Local Thermal Response Research Articles

Local electrochemical and thermal investigation of a segmented reversible solid oxide fuel cell and electrolyzer

A novel setup has been designed and mounted to investigate the local electrochemical and thermal behavior of a cell from a 4-cell short stack under reversible operation solid oxide fuel cell/solid oxide electrolyzer (SOFC/SOE). It consists in the partition of the cell's oxygen electrode into 20 segments, where each segment is controlled by a specific electronic load. This allows to control the segments independently in galvanostatic or potentiostatic mode. The configuration also enables local electrochemical impedance spectroscopy (EIS) measurements of each segment. 20 thermocouples were added to measure the local temperature of the segments in order to gain a deeper insight into the cell thermal distribution. This helps correlating the local thermal and electrochemical responses to the operating parameters. This specific setup allowed mapping the cell's local behavior based on a multidimensional operating conditions matrix, including current density, temperature, feed gas composition, sweep gas flow and polarization. Moreover, a durability test of more than 1,000 h helped investigating the local long-term degradation in a reversible (day SOE, night SOFC) configuration. These results are of significant importance towards optimal operation of a reversible SOC with enhanced durability.

Local thermal adaptation and local temperature regimes drive the performance of a parasitic helminth under climate change: The case of Marshallagia marshalli from wild ungulates.

Across a species' range, populations are exposed to their local thermal environments, which on an evolutionary scale, may cause adaptative differences among populations. Helminths often have broad geographic ranges and temperature-sensitive life stages but little is known about whether and how local thermal adaptation can influence their response to climate change. We studied the thermal responses of the free-living stages of Marshallagia marshalli, a parasitic nematode of wild ungulates, along a latitudinal gradient. We first determine its distribution in wild sheep species in North America. Then we cultured M. marshalli eggs from different locations at temperatures from 5 to 38°C. We fit performance curves based on the metabolic theory of ecology to determine whether development and mortality showed evidence of local thermal adaptation. We used parameter estimates in life-cycle-based host-parasite models to understand how local thermal responses may influence parasite performance under general and location-specific climate-change projections. We found that M. marshalli has a wide latitudinal and host range, infecting wild sheep species from New Mexico to Yukon. Increases in mortality and development time at higher temperatures were most evident for isolates from northern locations. Accounting for location-specific parasite parameters primarily influenced the magnitude of climate change parasite performance, while accounting for location-specific climates primarily influenced the phenology of parasite performance. Despite differences in development and mortality among M. marshalli populations, when using site-specific climate change projections, there was a similar magnitude of impact on the relative performance of M. marshalli among populations. Climate change is predicted to decrease the expected lifetime reproductive output of M. marshalli in all populations while delaying its seasonal peak by approximately 1 month. Our research suggests that accurate projections of the impacts of climate change on broadly distributed species need to consider local adaptations of organisms together with local temperature profiles and climate projections.

Modeling local thermal responses of individuals: Validation of advanced human thermo-physiology models

Human thermo-physiology models (HTPM) are useful tools to assess dynamic and non-uniform human thermal states. However, they are developed based on the physiological data of an average person. In this paper, we present a detailed evaluation of two sophisticated and well-known models, JOS3 and ThermoSEM, with the objective to evaluate their capabilities in predicting the local skin temperature of individual people as both models use individual parameters such as sex, height, weight, and fat percentage as input. For the purpose of validation, controlled experiments were conducted with six human subjects (3 males, 3 females) at different environmental conditions (22–28 °C). The measured core temperature and the local skin temperature at 14 locations were used to evaluate the predicted values. Outputs from both HTPMs followed the dynamic trend of the experiments, with a root mean squared error (RMSE) of 0.9–0.3 °C for core temperature and 1.3–0.9 °C for mean skin temperature from both ThermoSEM and JOS3 correspondingly. However, the main errors came from the body extremities. The RMSE was different for each subject, and both models showed lower errors in the warmer environment. The average RMSE for the hands of all subjects was 2 °C from ThermoSEM and 1.9 °C from JOS3, while it was 0.8 °C for the forehead in both models. The paper highlights the capabilities and limitations of the selected HTPMs and, furthermore, discusses the application of HTPMs in the field of personalized thermal comfort.

Occupant’s thermal comfort in a radiant ceiling cooling room with hot wall surface

A radiant ceiling cooling (CC) system integrated with a mechanical ventilation system was extensively applied in a modern office in a glass curtain wall building. Thermal comfort in a radiant ceiling cooling room with mixing ventilation (MV) or underfloor air distribution (UFAD) was investigated by objective measurements and subjective questionnaires. The external wall surface temperature and mean radiant temperature were 33.9–34.6°C and 27.2–27.4°C, respectively, with a heat transfer of 41.5 W/m2 from the external wall and 37.8–38.6°C and 27.4–28.2°C with a heat transfer of 69.5 W/m2 from the external wall. The indoor air velocity in the occupied zone was 0.17–0.23 m/s in the room with CC+MV and 0.09–0.16 m/s in the room with CC + UFAD. There was a considerable difference between occupants’ thermal perceptions with different distances away from the external wall. Both the ventilation system type and hot wall surface temperature did not influence occupants’ overall thermal perceptions, but their local thermal sensation and skin temperature. The results suggest that the impacts of ventilation system type and hot wall surface temperature on occupants’ local thermal response should be considered during the design of a radiant ceiling cooling system combined with a mechanical ventilation system.

Thermal responses and skin temperature to moderate temperature ramps in winter: An office-lab study

In order to explore the acceptable temperature limits of humans in temperature ramps by intermittent heating in the north China, the research was conducted in an office-lab. Four indoor dynamic heating environments with different initial temperatures (15–18 °C) and change rates (0.02–0.18 °C/min) were created. The room temperature gradually rose as people entered the room and divided into two phases by the ramping rates, which was fast in the first phase. During the filed experiments, the variations of overall and local thermal responses were investigated while environmental parameters was monitored. Additionally, the local skin temperatures of participants' hand and ankle were also recorded.The results indicated that the variations of skin temperature from different exposed parts were different. It indicated that humans can make active physiological adjustments according to environmental changes. Moreover, the subject's thermal responses were lagging and affected by the thermal experience. The thermal sensation vote (TSV) was statistically different between the two phases. The calf was the most significant factor on the overall thermal sensation. Furthermore, the TSV significantly affected other psychological responses. The relationships between the TSV and other thermal responses were observed. The thermal sensation evaluation models were established.In summary, the indoor temperature of 16–18 °C is recommended as the initial temperature when the temperature ramping rate is less than 0.2 °C/min. This study gives a theoretical guide for the creation of dynamic indoor thermal environments, which is beneficial for thermal comfort, health, and energy saving.

Torsion, energy magnetization, and thermal Hall effect

We study the effective action of hydrostatic response to torsion in the absence of spin connections in gapped $(2+1)$-dimensional topological phases at low temperatures. In previous studies, a torsional Chern-Simons term with a temperature-squared (${T}^{2}$) coefficient was proposed as an alternative action to describe the thermal Hall effect with the idea of balancing the diffusion of heat by a torsional field. However, the question remains whether this action leads to a local bulk thermal response that is not suppressed by the gap. In our hydrostatic effective action, we show that the ${T}^{2}$ bulk term is invariant under variations up to boundary terms considering the geometry dependence of local temperature, which precisely describes the edge thermal current. Furthermore, there are no local boundary diffeomorphism anomalies or bulk inflow thermal currents at equilibrium, and also there is no edge-to-edge adiabatic thermal current pumping upon changing the gravitational background. These results are consistent with exponentially suppressed thermal current for gapped phases.

Central Continental Boreal Summer “Warming Holes” Modulated by Atlantic Multidecadal Oscillation Via Low‐Level Jets

AbstractDespite the accelerated global warming, the central‐eastern U.S. experienced summer daytime cooling during the 20th century. A number of studies have attributed various factors responsible for this abnormal regional cooling, termed the “warming hole (WH)”. This study demonstrates that another WH also existed in the south‐central China that shares similar temporal trend and geographical location to the U.S. WH, including the cooling reversal around 1995. Generalizing the two WHs unravels that they both occurred (a) to the east of major mountain ranges, (b) in heavily cultivated agricultural regions, and (c) near the terminus of the low‐level jets. This study further finds that the WH patterns are the leading mode of surface maximum temperature variability in summer of their respective regions. The WH cooling was consistent with reduction in cloud‐forced solar radiation supported by moisture convergence through weakening of low‐level southerly flow downstream of China WH and strengthening of the southerly flow upstream of U.S. WH. The long‐term trends of WH temperature are highly correlated to the Atlantic Multidecadal Oscillation (AMO) and WH cooling turned into warming around 1995 when the AMO shifted to the positive phase, which combined with overall regional warming, may explain why the summer WH phenomenon has been in diminution for past two decades or so. Given the AMO's association with global climate trend, the WH phenomenon could also be viewed as a local thermal response to the global warming via AMO modulation of regional dynamic and moisture circulation.

On the use of effective thermophysical properties to predict the melting process of composite phase change materials with coarse structures

Composite PCMs combining metallic foam and paraffin are widely used as phase change materials (PCMs) to tailor the properties of pure PCMs and enhance the thermal energy storage/release. For the complex composites structures, the transient thermal response prediction by direct simulation (DS) is not easy in term of geometry generation and computation. The volume-averaged model (1T model) considering the composite PCMs as homogeneous media is sometimes used to deal with thermal transport in Composite PCMs, not always with a sufficiently good local description of non-steady conditions. The paper carries out a set of cases where a composite PCM modelled as an open-pore body-centred cell made of Aluminium (Al) filled with paraffin (i) to investigate the combined effects of the geometry of the unit cell (side length, porosity), the composite sample (sample height) and boundary conditions (heat input) on the heat response; (ii) to identify the local/overall errors in temperature and volume fraction of liquid PCM (and thus of stored heat) induced by the use of 1T model for various geometry/heat flux combinations. Analytical equations are proposed to predict the maximum temperature difference between Al and PCM as well as the maximum temperature difference calculated by applying the 1T or DS model as a function of the open cell structure geometry and heat flux. The main novelty introduced in the paper is the analytical model used to quantify the maximum local error on molten PCM volume fraction for the 1T model, and thus on heat stored/released. The model supplies good local thermal response predictions for fine structures and lower heat flux input. Nevertheless, errors in the volume fraction of molten PCMs predicted for the whole sample are far lower and the 1T model can be easily applied in a wider range of geometry/conditions.

Local Characterization of a Solid Oxide Cell Operated in Fuel Cell and Electrolysis Mode Using Lock-in Thermography

Operando characterization of SOCs generally relies on current–voltage measurements that provide the spatially averaged electrochemical response of the SOC. However, these methods do not fully capture the spatial distribution of the operating conditions (e.g., gas composition, current density). Local information on the operating conditions can be gained by using operando optical characterization methods. In this work, the spatial distribution of the electro-thermal response of an SOC with a 15 cm2 active area operated in fuel cell and electrolysis mode was investigated using lock-in thermography. Lock-in thermography consists of stimulating the solid oxide cell with a sinusoidal current perturbation and analyzing the local thermal response using Fourier transforms. A camera with a silicon-based sensor was used to record the transient temperature field on the oxygen electrode (i.e., the cathode in fuel cell operation) via a specifically designed optical access. The field of view of each pixel was approximately 0.03 mm x 0.03 mm. The Fourier transform generates a compact data set that can be conveniently represented by a phase and amplitude or a real and imaginary image. Using a real–imaginary representation provided a better thermal response contrast than an amplitude–phase representation. The local thermal response was found to be dependent on the direct current bias and the frequency of the current perturbation. The thermal response of the SOC was laterally and longitudinally inhomogeneous, thereby demonstrating the capability of active thermography to characterize the local behavior of an SOC in operando. Lock-in thermography is thus a promising method for defining regions of interest for post-mortem analysis using electron microscopy and helping to link highly localized post-test analysis with spatially averaged operando characterization methods.

Local Characterization of a Solid Oxide Cell Operated in Fuel Cell and Electrolysis Mode Using Lock-in Thermography

Operando characterization of solid oxide cells (SOCs) generally relies on current–voltage measurements that provide the spatially averaged electrochemical response of the SOC. However, these methods do not fully capture the spatial distribution of the operating conditions (e.g., gas composition). To overcome this limitation, lock-in thermography was used to investigate the local electro-thermal behavior of an SOC operated in fuel cell and electrolysis mode. The SOC is stimulated with a sinusoidal current perturbation and the local thermal response analyzed using Fourier transforms. A compact data set is obtained that can be represented by a phase–amplitude or a real–imaginary image, the latter of which offers a better contrast. Here, the local thermal response depended on the current bias and the frequency of the perturbation. The thermal response was laterally and longitudinally inhomogeneous, thereby demonstrating the capability of active thermography to characterize the local behavior of an SOC in operando.

Effects of general imperfect interface/interphase on the in-plane conductivity of thermal composites

The effects of general imperfect interphase/interface models on effective and local thermal conductive responses of fiber reinforced-composites are investigated. A physical interphase model is firstly introduced and then extended to the weakly conducting (WC) and highly conducting (HC) interfaces by satisfying the discontinuity conditions of temperature and normal heat flux, respectively. To simulate different geometric arrangements of fibers, hexagonal and square repeating unit cells (RUCs) are used in this paper. Regarding simulation technique, the locally-exact homogenization theory (LEHT) is extended by considering the aforementioned interphase/interface models to re-produce the localized temperature and heat flux distributions in the unit cells and then to predict the macroscopic thermal conductivities. The present method does not require mesh discretization and pre-processing, but directly obtains the accurate analytical expression of internal domains after solving the thermal differential equations. The unknown coefficients are obtained through applying imperfect interphase/interface conditions and weak-form periodic boundary conditions. Finally, the effective Fourier's formula is established to obtain the overall thermal conductivities of composites. The LEHT is advantageous in fast convergence, numerical stability and computational efficiency, thus providing a good numerical tool in studying the influence of interface parameters on composites. The generated numerical results are in good agreement with the analytical or numerical simulations in the literature. On this basis, the effects of interfacial geometric and physical parameters on the macroscopic coefficients and local thermal responses of the composites are tested. Finally, the thickness of a physical interphase is varied to test its applicability in generating equivalent effect with WC interface and HC interface. Generally, the imperfect interfacial effects play important roles in the thermal conductive response of composite materials. In the meantime, the proposed method is of great significance for the study of thermal conductions of composite microstructures.

Allele-Specific Expression and Evolution of Gene Regulation Underlying Acute Heat Stress Response and Local Adaptation in the Copepod Tigriopus californicus.

Geographic variation in environmental temperature can select for local adaptation among conspecific populations. Divergence in gene expression across the transcriptome is a key mechanism for evolution of local thermal adaptation in many systems, yet the genetic mechanisms underlying this regulatory evolution remain poorly understood. Here we examine gene expression in 2 locally adapted Tigriopus californicus populations (heat tolerant San Diego, SD, and less tolerant Santa Cruz, SC) and their F1 hybrids during acute heat stress response. Allele-specific expression (ASE) in F1 hybrids was used to determine cis-regulatory divergence. We found that the number of genes showing significant allelic imbalance increased under heat stress compared to unstressed controls. This suggests that there is significant population divergence in cis-regulatory elements underlying heat stress response. Specifically, the number of genes showing an excess of transcripts from the more thermal tolerant (SD) population increased with heat stress while that number of genes with an SC excess was similar in both treatments. Inheritance patterns of gene expression also revealed that genes displaying SD-dominant expression phenotypes increase in number in response to heat stress; that is, across loci, gene expression in F1's following heat stress showed more similarity to SD than SC, a pattern that was absent in the control treatment. The observed patterns of ASE and inheritance of gene expression provide insight into the complex processes underlying local adaptation and thermal stress response.

Transient conduction for thermal diffusivity simulation of a graphene/polymer and its full-field validation with image reconstruction

A 3D finite element model is presented to simulate the thermal transport properties of a polymer composite made of GradeM25 graphene nanoplatelets (GnP) in a low-viscosity bisphenol-A epoxy resin. This is a multi-scale approach that consists of a unit cell, a representative volume element (RVE) and a macroscopic specimen model. There is a hierarchy of structural scales, where the response at one size level is described by one (or more) parameters and passed to the next level up. At the unit cell level, the material nano-characteristics are used to calculate the local thermal response, while the material architecture is captured by the RVE. A statistical sample is studied and the average thermal response is compared to the macroscopic experimental data. Afterwards, the experimental reinforcement distribution is applied to the macro specimen model. The thermal diffusivity mapping was obtained numerically and compared to the flash method measurements following the CEN/CWA 16799 standard, through the decomposition and reconstruction of the fields with orthogonal Zernike polynomials and their comparison on a linear correlation plot. Finally, the simulation of the transient thermal response was successfully validated under both generic and full-field comparison. This research work is, therefore, proposing a validated simulation tool to estimate the thermal response of polymer nanocomposites, while being engineer-friendly to promote advanced material design that eliminates the trial and error approach.

Local thermal responses of male college students of three thermal preference groups

This study analyzes the differences in the local thermal responses of three thermal preference groups, namely, the cool preference group (Gcp), the neutral preference group (Gnp), and the warm preference group (Gwp). Eighteen male college students with different thermal preferences (6 in each thermal preference group) were subjected to climate chamber tests in three different thermal environments, at operative temperatures of 21 °C, 19 °C, and 17 °C. The local skin temperature, conductive heat flux, and thermal sensation vote (TSV) of seven body parts were recorded during the tests. Subsequently, the non-uniformity coefficients of skin temperature and conductive heat flux were calculated. The results indicate that there are statistically significant differences (p < 0.05) between each group in terms of the local skin temperature, conductive heat flux, and TSV, especially those recorded at the hand. Consequently, the hand is a key body part that can be used to distinguish between Gcp and Gwp. In addition, Gwp had higher non-uniformity coefficients of skin temperature and conductive heat flux than Gnp and Gcp, which indicates that non-uniformity coefficients can be used to evaluate the local physiological parameters of different thermal preference groups. The findings obtained herein provide fundamental knowledge for the evaluation of individual and local thermal comfort.

Discerning Localized Thermal Heating from Mechanical Strain Using an Embedded Distributed Optical Fiber Sensor Network.

Prior research has demonstrated that distributed optical fiber sensors (DOFS) based on Rayleigh scattering can be embedded in carbon fiber/epoxy composite structures to rapidly detect temperature changes approaching 1000 °C, such as would be experienced during a high energy laser strike. However, composite structures often experience mechanical strains that are also detected during DOFS interrogation. Hence, the combined temperature and strain response in the composite can interfere with rapid detection and measurement of a localized thermal impulse. In this research, initial testing has demonstrated the simultaneous response of the DOFS to both temperature and strain. An embedded DOFS network was designed and used to isolate and measure a localized thermal response of a carbon fiber/epoxy composite to a low energy laser strike under cyclic bending strain. The sensor interrogation scheme uses a simple signal processing technique to enhance the thermal response, while mitigating the strain response due to bending. While our ultimate goal is rapid detection of directed energy on the surface of the composite, the technique could be generalized to structural health monitoring of temperature sensitive components or smart structures.

Local thermal adaptation and limited gene flow constrain future climate responses of a marine ecosystem engineer.

Rising ocean temperatures and extreme temperature events have precipitated declines and local extinctions in many marine species globally, but patterns of loss are often uneven across species ranges for reasons that are poorly understood. Knowledge of the extent of local adaptation and gene flow may explain such patterns and help predict future trajectories under scenarios of climate change. We test the extent to which local differentiation in thermal tolerance is influenced by gene flow and local adaptation using a widely distributed intertidal seaweed (Hormosira banksii) from temperate Australia. Population surveys across ~2,000 km of the species range revealed strong genetic structuring at regional and local scales (global F ST = 0.243) reflecting extremely limited gene flow, while common garden experiments (14‐day exposures to 15, 18, 21°C) revealed strong site differences in early development and mortality in response to elevated temperature. Embryos from many sites spanning a longitudinal thermal gradient showed suppressed development and increased mortality to elevated water temperatures, but populations originating from warmer and more variable thermal environments tended to be less susceptible to warming. Notably, there was significant local‐scale variation in the thermal responses of embryos within regions which was corroborated by the finding of small‐scale genetic differences. We expect the observed genetic and phenotypic differentiation to lead to uneven responses to warming sea surface temperatures in this important marine foundation species. The study highlights the challenges of predicting species responses to thermal stress and the importance of management strategies that incorporate evolutionary potential for “climate‐proofing” marine ecosystems.

The effect of a power assisted filtering device on the local and whole body thermal response in cold and hot environments

The effect of a power assisted filtering device on the local and whole body thermal response in cold and hot environments

Assessment of overall body thermal sensation based on the thermal response of local cutaneous thermoreceptors.

In non-uniform environments, different body parts may experience different ranges of physical/environmental parameters. Therefore, to assess the overall thermal sensation in non-uniform environments, the local temperature/thermal sensation of various body parts should be calculated. The local temperature/thermal sensation based on cutaneous thermoreceptor (TRs) responses has been evaluated using MSTB (Multi-Segmental Thermoregulatory Bioheat) model and LTRESP (Local Thermal Response) index in our recent studies. In the present study, a new combined method was proposed to evaluate the overall thermal sensation considering the effects of local sensations of various body segments. In this new method, the local sensations predicted by LTRESP index were defined as the input data for UCB model to predict the overall thermal sensation. So, there was no need to feed it with experimental data to assess the whole-body thermal sensation. Meanwhile, in this method, the overall thermal sensation was predicted taking into account the cutaneous TRs thermal responses. The results indicated that the new combined method could evaluate the overall thermal sensation with a reasonable accuracy under different environmental conditions. Thus, the new method could be practical for predicting the overall thermal sensation in both uniform and non-uniform thermal environments.

Localised opto-thermal response of nematic liquid crystal to laser light

ABSTRACTWe report on the thermal response of a thin nematic liquid crystal layer to a strong laser pulse, which is partially absorbed by the Indium Tin Oxide electrodes of the measuring LC cell. We measure local increase and temperature profile of the heated region and we measure the time response of the birefringence of this nematic layer. It is found that local increase of the temperature due to absorption of a 90 Mw laser light of 10 MS duration can easily exceed °C and depends on the localisation and focusing of the laser beam. Local thermal response of the heated nematic cell is measured by monitoring the time dependence of birefringence during the cooling and we found that nematic layer can be cooled down at an extremely fast rate of 10000 K/s. Optical retardation of 200 nm can be switched in 100 μs by laser pulse absorption and heating/cooling.

A new local index for predicting local thermal response of individual body segments

Physiologically, the thermal sensation/perception of human body is related to the response of cutaneous thermoreceptors (TRs) to the environment. However, the thermal response of skin warm and cold TRs is a function of two important factors: TRs temperatures and their time derivative at the subcutaneous locations of TRs. The available thermal models based on TRs response consider the same sensitivity for all thermal receptors of body. Thus, they estimate an average value of thermal response for whole body TRs. Therefore, considering the physiological thermal perception of humans, this study has presented a local thermal response index for estimating local sensation of different body segments based on local thermal response of individual TRs. Further, this index has used the ASHRAE thermal sensation scales to express the TRs thermal responses. Also, the new multi-segmental thermoregulatory bioheat model (MSTB) is utilized to calculate the individual TRs temperature. Finally, the predicted local thermal sensation by the new local index has been compared with published measured data under uniform/non-uniform thermal conditions. The results show that the local thermal sensation of individual body parts could be evaluated by the new local predictive index (LTRESP) with reasonable accuracy under various thermal conditions.