Steady-state Temperature Research Articles

Energy dissipated by spherical nanoparticles debonding in nanocomposites under cryogenic and steady state conditions

In this paper, an analytical model was presented to estimate the influence of nanoparticles size and volume fraction on the debonding dissipation energy of nanoparticles/polymer nanocomposites in cryogenic temperature. A spherical representative volume element including a nanoparticle and a pure polymer phase was considered. It was assumed that the temperature is uniform within the whole RVE, i.e., a steady state temperature condition. Using the stress and displacement fields within the constituents of RVE, the dependence of the debonding dissipation energy on the nanoparticles size and volume fraction was obtained at a certain temperature. In addition to the analytical model, a finite element (FE) analysis using surface-based cohesive method was carried out to simulate the debonding process under cryogenic and steady state conditions. It was observed that the nanoparticles size has a significant effect on the energy dissipated by debonding. Moreover, the results manifested that the nanoparticles volume fraction affects the dissipation energy of debonding in nanocomposites reinforced by larger nanoparticles at cryogenic temperature. A good agreement was also found between the FE analysis results and the closed-form solution data. The conclusions obtained by this closed-form solution can be useful as a trigger for the other energy dissipation mechanisms occurred in the nanocomposites reinforced by nanofillers such as silica, alumina, titania, etc.

Junction temperature of CMOS electronics cooled by a Stirling cryocooler

This case study addresses the practical challenges associated with operating cryo-CMOS electronics. Previous research has been largely confined to impractical liquid cryogen cooling and the few under-reported examples of implementing electric cryocoolers. This study further clarifies the operation of cryo-CMOS devices cooled by electric cryocoolers. It develops and experimentally validates an analytical relation between the junction temperature and the parameters of a cryogenic system. To validate this relationship, we placed a printed circuit board in a thermal chamber, cooled it to 173 K using a Stirling cryocooler, and varied input clock frequencies. The measured values of the junction temperature were compared with calculations, which showed good prediction accuracy with a coefficient of variance of ±2%, a mean biased error of −2%, and a determination coefficient of 0.92. In addition, the measurements provided evidence for a multi-fold increase in the clock frequency of cryo-CMOS electronics. The results of this study help estimate accurately the steady-state junction temperature of cryo-CMOS devices in a wide range of cryogenic temperatures for different types of cryocoolers.

Safety and Efficacy of Extracorporeal Membrane Oxygenation Heating Units.

Patient temperature during extracorporeal membrane oxygenation (ECMO) is commonly managed by dedicated heating units (HUs) that are integrated into ECMO circuitry. Currently, no HU has received approval for ECMO by the FDA in the United States. Older FDA-approved HUs have been implicated in life-threatening patient infections and are no longer manufactured or available for use in the United States. We performed laboratory tests to evaluate the safety and efficacy of the Micro-Temp and the HTP-1500 HU systems that are potentially suitable for use in ECMO and describe our initial experience with the HTP-1500 HU after being placed in clinical service. Both units demonstrated similar heating efficacy, with the HTP-1500 achieving steady-state temperature approximately 5 h earlier than the Micro-Temp. Microorganisms were detected in the water compartment of all HUs prior to and after performing the manufacturer's recommended cleaning procedure, and after implementation of the HTP-1500 into clinical use we observed a decrease in the rate of bloodstream infection/ECMO days which did not reach statistical significance. Based on the results of this analysis and our institutional experience, we believe that integration of the HTP-1500 HU, an easily replaceable HU, into ECMO systems may reduce the risk of bacterial contamination and thus nosocomial infection when the devices are cleaned and maintained according to manufacturer's guidelines.

A feasibility study on using fNIRS brain signals to recognize personal thermal sensation and thermal comfort conditions.

Many studies have shown some relationships between thermal perception (including thermal sensation and thermal comfort) and human physiological parameters, such as brain signals. However, further research is still needed on how these parameters can help recognize the state of a human's personal thermal perception. This study aims to investigate the potential of using fNIRS brain signals to evaluate and predict personal thermal perception and cognitive performance in a steady-state temperature. The present study investigated changes in the fNIRS signal during ambient temperature manipulation. Thirty healthy young individuals were selected as the subjects, and they were exposed to two steady temperatures of 28.8 and 19 °C. After acclimatizing to either temperature, the oxy/deoxy-hemoglobin changes of the prefrontal cortex (PFC) were measured in both rest and cognitive task states using 16-channel fNIRS. Results showed that exposure to different temperatures was significantly associated with the brain signals recorded during the task state. Many significant correlations were discovered between fNIRS signals and thermal perceptionindices. Furthermore, subjects' performance changes led to changes in the fNIRS signals. Logistic regression showed that fNIRS can determine whether a person is thermally comfortable or uncomfortable.

Evaluation of a wind tunnel designed to investigate the response of evaporation to changes in the incoming long-wave radiation at a water surface

Abstract. To investigate the sensitivity of evaporation to changing long-wave radiation we developed a new experimental facility that locates a shallow water bath at the base of an insulated wind tunnel with evaporation measured using an accurate digital balance. The new facility has the unique ability to impose variations in the incoming long-wave radiation at the water surface whilst holding the air temperature, humidity and wind speed in the wind tunnel at fixed values. The underlying scientific aim is to isolate the effect of a change in the incoming long-wave radiation on both evaporation and surface temperature. In this paper, we describe the configuration and operation of the system and outline the experimental design and approach. We then evaluate the radiative and thermodynamic properties of the new system and show that the shallow water bath naturally adopts a steady-state temperature that closely approximates the thermodynamic wet-bulb temperature. We demonstrate that the long-wave radiation and evaporation are measured with sufficient precision to support the scientific aims.

The axial temperature distribution of the channel in the linear reactivity model

Employing a linear reactivity burnup-dependent model, we investigate how the new axial flattened power densities (Pontes and Driscoll models) affect the steady-state axial temperature distributions of the sub-channel in pressurized water reactors (PWR). Two approaches were used: analytical, using mean parameters, and numerical, using appropriate empirical correlations. The Pontes distribution showed advantages in all evaluated regions except in the centerline of the fuel rod, outperformed by the Driscoll distribution. The results indicate that the linear reactivity model (LRM) is extremely advantageous in the evaluated reactor, as it reduces axial temperatures on hot spots and has the potential to enhance the reactor’s safety, efficiency, and longevity.

Seismic structure beneath the Avacha and Koryaksky volcanoes in Kamchatka based on the data of permanent and temporary networks

Avacha and Koryaksky are active volcanoes located in the vicinity of Petropavlovsk-Kamchatsky, the main city of Kamchatka, and they represent a serious hazard to the surrounding population and infrastructure. Here we investigate the upper-crustal structure beneath these volcanoes by implementing local earthquake tomography based on data from permanent seismic stations and from a temporary network installed in 2018–2019. Although the total amount of seismic rays recorded by the temporary network dataset is much lower, adding this data and attributing an appropriate weight lead to considerable increase of the resolution compared to the case of using merely the permanent network data. The resulting distributions of the P and S wave velocities, and especially the Vp/Vs ratio, reveal two magma reservoirs located below Avacha and Koryaksky volcanoes. Different depths of their upper limits explain differences in the eruption activity styles of these volcanoes. Below the Avacha Pass, we observe a thick layer of low-velocity soft volcaniclastic sediments formed due to the activity of both volcanoes. A conservative numerical estimate of a steady-state conductive temperature field around the magma source below Avacha demonstrates that the high temperature zone can be reached by drilling a well to a reasonable depth, thus suggesting that the area might be exploited as a source of geothermal energy.

Transient thermal analysis of the rotary compressor during startup process

The transient temperature distribution and heat transfer characteristics of the rotary compressor are crucial to its reliability and efficiency of the compressor. In this paper, a transient mathematical model on predicting the temperature in the compressor during startup is proposed. Control volumes are divided including the fluid and solid domains. The convective heat transfer coefficient of each surface is discussed. A coupled solution method and its Fortran calculation program are developed. This mathematical model is experimentally validated by comparing the measured and calculated temperatures of the compressor. The results shows that calculated temperatures are consistent with the measured results during the startup process. The maximum error of the steady-state temperature is within 2 °C. The refrigerant in the compression unit mainly absorbs heat from the refrigerant in the lower chamber. Measures should be taken to reduce the heating of the upper bearing surface by the refrigerant in the lower chamber to improve the volume and indicated efficiencies.

Model-based battery thermal parameter optimization using symbolic regression

Lithium-ion battery packs are commonly used in electromobility and distributed energy storage. However, keeping both cell temperature and inter-cell temperature differences within operating ranges is important to avoid a negative impact on performance and lifespan. For this reason, modeling the thermal behavior of battery packs in different operating conditions is crucial for both design and practical use.In this work, we optimize the parameters of a battery thermal model using a symbolic regression method based on evolutionary algorithms. We obtain power-type expressions for the drag coefficient, friction factor, and heat transfer correlation (Nusselt number), as a function of the Reynolds number and the cell spacing factor, plus the Prandtl number in the case of the Nusselt number. The model is adjusted with CFD simulations of battery modules containing up to 102 cells to obtain the steady-state temperature distribution. Compared to CFD simulations, the proposed model gets a mean absolute percentage error of 2.39 % in estimating the temperature in a 53-cell battery pack. The adjusted parametric thermal model is validated with experimental data for cooling down a battery pack and a single cell, obtaining a mean absolute percentage error of 1.26 % and 4.68 %, respectively, in estimating the dynamic temperature balance.The adjusted parametric thermal model and the mathematical expressions obtained for the drag coefficient, friction factor, and Nusselt number, can be useful for designing battery thermal management systems in electromobility and distributed energy storage.

Evidence-based numerical building model enhancement and building energy efficiency evaluation in the case of Morocco

This paper presents a framework for numerical building validation enhancement based on detailed building specifications from in-situ measurements and evidence-based validation assessment undertaken on a detached sustainable lightweight building in a semi-arid climate. The validation process has been undergone in a set of controlled experiments – a free-float period, and steady-state internal temperatures. The validation was conducted for a complete year with a 1-min time step for the hourly indoor temperature and the variable refrigerant flow (VRF) energy consumption. The initial baseline model was improved by three series of validation steps per three different field measurements including thermal transmittance, glazing thermal and optical properties, and airtightness. Then, the accurate and validated model was used for building energy efficiency assessment in 12 regions of Morocco. This study aims to assess the effect of accurate building characteristics values on the numerical model enhancement. The initial CV(RMSE) and NMBE have improved respectively from 14.58 % and −11.23 %–7.85 % and 1.86 % for the indoor temperature. Besides, from 31.17 % to 14.37 %–20.57 % and 9.77 % for energy consumption. The findings demonstrate that the lightweight construction with the use of a variable refrigerant flow system could be energy efficient in the southern regions of Morocco.

The Experimental and Theoretical Effect of Fire on the Structural Behavior of Laced Reinforced Concrete Deep Beams

A Laced Reinforced Concrete (LRC) structural element comprises continuously inclined shear reinforcement in the form of lacing that connects the longitudinal reinforcements on both faces of the structural element. This study conducted a theoretical investigation of LRC deep beams to predict their behavior after exposure to fire and high temperatures. Four simply supported reinforced concrete beams of 1500 mm, 200 mm, and 240 mm length, width, and depth, respectively, were considered. The specimens were identical in terms of compressive strength ( 40 MPa) and steel reinforcement details. The same laced steel reinforcement ratio of 0.0035 was used. Three specimens were burned at variable durations and steady-state temperatures (one hour at 500 °C and 600 °C, and two hours at 500 °C). The flexural behavior of the simply supported deep beams, subjected to the two concentric loads in the middle third of the beam, was investigated with ABAQUS software. The results showed that the laced reinforcement with an inclination of 45˚ improved the structural behavior of the deep beams, and the lacing resisted failure and extended the life of the model. The optimal structural response was observed for the specimens. The laced reinforcement improved the failure mode and converted it from shear to flexure-shear failure. The parametric study showed that the lacing bars remarkably improved the strength of the deep beams and they were not affected more by the steady-state temperature and duration. Furthermore, a greater increase in load-carrying capacity was associated with an increase in the flexural diameter of approximately 12 and 16 mm by approximately 24.77% and 87.61%, respectively, compared to the reference LRC deep beams.

Parameter variation effects on millimeter wave dosimetry based on precise skin thickness in real rats

This study presents a parametric analysis of the steady-state temperature elevation in rat skin models due to millimeter wave exposure at frequencies from 6–100 GHz. The statistical data of the thickness of skin layers, namely epidermis, dermis, dermal white adipose tissue, and panniculus carnosus, were measured for the first time using the excised tissues of real male Sprague–Dawley rats. Based on the precise structure obtained from the histological analysis of rat skin, we solve the bioheat transfer equation to investigate the effects of changes in parameters, such as body parts and thermal constants, on the absorbed power density and temperature elevation of biological tissues. Owing to the notably thin dermal white adipose tissue layer, the surface temperature elevation in the rat head and dorsal skin at 6–100 GHz is 52.6–32.3% and 83.3–58.8% of the average values of different human skin models, respectively. Our results also reveal that the surface temperature elevation of rat skin may correlate with the tissue thickness and deep blood perfusion rates.

Thermal analysis methods for wound rotor synchronous motors with water-cooling jackets

A thermal equivalent circuit (TEC) was presented as an effective thermal analysis method for a wound rotor synchronous motor (WRSM) with a water-cooling jacket. The effectiveness of the TEC analysis was verified by comparison with the results of the experiments and numerical analysis. The steady-state temperature obtained from the TEC matched well with those obtained from the experiments and numerical analysis. The transient temperature variation in each part of the WRSM estimated by the TEC was in good agreement with the experimental results. Therefore, TEC can easily estimate the temperature information of the WRSM.

Inspecting the role of vapour loss and other model strategies in the mod-elling of a bentonite thermo-hydraulic cell

Inspecting the role of vapour loss and other model strategies in the mod-elling of a bentonite thermo-hydraulic cell

A Closer Look at the Evolution of Supercooled Cloud Droplet Temperature and Lifetime in Different Environmental Conditions with Implications for Ice Nucleation in the Evaporating Regions of Clouds

Abstract This study investigates the evolution of temperature and lifetime of evaporating, supercooled cloud droplets considering initial droplet radius (r0) and temperature (), and environmental relative humidity (RH), temperature (T∞), and pressure (P). The time (tss) required by droplets to reach a lower steady-state temperature (Tss) after sudden introduction into a new subsaturated environment, the magnitude of ΔT = T∞ − Tss, and droplet survival time (tst) at Tss are calculated. The temperature difference (ΔT) is found to increase with T∞, and decrease with RH and P. ΔT was typically 1–5 K lower than T∞, with highest values (∼10.3 K) for very low RH, low P, and T∞ closer to 0°C. Results show that tss is <0.5 s over the range of initial droplet and environmental conditions considered. Larger droplets (r0 = 30–50 μm) can survive at Tss for about 5 s to over 10 min, depending on the subsaturation of the environment. For higher RH and larger droplets, droplet lifetimes can increase by more than 100 s compared to those with droplet cooling ignored. Tss of the evaporating droplets can be approximated by the environmental thermodynamic wet-bulb temperature. Radiation was found to play a minor role in influencing droplet temperatures, except for larger droplets in environments close to saturation. The implications for ice nucleation in cloud-top generating cells and near cloud edges are discussed. Using Tss instead of T∞ in widely used parameterization schemes could lead to enhanced number concentrations of activated ice-nucleating particles (INPs), by a typical factor of 2–30, with the greatest increases (≥100) coincident with low RH, low P, and T∞ closer to 0°C. Significance Statement Cloud droplet temperature plays an important role in fundamental cloud processes like droplet growth and decay, activation of ice-nucleating particles, and determination of radiative parameters like refractive indices of water droplets. Near cloud boundaries such as cloud tops, dry air mixes with cloudy air exposing droplets to environments with low relative humidities. This study examines how the temperature of a cloud droplet that is supercooled (i.e., has an initial temperature < 0°C) evolves in these subsaturated environments. Results show that when supercooled cloud droplets evaporate near cloud boundaries, their temperatures can be several degrees Celsius lower than the surrounding drier environment. The implications of this additional cooling of droplets near cloud edges on ice particle formation are discussed.

Dry Friction and Wear Behavior of Laser-Sintered Graphite/Carbon Fiber/Polyamide 12 Composite.

Carbon fiber-reinforced polymers (CFRPs) are being used extensively in modern industries that require a high strength-to-weight ratio, such as aerospace, automotive, motorsport, and sports equipment. However, although reinforcement with carbon fibers improves the mechanical properties of polymers, this comes at the expense of abrasive wear resistance. Therefore, to efficiently utilize CFRPs in dry sliding contacts, solid lubricant is used as a filler. Further, to facilitate the fabrication of objects with complex geometries, selective laser sintering (SLS) can be employed. Accordingly, in the present work, graphite-filled carbon fiber-reinforced polyamide 12 (CFR-PA12) specimens were prepared using the SLS process to explore the dry sliding friction and wear characteristics of the composite. The test specimens were aligned along four different orientations in the build chamber of the SLS machine to determine the orientation-dependent tribological properties. The experiments were conducted using a pin-on-disc tribometer to measure the coefficient of friction (COF), interface temperature, friction-induced noise, and specific wear rate. In addition, scanning electron microscopy (SEM) of tribo-surfaces was conducted to specify the dominant wear pattern. The results indicated that the steady-state COF, contact temperature, and wear pattern of graphite-filled CFR-PA12 are orientation-independent and that the contact temperature is likely to approach an asymptote far below the glass transition temperature of amorphous PA12 zones, thus eliminating the possibility of matrix softening. Additionally, the results showed that the Z-oriented specimen exhibits the lowest level of friction-induced noise along with the highest wear resistance. Moreover, SEM of tribo-surfaces determined that abrasive wear is the dominant wear pattern.

Gravity modulation, thermal radiation and viscous dissipation impact on heat transfer and magnetic flux across gravity-driven magnetized circular cylinder

Heat transfer in burners, combustion engines and energy consumption through nuclear explosions is significantly influenced by radiations. In missile nozzles, nuclear power plants for aerospace uses, and gaseous-core nuclear rocket systems, the radiations are considered for evaluating heating significance. The significance of present study is to compute heat and magnetic flux behavior across various angles π/6, π/4, π/3, π/2, π and 3π/2 of gravity-driven magnetized cylinder under gravity modulation, thermal radiation and viscous dissipation. The aim of this research is to examine wave oscillations in heat and current density along magnetic-driven circular cylinder. The computational and mathematical model is evaluated in terms of coupled periodic partial differential equations (PDE). The appropriate dimensionless variables are used to convert governing periodic model into non-dimensional form. The dimensionless formulations are transformed into steady and oscillatory form. To explore physical and numerical findings, the finite difference method with primitive formulations is applied for smooth algorithm in FORTRAN language. The significant results are explored for various pertinent parameters. The oscillatory magnetic flux and heat transmission are plotted by using steady state temperature and magnetic boundary layers. It is found that the prominent amplitude in velocity increases as reduced gravity increases at each angle. The maximum oscillating amplitude in heat transfer enhances at each angle as viscous dissipations and solar radiation increases.

Efficient photothermal therapy with spatially localized high-temperature generation by refractory absorber

In this work, we propose a titanium nitride (TiN)-based ultra-broadband perfect absorber from the ultraviolet to near-infrared wavelength ranges with the average absorptivity up to 96.7%. The weighted absorption efficiency of the solar radiation energy reaches 95.6%. In addition, photothermal therapy is conducted on such absorber, showing the effectively confined local high-temperature in the vicinity of the device. The steady-state temperature reaches 327 K at a depth of 3 mm beneath the tissue surface, leading to the efficient optical damage exceeding 90% for the surrounding diseased tissue only by a 3-min illumination. Such moderate photothermal therapy adequately meets the requirements for inactivating tumor cells and hold wide applications in the photo-biomedical science and technology.

Penumbral cooling in ischemic stroke with intraarterial, intravenous or active conductive head cooling: A thermal modeling study

In ischemic stroke, selectively cooling the ischemic penumbra might lead to neuroprotection while avoiding systemic complications. Because penumbral tissue has reduced cerebral blood flow and in vivo brain temperature measurement remains challenging, the effect of different methods of therapeutic hypothermia on penumbral temperature are unknown. We used the COMSOL Multiphysics® software to model a range of cases of therapeutic hypothermia in ischemic stroke. Four ischemic stroke models were developed with ischemic core and/or penumbra volumes between 33–300 mL. Four experiments were performed on each model, including no cooling, and intraarterial, intravenous, and active conductive head cooling. The steady-state temperature of the non-ischemic brain, ischemic penumbra, and ischemic core without cooling was 37.3 °C, 37.5–37.8 °C, and 38.9–39.4 °C respectively. Intraarterial, intravenous and active conductive head cooling reduced non-ischemic brain temperature by 4.3 °C, 2.1 °C, and 0.7–0.8 °C respectively. Intraarterial, intravenous and head cooling reduced the temperature of the ischemic penumbra by 3.9–4.3 °C, 1.9–2.1 °C, and 1.2–3.4 °C respectively. Active conductive head cooling was the only method to selectively reduce penumbral temperature. Clinical studies that measure brain temperature in ischemic stroke patients undergoing therapeutic hypothermia are required to validate these hypothesis-generating findings.

Anti-cracking coating with wrinkled morphology for enhancing oxidation resistance of carbon-based fiber aerogel

In our previous work, ceramic precursor coating with wrinkled morphology was obtained by cross-linking gradient generated from ultraviolet and cross-linking agent to improve the anti-cracking of the coating in the pyrolysis. However, the cross-linking gradient was difficult to control with ultraviolet and cross-linking agent. Herein, a simple method was proposed to form the wrinkled morphology of the coating by the steady-state temperature gradient field generated from constant temperature pre-treatment. Composite aerogels were prepared by pyrolysis at high temperature. The thermal insulation and oxidation resistance of the composite aerogels were explored. The heat transfer behavior within the composite aerogels was analyzed by simulation. The results showed that the stored strain of wrinkled morphology counteracted the shrinkage of ceramic precursor polymer during the pyrolysis, which prevented the cracking of the coating. Compared with the aerogels of our previous work, the composite aerogels of this work demonstrated improved thermal insulation and oxidation resistance.