Thin Film Heater Research Articles

Ca3Co4O9-based transverse thermoelectric heat flux sensors with high sensitivity and fast response time

High-temperature thin film heat flux sensors have been fabricated by growing c-axis tilted epitaxial Ca3Co4O9 (CCO) thin films on 5° vicinal cut LaAlO3 (001) single crystal substrates. The layered structure of Ca3Co4O9 yields the significant Seebeck coefficient anisotropy between the ab-plane and c-axis, which could generate a voltage of the heat flux sensor via the transverse thermoelectric (TTE) effect of thin films. A sensitivity of 27.7 μV/(kW/m2) has been determined in such 5° tilted Ca3Co4O9 thin films, which is much larger than other reported ones based on the TTE effect from various materials. After a thermal treatment at 900 °C in air for 10 min, the sensitivity of such heat flux sensors is almost non-variable, which indicates that the temperature resistance of the CCO-based TTE heat flux sensor is as high as 900 °C. In addition, a fast response time of 45 μs has been identified in such CCO-based TTE heat flux sensors. These results demonstrate that the CCO is a promising candidate to manufacture the TTE heat flux sensors with the superiorly comprehensive performance, including the high temperature resistance, high sensitivity, and fast response.

Rapid laser fabrication of indium tin oxide and polymer-derived ceramic composite thin films for high-temperature sensors

Thin-film sensors are essential for real-time monitoring of components in high-temperature environments. Traditional fabrication methods often involve complicated fabrication steps or require prolonged high-temperature annealing, limiting their practical applicability. Here, we present an approach using direct ink writing and laser scanning (DIW-LS) to fabricate high-temperature functional thin films. An indium tin oxide (ITO)/preceramic polymer (PP) ink suitable for DIW was developed. Under LS, the ITO/PP thin film shrank in volume. Meanwhile, the rapid pyrolysis of PP into amorphous precursor-derived ceramic (PDC) facilitated the faster sintering of ITO nanoparticles and improved the densification of the thin film. This process realized the formation of a conductive network of interconnected ITO nanoparticles. The results show that the ITO/PDC thin film exhibits excellent stability, with a drift rate of 4.7 % at 1000 °C for 25 h, and withstands temperatures up to 1250 °C in the ambient atmosphere. It is also sensitive to strain, with a maximum gauge factor of −6.0. As a proof of concept, we have used DIW-LS technology to fabricate a thin-film heat flux sensor on the surface of the turbine blade, capable of measuring heat flux densities over 1 MW/m2. This DIW-LS process provides a viable approach for the integrated, rapid, and flexible fabrication of thin film sensors for harsh environments.

Near-Infrared Transparent Transition-Metal-Doped Indium Oxide Thin-Film Heater for LiDAR.

The evolving need for all-weather light detection and ranging (LiDAR) sensors and cameras for autonomous vehicles, remote sensing surveillance, and space exploration has spurred the development of transparent heaters. While LiDAR photon sources have shifted from the visible to the near-infrared (NIR) range, the use of transparent conductive oxides (TCOs) for heaters leads to significant optical losses due to their high plasmonic absorption and reflection in the NIR range. Although different TCO compositions can be employed to preserve transparency and electrical conductivity in this range, the choice of dopants, their concentrations, and the underlying mechanisms remain largely unknown. In this study, we present TCOs specifically designed for NIR applications with a focus on identifying new compositions that strike a balance between NIR transparency and electrical conductivity. We present a 4B-6B transition-metal-doped indium oxide thin-film heater that exhibits impressive NIR transmittance (>90%) surpassing that of commonly used indium tin oxide films. By incorporating effective dopants such as titanium, hafnium, and tungsten, we successfully reduced the resistivity and enhanced the electrical conductivity of indium oxide films. To enhance the practical utility of the film, we implemented post-treatments comprising argon plasma treatment and encapsulation with low-molecular-weight poly(dimethylsiloxane), which resulted in significantly improved performance. The optimized film exhibited a sheet resistance of 520 Ω/sq and excellent optical transmittance at 850 nm (89.1%), 905 nm (89.7%), and 1550 nm (92%). Moreover, we successfully integrated defogging and defrosting capabilities into a commercial LiDAR camera and demonstrated its reliable operation in challenging environments.

Numerical investigation and analysis of heat transfer and thin film flow of Fe3O4 and Al2O3 nanoparticles dispersed in H2O over vertical stretching sheet

Purpose This article presents a numerical investigation of thin film flow and heat transfer for lamina, tetrahedron, and hexahedron-shaped nanomaterials of F e 3 O 4 and A l 2 O 3 over a time-dependent radially vertical stretching surface. Moreover, magnetohydrodynamics and viscous dissipation effects are also incorporated. Thin-film treatment is especially beneficial in nanotechnology. As a result, the current study’s findings will be useful in a variety of thin film phenomena involving nanoparticles. F e 3 O 4 thin films have considerable potential in a variety of applications, including sensors and batteries. Aluminum oxide nanoparticles have two key applications: medicines and the materials manufacturing industries. Methodology A similarity transformation is employed to produce the nonlinear governing system of equations, which is numerically solved using the BVP4C method in MATLAB. As film thickness depends on the unsteadiness parameter, with an increase in the parameter causing a decrease in film thickness ( β ) , velocity, and temperature. Findings The lamina and hexahedron shapes provide maximum and minimum film thickness for F e 3 O 4 and A l 2 O 3 both nanoparticles, while the hexahedron and lamina shapes generate maximum and minimum skin friction. The Nusselt numbers exhibit the opposite effect. The highest and lowest heat transfer rates are noticed for lamina and hexahedron-shaped nanoparticles of A l 2 O 3 .

Self-protected high-temperature superconducting demonstrator magnet for particle detectors

A high temperature superconducting (HTS) demonstration coil has been developed in the frame of the Experimental Physics department Research and Development program at CERN The magnet extends the recent experimental demonstration of aluminium-stabilised HTS conductors and supports the development of future large scale detector magnets. The HTS magnet has five turns and an open bore diameter of 230 mm. Up to 30 K, the coil was measured to be fully superconducting across four central turns at 4.4 kA, the maximum available current of existing power supply. The central magnetic field is 0.113 T, the peak field on the conductor is 1.2 T and the coil has a stored magnetic energy of 0.1 kJ. A 3D-printed aluminium alloy (Al10SiMg) cylinder acts both as a stabiliser and a mechanical support for the superconductor. The resistivity of Al10SiMg was measured at cryogenic temperatures, and has a residual resistivity ratio of approximately 2.5. The ability to solder ReBCO tapes (a stack of four REBCO tapes, 4 mm wide, Fujikura) to Al10SiMg stabiliser, electroplated with copper and tin, forming a coil, is demonstrated using tin-lead solder at 188 ∘C. The HTS magnet was proven to be stable when superconductivity was broken locally using a thin-film heater. Despite voids in the solder joint between HTS and stabiliser, no degradation of the magnet’s performance was observed after 12 thermal cycles and locally quenching the magnet. A numerical model of the transient behaviour of solenoid with partially shorted turns is developed and validated against measurements. Our work experimentally and numerically validates that using an aluminium alloy as a stabiliser for HTS tapes can result in a stable, lightweight and transparent magnet.

Highly flexible and transparent electrodes for high-performance thin-film heaters with nanostructured micromesh Cu–Ag ultrathin films

Herein, we present a facile method to fabricate transparent, flexible, and high-performance thin-film heaters (TTFHs) based on nanostructured micromesh (NSMM) Cu–Ag/indium tin oxide bilayer transparent thin-film electrodes (TTFEs) with both nano- and microstructures. Our approach combines Ar-assisted thermal evaporation and pulsed laser ablation techniques to fabricate NSMM TTFEs with a low sheet resistance (∼2.1 Ω/sq) and high optical transmittance (∼80.1 %). By adjusting the spacing of microholes, we can achieve excellent figure of merit values (∼51.8 × 10−3 Ω−1) for the NSMM TTFEs. These electrodes also show excellent durability and flexibility, as evidenced by a resistance change of only 4 %–18 % in cyclic bending tests with up to 200,000 cycles. Finally, we demonstrate that the NSMM TTFEs can be used as high-performance TTFHs with short response times (3.97 s at a steady temperature of 87.5 °C under low-voltage operation (5 V)) and infrared shielding properties. Our results suggest that the Cu–Ag-alloy-based NSMM TTFEs are promising transparent electrodes for various applications in flexible electronics, smart windows, and wearable devices.

A thin-film polymer heating element with a continuous silver nanowires network embedded inside

This study presents a method for fabricating a film-based heating element using a polymer material with an array of intersecting conductive elements embedded within it. Track-etched membranes (TM) with a thickness of 10 μm were used as the template, and their pores were filled with metal, forming a three-dimensional grid. Due to the unique manufacturing process of TM, the pores inside intersect with each other, allowing for contacts between individual nanowires (NWs) when filled with metal. Experimental results demonstrated that filling the TM pores with silver allows for heating temperatures up to 78 degrees without deformation or damage to the heating element. The resulting flexible heating element can be utilized in medical devices for heating purposes or as a thermal barrier coating.

Thin film flow, heat transfer and viscous dissipation effects on vertical stretching sheet for different shapes of (Au-Np) dispersed in water

In this article, we present numerical investigation and analysis of thin film flow and heat transfer effects for different shapes of gold nanoparticles on a vertical stretching sheet. There are several uses for thin liquid films, including antireflection coating for lenses. Coating systems must have a smooth, polished surface, low friction, clarity, and strength to satisfy the demands of all of these applications. We consider thin film flow of nanoparticles on a vertical stretching sheet due to their numerous applications. Additionally, we employed water as the base fluid and considered different shapes of gold nanoparticles (blades, cylinders, and platelets). After formulating the problem, we convert nonlinear partial differential equations (PDEs) into ordinary differential equations (ODEs) using a transformation. The resulting nonlinear differential equations have been computed by the BVP4c method. It is examined and graphically assessed how the Nusselt number, temperature, skin friction, and fluid velocity are related. This research suggests that the blade shape has the maximum heat transfer rate and the lowest skin friction coefficient value.

Comparison of thermal and surface properties of silver and silver-graphene thin film heaters

Comparison of thermal and surface properties of silver and silver-graphene thin film heaters

Development and Performance Analysis of an Atomic Layer Thermopile Sensor for Composite Heat Flux Testing in an Explosive Environment

Traditional contact heat flux sensors suffer from a lack of dynamic performance, and existing non-contact optical heat measurement equipment fails to detect convective heat transfer effectively. This limitation precludes the effective testing of composite heat flux in explosive fields. This study introduces an ultra-responsive atomic layer thermopile (ALTP) heat flux sensor, developed and employed for the first time, to evaluate the transient heat flux associated with thermobaric explosions. Measurements reveal that the ALTP sensor’s temporal resolution surpasses that of the thermal resistance thin film heat flux sensor (TFHF), attaining a spectral response time of 10 μs under pulsed laser irradiation. Beyond these radiation-based tests, the present work also conducted novel simulation analyses of high-temperature jet impacts using COMSOL software. Static simulation discovered that fluid velocity significantly influences ALTP’s sensitivity, resulting in an error of 71%. Conversely, dynamic simulation demonstrated that an increase in fluid velocity reduces the ALTP’s time constant, whereas other factors such as fluid temperature exert minimal impact on its dynamic characteristics. This confirms that the simulation model compensates for the cost and accuracy deficiencies of convection heating tests. It also provides a new way to analyze the error of explosive heat flux measurement caused by sensitivity fluctuation and insufficient dynamic performance. In thermobaric explosive trials, the maximum heat fluxes recorded were 202 kW/m2 in semi-enclosed environments and 526 kW/m2 in open environments. A distinctive double-wave phenomenon was evident in the test curve. By a fast-response thermocouple, the study was able to differentiate between radiation and convective heat flux in the explosion field. The findings substantiate that the ALTP sensor amalgamates the benefits of optical thermal measurement tools with those of traditional contact heat flux sensors, thereby facilitating composite heat flux measurements in the challenging conditions of an explosive field.

Improved method for simultaneous determination of thermal properties

An improved method to simultaneously determine the heat capacity, thermal diffusivity, and thermal conductivity of a small-sized material is described. In this method, the heat of a square wave with a superimposed constant component is applied to one side of a plate-shaped sample using a thin-film heater, which is thermally linked to a heat reservoir. The response temperature is measured by a thermometer attached to the heater. In contrast to a previously reported method, the amplitude of the temperature oscillation detected by the thermometer is enhanced by the internal thermal relaxation in the improved method. This feature is advantageous for determining thermal properties with low-heat modulation. We theoretically analyzed the proposed method using a one-dimensional model and demonstrated the method on synthetic quartz (SiO2) and poly(methyl methacrylate) plates in the temperature range of 80–300 K. The thermal properties obtained for both samples using the proposed method were consistent with values reported in the literature. The deviations from the data for the specific heat capacity, thermal diffusivity, and thermal conductivity were estimated to be ∼1%, 2%, and 2%, respectively.

Novel four-port RF phase change switches based on GeTe thin film

An indirect-heated phase-change switch (PCS) using germanium telluride (GeTe) has been fabricated using thermal actuation driven by thin film heater on the model. Switches require a low ON-state resistance and a high OFF-state resistance with OFF/ON resistance ratio of 105. The finite element analysis simulation is applied to simulate the temperature of individual node GeTe with different microwave heating pulses. Finally, in order to reduce the phase-change time and increase the switching speed of indirectly heated switching structures, a new four-port indirectly heated phase change switching structure is proposed. In this paper, the heat dissipation of the switch is increased by etching deep grooves on the back of the switch. This structure obviously reduces the phase change time compared to conventional indirectly heated phase change switches the time between ON-state and OFF-state is reduced by more than 19% and the total process is reduced by more than 47%. The GeTe PCSs with etched grooves not only significantly increases the switching speed, but also reduces the risk of recrystallization of the phase change material.

Structural Design of Dual-Type Thin-Film Thermopiles and Their Heat Flow Sensitivity Performance.

Aiming at the shortcomings of the traditional engineering experience in designing thin-film heat flow meters, such as low precision and long iteration time, the finite element analysis model of thin-film heat flow meters is established based on finite element simulation methods, and a double-type thin-film heat flow sensor based on a copper/concentrate thermopile is made. The influence of the position of the thermal resistance layer, heat flux density and thickness of the thermal resistance layer on the temperature gradient of the hot and cold ends of the heat flow sensor were comprehensively analyzed by using a simulation method. When the applied heat flux density is 50 kW/m2 and the thermal resistance layer is located above and below the thermopile, respectively, the temperature difference between the hot junction and the cold junction is basically the same, but comparing the two, the thermal resistance layer located above is more suitable for rapid measurements of heat flux at high temperatures. In addition, the temperature difference between the hot and cold contacts of the thin-film heat flux sensor increases linearly with the thickness of the thermal resistance layer. Finally, we experimentally tested the response-recovery characteristics of the sensors, with a noise of 2.1 μV and a maximum voltage output of 15 μV in a room temperature environment, respectively, with a response time of about 2 s and a recovery time of about 3 s. Therefore, the device we designed has the characteristic of double-sided use, which can greatly expand the scope of use and service life of the device and promote the development of a new type of heat flow meter, which will provide a new method for the measurement of heat flow density in the complex environment on the surface of the aero-engine.

A high strength and flexible multilayered thin film laser induced graphene heater for thermal applications

Increasing demand for wearable sensors and heating elements has occurred recently. Herein, graphene has been observed as a biocompatible, cost effective, and multidimensional material catering to both sensing and heating applications. However, it still lacks essential features such as high temperature performance with low power usage, high strength, and robustness of thin films in tough environments such as heating elements in thermal socks. Hence, in this paper, we demonstrated laser induced graphene (LIG) as a suitable candidate for wearable thermal applications. LIG heaters were fabricated using a cost effective and environmentally friendly technique based on photothermal ablation of polyimide substrate using a 50 W CO2 laser. The heat flux of LIG heater was improved by stacking multiple films while their electrical connections are made in parallel. Upon joule heating, the heaters had excellent electrothermal performance, fast and stable response, achieving temperature of 195 °C using a relatively low DC voltage of 10 V. Most importantly, they showed good durability after bending, washing and repeated heating and cooling cycles. Due to these advantages, the LIG-based thin film heaters have potential as reliable and low-cost heating elements for variety of tough applications such as defrosting and wearable thermal pads.

Fabrication of High-Temperature Polymer- Derived Ceramic Thin-Film Heat Flux Sensor by 3-D Printing and Laser Pyrolysis

Heat flux density is an important parameter for evaluating the high-temperature performance of turbine blades. Accurate heat flux density data play a significant role in the design and manufacture of turbine blades and their heat-dissipation performance. Current studies have shown that thin-film heat flux sensors (TFHFSs) are suitable for signal monitoring of complex turbine blade surfaces. However, TFHFSs have a multi-layer structure, which is difficult to achieve using traditional physical vapor deposition (PVD). In this paper, we propose an approach to fabricating high-temperature polymer-derived ceramic (PDC) TFHFSs using 3D printing and laser pyrolysis. Through direct ink writing (DIW), sensitive, antioxidant, and thermal resistance layers were written directly on an alumina substrate. The sensitive layer was rendered electrically conductive owing to laser-induced graphitization. Thus, the structure of multi-layer TFHFS can be quickly achieved using the proposed method. The results showed that the sensor can operate at 800 °C. Its sensitivity was 1.349 mV/(kW/m²). Thus, it is feasible to prepare thin-film heat flux sensors by 3D printing and laser pyrolysis, which provides a new in situ integrated manufacturing method for fabricating heat flux sensors suitable for working in harsh environments such as aviation.

Gold nanostructures modified carbon-based electrode enhanced with methylene blue for point-of-care COVID-19 tests using isothermal amplification

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) envelope (E) and RNA-dependent RNA polymerase (RdRP) genes were detected via electrochemical measurements using a screen-printed carbon electrode (SPCE) (3-electrode system) coupled with a battery-operated thin-film heater based on the loop-mediated isothermal amplification (LAMP) technique. The working electrodes of the SPCE sensor were decorated with synthesized gold nanostars (AuNSs) to obtain a large surface area and improve sensitivity. The LAMP assay was enhanced using a real-time amplification reaction system to detect the optimal target genes (E and RdRP) of SARS-CoV-2. The optimized LAMP assay was performed with diluted concentrations (from 0 to 109 copies) of the target DNA using 30 μM of methylene blue as a redox indicator. Target DNA amplification was conducted for 30 min at a constant temperature using a thin-film heater, and the final amplicon electrical signals were detected based on cyclic voltammetry curves. Our electrochemical LAMP analysis of SARS-CoV-2 clinical samples showed an excellent correlation with the Ct value of real-time reverse transcriptase-polymerase chain reaction, indicating successful validation of results. A linear relationship between the peak current response and the amplified DNA was observed for both genes. The AuNS-decorated SPCE sensor with the optimized LAMP primer enabled accurate analysis of both SARS-CoV-2-positive and -negative clinical samples. Therefore, the developed device is suitable for use as a point-of-care test DNA-based sensor for the diagnosis of SARS-CoV-2.

Effect of thin-film sensors on local heat transfer in convective heat flux measurement

Thin-film heat flux sensors are usually attached to the interesting surface for the measurement of wall heat flux in the aerospace industry. However, the presence of the surface-mounted sensors may disturb the velocity and thermal boundary layer, alert the local wall heat flux, and induce erroneous measured results. This study numerically investigates the effect of the presence of thin-film heat flux sensors on the local flow and heat transfer. The effects of both Reynold number of the flow and the geometry of the sensor are investigated. The results show that the local convective heat transfer can be remarkably enhanced by the presence of the sensor. In particular, when the height of the thin-film heat flux sensor is within 2% of the flow boundary layer, the enhancement of the convection heat transfer caused by the heat flux sensor is independent with the inlet velocity of the flow. Finally, an empirical model for estimating the influence of the sensor on the heat transfer is established based on the numerical findings, which can provide a useful tool for practical design to evaluate and minimize the effect of the sensor on the local convective heat transfer.

A numerical study on thin film flow and heat transfer enhancement for copper nanoparticles dispersed in ethylene glycol

Abstract The current study examines thin film flow and heat transfer phenomena with some additional effects such as magnetohydrodynamic, viscous dissipation, and slip condition over unsteady radially stretching surfaces for various shapes of copper ( Cu ) \left({\rm{Cu}}) nanoparticles dispersed in ethylene glycol ( EG ) \left({\rm{EG}}) . The effective thermal conductivity of a nanofluid made of Cu nanometer-sized particles distributed in EG {\rm{EG}} is significantly higher than that of pure EG. Partial differential equations are transformed into ordinary differential equations using the proper transformations. An effective convergent technique (i.e., BVP4C) is used to compute the solutions of nonlinear systems. MATLAB software is used to perform the calculations. The effect of numerous emerging physical characteristics on temperature and velocity, such as unsteadiness parameter ( S ) \hspace{ 1em}\left(S) , slip parameter ( K ) \left(K) , Hartmann number ( M ) \left(M) , solid volume fraction ( ϕ ) (\phi ) , and Eckert number ( EC ) \left({\rm{EC}}) is investigated and illustrated graphically. The physical quantities, such as the skin friction coefficient and the Nusselt number, are calculated, described, and displayed in tabular form. It is observed that blade-shaped Cu nanoparticles had the lowest surface drag, highest heat transfer rate, and minimum film thickness compared to the brick and cylinder-shaped nanoparticles. According to our detailed investigation blade-shaped Cu {\rm{Cu}} nanoparticle is the most suited solution for manufacturing unsteady radially stretching modules.

Design and performance evaluation of a novel thin-film heat flux sensor

Thin-film heat flux sensor is suitable for the harsh environment in aerospace application. To further improve the accuracy of testing and to realize the measurement in two directions, this work proposes a new design of the thin-film heat flux sensor. Based on the numerical simulation method, this work investigates the influence of geometric parameters, physical property and working conditions on the sensor test error, and analyzes the testing performances under steady and transient states. Results indicate that the sensor test error is mainly related to the thermal resistance ratio of the sensor in the measurement system. The accuracy of the thin-film heat flux sensor increases with the increase of sensor size or local total thermal resistance. Besides, the newly designed sensor has satisfying steady and transient characteristics, including the small time constant, fast response, and good linear relationship between the measured temperature difference and the surface heat flux.

Heat-Transfer Gauge Arrays for Identifying Spot Initiation in Hypersonic Transitional Boundary Layers

The initiation and growth of turbulent spots in transitional hypersonic boundary layers can influence the transition length and the distribution of heat transfer and skin friction through the transitional region. There is debate in the literature about whether spots initiate in a small band at the start of transition or throughout the transitional region. This paper presents a new design of arrays of thin-film heat transfer specifically designed to detect whether spots initiate in a small band. The gauges were arranged in two spanwise rows at different streamwise locations and were tested on a 7° blunt cone in the T4 Stalker Tube. It is shown that such instrumentation is capable of identifying that some spots initiate between the rows when other spots have already formed upstream of the first row. This demonstrates that the breakdown of laminar boundary layers is not concentrated in a region of small streamwise extent in the current hypersonic flows.