Local Thermal Response Research Articles

Pore-scale visualization and measurement of paraffin solidification in high porosity open-cell copper foam

In this work, a pore-scale experimental investigation on solidification of paraffin in high porosity open-cell copper foam is performed based on the visualization and measurement technique. With the use of high definition camera and infrared camera, the phase and temperature fields of the copper foam/paraffin sample are obtained to directly visualize the solidification process. Simultaneously, T-type thermocouples are employed to measure the local thermal response characteristic and thermal non-equilibrium effect of the copper foam/paraffin sample. For comparison, the corresponding solidification experiment with pure paraffin sample is also conducted. Local details of solidification phase change including the evolution of phase change interface within foam pore region, the liquid phase flow and air gap formation due to the volume shrinkage effect of paraffin are revealed. It is found that the highly conductive copper foam remarkably extends the phase change interface, avoids the formation of overlarge-size air gap that forms in the pure paraffin sample and enables a higher thermal response rate of the copper foam/paraffin sample. As a result, an attractive solidification enhancement (about 2.8 times) of paraffin in copper foam is achieved. Moreover, strong effect of local thermal non-equilibrium between copper foam and paraffin is detected during the solidification process. Finally, through generalizing the present experimental results, a correlation for dimensionless solidification time of the copper foam/paraffin sample is developed at pore scale.

Desconforto térmico durante a estação seca em uma cidade de Clima Tropical Chuvoso na Amazônia

A avaliação da sensação térmica em Santarém é importante, devido à recente expansão física e populacional da cidade. Santarém é a terceira maior cidade do Pará, tanto em tamanho, quanto em população. O clima Equatorial, caracterizado com temperatura do ar e umidade relativa do ar elevadas ao longo do ano, associado a variações diurnas de temperatura, mesmo que pequenas, podem representar alterações importantes no conforto/desconforto térmico do ambiente urbano. Neste sentido, o conforto térmico horário foi testado por meio de quatro modelos capazes de retorna a resposta térmica local, focados neste estudo na estação seca de 2016 (julho a novembro), utilizando dados da estação meteorológica automática de superfície de Santarém. Entre os resultados encontrados podemos destacar que, no intervalo de 11 às 18h, em ambiente aberto, a sensação térmica varia de desconfortável a extremante desconfortável. Entre 14 e 17h, os índices apontam sensação muito quente com falha na termorregulação do corpo e cautela extrema, estas sensações térmicas estão associadas aos valores máximos de temperatura ar em torno de 31°C e umidade relativa inferior a 60%. A compreensão acerca da sensação térmica atual em Santarém e dos horários mais críticos, servem como subsidio para medidas de prevenção a exposição a ambientes abertos, além de possibilidade de emissão de alertas a sociedade e poder público.

Time-resolved measurements of liquid–vapor thermal interactions throughout the full life-cycle of sliding bubbles at subcooled flow boiling conditions

The local thermal response of the liquid phase to the presence of sliding bubbles was measured with an infrared camera in subcooled flow-boiling conditions. These measurements were complemented with two high-speed cameras to capture the corresponding bubbles’ dynamics. The liquid–vapor interactions were captured in detail over the full life-cycle of sliding bubbles. Four distinctive phases for the bubble life-cycle were identified: A) Spherical bubble growth with strong attachment, B) Deformed bubble growth with weak attachment, C) Detachment with hot liquid quenching, and D) Cold liquid quenching. To the best of the authors’ knowledge, it is the first time that the “detachment with hot liquid quenching phase has been observed. This phase is characterized by a “hot” thermal footprint during the bubble detachment process. It is believed that this footprint is constituted partially from hot liquid released during the condensation of the recently detached bubble, and from released hot fluid previously collected by the bubble during sliding. In addition, this work reveals that using traditional high-speed visualization techniques (side-view camera only) can lead to an underestimation of approximately 40% of the actual bubble–wall contact diameter (dc) which was inferred from the infrared camera measurements.

Thermal comfort and skin temperature responses to the supplied air from personal air nozzles in aircraft cabins

For investigating the thermal comfort impact of supply air from personal nozzles on body positions of human bodies in aircraft cabins, a mock aircraft cabin with three rows of seats was built to investigate the effect of personal nozzle on thermal comfort of three main body parts, including head, upper body and lower body. In total, 12 tests were performed on 16 volunteers. Every test lasted 3 h and 40 minutes. Simultaneously, volunteers’ responses for both local and overall thermal responses were recorded. Skin temperatures were monitored. The results showed that when cooling the upper body, variation in local thermal sensation, overall thermal sensation and average skin temperature were the most significant responses produced by 16 young healthy human volunteers taking part in the experiment. However, for the airflow sensation, the strongest impact was at the head (including forehead and face), followed by the upper body part (breast, back, shoulder, abdomen) and then the lower body part (buttock, sex organ, thighs, legs and feet). In order to minimize draft discomfort, the air supply from nozzles should be delivered directly to the upper body, which would make the passengers more comfortable and benefit the optimization of the design of the nozzle.

Local quantum thermal susceptibility.

Thermodynamics relies on the possibility to describe systems composed of a large number of constituents in terms of few macroscopic variables. Its foundations are rooted into the paradigm of statistical mechanics, where thermal properties originate from averaging procedures which smoothen out local details. While undoubtedly successful, elegant and formally correct, this approach carries over an operational problem, namely determining the precision at which such variables are inferred, when technical/practical limitations restrict our capabilities to local probing. Here we introduce the local quantum thermal susceptibility, a quantifier for the best achievable accuracy for temperature estimation via local measurements. Our method relies on basic concepts of quantum estimation theory, providing an operative strategy to address the local thermal response of arbitrary quantum systems at equilibrium. At low temperatures, it highlights the local distinguishability of the ground state from the excited sub-manifolds, thus providing a method to locate quantum phase transitions.

Universal scaling behavior of the temperature increase of a heat nanoparticle on a substrate

Knowledge of temperatures at the nanoscale is essential for studying and controlling the heat-induced local thermal responses. The temperature rise of a heated nanoparticle (NP) near the interface of two kinds of media with different thermal conductivities is numerically investigated. We find that the temperature rise becomes size independent if it is scaled by the temperature rise in the case where the particle-interface distance is zero and the distance is scaled by the equivalent radius of the NP. This universal scaling behavior can be understood with the principle of dimensional homogeneity. An empirical equation is retrieved to predict the actual particle temperature at a given position. Our results may benefit precise control of heat at the nanoscale with applications in plasmonic absorbers, immunotargeted photothermal cancer cell killing, etc.

Thermal response in pre-imaginal biology of Ochlerotatus albifasciatus from two different climatic regions.

The biological processes on mosquito could be variable in response to local climatic characteristics. The thermal effects on time and the rate larval development, immature survival and adult size in local populations of Ochlerotatus albifasciatus (Macquart) (Diptera: Culicidae) from cold (Sarmiento) and temperate (Buenos Aires) regions from Argentina were evaluated. This species affects livestock production and human health. Larvae of both regions were placed in breeding thermal baths (11-32 °C range). Development and survival were recorded daily until adult emergence. The development temperature threshold and thermal constant for Sarmiento (4.59 ± 3.08 °C, 204.08 ± 7.83 degree days) was lower and higher than Buenos Aires, respectively (8.06 ± 1.81 °C, 149.25 ± 2.6 degree days). At cold temperatures (11-16 °C), Sarmiento larvae demonstrated 5 days faster development and higher survival (56%) than Buenos Aires (15%), whereas at warm temperatures (20-32 °C) were up to 2 days slower and similar survival (16% vs. 18%). The size did not show differences between populations. An Ochlerotatus albifasciatus population seems to present local thermal responses. The favourable temperature for survival and rate of development would vary within a cold or warm range, and these differential responses would explain the wide geographical distribution in different climatic regions of southern South America.

Local Piezoresponse and Thermal Behavior of Ferroelastic Domains in Multiferroic BiFeO3 Thin Films by Scanning Piezo-Thermal Microscopy

A dual probe, i.e., high resolution scanning piezo-thermal microscopy, is developed and employed to characterize the local piezoresponse and thermal behaviors of ferroelastic domains in multiferroic BiFeO3 thin films. Highly inhomogeneous piezoelectric responses are found in the thin film. A remarkably local thermal transformation across ferroelastic domain walls is clearly demonstrated by the quantitative 3ω signals related to thermal conductivity. Different polarization oriented ferroelastic domains are found to exhibit different local thermal responses. The underlying mechanism is possibly associated with the inhomogeneous stress distribution across the ferroelastic domain walls, leading to different phonons scattering contributions in the BiFeO3 thin film.

Influence of the fiber geometry on the macroscopic elastic and thermal properties

This work focuses on the linear elastic and thermal properties of real and virtual, computer-generated fibrous composites. A stochastic microstructure model is used to generate densely-assembled 3D systems of curved, non overlapping fibers with specific orientation distributions. This model is first optimized to approach the characteristics of a real fiber glass polymer by fitting geometrical and statistical parameters, such as fiber orientation, radius, length, and curvature. Second, random realizations of the stochastic models that depart from the characteristics of the fiber glass polymer are generated. The latter, which range from isotropic to transversely isotropic and to orthotropic materials, represent plausible virtual fibrous materials. Full-field numerical computations, undertaken by means of the Fourier-based (FFT) method, are used to estimate the local and effective mechanical and thermal responses of the fibrous composites. The anisotropy of the macroscopic responses as well as the size of the corresponding representative volume element (RVE) are examined numerically. It is found that the variance of the properties on a volume V scales as a powerlaw ∼1/Vα where α<1, an effect of long-range correlations in the microstructure. Finally, the overall behavior of the fiber composites are computed for varying fiber curvature and orientation distributions, and compared with available analytical bounds. We find that the fiber arrangement strongly influences the elastic and thermal responses, less so for the fiber curvature.

Maximal local thermal hyperemia in able‐bodied and spinal cord injured humans (677.10)

Paraplegic spinal cord injury alters local thermal hyperemic responses. We hypothesized that a similar effect would be observed in tetraplegia. 6 able‐bodied (AB), 5 paraplegic (PARA), and 5 tetraplegic (TETRA) age and gender matched subjects participated. Skin blood flow (SkBF) was monitored by laser‐Doppler flowmetry (LDF) from forearm and calf sites. Local skin temperature (Tloc) was controlled with combined LDF/local heating probe holders. Tloc was measured with thermocouples placed between the probe holders and the skin. Mean arterial pressure (MAP) was recorded by Finapres. After instrumentation, Tloc was increased slowly from normothermic levels to 42°C and maintained at that temperature for at least 25 minutes to cause maximal local vasodilation. Cutaneous vascular conductance was calculated as CVC=LDF/MAP and analyzed by ANOVA. Results: At Tloc=42°C, CVC measured from forearm skin was 47±7mV in AB, 49±8mV in PARA, and 42±8mV in TETRA. These responses did not statistically differ among groups. At Tloc=42°C, CVC measured from calf skin was 26±7mV in AB, 50±8mV in PARA, and 42±8mV in TETRA. These responses differed between AB and PARA (p=0.04) and tended to differ between AB and TETRA (p=0.15). Within groups, forearm responses tended to be greater than calf responses in AB (p=0.06), but not in PARA and TETRA groups. We conclude that spinal cord injury alters maximal SkBF levels in the calf, but not the forearm. In AB persons, maximal SkBF tends to be lower in the calf than the forearm (supported by NIH Grant R03NS083961).Grant Funding Source: Supported by NIH R03NS083961

Coupling of a Thermal Sweating Manikin and a Thermal Model for Simulating Human Thermal Response

This paper is dedicated to simulate human thermal response in transient condition with a coupling system which combines a thermal sweating manikin with a thermal model. The thermal model is applied to provide skin temperature and sweating rate for the thermal sweating manikin, the thermal sweating manikin is used to measure the heat exchange between the human body and the environment. The performance of the coupling system is validated by comparison with human tests from literature. The predicted results show a good agreement with the experimental results in terms of both the tendency and absolute values for mean skin temperature, local skin temperature, and core temperature. The results suggest the coupling system can accurately predict local and overall human thermal response in transient conditions.

Observation of Nanoscale Cooling Effects by Substrates and the Surrounding Media for Single Gold Nanoparticles under CW-Laser Illumination

Understanding the nanoscale heating-induced local thermal response is important but hampered by lack of information on temperatures at such small scales. This paper reports laser-induced heating and thermal equilibration of metal nanoparticles supported on different substrates and immersed in several media. We use single-particle spectroscopy to monitor nanoparticle temperature rises due to laser excitation. Because of changes in the refractive index of the surrounding medium, the scattering spectrum of the gold nanoparticles undergoes a shift that is related to the temperature of the system. We find that the temperature increase depends on both the surrounding medium and the supporting substrate. We furthermore model the nanoparticle temperature using a simplified 1-D heat conduction model with an effective thermal conductivity that takes both substrate and environment into account. The results from this model are also compared to a more detailed 2-D heat transfer analysis. The results presented here are quite new and important to many plasmonic nanoparticle applications where the strong absorption cross section of the nanoparticles leads to a significant temperature rise. In particular, the current work introduces an analysis that can be easily implemented to model the temperature of a nanoparticle supported on a substrate, as is the case in many single-particle measurements.

Local oceanic response to atmospheric forcing in the Gulf Stream region

The dominance of shifts in the location of the Gulf Stream (GS) in the local heat balance was observed in an hourly 15-month record of unprecedented surface mooring measurements at a site in the western North Atlantic occupied from November 2005 to January 2007. Instrumentation on the buoy provided a high quality record of air-sea exchanges of momentum, heat, and freshwater flux; and oceanographic sensors recorded ocean variability in the upper 640m. The mooring was at times in the GS and at other times north of the GS. Our intent was to isolate the local oceanic response to the atmosphere from the influence of the GS shifts. A one-dimensional heat budget analysis indicated that the advective contribution from the GS shifts dwarfed the heat contribution by atmospheric forcing and therefore played the dominant role for upper oceanic thermal variability during the whole time record. A GS case study (i.e., when the surface mooring was in the GS), isolated the upper oceanic response to the atmospheric forcing in the GS and supported the critical role of GS shifts in total oceanic heat content. Through both an Empirical Orthogonal Function (EOF) analysis and by referencing temperatures to that observed at 200m, the impact of GS shifts and atmospheric forcing were decomposed, allowing the local oceanic thermal response to be isolated. This local oceanic response was particularly prominent during the period of sustained heating during summer. A case study of summer conditions revealed a near surface flow consistent with Ekman dynamics within a shallow, warm ocean mixed layer.

Human thermal response with improved AVA modeling of the digits

The arterio-venous anastomoses (AVA) play a major role in the blood circulation in the peripheral body parts. In this work, the segmental bioheat model of Salloum et al. [1] is improved to accurately predict skin blood flow rate in the hands and fingers, and the local and overall human thermal responses in transient environments. The improvements in the model include: 1) extending the artery tree to include the arterial branching to the five fingers; 2) modeling and distribution of the blood flow between the deep and superficial veins in the peripherals; 3) adjusting arteries' radii during dilation and constriction; 4) innovative modeling of AVA of the fingers. The model focus is on the accurate blood flow calculation to the different body segments proposing a better blood control mechanism through relating the arterial tree radii as well as the AVA control mechanism to cardiac output. The skin blood flow and digits' dynamic thermal response predicted by the model were compared with published experimental values on body core and skin temperatures and local skin temperatures of fingers. Good agreement was obtained with experimentally reported values on average skin, core, and finger skin temperature response of subjects exposed to gradual decrease in air temperature from 32.3 °C to 13 °C. The new integrated AVA model of the fingers with the bioheat model is capable of predicting digits' dynamics thermal response with better accuracy than some previous models while also incorporating the complex central and local thermoregulatory functions.

Thermal physiological response to local heating and cooling during sleep

For a healthy and productive life, good sleep is essential, which has prompted studies on how comfortable sleep can be achieved. Understanding the relationship between thermal environment and physiological responses such as skin and core temperatures, and psychological responses such as thermal and sleep sensations is necessary to identify the most suitable thermal environment for sleep. As an energy-saving and practical method of creating the most appropriate thermal environment for sleep, local heating or cooling is sometimes used, which takes into consideration the differences in local thermal responses. We performed this study to identify the most effective thermal environment for inducing comfortable sleep by identifying the physiological responses during sleep on the basis of sleep experiments conducted under local body heating or cooling conditions. We also used a human thermal model, which can be applied for predicting physiological responses.In the experiments, the feet of the subject were the primary area to be heated or cooled, which was achieved by installing a flexible duct with an outlet placed close to the subject's feet and inlet connected to an air conditioner. Differences in the fluctuation of body temperature and sleep stage depended on the airflow direction from the duct to the feet. When air was blown downward towards the feet, body temperature decreased and the subject was able to sleep well. Measured skin and core temperatures were calculated using an improved 27-node human thermal model that was originally developed for use in subjects who are not in sleep. Although skin temperature fluctuated significantly under local cooling, the results calculated using the proposed model agreed well with the measured results since the changes in heat conductance between the skin surface and surrounding environment as a result of the changes in the posture and feet position were taken into account. This result indicates that posture-associated changes in the heat conductance significantly influence skin temperature.

Microstructure-based analysis of thermal- and mechanical behaviors of W/CuCrZr composites and porous W coating

In this work we applied an advanced simulation procedure on two heterogeneous random materials relevant for fusions, mapping high resolution micrographic images of their microstructures into FEM (finite element method) models. This technique enables one to calculate the local thermal and mechanical responses of a material on his real microstructure. This technique also allows one to interpret experimental observations based on the local effects captured by the simulation (within a two-dimensional approximation). The inputs for the FE simulations were created from SEM (scanning electron microscopy) micrographs using the dedicated software OOF2. In this paper, two examples are presented: tensile deformation up to plastic rupture of the W–CuCrZr particulate composite and thermal conduction of plasma-sprayed porous tungsten taking into account its dual-scale porosity. Essential role of the heterogeneous, random morphology of the microstructures is highlighted. Comparison with experimental measurements is discussed.

Acute Endotoxemia Inhibits Microvascular Nitric Oxide-Dependent Vasodilation in Humans

Nitric oxide (NO) is crucial for the microvascular homeostasis, but its role played in the microvascular alterations during sepsis remains controversial. We investigated NO-dependent vasodilation in the skin microcirculation and plasma levels of asymmetric dimethylarginine (ADMA), a potent endogenous inhibitor of the NO synthases, in a human model of sepsis. In this double-blind, randomized, crossover study, microvascular NO-dependent (local thermal hyperemia) and NO-independent vasodilation (post-occlusive reactive hyperemia) assessed by laser Doppler imaging, plasma levels of ADMA, and l-arginine were measured in seven healthy obese volunteers, immediately before and 4 h after either a i.v. bolus injection of Escherichia coli endotoxin (LPS; 2 ng/kg) or normal saline (placebo) on two different visits at least 2 weeks apart. LPS caused the expected systemic effects, including increases in heart rate (+43%, P < 0.001), cardiac output (+16%, P < 0.01), and rectal temperature (+1.4°C, P < 0.001), without change in arterial blood pressure. LPS affected neither baseline skin blood flow nor post-occlusive reactive hyperemia but decreased the NO-dependent local thermal hyperemia response, l-arginine, and, to a lesser extent, ADMA plasma levels. The changes in NO-dependent vasodilation were not correlated with the corresponding changes in the plasma levels of ADMA, l-arginine, or the l-arginine/ADMA ratio. Our results show for the first time that experimental endotoxemia in humans causes a specific decrease in endothelial NO-dependent vasodilation in the microcirculation, which cannot be explained by a change in ADMA levels. Microvascular NO deficiency might be responsible for the heterogeneity of tissue perfusion observed in sepsis and could be a therapeutic target.

Decreased Microvascular Nitric Oxide–Dependent Vasodilation in Postural Tachycardia Syndrome

One variant of postural tachycardia syndrome (POTS), designated low-flow POTS, is associated with decreased peripheral blood flow related to impaired local vascular regulation. To investigate the hypothesis that microvascular endothelial dysfunction produces decreased peripheral blood flow in low-flow POTS, we performed experiments using laser-Doppler flowmetry (LDF) combined with iontophoresis in 15 low-flow POTS patients, 17 normal-flow POTS patients, and 13 healthy reference volunteers varying in age from 14 to 22 years. We tested whether alpha-adrenergic vasoregulation was impaired using iontophoretic delivery of tyramine, phentolamine, and bretylium followed by a norepinephrine dose response. We tested endothelial-dependent and -independent receptor-mediated vasodilation by measuring acetylcholine and sodium nitroprusside dose responses. We tested whether nitric oxide-dependent vasodilation was different in these groups by testing the local thermal hyperemic response to saline used as a reference compared with the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME). Adrenergic and receptor-dependent cutaneous vasoregulation was similar for low-flow POTS, normal-flow POTS, and reference subjects. Thermal hyperemia produced distinctly different findings: there was marked attenuation of the nitric oxide-sensitive plateau during prolonged heating, which was insensitive to L-NAME in low-flow POTS subjects. The pattern of thermal hyperemia response in low-flow POTS subjects during saline administration resembled the pattern in reference subjects during L-NAME administration and was minimally affected by L-NAME. The data suggest that flow-dependent nitric oxide release is reduced in low-flow POTS. This may account for local flow regulation abnormalities.

Microthermal Analysis of Heat Conduction in Silicon Nitrides

Local thermal response in silicon nitride materials was investigated with a microthermal analyzer. Two gas‐pressure‐sintered silicon nitride materials having basically different ultimate firing temperatures were examined. In sintered materials with coarse grains grown at higher temperatures, the bulk thermal conductivity was high while that of individual particles was rather lower due to the presence of impurities. The higher bulk thermal conductivity may be attributed to heat conduction through coarser grains. In sintered materials with finer grains, the bulk thermal conductivity was lower owing to the effects of grain boundaries, despite higher conductivity within individual grains.

Thermal distribution over the cortical surface of the rat brain under direct electrical stimulation

The dynamics of thermal diffusion from the dorsal brain surface were studied in white rats through the intact skull during acute experiments on immobilized or Nembutal anesthetized white rats using a new thermovisualization technique involving direct electrical stimulation of the cortex. Local cortical heating of a 1–4 mm site in the vicinity of the electrodes set in within 160 msec after presentation of a single stimulus, reaching a maximum of 0.2°C by the 2nd-5th sec and slowly decaying to the initial level by the 2nd-3rd min. At the same time, but at a somewhat slower rate, the symmetrically opposite local site in the other hemisphere heated up, followed by a small area in the ipsilateral motor cortex and a number of other zones. Depending on the dose administered, Nembutal inhibits and decelerates the development of these effects and localizes them, raises the minimum threshold of their occurrence, and prolongs their closed state. As anesthesia deepened, the primary heat focus near the stimulating electrodes persisted the longest. The mechanisms underlying local cortical thermal responses and the time parameters of these are discussed and compared with those of the dynamics of standard electrographic effects.