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During the cold period, the heat transferred through the building’s external boundaries to the environment changes the naturally established heat balance between atmospheric air and soil layers. The process of the heat transfer into the ground was investigated experimentally in the cases of the relatively high and low levels of the water table. The first part of each experiment was the research of the heat transfer into the soil from the heating surface. The second part was monitoring the heat dissipation in the ground until the return to the initial natural thermodynamic equilibrium after the heating is intercepted. The heating device was installed into the clay at a one-meter depth, and its surface temperature was kept constant at 20 degrees Celsius. The ground was warmed up in contact with the heating surface. The heat spread to other soil layers and transformed the temperature distribution. A new thermodynamic equilibrium was reached six days after the heating started at an initial temperature of 4.4 degrees Celsius. The intensity of the heat flux density approached a stable value equal to 117.4 W/m2, which is required to maintain this thermodynamic equilibrium, as the heat was dissipating in the large volume of the surrounding soil. The heating was turned off, and the natural initial heat balance was reached after two weeks.

Thermoelectric devices may have an essential role in the development of fuel-saving, environmentallyfriendly, and cost-effective energy sources for power generation based on the direct conversion of heat into electrical energy. A wide usage of thermoelectric energy systems already exhibits high reliability and long operation time in the space industry and gas pipe systems. The development and application of solar thermoelectric generators (TEGs) arelimited mainly by relatively low thermoelectric conversion efficiency. Forthe first time, we propose to use the direct energy conversion of solar energy by TEGs based on the high-performance multilayer thermoelectric modules with electric efficiency of ~15%. Solar energy was absorbed and converted to thermal energy, which is accumulated by a phase-change material (aluminum alloys at solidification temperature ~900 K). The heat flow from the accumulator through the thermoelectric convertor (generator) allows electrical power to be obtained and the exhaust energy to be used for household purposes (heating and hot water supply) or for the operation of a plant for thermal desalination of water.

[EN] Stained-glass windows form an important part of cultural heritage. Short pulse lasers open new opportunities for safe decontamination. In this work, and for the first time, the interaction of sub-nanosecond and femtosecond pulsed lasers with some contemporary stained-glasses has been analyzed exploring their applicability to safely clean stained-glass windows. The results show that, in these materials, damage can be induced using energy levels below damage thresholds due to the heat accumulation in the coating layer that is being eliminated. The latter generates significant thermal stresses on the glass volume, which induce crack formation. In consequence, in order to apply safe stained-glass cleaning protocols, laser parameters have to be selected to control the temperature increase within this layer. To achieve the latter goal, two alternative irradiation procedures were explored in this work. As a first option, a reduction of the effective pulse repetition frequency to values lower than 20 kHz was applied. A second alternative was used for lasers with pulse repetition rates in the hundreds of kHz. In this case, the burst mode was employed controlling the number of pulses emitted and combined with an adequate time lapse selection between two consecutive burst runs. A proof of concept demonstration was carried out on a stained-glass sample from the Cathedral of Cuenca, dated at the end of the XV century., [ES] Las vidrieras constituyen un elemento esencial de nuestro patrimonio cultural. Los láseres de pulsos ultracortos ofrecen nuevas oportunidades para desarrollar procesos de restauración seguros. En este trabajo, por primera vez, se estudia la interacción de láseres pulsados emitiendo pulsos en el rango de los subnanosegundos y femtosegundos con piezas de vidrieras contemporáneas, con el fin de explorar la posibilidad de desarrollar procesos seguros de restauración de vidrieras. Los resultados muestran que, en estos materiales, incluso trabajando con niveles de energía por debajo de los umbrales de daño, se puede generar deterioro por la acumulación de calor generada en la capa que se está eliminando, lo cual puede generar niveles de tensiones térmicas que provocan la ruptura del vidrio. Por tanto, para desarrollar protocolos de limpieza seguros, los parámetros de procesado deben escogerse de tal manera que se minimice la temperatura que se alcanza en esta capa. Se han explorado dos alternativas. Una es reducir la frecuencia de trabajo hasta valores por debajo de los 20 kHz. En el caso de láseres que trabajen a frecuencias más elevadas, la alternativa es trabajar en modo burst, limitando el número de pulsos en cada serie y estableciendo tiempos de espera entre dos series. Estas ideas se han aplicado sobre una pieza de vidriera de la Catedral de Cuenca de finales del siglo XV., This work was supported by European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement N.° 766311. Partial support is obtained from Gobierno de Aragón “Construyendo Europa desde Aragón” (research group T54_20R). The use of Servicio General de Apoyo a la Investigación at the University of Zaragoza is acknowledged. This work has been performed in the framework of the Unidad Asociada de I+D+I al CSIC “Vidrio y Materiales del Patrimonio Cultural (VIMPAC)”, by INMA (CSIC-University of Zaragoza) and University of Burgos.

In case of emergency situations in heat supply systems, the water temperature in the supply line of the system decreases. It is necessary to determine the allowable operational duration of the heating system in case there is an accident, taking into account heat accumulation in exterior building envelopes and the variable flow of water in the hot water supply system. Operational modes of the heat supply system during emergency heat release from the CHP are studied. Factors affecting the thermal regime of buildings with external fences of various levels of heat accumulation are considered. A method is developed for calculating the cooling rate of the inner surface of the outer fence and the temperature on this surface at a given time. Calculated dependences are obtained for determining the permissible operating time of the heat supply system with a limited heat supply.

This paper presents a simple novel mathematical model of a heat accumulator with an arranged packing in the form of ceramic cylinders. The accumulator analysed in the paper can be heated with inexpensive electricity overnight or excess electricity from wind farms. It can be used as a heat source in a hydronic heating system or for domestic hot water. The differential equations describing the transient temperature of the accumulator packing and flowing air were solved using the explicit Euler and Crank–Nicolson methods. The accuracy of both methods was assessed using exact analytical solutions and the superposition method for a uniform initial temperature and accounted for time changes in inlet air temperature. A numerical simulation of the accumulator cooled by flowing air was carried out. The correlation for the air-side Nusselt number was determined using the method of least squares based on experimental data. The calculated exit air temperature was compared with the measured data. The accumulator can operate as a heat source with dynamic discharge. The developed mathematical model of the accumulator can be used in a system to adjust the fan rotational speed so that the air temperature in the room is equal to the preset temperature.

The heat transfer performance of ground heat exchanger is significant to the ground source heat pump. The soil thermal parameters, the groundwater advection and the different borehole field layout are important factors to affect the performance of ground heat exchanger. Therefore, the influence of groundwater advection velocity, soil physical parameters and different borehole field layout on the soil temperature distribution and evolution around the ground heat exchanger has been analyzed and studied with unbalanced seasonal thermal load based on the moving finite line heat source model with groundwater advection. The results show that the heat accumulation is easy to occur as the time develops when the groundwater advection is taken into consideration. No matter what type of geological condition is employed, a reasonable borehole field layout can effectively avoid heat accumulation problems under the condition of keeping the same amount boreholes without changing the original ground area. The borehole field layout dispersed along the center line of the advection and concentrated in the advection downstream relatively can effectively reduce the heat accumulation.

This research work was presented at the: LVIII Congress of the Spanish Society of Ceramics and Glass – Madrid, Spain May 3-6, 2022. Ps and fs lasers wereused to understand the response of stained-glasses to the radiation, analyzing the different levels of damage that the laser can induce on the glass sample (chemical, mechanical or thermal) depending on the laser wavelength. In addition, the adequate selection of the laser parameters that can limit the maximum temperature reached on the glass surface due to heat accumulation, avoiding crack generation due to thermal stresses created during laser cleaning was presented.

The object of research: the process of heat exchange in a packing in the form of a dense layer of crushed stone as part of a thermal regenerator designed to utilize the low-grade heat of the air in a greenhouse. Investigated problem: increasing the efficiency of air heat accumulation in the greenhouse during the daytime by a regenerative heat exchanger with a granular packing. Conducting experimental tests of regenerator models with a packing in the form of a dense layer of granular material under natural conditions is necessary to improve the design and optimize technological parameters. The main scientific results: the analysis of temperature curves of air changes at the inlet and outlet of the regenerator installed in the mock-up greenhouse with a volume of 0.25 m3, and the packing material was carried out. During the heating period of the nozzle, the accumulated heat was Q=8•104 J, which can be used when the temperature in the greenhouse decreases. During the pause, the loss from the heat exchange channel to the environment is 48,000 J. The duration of the period was 358 min, while the average heat flux corresponded to 2.2 W. Heat losses during the pause period are significant due to its duration, however, the average heat transfer coefficient has a low value of k=2.3 W/m2K, so strengthening the insulation of the heat exchange channel is irrational. The area of practical use of the results of the study: greenhouses, allowing the possibility of installing additional heat exchange equipment. Innovative technological product: the innovativeness of the technical solution is determined by the possibility of using the heat of the air in the greenhouse and the implementation of contact heat exchange between the air flow and the packing particles. The design of the regenerator, the simplicity of its manufacture and operation, as well as the efficiency of air heat accumulation in the greenhouse during the daytime, allow to recommend it for use in greenhouse farms. The scope of the innovative technological product: regenerative heat exchangers with a dense layer of granular material for the utilization of low-grade air flows generated in food production enterprises, ventilation systems and greenhouses

The intrinsic heat-affected zone (HAZ) during the microsecond pulsed laser processing significantly affect the surface quality of the fused silica optics. This study employed both three-dimensional numerical simulations and experiments to analyze the heat accumulation effect, morphology evolution mechanism, and the HAZ distribution during CO2 laser processing of fused silica. Simulation results show that with the increases of process parameters such as the laser frequency, the overlap rate, and the pulse width, the residual temperature of the substrate rises gradually. The excessive laser repetition frequency mainly causes the heat accumulation and over-ablation. Analysis of the laser processed surface demonstrates that the superposition of the laser spot energy results in the periodic texture whose spatial internal is equal to the feeding distance of the laser spot. Increasing the track pitch will make the ridges and grooves of the ripple structure discrete, while reducing the laser moving speed within a certain range can improve the surface quality. Besides, the fictive temperature of the substrate tends to stabilize after the third laser pulse in each track. The thickness of the HAZ is close to the material removal depth, but it can be effectively suppressed with a pulse width less than 10 μs. Experiments are conducted to validate the simulation and the results match well with each. This study can provide a theoretical guidance for producing high-quality fused silica optics in high-power laser device applications.

C.R.'s portion of the work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). This work used JASMIN, the UK collaborative data analysis facility. Anthropogenic forcing is driving energy accumulation in the Earth system, including increases in the sensible heat content of the atmosphere, as measured by dry-bulb temperature—the metric that is almost universally used for communications about climate change. The atmosphere is also moistening, though, representing an accumulation of latent heat, which is partly concealed by dry-bulb temperature trends. We highlight that, consistent with basic theory, latent heat gains are outpacing sensible heat gains over about half of the Earth's surface. The difference is largest in the tropics, where global “hotspots” of total heat accumulation are located, and where regional disparities in heating rates are very poorly represented by dry-bulb temperatures. Including latent heat in climate-change metrics captures this heat accumulation and therefore improves adaptation-relevant understanding of the extreme humid heat and precipitation hazards that threaten these latitudes so acutely. For example, irrigation can lower peak dry-bulb temperatures, but amplify latent heat content by a larger margin, intensifying dangerous heat stress. Based on a review of the research literature, our Perspective therefore calls for routine use of equivalent temperature, a measure that expresses the combined sensible and latent heat content of the atmosphere in the familiar units of °C or K. We recognize that dry-bulb air temperature must remain a key indicator of the atmospheric state, not least for the many sectors that are sensitive to sensible heat transfer. However, we assert here that more widespread use of equivalent temperature could improve process understanding, public messaging, and adaptation to climate change. Publisher PDF

This article deals with the possibility of using PCMs in cooling ceiling systems to reduce significantly air temperature fluctuations and energy demands for cooling. The PCM-based cooling ceiling's technical design was performed, and a prototype was realized in this research. The experimental verification of the proposed system was performed to determine the actual parameters in different operational modes and their comparison with the same cooling ceiling system without PCM. The transient simulations in the TRNSYS simulation software were also carried out and validated with experiments. Based on the findings, the complex simulations were performed for application under the specific climatic conditions of Czechia. This work contains a comprehensive approach from the prototype design, through the experiments and partial simulations, to complex simulations based on the specific parameters and an economic evaluation. The results of this work show the ability of the proposed cooling ceiling solution to reduce temperature peaks by up to 3.2 °C, while energy savings can be up to 27%, depending on the air change rate. These results can also help significantly determine the economic feasibility of a PCM-based solution for ceiling cooling systems. © 2021, Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT: LO1303, MSMT-7778/2014, NFP304010Y280; European Regional Development Fund, ERDF: CZ.1.05/2.1.00/19.0376, European Regional Development Fund under the project CEBIA-Tech Instrumentation [CZ.1.05/2.1.00/19.0376]; Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Programme [LO1303 (MSMT-7778/2014)]; project INTERREG V-A [SK-CZ/2019/11, NFP304010Y280]

Formation of Laser Induced Periodic Surface Structures (LIPSS) is a very interesting phenomenon. As the process is now moving towards the industry for the production of functional surfaces, a monitoring technique for online process control is needed. In the present work, the process was investigated for the first time using fast infrared radiometry. An advanced multi-beam laser system with 2601 beams using DOE and 200 W picosecond laser was used. Heat accumulation was measured during the 50 pulses of LIPSS fabrication on steel for fluences from 0.07 to 0.31 J/cm2 and frequency 50 kHz. Interestingly, on the cooling part of the curves, plateaus were observed after each laser pulse, for high pulse energies even double plateaus. The observed shapes of the signal evolution in time represent thermal signature of the LIPSS formation. The results are promising that process control will be feasible by monitoring heat accumulation or plateau length.

Titanium alloy Ti6Al4V is one of the most utilized alloys in the field of additive manufacturing due to the excellent combination of mechanical properties, density and good corrosion behavior. These characteristics make the use of this material particularly attractive for additively manufacturing components with complex geometry in sectors such as aeronautics and biomedical. Selective Laser Melting (SLM), by which a component is fabricated by selectively melting of stacked layers of powder using a laser beam, is the one of most promising additive manufacturing technologies for Ti6Al4V alloy. Although this technique offers numerous advantages, it has some critical issues related to the high thermal gradients, associated with the process, promoting the formation of a metastable martensitic microstructure resulting in high tensile strength but poor ductility of the produced parts. The formation of microstructural defects such as balling and porosity can occur together with the presence of residual stresses that may significantly affect the mechanical characteristics of the component. Specific process parameters and geometries can determine heat accumulation phenomena that result in a progressive decrease in thermal gradients between layers. These heat accumulation phenomena are influenced by the number of layers deposited, but also by the building orientation that, for a given geometry, determines a variation of the deposited surface for each layer. © 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

The present paper deals with the evaluation of the unique design of the thermal energy storage unit and its impact on the overall heat exchange efficiency. The proposed thermal energy storage unit consists of a gyroid thermally conductive structure, the voids of which are filled with sodium acetate trihydrate. The presented concept is focused on the use in the field of heavy machinery, where it is possible to accumulate and re-use waste heat from internal combustion engines from the cooling liquid or lubricating products. The evaluation of designs took place through numerical simulations on three models characterized by different levels of the introduction of the gyroid structure into the design. From the design point of view, the gyroid structure was considered as an object produced by additive manufacturing methods from a thermally conductive filament based on a thermoplastic polymer, which enables considerable simplification of production compared to the use of suitable anti-corrosion metals. A comparison of the essential thermophysical parameters in the process of charging and discharging of the proposed thermal energy storage unit quantified a significant increase in the rate of the charging, respectively, of the discharging process, manifested by a rapid increase in the temperature of the sodium acetate trihydrate volume, respectively, of the output temperature of the heat transfer medium that removes the accumulated heat for further use.

Stained-glass windows play an important role in cultural heritage. Human and environmental factors have subjected these pieces to risks of damage. Mechanical and chemical-based cleaning methods have been used for their restoration and conservation. Additionally, short-pulse lasers have opened new opportunities for safe and controlled cleaning and restoration of these important materials. In this work, ultra-short pulsed lasers were used to clean an artificially applied coating from the surface of a contemporary colorless glass frequently used in the restoration of stained-glass windows. One of the objectives was to explore the applicability of using these types of lasers to safely clean historical stained-glass windows. It was observed that temperature rise and subsequent heat accumulation in the coating layer being removed was sufficient to generate significant thermal stresses on the underlying glass surface leading to damages even when the laser energies are lower than the damage thresholds. Some laser treatments that limit this heat accumulation were designed in this study. For laser systems operating at frequencies in the range of several hundreds of kHz, the option was to work in burst mode, limiting the number of pulses in each burst and selecting an adequate time lapse between two consecutive burst runs. A method to uniformly clean a given surface is proposed in this work. When lower frequencies are available, treatments using frequencies lower than 20 kHz are enough to safely clean the glass. When UV laser radiation is used, optical damage is also an important aspect to be considered. In this case, the cleaning protocol has to deal with both issues, to avoid heat accumulation and chemical damage.

Ultrafast lasers micromachining results depend on both the processing parameters and the material properties. The obtained thermal effects are negligible if a good combination of processing parameters is chosen. However, optimizing the processing parameters leading to the required surface quality on a given material can be quite complex and time consuming. We developed a semi-empirical model to estimate the heat accumulation on a surface as a function of the laser fluence, scanning speed and repetition rate. The simulation results were correlated with experimental ones on different materials, and compared with the transient temperature distributions calculated using an analytical solution to the heat transfer equation. The predictions of the proposed model allow evaluating the heat distribution on the surface, as well as optimizing the ultrafast laser micromachining strategy, yielding negligible thermal damage.

The core carrier working substances of heat accumulation of solar thermal generator units are analyzed through computer numerical simulation analysis and simulation experiments, including the selection criteria of working substances, the mechanism of heat accumulation system, the correlation between power generation efficiency and the evaporation temperature of working substance, the correlation between the condensing temperature and condensing pressure of working substance, and the influence of working substance velocity on heat accumulation capacity. The results show that under the same radiation intensity, the greater the flow velocity of the working substance is, the worse the heat accumulation and heat conduction of the working substance is. As the condensing temperature of the working substance increases, the condensing pressure also increases. As the evaporation temperature of the working substance increases, the power generation efficiency of the working substance also increases significantly. In summary, the heat accumulation system based on the high efficiency working substances is vital for the normal operation of solar thermal generator units. Once the solar radiation intensity cannot meet the needs of power generation, the heat accumulation system will output previously-stored thermal energy. Meanwhile, its collection and release of thermal energy depend on the photovoltaic intensity. The constructed hot-oil working substance-based heat accumulation system satisfies the normal operation needs for thermal generator units, which is significant for subsequent research.

The energy used to melt the material at each layer during laser-directed energy deposition (L-DED) accumulates in the solidified layers upon layer deposition and leads to an increase in the temperature of the part with an increasing number of layers. This heat accumulation can lead to inhomogeneous solidification conditions, increasing residual stresses and potentially anisotropic mechanical properties due to columnar grain structures. In this work, infrared imaging is applied during the directed energy deposition process to capture the evolution of the temperature field in high spatial and temporal evolutions. Image processing algorithms determined the solidification rate and the temperature gradient in the spatial and temporal evolutions and evidenced their change with the proceeding deposition process. Metallographic analysis proves that these changes significantly affect the local grain structure of the L-DED fabricated parts. The study provides comprehensive quantitative measurements of the change in the solidification variables in local and temporal resolutions. The comprehensive comparison of different parameter combinations reveals that applied power, and especially the frequency of the consecutive deposition of the individual layers, are the key parameters to adjusting heat accumulation. These findings provide a methodology for optimising L-DED manufacturing processes and tailoring the local microstructure development by controlling heat accumulation.

Undetected and undesired microstructural variations in components produced by laser powder bed fusion are a major challenge, especially for safety-critical components. In this study, an in-depth analysis of the microstructural features of 316L specimens produced by laser powder bed fusion at different levels of volumetric energy density and different levels of inter layer time is reported. The study has been conducted on specimens with an application relevant build height (&gt, 100 mm). Furthermore, the evolution of the intrinsic preheating temperature during the build-up of specimens was monitored using a thermographic in-situ monitoring set-up. By applying recently determined emissivity values of 316L powder layers, real temperatures could be quantified. Heat accumulation led to preheating temperatures of up to about 600 °C. Significant differences in the preheating temperatures were discussed with respect to the individual process parameter combinations, including the build height. A strong effect of the inter layer time on the heat accumulation was observed. A shorter inter layer time resulted in an increase of the preheating temperature by more than a factor of 2 in the upper part of the specimens compared to longer inter layer times. This, in turn, resulted in heterogeneity of the microstructure and differences in material properties within individual specimens. The resulting differences in the microstructure were analyzed using electron back scatter diffraction and scanning electron microscopy. Results from chemical analysis as well as electron back scatter diffraction measurements indicated stable conditions in terms of chemical alloy composition and austenite phase content for the used set of parameter combinations. However, an increase of the average grain size by more than a factor of 2.5 could be revealed within individual specimens. Additionally, differences in feature size of the solidification cellular substructure were examined and a trend of increasing cell sizes was observed. This trend was attributed to differences in solidification rate and thermal gradients induced by differences in scanning velocity and preheating temperature. A change of the thermal history due to intrinsic preheating could be identified as the main cause of this heterogeneity. It was induced by critical combinations of the energy input and differences in heat transfer conditions by variations of the inter layer time. The microstructural variations were directly correlated to differences in hardness.

This work focuses on the thermal modeling of the Directed Energy Deposition of a composite coating (316L stainless steel reinforced by Tungsten carbides) on a 316L substrate. The developed finite element model predicts the thermal history and the melt pool dimension evolution in the middle section of the clad during deposition. Numerical results were correlated with experimental analysis (light optical and scanning electron microscopies and thermocouple records) to validate the model and discuss the possible solidification mechanisms. It was proven that implementation of forced convection in the boundary conditions was of great importance to ensure equilibrium between input energy and heat losses. The maximum peak temperature shows a slight increase trend for the first few layers, followed by an apparent stabilization with increasing clad height. That demonstrates the high heat loss through boundaries. While in literature, most of the modeling studies are focused on single or few layer geometries, this work describes a multi-layered model able to predict the thermal field history during deposition and give consistent data about the new materiel. The model can be applied on other shapes under recalibration. The methodology of calibration is detailed as well as the sensitivity analysis to input parameters.

Wire-arc additive manufacturing (WAAM) provides an alternative for the production of various metal products needed in medium to large batch sizes due to its high deposition rates. However, the cyclic heat input in WAAM may cause local overheating. To avoid adverse effects on the performance of the part, interlayer dwelling and active cooling are used, but these measures increase the process time. Alternatively, the temperature during the WAAM process could be controlled by optimizing the welding power. The present work aims at introducing and implementing a novel temperature management approach by adjusting the weld-bead cross-section along with the welding power to reduce the heat accumulation in the WAAM process. The temperature evolution during welding of weld beads of different cross-sections is investigated and a database of the relation between optimal welding power for beads of various sizes and different pre-heating temperatures was established. The numerical results are validated experimentally with a block-shaped geometry. The results show that by the proposed method, the test shape made was welded with lower energy consumption and process time as compared to conventional constant-power WAAM. The proposed approach efficiently manages the thermal input and reduces the need for pausing the process. Hence, the defects related to heat accumulation might be reduced, and the process efficiency increased., The International Journal of Advanced Manufacturing Technology, 117 (7), ISSN:0268-3768, ISSN:1433-3015

This study presents a detailed characterization of self-organized nano- and microstructures on Ti6Al4V evoked by different scanning strategies and fluences with a 300 fs laser operating at a laser wavelength of 1030 nm. The resulting surface morphology was visualized via field emission scanning electron microscopy (FEG-SEM) images of the surface and cross-sections. X-ray diffraction (XRD)-analysis was performed to analyse changes in crystal structures. The chemical surface composition of the near-surface layer was determined by X-ray photoelectron spectroscopy (XPS). Results show a significant influence of heat accumulation while processing with high laser repetition rates on the formation, crystallinity and chemical composition of self-organized structures depending on the scanning strategy. The ablation with different laser scanning strategies led to varying dynamics of growth-mechanisms of self-organized structures, formation of intermetallic phases (Ti3Al), sub-oxides and oxides (Ti6O, TiO) as well as ions (Ti3+, Ti4+) in surface layer reliant on applied fluence. Furthermore, investigations revealed a heat-affected zone up to several micrometers in non-ablated material. © 2021 The Authors

Recently, process monitoring emerges as a breakthrough technology in industrial laser machines applications to enhance process stability and economic efficiency while ensuring high-quality pro-cessing parts and significantly reducing scrap rate. Furthermore, the latest advances in monitoring systems open a broad range of new opportunities to increase the capabilities of laser surface structur-ing. In this study, stainless steel and aluminum substrates are structured with a line-like geometry by Direct Laser Interference Patterning. A high-speed infrared camera is used to detect the thermal effects throughout the laser process. Simultaneously, a diffraction measurement system is implemented to analyze the quality of the fabricated periodic patterns by comparing the diffraction order characteris-tics. This specific combination of the systems allows a remarkably high-performance process moni-toring and quality assurance. The obtained results reveal a correlation between the signals detected by the infrared camera and the intensity of the diffraction orders recorded with the quality of the surface reached.

Quartz glass is frequently used for optical components, but traditional machining methods, particularly for aspherical optics, are often associated with long process times and high costs. One possible approach to achieve higher efficiencies and higher speeds in contactless processing is laser ablation using CO2 laser radiation. This study investigates the evolution of surface topography during laser ablation of quartz glass using nanosecond pulses from a Q-switched CO2 laser beam source. The special focus of a broad empirical study lay on ablation depth, ablation rate, ablation efficiency and resulting surface roughness for an ablation process using 300 ns laser pulses at a maximum laser power of 115 W and pulse frequencies up to 150 kHz. Ablation efficiency shows a characteristic logarithmic dependency on laser fluence. It was revealed that local heat accumulation significantly affects the optical penetration depth, which reduces the threshold fluence for multi-pulse laser ablation down to approx. 0.37 J/cm2. Ablation rates of up to 1.48 mm3 min−1 W−1 were achieved, which exceeds results achieved for laser ablation using cw laser radiation or ultra-short pulses. An ablation rate of up to 170 mm3/min is a particularly noteworthy result. Therein, a maximum ablation efficiency of approx. 64% shows that the largest part of the incident laser energy was used for material ablation. Finally, based on a simplified model, numerical calculations and experimental results, pulse stability was identified to have a decisive impact on the evolution of the resulting surface roughness. The resulting surface roughness Sa is typically increased in pulsed laser processing and depends linearly on standard deviation of ablation depth and the square root of the number of ablation layers.

Ultrakrátké pulzní laserové mikroobrábění je ovlivněno akumulací tepla, která je výsledkem zbytkového tepla z předchozích laserových pulzů na povrchu vzorku. Až dosud většina prací analyzovala akumulaci pomocí numerického modelování. Předkládaná práce se zaměřila na vývoj a první použití systému měření teploty akumulace tepla přímo během procesů v časových rozsazích nanosekund a mikrosekund. Měřicí systém byl založen na infračervené radiometrii a obsahoval rychlý fotodetektor HgCdTe chlazený kapalným dusíkem a paraboloidní zrcadla. Mikroobrábění drážek bylo prováděno pomocí 14 W pikosekundového laseru s různými energiemi v pulzu, opakovacími frekvencemi a rychlostmi skenování. Kalibrace měřicího systému byla provedena za účelem získání teplot z měřeného signálu. Kalibrace nebyla jednoduchá kvůli velmi malé laserové stopě (25 μm), malému signálu a změně velikosti vyhřívané oblasti pro nízké rychlosti skenování. Získaná teplota akumulace tepla se pohybovala od 300°C do 2600°C pro rychlosti skenování od 8 m/s do 0,07 m/s a pulzní energie od 0,1 µJ do 100 µJ. Podle obrázků ze skenovacího elektronového mikroskopu (SEM) byl materiál již částečně roztaven (malé kapičky na hranicích) pro nízkou rychlost skenování. Drsnost povrchu a účinnost ablace byly stanoveny pomocí 3D konfokálního laserového mikroskopu. Byla nalezena dobrá korelace mezi drsností a teplotou akumulace tepla, což potvrdilo platnost kalibrace. Naměřená teplota akumulace tepla byla překvapivě nejvyšší pro nejúčinnější ablační parametry a současně byla dosažena nízká drsnost povrchu. Ultrashort pulse laser micromachining is affected by the heat accumulation resulting from the residual heat from previous laser pulses on the sample surface. Up to now, most of the works analysed the accumulation by numerical modelling. The present work focussed on development and application for the first time of a measurement system of heat accumulation temperature directly during the processes in nanosecond and microsecond time ranges. The measurement system was based on the infrared radiometry and contained liquid nitrogen cooled fast HgCdTe photodetector and paraboloid mirrors. Micromachining of grooves was done using a 14 W picosecond laser with different pulse energies, repetition frequencies and scanning speeds. Calibration of the measurement system was done in order to obtain temperatures from the measured signal. The calibration was not straightforward due to very small laser spot (25 μm), small signal and changing of the size of the heated area for low scanning speeds. Obtained heat accumulation temperature ranged from 300°C to 2600°C for scanning speeds from 8 m/s to 0.07 m/s and pulse energies from 0.1 µJ to 100 µJ. According to the scanning electron microscope (SEM) images, the material was already partially melted (small droplets on boarders) for low scanning speeds. Surface roughness and ablation rate were determined by 3D confocal laser microscope. Good correlation was found between the roughness and the heat accumulation temperature, thus confirming the validity of calibration. Measured heat accumulation temperature was surprisingly the highest for the most efficient ablation parameters and at the same time low surface roughness was achieved.

Resumo A transformação de um ambiente natural em um ambiente construído ocasiona a formação de diferentes climas urbanos, de acordo com geometria urbana, materiais e atividades. O objetivo deste artigo é apresentar uma metodologia para se estimar o acúmulo de calor em recintos urbanos, considerando a influência de dez fatores climáticos, avaliados através de uma escala graduada em cinco níveis: acúmulo de calor negativo, nulo, baixo, médio e alto, podendo chegar a um total de seis graus positivos (+6,0 °C), em relação àquele valor verificado na estação meteorológica de referência. A aplicação dessa metodologia, desenvolvida a partir de pesquisas diversas, poderá embasar comparações entre metrópoles e orientar intervenções que visem à satisfação do usuário, à eficiência dos espaços e à sustentabilidade ambiental. Abstract The transformation from a natural environment to a built environment causes the formation of different urban climates, according to urban geometry, materials and activities. The objective of this article is to present a methodology to estimate heat accumulation in urban precincts, according to the influence of ten climatic factors, assessed through values on a scale graduated into five levels: accumulation of negative, null, low, medium and high heat, the latter being able to reach six positive degrees (+6.0°C) in relation to the value verified in the reference meteorological station. The application of this methodology can support comparisons between metropolises and guide interventions aimed at user satisfaction, the efficiency of the built space and environmental sustainability.

The selective surface activation induced by laser (SSAIL) for electroless copper deposition on Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS) blend is one of the promising techniques of electric circuit formation on free-shape dielectric surfaces, which broadens capabilities of 3D microscopic integrated devices (3D-MIDs). The process consists of laser excitation, chemical activation of laser-excited areas by dipping in a liquid and electroless copper deposition of the laser-treated areas. The limiting factor in increasing throughput of the technology is a laser activation step. Laser writing is performed by modern galvanometric scanners which reach the scanning speed of several meters per second. However, adverse thermal effects on PC/ABS polymer surface abridge the high-speed laser writing. In this work, an investigation was conducted on how these thermal effects limit surface activation for selective metal deposition from the view of physics and chemistry. An advanced laser beam scanning technique of interlacing with precise accuracy and the pulse-on-demand technique was applied to overcome mentioned problems for fast laser writing. Initially, the modelling of transient heat conduction was performed. The results revealed a significant reduction in heat accumulation. Applied methods of laser writing allowed the overall processing rate to increase by up to 2.4 times. Surface morphology was investigated by a scanning electron microscope. Energy-dispersive X-ray spectroscopy was used to investigate the modification of atomic concentration on the surface after laser treatment. Experiments did not show a correlation between surface morphology and electroless plating on laser-treated areas. However, significant variation in the composition of the material was revealed depending on the surface activity for electroless plating.

The results of the development of a regenerative-type heat exchange unit for greenhouses are presented. The creation of a soil regenerator is conditioned by energy and economic expediency. In spring in the daytime, the air in greenhouses is intensely heated by solar radiation, and at night it can be cooled below the allowable temperature. Heat accumulation during the day and using this heat at night will reduce the need for heaters even to their complete exclusion. The soil regenerator contains a dense layer of granular material that is blown through by the air from the inner space of a greenhouse. This solution makes it possible to intensify significantly the heat exchange. To determine the mean intercomponent heat exchange factor, the empirical dependence, taking into consideration the effect of duration of the heat exchange process, was obtained. We developed the procedure of thermal design calculation of a regenerator, using which the main geometric characteristics of the heat exchange area are determined. The results of the calculation of the soil regenerator for a greenhouse with the surface area of 18 m2 for the conditions of the warm continental climate were presented. The developed soil regenerator contains 5 channels that are 5.75 m long, filled with rubble. It was obtained that for the average solar radiation flow Qc=2,160 W and the duration of operation of the soil regenerator τΣ=6 hours, the accumulated heat at night can be consumed for 2.6 hours at the average ambient temperature t1=7 °C. As the ambient temperature rises, the time of regenerator operation will increase. The proposed soil regenerator is characterized by the design simplicity and its application will lead to an increase in energy costs to maintain the temperature mode in a greenhouse, Представлены результаты разработки теплообменного аппарата регенеративного типа для теплиц. Создание грунтового регенератора обусловлено энергетической и экономической целесообразностью. В весенний период в дневное время воздух в теплицах интенсивно нагревается от солнечного излучения, а в ночное может охладиться ниже допустимой температуры. Аккумуляция теплоты в дневное время и использование этой теплоты в ночное время снизит необходимость в подогревателях вплоть до полного их исключения. Грунтовой регенератор содержит плотный слой гранулированного материала, который продувается воздухом из внутреннего пространства теплицы. Такое решение позволяет существенно интенсифицировать теплообмен. Для определения среднего коэффициента межкомпонентного теплообмена получена эмпирическая зависимость, учитывающая влияние продолжительности процесса теплообмена. Разработана методика теплового конструкторского расчета регенератора, в результате которой определяются основные геометрические характеристики теплообменного участка. Представлены результаты расчета грунтового регенератора для теплицы с площадью поверхности 18 м2 для условий теплого континентального климата. Разработанный грунтовой регенератор содержит 5 каналов длиной 5,75 м, заполненных щебнем. Получено, что для среднего потока солнечного излучения Qc=2160 Вт и длительности работы грунтового регенератора τΣ=6 часов аккумулированная теплота может в ночное время расходоваться в течение 2,6 часа при средней температуре окружающей среды t1=7 °C. При повышении температуры окружающей среды время работы регенератора будет увеличиваться. Предлагаемый грунтовой регенератор характеризуется простотой конструкции, а его применение приведет к снижению затрат энергии на поддержание температурного режима в теплице, Представлені результати розробки теплообмінного апарату регенеративного типу для теплиць. Створення ґрунтового регенератора обумовлено енергетичною та економічною доцільністю. У весняний період в денний час повітря в теплицях інтенсивно нагрівається від сонячного випромінювання, а в нічний може охолодитися нижче припустимої температури. Акумуляція теплоти в денний час і використання цієї теплоти в нічний час знизить необхідність в підігрівачах аж до повного їх виключення. Ґрунтовий регенератор містить щільний шар гранульованого матеріалу, що продувається повітрям з внутрішнього простору теплиці. Таке рішення дозволяє істотно інтенсифікувати теплообмін. Для визначення середнього коефіцієнта міжкомпонентного теплообміну отримана емпірична залежність, що враховує вплив тривалості процесу теплообміну. Розроблено методику теплового конструкторського розрахунку регенератора, в результаті якої визначаються основні геометричні характеристики теплообмінної ділянки. Представлені результати розрахунку ґрунтового регенератора для теплиціз площею поверхні 18 м2для умов теплого континентального клімату. Розроблений ґрунтовій регенератор містить 5 каналів довжиною 5,75 м, заповнених щебенем. Отримано, що для середнього потоку сонячного випромінювання Qc=2160 Вт і тривалості роботи ґрунтового регенератора τΣ =6 годин акумульована теплота може в нічний час витрачатися протягом 2,5 годин при середній температурі навколишнього середовища t1=7 °C. При підвищенні температури навколишнього середовища час роботи регенератора буде збільшуватися. Запропонований ґрунтовийрегенератор характеризується простотою конструкції, а його використання призведе до зниження витрат енергії на підтримку температурного режиму в теплиці

The results of the development of a regenerative-type heat exchange unit for greenhouses are presented. The creation of a soil regenerator is conditioned by energy and economic expediency. In spring in the daytime, the air in greenhouses is intensely heated by solar radiation, and at night it can be cooled below the allowable temperature. Heat accumulation during the day and using this heat at night will reduce the need for heaters even to their complete exclusion. The soil regenerator contains a dense layer of granular material that is blown through by the air from the inner space of a greenhouse. This solution makes it possible to intensify significantly the heat exchange. To determine the mean intercomponent heat exchange factor, the empirical dependence, taking into consideration the effect of duration of the heat exchange process, was obtained. We developed the procedure of thermal design calculation of a regenerator, using which the main geometric characteristics of the heat exchange area are determined. The results of the calculation of the soil regenerator for a greenhouse with the surface area of 18m2for the conditions of the warm continental climate were presented. The developed soil regenerator contains 5channels that are 5.75m long, filled with rubble. It was obtained that for the average solar radiation flow Qc=2,160W and the duration of operation of the soil regenerator τΣ=6hours, the accumulated heat at night can be consumed for 2.6hours at the average ambient temperature t1=7°C. As the ambient temperature rises, the time of regenerator operation will increase. The proposed soil regenerator is characterized by the design simplicity and its application will lead to an increase in energy costs to maintain the temperature mode in a greenhouse

This study aimed to understand the effect of heat accumulation on microstructure formation on STS 316L during multilayer deposition by a laser metal deposition (LMD) process and to predict the microstructure morphology. A comprehensive experimental and numerical study was conducted to quantify the solidification parameters (temperature gradient (G) and growth rate (R)) in the LMD multilayer deposition process. During deposition, the temperature profile at a fixed point in the deposit was measured to validate the numerical model, and then the solidification parameters were quantified using the model. Simultaneously, the microstructure of the deposit was investigated to confirm the microstructure morphology. Then, a relationship between the microstructure morphology and the G/R was proposed using a solidification map. The findings of this study can guide the design of scanning paths to produce deposits with a uniform structure.

A shifted laser surface texturing method (sLST) was developed for the improvement of the production speed of functional surface textures to enable their industrial applicability. This paper compares the shifted method to classic methods using a practical texturing example, with a focus on delivering the highest processing speed. The accuracy of the texture is assessed by size and circularity measurements with the use of LabIR paint and by a depth profile measurement using a contact surface profiler. The heat accumulation temperature increase and laser usage efficiency were also calculated. The classic methods (path filling and hatch) performed well (deviation &le, 5%) up to a certain scanning speed (0.15 and 0.7 m/s). For the shifted method, no scanning speed limit was identified within the maximum of the system (8 m/s). The depth profile shapes showed similar deviations (6% to 10%) for all methods. The shifted method in its burst variant achieved the highest processing speed (11 times faster, 146 mm2/min). The shifted method in its path filling variant achieved the highest processing efficiency per needed laser power (64 mm2/(min&middot, W)), lowest heat accumulation temperature increase (3 K) and highest laser usage efficiency (99%). The advantages of the combination of the shifted method with GHz burst machining and the multispot approach were described.

We report on a comprehensive study of laser percussion microvia drilling of FR-4 printed circuit board material using ultrashort pulse lasers with emission in the green spectral region. Laser pulse durations in the pico- and femtosecond regime, laser pulse repetition rates up to 400 kHz and laser fluences up to 11.5 J/cm2 are applied to optimize the quality of microvias, as being evaluated by the generated taper, the extension of glass fiber protrusions and damage of inner lying copper layers using materialography. The results are discussed in terms of the ablation threshold for FR-4 and copper, heat accumulation and pulse shielding effects as a result of pulse to pulse interactions. As a specific result, using a laser pulse duration of 2 ps appears beneficial, resulting in small glass fiber protrusions and high precision in the stopping process at inner copper layer. If laser pulse repetition rates larger than 100 kHz are applied, we find that the processing quality can be increased by heat accumulation effects.

The time to complete fatigue tests can be rather long, especially with high cycle fatigue. Increasing frequency in fatigue tests decreases the time needed to complete material characterisation. For rubber materials, considerable internal heat generation and relatively low thermal conductivity causes temperature rises that can greatly reduce fatigue lifetime. Based on both experimental tests under fully relaxing uni-axial loading conditions on a non-crystallising rubber compound and numerical simulations, a method for estimating test temperature and isothermal fatigue life curves is presented. The results of the comparison between measured and estimated surface temperature of the specimen show that the maximum estimation error is below 10 %.

This article discusses the influence of passive solar systems auxiliary mounted in office building on thermal comfort. Applicable measurement methods are compared on real passive solar systems including the elimination and correction of instrumentation uncertainities. The main chapter deals with results of long time measurements performed on various types of passive solar systems applied on model office rooms. Ideal passive system assessment and evolution of optimal operation mode is explained as the main contribution of this research.

In recent decades, the focus of research has shifted towards new production technologies with the aim of optimizing production and reducing costs. These innovative technologies include additive manufacturing processes as Selective Laser Melting (SLM). The analysis of the literature on the identification of optimal building orientation to maximize the mechanical properties and minimize porosity of the final products highlights contrasting results, denoting that the thermomechanical complexity of the process, as associated with the variation of the building orientation, has not been fully clarified. A study in which the building orientation effect was evaluated together with the geometry of the sample and characterized as a function of the preferentially active heat exchange phenomena was carried out with the aim to provide guidelines for the choice of the orientation angle. Heat accumulation phenomena observed in SLM were taken into account to define three geometrical parameters able to identify the causes of the decrease of mechanical properties due to incorrect choice of the orientation angle.

CMT welding sources are garnering attention as alternative heat sources for wire arc additive manufacturing because of their low-heat input. A comprehensive experimental and numerical study on the multi-layer deposition of STS316L was performed to investigate effect of heat accumulation during the deposition. The numerical model which is appropriate for WAMM was developed considering the characteristics of the CMT heat source for the first time. Using a high-speed camera, the transient behavior of the CMT arc was investigated, and applied to the heat source of the numerical model. The model was then used to analyze 10-layered deposits of STS316L, fabricated using CMT-based WAAM. During deposition, the temperature is measured using a pyrometer to analyze the microstructure, after which the cooling rate of each layer is estimated. The measured and simulated SDAS were compared. Based on the comparison, a guideline for the equation regarding the SDAS size and cooling rate was suggested.

Metallic samples with unique micro- and nano-scale surface structures can easily be fabricated with Direct Laser Interference Patterning. Like in all laser processes, the material interacts with the laser radiation and as a result, thermal effects occur. These effects have a significant influence on the resulting quality of the surface patterns. In this study, the thermal effects occurring during Direct Laser Interference Patterning of stainless steel and aluminum sheets are investigated. The used experimental setup consisted of a picosecond pulsed laser source operating at 532 nm wavelength, combined with a two-beam interference optical head. An infrared camera in an off-axis position is used to detect the resulting thermal radiation of the laser process varying different process parameters such as laser power and repetition rate. The obtained results reveal a correlation between the recorded signal by the infrared camera and the reached surface quality. They show an impact of the thermal effects on the quality of the surfaces and the amount of solidified material on the resulting line-like pattern. Threshold values of the detected infrared signal detected are determined to classify the obtained surface conditions.

Ultrashort pulse (USP) laser processing with pulse durations below 10 ps enables laser structuring with good surface quality, highest precision and low thermal load for the processed workpieces. How-ever, when it comes to scale up the productivity of such processes by increasing the average power, accumulation of the remaining residual energy gets relevant and can influence the processing results significantly. For instance, heat accumulation can induce distinct melt layers. Thus the melt-free, high precision ablation, which is the main advantage of USP processing, is compromised. This is especially pronounced for high repetition rate processes. For a better insight into this effect, the development of the workpiece temperature during USP ablation processes is measured with a thermographic system. With this setup, the residual energy is determined and changes of the heat input during the processing time are identified. These changes are attributed to changes of the surf ace roughness during the processes within this work. Furthermore, the validity of simple physical model considerations is discussed.

Metoda posuvného laserového texturování povrchu (sLST) byla vyvinuta pro zlepšení produkční rychlosti funkčních textur a k jejich průmyslové využitelnosti. Tento článek porovnává metodu sLST s klasickými metodami na praktickém příkladu strukturování se zaměřením na dosažení nejvyšší rychlosti zpracování. Přesnost textury je hodnocena měřením velikosti a kruhovitosti spotu (s použitím LabIR barvy) a měřením hloubkového profilu pomocí kontaktního profilometru. Byly vypočteny zvýšená teplota tepelné akumulace a účinnost využití laseru. Klasické metody (vyplňování po křivkách a šrafování) fungovaly dobře (odchylka ≤ 5 %) až do určité skenovací rychlosti (0,15 a 0,7 m/s). Pro metodu sLST nebyl nalezen žádný limit způsobený skenovací rychlostí do maxima systému (8 m/s). Tvary hloubkového profilu vykazovaly pro všechny metody podobné odchylky (6 % až 10 %). Metoda sLST v dávkové variantě dosáhla nejvyšší rychlosti zpracování (11x rychlejší, 146 mm2/min). Metoda sLST ve variantě vyplňování po křivkách dosáhla nejvyšší účinnosti zpracování na potřebný výkon laseru (64 mm2/(min·W)), nejnižší zvýšení teploty akumulace tepla (3 K) a nejvyšší účinnost využití laseru (99 %). Byly popsány výhody kombinace posuvné metody s GHz dávkovým obráběním a s použitím mnoha laserových stop. Shifted laser surface texturing method (sLST) was developed for increasing of production speed of functional surface textures to enable their industrial applicability. In this work, the shifted method is compared with classic methods on real texturing example with focus on achieving highest processing speed. The texture accuracy is assessed by size and circularity measurement with use of LabIR paint and by depth profile measurement using contact surface profiler. Heat accumulation temperature difference was also calculated. The classic methods (path filling and hatch) performed well (deviation ≤ 5%) up to certain scanning speed (0.15 and 0.7 m/s). For the shifted method, no scanning speed limit was found up to the maximum of the system (8 m/s). The depth profile shapes showed similar deviations (6 to 10%) for all methods. The shifted method in burst variant achieved highest processing speed (11 times faster, 146 mm2/min). The shifted path method achieved highest processing efficiency per needed laser power (64 mm2/(min·W)). The heataccumulation was minimal for the shifted path method (3 K). Laser usage efficiency of different methods was compared. The shifted path method (99% efficiency) is very promising. Its advantages in combination with GHz burst machining and multibeam were highlighted.

Cold metal transfer (CMT) has been widely used in metal additive manufacturing for its low heat input, less splashing and high efficiency. Wire feeding speed and travelling speed are important processes that affect morphology in CMT deposition. This study optimized the forming process of 30-layer stainless-steel part deposited by double-wire and double-arc CMT plus pulse (CMT+P) process, and investigated the effect of the ratio of wire feeding speed to travelling speed on deposition morphology. The results show that asynchronous arc striking and extinguishing can improve the forming. Moreover, the deposition molding is affected by the interaction of heat input and heat accumulation. With the similar ratio of wire feeding speed to travelling speed and the similar heat input, increasing the wire feeding speed can increase the heat accumulation and the width of sample, and decrease the height. The optimum process interval of wire feeding speed to travelling speed ratio and heat input is 3.9&ndash, 4.2 and 70&ndash, 74.8 J/mm, respectively. Although the increasing heat accumulation makes grain coarse and slight decreases mechanical property, the highest deposition rate can be up to 5.4 kg/h, when wire feeding speed and travelling speed are 5 m/min and 120 cm/min, respectively, and the tensile strength and elongation rate of which can reach the basic standard requirements for stainless-steel forgings.

Changes in climate, which in recent years have become more and more visible all over the world, have forced scientists to think about technologies that use renewable energy sources. This paper proposes a passive solar heating and cooling system, which is a Trombe wall located on the southern facade of a room measuring 4.2 m &times, 5.2 m &times, 2.6 m in Wrocław, Poland. The studies were carried out by conducting a series of numerical simulations in the Ansys Fluent 16.0 environment in order to examine the temperature distribution and air circulation in the room for two representative days during the heating and cooling period, i.e., 16 January and 15 August (for a Typical Meteorological Year). A temperature increase of 1.11 &deg, C and a temperature decrease in the morning and afternoon hours of 2.27 &deg, C was obtained. Two options for optimizing the passive heating system were also considered. The first involved the use of triple glazing filled with argon in order to reduce heat losses to the environment, and for this solution, a temperature level that was higher by 8.50 &deg, C next to the storage layer and an increase in the average room temperature by 1.52 &deg, C were achieved. In turn, the second solution involved changing the wall material from concrete to brick, which resulted in a temperature increase of 0.40 &deg, C next to the storage layer.

V prvem delu diplomskega dela so predstavljene teoretične osnove akumulacije toplote in opis delovanja fazno spremenljivih snovi (FSS). Prikazana je njihova razdelitev ter našteti osnovni kriteriji, ki jih moramo poznati pri izbiri FSS materiala. Opisani so pogosti problemi, ki so značilni za določeno vrsto FSS, ter kako se lahko le-tem izognemo. V teoretičnem delu so prav tako na kratko opisane metode za določevannje termičnih lastnosti in predstavljene so še vrste latentnih akumulatorjev toplote z izmenjavo toplote na notranjih površinah. V drugem delu smo preučevali vpliv števila ciklov obratovanja fazno spremenljive snovi na termične lastnosti izbranega FSS materiala, in sicer magnezijevega klorida heksahidrata. FSS smo segrevali do 160 ºC in ohlajali do 50ºC za 30 faznih sprememb. Temperaturo tališča in izgubo mase smo določili z TGA/DSC1 analizo. Ugotovili smo, da se temperatura tališča in temperatura kristalizacije minimalno spreminjata. Potrdili smo dejstvo, da pride do nekongurentnega taljenja in do podhlajevanja, kar predstavlja največji problem. Prav tako smo ugotovili, da izguba mase po vsaki fazni spremembi ne vpliva na temperaturo tališča. Izkazalo se je, da je magnezijev klorid heksahidrat ugoden FSS material za akumulacijo toplote, še posebno, če upoštevamo dejstvo, da je problem podhlajevanja možno zmanjšati. Na koncu smo želeli prikazati še, kako bi izgledal FSS akumulator toplote, ki je tipa s prenosnikom toplote. The first part of the thesis presents the theoretical bases of heat accumulation and the description of the operation of phase change materials (PCM). Listed is their distribution and the basic criteria we need to know when choosing PCM materials. Common problems specific to a particular type of PCM are described, and how they can be avoided. The theoretical part also briefly describes methods for determining thermal properties and presents types of latent heat accumulators with heat exchange on internal surfaces. In the second part, the influence of the number of cycles of phase change materials operation on the thermal properties of the selected PCM material, namely magnesium chloride hexahydrate, was studied. The PCM was heated to 160ºC and cooled to 50ºC for 30 phase changes. Melting point and mass loss were determined by TGA / DSC1 analysis. It was found that the melting point and crystallization temperature varied minimally. We confirmed the fact that incongruently melting and subcooling occur, which is the biggest problem. We also found that the mass loss after each phase change did not affect the melting point. Magnesium chloride hexahydrate has proven to be a favorable PCM material for heat accumulation, especially given the fact that the problem of subcooling can be reduced. Finally, we wanted to show you what the PCM heat accumulator looks like with a heat exchanger.

This paper presents an analysis of thermal interaction between a building and surrounding soil. The examined building was located in southern Poland. Measurements of selected indoor and outdoor air temperature parameters were made in order to determine the boundary conditions. The soil temperature measurements were conducted at 42 points. The analysis of results is divided into four periods: summer, autumn, winter, and spring. The analysis show that weather conditions significantly affect the temperature in soil, but the range of residential building impact decreases with distance, and it varies depending on the season. The residential building impact on the soil temperature is in the range of 1.2−3.3 m. This paper also includes a study of the heat flow direction in soil and a quantitative estimate of heat exchange between a building and the soil. The greatest energy losses 2082 kWh (21.24 kWh/m2) from the building to the soil were recorded in winter. In spring, the energy losses were reduced by about 38% as compared with the energy losses in winter, and the energy losses in spring were comparable to autumn.

Aim: While it is well recognised that climate can vary spatially so that grapevine phenology significantly varies within a winegrowing region, the magnitude of temporal variability in climate determining factors to engender a significant difference in phenology over time can only currently be described in general terms. This study’s aim was to quantify and compare the temporal variability, and its interaction with spatial variability, in grapevine phenology and three derived viticulture climate indexes for three viticulture regions in eastern Australia with varying topographies, latitudes and continentalities.Methods and Results: Maximum and minimum temperature data were spatially interpolated to produce fine scale topoclimate maps at 30 m resolution for every day of a 20 year period from 1998 to 2018 for the three viticulture regions. Grapevine phenology modelling using a heat accumulation methodology was then applied to estimate growing season temperature, cool night index and post-harvest growing degree days (GDD) for every 30 m map pixel of the three regions in each of the 20 growing seasons.Conclusions: Summary statistics that quantify the spatial and year-to-year temporal variability and the interaction of spatial and temporal variability (i.e. spatiotemporal variability) demonstrated significant differences in grapevine phenology between each of three regions. The key conclusion was that within-region temporal variability in growing season temperature, cool night index and post-harvest GDD exceeded within-region spatial variability.Significance and impact of the study: This is the first study to quantify temporal variability in modelled grapevine phenology, compare this with the level of spatial variability and also consider the interaction of spatial and temporal variability in grapevine phenology within viticultural regions. This study opens many potential lines of further investigation into the effect of temporal variability on wine production and the cultural terroir factors that develop within a wine region as a result, particularly in the context of forecast future increases in inter-annual temperature variability.

Fruit and nut trees production is an important activity across the southwest United States and this production is greatly impacted by the local climate. Temperature is the main environmental factor influencing the growth and the productivity of the fruit and nut trees as it affects the trees’ physiology and the vulnerability of flower bud, flowers, and young fruit and nut to the low temperatures or spring frost. The objective of the present study is to estimate the chilling and heat accumulation of fruit and nut trees across New Mexico. Three study sites as Fabian Garcia, Los Lunas, and Farmington were considered and climate variables were collected at hourly time step. The Utah model and the Dynamic model were used to estimate the accumulated chilling while the Forcing model was used for the heat accumulation. The possible fruit and nut trees endodormancy and ecodormancy periods were also determined at the study sites. The results obtained chilling hours of 715 ± 86.60 h at Fabian Garcia, 729.53 ± 41.71 h at Los Lunas, and 828.95 ± 83.73 h at Farmington using the Utah model. The accumulated chill portions during trees’ endodormancy was 3.12 ± 3.05 CP at Fabian Garcia, 42.23 ± 5.08 CP at Los Lunas, and 56.14 ± 1.84 CP at Farmington. The accumulated heat was 8735.52 ± 1650.91 GDH at Fabian Garcia, 7695.43 ± 212.90 GDH at Los Lunas, and 5984.69 ± 2353.20 GDH at Farmington. The fruit and nut trees are at no risk of bud flowers vulnerability at Fabian Garcia while they are under high risk of bud flowers and or young fruit and nut vulnerability to low temperatures early spring as hourly temperature can still drop below 0 °C in April at the end of ecodormancy and flower blooming and young fruits and nuts development stage at Los Lunas and Farmington. Severe weather, especially frost conditions during winter and early spring, can be a significant threat to sustainable nut and fruit production in the northern New Mexico while high chilling requirement fruit and nut trees might not meet chill requirements in the southern New Mexico.

In this study, the two key factors affecting the thermal performance of the insert rubber and stress distribution on the tire sidewall were analyzed extensively through various performance tests and simulations to promote the development of run-flat tires. Four compounds and two structures of insert rubber were designed to investigate the effects of heat accumulation and stress distribution on durability testing at zero pressure. It was concluded that the rigidity and tensile strength of the compound were negatively correlated with temperature. The deformation was a key factor that affects energy loss, which could not be judged solely by the loss factor. The stress distribution, however, should be considered in order to avoid early damage of the tire caused by stress concentration. On the whole, the careful balance of mechanical strength, energy loss, and structural rigidity was the key to the optimal development of run-flat tires. More importantly, the successful implementation of the simulations in the study provided important and useful guidance for run-flat tire development.

This study investigates the impact of bunch microclimate on the evolution of some relevant carotenoids in Nebbiolo grapes. Four bunch-zone microclimates, defined by different vineyard aspect and vine vigor, were characterized by radiation and temperature indices. Berry samples were collected from green phase up to harvest, during two consecutive seasons and carotenoid determination was assessed by High-Performance Liquid Chromatography (HPLC). High carotenoid concentrations were highlighted in Nebbiolo. Lutein and neoxanthin contents (&mu, g berry&minus, 1) varied similarly in both seasons achieving a concentration peak after veraison especially in the cooler plots while a variety effect on the lutein seasonal trend was presumed. Conversely, &beta, carotene content remained generally constant during ripening, with the exception of the south plots showing dissimilar evolution between the seasons. Furthermore, higher temperature in the less vigorous and south facing vineyards led to lower amounts of carotenoids, both during ripening and at harvest. Bunch zone temperature and light condition may affect both synthesis and degradation of grape carotenoids determining their amount and profile at harvest. These findings add further knowledge about the influence of climate changes on grape aroma precursors, and are useful to adapt cultural strategies and preserve grape quality consequently.

Heat accumulation due to successive laser pulse (HAP) incident on the same spot and heat accumulation due to successive scans (HAS) of the laser beam over the same spot significantly influences the process result, especially when the resulting temperature of the workpiece exceeds the melting temperature. In particular, heat accumulation is one of the dominating effects during short-pulse laser functionalization of surfaces and strongly affects the resulting surface structures. Within this study, a novel heat accumulation model is introduced to calculate the temperature increase in the workpiece for the whole process including the effects of HAP and HAS in which the latter is differentiated between heat accumulation due to multiple passes (HAS-I) and heat accumulation due to multiple layers (HAS-II). With the new model, the surface structure was successfully predicted when using an ultra-short pulsed (USP) laser with an average power of 420W for laser surface structuring of polished AISI 316L.

Small-sized space debris objects pose a challenging threat for space security: Within a size range of 1 to 10 centimeters they are still large enough to cause severe damage to space assets but, moreover, they are almost too small to be detected and monitored. Recent progresses in laser-based debris monitoring yield promising results in detection and tracking of debris objects and enable for the short-term solution of obstacle avoidance maneuvers. For the long run, however, it has to be analyzed whether and how the usage of high energy lasers can provide for a reliable solution of the space debris problem in the abovementioned particle size range. Laser-based space debris removal concepts have been around for decades now. Nevertheless, practical implementation is still connected to great technological risks. Most of the concepts plan to utilize the laser ablative process at the target. To investigate this common aspect in detail and to reduce the risk of misleadingly extrapolating parameters, we now experimentally investigated the generation of impulse under realistic conditions as to be expected in a real space scenario. A Nd:YAG based, 10 ns pulsed MOPA laser system providing a pulse energy of 80 J was weakly focused to a diameter of 3 cm onto debris-like targets with different sizes, shapes and materials. The target masses ranged between 1 g to 3 g, indeed representing dangerous objects, and were in free fall within a vacuum during single pulse irradiation. High speed 3Dtracking was applied to deduce the kinetic properties induced by the ablation process. Finally, the data was compared to raytracing based simulation results. Differences between materials and mechanical dynamics are discussed. In simulations we explore operational safety issues as well as both potential and limitations of laser-ablative momentum generation, in particular with respect the accumulation of residual heat from the ablation process. For this purpose, we use Monte Carlo simulations in order to analyze how restrictions in laser pointing accuracy as well as random target orientation affect the predictability of laser-ablative momentum generation. Moreover, pulse number restrictions are discussed in order to avoid target melting and its compactification.