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Influence of ICHTC correlations on the thermal characterization of fa?ades using the quantitative internal infrared thermography method
摘要： The thermal characterization of fa?ades of the existing building stock is essential to establish optimal energy conservation measures. There are different methods to characterize thermal properties of fa?ades. The quantitative internal infrared thermography method is among those most developed. Given the existing differences in the scientific literature among the proposals of the method, this study analysed the influence of the internal convective heat transfer coefficient (ICHTC). In total, 25 correlations of temperature differences (temperature of the wall and internal air temperature) were analysed, as well as 20 correlations of dimensionless numbers. To do this, an experimental campaign was performed in 3 fa?ades belonging to the most representative building periods of the building stock in Spain. First, a cluster analysis was carried out to determine similarities among the equations analysed, using the Ward method as an agglomerative hierarchical method and the Euclidean distance as an association measurement. In total, 12 and 8 groups were obtained for correlations of temperature difference and of dimensionless numbers, respectively. Afterwards, results associated with each approach were obtained. These results showed that a better adjustment was obtained for correlations of dimensionless numbers by using the approach of convection and radiation, with an average value of representative results higher than 80%.
关键词： Fa?ades,Internal convective heat transfer coefficient (ICHTC),U-value,Quantitative internal infrared thermography method
更新于2025-09-23 15:22:29
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New Method for Studying the Ignition Characteristics of Condensed Systems by Laser Radiation
摘要： A method for determining the characteristics of laser ignition of the condensed systems is presented, which ensures uniform distribution of the heat flux density over the surface during ignition. The method consists in measuring the ignition delay time of a rotating cylindrical sample when the continuous laser heat flux is applied to its end surface. The theoretical estimation of the required angular rotation velocity of the sample is carried out, which ensures averaging with a given error of the radiation flux density on the surface of the sample, as well as the degree of surface cooling due to the convective heat transfer. The experimental results on the pyroxylin sample ignition at the radiant heating by a CO2 laser with and without rotation of the sample are presented.
关键词： pyroxylin,laser ignition,ignition delay time,condensed system,convective heat transfer,angular velocity of rotation
更新于2025-09-23 15:19:57
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Intensification of the Plant Products Drying Process by Improving Solar Dryer Design
摘要： The article presents the rationale for production of dried fruits and vegetables using a solar drying unit. To intensify the drying process, convection of drying agent ?ow in the proposed drying chamber is studied using Navier–Stokes equations. Numerical methods are used for solving equations describing the process of convective heat transfer. As a result, graphical interpretations of isolines of drying agent ?ow are obtained and location of passive zones in the dryer chamber are identi?ed. Uniformity of the temperature zones in the chamber is ensured by supplying additional drying agent into the passive zones. Temperature values at various levels of the drying chamber are experimentally obtained. Results for drying cut-up mass of vegetables and fruits are presented.
关键词： solar drying,passive zones,convective heat transfer,Navier–Stokes equations,temperature uniformity
更新于2025-09-23 15:19:57
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Thermal regulation of PV fa?ade integrated with thin-film solar cells through a naturally ventilated open air channel
摘要： Thermal regulation of photovoltaic fa?ade through passive air channel provides a cost effective measure for improving solar to electrical energy conversion efficiency. This study presents a 2D numerical investigation of the fluid flow and heat transfer characteristics of natural convection driven by buoyancy force inside the passive cooling air channel created by two vertical parallel walls. One wall is heated by absorbed heat by photovoltaic (PV) cells from solar radiation. Numerical solutions for open and closed channel are obtained for the channel of 1.05 m in height and 0.16 m in width, respectively. The natural convective cooling effect on the PV cells for different ventilation strategies were examined considering the surface temperature of PV panels. It is found that the maximum surface temperature reaches 57.1 oC for closed channel, 49.1 oC for opened channel. Opened channel behind the PV panel is an economic way of heat releasing for the benefit of PV power generation. However, other issues such as noise control and cleaning difficulty may also be encountered by fa?ade designers. At the same time, understanding the mechanisms involved in the fluid flow and heat transfer in the channel back the PV panel through examining the pressure distribution along the cavity is required and equally important for the design improvements of PV fa?ade especially for the design of the air channel entrance to lower its pressure drop.
关键词： Ventilated and closed PV facade,Building integrated photovoltaic (BIPV),Convective heat transfer
更新于2025-09-12 10:27:22
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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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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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Tomography-based determination of Nusselt number correlation for the porous volumetric solar receiver with different geometrical parameters
摘要： Pore-scale numerical models of the porous volumetric solar receiver are established in this paper. By using the X-ray computed tomography and the imaging processing techniques, models of porous media with different geometrical parameters are reconstructed. The conjugate heat transfer process in the porous volumetric solar receiver is solved based on the direct pore-scale numerical simulation. The turbulent effect of fluid flow inside porous geometry is considered by the Shear-Stress Transport k-ω model and the absorbed solar energy is simulated by following the Beer’s law. The results present that the inlet velocity and the geometrical parameters influence the thermal performance of the porous volumetric solar receiver. Larger inlet velocity tends to enhance the convective heat transfer between fluid and solid phases meanwhile decreases noticeably the overall temperature. Receiver with larger porosity is preferred because it limits the reflection losses. The Nusselt number increases as the porosity becomes larger. As a result, the general correlation of Nusselt number for the porous volumetric solar receiver is derived as a function of porosity and Reynolds number. This correlation is applicable with the porosity ranging from 0.74 to 0.89 and the pore Reynolds number ranging from 3 to 233.
关键词： Solar energy,Pore-scale numerical simulation,Convective heat transfer,Volumetric solar receiver,Nusselt number correlation,Porous media
更新于2025-09-09 09:28:46