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Wettability Control of Copper Surface Using Picosecond Laser for Enhancing Condensation Heat Transfer
摘要： One of the most important and widely visualized process taking place in nature is condensation. Superhydrophobic surfaces, which facilitates dropwise condensation has been the principal area of research in the last decade or so. Fabrication of superhydrophobic surface can be achieved by either surface modification using mechanical process, surface treatment like coating or by the combination of both. But, the major drawback of coating is its durability and vulnerability. So, in this work we have fabricated a robust surface by means of picosecond laser machining. Apart from being a simple process, this method has an advantage of cutting down the surface fabrication time by several hours as compared to other methods like one-step immersion, electro-deposition, top-down fabrication method, etc. In our work three different work specimens irradiated with different laser power were studied for its surface morphologies by scanning electron microscope (SEM) images and its wettability was measured using contact angle meter. It is found that the wettability of surface changes with different laser power and hence it is possible to control the wettability by adjusting the laser parameters. Condensation experiment was carried out on these different surfaces and its performance was compared with plain surface.
关键词： Wettability control,micro grooves,Condensation heat transfer,Contact angle,Picosecond laser
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Direct Fluid Cooling of Concentrator Photovoltaics for Hybrid Photovoltaic-Solar Thermal Energy Conversion
摘要： A spectrum-splitting photovoltaic module is developed for hybrid photovoltaic-solar thermal energy conversion using direct fluid cooling (DFC) of partially transmissive concentrator photovoltaic cells. The waste heat generated in photovoltaic cells can be more efficiently extracted by flowing a heat transfer fluid in direct contact with both sides of the cells. The module also acts as a beam splitter, dividing the incident light into two parts. Photons with higher energy than the bandgap of the cells are absorbed in cells, while photons with lower energy are passed through the infrared-transmissive module to a thermal receiver. Optical modeling (experimental) shows 63.2% (34.3%) out-of-band transmittance through the cell regions and 90.4% (89.0%) full spectrum transmittance through the surrounding bypass region. Thermal modelling verifies the direct cooling fluid method is an effective way to maintain cell temperature < 110℃. Electrical power conversion efficiency in a first prototype module is 79% of the bare cell efficiency. Fluid flow characterization shows laminar flow. The modules are currently undergoing field testing.
关键词： hybrid CPV/T system,active cooling,silicone oil heat transfer fluid,CPV
更新于2025-09-23 15:21:01
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Study on ?′-ferrite evolution and properties of laser fusion zone during post-weld heat treatment on Al-Si coated press-hardened steel
摘要： Laser welding of Al-Si coated press-hardened steel (PHS) was still a challenging due to the formation of ?-ferrite in the fusion zone. However, it was ambiguous on the ?-ferrite evolution during post-weld heat treatment (PWHT). In this study, Al-Si coated PHS was welded by laser ?ber and then heat-treated at various temperatures (650 ?C, 950 ?C and 1050 ?C), and the microstructure evolution was investigated by in situ-observation. Mechanical properties and formability of welded joints was analyzed. The results showed that ?-ferrite did not go through phase transformation during PWHT regardless of any temperature, but with a grain boundary ?atted and movement. The presence of coarse ?-ferrite after PWHT was the responsible for the decreasing of tensile strength and formability of welded joints. The initiation crack was easy to generate in the phase interface between ?-ferrite and martensite to form a local brittle fracture zone ?nally. This study results provides a new theoretical criterion for the properties improvement on the laser welding of PHS without removing Al-Si coating.
关键词： Laser welding,Post-weld heat treatment,Al-Si coating,Press hardened steel ?-ferrite
更新于2025-09-23 15:21:01
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Continuous-wave operation of a 1.3 <i>??</i> m wavelength npn AlGaInAs/InP transistor laser up to 90 ?°C
摘要： A transistor laser (TL) is a device that operates at a high-speed with multiple functions such as output control with low wavelength shift and signal mixing. By adopting a high heat dissipation structure with a high-speed compatible wide electrode pad and thick Au plating in TLs, improvement of temperature performance in 1.3 μm wavelength npn AlGaInAs/InP TL was demonstrated. As a result, continuous-wave operation of a 1.3 μm TL up to 90 °C was achieved. The thermal resistance was estimated to be 25 K W?1, based on the spectrum behavior, which is at least four times lower than the previously observed value.
关键词： transistor laser,AlGaInAs/InP,continuous-wave operation,thermal resistance,high heat dissipation structure
更新于2025-09-23 15:21:01
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Performance analysis of a heat pump-based photovoltaic/thermal (PV/T) system
摘要： Photovoltaic/thermal (PV/T) system produces both heat and electricity simultaneously with the advantages of better space utilization and higher conversion efficiency over individual solar thermal and solar photovoltaic (PV) system when operated separately. The PV/T system can control the operating temperature of PV by passing a heat transfer fluid through a heat exchanger attached to the rear of the modules. The present study analyses the performance of one such in-house built system, where the heat transfer fluid is refrigerant. Refrigerant-based PV/T system involves the integration of evaporator coils of the heat pump and PV module to form a cogeneration type system known as photovoltaic/thermal–solar assisted heat pump (PV/T–SAHP). The prototype of the PV/T–SAHP was fabricated with a double glass PV module instead of a conventional module with polyvinyl fluoride backsheet. Initially, the performance characteristics of the system are analyzed in detail using the experimental observations under a typical clear sky condition during the transition season. Following, the year-round performance of the system is predicted using an already validated numerical model. It was found that the present system can improve the average electrical efficiency by 15.20% and can achieve a coefficient of performance of 2.96.
关键词： Refrigerant-based PV/T system,Thermal management of PV module,Double glass PV module,Heat pump
更新于2025-09-23 15:21:01
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Experimental study on direct fabrication of micro channel on fused silica by picosecond laser
摘要： Ultrafast laser ablation, known for its high precision and the depressed thermal influence during processing, is fevered in micro channel fabrication on the glass bulk. In present work, a micro channel structure fabricated on fused silica bulk by a picosecond pulsed laser is parametrically investigated with different processing environments, scanning velocities, pulse energies, hatch distances and repetitive scans. The best processing parameters are determined through the material remove rate and the bottom surface roughness of the channel. Moreover, the fabrication defect attributed to the heat accumulation effect is analyzed by Raman spectrum. A scanning strategy is put forward to compensate the asymmetry in the cross section of the micro channels.
关键词： Heat accumulation,Surface roughness,Scanning strategy,Micro channel,Picosecond laser
更新于2025-09-23 15:21:01
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Thermal management of concentrator photovoltaic systems using nanoa??enhanced phase change materialsa??based heat sink
摘要： Temperature regulation of concentrator photovoltaic systems is essential in reducing operating temperatures with higher system performance. A new nano-enhanced phase change material, with multi-cavity heat sinks, integrated with a concentrator photovoltaic (CPV) system is developed. The multi-cavity heat sink includes a single-, triple-, and quintuple-cavity configuration in both parallel and series pattern filled with n-octadecane PCM and graphene nanoparticle additives with 2% and 5 wt%. Numerical simulations are performed using the developed two-dimensional model for photovoltaic layers integrated with the nano-enhanced phase change material-based heat sink. The predicted results are compared with the available numerical results and measurements. Results indicate that increasing the number of parallel cavities, along with weight fraction of nanoparticles, significantly improves the thermal conductivity, and consequently attains better performance for the CPV system. Using a parallel quintuple-cavity configuration, with 5 wt% NPCM, achieves maximum reduction in the solar cell mean temperature along with the best temperature uniformity compared to other configurations. At a concentration ratio of 20, the thermal efficiency is 65%, the electrical efficiency is about 10%, and the output electrical power of the system is 235 W per m width of the cell. On the contrary, using a series pattern of the heat sink has an unfavorable effect on the mean solar cell temperature, as well as on electrical efficiency and thermal performance of the CPV system. The obtained result can assist in identifying the best possible design of the heat sink in addition to the most appropriate selection of PCM and nanoparticle additives.
关键词： electrical efficiency,graphene nanoparticles,concentrator photovoltaic system,multi-cavity heat sink,nano-enhanced phase change materials
更新于2025-09-23 15:21:01
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Single-step process of microstructural functionally graded Ti6Al4V by laser powder bed fusion additive manufacturing
摘要： The objectives of this study are: (1) to verify whether using linear heat input alone is sufficient to predict the resulting microstructure of Ti6Al4V and (2) to demonstrate the potential of single-step process of functionally graded material using powder bed fusion. In laser powder bed fusion, linear heat input is defined as the ratio of laser power to scan speed. It is a key process variable that describes the unit energy input. Therefore, linear heat input has been extensively linked with the resulting microstructure. However, review of existing studies shows that when similar linear heat input was used, a marked difference in mechanical properties exists. Using proportionally changed laser power and scan speed in five zones, functionally graded specimens were fabricated in this study. All other parameters remain the same for these zones. Variation of microstructure and hardness across the five zones were obtained. This implies that linear heat input is not sufficient to determine the resulting microstructure and mechanical properties. The amplitude of laser power and scan speed has an effect on the resulting microstructure, so they need to be separately considered in future studies.
关键词： Linear heat input,Functionally graded material,Ti6Al4V,Microstructure,Powder bed fusion
更新于2025-09-23 15:21:01
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Local Overheating of Biotissue Labeled With Upconversion Nanoparticles Under Yb3+ Resonance Excitation
摘要： Local overheating of biotissue is a critical step for biomedical applications, such as photothermal therapy, enhancement of vascular permeability, remote control of drug release, and so on. Overheating of biological tissue when exposed to light is usually realized by utilizing the materials with a high-absorption cross section (gold, silica, carbon nanoparticles, etc.). Here, we demonstrate core/shell NaYF4:Yb3+, Tm3+/NaYF4 upconversion nanoparticles (UCNPs) commonly used for bioimaging as promising near-infrared (NIR) absorbers for local overheating of biotissue. We assume that achievable temperature of tissue labeled with nanoparticles is high enough because of Yb3+ resonance absorption of NIR radiation, whereas the use of auxiliary light-absorbing materials or shells is optional for photothermal therapy. For this purpose, a computational model of tissue heating based on the energy balance equations was developed and verified with the experimentally obtained thermal-graphic maps of a mouse in response to the 975-nm laser irradiation. Labeling of biotissue with UCNPs was found to increase the local temperature up to 2?C compared to that of the non-labeled area under the laser intensity lower than 1 W/cm2. The cellular response to the UCNP-initiated hyperthermia at subcritical ablation temperatures (lower than 42?C) was demonstrated by measuring the heat shock protein overexpression. This indicates that the absorption cross section of Yb3+ in UCNPs is relatively large, and microscopic temperature of nanoparticles exceeds the integral tissue temperature. In summary, a new approach based on the use of UCNP without any additional NIR absorbers was used to demonstrate a simple approach in the development of photoluminescent probes for simultaneous bioimaging and local hyperthermia.
关键词： near-infrared irradiation,local overheating,photothermal material,bioimaging,heat shock proteins,biotissue laser heating,hyperthermia,upconversion nanoparticles
更新于2025-09-23 15:21:01
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Remote Welfare Monitoring of Rodents Using Thermal Imaging
摘要： Animal research has always played a crucial role in various medical and scientific breakthroughs. They offer, inter alia, insights into diseases mechanisms, genetic predisposition to a disease, and drug therapy. However, the use of animals for medical research is a cause of major controversies and debates in modern science. To warrant high bioethical standards, new directives have been being adopted to replace animal research whenever possible, to reduce the number of animals, and to refine the procedures to minimize stress and pain. Here, we present two new approaches, based on thermal imaging (a remote and passive technology), to assess respiratory rate (RR) as well as exploratory behavior and general activity in rodents. In animal research, these parameters are gold standards for welfare assessment. The approaches were validated in a study conducted with both rats and mice. To test the feasibility of our algorithm to estimate RR, thermal videos from anesthetized rodents were acquired. The capability of the second approach to monitor activity was tested with videos of Open Field tests. Regarding RR, a high agreement between thermal imaging and gold standard (electrocardiography-derived RR) was achieved. The mean relative error averaged 0.50 ± 0.15 breaths/min and 4.55 ± 2.94 breaths/min for rats and mice, respectively. The second approach was capable of monitoring and tracking the activity of the rodents very well. This paper demonstrates that thermal imaging is a promising and relevant alternative for monitoring of RR and activity in rodents, thus contributing to the remote assessment of animal welfare.
关键词： vital signs,infrared thermography,respiratory rate,remote monitoring,locomotor activity,motion heat maps,thermal imaging,animal research
更新于2025-09-23 15:21:01