Thermal Response Time Research Articles

Diagnostic Protocol for Thermal Performance of District Heating Pipes in Operation. Part 1: Estimation of Supply Pipe Temperature by Measuring Temperature at Valves after Shutdown

This study evaluates temperatures measured at district heating (DH) valves in manholes and their usability for non-destructively assessing the thermal performance of buried DH pipes. The study was conducted as a field test in which part of a DH network was shut down and the temperature decline in the valves was analysed in terms of absolute temperature and thermal response time from the DH pipe to the top of the valve. The calculated and measured supply pipe temperatures by the drainage valves were in good agreement, with 1% deviation. The valve measurement analysis from this study shows that the drainage valve has good potential to serve as a measurement point for assessing the thermal status of a DH network. However, the shutdown valve measurements were greatly affected by the manhole environment.

Hybrid Nanocomposite Based Graphene Sensor for Ultrasensitive Clomipramine HCl Detection

AbstractA potentiometric sensor modified with a nanocomposite of montmorillonite sheets decorated with polyaniline nanofibers (MT‐PANI‐NFs) as an efficient electroactive material and tricresyl phosphate (TCP) as a solvent mediator has been developed for the estimation of clomipramine HCl (CLP.HCl). The optimum potentiometric performance of the sensor was achieved by mixing of MT‐PANI‐NFs : TCP : graphene with a ratio of 2.69 : 30.11 : 67.20 (% wt/wt). The sensor exhibited a Nernstian slope of 59.0±0.1 mV decade−1 over the concentration range of 1.0×10−5−1.0×10−2 mol L−1 with a theoretically calculated detection limit of 5.0×10−6 mol L−1. The sensor performance was scrutinized in terms of several factors including thermal stability, pH effect, response time and selectivity. As, it displayed a high thermal stability at various temperature degrees (10–60 °C) with pH independency in the range of 3.5–8.5. Additionally, the developed sensor exhibited a very rapid performance for CLP.HCl detection with a fast response time of 4 s and reflecting a superior selectivity towards CLP.HCl over the other interfering species. SEM (scanning electron microscope) was used as a characteristic tool for the investigation of the proposed graphene sensor surface. Furthermore, the graphene sensor has been efficiently used for CLP.HCl estimation in its pharmaceutical formulations.

Synthesis and properties of high thermal conductivity Ag shell-coated phase change materials

Phase change micro/nanocapsules with high thermal conductivity shells have extensive application prospects in solar energy storage systems and electronics cooling. To improve the heat transfer of the capsules, a method of preparing Ag-shell coated phase change micro/nanocapsules was developed, where the AgBr ultrafine solid particles are introduced to enhance the rigidity of emulsion droplets in the liquid-solid phase transition process, and by employing hydroquinone as the reductant to repeatedly reduce the AgBr that had been adhered to the surface of the emulsion droplets, an Ag shell is formed on the surface of the cores. In this work, palmitic acid (PA) is used as the core material, and the prepared PA/Ag nanocapsules (100–600 nm) exhibit high thermal storage capability and good thermal reliability. The bulk thermal conductivity of the nanocapsules can be as high as 4.072 W/(m·K), indicating that the Ag shell can effectively improve the thermal conductivity of the nanocapsules. Besides, the thermal response of the nanocapsules is estimated by simulating a single-particle heat transfer process considering nanoscale effects, and the results demonstrate that the thermal response time of PA/Ag nanocapsule (350 nm) in working fluid (water, 80 °C) could be as short as 150ns.

Numerical investigation of skin and subcutaneous tissue thermal injury during elevated heating

SummaryThis paper presents the non‐Fourier bioheat transfer prediction methodology of human skin to determine skin burn injury with non‐ideal properties of tissue, metabolism and blood perfusion. The dual‐phase lag bioheat transfer model with the inclusion of evaporation is developed for the triple‐layer skin tissues. The developed models are solved numerically using Galerkin's finite element method. Parametric studies on the effects of skin tissue properties, initial temperature, blood perfusion rate and heat transfer parameters for the thermal response and exposure time of the layers of the skin tissue are carried out. The results of the investigation are compared with experimental results in the literature. The study demonstrates that the initial tissue temperature, the thermal conductivity of the epidermis and dermis, relaxation and thermalisation time and convective heat transfer coefficient are critical parameters to examine skin burn injury threshold. The study also shows that thermal conductivity and the blood perfusion rate exhibits negligible effects on the burn injury threshold. The objective of the present study is to support the accurate quantification and assessment of skin burn injury for reliable experimentation, design and optimisation of thermal therapy delivery.

Level-set topology optimization for effective control of transient conductive heat response using eigenvalue

Designing thermally efficient devices for an instantaneous heating condition is a challenging task, since a structure that simultaneously satisfies a lower peak temperature as well as a slower thermal response time must be achieved. In order to design a structure for both of the requirements, a transient analysis-based structural topology optimization method can be usually employed. However, the overall thermal response time of a heat conduction system can be modelled simply via the fundamental thermal eigenvalue, which is a physical quantity. This suggests that a thermal eigenvalue analysis can be adopted instead of transient analysis for an effective design of the structure controlling its thermal response time. In this study, we aim at developing a level-set topology optimization method to effectively optimize the overall response time of heat conduction systems using the thermal eigenvalue. The proposed level-set thermal eigenvalue topology optimization updates the structural boundary based on the common fixed grid approach, and the adjoint variable method is applied to compute shape sensitivity. Numerical examples clearly show the controllability of overall heat response time through the thermal eigenvalue, and especially, it is demonstrated that the proposed method is useful in designing an effective cooling structure for an instantaneous heating.

Quick Thermal Response‐Transparent‐Wearable Heater Based on Copper Mesh/Poly(Vinyl Alcohol) Film

High‐performance, transparent, wearable heaters with fast thermal response are developed. To accomplish this, highly conductive and transparent copper (Cu) mesh films are transfer printed onto flexible poly(vinyl alcohol) (PVA) substrates of different thicknesses. The thermal response characteristics of the heaters, with different PVA substrate thicknesses, are analyzed and results are recorded. The Cu mesh/PVA film heater shows a favorable figure of merit value of 228.4 and outstanding durability in response to mechanical stress tests for bending, crumpling, and detaching. Through the test results, it is concluded that the thermal response time of the heater is directly related to the thickness of the PVA substrate. The optimized Cu mesh/PVA film heater, with a substrate thickness of ≈60 μm and input voltage of 3 V (DC), exhibits a fast Joule heating effect with a response time of ≈12 s and a ramping rate of ≈7.5 °C s−1. These are excellent results, compared with the previously reported studies with other metal‐based flexible transparent heaters. A flexible transparent heater with low applied voltage and fast response time is expected to have innovative electrothermal applications, such as transparent soft actuators, wearable heaters, and medical thermotherapy pads.

Highly Responsive Metal Oxide (V2O5)-Based NEMS Pirani Gauge for In-Situ Hermeticity Monitoring

The letter reports highly sensitive metal oxide (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> ) based NanoElectromechanical Systems (NEMS) Pirani gauge for pressure monitoring of a packaged device. The absence of additional supplementary material in the sensing element increases the sensing area and enables the in-situ monitoring capability. Considering the feasibility of the idea, the design is simulated and verified with the experimental results of the fabricated device. The device shows a sensitivity of 5.76 % per decade-Pa in the working range from 4 Pa to 2.7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> Pa. The maximum average temperature of the sensing element is 48 °C at 4 Pa. It ensures corrosion-free operation and increases the lifetime of the device. The computed thermal response time of the device is ~500 ms at a power consumption of 285μW. [2020-0335]

Triple-layer Tissue Prediction for Cutaneous Skin Burn Injury: Analytical Solution and Parametric Analysis

This paper demonstrates a non-Fourier prediction methodology of triple-layer human skin tissue for determining skin burn injury with non-ideal properties of tissue, metabolism and blood perfusion. The dual-phase lag (DPL) bioheat model is employed and solved using joint integral transform (JIT) through Laplace and Fourier transforms methods. Parametric studies on the effects of skin tissue properties, initial temperature, blood perfusion rate and heat transfer parameters for the thermal response and exposure time of the layers of the skin tissue are carried out. The study demonstrates that the initial tissue temperature, the thermal conductivity of the epidermis and dermis, relaxation time, thermalisation time and convective heat transfer coefficient are critical parameters to examine skin burn injury threshold. The study also shows that thermal conductivity and the blood perfusion rate exhibits negligible effects on the burn injury threshold. The objective of the present study is to support the accurate quantification and assessment of skin burn injury for reliable experimentation, design and optimisation of thermal therapy delivery.

Melting process of the nano-enhanced phase change material (NePCM) in an optimized design of shell and tube thermal energy storage (TES): Taguchi optimization approach

Abstract The thermal performance and response time of Thermal Energy Storage (TES) units are mainly limited by the enclosure design and the low thermal conductivity of the storage medium. In the present study, the performance of petal-shape pipes in a shell and tube TES unit was numerically modeled and analyzed. The integration of the finite element method, a mesh adaptation approach, and an adaptive time-step scheme, was used to robustly simulate the phase change process and energy storage in the TES unit. The enclosure was considered fixed both dimensionally and by volume, which acts as a design constraint. The impacts of using two types of nano-additives, Cu and GO nanoparticles, and the geometrical aspects of the petal pipe on the thermal behavior of the TES unit were investigated. To find the optimal design of the TES unit with the maximum thermal energy power, the Taguchi optimization method was employed and a sensitivity analysis was performed. The copper nano-additives showed a better performance than the graphene oxide nano-additives. Although the surface area of the petal-pipe was fixed, its geometric shape was the most important parameter for maximizing the energy storage power of the TES unit. The optimum design could improve the amount of storage energy by 23.3% (Cu) and 22.5% (GO) NePCM compared to average designs. Based on an ANOVA analysis, the amplitude of petal shape could influence the total energy storage with a contribution ratio of about 41%, while the nanoparticles' contribution was 5–6%. An optimal design of a petal tube and Cu nanoparticles could improve the heat transfer by 45% compared to a circular tube with no nanoparticles.

Photocurrent in carbon nanotube bundle: Graded Seebeck coefficient phenomenon

Polarized photovoltage of a suspended aligned carbon nanotube (CNT) bundle under uniform optical irradiation is discovered without additional structural modification or bias voltage. Such a phenomenon is very surprising considering the metallic behavior of the overall bundle and zero temperature difference between ends. The photovoltage characteristic time is found similar to the thermal response time under step Joule heating and implies a relation to the thermal behavior of the CNT bundle. A similar thermoelectric voltage is also observed during step Joule heating. Localized laser heating and scanning along the axial direction of the bundle uncovers a linear spatial variation of the local Seebeck coefficient. The Seebeck coefficient linearly decreases from root to tip of the CNT bundle with a rate of a few - µV∙K−1·mm−1. Deep investigation in both the microscopic and macroscopic structures of the CNT bundle reveals that the local alignment of CNT assemblies rather than the minor defects in individual CNTs brings about this linear distribution of Seebeck coefficient in space. The finding presents a new way for direct photon-to-electric energy conversion via Seebeck coefficient grading in CNT structures.

Accurate Compensation of Armored Thermocouple Based on Fireworks Algorithm

Measurement error occurs if the requirements of undistorted measurements cannot be satisfied by dynamic component characteristics of the sensor. Amplified time constant and longer thermal response time of armored thermocouple is caused by its additional protective cover structure and the inherent thermal inertia of the internal temperature measuring element. Therefore, there is hysteresis dynamic characteristic in actual measurement of sensor. This paper proposes an accurate compensation of armored thermocouple based on fireworks algorithm that balances the contradiction between the accuracy of the existing solution and the complexity of the solution, corrects the measured thermocouple temperature signal. Weight factor is innovatively introduced to design the fitness function of fireworks algorithm, and the iterative process is sectionally executed that achieves the improvement of time constant and thermal response time of armored thermocouple. Finally, results are given in the simulation section. Dynamic compensation time is reduced from 537ms to 130ms, which is 75.79% lower than before compensation result. Moreover, the thermal response time is reduced from 345ms to 110ms, which is 68.16% lower than the before compensation result. From the experimental results, we can observe that the proposed method in this paper can broaden the working bandwidth of the thermocouple sensor through establishing dynamic mathematical model of thermocouple. After compensation, the dynamic characteristics of armored thermocouple are close to bare bead thermocouple without protective sleeve. The proposed method can replace easily damaged bare bead thermocouple to realize accurate measurement in harsh temperature measurement environments without need frequent replacement, which also improves economic benefits.

Fiber optic quench detection for large-scale HTS magnets demonstrated on VIPER cable during high-fidelity testing at the SULTAN facility

Fiber-optic thermometry has the potential to provide rapid and reliable quench detection for emerging large-scale, high-field superconducting magnets fabricated with high-temperature-superconductor (HTS) cables. Developing non-voltage-based quench detection schemes, such as fiber Bragg grating (FBG) technology, are particularly important for applications such as magnetic fusion devices where a high degree of induced electromagnetic noise impose significant challenges on traditional voltage-based quench detection methods. To this end, two fiber optic quench detection techniques—FBG and ultra-long FBG (ULFBG)—were incorporated into two vacuum pressure impregnated, insulated, partially transposed, extruded, and roll-formed (VIPER) high-current HTS cables and tested in the SULTAN facility, which provides high-fidelity operating conditions to large-scale superconducting magnets. During surface heater induced quench-like events under a variety of operating conditions, FBG and ULFBG demonstrated strong signal-to-noise ratios (SNRs) ranging from 4 to 32 and measured single-digit temperature excursions; both the SNR and temperature sensitivity increase with temperature. Fiber thermal response times ranged between effectively instantaneous to a few seconds depending on the operating temperature. Strain sensitivity dominates the thermal sensitivity in the conditions achievable at SULTAN; however, measurements at higher quench evolution temperatures, coupled to future work to increase the thermal-to-strain signal, show promise for quench detection capability in full-scale magnets where temperature and strain may occur simultaneously. Overall, FBG and ULFBG were proven capable to quickly and reliably detect small temperature disturbances which induced quench initiation events for high current VIPER HTS conductors in realistic operating conditions, motivating further work to develop FBG and ULFGB quench detection systems for full-scale HTS magnets.

Operational challenges for low and high temperature electrolyzers exploiting curtailed wind energy for hydrogen production

Understanding the system performance of different electrolyzers could aid potential investors achieve maximum return on their investment. To realize this, system response characteristics to 4 different summarized data sets of curtailed renewable energy is obtained from the Irish network and was investigated using models of both a Low Temperature Electrolyzer (LTE) and a High Temperature Electrolyzer (HTE). The results indicate that statistical parameters intrinsic to the method of data extraction along with the thermal response time of the electrolyzers influence the hydrogen output. A maximum hydrogen production of 5.97 kTonne/year is generated by a 0.5 MW HTE when the electrical current is sent as a yearly average. Additionally, the high thermal response time in a HTE causes a maximum change in the overall flowrate of 65.7% between the 4 scenarios, when compared to 7.7% in the LTE. This evaluation of electrolyzer performance will aid investors in determining scenario specific application of P2G for maximizing hydrogen production.

A Review On Transient Thermal Management of Electronic Devices

Abstract Much effort in the area of electronics thermal management has focused on developing cooling solutions that cater to steady-state operation. However, electronic devices are increasingly being used in applications involving time-varying workloads. These include microprocessors (particularly those used in portable devices), power electronic devices such as IGBTs, and high-power semiconductor laser diode arrays. Transient thermal management solutions become essential to ensure the performance and reliability of such devices. In this review, emerging transient thermal management requirements are identified, and cooling solutions reported in the literature for such applications are presented with a focus on time scales of thermal response. Transient cooling techniques employing actively controlled two-phase microchannel heat sinks, phase change materials (PCM), heat pipes/vapor chambers, combined PCM-heat pipes/vapor chambers, and flash boiling systems are examined in detail. They are compared in terms of their thermal response times to ascertain their suitability for the thermal management of pulsed workloads associated with microprocessor chips, IGBTs, and high-power laser diode arrays. Thermal design guidelines for the selection of appropriate package level thermal resistance and capacitance combinations are also recommended.

Thermal conductivity of nano- and micro-crystalline diamond films studied by photothermal excitation of cantilever structures

Polycrystalline diamond films have unique structural and thermal properties that make them suitable for use in extreme environments. Recently, they have been utilized in accelerator beamlines for electron stripping due to their unique combination of mechanical and thermal properties. Thermal conductivities of nanocrystalline diamond (NCD) and microcrystalline diamond (μCD) films were characterized using photothermally actuated bimaterial cantilevers. Approximately one micrometer thick NCD and μCD cantilevers were fabricated from microwave plasma enhanced chemical vapor deposition grown polycrystalline diamond (PD) films. A layer of gold was sputtered on the diamond film surfaces to make bilayer cantilevers and the thermal response time was measured by photothermally exciting the bilayer cantilevers, causing them to deflect. Finite element thermomechanical modeling of the deflection dynamics in response to photothermal actuation was performed to determine the NCD and μCD thermal diffusivities and conductivities. By fitting the simulated and experimentally observed response times, thermal conductivities of 10 and 60 W/(m-K) were extracted for the NCD and μCD samples, respectively. Expected changes in thermal conductivity of PD in higher temperature regimes are also discussed. In addition to applications of PD films as electron stripping foils, these findings also have implication in fields such as micro/nano-electromechanical systems.

A Hybrid Lister‐Outrigger Probe for Rapid Marine Geothermal Gradient Measurement

AbstractWe have successfully constructed and tested a new, portable, Hybrid Lister‐Outrigger (HyLO) probe designed to measure geothermal gradients in submarine environments. The lightweight, low‐cost probe is 1–3 m long and contains 4–12 semiconductor temperature sensors that have a temperature resolution of 0.002°C, a sample rate of &lt;2 s, and a maximum working depth of ~2,100 m below sea level (mbsl). Probe endurance is continuous via ship power to water depths of ~700 mbsl or up to ~1 week on batteries in depths &gt;500 mbsl. Data are saved on solid‐state disks, transferred directly to the ship during deployment via a data cable, or transmitted via Bluetooth when the probe is at the sea surface. The probe contains an accelerometer to measure tilt, internal pressure, temperature, and humidity gauges. Key advantages of this probe include (1) near‐real‐time temperature measurements and data transfer; (2) a low‐cost, transportable, and lightweight design; (3) easy and rapid two‐point attachment to a gravity corer, (4) short (3–5 min) thermal response times; (5) high temporal/spatial resolution; and (6) longer deployment endurance compared to traditional methods. We successfully tested the probe both in lakes and during sea trials in May 2019 offshore Montserrat during the R/V Meteor Cruise 154/2. Probe‐measured thermal gradients were consistent with seafloor ocean‐drilling temperature measurements. Ongoing probe improvements include the addition of real‐time bottom‐camera feeds and long‐term (6–12 months) deployment for monitoring.

VALIDATION OF COOLANT THERMAL RESPONSE IN A TRANSIENT FINITE DIFFERENCE THERMAL TRANSPORT MODEL WITH APPLICATIONS TO FAST SPECTRUM REACTORS

Transient behavior in nuclear reactors is important in accidents and with reactivity control systems that are driven by thermal feedback. Here, we describe a transient finite difference model for a pin cell system. The fidelity of the model is shown by validation against the thermocouple measurements of the CABRI BI1 experiment and the Safety Analysis System-Sodium Fast Reactor model of the experiment. In the BI1 experiment, a sodium-cooled mixed oxide fuel pin was subject to a loss of flow transient to coolant boiling within a sodium test loop positioned in the center of the CABRI research reactor. Comparisons to the initial steady-state coolant temperature profile, coolant temperature profile at twenty seconds into the transient, and at four axial locations within the coolant show agreement of the simple model with the experimental results better than or similar to those of the Safety Analysis System-Sodium Fast Reactor model. The model can be used to determine the thermal response times of coolant in fast reactors currently operating or in the design phase when subject to loss of flow accidents or other transients. Here, we investigate the difference in coolant thermal response for metal fueled and mixed oxide fueled sodium fast reactors when subject to transient overpower and loss of flow events. Additionally, we determine the effect of pin pitch on outlet coolant temperatures during the overpower event. Finally, we return to the CABRI experiment and show the importance of porosity in fuel temperature calculations.

Facile preparation of wearable heater based on conductive silver paste with low actuation voltage and rapid response

Towards emerging electric heaters for wearable electronics, actuators and high-performance heating systems, various properties including flexibility, low actuation voltage, rapid response, facile adaptability, thermal and mechanical stability are highly desired. Herein, a high-performance heater based on commercial conductive silver paste is proposed, through quite simple scrape coating, painting and pen writing. Benefiting from its excellent viscosity, the silver paste can be firmly coated on a variety of substrates, even including hydrophobic and oleophobic polytetrafluoroethylene and cotton thread of high curvature. After curing the silver paste, the silver nanoflakes inside are encapsulated in a polymer framework and are closely interconnected, forming a reliable conductive network with low sheet resistance ( $${\text{minimum }}0.{18 }\Omega /{\text{sq}}$$ ). This structure protects the silver nanoflakes from oxidation and provides this flexible silver heater (FSH) excellent thermal and mechanical stabilities, as demonstrated by long-time heating, cyclic heating and multiple deformation tests. The FSH achieves high surface temperature (280 °C) at a low operation voltage (2 V), with rapid thermal response time (less than 7 s). The application demonstrations of FSHs in custom-shaped wearable heaters and heating patterns, thermal therapy, flexible heating thread and thermal switch suggest the distinct advantages of FSHs in flexible and wearable devices.

Soft Matter Mechanics and the Mechanisms Underpinning the Infrared Vision of Snakes

Summary Pit-bearing snakes (vipers, pythons, and boas) have the extraordinary ability to “see” and accurately locate their prey and predators in total darkness. These animals use the infrared radiation emanating from objects that are warmer relative to the background environment to form a thermal image. Although enormous progress has been made to identify the key physiological features that enable the infrared vision of these snakes and a few other animals, the precise thermoelectric transduction mechanism that mediates the conversion of infrared heat to processable electrical signals has remained elusive. In this work, we quantitatively outline how cells in the snake's pit membrane organ act as apparent pyroelectric materials and convert infrared radiation into electrical signals. Despite the exceptional simplicity of our proposed mechanism and model, we are able to explain many central experimental results pertaining to the transduction process.

Study on the synergism of thermal transport and electrochemical of PEMFC based on N, P co-doped graphene substrate electrode

In this work, a metal-free electrode substrate with unequal amounts of nitrogen and phosphorus co-doped graphene (N, P-G) and different spacer contents is synthesized from activated carbon (AC) via a one-step synthesis technique. Characterization of the chemical structures of this material shows that it has more active bonds and improves electrochemical performance as the anneal temperature increase. The unequal dope by the ratio of nitrogen to phosphorus is more than 2:1 can significantly improve oxidation-reduction reaction (ORR). With a mass ratio of 10% platinum, carbon (Pt/C) to 10% AC @ N, P-G as 2:1, the P-G composite electrodes demonstrate superior heat dissipation performance in comparison to traditional Pt/C electrodes due to the higher thermal uniformity and shorter thermal transport response time. With AC @ N, P-G as the electrode substrate material, a maximum output performance of 0.551 Wcm−2 is obtained at various temperatures, humidities, and mass ratio conditions, indicate a composite material with excellent ORR stability and high heat dissipation capacity on the electrode surface. Our experimental results show that an electrode substrate material with unequal amounts of N, P-G with AC spacer content is a promising candidate as a non-metallic substrate for proton exchange membrane (PEM) fuel cells.