Film Heat Research Articles

Numerical investigation on falling film flow and heat transfer characteristics over corrugated plates

Falling film flow is commonly utilized in engineering applications. To explore the heat transfer process over falling film plates, the effects of structure and liquid inlet Reynolds number on flow and heat transfer characteristics are studied. The results indicated that corrugation amplitude and flow rate thicken the liquid film. As the corrugation amplitude increased, the critical inlet flow velocity for smooth flow gradually rose. The local heat transfer coefficient was great in the thin fluid film. The heat transfer performance of the optimum corrugated plate was 45%–77 % higher than that of a flat plate. An empirical correlation equation for Nusselt number was developed at Reynolds number of 149.28–398.09 and corrugation amplitude to wavelength ratio of 0.025–0.1. The deviation was less than ±21 %. These findings are significant for necessary temperature regulation in the CO2 capture packed column and also provide references for falling film equipment design and evaluation.

Numerical simulation of non-linear film variation and heat transfer characteristics in falling film evaporation around in-line horizontal tubes

Numerical simulation of non-linear film variation and heat transfer characteristics in falling film evaporation around in-line horizontal tubes

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.

Heat transfer and irrigating liquid hydrodynamics on one-row vertical bundle of inclined tubes in falling film heat exchanger

Spiral-wound heat exchangers widely used currently in various industries provide efficient heat transfer between media through spiral tube winds at evaporation and boiling of falling liquid film. The investigated bundle in the form of one-row vertical bundle of inclined tubes (5 degrees to the horizon) simulates a part of a spiral-wound heat exchanger. Heat transfer and hydrodynamics processes are studied at falling film irrigation by liquid R21 refrigerant at 3 bar of absolute pressure with water as heat carrier. The bundle is placed inside of rectangular heat exchanger with optical windows. Heat transfer measurements are performed for tubes at different positions on the bundle height. Irrigation densities corresponded to falling film Reynolds numbers 300 – 1100, heat flux values within the range of 5000 – 10000 W/m2.

Sandwiched film of graphene/silver nanowire conductive layer reinforced by hydroxyethyl cellulose bond layer

Multilayer nanocomposite film made of different materials has multifunctional properties and is applied in the field of flexible electronic devices. Herein, hydroxyethyl cellulose (HEC) and boron nitride nanosheets (BNNS) were used as the matrix and thermal conductivity material of the HEC/BNNS (HB) insulation layer and were combined with conductive blade structure graphene/silver nanowires (GA) film to prepare a three-layer HB/GA20/HB film. Using the high mechanical properties of the HEC based film, the tensile strength of the three-layer film is increased to 22.0 MPa, 633 % higher than that of the pure conductive film. The sensor prepared by multilayer film has good bending sensing performance (1500 cycles) and electromagnetic shielding performance (29.3 dB). The heating temperature of HB/GA20/HB film heater is up to 107.9 °C at 20 V. In the HB/GA20/HB film, the external HB layer provides insulation, thermal conductivity and physical support, and the internal GA layer with good conductive and sensing properties is combined to build a multi-functional sensor, which can be applied as a mobile sensor, heater and electromagnetic shielding material in the flexible wearable field.

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 .

Upravlyaemaya lazernym izlucheniem spin-volnovaya interferentsiya v neregulyarnoy magnonnoy strukture

Using experimental and numerical investigation, we demonstrate laser-controlled propagation and interaction of spin waves in an irregular magnetic structure in the geometry of the Mach–Zehnder interferometer. It is shown that the use of laser radiation for heating one of the interferometer arms leads to controlled interference of a spin-wave signal in the output section. The yttrium–iron garnet film heating under the action of laser radiation is measured experimentally. Using micromagnetic modeling, the evolution of the spin-wave interference pattern under the action of laser heating of one of the interferometer arm is demonstrated. The results of this study ensure a simple solution for developing tunable spin-wave interferometers for the paradigm of the magnonic logics.

Magnetic Chitosan Bionanocomposite Films as a Versatile Platform for Biomedical Hyperthermia.

Responsive magnetic nanomaterials offer significant advantages for innovative therapies, for instance, in cancer treatments that exploit on-demand delivery on alternating magnetic field (AMF) stimulus. In this work, biocompatible magnetic bionanocomposite films are fabricated from chitosan by film casting with incorporation of magnetite nanoparticles (MNPs) produced by facile one pot synthesis. The influence of synthesis conditions and MNP concentration on the films' heating efficiency and heat dissipation are evaluated through spatio-temporal mapping of the surface temperature changes by video-thermography. The cast films have a thickness below 100µm, and upon exposure to AMF (663kHz, 12.8 kA m-1), induce exceptionally strong heating, reaching a maximum temperature increase of 82 °C within 270 s irradiation. Further, it is demonstrated that the films can serve as substrates that supply heat for multiple hyperthermia scenarios, including: i) non-contact automated heating of cell culture medium, ii) heating of gelatine-based hydrogels of different shapes, and iii) killing of cancerous melanoma cells. The films are versatile components for non-contact stimulus with translational potential in multiple biomedical applications.

Numerical study of falling film flow and heat transfer on the horizontal tube with a porous coating layer

Porous surfaces often exhibit exceptional performance in liquid spreading and heat transfer, making them promising candidates for enhancing falling film heat transfer on solid surfaces. This paper delves into the flow and heat transfer characteristics occurring within falling films on horizontal tubes coated with a porous layer. To achieve this, a three-dimensional numerical model that couples the Volume of Fluid (VOF) method with porous media considerations was employed. The investigation comprehensively covers film spreading behavior, flow patterns, film velocity, film thickness, temperature distribution, and heat transfer coefficients, for both plain and porous tubes. Furthermore, we delve into the effects of key parameters, such as porosity, layer thickness, and material properties, on the overall heat transfer process. The results demonstrate the accuracy of our model in reproducing film thickness and heat transfer coefficients within falling films on horizontal porous tubes. When comparing plain tubes to porous ones, some key differences emerge. Specifically, the liquid film on porous tubes spreads more slowly, leading to increased film thickness and fewer occurrences of dry patches. Additionally, porous tubes result in lower film velocity and a more uniform temperature field compared to plain tubes. Interestingly, the findings reveal that smaller porosities yield thicker films and higher heat transfer coefficients, particularly when the porosity is below 0.4. Moreover, thicker porous layers result in thinner films, higher wetting ratios, and increased heat transfer coefficients. Among the materials we tested, aluminum and copper porous layers exhibit the highest heat transfer performance, while steel demonstrates the lowest.

Numerical and experimental investigation of the electrical and thermal behaviors of the Li-ion batteries under normal and abuse operating conditions

This paper presents the results of a comprehensive investigation of the electrical and thermal behaviors of the Lithium (Li)-ion batteries under normal and abuse conditions. In the first part of the study, an electrochemical-thermal coupled model is developed to predict the thermal and electrical characteristics of a Li-ion battery at 20 and 50 °C temperatures for varying discharge rates based on a detailed sensitivity analysis of the electrochemical and thermal model parameters. The experimental and model data are consistent, considering the discharging processes at 0.5, 1, and 1.5C rates under 20 and 50 °C operating temperatures. In the second part of the study, thermal abuse experiments are conducted by heating the Li-ion cell using the film heater at various charge states of battery. Simulations are carried out for the heating tests by enhancing the electrochemical-thermal model using the temperature-dependent Arrhenius equations. The results show that the thermal abuse model can predict the thermal runaway initiation time within the approximate 10 % margin of error, and the maximum surface temperature with 10.5 % of error compared to the experimental results of the completely charged Li-ion cell.

Thermal Characteristics of Dry Gas Seal in Startup Process Considering Microscale Effects

The heat generated during the startup process of dry gas seals, such as the friction heat of the asperities, viscous shear heat, and the expansion heat of the gas film, easily leads to seal failure and endangers the stable operation of turbomachinery. This study combines the statistically modified contact model and the average Reynolds equation by considering the adiabatic index and the microscale effects of dry gas seals to explore the heat generation characteristics of dry gas seals formed in series at multiple times. In particular, the change laws and influencing factors among the components, including the friction heat of asperities and the shear heat and expansion heat of the gas film and total heat, are investigated. A comparative analysis indicates that the slip flow effect increases the total heat during the startup process. The friction heat is much greater than expansion heat and shear heat. Despite constant acceleration, exponential acceleration, or Harrison acceleration, the heat changes are uneven during the startup process. In particular, the heat changes sharply in the early stage and slowly in the later stage. The Harrison acceleration mode is the most conducive to sealing stability.

Study on temperature distribution of vertical liquid falling film heat transfer with Al2O3 nanofluid

This study presents a laminar smooth 2-D theoretical model of the falling liquid film using an in-house code and validated with experimental results. The numerical model considers thermophysical property enhancements with nanoparticles Al2O3 to different liquids such as water, ethylene glycol (EG), and LiBr-H2O. An experimental setup has been developed to validate the pure heat transfer process in the falling liquid film, using the measurement of the falling film interface temperature. The simulation results agreed well with the experimental results for various liquids at low flow rates. The discrepancy increases as the flow rate increases due to the limitations of the laminar smooth film model in the numerical simulation. With a volumetric concentration of ϕ=4% nanoparticle Al2O3, the heat transfer coefficient of nanofluid water, EG, LiBr-H2O increased around 15%–20% compared with the baseline fluid. A new correlation was obtained to predict the average heat transfer coefficient based on experimental data. The experimental results have an uncertainty at 9.3% for the surface temperature and 5.5% for the falling film bulk temperature. The maximum deviation between the calculated heat transfer coefficient by the model and experimental data is around 25%, at Re<1000. The average error has decreased by 23% when comparing the new correlation considering Ka and the conventional form.

Efficient hydrogen generation of ammonia borane by direct heat supply using a polyimide film heater

This study developed a novel approach to ammonia borane (AB) and silica assembly for all-solid-state thermal dehydrogenation, which can be integrated into current hydrogen generation systems. The AB/silica assembly apparatus is created by attaching pelletized AB specimens to both sides of a polyimide film heater, thus facilitating direct heat supply. The temperature, pressure, and power consumption data of the heater demonstrate that the dehydrogenation reaction is completed within 2 min from the initiation of the electric heating signal. Notably, the temperature and pressure of the generated hydrogen gas reach 39.5 °C and 1.95 barg, respectively, and the maximum hydrogen yield reached 11.46 wt% during the experiment. The infrared spectroscopy analysis indicates that all AB/silica samples inside the assembly undergoes complete reaction. This direct heating method significantly reduces the energy required for AB thermal decomposition and it increases the amount of AB that can be used at once.

HIGHLY EFFECTIVE DIRECT CONTACT HUMIDIFIER FOR THERMAL DESALINATION SYSTEM

The aim of the work is to increase the efficiency of thermal desalination systems with a humidification-dehumidification air cycle due to the reduction of electricity consumption. The most common designs of heat exchangers for air humidification have significant aerodynamic and hydraulic drops. To eliminate this disadvantage, it is proposed to use the internal volume of the vertical tube as an active heat and mass transfer zone during moisture evaporation from salt water to air. The operation of such desalination system has been mathematically modeled and its energy characteristics were determined. A special feature of the mathematical model is the consideration of heat and mass transfer equations for the humidifier and dehumidifier. The effective air velocity in the tube is 3 m/s. Effective operation of thermal unit with a film humidifier is possible then air mass flow is equal to the salt water flow. In this case, the geometric dimensions of the tube must be within the following limits: diameter 20...30 mm, height 2...2.5 m. The conducted mathematical modeling and obtained results give reasons to assert, that for the same rate of evaporation, the film heat exchanger has the lowest aerodynamic and hydrodynamic drops compared to other types of humidifiers. The use of such direct contact device will lead to a decrease in the electricity consumption necessary for salt water and air circulation in the humidification-dehumidification thermal installation.

Synthesis and properties of highly thermally stable ultrathin films of fluorine‐containing hyperbranched polybenzoxazoles

AbstractIn this paper, we aimed to develop ultrathin films of hyperbranched polybenzoxazole with a thickness in the range between 1 and 100 nm. They are expected to have great potential for various applications as functional materials due to their high thermal stability, good chemical resistance and mechanical strength. The synthesis of various hyperbranched poly(o‐hydroxyamide)s as precursors of polybenzoxazole was examined by the polycondensation of 2,2‐bis(3‐amino‐4‐hydroxyphenyl)propane (AHP) and 2,2‐bis(3‐amino‐4‐hydroxyphenyl)hexafluoropropane (AHFP) with 1,3,5‐benzenetricarbonyl trichloride (BCC), yielding the corresponding hyperbranched poly(o‐hydroxyamide), poly(AHFPm‐co‐AHPn‐co‐BCC2.0), with Mn in the range between 12,870 and 22,210 in satisfactory yields. Poly(AHFP3.0‐co‐BCC2.0), poly(AHFP2.25‐co‐AHP0.75‐co‐BCC2.0), and poly(AHFP1.50‐co‐AHP1.50‐co‐BCC2.0) showed good solubility and film‐forming ability, and ultrathin films 8.9–88.6 nm thick were prepared on silicon wafers. Heating of the ultrathin films of poly(AHFPm‐co‐AHPn‐co‐BCC2.0) on a hot plate at 350 °C for 1 h afforded the corresponding ultrathin films of hyperbranched polybenzoxazole, poly(AHFPm‐cyclo‐AHPn‐cyclo‐BCC2.0), with a thickness of 5.3–82.4 nm. Double‐layer thin films consisting of resist materials on top of hyperbranched polybenzoxazole were also prepared.

Thermal Lattice Field during Ultra-Short Laser Pulse Irradiation of Metal Targets: A Fokker–Planck Analytical Model

The ultrafast fs laser pulse heating of thin metal films is studied for the first time using the two-temperature model on the basis of the Fokker–Planck formalism. The incident laser radiation is multi-modal, while the electron temperature is described during the first 2 fs. The predictions are intended for use by experimentalists in optoelectronics, photonics, laser processing, electronics, and bio- and nanomedicine. The crucial role of the nano-sized spatial dimensions of the metal sample is highlighted. A significant result of this study is the interdependence between the target’s size, the phonon/lattice characteristics, and the coefficient β (the quotient of non-diffusive phenomena), which varies between zero (pure diffusive case) and one (pure non-diffusive case).

Facile filter cloth brush-coating of large-area uniform silver nanowire conductive films for paper-based heater

Filter cloth brush-coating (FCBC), using soft filter cloth as a brush-coating medium, in conjunction with viscous silver nanowire (AgNW) conductive solution, is used to prepare AgNW conductive films. The density and uniformity of AgNWs deposited on the substrate are controlled by the interplay between the filter cloth aperture, the conductive solution viscosity, and the brush-coating speed. Further, with appropriate AgNW concentration and flow rate, uniform AgNW transparent conductive film with sheet resistance of 18 Ω sq−1 and transmittance of 94% at 550 nm is acquired by FCBC. Due to the precise control of the coating process in FCBC, large-area uniform AgNW conductive film fabricated on printing paper has a low non-uniformity factor of 1.2% at a sheet resistance of 19.0 Ω sq−1. The resultant paper-based AgNW film heater shows sensitive and stable heating performance. FCBC shows great potential in producing large-area uniform AgNW films on various substrates.

Magnetic-field induced flattening of evaporating ferro-nanofluid meniscus for enhanced cooling

This work envisages applying magnetic fields to flatten thin ferro-nanofluid film meniscus for enhanced heat transfer during evaporative cooling process. Experiments are conducted to examine the shape of the evaporating extended meniscus of ferro-nanofluid (Fe304 nanoparticles in water suspension 0.01% v/v) under axisymmetric vertical magnetic fields (∼10−2T) generated by solenoid placed below the heated substrate. The study includes measuring the thickness profile of the meniscus evaporating region using high nano-scale resolution reflectometry and theoretically interpreting meniscus shape in terms of flow and film heat transfer. Profile measurements reveal an increasing influence of magnetic fields in thinning of the adsorbed region and stretching of the transition region, which effectively reduce the thermal resistance across meniscus width. Data reduction based on thickness as well as the derived curvature profiles yields a high-pressure gradient driving flow along the evaporating thin film region. The results imply additional suction induced by disjoining pressure of thinner adsorbed layer which sustains replenishment of lost evaporative mass across a longer transition region interface. Subsequent heat transfer analysis reveals up to 156 % enhancement in overall heat flux and 101 % in average heat transfer with increasing magnetic field intensity. The findings establish proof of concept of applying magnetic field to augment film-based cooling.

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.

A numerical study on fluid flow and heat transfer characteristics of oily wastewater falling film outside an elliptical tube

Falling film heat exchangers have recently been widespread as a heat transfer technique for oily wastewater. Researching the characteristics of fluid mechanism for heat transmission is crucial. In this research, numerical models are applied to simulate the heat transmission and flow of falling film outside ellipse tube. In order to emulate fluid flow and heat transmission, the oily wastewater falling film is analyzed utilizing the VOF approach under circumstances of constant thermal flow. On the flow properties and heat transfer coefficient distribution of liquid film, the impacts of the input height, contact angle, liquid film flow rate, and oil content are examined. These computational outcomes are attained: (1) More so than film thickness, according to the simulation results, increasing liquid film flow significantly affects velocity;(2) One of the main causes of how oil concentration affects heat transmission is the complex disturbance process of liquid film and the force change around tube structure;(3) Around 40°, inlet height has the greatest impact on local heat transfer coefficient;(4) The overall heat transmission will deteriorate due to the hydrophobic impact brought on by increased contact angle.