Planar Heater Research Articles

Development and evaluation of cable-less heating mats utilizing low-power carbon nanotube planar heaters

We aimed to develop a low-power heating mat based on a carbon nanotube (CNT) planar heater and verify its performance by utilizing the heating element. The cell samples were manufactured, and their electrical and thermal properties were evaluated to conduct heating tests. The developed CNT planar heater was tested in four ways, namely heating one cell individually and heating two/three/four cells simultaneously. When operating multiple cells, the resistance decreased, and the power increased. The temperature averaged 37°C even when multiple cells were operating, and the power consumption per unit area was at a similar level. In addition, a prototype heating vest was fabricated using the cells, and a performance comparison was conducted with a third-party heating vest product. The heating efficiency was more than twice as high as that of the third-party product, and the heating area was more than twice as large. Prototype heating pads were made using the cells and compared with two other third-party samples that are heated by thermal wires, and the developed prototype was found to have a heating efficiency more than 20% higher than the other samples, with the lowest temperature deviation. The CNT planar heater developed in this study can be realized in various shapes without wires and can be used safely. It is economical because it can be set to the appropriate temperature in the desired area with a controller, and it is eco-friendly because it prevents mold growth by emitting far-infrared radiation.

Towards real-time airborne pathogen sensing: Electrostatic capture and on-chip LAMP based detection of airborne viral pathogens

Considerable loss of life, economic slowdown, and public health risk associated with the transmission of airborne respiratory pathogens was underscored by the recent COVID-19 pandemic. Airborne transmission of zoonotic diseases such as the highly pathogenic avian influenza (HPAI) and porcine reproductive and respiratory syndrome virus (PRRSV) has caused major disruptions to domestic and global food security. Current ambient air pathogen monitoring systems involves the collection of air samples from indoor settings suspected of viral contamination, followed by subsequent processing of capture samples to determine the presence and species of airborne viral matter. Nucleic acid amplification techniques are considered the gold standard for pathogen diagnostics. Currently, the necessary extraction and purification of viral RNA from air collector systems prior to sample analysis is both time consuming and performed manually. A monitoring system with separate air sampling and biochemical detection procedures is prone to delay the response to emergent viral threats. In this paper, we present a pathogen monitoring system that overcomes these limitations related to extraction and purification of viral samples and lays the groundwork for a real-time monitor for airborne viral pathogens. We demonstrate a high flow electrostatic precipitator system, that uses small collection wells as counter electrodes for pathogen collection. Integrated reverse-transcriptase loop-mediated isothermal amplification (RT-LAMP) is used for detection of captured viral matter within wells. On-chip heating of collection wells is enabled by integrated planar heaters and small volumes of reagent (30 μL) directly to the collection wells. We present the design of such a system and show experimental results that demonstrate the use of this device for detection of aerosolized SARS-CoV-2 virus like particles (VLPs), a model pathogen for SARV-CoV-2.

Plane heating with a transparent heater film in a fish tank

The water temperature in a fish tank is important for fish health. A conventional aquarium heater produces localized heating that causes water temperature variation, resulting in thermal stress to fish. This study presents plane heating with a transparent heater film that is aesthetically attractive when applied to fish tanks. The transparent heater film comprises a metal mesh with an optical transparency of 81 %, sheet resistance of 0.6 Ω/□, and mean heating surface temperature of 57 °C at 20 W. In the test setup, 100 W is applied to compare an aquarium heater and a transparent heater film. Increasing the water temperature from 23 °C to 24 °C at the center of the fish tank needs 28 min with the transparent heater film operating at 33 °C, whereas the same temperature increase needs 50 min with an aquarium heater operating at 49 °C. The planar heater thus results in enhanced heat diffusion and reduced water temperature variation due to its extended heating surface area.

Low-dimensional composites-based planar heater with high-exothermic characteristics in cold water environments

This work presents a high-performance planar heater that generates a high-temperature heat even in cold water environments. The planar heater was fabricated with low-dimensional composites prepared with MXene, carbon nanotube (CNT), and waterborne polyurethane (WPU) on polyimide (PI) film by blade coating. The planar heater installed in life-jacket was rapidly heated up to 73 °C in 1 min at 3.6 V in the atmosphere. For a cold water of 5 °C, the planar heater combined with the insulating film was effectively heated and maintained in 45–50 °C at 3.6 V due to the insulation effect for cold water. Thus, the insulated planar heater generates a heat of high temperature and can effectively transfer more heat to the body even in the cold water. Our developed planar heater will be expected to be utilized as a suitable wearable heating device for cold environments.

Tailorable activation of thermoresponsive composite structures incorporating wavy heaters via hybrid manufacturing

The activation method of thermoresponsive materials greatly affects the practical use of smart structures composed thereof. Despite extensive research that relies on methods using high ambient temperatures or planar heaters, the efficient and tailorable activation of relatively thick thermoresponsive composite structures remains challenging. Herein, we present a concept of embedding a wavy heater into a thermoresponsive material matrix to form a composite structure with parametrically designed thermal activation behavior, through a facile manufacturing approach combining 3D-printing and laser-cutting. We develop a numerical model to predict the transient heat transfer for varying wavy shapes of heater, and experimentally validate the numerical results. The exploration of the design space using the numerical model shows a reduction of up to 82% in heating time using the wavy design compared with the flat design. Finally, we demonstrate experimentally the stiffness tuning in thermoresponsive composite structures. This work paves the way for large-scale thermoresponsive composite structures with applications in aerospace and architecture.

On critical heat flux and its evaporation momentum and hydrodynamic limits

The upper limit of heat transfer from a heated surface to a surrounding boiling liquid has been the subject of numerous studies ever since Nukiyama (1934) discovered this limit. The underlying physics governing this phenomenon, universally known as the critical heat flux (CHF) limit, has been extensively debated for nearly a century. Two prevailing hypotheses have emerged including hydrodynamic instability and evaporation momentum force thresholds proposed by Kutateladze (1948) and Steinchen and Sefiane (1996), respectively. Zuber (1959) and Kandlikar (2001) developed correlations based on these hypotheses that predict roughly similar CHF values i.e., ∼100 W/cm2 for water at 1 atm on a copper surface. Here, we present experimental and analytical studies conducted on liquids with a wide range of thermophysical properties on planar heater surfaces of different size (to stabilize the flow hydrodynamics) that show the evaporation momentum limit (CHFEM) is roughly 4 times the Zuber's limit (CHFZuber). We show that CHFEM can only be observed when hydrodynamics of liquid and vapor above the surface is stabilized, delineating an ultimate limit governed by a force balance at the surface-fluid interface rather than the instability of liquid and vapor interface away from the surface. We find that CHF/CHFEM varies from 0.2 to 1 for all fluids, saturation temperatures, and heater geometries tested, representing 48 conditions.

Boiling and cavitation caused by transient heat transfer in superfluid helium-4

Superfluid helium-4 (He II) has been widely utilized as a coolant in various scientific and engineering applications due to its superior heat transfer capability. An important parameter required in the design of many He II based cooling systems is the peak heat flux ${q}^{*}$, which refers to the threshold heat flux above which boiling spontaneously occurs in He II. Past experimental and numerical studies showed that ${q}^{*}$ increases when the heating time ${t}_{h}$ is reduced, which leads to an intuitive expectation that very high ${q}^{*}$ may be achievable at sufficiently small ${t}_{h}$. Knowledge on how ${q}^{*}$ actually behaves at small ${t}_{h}$ is important for applications such as laser ablation in He II. Here we present a numerical study on the evolution of the thermodynamic state of the He II in front of a planar heater by solving the He II two-fluid equations of motion. For an applied heat flux, we determine the heating time beyond which the He II near the heater transits to the vapor phase. As such, a curve correlating ${q}^{*}$ and ${t}_{h}$ can be obtained, which nicely reproduces some relevant experimental data. Surprisingly, we find that there exists a critical peak heat flux ${q}_{c}^{*}$, above which boiling occurs nearly instantaneously regardless of ${t}_{h}$. We reveal that the boiling in this regime is essentially cavitation caused by the combined effects of the first-sound and the second-sound waves in He II. Based on this physical picture, an analytical model for ${q}_{c}^{*}$ is developed, which reproduces the simulated ${q}_{c}^{*}$ values at various He II bath temperatures and hydrostatic head pressures. This work represents a major progress in our understanding of transient heat transfer in He II.

Complementary Split-Ring Resonator for Microwave Heating of µL Volumes in Microwells in Continuous Microfluidics

This work presents the design and evaluation of a planar device for microwave heating of liquids in continuous microfluidics (CMF) made in polydimethylsiloxane (PDMS). It deals with volumes in the µL range, which are of high interest and relevance to biologists and chemists. The planar heater in this work is conceived around a complementary split-ring resonator (CSRR) topology that offers a desired electric field direction to—and interaction with—liquids in a microwell. The designed device on a 0.25 mm thick Rogers RO4350B substrate operates at around 2.5 GHz, while a CMF channel and a 2.45 µL microwell are manufactured in PDMS using the casting process. The evaluation of the performance of the designed heater is conducted using a fluorescent dye, Rhodamine B, dissolved in deionized water. Heating measurements are carried out using 1 W of power and the designed device achieves a temperature of 47 °C on a sample volume of 2.45 µL after 20 s of heating. Based on the achieved results, the CSRR topology has a large potential in microwave heating, in addition to the already demonstrated potential in microwave dielectric sensing, all proving the multifunctionality and reusability of single planar microwave-microfluidic devices.

(IMCS Third Place Best Paper Award) Experimental Verification of the Temperature Homogeneity of Heated Gas Sensor Transducers inside a Protection Cap

Introduction High temperature gas sensors play an important role in monitoring or controlling energy conversion processes. Sensors containing functional materials often need to be heated to a certain operating temperature to achieve functionality. This can be realized using planar thick-film heaters, which are screen-printed on the sensor substrate. When sensors are installed in the exhaust gas flow in order to achieve a fast response behavior, high volume flow has cooling effects on the sensor and leads to an inhomogeneous temperature distribution. This might cause a changed sensor function and cross-sensitivities [1]. For this reason, protective caps are used to reduce the flow influence on the temperature distribution with sufficient response time [2]. Resulting temperature distribution can be simulated using FEM models but cannot be verified directly inside protective caps [3, 4]. The present work solves this uncertainty in two ways to directly measure the temperature homogeneity within a cap. Methods and Setup Sensors are built up on alumina substrates (Figure 1a). On the reverse side, a meander-shaped platinum structure acts as heating element. Two methods are used to determine the temperature distribution on the front side.Firstly, the temperature distribution is recorded by an IR camera (Figure 1c). For optically access, an IR-transparent glass replaces one part of the cap. The requirements for this glass are the transmission of the IR radiation (here attention must be paid to the appropriate wavelength of the camera) and a certain temperature resistance, since the cap and the glass are also heated by the heat radiation of the sensor.Secondly, the temperature distribution is directly measured by means of thermocouples (Figure 1b). Instead of a sensor structure, a matrix of planar screen-printed thermocouples (Figure 1d) is applied onto the front side of the transducer. For this purpose, Pt and Au feedlines are arranged so that five different measuring points are realized at the sensor tip, i.e., that area where a gas sensitive layer would be located. Temperature values are derived from the measured thermvoltage on basis of Seebeck coefficients for Pt/Au given in the literature. Results and Discussion In order to verify the function of the printed thermocouples, the sensor temperature was increased to 600 °C by means of the heater on the reverse side. The heat distribution was recorded by the thermocouples without the protective cap. Thermal images were taken simultaneously with the IR camera. The measured temperature of the thermocouples corresponds well to the thermal images.Afterwards the sensor was placed inside a protective cap containing the described IR-permeable glass window. After increasing the sensor temperature to 600 °C, thermal images of the sensor tip could be taken again. The transmission coefficient of the glass is required for this purpose. To check the accuracy of the transmission coefficient, the temperatures of the thermocouples were recorded simultaneously. The temperature measured by the IR camera again corresponds to the thermocouples values. Thus, the application of this method was also checked and confirmed.Both methods were used to investigate the influence of a protective cap on the temperature distribution on the front side of the sensor at 600 °C operating temperature. Figure 1e) and f) show the temperature distribution of a sensor in a horizontal mounting position recorded by an IR camera (temperature gradients in general come from the individual heater structure and several heat losses, especially heat flow along the substrate material). Figure 1e) shows the measurement without a protection cap. The thermocouple measurement shows a temperature gradient of 6.78 °C/mm between point 1 and 2. The temperature gradient derived from the thermal image is 5.88 °C/mm. Both data (thermocouple and thermal image) agree very well. Then the same measurement was carried out with a protective cap (Figure 1f). The temperature gradient, measured with the thermocouples, is 4.97 °C/mm. The thermal image shows a value of 4.43 °C/mm. The protective cap thus has a positive influence on the temperature homogeneity of a sensor even without a flow. Outlook In the next steps, the temperature distribution in an exhaust flow is investigated by means of the thermocouples. Variations in sensor orientation or mounting positions is possible. Here as well it is possible to investigate the influence of a protection cap. A high temperature setup might be realized by use of screen-printed Pt/PtRh thermopiles [5].

Transparent planar layer copper heaters for wearable electronics

To keep up with the progress in wearable electronics, it is imperative to create flexible transparent heaters with low sheet resistance and high transmittance. This allows for low-voltage operation. In this study, we fabricated highly flexible ultrathin transparent heaters composed of Cu layers with a thickness in the range of 4–40 nm sandwiched between ZnO layers. The sheet resistance (0.8–165 Ω/sq) and optical transparency (average visible light transmittance of 29.3–90.0%) can be considerably modulated by varying the Cu layer thickness. The fabricated transparent heaters exhibited superior heating capability over reported network-type transparent heaters, i.e., extremely fast thermal response (90% of target temperature reached within 5 s), excellent thermal uniformity (less than 2.5% thermal variation at a heater temperature of 100 °C), and outstanding heater durability (no degradation with a continuous heating test at 80 °C for 10,000 min). Based on the area-dependent thermoelectrical parameters, it was shown that large heaters could reach 50 °C with a portable rechargeable lithium-ion battery with 12 V DC output. The excellent flexibility in the bent and unbent state, when subjected to various bending tests, confirmed the high suitability of the ultrathin transparent Cu heaters for wearable electronics, such as biomedical devices.

Transient heat transfer of superfluid He4 in nonhomogeneous geometries: Second sound, rarefaction, and thermal layer

Transient heat transfer in superfluid $^{4}\mathrm{He}$ (He II) is a complex process that involves the interplay of the unique counterflow heat-transfer mode, the emission of second-sound waves, and the creation of quantized vortices. Many past researches focused on homogeneous heat transfer of He II in a uniform channel driven by a planar heater. In this paper, we report our systematic study of He II transient heat transfer in nonhomogeneous geometries that are pertinent to emergent applications. By solving the He II two-fluid equations of motion coupled with Vinen's equation for vortex-line density, we examine and compare the characteristics of transient heat transfer from planar, cylindrical, and spherical heaters in He II. Our results show that as the heater turns on, an outgoing second-sound pulse emerges, within which the vortex-line density grows rapidly. These vortices attenuate the second sound and result in a heated He II layer in front of the heater, i.e., the thermal layer. In the planar case where the vortices are created throughout the space, the second-sound pulse is continuously attenuated, leading to a thick thermal layer that diffusely spreads following the heat pulse. On the contrary, in the cylindrical and the spherical heater cases, vortices are created mainly in a thin thermal layer near the heater surface. As the heat pulse ends, a rarefaction tail develops following the second-sound pulse, in which the temperature drops. This rarefaction tail can promptly suppress the thermal layer and take away the deposited thermal energy. The effects of the heater size, heat flux, pulse duration, and temperature on the thermal-layer dynamics are discussed. We also show how the peak heat flux for the onset of boiling in He II can be studied in our model.

Low-temperature co-fired ceramic-based thermoelectric generator with cylindrical grooves for harvesting waste heat from power circuits

This paper investigates the optimal design permitting to recover thermal heat released from electronic power components mounted on ceramic substrates. Accordingly, the methodology and the characterization of thick-film/LowTemperature Co-fired Ceramic (LTCC)-based multilayer thermo-electric micro-generators (TEGs) fabrication were detailed. Hence, two different TEGs, based on the Seebeck effect, with different thermocouples materials, Ag/Ni and Ag/PdAg, were fabricated, simulated, analytically studied and compared. Each designed generator contains 104 thermocouples, with 300 µm-width and space between them. The required heating was produced by a meander-shaped planar heater, simulating the presence of an electronic power device. As well, two heaters are compared, made by Ni and PdAg, and each one is tested in the absence/presence of cylindrical grooves added on the backside of the LTCC substrate. It has been shown that adding grooves around the hot element allows an average improvement of 160% of the temperature difference along the generator. Concerning TEGs, Ag/PdAg-based TEG was able to generate a higher output power of 81 μW for a temperature difference of 114 °C, than the Ag/Ni-based TEG with an output power of 4.6 µW at ΔT = 62 °C. The conversion efficiency was 0.5% and 0.08% for the Ag/PdAg-based and the Ag/Ni-based TEG, respectively.

Improved 3D electromagnetic analytical model for planar induction heater with consideration of transverse edge effects

PurposeThis paper aims to propose a new 3D electromagnetic model to compute translational motion eddy current in the conducting plate of a novel linear permanent magnet (PM) induction heater. The movement of the plate in a DC magnetic field created by a PM inductor generates induced currents that are at the origin of a heating power by Joule effect. These topologies have strong magnetic end effects. The analytical model developed in this work takes into account the finite length extremity effects of the conducting plate and the reaction field because of induced currents.Design/methodology/approachThe developed model is based on the combination of the sub-domain’s method and the image’s theory. First, the magnetic field expressions because of the PMs are obtained by solving the three-dimensional Maxwell equations by the method of separation of variables, using a magnetic scalar potential formulation and a magnetic field strength formulation. Then, the motional eddy currents are computed using the Ampere law, and the finite length extremity effects of the conducting plate are taken into account using the image’s method. To analyze the accuracy of the proposed model, the obtained results are compared to those obtained from 3D finite element model (FEM) and from experimental tests performed on a prototype.FindingsThe results show that the developed analytical model is very accurate, even for geometries where the edge effects are very strong. It allows directly taking into account the finite length extremity effects (the transverse edge effects) of the conducting plate and the reaction field because of induced currents without the need of any correction factor. The proposed model also presents an important reduction in computation time compared to 3D finite element simulation, allowing fast analysis of linear PM induction heater.Practical implicationsThe proposed electromagnetic analytical model can be used as a quick and accurate design tool for translational motion PM induction heater devices.Originality/valueA new 3D analytical electromagnetic model, to find the induced power in the conducting plate of a novel translational motion induction heater has been developed. The studied heating device has a finite length and a finite width, which create edge effects that are not easily considered in calculation. The novelty of the presented method is the accurate 3D analytical model, which allows finding the real power heating and real distribution of the induced currents in the conducting plate without the need to use correction factor. The proposed model also takes into account the reaction field because of induced currents. In addition, the developed model improves an important reduction in the computation time compared with 3D FEM simulation.

Thermal counterflow of superfluid He4 : Temperature gradient in the bulk and in the vicinity of the heater

We report measurements of longitudinal temperature gradient in thermal counterflow of superfluid $^{4}\mathrm{He}$ performed directly in the 17.5 cm long channel of a square cross section of 7 mm side using static temperature sensors placed on its wall and one small sensor movable along its axis. For various temperatures and heat inputs, we verify linear temperature gradient in the bulk and detect a ``boundary layer''---a region with increased temperature gradient---adjacent to the planar heater. We verify this result using three different heater geometries, all of which display similar thickness of this region but differ in exact details of the temperature profile. We propose that the observed temperature gradient enhancement is at least partly due to an increase of the density of the vortex tangle induced by the inhomogeneity of areal heat input distribution and support this claim by numerical simulations.

Low Temperature Co-Fired Ceramic-Based and Heater-Embedded Toxic Gas Sensors with Nanostructured SnO₂ Thick Films.

In this study, we designed, prepared, and characterized Low Temperature Co-fired Ceramic (LTCC) toxic gas sensor devices with nanostructured SnO₂ semiconducting thick films. In order to promote the reaction of carbon monoxide (CO) toxic gas molecules on the SnO₂ thick films, a RuO₂ planar heater was inserted into the LTCC substrate. Using an optimized RuO₂ heater, the surface temperature of the LTCC substrate reached 360 °C within 25 seconds at an applied voltage of 5 V. The power consumption for the surface of the LTCC substrate to reach 300 °C was 778 mW. A nanostructured SnO₂ thick film as a gas sensing layer was prepared by the ink dropping method on Pt electrodes patterned on the LTCC substrate. The gas sensor device was packaged in a commercial housing to measure the CO gas response. The fabricated gas sensor showed a gas response (Rair/Rgas) of 5.26 at a CO gas concentration of 500 ppm and a temperature of 300 °C. Additionally, a mild plasma post-treatment using Ar discharge gas improved the gas response up to 6.35 at the equivalent measurement conditions.

Improving degree of cure in pultrusion process by optimizing die-temperature

Pultrusion is a continuous process for manufacturing polymer composite with uniform cross-sectional profiles. In this process the die temperature process variable can be used to improve the chemical and mechanical properties of the polymer composite. Several works have been done regarding simulation tools for pultrusion analysis. Usually, the development of manufacturing processes is mostly a trial-and-error exercise. However, few studies focus on optimizing this manufacturing process. In this paper, the pultrusion process of a glass fibre-epoxy set with different geometries are simulated by using a three-dimensional finite element-nodal control volume (FE/NCV) approach, a quadratic programming algorithm and a particle swarm heuristic was used to optimize the manufacturing process. The aim is to show that to optimize pultrusion process, quadratic programming algorithm can also be very efficient in finding the optimal distribution of the temperature in the pultruded material. The second proposal of this paper is to present a simulation for pultrusion process based on a total number of 16 heaters embedded into die block, instead of external planar heaters. The results show that the mean of the cure degree is satisfactory when used with many internal heaters.

Simultaneous estimation of thermal properties of orthotropic material with non-intrusive measurement

This article presents a simple in-house laboratory experiment method for the simultaneous estimation of principal thermal conductivity and specific heat capacity of an orthotropic composite with non-intrusive temperature measurement. The principle of method involves in symmetrical heating of two identical samples with a planar heater sandwiched in-between them and measuring the temperature of non-heated surface non-intrusively using IR camera. The forward problem that mimics the heat conduction from heater to sample and then to ambient is a 3-D transient conduction equation which is solved using finite volume method whereas inverse problem is solved using Levenberg-Marquardt algorithm. At first numerical estimations are carried out with synthetic temperature data to decide upon the parameters to be identified/fixed as well as to find optimal experimental variables. Then, using measured temperature response of the non-heated surface, the thermal properties of unidirectional fiber reinforced carbon composite are estimated. Induced bias errors in the estimated parameters because of error in the fixed parameters are also approximately quantified. The estimated transverse thermal conductivity is found to be 0.72 W/m K whereas the in-plane conductivities parallel and perpendicular to fiber are 5.43 W/m K, 0.64 W/m K respectively. Also, the estimated specific heat capacity is found to be 1044 J/kg K. A maximum deviation of 10% from the absolute Guarded Hot Plate measurement is found in the estimated thermal conductivity parallel to fiber.

Planar Microstrip Ring Resonators for Microwave-Based Gas Sensing: Design Aspects and Initial Transducers for Humidity and Ammonia Sensing.

A planar microstrip ring resonator structure on alumina was developed using the commercial FEM software COMSOL. Design parameters were evaluated, eventually leading to an optimized design of a miniaturized microwave gas sensor. The sensor was covered with a zeolite film. The device was successfully operated at around 8.5 GHz at room temperature as a humidity sensor. In the next step, an additional planar heater will be included on the reverse side of the resonator structure to allow for testing of gas-sensitive materials under sensor conditions.

Thermal analysis of wirelessly powered thermo-pneumatic micropump based on planar LC circuit

This paper studies the thermal behavior of a wireless powered micropump operated using thermo-pneumatic actuation. Numerical analysis was performed to investigate the temporal conduction of the planar inductor-capacitor (LC) wireless heater and the heating chamber. The result shows that the temperature at the heating chamber reaches steady state temperature of 46.7°C within 40 seconds. The finding was further verified with experimental works through the fabrication of the planar LC heater (RF sensitive actuator) and micropump device using MEMS fabrication technique. The fabricated device delivers a minimum volume of 0.096 μL at the temperature of 29°C after being thermally activated for 10 s. The volume dispensed from the micropump device can precisely controlled by an increase of the electrical heating power within the cut-off input power of 0.22 W. Beyond the power, the heat transfer to the heating chamber exhibits non-linear behavior. In addition, wireless operation of the fabricated device shows successful release of color dye when the micropump is immersed in DI-water containing dish and excited by tuning the RF power.

Estimating Thermal Parameters of Large-Format Laminated Lithium-Ion Batteries Using Thermal Impedance Spectroscopy

The accuracy of battery thermal parameters is crucial to the accuracy of thermal simulations for batteries. Given the structural characteristics of the large-format laminated lithium-ion battery [1], effective methods to determine multiple thermal parameters, such as the thermal conductivity and the specific heat capacity, should be developed to achieve better prediction of battery thermal behaviors.Generally, the methods for measuring the thermal parameters of batteries can be divided into two categories, the time-domain method and the frequency-domain method. The authors developed a joint computational and experimental time-domain method to estimate the multiple thermal parameters for a 25 Ah laminated lithium-ion battery both in-situ and simultaneously [1]. However, the battery temperature changed from 25 to 35°C in the experiment, hence the estimated thermal parameters were the average properties over 25~35°C. In contrast, the change in the temperature of the sample can be greatly reduced in the frequency-domain method, making it possible to obtain the thermal parameters at different temperatures.In this work, a frequency-domain method, the thermal impedance spectroscopy (TIS) method is used to simultaneously and in-situ determine two thermal parameters, i.e. thermal conductivity and specific heat capacity, for the large-format laminated lithium-ion battery.In the experiment, a planar electric heater is sandwiched between two identical batteries (25 Ah, 250 mm × 220 mm × 7.2 mm，NMC-LMO/Graphite), as shown in Fig. 1(a). The electric power for the heater is adujusted at different frequencies (0.1, 0.2, 0.4, 0.6, 0.8 and 1 mHz) and the temperature response on one outer surface is recorded with the attached thermocouple. The entire set-up is placed in an environment chamber.The heat transfer behavior between the heating power and the temperature response is examined in the frequency domain. An equivalent thermal circuit including thermal capacity and resistance is introduced to derive the analytical expression of thermal impedance, as shown in Fig. 1(b). The thermal circuit is simplified from the 1D heat conduction model, which also takes the covering aluminum-plastic film into account. The thermal conductivity and capacity of the battery core are estimated using the least-square fitting algorithm. The experimental and fitted thermal impedance are shown in Fig. 1(c).The estimated parameters are validated against the results from the accelerating rate calorimeter (ARC), the heat flow calorimeter (HFC) and the joint computational and experimental time-domain method [1]. Reference [1] Zhang J, Wu B, Li Z, et al. Simultaneous Estimation of Multiple Thermal Parameters of Large-Format Laminated Lithium-Ion Batteries[C]//Vehicle Power and Propulsion Conference (VPPC), 2013 IEEE. IEEE, 2013.