation for long duration are desirable qualities which may be found in latent heat thermal energy storage (LHTES) system. To exploit the advantage of LHTES, the most common design reported in the literature is shell-and-tube type latent heat thermal energy storage (ST-LHTES) systems with phase change material ?lled in shell side, while (heat transfer ?uid) HTF ?ows in the tubes (or vice versa). The present chapter gives a detailed classi?cation of ST-LHTES systems based on geometry, orientation and relative position of PCM and HTF in heat exchanger along with the classi?cation of phase-change materials. Numerical modelling of heat transfer phenomenon is presented along with some simulated results for enhanced PCM, clearly describing the coupling between PCM and HTF domain. Various heat transfer enhancement techniques and parametric analysis have been discussed with challenges and future scope.
关键词： Latent heat,Thermal energy storage,Coupling,Shell and Tube Heat Exchanger,Heat transfer ?uid,Phase change material
更新于2025-09-10 09:29:36
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Energy performance analysis of a novel solar PVT loop heat pipe employing a microchannel heat pipe evaporator and a PCM triple heat exchanger
摘要： This study presents a numerical analysis of the energy efficiency for a novel solar PVT Loop Heat Pipe (PVT-LHP) employing a novel Micro-channel evaporator and a novel PCM heat storage exchanger. It presents a description of the different sub-models in the PVT-LHP system (the PVT model, the microchannel heat collector model and the novel PCM triple heat exchanger model) and the integrated model of the system. The integrated model of the system was solved by ensuring a heat balance at the condenser and the evaporator. A parametric analysis has been performed in order to assess the influence of the environmental parameters (i.e. solar radiation, air temperature, wind velocity), structural parameters (i.e. glazing cover, the number of absorbing microchannel heat pipes, PV cell packing factor), the circulating fluid variables (i.e. cold-water inlet temperature and water mass flow rate) on the energy performance of the system. The novel PVT-LHP has been compared with a conventional Solar PVT-LHP system. It was found that lower solar radiation, lower ambient air temperature, higher wind speed, higher packing factor, lower cold-water inlet temperature and a smaller cover number led to an enhanced electrical efficiency, but a reduced thermal efficiency of the module; whereas a higher cold-water mass flow rate and a greater number of microchannel heat pipes gave rise to both thermal and electrical efficiencies of the module. It was also found that an increase of solar radiation, ambient temperature, cover number, microchannel heat pipe number and packing factor are favourable factors for the overall COP (Coefficient Of Performance) of the system, whereas an increase of wind velocity and cold water mass flow rate are unfavourable. The study indicated the existence of an optimal cover number, number of microchannel heat pipes and mass flowrate. Under the given design conditions, the electrical, thermal and overall efficiency of the PV/LHP module were 12.2 %, 55.6 % and 67.8% respectively and the novel system can achieve 28% higher overall energy efficiency and 2.2 times higher COP compared to a conventional system. The integrated computer model developed in this study can be used to design and optimize the novel PVT-LHP heating system.
关键词： microchannel,power supply,PVT,Loop Heat Pipe,PCM triple heat exchanger,heating
更新于2025-09-10 09:29:36
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Thermal meta-device in analogue of zero-index photonics
摘要： Inspired by the developments in photonic metamaterials, the concept of thermal metamaterials has promised new avenues for manipulating the flow of heat. In photonics, the existence of natural materials with both positive and negative permittivities has enabled the creation of metamaterials with a very wide range of effective parameters. In contrast, in conductive heat transfer, the available range of thermal conductivities in natural materials is far narrower, strongly restricting the effective parameters of thermal metamaterials and limiting possible applications in extreme environments. Here, we identify a rigorous correspondence between zero index in Maxwell’s equations and infinite thermal conductivity in Fourier’s law. We also propose a conductive system with an integrated convective element that creates an extreme effective thermal conductivity, and hence by correspondence a thermal analogue of photonic near-zero-index metamaterials, a class of metamaterials with crucial importance in controlling light. Synergizing the general properties of zero-index metamaterials and the specific diffusive nature of thermal conduction, we theoretically and experimentally demonstrate a thermal zero-index cloak. In contrast with conventional thermal cloaks, this meta-device can operate in a highly conductive background and the cloaked object preserves great sensitivity to external temperature changes. Our work demonstrates a thermal metamaterial which greatly enhances the capability for molding the flow of heat.
关键词： thermal cloak,zero-index photonics,thermal metamaterials,convective heat transfer,heat conduction
更新于2025-09-10 09:29:36
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Measurements, Mechanisms, and Models of Heat Transport || Macroscopic Analysis of the Flow of Energy Into and Through Matter From Spectroscopic Measurements and Electromagnetic Theory
摘要： That light (what we see) and heat (what we feel) traveling through air or vacuum are the same phenomena is now well-known. However, heat transfer within a solid is treated differently: most researchers consider elastic waves as the main carrier of interior heat, after Debye (1914). This situation in part stems from the vibrations of molecules or ions in condensed matter, which are connected with the heat capacity of a solid, not being probed by spectroscopy until B1930 due to instrumental limitations (Sawyer, 1963).
关键词： radiative transfer,spectroscopy,infrared,heat transfer,light,vibrational spectroscopy
更新于2025-09-10 09:29:36