Flexible Heater Research Articles

Revisiting heat losses in lab-scale distillation columns: Quantification, improvement, and influence on miniaturized 3D-printed packings

Lab-scale distillation columns with a diameter of 50 mm (DN50) are widely established for experimental investigations during process development and scale-up. In recent years, the diameter was successfully reduced to 20 mm (DN20) by utilizing additive manufacturing to attain new miniaturized packings that attend to the specific miniaturization obstacles. However, since heat losses have a higher influence in a DN20 column, this publication investigates their impact on the operation and data obtained from an additively-manufactured laboratory distillation column. A comparison is provided between the state-of-the-art DN50 size and a miniaturized DN20 size. The heat loss rate is estimated by simulations and experimentally measured for both column diameters with and without thermal insulation. The impact on the internal flow variation and the gas load (F-factor) uncertainty is presented. The findings provided motives for further improvement to minimize the heat loss rate in the DN20 column. This led to the development of a novel active insulation system where custom-dimensioned flexible silicon heaters are utilized for external heat compensation. The system reduces the heat losses significantly and led to a decrease in the F-factor uncertainty from ± 0.09 Pa0.5 to 0.04 Pa0.5 compared to the passively insulated case. Finally, the effect of the heat loss reduction on the mass transfer efficiency is discussed using two additively-manufactured packings, a 3D-printable version of the Rombopak 9M structure (RP9M-3D) and a new miniaturized packing (XW-Pak). The RP9M-3D showed a decrease in separation performance with heat loss reduction while the performance of the XW-Pak remained unaffected.

Structural Design and Sealing Performance Analysis of a Nanofluidic Self-Heating Unsealing Rubber Cylinder

As a crucial component for temporary blocking of layer segments in the segmental fracturing process, bridge plugs are difficult to unseal by conventional methods and may cause major downhole accidents if not handled properly. In this paper, a nanofluidic self-heating unsealing rubber cylinder is designed, which is equipped with a nanofluidic self-heating unsealing sandwich inside the conventional rubber cylinder, consisting of a nanofluidic system and an annular flexible heater. When unsealing, the nanofluidic self-heating unsealing sandwich is heated by the annular flexible heater, and the nanofluidic system can help the bridge plug rubber cylinder shrink in volume and unseal smoothly by the characteristics of heat shrinkage and cold expansion. The nanofluidic system, consisting of porous carbon with an exceptionally large specific surface area and glycerol, serves as a prime example for filling the sandwich layer, and the design parameters calculation was carried out. The sealing performance of the designed nanofluidic self-heating unsealing rubber cylinder was analyzed based on the Mooney–Rivlin principal structure by finite element modeling. The results show that the maximum contact stress between the nanofluidic self-heating unsealing rubber cylinder and the casing wall increases by 9.73%, the compression distance reduces by 24.47%, and the maximum equivalent force decreases by 12.17% on average compared with a conventional rubber cylinder under the same seating load. The designed nanofluidic self-heating unsealing rubber cylinder can satisfy the requirements of pressure-bearing capacity and sealing performance and performs better than a conventional rubber cylinder.

Ultrahigh-Temperature-Tolerant NiO@Ag NW-Based Transparent Heater with High Stability, Durability, Ultraflexibility, and Quick Thermal Response

High-performance electrical heaters with high transmittance, fast response speed, superior heat resistance, ultraflexibility, high working temperature, and sufficient stabilities are highly desirable for application in heating systems in areas such as healthcare and aerospace. Herein, we demonstrate an ultrahigh-temperature-tolerant flexible transparent heater (FTH) consisting of a NiO@Ag core–shell nanowire (NiO@Ag NW) network and a colorless polyimide (cPI) film. NiO nanoshells are formed uniformly on the surface of Ag NWs through the solution process, which enhances the stability of Ag NWs. The heating behaviors and transmittance can be controlled by the NiO@Ag NW spin-coating cycle. The NiO@Ag NW-based FTHs show a fast thermal response of ∼15 s, a high transmittance of 86.2% in the visible region, and a large thermal figure of merit of 30.7 m2·°C/W under optimal preparation conditions. The saturation temperature of FTHs has barely changed after 20 taping tests and 1000 bending cycles at a bending radius of 0.5 mm. Particularly, the heating temperature of FTHs can reach 266 °C in the air under an applied voltage of 9 V. Moreover, the FTHs possess sufficient heating reliability, stability, and repeatability during the long-term and repeated heating cycles. In addition, the FTHs are resistant to a number of harsh environments.

Flexible Coated Conductive Textiles as Ohmic Heaters in Car Seats

Pleasant interior conditions within cars, as well as a comfortable feeling, are primary needs of car drivers to perform vital body functions during driving. In a cooler outer environment, a warming system within seats can quite feasibly maintain a realistic thermal balance in the body. An inbuilt heating system in car seats can not only provide adequate heat to the driver but is also relevant to minimizing the energy consumption within the vehicle interior. In order to evenly distribute the heat over the body contact area of the automotive seats, conductive textiles are proposed. In fact, these textiles behave as a semiconductor (as an electrical conductor and also creating resistance, which in turn creates heat). Flexible textile ohmic heaters present great advantages due to their ability to bend, stretch, and stitch. These properties make them valuable to ensure uniform heaters for irregular geometries. The present review highlights the use of different textile-based ohmic heaters, their fabrication methods, range of heating, and durability. Moreover, this review also focuses on the comparative mechanical performance and comfort properties of the presented fabrics (used in car seats). This study is beneficial for future trends of minimizing energy consumption and providing an effective way to reduce the carbon emissions and air pollution produced by vehicles.

Self-assembled Growth of SnO2 Nanoshells on Copper Nanowires for Stable and Transparent Conductors

Despite a century of research, the inability to design flexible transparent electrodes with low cost and high stability has been the greatest obstacle in realizing flexible electronics. Herein, we report the growth of self-assembled SnO2 nanoshells on thin copper nanowire (Cu NW) networks using a simple and effective solution method. In addition, the SnO2–Cu NW flexible films exhibit an extremely low sheet resistance of ∼13.6 Ω/sq, with ∼83.5% optical transparency. In harsh environments (such as strong oxidation, heat, and humidity conditions), the films demonstrate excellent resistance stability, which can compete with the resistance stability of noble silver nanowire films. Particularly, the films are robust and able to withstand a high temperature of 210 °C without any deterioration of performance. Employing the outstanding stability of SnO2–Cu NWs, we also demonstrate the macroscopic use of a transparent conductor in a flexible transparent heater.

Network structural carbon nanotubes covalently linked graphene composite film for flexible electro-thermal heater with enhanced performance

Network structural carbon nanotubes covalently linked graphene composite film for flexible electro-thermal heater with enhanced performance

Low-temperature polyol synthesis of millimeter-scale-length silver nanowires enabled by high concentration of Fe3+ for flexible transparent heaters

Silver nanowires (AgNWs) emerge as a promising candidate for flexible electronic devices. AgNWs with high aspect ratios improve the optoelectronic properties of transparent conductive electrodes. However, syntheses conducted at a high temperature usually produce AgNWs either too short or too thick. Here, we report a one-pot low-temperature polyol method using a high concentration of Fe(NO3)3 (up to 160 mM). Fe3+ was found to accelerate AgNWs growth by five times, possibly reduced to Fe2+ and functioning as an oxygen scavenger to preserve Ag seeds, allowing the synthesis to be conducted at as low as 70 °C, which was about 100 °C lower compared with a common polyol method. Low temperature suppressed excessive nucleation, producing AgNWs longer than 1100 μm. AgNWs were dispersed in an acidic solution and purified with a non-pressure filtration method. transparent conductive electrodes fabricated with long AgNWs on polyethylene terephthalate exhibited a sheet resistance of 7.8 Ω/sq at a transmittance of 95.0% without heat treatment. Transparent heaters of AgNWs on polyethylene terephthalate and polydimethylsiloxane substrates were heated to 79.1 °C at 3 V and 174.1 °C at 8 V power supply, respectively, and their application was demonstrated in a quick defogging process. The simple synthesis method of ultralong AgNWs may expand their applications in high-performance flexible transparent electronic devices.

Fluid-structure interaction of a thin flexible heater inside a lid-driven cavity

The purpose of this study is to explore the characteristics of fluid-structure interaction and heat transfer enhancement from a hot flexible thin plate during mixed convection. The mixed convection condition of the plate heater is assumed by placing it inside a lid driven cavity with top and bottom cavity walls being fixed and insulated while left and right cavity walls maintained at constant low temperature move in downward and upward direction respectively. The Galerkin Finite Element Approach has been used to numerically solve equations describing unsteady flow, thermal and stress fields in the Arbitrary Lagrangian-Eularian (ALE) framework. Key parameters include Reynolds number ( Re) and Richardson number ( Ri), and Cauchy number ( Ca) which are varied in the range of 100 ≤ Re ≤ 500, 0.1 ≤ Ri ≤10, and 10−4 ≤ Ca ≤ 10−7 respectively. To investigate the effect of the heater’s geometry, the plate length ( l) has been varied within 0.1 ≤ l ≤ 0.7. The results have been presented in terms of the distribution of streamline and isotherm, heat transfer rate from the flexible heater as well as its deformation. The outcomes reveal that heat transfer enhances with the increase in Reynolds number and Richardson number while it degrades with the extension of the heater. Moreover, thermal frequency obtained by Fast Fourier Transform (FFT) indicates dominant peaks at higher Reynolds number and Richardson number although these become insignificant as the plate becomes rigid.

Multifunctional Ultraviolet Laser Induced Graphene for Flexible Artificial Sensory Neuron

AbstractNeuromorphic perceptual system (NPS) is inspired by the interaction between organisms and environment, which has boosted many emerging fields like human–machine interfaces and bionic robots. Laser‐induced graphene (LIG) can be a fast, low cost, and accurate patterning technology toward a flexible and biological plausible NPS. While, to unleash the full potential of LIG, thorny issues like low endurance and limited stretchability should be addressed. Herein, high‐performance ultraviolet LIG (UV‐LIG) based sensors and electrodes are introduced for building flexible artificial sensory neuron (ASN). The UV‐LIG can be fabricated with a fine linewidth of ≈75 µm and a high conductivity of 3900 ± 150 S cm−1, which facilitates the demonstration of LIG toolbox, containing bending sensors, flexible heaters, etc. The transferred LIG electrodes retain good conducting property (only ≈12.7% increment in resistance) and enable large stretchability (up to 150% strain), outperforming most of the LIG‐based strain sensors. As a proof‐of‐concept, an artificial sensory neuron that is able to mimic the strain perception of somatosensory system is realized based on the integration of LIG‐based functional components and an InGaZnO (Indium‐Gallium‐Zinc Oxide, IGZO)‐based synaptic transistor. This work can provide an efficient patterning methodology as well as essential components for neuromorphic perceptual systems.

Pattern-Dependent Radio Frequency Heating of Laser-Induced Graphene Flexible Heaters.

Graphene is an excellent choice for heating applications due to its high thermal conductivity and is considered an interesting candidate for application in flexible heaters. The major challenge, though, is the costly and chemical-intensive pathways to produce graphene on a large scale. Laser ablation of polymeric substrates is a relatively recent technique for a facile, single-step, chemical-free fabrication of graphene, referred to as laser-induced graphene (LIG). This work demonstrates the fabrication of patterned LIG-based flexible heaters and their response to radio frequency (RF) electromagnetic waves. Polymeric substrates were scribed with laser patterns in both raster and vector modes and subjected to RF electromagnetic fields to test their heating response. We confirmed different graphene morphologies of the lased patterns through various materials characterization methods. The maximum steady-state temperature observed for the LIG heater was approximately 500 °C. Unprecedented heating rates, as high as 502 °C/s, were observed when LIG heaters were exposed to RF fields at 200 MHz frequency and 4.6 W power. Mechanical and thermal stability tests for the best heater were also performed showing a stable thermal response for 1000 bending cycles and 20 cycles of the heating test for 8.5 h, respectively. Our work suggests that LIG heaters produced in vector mode lasing outperformed those lased in raster mode which can be attributed to the improved graphene quality for RF absorbance.

Microscale hybrid 3D printed ultrahigh aspect ratio embedded silver mesh for flexible transparent electrodes

Increasing the aspect ratio (AR) of embedded metal meshes (EMMs) is an effective approach to solve the “trade-off” effect of flexible transparent electrodes (FTEs). However, achieving low-cost and green manufacturing of ultrahigh AR EMM still faces great challenges. Here, we report a novel solution for the ultrahigh AR EMMs by microscale hybrid printing nano silver paste. An improved printed nozzle is introduced to facilitate the stable electric-filed-driven 3D printing, then the imprinting process is used to achieve an EMM with AR of up to 20.1, which is the highest AR ever reported. The fabricated FTE exhibits unprecedented photoelectric performance with a figure of merit of up to 88,194 and excellent optoelectronic properties after rigorous mechanical and environmental stability tests. Its practical application was also demonstrated to be feasible through flexible transparent heater and electromagnetic shielding. The proposed method provides a promising strategy to fabricate FTEs with ultrahigh AR EMM.

AuCu decorated MXene/RGO aerogels towards wearable thermal management and pressure sensing applications

MXene based aerogels with efficient thermal insulation, excellent electrical conductivity, reversible compressibility, and high durability hold great potential for various applications, ranging from wearable electronics to multifunctional scaffolds. How to balance various performance to adapt to more application scenarios is an urgent problem to be solved. In the present work, honeycomb AuCu alloy nanoparticles decorated Ti3C2Tx MXene/RGO aerogels (MXene/RGO/AuCu NPs aerogels) were prepared by a simple reduction and directional freeze-drying method. The optimized MXene/RGO/AuCu NPs aerogels have low density (0.023 g/cm3), flame retardant, robust mechanical properties (longitudinal and transverse compressive modulus of 450.9 kPa and 79.9 kPa at 90% strain, respectively) and 80% compressive elasticity. The deformable porous structure enables it to respond to pressure, which has been proved to be applied to pulse and human respiration monitoring. The ordered pore structure and the LSPR effect of MXene and AuCu particles make aerogels have heat resistance, flame retardancy, good electrothermal (can rise to 245.2 °C in 6 s at 7 V drive voltage) and photothermal properties (109 °C in 10 s at 1sun sunlight intensity). The excellent thermal management capability and pressure sensing characteristics make it a prospect application in wearable flexible heaters and artificial skin.

Highly stable phosphotungstic acid/Au dual doped carbon nanotube transparent conductive films for transparent flexible heaters

Phosphotungstic acid (PTA) is a highly stable dopant. In this research, transparent conductive films (TCFs) with polyethylene terephthalate as a substrate and PTA/Au secondary p-type doped single-walled carbon nanotubes (SWCNTs) as a conductive layer were prepared by spraying and employed as heating devices. The films had excellent optoelectronic properties (sheet resistance of 46.7 Ω/sq with 87.1% transmittance), mechanical properties (only 0.03 change in sheet resistance after 5000 bending cycles), stability (29.4% change in sheet resistance after one week of exposure to 95% humidity) and electrical heating properties. Transparent flexible heaters (TFHs) made of PTA/Au dual p-type doped SWCNT TCFs have a quick response to temperature changes and outstanding cycling stability. At an operating voltage of 20 V, the temperature of the TFH rapidly reached its maximum steady-state temperature (Tmax) of ∼120 °C within less than 90 s. After 50 cycles at 15 V in the voltage-on-off cycle test, the Tmax achieved by the TFH did not change appreciably. The results of the performance evaluation indicate that the film has a bright future in flexible wearable devices for warmth, physiotherapy, or deicing/defrosting applications.

Chemically Welding Silver Nanowires toward Transferable and Flexible Transparent Electrodes in Heaters and Double-Sided Perovskite Solar Cells

Silver nanowires (AgNWs) are important materials for flexible transparent electrodes (FTEs). However, the loose stacking of nanowire junctions greatly affects the electric conductivity across adjacent nanowires. Soldering can effectively reduce the wire-wire contact resistance of AgNWs by epitaxially depositing nanosolders at the junctions, but the process normally needs to be performed with high energy consumption. In this work, we proposed a simple room-temperature method to achieve precise welding of junctions by adjusting the wettability of the soldered precursor solution on the surfaces of AgNWs. The nanoscale welding at nanowire cross junctions forms efficient conductive networks. Furthermore, reduced graphene oxide (rGO) was used to improve the stability of FTEs by wrapping the rGO around the AgNW surface. The obtained FTE shows a figure-of-merit (FoM) of up to 439.3 (6.5 Ω/sq at a transmittance of 88%) and has significant bending stability and environmental and acidic stability. A flexible transparent heater was successfully constructed, which could reach up to 160 °C within a short response time (43 s) and exhibit excellent switching stability. When laminating this FTE onto half perovskite solar cells as the top electrodes, the obtained double-side devices achieved power conversion efficiencies as high as 16.15% and 13.91% from each side, pointing out a convenient method for fabricating double-sided photovoltaic devices.

Conformal and Transparent Al2O3 Passivation Coating via Atomic Layer Deposition for High Aspect Ratio Ag Network Electrodes

We demonstrated conformal Al2O3 passivation via atomic layer deposition (ALD) of a flexible Ag network electrode possessing a high aspect ratio. The Ag network electrode passivated by the ALD-grown Al2O3 film demonstrated constant optical transmittance and mechanical flexibility relative to the bare Ag network electrode. Owing to the conformal deposition of the Al2O3 layer on the high aspect ratio Ag network electrode, the electrode exhibited more favorable stability than its bare Ag-network counterpart. To demonstrate the feasibility of Al2O3 passivation via ALD on a flexible Ag network, the performances of flexible and transparent thin-film heaters (TFHs) with both a bare Ag network and that passivated by ALD-grown Al2O3 were compared. The performance of Al2O3/Ag network-based TFHs was minimally altered even after harsh environmental tests at 85% relative humidity and a temperature of 85 °C, while the performance of bare electrode-based TFHs significantly deteriorated. The improved stability and reliability of the Al2O3/Ag network-based TFHs indicate that the ALD-grown Al2O3 film effectively prevents the introduction of moisture and impurities into the Ag network with a high aspect ratio. The improvement in the stability of the Ag network through Al2O3 passivation implies that the ALD-grown Al2O3 film represents a promising transparent and flexible thin film passivation material for high quality Ag network electrodes with high aspect ratios.

Two-step thermal treatment of electrochemical graphene oxide films for high-performance electrical heating and electromagnetic interference shielding

Electric heaters have attracted growing interest due to their wide applications in healthcare, smart wear, and aerospace. Contrarily, conventional heaters fail to meet the expectations of flexibility, high temperature, and efficiency. The current protocol focus on the fabrication of a flexible, high-temperature, and high-performance heater through a multi-step strategy. The modified two-step electrochemical exfoliation approach facilitated the formation of electrochemical graphene oxide (EGO). The simple two-step thermal treatment of EGO produced graphene film. The EGO structure exhibits excellent flexibility, good electrical conductivity, and thermal stability after thermal treatment. Consequently, graphene film showed good flexibility and efficient electric heating performance. It only required 13 s to reach 401.2 °C at 3.5 V. Additionally, graphene film displays sufficient heating reliability, stability, and repeatability under heating cycles and prolonged heating. Moreover, it demonstrates electromagnetic interference shielding effectiveness of up to 30383.6 dB cm2/g. Therefore, graphene film has emerged as a promising alternative for developing intelligent clothes, wearable devices, and healthcare devices.

Gallic Acid-Reduced Graphene Oxide Deposited with Carbon Nanotubes for Transparent Film Heaters

The flexible transparent film heater described in this research was based on graphene, carbon nanotubes (CNTs), and polyethylene terephthalate (PET). Natural polyphenols gallic acid (GA) was chosen as the “green” reducing agent of graphene oxide (GO) to prepare the GA-functionalized GO (GGO). Then, the GGO nanosheets were introduced into the CNT network, and the GGO/CNT-PET composite films were successfully prepared by a simple spraying method. This type of transparent conductive film (TCF) possesses an excellent optoelectronic performance (Rs = 49.1 Ω/sq., T = ca. 80% at 550 nm) and a very low RMS roughness (approximately 6.89 nm). The sheet resistance of the films changed slightly after the 1000 bending cycles and 100 h of air exposure time, which indicated that the film has good mechanical properties and environmental stability. The composite TCFs were further applied to fabricate transparent film heaters (TFHs) and showed excellent Joule heating performance, fast response speed, good cycling stability, long-term stability, and controllable operating temperature (the power density of the TFHs shows an approximate linear behavior), which satisfy the requirements of TFHs in practical applications, such as safe voltage and temperature in wearable devices, the stable controlling temperature in smart windows, fast heating in defoggers, and so on.

Oxide/Metal/Oxide 구조의 유연하고 투명한 히터

Optically transparent and electrically conductive films were investigated for the flexible and transparent heaters. Metal (Ag), silver nanowires (AgNWs) and metal oxide (ITO or ZnO) were employed to form the various types of transparent heaters. A single-layered ITO, metal hybrid AgNWs (ZnO/AgNWs) and ZnO/Ag/ZnO composite were manufactured on PET substrates. Each case was tailored by large-scale device (150 mm x 100 mm).BRFor each structure, visible light transmittance, electrical conductivity, and heating performances were investigated to show the enhanced performances from the ZnO/Ag/ZnO composite, which showed the excellent transmittable (77% at wavelength of 550 nm) and outperforming heating performances to reach 146°C with fast heating speed. The improved performances are mainly attributed to the structure of ZnO/Ag/ZnO, where the thin Ag governs the electrical property with good optical feature. This study suggests that the ZnO/Ag/ZnO transparent heater has the excellent optical and electrical properties with good flexibility and affordable scalability to enlighten the large-scale and flexible heating applications.

Washable and Flexible All Carbon Electrothermal Joule Heater for Electric Vehicles

AbstractAmid the rapid development of electric vehicles, a flexible and waterproof radiant heater that can withstand repeated bending and washing is highly desirable. Herein, a freestanding, ultra‐flexible, and washable joule heater is constructed using a biocompatible poly(styrene‐isoprene‐styrene) (SIBS) polymer as binder and carbon black (CB) as heating material. By controlling the amount of CB and the thickness of the film, a minimum resistivity, and conductivity of 26 mΩ cm and 7.4 S cm−1, respectively, is achieved. Remarkably, the 28% CB/SIBS film can reach a maximum temperature of 201 °C while maintaining a stable temperature at 130 °C for repeated ON/OFF cycles. Time‐of‐flight secondary ion mass spectrometry of post‐mortem material analysis shows that a 1 h stability test at 130 °C has no sign of degradation and the films remain extremely stable. The films also show exceptional electrothermal heater performance after carrying out mechanical property tests such as bending (over 30°), repetitive bending (1000 cycles), twisting (two turns), and washing (soaked in distilled water for over 12 h). These outstanding heater performances incorporate extreme chemical stability and mechanical flexibility proposing that the CB/SIBS‐based electrothermal elements hold great potential for numerous practical applications, such as heating systems in electric vehicles and wearable electronics.

Portable in situ temperature-dependent spectroscopy on a low-cost microfluidic platform integrated with a battery-powered thermofoil heater.

A low-cost microfluidic platform integrated with a flexible heater was developed for in situ temperature-dependent spectroscopic measurement at the point of care. After verifying the system by comparing on-chip spectroscopic measurement of methylene blue with the conventional spectroscopy, we demonstrated its applications in temperature-dependent absorption spectroscopy of a model biomolecule, curcumin. The system is portable, battery-powered and requires ultra-low volumes of analytes, which is highly suitable for point-of-care characterization.