Film Heat Research Articles

Radio frequency heating and reduction of Graphene Oxide and Graphene Oxide - Polyvinyl Alcohol Composites

Graphene oxide (GO) is one of the most frequently-used graphene-family materials, but it must often be reduced in order to restore electrical conductivity for the target applications. We have demonstrated the use of non-contact fringing field RF applicators to rapidly heat and reduce GO, both in its neat form and inside a polymer matrix such as polyvinyl alcohol (PVA). For this study, GO and GO-PVA films were prepared by the vacuum filtration method. The results demonstrate quick non-contact heating of GO and GO-PVA composite films by application of RF fields. Heating rates as high as 10.9 °C/s and 1.5 °C/s have been observed for GO and GO-PVA, respectively. RF-reduced GO and GO-PVA samples have shown conductivities of 102 S/m and 10−1 S/m, respectively. In addition, C/O ratio has increased from 2.44 to 5.22 when GO is exposed to RF waves which confirm that GO samples are reduced by the RF treatment. Unlike time-consuming or hazardous conventional reduction methods, RF waves resistively heat GO with electric fields in seconds to form reduced GO.

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.

Water spray heat transfer through a piezoelectric atomizer with a single-hole micronozzle

We report an experimental study on the flow and heat transfer for a single microhole of water spray impingement on an indium tin oxide (ITO) heating plate using a piezoelectric atomizer. A microhole of dj = 35 µm was used and tested with a volumetric flow rate of 0.22 cm3/min for three different spray heights of 10, 20 and 30 mm and five heater initial temperatures of 25 °C, 50 °C, 100 °C, 150 °C, and 200 °C. Through the optical measuring techniques of the microparticle image velocimetry (μPIV) as well as interferometric particle imaging (IPI) and micro laser-induced fluorescence (μLIF), the velocity field, such as spray centerline velocity, droplet impact velocity and impact crater diameter, including impinged liquid film thickness and heat transfer performance (CHF) can be measured and calculated. The effects of the spray height and initial heater temperature on the flow and thermal characteristics are presented and discussed herein. The experimental results show that both the spray centerline velocity and spray droplet impact velocity were significantly influenced by the initial surface temperature as well as by the spray height. As a result, the cooling performance would be, in turn, affected by the aforesaid two parameters.

Numerical Simulation for Falling Film Thickness around Horizontal Tube in MVC and MED Evaporators

Falling film on horizontal tube evaporators, of both Mechanical Vapor Compression (MVC) and the Multi-Effect Distillation (MED) desalination systems, plays an important role in the heat and mass transfer (evaporation) and accordingly the systems productivity. Falling film thickness is mainly influenced by the intertube space, circumferential angle and the film’s Reynolds number. This paper presents two-dimensional numerical study of falling film thickness around horizontal tube in MVC and MED evaporators. The study is based on computational fluid dynamics (CFD) using volume of fraction (VOF) as a multi-phase technique in ANSYS Fluent. The numerical model is developed in order to study the heat and mass transfer charactristics, the liquid falling film behaviour and thickness distribution around circular horizontal. Four CFD study cases are developed to simulate the falling film behaviour at circumferential angle range from 150 to 1650 with inter-tube spacing of 10 mm, 16 mm, 33 mm and 40 mm and for constant value of flow rate and at the same surrounding conditions. Simulations are conducted using a domain of only two tubes with 20 mm outer diameter.The results from the numerical models are compared with the published experimental correlations, showing a comparatively reasonable agreement. In addition, a parametric study is carried out to illustrate the effect of flow Reyonlds number (Re) and intertube space on the average circumferential film thickness and heat transfer rates.

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.

An On-Device Deep Learning Approach to Battery Saving on Industrial Mobile Terminals.

The mobile terminals used in the logistics industry can be exposed to wildly varying environments, which may hinder effective operation. In particular, those used in cold storages can be subject to frosting in the scanner window when they are carried out of the warehouses to a room-temperature space outside. To prevent this, they usually employ a film heater on the scanner window. However, the temperature and humidity conditions of the surrounding environment and the temperature of the terminal itself that cause frosting vary widely. Due to the complicated frost-forming conditions, existing industrial mobile terminals choose to implement rather simple rules that operate the film heater well above the freezing point, which inevitably leads to inefficient energy use. This paper demonstrates that to avoid such waste, on-device artificial intelligence (AI) a.k.a. edge AI can be readily employed to industrial mobile terminals and can improve their energy efficiency. We propose an artificial-intelligence-based approach that utilizes deep learning technology to avoid the energy-wasting defrosting operations. By combining the traditional temperature-sensing logic with a convolutional neural network (CNN) classifier that visually checks for frost, we can more precisely control the defrosting operation. We embed the CNN classifier in the device and demonstrate that the approach significantly reduces the energy consumption. On our test terminal, the net ratio of the energy consumption by the existing system to that of the edge AI for the heating film is almost 14:1. Even with the common current-dissipation accounted for, our edge AI system would increase the operating hours by 86%, or by more than 6 h compared with the system without the edge AI.

Experimental study of the falling film evaporation coefficients of R290 in a horizontal enhanced tube array

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.

Understanding and enhancing the direct contact membrane distillation performance by modified heat transfer correlation

AbstractThe sensitivity of direct contact membrane distillation to feed temperatures and feed flow rate is investigated experimentally. At very low flow rates, the process becomes heat transfer limited where the thermal energy of the aqueous feed solution is lost by the conduction resistance minimizing the distillate production. At high flow rates, the film heat transfer coefficient for both liquid solutions increases, creating a larger temperature difference across the membrane boundaries. Hence, the mass fluxes increase linearly with the water flow rate. These findings are also assessed by simulating the heat and mass transfer equations that describe the membrane distillation (MD) thermo‐physical operation. It is found that the underlying physics of the MD module must faithfully capture and explain the true process behaviour. Hence, a modified correlation for the Nusselt number is developed and tested.

Al/Ti-film-resistor based thermal heater with Zig-Zag configuration for MEMS application

In this paper, we proposed a micro-heater based on Al/Ti-film resistors for MEMS application. The film heater, designed with unique Zig-Zag configuration, has a high heating efficiency as generated Joule heat could be confined in Zig-Zag area. Consequently, much higher maximum temperature could be achieved under the lower applied voltage, compared with conventional strategy. Based on MEMS technique, thin film based micro-heater was fabricated, and experimental characterization was carried out in room temperature. Since the micro-heaters are all in the form of thin film-resistors, the structure design is simple and fabrication process compatibility is good, which is particularly suitable in the fields of MEMS integration and actuation application.

A study of the increased temperature influence on the electrochromic and electrochemical characteristics of Ni(OH)2-PVA composite films

Electrochromic devices, as an element of “smart” windows, can be exposed to extreme temperatures due to their purpose and location. Exposure to high temperatures can change the characteristics of electrochromic devices and lead to malfunction. The present study is intended to fill in the gaps related to the stability of electrochemical and electrochromic parameters of one of the known materials – nickel hydroxide (II). The present study highlights changes in some physico-chemical characteristics that occur during prolonged exposure to high temperature in different media. Ni(OH) 2 -polyvinyl alcohol, prepared using the cathodic template method, was aged at 80 °С under the air atmosphere and in the working electrolyte solution – 0.1 М KOH for 8 hours. The temperature was chosen based on the maximum registered temperature on Earth, possible film heat up and possible rapid degradation of electrochromic films. As a result, it was found that degradation does occur in a basic solution, while on air some improvement was observed instead. The authors propose the mechanism that explains experimental results, which lies in “ageing” of active material Ni(OH) 2 . The latter occurs in the active mass of alkaline batteries. Possible methods for preventing degradation are also proposed, which can be realized with the use of thickened electrolytes or special films that are deposited onto the electrochrome

NONSTATIONARY HEAT CONDUCTION IN MULTILAYER GLAZING SUBJECTED TO DISTRIBUTED HEAT SOURCES

A method for calculation of nonstationary thermal fields in a multilayer glazing of vehicles under the effect of impulse film heat sources is offered. The glazing is considered as a rectangular multilayer plate made up of isotropic layers with constant thickness. Film heat sources are arranged on layers' interfaces. The heat conduction equation is solved using the Laplace transformation, series expansion and the second expansion theorem. The method offered can be used for designing a safe multilayer glazing under operational and emergency thermal and force loading in vehicles.

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.

Simulation of a Set of Lithium-Ion Batteries With Composite Phase Change Materials and Heating Films Thermal Management System at Low Temperature

Abstract Two different kinds of composite phase change materials (PCMs)—a high thermal conductive 80 wt% paraffin wax (PW)/expanded graphite (EG) composite and a 75 wt% PW/silica aerogel (SA) with a low thermal conductivity—are prepared and they characterized the thermophysical parameters. Then, a numerical model of battery pack based on composite phase change materials coupled with polyimide (PI) electric heating films is established at −20 °C. The temperature of monitoring points set in model and maximum and minimum temperature of the batteries in the pack are measured during discharge at 1C and 2C. By comparing the battery pack filled with PW/EG composite and the pack consisting of PW/SA composite, we intend to choose an appropriate one of the two composite PCMs to improve the lithium-ion batteries performance at low temperature. The results indicate that in spite of a good heating performance in heating process, the PW/SA composite induces an even higher temperature difference over the battery pack. Although PW/EG composite causes a large temperature difference at the end of heating film heating, it can quickly restore the uniformity of the battery pack. The PW/EG composite plays a more important role in improving the performance of the lithium-ion batteries at low temperature.

Investigation of magnetic anisotropy and heat dissipation in thin films of compensated antiferromagnet CuMnAs by pump–probe experiment

We recently reported on a method to determine the easy axis position in a 10 nm thick film of the fully compensated antiferromagnet CuMnAs. The film had a uniaxial magnetic anisotropy and the technique utilized a magneto-optical pump and probe experiment [Saidl et al. Nat. Photonics 11, 91 (2017)]. In this contribution, we discuss the applicability of this method for the investigation of a broader set of epitaxial CuMnAs films having different thicknesses. This work reveals that the equilibrium magnetic anisotropy can be studied only in samples, where this anisotropy is rather strong. However, in the majority of CuMnAs films, the impact of a strong pump pulse induces nano-fragmentation of the magnetic domains and, therefore, the magnetic anisotropy measured by the pump–probe technique differs substantially from that in the equilibrium conditions. We also demonstrate that the optical pump–probe experiment can be used very efficiently to study the local heating and heat dissipation in CuMnAs epitaxial layers. In particular, we determined the electron–phonon relaxation time in CuMnAs. We also observed that, for a local film heating by a focused laser, the thinner films are heated more, but the heat is dissipated considerably faster than in the case of thicker films. This illustrates that the optical pump–probe experiment is a valuable characterization tool for the heat management optimization in the CuMnAs memory devices and can be applied in a similar way to those used during the heat-assisted magnetic recording technology development for the latest generation of hard drive disks.

Innovative focused ultrasound‐based sealing method of flexible packaging films—Principles and characteristics

A key process to package goods is the closure procedure. It ensures the good protection against the environment and vice versa. Ultrasonic sealing presents the advantage of converting locally ultrasound into heat, which is optimal for temperature sensitive goods. The disadvantages remain, however, the equipment cost, the noise generation, and the process sensitivity to materials. It is necessary to develop a sealing process to decrease the acquisition cost of the sealing equipment and cover a wide range of polymer films.This paper focuses on a new sealing method based on high‐intensity focused ultrasound. The principles and characteristics of this process are discussed and underpinned with experimental results.Both the acoustic and thermal effects of the sealing process are summarized. A study of the process parameter impact on the seam strength in static and dynamic operating is proposed. Low‐density polyethylene films with a carrier layer of bi‐oriented polypropylene and polyethylene terephthalate are used. A first test bench generates point‐shaped seam. The heat generation is recorded with an infrared thermography system. A second test bench, a horizontal form fill and seal machine, produces longitudinal seams. The seam quality is controlled by tensile test and tightness test.A quick heating of the polymer films is found. Point seams and longitudinal seams are successfully generated. The seams behave similarly to the ones generated with ultrasonic sealing process. However, the sealing velocity is limited to 3 m/min.This work provides a summary of the characteristics and principles of the new sealing method in packaging applications.

Flexible electrothermal polymer film based on reduced graphene oxide–water polyurethane

In this paper, waterborne polyurethane (WPU) conductive films incorporated with reduced graphene oxide (RGO) as conductive fillers were prepared by solution blending and tape casting method. The electrical conductivity, thermal conductivity and microstructures of the composite films were systematically investigated. The experimental results demonstrate that the electrical conductivity and thermal conductivity of the RGO–WPU composite films first increased then decreased with the increase of the RGO content. The resistivity of composite film with 7% RGO reaches to the smallest that is about [Formula: see text], and the thermal conductivity of the composite film with 7% graphene was about 0.29 W.m.K[Formula: see text], which an increase of 70% compared with pure WPU. The electrical conductivity of the composite film decreased with the increase of the original concentration of WPU solution and thickness of the composite film. As film heater, the composite film displayed effective and rapid heating at low input voltages owing to the good conductivity. With an input voltage was in the range of 10–24 V, the film took less than 30s to reach a steady-state temperature, demonstrating the fast response of the composite film heater and suitable for applications in the field of the fast temperature switching with low input voltages as flexible electrothermal heater.

Development of switchless thin-plate type sorption compressor cell for 5 K sorption J-T refrigerator

A sorption J-T (Joule-Thomson) refrigerator is a J-T refrigerator using a sorption compressor that compresses refrigerant by adsorption and desorption in sorption cells. When the sorption cell of the compressor is cooled, the refrigerant is adsorbed on the adsorbent, reducing the pressure of the cell. In contrast, when the cell is heated, its pressure increases due to desorption of the refrigerant from the adsorbent. The sorption cells should operate in pairs to produce a continuous pressure gradient for J-T expansion since the cell can create pressure periodically. Therefore, to increase cooling capacity of the refrigerator, it is indispensable to reduce the cycle time by accelerating thermal response of the sorption cell. This paper suggests a thin-plate type sorption cell to maximize the heat diffusion to the adsorbent. Furthermore, because its temperature can be altered rapidly, the sorption compressor can operate without a heat switch to regulate heating and cooling of the sorption cell. The sorption cell is made of stainless steel 304 with width and length of 100 mm and height of 4.6 mm, respectively. The activated charcoal with two different nominal sizes is charged into the cell as an adsorbent of helium for cooling at 5 K. On the top and the bottom side of the cell, the cold head of G-M (Gifford-McMahon) refrigerator and the polyimide film heater are attached to adsorb and desorb helium in the cell, respectively. Its ability to build the pressure is verified by heating the cell which contains constant mass of helium. Furthermore, the mass of helium adsorbed on activated charcoal at various temperature are measured by expanding helium from a reservoir to the sorption cell to construct the precise prediction model. Subsequently, the operation parameters for sorption compressor are determined employing a prediction model which is validated by the cooling-down and the heating-up experiment. The predicted mass flow rate and the cycle time of the compressor are 2.37 mg/s and 55.4 s, respectively. Consequently, the cooling capacity of the sorption J-T refrigerator with recuperative heat exchanger is predicted as 2.2 mW at 5 K.

Nonlocal dual-phase-lag heat conduction and the associated nonlocal thermal-viscoelastic analysis

In this paper, the extension of the nonlocal dual-phase-lag (DPL) theory is formulated to account for the heat conduction at nanoscale. Both the temporally and spatially nonlocal effects are considered in heat conduction, which are verified experimentally by the size-dependent thermal conductivity of silicon nanofilms and the transient temperature variation during the femtosecond laser heating of gold films. A generalized uncoupled nonlocal thermoviscoelasticity is hence proposed, which is applied to a one-dimensional analysis of a finite plate under sudden thermal shock. Non-dimensional numerical analyses are performed to illustrate the effects of both nonlocal heat conduction and nonlocal elasticity on thermal propagations and thermoviscoelastic responses.