Thin Film Heater Research Articles

Random Ag mesh transparent heater obtained with a cracked template technique

The results of a study of thin-film transparent heater based on silver micromesh coatings obtained using a self-organized template are presented. Ag mesh with sheet resistance of 1.6 Ω/sq and integral transparency in the visible range of ∼84 % was obtained. The influence of the filling factor (FF) and the thickness of the Ag mesh on the uniformity of heating of a transparent heater and the response time was studied by the method of thermal imaging analysis. We have shown a stable, reproducible operation of the crack templated Ag mesh transparent heater on glass and PET in static heating and cycling mode.

Impact of low temperature plasma annealing for flexible, transparent and conductive ITO/PEDOT:PSS composite electrode

We report on the development of a cost effective, highly transparent flexible conductive electrode for energy conversion devices using the ITO/PEDOT:PSS nanocomposite. The ITO/PEDOT:PSS nano composite thin film was deposited via bar coating, then its characteristics were examined. In particular, we study any changes in its transparency and resistance. The thin film transparent ITO/PEDOT:PSS was annealed using a low temperature annealing technique called plasma annealing. The purpose of low temperature plasma annealing is to help excite the electrons from their bonding states in the valence band into the antibonding states of the conduction band where a second order phase transition occurs. This study investigates the influence of O2 plasma annealing on the resistance of the nano composite thin films. The included PEDOT:PSS supports the flexibility of the ITO, as pristine ITO is brittle. High optical transmittance of 93.73% at 550nm and a reduction in the sheet resistance were achieved using this plasma annealing from 1105 Ω/□ to 535 Ω/□ on the ITO/PEDOT:PSS nano composite making them excellent candidates to develop as cost effective flexible transparent electrodes that can be used as thin film heaters.

Thermal Profiles of Carbon Fiber Based Anisotropic Thin-Films: An Emerging Heat Management Solution for High-Current Flow Electrocatalysis and Electrochemical Applications

Carbon fiber has been extensively used in the photocatalysis, electrocatalysis and energy storage fields as supporting platform and conductive media. However, less attention has been paid with regards to its function in phonon transport and thermal management. We have investigated the effect of current flow direction on the heat management performance of carbon fiber based thin film heaters (CFTFHs) with anisotropic percolation network of carbon fibers (CFs). The anisotropic percolation network of carbon fibers (CFs) formed by roll-to-roll spray coating leads to the anisotropic electrical properties of CFs. As a result, CFs based thin films (CFTFs) have lower sheet resistance when measured parallel to the CFs alignment, compared to when they are aligned perpendicular. Because connectivity and current flow in CFs are critically dependent on the direction alignment of CFs, the saturation temperature (106.4 °C) of CFTFH with parallel aligned carbon fiber is higher than that (117.3 °C) of CFTFH with perpendicular alignment. Therefore, current flow in the same direction as the alignment of CFs is very important to achieve high-performance. Moreover, our study on thermal profile of anisotropic CFTFs under high current flows illustrates that carbon fiber thin films have great potential in thermal management solution for electrocatalytic and electrochemical energy storage applications.

General formula for the temporal and spatial resolutions in measuring the heat transfer fluctuation on a thin-film heater formed on a window material by infrared camera

General formula for the temporal and spatial resolutions in measuring the heat transfer fluctuation on a thin-film heater formed on a window material by infrared camera

Highly sensitive heat flux sensor based on the transverse thermoelectric effect of YBa2Cu3O7− δ thin film

Thin film heat flux sensors with the size of 5 mm × 3 mm have been fabricated by growing c-axis tilted YBa2Cu3O7−δ thin films on miscut SrTiO3 (001) substrates. The Seebeck coefficient anisotropy between the ab-plane and the c-axis of the YBa2Cu3O7−δ thin film is utilized to generate the output voltage of the heat flux sensor via the transverse thermoelectric effect. The sensitivities of 104.9, 174.1, and 220.9 μV cm2/W have been achieved in nominal 5°, 10°, and 15° inclined thin films, respectively. Such a sensitivity of 220.9 μV cm2/W exceeds a sensitivity of 180.3 μV cm2/W from a standard and water-cooled Gardon gauge. In addition, the fast response time in the range of 15–40 ms has been identified in these sensors based on the transverse thermoelectric effect, which is significantly superior to 400 ms of the Gardon gauge. These results may provide an approach to manufacture highly sensitive heat flux sensors with a low cost, in contrast to the traditional thin film heat flux sensors with complicated micro-fabrication processes.

Management of surface cooling non-uniformity in spray cooling

The existence of the hot spot area in the impact center of spray cooling indicates that the temperature is not uniform on a relative large spray-covered surface. In this study, the temperature distribution on a large spray-cooled surface is experimentally studied, and cooling non-uniformity (CNU) is defined to quantify the global and local temperature fluctuations. A flat thin film heater is newly designed, and surface temperature is measured using high-resolution infrared thermography. Particle Imaging Velocimetry (PIV) is used to acquire the droplet velocity of the spray. In the present work, three methods are investigated to reduce the CNU. One method is to change the height, the vertical spacing between the spray nozzle and surface. It is found that with the increasing spray height, the CNU first decreases to the lowest point and then rises to the peak value. The second method is to incline the spray. It is discovered that inclined spray impact benefits the cooling uniformity at the larger spray height. The third method is spray-jet cooling, in which a liquid jet is added to impinge at the center of the spray cooling. It shows that the spray-jet cooling does not only reduce CNU but also increases CHF.

Non-uniqueness solutions for the thin Carreau film flow and heat transfer over an unsteady stretching sheet

The present paper probed the problem of thin liquid film flow and heat transfer in the Carreau fluid past a permeable stretching sheet. The similarity transformation reduced the partial differential equations into a system of ordinary differential equations, which was then solved numerically by a collocation method. The influence of the governing parameters towards the model was discussed and presented graphically. The non-uniqueness solutions are observable as the governing parameters vary.

Journal of Physics: Conference Series High-pressure specific heat technique to uncover novel states of quantum matter

AC-specific heat measurements remain as the foremost thermodynamic experimental method to underpin phase transitions in tiny samples. However, its performance under combined extreme conditions of high-pressure, very low temperature and intense magnetic fields needs to be broadly extended for investigation of quantum phase transition in strongly correlated electron systems. In this communication, we discuss the determination of specific heat on the quantum paramagnetic—insulator SrCu2(BO3)2 by applying the AC-specific heat technique under extreme conditions. In order to apply this technique to insulating samples we sputtered a metallic thin film-heater and attached thermometer onto sample. Besides that, we performed full frequency scans with the aim to get quantitative specific heat data. Our results show that we can determine the sample heat capacity within 5% of accuracy respect to an adiabatic technique. This allows to uncover low energy scales that characterize the ground state of quantum spin entanglement in SrCu2(BO3)2.

Performance of 9.0 W light-emitting diode on various layers of magnesium oxide thin film thermal interface material

MgO thin films were spin coated on aluminum (Al) substrate and used between LED package and heat sink as thin-film heat spreader. Crystallographic studies showed the presence of (111), (200) and (220) orientations related to MgO phases. From the XRD analysis, 10-layers of MgO showed a favorable film thickness (424 nm), crystal size (11.6 nm), microstrain (0.4860 nm) and dislocation density (0.0078 lines/m2). Similarly, low surface roughness (14.6 nm) and depth of peak–valley (71.6 nm) were recorded from 10-layers MgO thin film using Atomic Force Microscopy (AFM) analysis. Relative thermal conductivity of 22.93 W/mK was recorded from the 10-layers MgO film. High value of the difference in total thermal resistance (ΔRth-tot = 3.01 K/W) and rise in junction temperature (ΔTJ = 18.92 °C) were recorded along with good thermal impedance (35 °C) from the 10-layers MgO thin film measured at 700 mA using thermal transient analysis. Overall, MgO thin film coated Al substrates showed an improved performance for the tested LED and, therefore, can be considered as an alternative thermal substrate for LED thermal management.

Comparison of Thin Film Heat Flux Gauge Technologies Emphasizing Continuous-Duration Operation

Abstract Thin-film heat flux gauges (HFGs) have been used for decades to measure surface temperatures and heat flux in test turbines with the majority being used in facilities that are short-duration. These gauges are typically composed of two resistive temperature devices deposited on opposing sides of a dielectric. However, because these sensors have been traditionally applied for measurements in transient-type facilities, the challenges facing adaptation of this technology for a steady facility warrant investigation. These challenges are highlighted, and the solutions are presented throughout the paper. This paper describes the nanofabrication process for heat flux gauges and a new calibration method to address the potential deterioration of gauges over long runtimes in continuous-duration facilities. Because the primary uncertainty of these sensors arises from the ambiguity of the thermal properties, the emphasis is placed on the property determination. Also, this paper presents a discussion on the use of impulse response theory to process the data showing the feasibility of the method for steady-duration facilities after an initial settling time. The latter portion of the paper focuses on comparing well-established heat flux gauges developed for short-duration turbine test facilities to recently developed gauges fabricated using modern nanofabrication techniques for a continuous turbine test facility. The gauges were compared using the test case of an impinging jet over a range of Reynolds numbers. The comparison between the PSU gauge and the reference device indicated agreement within 14%, and similar results were achieved through comparison with established sensors from partner institutions.

An Integrated Smartphone-Based Genetic Analyzer for Qualitative and Quantitative Pathogen Detection.

The use of the smartphone is an ideal platform to realize the future point-of-care (POC) diagnostic system. Herein, we propose an integrated smartphone-based genetic analyzer. It consists of a smartphone and an integrated genetic analysis unit (i-Gene), in which the power of the smartphone was utilized for heating the gene amplification reaction, and the camera function was used for imaging the colorimetric change of the reaction for quantitative and multiplex foodborne pathogens. The housing of i-Gene was fabricated by using a 3D printer, which was equipped with a macro lens, white LEDs, a disposable microfluidic chip for loop-mediated isothermal amplification (LAMP), a thin-film heater, and a power booster. The i-Gene was installed on the iPhone in alignment with a camera. The LAMP mixture for Eriochrome Black T (EBT) colorimetric detection was injected into the LAMP chip to identify Escherichia coli O157:H7, Salmonella typhimurium, and Vibrio parahaemolyticus. The proportional–integral–derivative controller-embedded film heater was powered by a 5.0 V power bank to maintain 63 °C for the LAMP reaction. When the LAMP proceeded, the color was changed from violet to blue, which was real-time monitored by the smartphone complementary metal oxide semiconductor camera. The images were transported to the desktop computer via Wi-Fi. The quantitative LAMP profiles were obtained by plotting the ratio of green/red intensity versus the reaction time. We could identify E. coli O157:H7 with a limit of detection of 101 copies/μL within 60 min. Our proposed smartphone-based genetic analyzer offers a portable, simple, rapid, and cost-effective POC platform for future diagnostic markets.

Rapid Defrost Transparent Thin-Film Heater with Flexibility and Chemical Stability

Zn-doped SnOx/Ag/Zn-doped SnOx(ZTO/Ag/ZTO) multilayer thin films fabricated on a polyethylene terephthalate (PET) substrate using an optimized N2-to-(Ar + O2) gas ratio are used for transparent thin-film heaters with high performance and chemical stability. The ZTO/Ag/ZTO-based multilayer thin film exhibits enhanced durability at high temperatures and humid environments by incorporating nitrogen. The bending test results-there was no significant change in the sheet resistance even after 10,000 bending cycles-highlight the mechanical flexibility of the ZTO/Ag/ZTO multilayer thin film. The ZTO/Ag/ZTO-based thin-film heater on PET, fabricated under optimized deposition gas conditions, exhibits a fast thermal response time of 30 s and a low driving voltage of 6 V to attain 100 °C. It also exhibits uniform heat distribution at saturated temperature and chemical stability after 100 heating-cooling cycles. Hence, the proposed ZTO/Ag/ZTO-based thin-film heater is applicable for use in front and rear window automobile and building applications.

A SiN Microcalorimeter and a Non-Contact Precision Method of Temperature Calibration

A dual-channel flow-through microcalorimeter device is presented along with a non-contact precision method of temperature calibration. A microfluidic channel with a volume of ≈550 pL in a spiral layout was fabricated from low-stress nitride suspended over a cavity in a silicon substrate. The thin-film heater and resistive temperature detector (RTD) on the channel were defined by a patterned Ti layer. The device exhibited a rapid thermal response with the following thermal characteristics: a time constant of ≈10.5 ms, a heat conductance of $\approx 152~\mu ~\text{W}\,\cdot ~{\mathrm {K}}^{-{1}} $ and a heat capacitance of $\approx 1.6~\mu \text{J}\,\cdot {\mathrm {K}}^{-{1}} $ on average based on the measurements of nine separate units fabricated on the same wafer. Further, the melting curve analysis (MCA) of a double-stranded DNA was proposed as a non-contact method of microcalorimeter RTD calibration. The method revealed that the measurement by the RTD underestimates the temperature of the channel interior by an amount of nearly 15%, at ≈ 9 mW. At this dissipated power level, the method also revealed a spatial nonuniformity of ≈ ± 0.8 °C across the microcalorimeter. [2020-0173]

Triple Solutions of Carreau Thin Film Flow with Thermocapillarity and Injection on an Unsteady Stretching Sheet

Thin films and coatings which have a high demand in a variety of industries—such as manufacturing, optics, and photonics—need regular improvement to sustain industrial productivity. Thus, the present work examined the problem of the Carreau thin film flow and heat transfer with the influence of thermocapillarity over an unsteady stretching sheet, numerically. The sheet is permeable, and there is an injection effect at the surface of the stretching sheet. The similarity transformation reduced the partial differential equations into a system of ordinary differential equations which is then solved numerically by the MATLAB boundary value problem solver bvp4c. The more substantial effect of injection was found to be the reduction of the film thickness at the free surface and development of a better rate of convective heat transfer. However, the increment in the thermocapillarity number thickens the film, reduces the drag force, and weakens the rate of heat transfer past the stretching sheet. The triple solutions are identified when the governing parameters vary, but two of the solutions gave negative film thickness. Detecting solutions with the most negative film thickness is essential because it implies the interruption in the laminar flow over the stretching sheet, which then affects the thin film growing process.

Testing of the heating element integrated into the honeycomb sandwich structure for active thermography inspection

The honeycomb sandwich structures with carbon composite face sheets combined with aluminium or Nomex® honeycomb core are extensively used in the aircraft airframe structure. They provide some key benefits over conventional structures such as increased bending strength and stiffness combined with low weight. However, they show high sensitivity to a certain type of damage, such as object impact, mishandling, etc. Non-destructive inspection methods are needed for a structural health examination. Active infrared thermography is one of them. The quality of the inspection and defect detection depends heavily on the proper application of the external thermal excitation. This paper presents a concept of the sandwich structure with internal excitation by means of an integrated thin-film resistive heating element.

Thin-Film Evaporation Heat Transfer of Liquid Nitrogen and Its Application in Cell Vitrification

Abstract Cell vitrification has been an important method of cell cryopreservation. The faster the cooling rate is, the higher the cell survival rate is. However, in conventional cell vitrification methods, film boiling forms a vapor-blanket on the surface, which hinders further improvement of the cooling rate. To eliminate the problem, this article attempted to replace film boiling with thin-film evaporation (TFE) of liquid nitrogen. The experimental system was developed to investigate the TFE heat transfer characteristics of liquid nitrogen. Then, prostate cancer cells were cryopreserved by TFE vitrification method, open pulled straw vitrification method, and equilibrium freezing method. The results showed that the vitrification method of TFE obtained a higher cooling rate and better cell survival rate than the two other cell cryopreservation methods. Thus, the feasibility of this method was preliminarily proved viable when applied to the cell vitrification process. In addition, both the cooling rate and the cell survival rate are affected by the concentration of the cryoprotectant in the cell suspension. The cooling rate decreases as the concentration of the cryoprotectant increases, but the cell survival rate increases first and decrease afterward with an increase in the cryoprotectant concentration, in which an optimum value exists. This study demonstrates the practicality of the new ultrafast cell vitrification method.

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.

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.

Portable and Battery-Powered PCR Device for DNA Amplification and Fluorescence Detection.

Polymerase chain reaction (PCR) is a technique for nucleic acid amplification, which has been widely used in molecular biology. Owing to the limitations such as large size, high power consumption, and complicated operation, PCR is only used in hospitals or research institutions. To meet the requirements of portable applications, we developed a fast, battery-powered, portable device for PCR amplification and end-point detection. The device consisted of a PCR thermal control system, PCR reaction chip, and fluorescence detection system. The PCR thermal control system was formed by a thermal control chip and external drive circuits. Thin-film heaters and resistance temperature detectors (RTDs) were fabricated on the thermal control chip and were regulated with external drive circuits. The average heating rate was 32 °C/s and the average cooling rate was 7.5 °C/s. The disposable reaction chips were fabricated using a silicon substrate, silicone rubber, and quartz plate. The fluorescence detection system consisted a complementary metal-oxide-semiconductor (CMOS) camera, an LED, and mirror units. The device was driven by a 24 V Li-ion battery. We amplified HPV16E6 genomic DNA using our device and achieved satisfactory results.

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.