Low External Temperatures Research Articles

Temperature tunable broadband filter based on hybridized vanadium dioxide (VO2) metasurface

Abstract In this paper, a novel temperature tunable terahertz (THz) broadband filter based on hybridized vanadium dioxide (VO2) metasurface (MS) was proposed. The designed MS is composed of subwavelength metallic square-grid structure situated between two layers of metallic square-patch structure integrated with VO2 film pad spaced with two layers of dielectric substrate. Utilizing the insulator-metal phase transition characterizations of VO2 in the THz regime, the operation mode of the proposed MS filter accomplishes the broadband transmission-to-reflection transition. Simulation results show that when VO2 is in the insulating state with a lower external temperature, the proposed MS behaves like a broadband filter with transparent window and a transmittance of above 80% over the frequency range of 0.66–1.12 THz. However, when VO2 undergoes the metallic state with a higher external temperature, the MS becomes a broadband filter with low-transmission shielding and exhibiting a transmittance of below 10% across the frequency spectrum from 0.56 THz to 1.4 THz. The physical mechanism of the proposed MS based tunable broadband filter is illustrated by introducing impedance matching theory, equivalent circuit model and field analysis. In addition, the proposed MS structure offers exceptional angular stability and polarization insensitivity, opening up new opportunities for the utilization of energy selective surface in THz applications.

On-Site Application of End-Grain Bonded Timber Under Low Curing Temperatures

The end-grain bonding of timber components using the Timber Structures 3.0 technology (TS3) is an advancing construction method in timber engineering. This technology allows the realisation of any plate size by bonding plates on-site where low temperatures influence the performance. Therefore, investigations are underway to evaluate the influence of the low temperatures on the curing process. Additionally, research is in progress to discover techniques to reduce any adverse effects of low curing temperatures on the mechanical properties of the bond. The implementation of particular measures, such as the inclusion of milled heating wires into the joint and the pre-heating of the joint with a hot air blower, has been identified as advancing the potential for grouting even in the face of low external temperatures, as recent research has indicated.

From suicide to accident – Case report – The significance of the medico-legal autopsies

IntroductionSuicide is the intentional and voluntary act of destroying one's own life, while an accident is an unintended event that involuntarily causes injury to one's health or destruction of life. Case presentationWe report a case of a 54-year-old male who was found in a forest in late November, approximately 500 m away from his car. He was positioned bent over a trunk of a tree with his head beneath the rest of his body. His pants were down to his knees, and there were soiled blades of grass and leaves on his body. Investigation of the case circumstances revealed that he had attempted suicide by carbon monoxide poisoning, using a hose connected to the exhaust pipe and running it through the window into the cabin. Window on the driver’s side was broken with glass particles on the driver's seat. Wrappers from “Rivotril” tablets, a generic benzodiazepine, were also found in the car.Autopsy revealed the following: postmortem hypostasis was of a cherry red color and well pronounced on the upper part of the front of the body and face. Numerous bruises, contusions, and erosions were present all over the body. Frostbites were especially pronounced in the knees and elbows area. The synovial membranes were partially bloodstained and reddish in color. Opening the stomach revealed erosions of the gastric mucosa (Wischnewsky sign).Chemical toxicological analysis detected presence of benzodiazepines and carboxyhemoglobin (25%). ConclusionBased on the autopsy findings, chemical toxicological analyses, and investigation of the case circumstances, it has been concluded that the death occurred due to the combined effects of hypothermia, postural asphyxia and carboxyhemoglobin and benzodiazepine intoxication. The manner of death in this case is a combination of accidental and suicidal, as the victim attempted suicide but ultimately died due to exposure to low external temperature.

Seasonal and fasting induced changes in iron metabolism in Djungarian hamsters

Djungarian hamsters are small rodents that show pronounced physiological acclimations in response to changes in photoperiod, and unfavorable environmental conditions such as reduced food availability and low external temperature. These include substantial adjustments, such as severe body weight loss and the use of daily torpor. Torpor is a state of decreased physiological activity in eutherms, usually marked by low metabolic rate and a reduced body temperature. In this study, we investigated the effects of photoperiodic acclimation and food deprivation on systemic iron metabolism in Djungarian hamsters. Our study illustrates the association between liver iron levels and the incidence of torpor expression during the course of the experiment. Moreover, we show that both, acclimation to short photoperiods and long-term food restriction, associated with iron sequestration in the liver. This effect was accompanied with hypoferremia and mild reduction in the expression of principal iron-hormone, hepcidin. In addition to iron, the levels of manganese, selenium, and zinc were increased in the liver of hamsters under food restriction. These findings may be important factors for regulating physiological processes in hamsters, since iron and other trace elements are essential for many metabolic and physiological processes.

An analysis of the periodic counterflow heat exchanger for air-to-air heat recovery ventilators

The proper operation of the ventilation system under very low external air temperature is still a great challenge. Due to the icing of the ventilation unit, maintaining appropriate air parameters in rooms during the winter period typically requires additional external energy for the devices. In this research work, a unique system with a periodic counterflow heat exchanger was presented. The proposed system characterized by a high efficiency of heat and moisture recovery operates continuously, regardless of the prevailing external weather conditions. An experimental and numerical analysis of the periodic counterflow heat exchanger for air-to-air heat recovery ventilators was carried out to verify and determine the key parameters of the system operation. It has been shown that simple modification of a typical counterflow heat exchanger allows moisture recovery from the extract air. The developed model of the proposed solution allowed for a detailed analysis of the operation of the system depending on weather conditions. As a result of the simulations, the impact of the temperature, velocity, and humidity of fresh and extract air on heat and moisture recovery efficiency was determined.

Biodigestion System Made of Polyethylene and Polystyrene Insulator for Dog Farm (on the Example of the Republic of Chile).

Anaerobic digestion is a system that can have a high environmental impact through the use of different wastes to obtain biogas and its consequent use for the generation of renewable energy. The objective of this study was to implement a polyethylene biodigester, using polystyrene for thermal insulation in a dog kennel, using canine feces collected in the same place during a period of 5 months to obtain biogas and energy. The results indicated that biogas production started on day 30 and stopped during the winter period with low temperatures; therefore, from day 54 onwards, equine manure was added to continue producing biogas. Although biogas was obtained, the biodigester did not function optimally, due to the fact that the materials used in its construction did not provide efficient insulation from the low external temperatures; the low C/N ratio of the canine feces, which led to a reduction in the processing of the methanogenic bacteria; and the low amount of feces collected for use. In general, the use of a biodigester can provide a tool for the biological processing and management of organic waste, yielding a cumulative source of renewable energy and ensuring environmental safety.

Determination of the Temperature Graph of Heat Supply With Minimal Heat Losses

Heat losses by pipelines of heat supply systems are calculated for the average temperature of the heat carrier per year or for the heating period for the conditions of a qualitative method of regulating the heat load. The presence of cuts of the temperature graph, the use of other methods of central regulation, are not reflected in the regulatory documents and require special research, which determines the relevance of the work. Heat losses through thermal insulation structures of pipelines have been determined for various graphs of central regulation. Heat losses were determined for each external temperature, taking into account its duration. It is shown that the average linear annual heat losses for most of the graphs correspond to a lower external temperature than the average external temperature for the heating period. Therefore, the calculation must be performed for a higher temperature of the heat carrier than is accepted according to regulatory documents.

Study of Universal Thermal Comfort Index in Hosing Estate Public Space in Bangkok, Thailand

A lower external temperature increases comfort and reduces the chance of heat stress; it can be impacted by the density of the urban area, and this is an important issue for the residents in housing estate developments. Therefore, to sustainably reduce this issue, the external temperature is important to manage for urban public spaces’ development. This article reports the results of studies on increasing thermal comfort in public areas by adding different types of shading into computer programs, Rhinoceros and Grasshopper, to calculate the Universal Thermal Comfort Index (UTCI). Increasing the outdoor comfort can be done by adding shaded areas via large trees that can result in thermal reduction and humidity increase, but they do not obstruct air circulation. The result can be used as a guideline for the design of public spaces in housing estates to meet the outdoor comfort efficiently and support the users’ expectations.

A Method to Reduce Air Heating Costs in Winter Period in the Królowa Luiza Mining Museum in Zabrze – Case Study

Abstract The Królowa Luiza Mining Museum is one of the touristic objects of the Coal Mining Museum in Zabrze. In the study in concern, an assessment of ventilation of the facility was conducted. Following the assessment of the ventilation, the operating parameters of the fans were changed, inlets were sealed and a system of air ducts was designed and constructed. The ducts reintroduce the heated air from the facility to workings. The conducted activities aimed to decrease the amount of air has increased the temperature in the entire object by from 3 to 10°C, which translated into a profit of approximately 200 Euro a day. Before changing the heating system it was impossible to achieve a positive temperature in the entire object at an external temperature of −10°C. It was necessary to close the Museum for tourists. Trials conducted for the external temperature from −2 to −6°C have exhibited that it will be possible to achieve positive temperatures in the entire facility even in case of very low external temperatures. The costs borne for the change of the heating system may be estimated at a level of 25000 Euro. The return of the investment should occur in the first Winter period.

ADAPTOGENESIS AND BIOLOGICAL POTENTIAL OF CATTLE ON СOMMERCIAL DAIRY FARM

The possibility of activating adaptive processes and organism resistance of cattle on commercial dairy farms under the influence of biological stimulants (polystim and PV-1) is proved. Biostimulants reduced the risk of gynecological disorders in cows: they reduced the retention time of placenta and subinvolution of uterus, reduced the endometritis and mastitis occurrence; increased reproductive function: shortened the time of the first estrus coming, increased the fertility, reduced the conception rate and duration of the service period, and improved the physicochemical composition of colostrum. The used biostimulants contributed to the increase in live weight of calves while increasing the relatively high level of assimilative processes associated with the fact that their forage energy was mainly spent on increasing body weight. At the same time, in calves not injected with biological preparations, it was mainly spent on providing homeothermia (i.e., maintaining constant body temperature), which was especially evident at low external temperatures. In calves raised in the conditions of intensive technology in winter, after the administration of dostim and polystim, the following indicators were significantly higher: the phagocytic activity of leukocytes by 5.4% - 6.4%, the lysozyme activity of plasma - by 3.0% - 6.2%, the blood serum bactericidal activity - by 7.1% - 9.5% and the content of immunoglobulins - by 2.5 mg/ml - 3.1 mg/ml. With the adaptive technology, the data of these indicators were higher: in winter period - by 5.2 - 6.4%, 3.1 - 6.2%, 6.0 - 8.7% and 4.7 - 5.7 mg/ml; and in spring-summer period - by 0.2 - 0.6%, 4.6 - 5.7%, 4.9 - 7.2% and 3.4 - 4.8 mg/ml (P<0.05-0.001), respectively.

DESEMPENHO TÉRMICO DE UMA RESIDÊNCIA COM DIFERENTES CONFIGURAÇÕES DE PAREDES TROMBE: ESTUDO PARA CURITIBA - PR

RESUMO: O uso de tecnologias passivas para climatizar os ambientes, tal como a parede Trombe, é uma forma reconhecida para minimizar o gasto energético com a climatização artificial do ar. Este artigo tem como objetivo avaliar, através do software EnergyPlus, a influência de diferentes paredes Trombe em uma edificação residencial, considerando o contexto climático de Curitiba, cidade que apresenta baixas temperaturas médias mensais. Para uma análise mais completa a respeito das vantagens em utilizar uma parede Trombe, foi realizado ainda um levantamento de custo do sistema. A partir das análises realizadas, constatou-se que o uso de paredes Trombe permitiu a elevação das temperaturas internas, especialmente quando foram abertas as janelas de ventilação interna. Contudo, nos dias de temperaturas externas muito baixas o uso da parede Trombe não foi suficiente para garantir o conforto térmico dos ocupantes. Durante o verão, a parede Trombe não provocou desconforto térmico por calor. Apesar de ter sua eficiência comprovada, verificou-se que o preço da esquadria pode ser um impedimento para a adoção do sistema. Sendo assim, ressalta-se a importância de um estudo a respeito do desempenho da parede Trombe combinado com outras estratégias bioclimáticas. Do contrário, o uso de climatização artificial será necessário.
 ABSTRACT: The use of passive technologies to climatize the environment, as the Trombe wall, is a recognized way to minimize energy waste with artificial air conditioning This paper aims to evaluate, through use of the software EnergyPlus, the influence of different Trombe walls on a residential building, considering the climate context of Curitiba, city where the monthly mean temperatures are low. For a more complete analysis of the advantages in using a Trombe wall, the cost of the system was also verified. From the analyzes carried out, the use of Trombe walls was found to be an alternative to allow the increase of internal temperatures, especially when the internal ventilation windows where opened. However, on days of very low external temperatures the use of the Trombe wall was not enough to guarantee the thermal comfort of the occupants. During the summer, the Trombe wall did not cause thermal discomfort by heat. Despite its proven efficiency, the window price was found to be an impediment for the system adoption. Thus, is emphasized the importance of a study on the performance of the Trombe wall combined with other bioclimatic strategies. Otherwise, the use of artificial air conditioning will be necessary.

Heating design of cowshed floor heating system based on solar energy / air source heat pump in plateau cold area

According to the high altitude and cold environment of the agricultural and pastoral areas, it is of great significance for the growth of yaks to adjust the ambient temperature of the cowshed appropriately so that yaks can have a more comfortable growth environment under the condition of low external temperature. Floor heating technology is a new scientific feeding technology, which can save labor, increase efficiency, reduce investment and operate easily, and adapt to the development of modern yak breeding industry. At the same time, the solar energy system and the air source heat pump system are coupled to operate as the heat energy source, that is, energy saving and environmental protection, with the best economic benefits. In this paper, through coupling the advantages of these three systems, we design the “Cowshed floor heating system based on solar / air source heat pump”.

Sliding wear of CoCrNi medium-entropy alloy at elevated temperatures: Wear mechanism transition and subsurface microstructure evolution

To gain a comprehensive understanding of the wear mechanism and the combined effect of low stacking fault energy (SFE) and external elevated temperature on sliding-induced plastic deformation of CoCrNi medium-entropy alloy (MEA), herein, we report on the wear response of fine-grained CoCrNi MEA against Inconel alloy 718 counterparts between room temperature (RT) and 300 °C, with particular focus on the wear mechanism transition and sliding-induced subsurface microstructure evolution. The results show that the hardness of the MEA and coefficients of friction (CoFs) start to decrease at 200 °C, but wear rates monotonously decrease with rising temperatures. The wear mode changes from abrasive wear at RT to oxidative and adhesive wear at 200 °C. Between RT and 150 °C, stacking faults and deformation twins play a significant role in the formation of gradient subsurface microstructure. The improved wear resistance is mainly attributed to the thermal softening of the mating material and the increased contribution of adhesive wear. However, at 200 °C and above, the reduced wear rates and CoFs are associated with the formation of glaze layer. The present findings provide insights into understanding the wear mechanism and sliding-induced deformation of metallic alloys with low SFE at elevated temperatures.

Building Physics as a Tool for Development of New Components: Roof Window

Knowledge and instruments of building physics (calculation methods and measuring procedures) can be used as key tools and perspectives to develop new components for building envelopes. This paper illustrates this fact by presenting the successful development of a roof window fulfilling higher requirements on reduction of overall heat losses and avoiding the risk of water vapor condensation on surfaces at very low external temperatures (thermal transmittance below 0.7 W/m2K in the first generation, close to 0.5 W/m2K in the second one) and better daylight distribution for the interior. This is the result of a publicly supported project with an industrial partner: from a general idea through detailed analysis of thermal performance in geometrical and material alternatives up to construction, prototyping, and verification by measurements and certification. Building physics tools applied in the project are discussed here together with lessons learned which are important for technical design. An effective shading system equipped with PV elements for energy smart harvesting is mentioned in the conclusion.

Offshore Natural Gas Conditioning and Recovery of Methanol as Hydrate Inhibitor with Supersonic Separators: Increasing Energy Efficiency with Lower CO<sub>2</sub> Emissions

The oil and gas industry represents an important contributor to CO2 emissions as offshore platforms are power intensive for producing, processing and transporting hydrocarbons. In offshore rigs CO2 emissions mainly come from on-site gas-fired power generation for heat and electricity production. The accumulation of atmospheric CO2 is one of the main causes of the planetary greenhouse effect, thus CO2 emissions should be minimized. To achieve that, more energy efficient processes for natural gas (NG) conditioning are needed in order to minimize platform power consumption and thus lowering the associated generation of CO2. In addition, in offshore scenarios gas-hydrate obstructions are a major concern in flow assurance strategies, since thermodynamic conditions favoring hydrate formation are present, such as high pressure, low external temperature and gas contact with free water. To avoid hydrate issues, hydrate inhibition is carried out by the injection of a thermodynamic hydrate inhibitor (THI) in well-heads such that it flows along with production fluids, thus removing the thermodynamic conditions for hydrate formation and ensuring unimpeded flow. Therefore, the three-phase high-pressure separator (HPS) is fed with production fluids, where the HPS splits the feed into: (i) an upper gas phase, (ii) hydrocarbon condensate, and (iii) a bottom aqueous phase. The gas phase goes to NG conditioning for hydrocarbon dew point adjustment (HCDPA) and water dew point adjustment (WDPA) so as to make NG exportable. The hydrocarbon condensate (if present) is collected for stabilization and the bottom aqueous phase consisting of water, salts and THI is sent to a THI recovery unit (THI-RU) for THI re-concentration and reinjection. In conventional plants, WDPA and HCDPA are done by glycol absorption and Joule-Thomson expansion respectively. Moreover, the HPS gas carries some THI such as methanol that is lost in the processing. This work analyses a new process – SS-THI-Recovery – where HPS gas feeds a supersonic separator (SS) with injected water and compares it to the conventional processing. As a result, SS ejects a cold two-phase condensate with almost all water, THI and C3+ hydrocarbons, discharging exportable NG with enough HCDPA and WDPA grades, while the condensate gives aqueous THI returned to the THI-RU and LPG with high commercial value. Thus, SS-THI-Recovery not only avoids THI losses as well as exports NG and LPG. Both conventional gas plant and SS-THI-Recovery alternative coupled to THI-RU were simulated in HYSYS 8.8 for a given NG field and targeting the same product specifications. SS-THI-Recovery presented lower power consumption and thus less associated CO2 emissions, while potentially increasing the gas plant profitability, as THI losses are significantly reduced and higher flow rate of LPG with higher commercial value is produced in comparison with the conventional alternative. Hence, the higher efficiency of SS-THI-recovery makes it not only more environmentally friendly with lower CO2 emissions, but also a potential alternative for improving process economics and thus providing an economic leverage that could justify investments in carbon capture technologies, contributing to avoid CO2 emissions even more with cleaner NG and LPG production.

Experimental investigations on a transcritical CO2 refrigeration plant and theoretical comparison with an ejector-based one

The paper presents the development of an experimental research facility based on a transcritical single stage vapour compression refrigeration cycle with CO2 as the working fluid. The experimental setup includes instrumentation and controls which enable tests in a broad range of operating conditions. The measurements presented refer to external temperatures between 21.0°C and 33.5°C; in this latter operating point, energy and exergy analysis allowed the breakdown of irreversibilities. In particular, the gas cooler contributes to the 42.6% of the total exergy losses while the share due to the high-pressure expansion valve is 27.2%. In order to improve the performance of the refrigeration system, a theoretical model was developed including an ejector as the replacement of the expansion valve. The results show that the Coefficient of Performance (COP) is strongly dependent on the entrainment ratio; a value of greater than 0.6 seem to lead to higher COP values, even at low external temperatures.

The influence of crop dryer operation parameters on the efficiency of energy recovery from extract air

Crop drying, especially maize drying, occurs at low external air temperatures, which are lower than the extract air temperature. Therefore, using heat exchangers, to recover thermal energy from the extract air to preheat the cold and dry external air, results in a significant reduction in the primary energy demand for crop drying. The measurements of air parameters in the crop dryer, with a drying capacity of 19 Mg/h of maize, confirm the assumptions undertaken for the production of the heat recovery system. We apply the cross-counter-flow surface heat exchanger system to provide a significant improvement in the efficiency of crop drying. We perform the analysis of the thermal energy recovery system operation. Our results indicate the influence of the drying air set-point and the crop specific humidity on the efficiency of energy recovery from the exhaust air. We performed our measurements at different drying air temperature set-points and different crop relative humidity.

Model predictive control of a hybrid heat pump system and impact of the prediction horizon on cost-saving potential and optimal storage capacity

The present paper analyses the cost-optimal sizing and hourly control strategy of a hybrid heat pump system for heating application, composed by an electrically-driven air source heat pump and a gas boiler. These hybrid systems represent a promising solution for the energy retrofit of existing buildings and new installations, being able to increase the efficiency of monovalent systems, especially at low external temperatures. The use of thermal storage can furtherly minimize both the operating cost and the primary energy consumption, shifting the operation of the heat pump to the most profitable periods. In this work, the optimal control problem has been investigated by means of mixed-integer linear programming, considering an ideal forecast of external temperature and thermal load on given horizon periods (i.e. model predictive control). Achievable cost savings with respect to a traditional rule-based control strategy with no storage are presented as a function of both prediction horizon and storage capacity in a dimensionless form. A relation between prediction horizon length and optimal storage capacity is shown. An example of application of the method is illustrated, showing cost savings up to 8%. A sensitivity analysis on the storage tank losses, climatic conditions, generators efficiency, and energy prices is also presented, showing the cost saving potential in all these different conditions.

Effect of shot peening on the fatigue properties of nickel-based superalloy GH4169 at high temperature

Abstract This study investigates the influence of shot peening on the fatigue properties of GH4169 alloy at 20 °C, 350 °C and 650 °C in air. Work hardened layer with nanocrystals and deformation twins was generated in GH4169 surface after shot peening. Nanocrystallization process of microstructures was deeply discussed. The effect of twin morphology and compressive residual stress on fatigue properties was then analyzed in detail. Also, the fatigue fracture mechanism was systematically investigated. Results show that the depth of work hardened layer is about 96 μm and the increment of microhardness for the topmost surface reaches approximately 34.6%. Grains are refined to about 9 nm in the topmost surface after shot peening. Original twins are roughened or even disappear as test temperature gradually increases. The fatigue properties of shot peening specimens can be greatly improved by shot peening, especially at low external stress and test temperature (20 °C and 350 °C). The improvement of fatigue properties is mainly attributed to the induced nanocrystals and deformation twins, as well as strain hardening and compressive residual stress in surface layer.

Robust microclimate control for artwork preservation in response to extreme climatic conditions: simulation of museum halls for temporary exhibitions with a validated dynamic tool

In museums, artworks preservation is hampered by several factors, in particular temperature and relative humidity as inappropriate values of these parameters can cause biological, mechanical, and chemical degradation. Thus, HVAC systems must be able to maintain specific suitable indoor microclimate also in critical conditions, such as variation of external climate and huge presence of visitors. In this paper, we first present the results of a monitoring campaign conducted in some rooms of an Italian museum in the 2015-2016 winter exhibition. The current HVAC system was able to maintain the required microclimate. A dynamic model (using TRNSYS for the envelope modeling and an in-house developed tool for the HVAC system) has been validated through the measured data. The dynamic model allows performing additional simulations characterized by critical boundary conditions (e.g., low external temperature and/or high relative humidity, and high number of visitors). In current conditions, these conditions would have caused unacceptable microclimate in the exhibition rooms, meaning higher risks for artworks. Through a rational rearrangement of the current HVAC system (both generators and terminal units), the microclimate was found to be suitable also in critical situations. This outcome is particularly important in exhibition rooms with temporarily borrowed artworks, since climatic conditions are basically unpredictable for the season of exhibition and so a robust HVAC system is needed.