Limit Heat Loss Research Articles

Footedness in merlins: Raptors perching in a cold climate

ABSTRACT Perching or standing on one foot is commonly reported in birds but the level of consistency in using one foot over the other has been less-well documented in most species, particularly birds of prey. For birds experiencing colder temperatures, unipedal perching has been attributed to limiting heat loss through unfeathered legs and feet; individuals should spend longer periods of time perched on one foot as temperatures decrease. Using radio tracking, I collected 486 hours of observations on nine overwintering, free-living merlins (Falco columbarius) in Saskatoon, Canada. Five merlins displayed clear preferences to perch on one foot, however the direction of preference was not consistent and four birds were ambidextrous. There was a curvilinear response in the proportion of time spent in unipedal posture versus temperature, with a peak of ∼22% of the time at moderate temperatures (−10 to −19°C), but lower values at warmer and colder temperatures; the main effect of the squared term for temperature was highly influential while individual foot preference had no impact on the use of unipedal perching. Although preferential use of one foot for perching was displayed by some individuals, thermoregulation may not be the primary driver of this behaviour at colder temperatures.

Development and experimental characterization of the thermomechanical behavior of a scaled steel ladle

AbstractA steel ladle usually employs mortarless refractory masonry in the innermost layer in direct contact with molten steel. The behavior of such masonry under high thermal loading is complex and essential for designing such installation. A large‐scale experimental campaign was carried out focusing on a simplified, laboratory‐scaled, pilot steel ladle built with multiple refractory linings as in an industrial ladle. Tests were performed under transient thermal loading up to 1400°C with new and used working linings. The results showed that the distribution of temperatures between the refractory linings was similar for all specimens and confirmed the importance of the selection of the refractory materials in the distinct linings of the ladle to limit heat losses. The heterogeneity in the distribution of dry joints and the effect of the dry joint thickness were also measured using strain gauges. The measurements indicate the effect of viscoplasticity in the working lining on the steel shell, which shows a progressive reduction in the strain starting at 1200°C. The tests performed on the working linings show lower strain built‐up due to large viscoplastic deformation and increased joint thickness.

Energy and economic analysis of flue gas heat recovery systems improving the energy efficiency of gas cogeneration units

This paper presents the results of energy and economic analyses of a gas-fired CHP plant. The analyses were carried out for three variants of technical solutions to improve the thermal efficiency of the CHP plant. The fuel combustion process involves the generation of a large amount of heat. In addition, the heat is dissipated to the surroundings through the exhaust gas with a high temperature of 300÷350 °C. Therefore, to limit heat loss, a heat recovery system is used, which removes heat from the engine body and from the hot exhaust gases through a heat exchanger, allowing the exhaust gases to be cooled to a temperature of 100÷120 °C. In addition, heat is recovered from the oil cooling process and intercoolers. The recovered heat is usually supplied to the heating water in the district heating network. For the calculations, the temperature distribution of the return water from the district heating network during the year was assumed. First, the benefits of adding an additional economizer to pre-heat district heating water were analysed, Next, a heat recovery system was simulated to cool the flue gases to lower temperatures using an absorption heat pump or a compressor heat pump.

An evaluation of a healthy participant laboratory model of epidural hyperthermia: a physiological study

BackgroundHyperthermia complicates 21% of cases of intrapartum epidural analgesia, but the mechanism is unclear. One hypothesis is that blockade of cholinergic sympathetic nerves prevents active vasodilation and sweating, thus limiting heat loss. Because labour increases heat production, this could create a situation in which heat production exceeds loss, causing body temperature to rise. This physiological study tested a novel laboratory model of epidural-related hyperthermia, using exercise to simulate the increased heat production of labour and surface insulation to simulate the effect of epidural analgesia. MethodsTwelve healthy non-pregnant participants (six female) cycled an ergometer for two hours at 20 Watts (W) on two occasions: once with surface insulation (intervention) and once without (control). Core temperature, skin temperature (eight sites), and heat loss (eight sites) were recorded. Mean body temperature and heat production were calculated. Values are mean (SD). ResultsExercise increased heat production on both visits (intervention 38 (18) W; control 37 (31) W; P = 0.94). Total heat loss was less on the intervention visit (intervention 115 (19) W; control 129 (23) W; P = 0.002). Core temperature increased on both visits (intervention 0.21 (0.37)°C; control 0.19 (0.27)°C; P < 0.001). The increase in mean body temperature was greater on the intervention visit (intervention 0.47 (0.41)°C; control 0.25 (0.19)°C; P = 0.007). ConclusionsThis laboratory model predicts that labour epidural analgesia limits heat loss by >14 W. Once the model is validated, it could be used to test the efficacy of potential interventions to prevent and treat epidural-related maternal hyperthermia.

Effects of thermal stress on calf welfare

Cold and heat stress present welfare challenges for dairy calves. The consequences of thermal stress on biological functioning have been well documented, and many housing and management strategies have been evaluated to mitigate those detrimental impacts. In cold weather, mitigation strategies have largely focused on nutritional interventions or limiting heat loss with resources such as bedding or jackets. In hot weather, heat abatement strategies such as supplemental shade, increased environmental air exchange through passive ventilation, and forced air movement through mechanical ventilation have been evaluated. Recently in Wisconsin's continental climate, our group evaluated how 2 aspects of calf welfare—the needs for thermal comfort and social contact (i.e., pair or group housing vs. individual housing)—may align or conflict in winter and summer, respectively. In both seasons, calves pair-housed in outdoor hutches preferred social proximity. When 2 calves shared a hutch, the heat load was greater than for a single calf, which may be beneficial for thermal comfort in winter. In summer, the potential detriments from the additional heat load of 2 calves was mitigated with passive hutch ventilation, which calves preferred. Nonetheless, knowledge gaps remain regarding the impacts of thermal stress on calves' affective states, and much remains unknown about their preferences and motivations for specific thermal stress mitigation resources. Future research to address these gaps could improve our understanding of calf welfare and inform best practices for calf management.

Applicability evaluation of internal heat exchanger in CO2 transcritical cycle considering compressor operation boundaries

CO2 transcritical cycle has been widely promoted as a green energy utilization technology. Internal heat exchanger (IHX) is under consideration for cycle efficiency improvement. However, the interaction between IHX and compressor in CO2 cycle has not yet been fully explored. In this regard, compressor operating boundaries are introduced as constraints to IHX applicability evaluation in CO2 cycle. It indicates that considering compressor limits, IHX can either benefit or attenuate the CO2 cycle performance, depending on operating conditions. By reducing optimal discharge pressure, IHX helps CO2 cycle avoid the upper pressure limit, further improving performance by 5%. Over a wide range, however, IHX increases compressor discharge temperature, indirectly resulting in up to 50% performance degradation. The major factors affecting the duality of IHX in CO2 cycle are compressor discharge temperature limit, IHX efficiency and motor heat loss. Finally, performance-oriented IHX design guidelines for mainstream single-stage CO2 applications are provided. For automotive air conditioner, optimum IHX efficiency improves cycle performance by up to 30% in cooling mode. By contrast, IHX contribution is negligible in heating mode. For heat pump water heater and refrigeration system, both can benefit from IHX, particularly when compressor discharge temperature tolerance is high.

Ecological rules for global species distribution also predict performance variation in Ironman triathletes.

Bergmann's and Allen's rules predict changes in body size and appendage length across temperature gradients for species with broad geographic distributions. Larger bodies and longer limbs facilitate cooling whereas smaller bodies and compact limbs limit heat loss. Although these patterns are highly repeatable (hence "rules" of ecology) the patterns and underlying mechanisms are less-well understood in humans. Here I show that variation in running performance among human male triathletes is consistent with both Bergmann's and Allen's rules. Males (but not females) with relatively larger body size and longer limbs performed better at hot compared to cold race venues and vice-versa. Consistent with results in other taxa, sex-specificity may reflect selection for sexual dimorphism. Results suggest that ecological patterns detected over large-spatial scales may arise from fine-scale variation in locomotor performance.

Historic building and green energy. Strategies to make supply from renewable sources compatible with conservation

The challenges of today are largely summarized in the United Nations 2030 Agenda. Buildings are also part of the 17 sustainability goals in several respects, one of them being the role of reducing climate-altering emissions, reducing waste, assessing the life cycle of materials, limiting heat loss and introducing renewable energy sources. In particular, the contribution deals with how to ensure the supply of energy from renewable sources for cultural assets and buildings that are part of historic centers. In these cases it can be very difficult to achieve both the objective of protecting the monument or landscape as well as that of installing or connecting the building or urban or rural settlement to renewable energy sources. Through some European and Italian examples in particular, where about 8 million buildings were constructed before 1945, about 25% of the total, virtuous ways will be presented that make it possible to achieve both objectives simultaneously. The regulations that favor this dual objective will also be highlighted, such as the one of the Veneto Region on so-called energy communities and the national one that allows the deferral of energy production from one place of cultural interest to another that has none, without serious costs for the final beneficiary and safeguarding the cultural asset.

Maintaining control: metabolism of molting Arctic seals when hauled out and in water.

Seals haul out of water for extended periods during the annual molt, when they shed and regrow their pelage. This behavior is believed to limit heat loss to the environment given increased peripheral blood flow to support tissue regeneration. The degree to which time in water, particularly during the molt, may affect thermoregulatory costs is poorly understood. We measured the resting metabolism of three spotted (Phoca largha), one ringed (Pusa hispida), and one bearded (Erignathus barbatus) seal during and outside the molting period, while resting in water and hauled out. Metabolic rates were elevated in spotted and ringed seals during molt, but comparable in water and air for individuals of all species regardless of molt status. Our data indicate that elevated metabolism during molt primarily reflects the cost of tissue regeneration, while increased haul out behavior is driven by the need to maintain elevated skin temperatures to support tissue regeneration.

Characterisation of mortarless refractory masonry joints under elevated temperatures

Refractory linings are commonly employed in Industrial vessels used in high-temperature processes to protect them against extreme working environments. The working lining of an industrial steel ladle frequently employs mortarless refractory masonry to contain the molten steel and limit heat losses. Such masonry lining undergoes high thermomechanical loads, primarily due to thermal expansion arising from thermal and mechanical boundary conditions. Dry joints, described as a physical break in the continuum, reduce some of these effects. Therefore, understanding dry joints is an essential factor for developing numerical constitutive models that employ a meso or macro modelling approach. This work aims to experimentally investigate the normal compressive behaviour of dry joints in refractory masonry. For this purpose, various refractory specimens of alumina-spinel material are tested from ambient temperature to 1200 °C. The results obtained from these experiments are then used to identify critical joint parameters with different mathematical models for the interface. The outcome describes exponential joint closing behaviour with respect to the force applied. It was observed that the pressure required to close a joint reduces with an increase in temperature. The exponential model was then used to numerically simulate the joint closure of mortarless refractory masonry. Finally, numerical and experimental results were compared.

Synergy of copper Selenide/MXenes composite with enhanced solar-driven water evaporation and seawater desalination

Despite significant of solar energy to power water evaporation in seawater desalination, the commercial application of this technology is limited by the poor light absorption and low photothermal conversion of existing photothermal materials. Herein, we report a simple method for solar-driven water evaporation using a device comprising Cu2-xSe/Nb2CTx nanocomposites supported by a glass microfiber membrane, which utilizes cotton thread as water transport pathway. The proposed device demonstrates excellent light absorption, water transportation, and thermal management. Benefiting from the strong synergetic photothermal effect of Cu2-xSe and Nb2CTx, the Cu2-xSe/Nb2CTx nanocomposites function as an efficient solar absorber with excellent photothermal conversion efficiency. The rough surface, low thermal conductivity and good hydrophilicity of glass microfiber membrane could maximize light capture, limit heat loss, and timely replenish water during the water evaporation process. When evaluated as a water evaporation system for outdoor seawater desalination, the system achieved a water evaporation of 12.60 kg·m−2 within 6 h. High fresh water generation rate is an important embodiment of high photothermal conversion efficiency. This study demonstrates a new route for designing solar desalination devices with high photothermal conversion properties.

Comparative Analysis of Overheating Risk for Typical Dwellings and Passivhaus in the UK

There is growing concern that airtight and well-insulated buildings designed to limit heat loss in temperate and cold climates could unintentionally elevate the risk of overheating in summers. Existing literature primarily uses dynamic simulation to investigate this problem due to the difficulty of obtaining large-scale in-performance data. To address this gap, we undertake a meta-analysis of large-scale indoor air temperature data for 195 UK dwellings, as a study of performance in a temperate climate. Of these, 113 are baseline (i.e., typical existing dwellings) and the rest designed to the high-performance Passivhaus standard. Using both Passivhaus and the well-known CIBSE TM59 overheating standards, this study found that there were few overheated cases for any building type. However, the average summer nighttime temperature of Passivhaus bedrooms was 1.6 °C higher than baseline, with 20 out of 31 measured bedrooms exceeding the overheating criterion, and the average overheating hours constituting approximately 19% of the total summertime observation period. These findings suggest that bedrooms in highly insulated dwellings may pose an overheating risk although whole-dwelling overheating risk is low.

Experimental study of N2 and CO2 dilution in CH4 fuel stream with buoyancy-induced low-stretch diffusion flames

This study experimentally investigated the structures, dynamics and extinction behaviors of buoyancy-induced ultra-low-stretch diffusion flames with N2/CO2 dilution in a CH4 stream, using porous spherical burners with large radii. In quasi-steady states associated with low dilution and comparatively small fuel mixture injection speeds (uF), as stretch rate dropped and uF enlarged, the flame standoff distance increased, while the burner surface temperature decreased due to surface heat losses. The flame temperature, Tf, dropped at lower uF and smaller stretch rates, primarily because of reduced heat generation and increased flame radiative loss, respectively. The dilution effect of N2/CO2 reduced Tf. Moreover, the chemical and thermal effects of CO2 further decreased Tf and soot formation. With increased dilution, two instability patterns occurred before extinction. One was a stripes/holes pattern, evolving from waves/bumps and cellular flames, at higher uF. The other was a periodic holes pattern appearing at lower uF. These patterns were associated with Rayleigh-Taylor instability, thermal-diffusive instability and instability related to heat loss. The dilution extinction limits at varied stretch rates increased with increases in uF until they reached constant levels, corresponding to the intrinsic dilution limits of N2 and CO2 for CH4, and the suppression effect of CO2 was greater than that of N2. At the high dilution extinction limit, extinction was independent of uF and stretch rate, but dominated by lower heat release compared with robust flames, and also by substantial flame heat losses. At the low dilution extinction limit, both gas-phase and burner surface heat losses contributed to extinction, furthermore, lower stretched flames had obvious higher dilution extinction limits, primarily due to smaller gas-phase heat losses requiring less heat generation to balance. This work enriches the knowledge of ultra-low-stretch gaseous diffusion flames, especially the flame structure, instability and extinction, and also provides information regarding the dilution gas effects.

Comparative performance evaluation of candidate receivers for an etendue-conserving compact linear Fresnel mirror field

While several studies of multitube and monotube linear Fresnel receivers exist in the literature, comparative studies on different types of receivers are limited. This paper therefore aims to address this gap within literature by comparing the optical and thermal performance of four different receivers: an adapted compound parabolic concentrator (CPC)-type monotube receiver, an adapted tailored edge ray concentrator (TERC)-type monotube receiver, a trapezoidal multitube receiver and an adapted TERC-type multitube receiver. Existing literature was used to determine the design elements limiting heat loss, which were then incorporated into the receiver design and optical optimisation of the four receivers. Once the geometry was determined through a series of Monte Carlo ray tracing (MCRT) simulations, a validated two-dimensional computational fluid dynamic (CFD) model was used to determine the heat loss of each receiver for the same thermal conditions. Given that these heat loss studies were decoupled from the optical study, they are valid for any type of mirror field. While both adapted TERC-type receivers performed well optically (with daily optical efficiencies of 56.93% and 56.6% for the monotube and multitube receivers, respectively), the adapted TERC-type multitube receiver had the highest thermal loss of all the receivers, increasing the heat loss of the TERC-type monotube receiver by a factor of 2.5. In contrast, the adapted CPC-type monotube receiver had a lower daily optical efficiency of 51.29% when paired with an etendue-conserving compact linear Fresnel mirror field, but had low thermal loss, second only to the lower heat loss of the adapted TERC-type monotube receiver by a factor of 1.26. The standard trapezoidal receiver had a relatively low daily optical efficiency of 53.69% and relatively high heat losses, higher than the adapted CPC- and TERC-type monotube receivers by a factor of 1.5 and 1.9, respectively. The adapted TERC-type monotube receiver was therefore determined to be the best candidate receiver for an etendue-conserving compact linear Fresnel field.

Heating Intravenous Fluid Tubing in an Experimental Setting for Prehospital Hypothermia

ObjectiveHypothermia secondary to environmental exposure is a serious condition. Active external warming measures to treat it may prove challenging in the prehospital setting. We conducted an experimental study to measure the ability of commercially available heating elements to warm intravenous (IV) fluids during infusion. Methods250-milliliter bags of dextrose 10% solution were suspended inside a refrigerator. IV tubing was coiled, and the tubing output was placed inside a thermally insulated cup. The tubing was heated directly with a hand warmer, a meals ready-to-eat heater, or a heating blanket. Fluids were run through the IV line. The temperature of the fluid at the tubing output was measured. The initial and final infusion temperatures for the methods were compared. ResultsThe use of hand warmers, meals ready-to-eat heaters, and heating blankets to warm IV tubing did increase the temperature of the fluids but was ineffective at achieving the desired mean infusion temperature of 35°C to 42°C. ConclusionAlthough the mean temperature increase did not meet the established experimental threshold, further research is needed to determine whether the fluid warming effect of these commercial heating elements used in the prehospital environment is significant enough to limit heat loss while repleting the dextrose of a hypothermic, hypoglycemic patient.

Energetische upgrading van Nederlandse Wederopbouw flats

Energetische upgrading van Nederlandse Wederopbouw flats

Energetische upgrading van Nederlandse Wederopbouw flats

Energetische upgrading van Nederlandse Wederopbouw flats

Active thermal insulation as an element limiting heat loss through external walls

The authors present the preliminary results and analyses of research performed in an experimental residential building located in the town of Nyiregyhaza in Hungary. The building is equipped with an innovative system for direct coupling a ground heat exchanger with a wall heat exchanger. In 2012, the creator of the system, Tamas Barkanyi, obtained patent for active thermal insulation of buildings. In this paper, the authors attempt to answer the question of to what extent the active insulation system can replace the commonly used standard passive insulation systems. The initial results of the research lead to the conclusion that active thermal insulation significantly improves the insulation parameters of the external wall. In the analyzed periods, the reduction of the total amount of heat loss through external walls was from 53% in February to 81% in November. The equivalent thermal transmittance Ueq of the analysed wall was dependent upon local climate conditions and amounted to 0.047 W/(m2K) in November and 0.11 W/(m2K) in March, while the standard transmittance value was 0.282 W/(m2K).The obtained positive research results should be the basis for the implementation of an innovative system in NZEB buildings.

Numerical Analysis of Building Envelope with Movable Phase Change Materials for Heating Applications

Latent heat storage materials have been tested by several researchers for decades to be used as passive heating and cooling systems in buildings but their implementation into building components is still stacked as is facing specific technical limitations related to difficulties to be charged both in heating and cooling periods. This paper presents a numerical analysis to evaluate the potential of a disruptive system, which is designed to solve the main drawbacks and to convert phase change materials (PCM) passive heating technology into a competitive solution for the building sector. The novel technology moves PCM layer with respect to the insulation layer inside the building component to maximize solar benefits in winter and be able to actively provide space heating. Design variables such as PCM melting point and control schemes were optimized. The results demonstrated that this technology is not only able to limit heat losses towards outdoors but it can provide space heating from stored solar energy when required. The promising numerical results endorse the possibility to build a future experimental prototype to quantify more in detail the benefits of this system.

Waterbowls: Reducing Impacting Droplet Interactions by Momentum Redirection.

Superhydrophobic surfaces can dramatically reduce the transport of mass or energy from impacting droplets by making them bounce off. Such transport processes are dependent on both the contact time and the contact area between the drop and the surface. To reduce transport, recent studies have focused on reducing the contact time. However, the contact area, which is dictated by the conformal spreading of the droplet, remains large, thereby limiting the reduction in the overall transport. Here, we show how surfaces can be designed to redirect the momentum of the spreading lamella causing it to lift off into 3-dimensional shapes, thereby dramatically reducing the contact area. We design superhydrophobic surfaces with an in-plane discontinuity leading to the accumulation of vertical momentum resulting in the out-of-plane ejection of the lamella into water bowls. We demonstrate a 2-fold reduction in the heat transfer between a cold rain and a warm surface. These insights can be broadly applied to other transport phenomena involving mass and energy exchange to limit heat loss under precipitation, icing of surfaces, reduce salt deposition on a surface exposed to ocean spray, or inhibit the formation of a water film on wings or wind turbine blades.