Film Heat Research Articles

Deposition Rate Effect on Optical and Electrical Properties of Thermally Evaporated WO3\u2212x/Ag/WO3\u2212x Multilayer Electrode for Transparent and Flexible Thin Film Heaters

We investigated the deposition rate effect on the optical, electrical, and morphological characteristics of thermally evaporated WO3−x/Ag/WO3−x (WAW) multilayer electrodes. By controlling the deposition rate of the WO3−x and Ag layers, we can control the interface structure between WO3−x and Ag and improve both the optical and electrical properties of the thermally evaporated WAW multilayer electrodes. At the optimized deposition rate of WO3−x (2.5 Å/sec) and Ag (10 Å/sec), the symmetric WAW multilayer exhibited a high optical transmittance of 92.16% at a 550 nm wavelength and low sheet resistance of 3.78 Ω/square. During repeated bending, rolling, and twisting, there was no resistance change indicating the superior flexibility of WAW multilayer electrodes. As a promising application of the WAW multilayer electrodes, we suggested the transparent and flexible thin film heaters (TFHs) to substitute the high cost indium tin oxide-based TFHs. In comparison to the ITO-based TFHs, the WAW based TFHs showed higher convective heat transfer property and higher saturation temperatures are achieved at lower input voltages due to lower sheet resistance. This indicates that the WAW multilayer is suitable as the electrode for high performance transparent and flexible TFHs.

Structure evolution during deposition and thermal annealing of amorphous carbon ultrathin films investigated by molecular dynamics simulations

The evolution of the structure of amorphous carbon (a-C) films during deposition and thermal annealing is of significant interest from both the materials science and application perspectives. However, despite the voluminous literature of studies dealing with the deposition and physical properties of a-C films, basic understanding of the structure evolution due to phase change during film growth and heating is fairly sparse and empirical, presumably due to the lack of high-resolution instruments that can probe structural changes at the atomic and molecular levels in real time. Molecular dynamics (MD) is a powerful computational method for studying atomic/molecular-scale movement and interactions. Thus, the objective of this study was to perform MD simulations that provide insight into changes in the structure of ultrathin a-C films during deposition and annealing. Simulation results reveal a multi-layer film structure, even for a-C films as thin as ~20 Å, the existence of a deposition energy that yields a-C films with the highest sp3 content, the transient and steady-state stages of the structure evolution during annealing at different temperatures, and the changes in the hybridization state (mainly in the bulk layer) encountered during annealing at elevated temperatures. The MD results of this study are of particular importance to applications where the deposition conditions and operation temperature affect the structure and, in turn, the physical properties of ultrathin a-C films used as protective overcoats.

Numerical simulation of fractional non-Fourier heat transfer in thin metal films under short-pulse laser

In this paper, heat transfer is investigated in thin metal films subjected to a short-pulse laser. Due to the short temporal scales and high intensity of laser pulses during the heating process, the non-Fourier phenomenon can be observed in the temperature response of thin metal films. Therefore, the fractional non-Fourier model has been applied to investigate the heat transport in thin metal films to capture the thermal behaviors of nano-scale metal films. The fractional non-Fourier model is presented to investigate the heat transfer in single-layer gold film and gold‑chromium double-layer films under short-pulse laser. The governing fractional heat conduction equation is solved numerically using the finite difference method based on implicit scheme, and the obtained results are compared to the experimental data. The numerical results obtained from the fractional model represent its accuracy and suitability to predict the thermal behavior of the thin metal films irradiated by short-pulse laser. In addition, upon comparing the results of the fractional model with the results of other models which have been employed in this field, it can be seen that the fractional model has a higher capability than others to examine the non-Fourier effects during laser heating of thin metal films.

Solution‐Processable Transparent Organic Molecular Nanoadhesives for Exceptionally Durable Nanowire Electrodes

AbstractSilver (Ag) nanowires (NWs) are promising building blocks for fabrication of flexible transparent electrodes, but their poor adhesion to polymeric substrates causes delamination of NWs from a substrate during repeated deformation, which leads to degradation in electrical performance. A new and simple approach is developed to dramatically improve mechanical, chemical, and thermal stability of a Ag NW electrode by hybridizing a NW network film with an organic molecular nanoadhesive layer without sacrificing its inherent excellent optoelectrical properties. It is discovered that some of pyridine derivatives such as 4‐dimethylaminopyridine can be solution‐processed and annealed to form a transparent layer with high adhesion to polymeric substrates such as poly(ethylene terephthalate). In addition to high optical transparency and electrical conductivity, the NW‐nanoadhesive hybrid film exhibits low surface roughness, reduced optical haze, and excellent adhesion to the substrate without delamination against 100 cycles of tape detachment and 10 000 cycles of bending tests at 1 mm of bending radius. Furthermore, the hybrid film exhibits good air‐oxidation and thermal stability over 24 h at 100 °C. The hybrid electrodes show good performance in applications for flexible touch panel and thin film heater.

Laser-induced depletion of ultrathin PFPE lubricants using a quantitative coarse-grained model.

Knowledge of laser-pulsed processing of ultrathin liquids on solid surfaces is of great importance in advancing the understanding of synthesis, characterization and applications of functional nanofilms. In this work, we performed molecular dynamics simulations coupled with a novel quantitative coarse-grained model to study laser-induced local heating and depletion behaviors of Fomblin Z2000 lubricants. It was found that the Fomblin lubricant films experience severe evaporation and thermodiffusion-related degradation under laser heating. The ultrathin lubricants inevitably lose their frictional resistance under extremely high temperatures and thermal gradients (i.e., up to 990K and 65.4K/nm) that are required for FePt media in HAMR systems. The factors that influence the local thermal depletion, such as laser power, spot size, and scanning velocity, were investigated as well. The results clearly show that the laser power has the greatest influence on the relative maximum temperature change and subsequently the severe lubricant film depletion during rapid laser heating, while the spot size and scanning velocity play a relatively weaker role in the laser-induced local thermal instability. The findings in this work are thus believed to provide molecular scale insights into laser-induced local heating and depletion of ultrathin lubricant films from a precise quantitative perspective.

Nanoceramic Powder Based Thermometer for Basal Body Temperature Monitoring System to Estimate Ovulation

In this paper, Basal body temperature (BBT) monitoring IoT enabled system is designed and developed using a nanomaterial based thermistor. BBT is the lowest body temperature attained at rest and normally ranges from 96°F to 99.5°F. The NiMn2O4 nanoceramic powder based thermistor is used as a temperature sensor which is fabricated by synthesizing NiMn2O4 nanomaterial powder by the modified wet chemical method. This nanomaterial powder is pressed in an insulated cylindrical tube with aluminum electrodes. The average crystallite size of the NiMn2O4 was found to be 26.8nm from the XRD characterization. The calibration of the sensor was performed by using thin film heater, combination of LM35 and fabricated thermistor with Atmega328 microcontroller. The system so developed effectively measures the BBT at axillary (armpit) with precision more than three digits. Further this system is IoT facilitated using ThingSpeak IoT platform in order to privilege real time monitoring. Analysis of the biphasic temperature pattern of the obtained BBT graph is more convenient to predict ovulation period in women accurately. This information is helpful in enhancing the effectiveness of Natural Family Planning (NFP) to achieve or avoid pregnancy naturally.

Comparison of apparatus and methods for tactile marking of polymeric films with Braille alphabet

This article analyzes contact and non-contact methods for local heat treatment of heat shrink films in tactile marking devices. The characteristics of polymeric film heating processes under heat transfer from metal stamps and laser emitters were investigated. The article contains diagrams obtained by differential scanning calorimetry of polymeric heat shrink film exposed to thermal effect of different tactile marking devices. The article also describes stereometry of Braille elements obtained by using a metal stamp and a laser emitter.

Essential Oils Encapsulation into Nanoliposome and Novel Application of Nanoliposome as a Storage Pesticide

This study attempted to evaluate the physicochemical characteristics of essential oil nanoliposomes from three plants by two preparation methods including thin film sonication and heating. Also, the durability of fumigation toxicity of the essential oil nanoliposome and pure essential oil of Mentha pulegium against Tribolium castaneum Herbst adults were compared. The smallest mean size of the nanoliposome was prepared by the thin film sonication method (P<0.05). The encapsulation efficiency of the nanoliposome was higher than 96%. Nanoliposmes prepared by using two methods showed high stability during storage. The release profile of essential oils at the heating method showed that the essential oil diffusion from the nanoliposome was in the following order: Mentha pulegium > Ferula gummosa > Zattaria multiflora. These findings indicate that both preparation methods had the same effect on the formation of nanoliposomes, their characteristics, and their storage stability. The durability of fumigation toxicity of the nanoliposome M. pulegium essential oil had a significant effect on mortality of T. castaneum adults in comparison with pure essential oil of this plant. The result showed that nanoliposome encapsulation of M. pulegium essential oil significantly increased fumigation toxicity against T. castaneum. Therefore, essential oil encapsulation into a nanoliposome carrier can potentially be used in pest management.

Electrical Resistance of Polymeric Compounds Filled with SHS-Produced TiC–Al2O3 Powders

SHS-produced TiC–Al2O3 powders were used as a filler of organosilicon polymers and ethoxyline resin to prepare electroconducting polymeric compounds. The electrical conductivity of thus prepared polymeric compounds was found to depend on the amount of added ceramic powder, temperature, and type of polymer binder. A threshold effect observed for the temperature dependence of compound resistance can be used in designing temperature sensors and temperature/current-limiting devices. Our polymeric compounds can also be recommended as a material for film heaters with a working temperature of below 300°С.

Robust ultrathin and transparent AZO/Ag-SnOx/AZO on polyimide substrate for flexible thin film heater with temperature over 400 °C

We developed flexible and transparent thin film heaters (TFHs) with a structure of AZO/Ag-SnOx/AZO/polyimide (PI) which exhibited superior stability under operational conditions. Ultrathin and robust doped silver (Ag) films were produced by introducing a small amount of SnOx during the sputtering process. The AZO/Ag-SnOx/AZO stacks showed the best figure of merit value of 139.9, which was higher than that of ITO counterpart (25.5) with the same thickness. In addition, it exhibited excellent durability, which showed unaffected optical and electrical properties under the heat treatment of 500 °C for 30 min in air, highly-accelerated temperature and humidity stress test (HAST) at 121 °C and 97%RH for 36 h, 10,000 times of scratching and 1500 times of inner and outer bending test. Furthermore, the TFHs based on AZO/Ag-SnOx/AZO/PI achieved a high temperature of 438.8 °C with response time in several seconds, which outperformed most previous studies. The robust high-temperature TFHs in this research hold promising commercial applications in flexible and high temperature occasions.

Numerical treatment of a physical problem in fluid film flow using the differential transformation method

The problem of thin liquid film flow over a heated horizontal stretching surface permitted by uniform transverse magnetic field in the presence of variable heat flux is studied numerically. The ordinary differential equations describing the physical problem are solved approximately by the differential transformation method (DTM). A study of the convergence analysis of the proposed method is given. The effects of the various parameters governing the thin film flow and heat transfer in this study are discussed and presented graphically. Our paper contributes to the existing literature by introducing the numerical treatment using the DTM for the nonlinear system of ordinary differential equations, which describe a thin film fluid flow affected by the variable heat flux.

PII: S0928-1258(20)30052-8

In this study, the falling film evaporation heat transfers of R290 on an array composed of five enhancement horizontal tubes (groove tubes) are studied. The tests are performed at constant saturation temperatures 5.5 °C with change of heat flux from 10 to 40 kW/m2. The film Reynolds number ranges from 200 to 2200 and the film flow rate of refrigerant is between 100 and 660 kg/h.The results show that the film flow rate and heat flux have significant effects on R290 falling film evaporation heat transfer coefficients (HTCs) of the tubes in the tube array. With decreasing the film flow rate on the five tubes the tube HTCs display two stages, a plateau stage and a sharp drop stage. The heat transfer coefficients firstly keep more or less constant at the plateau stage and then decreasing rapidly. At the same nominal film Reynolds number the tube averaged heat transfer coefficients of tube No. 1 to tube No. 5 decrease in order of the increasing tube number from top to bottom of the array. The falling film evaporation HTC of R290 on single enhanced tube is about 4.5 times of single smooth tube HTC, and the HTCs of the enhanced tube array is higher than single smooth tube by more than 2.5 times. In addition, the R290 HTCs of the tube array are higher than those of R134a for the same tube array in the plateau region by about 25%. It is found that at high heat flux of 30–40 kW/m2, the heat transfer coefficient variation with film Reynolds number of the lower enhanced tubes in the tube array exhibits severe undulating characteristics.

The Influence of Catalysts on the Gas Sensitivity of a Gas Sensor Based on SnO<sub>2</sub> Films + 1 % at. Si

The paper is devoted to the study of the influence of surface modification by catalysts on the gas sensitivity of a gas sensor. The sample for the study is a gas sensor crystal with dimensions of 1 × 1 mm2, manufactured using microelectronic technology. Its design is represented by a film heater, two sensitive elements (SE) based on tin dioxide with the addition of 1 % at. Si (film thickness = 250 nm, the size of the SE area is 200 x 320 μm2) and contacts for the sensitive layer in the form of an interdigital platinum structure with a distance between contacts of 10 μm. It is established that doping increases the gas sensitivity and lowers the operating temperature.

Nanoporous WO3 films synthesized by tuning anodization conditions for photoelectrochemical water oxidation

Morphology engineering is of prime significance in designing semiconductor photoelectrodes for efficient photoelectrochemical (PEC) fuel generation. Herein, we report a strategy to fabricate nanostructured tungsten oxide films using anodic oxidation of tungsten and their performance as photoanodes for PEC water splitting. A solution of an organic compound, dimethyl sulfoxide, with hydrofluoric acid was used as the electrolyte. The anodization parameters such as voltage and electrolyte temperature were found to have a critical influence in determining the porous nature and dimensions of the resulting oxide film. Anodization conducted at a voltage ~10 V and a temperature ~40 °C led to the formation of compact tungsten oxide films due to the low strength of the electric field partially responsible for the porous morphology development. The surface of the film became porous at elevated temperatures. At higher voltages, a thin nanoporous film atop a thicker compact layer was formed; however, the structure became more disordered and less porous when the electrolyte temperature was increased. The study demonstrated that by adjusting the voltage and temperature, the oxide film morphology could be varied from a compact layer to a porous structure resembling nanotubes. The films heat treated at 500 °C attained the monoclinic phase of WO3. The PEC performance was influenced strongly by the morphology of the films. The films with nanotube like morphology yielded incident photon to current conversion efficiency values of over 40%. This study would provide a practical basis for developing optimal WO3 nanostructures for efficient PEC fuel generation.

Polymer Film Heat Transfer Surfaces in Seawater Desalination: Fouling Layer Formation and Technology

AbstractThe emerging polyether ether ketone (PEEK) films were evaluated as future heat exchanger materials in seawater thermal desalination processes. Fouling resistance curves were measured in a pilot plant for pure PEEK films, talcum‐filled PEEK films, and stainless‐steel films with artificial seawater, showing that pure PEEK films have the advantage of weaker forces of adhesion or cohesion between the scaling materials and the film surface. Increasing the flow rate from 18 to 24 L min−1 results in decreases of both the fouling rate and the asymptotic values. This was attributed to the lower polarity of 10.4 %, the lower arithmetic average roughness of 0.06 μm, and the homogeneous topography of the PEEK film. This polymer film is adaptable to in situ cleaning in thermal seawater desalination processes.

Highly flexible and transparent film heaters based on colorless polyimide substrate with a GZO/AgNW/GZO sandwich structure

In the past years, transparent film heaters (TFHs) based on silver nanowires (AgNWs) have attracted much attention because of their high transmittance, excellent flexibility, and great thermal response. In this paper, we fabricated flexible TFHs with a sandwich structure composed of Ga-doped ZnO (GZO) and AgNWs on the colorless polyimide (cPI) substrate. The optimized hybrid film exhibited a sheet resistance of 14.6 Ω sq−1 with a transmittance of 79%. Excellent thermal uniformity and heating stability of TFHs were demonstrated. The thermal response tests of the GZO/AgNW/GZO/cPI TFHs showed high saturation temperature (~ 176 ℃) with low input voltage (~ 6 V), fast response time (~ 15 s), and stable heating performance. These results indicate that the flexible TFHs with a GZO/AgNW/GZO sandwich structure have broad potential applications in flexible electronic devices.

Experimental assessment of a detachable plate falling film heat and mass exchanger couple using lithium bromide and water as working fluids

Abstract Absorption heat pumps and absorption heat exchangers play an important role in the district heating in China. However, the structure of existing systems leads to weaknesses such as low heat transfer performance and large areas. A detachable plate-type falling film heat and mass exchanger (HMX) couple utilizing lithium bromide (LiBr) and water as working fluids are proposed to address these problems. The performance of the first-generation prototype left room for improvement, with the overall heat transfer coefficient ranging from 0.4 to 0.7 kW·m−2·K−1 under generator-condenser conditions. In addition, working conditions could not be established under absorber-evaporator conditions. Optimization of the structure of the liquid distributor in the heat exchanger is also accomplished through this research. The overall wetting rate of the heat exchange plate exceeds 90% during the design flow rate. The liquid distributor for the first-generation prototype is optimized using this method, and the performance of the system is tested. The average heat transfer coefficient of condenser rises to the level of 1 kW·m−2·K−1 during the generator-condenser condition. Furthermore, the absorber-evaporator condition can be established, wherein the heat transfer coefficient of the absorber ranges from 0.235 to 0.422 kW·m−2·K−1. The results of the improved HMX couple improve the feasibility of this system, reduce the size of the AHP system, and improve the heat transfer performance.

Highly flexible, transparent and conductive ultrathin silver film heaters for wearable electronics applications

We fabricate highly flexible and conductive (sheet resistance of 6.2 Ohm/sq.) ultrathin Ag film heaters sandwiched by ZnO layers to achieve high visible light transparency (average transmittance of 90.2%). The transparent resistive heaters exhibit high spatial thermal uniformity, fast thermal response time, outstanding heater durability, robustness under mechanical bending and low-voltage operation enabled by the high conductivity. The excellent heating capability was evident with various heating tests either in the bent or unbent form, which qualifies this heating element for various wearable electronics including biomedical devices. The electrical parameters required to reach various temperatures were evaluated based on the square-shaped heaters having areas in the range of 25–2,025 mm2, which confirms the suitability of the heating element for large-scale (200 mm × 200 mm) applications via a direct connection with a portable rechargeable battery having the output dc 12 V.

Closed-Loop, Axial Temperature Control of Etched Silicon Microcolumn for Tunable Thermal Gradient Gas Chromatography

Combining the resolution of conventional gas chromatography systems with the size factor of microGC systems is important for improving the affordability and portability of high performance gas analysis. Recent work has demonstrated the feasibility of high resolution separation of gases in a benchtopscale short column system by controlling thermal gradients through the column. This work reports a microfabricated thermally controllable gas chromatographic column with a small footprint (approximately 6.25 cm2). The design of the 20 cm column utilizes 21 individually controllable thin film heaters and conduction cooling to produce a desired temperature profile. The reported device is capable of heating and cooling rates exceeding 8000 °C/min and can reach temperatures of 350 °C. The control methods allow for excellent disturbance rejection and precision to within +/− 1 °C. Each length of the column between heaters was demonstrated to be individually controllable and displayed quadratic temperature profiles. This paper focuses on the fabrication process and implementation of the thermal control strategy. [2019–0113]

Highly flexible, hydrophobic, and large area plasma‐polymer‐fluorocarbon/Cu/SiNx transparent thin film heater and thermotherapy pad application

AbstractIn this study, we prepared a plasma‐polymer‐fluorocarbon/Cu/SiNx (PCS) film heater with a transparent, self‐cleaning surface and excellent mechanical flexibility by using Cu as the heating metal. The PCS film heater exhibited a maximum transmittance of 78.3% in the visible region, a sheet resistance of 4.6 Ω/sq, and a water contact angle of 105° on the film surface. The maximum mechanical inner bending radius was 4 mm, and the cyclic reliability was excellent. In particular, despite the lower optical properties, compared with those of the Ag‐based heater, the maximum transmittance of the PCS film heater in the visible light region was almost the same as that of Ag, and the maximum bending radius was smaller. To evaluate the industrial applicability of the PCS film heater, various sizes were fabricated to evaluate the electrical and heating properties, and a thermotherapy pad was fabricated to demonstrate its applicability as a medical device.