Film Thermal Resistance Research Articles

Halochromic smart packaging film based on montmorillonite/polyvinyl alcohol-high amylose starch nanocomposite for monitoring chicken meat freshness

Polyvinyl alcohol (PVA) was blended with high amylose starch (HAS) at a ratio of 3:1, and reinforced with montmorillonite (MMT K10) at different concentrations (1, 2, 5, and 7 % w/w of polymers) and anthocyanins (ANT) to develop an active and smart packaging film. MMT addition enhanced the film's mechanical, barrier, thermal, and water resistance properties. Incorporating ANT extracted from roselle calyx into the optimal nanocomposite film (MMT/PVA-HAS II) increased the films' antioxidant, pH-response, and antibacterial properties. FTIR, XRD, and SEM confirmed the intermolecular interactions and even distribution of ANT and MMT in the film matrix. Release rate of ANT was dependent on type of simulant, with higher rate in aqueous solutions compared to alcoholic/fatty food simulants, and cytotoxicity evaluation proved safety of films for food packaging applications. Storage experiments confirmed the potential applicability of the novel halochromic smart film as a promising candidate for monitoring chicken spoilage under abusive storage conditions.

Condensation characteristics of air–water vapor mixture on the surface of vertical flat plate

The condensation heat transfer of air–water mixed vapor is an important heat transfer phenomenon in production life. An experimental system for condensation heat transfer of the air–water vapor mixed vapor is built in this paper. The condensation characteristics of the mixed vapor and the double boundary layer structure characteristics were investigated. The study mainly discussed the influence of flow velocity on the condensation performance of mixed vapor and summarized the experimental correlation equations considering flow velocity. Results indicate that the condensation performance decreases significantly as the air concentration increases. The mixed vapor flow velocity was increased from 1 to 3 m/s, and the condensation heat transfer coefficient was increased by 34.9–121.0%. The enhanced effect of flow velocity was also observed at high air concentration and low subcooling. The ratio of convective and condensation heat transfer coefficients increases with the rise in air concentration, reaching a maximum of 0.12. The proportion of convective heat transfer can be reduced by increasing the mixed vapor flow velocity. The gas film thickness is substantially higher than the liquid film thickness in mixed vapor condensation, and the gas/liquid film thermal resistance ratio can be more than 30 times. And increasing the flow velocity can significantly reduce the gas film/liquid film thermal resistance ratio. A new experimental correlation equation is fitted based on the experimental results, and this equation can be used as a reference for the design of related heat exchangers.

Measurements of the liquid film thickness for annular flow during flow condensation in a circular tube

Liquid film thicknesses of R245fa and zeotropic mixtures of R134a/R245fa were measured during flow condensation in circular micro-channel using a CCD camera and a Laser Focus Displacement Meter (LFDM). The fluctuation characteristics were studied along with the average liquid film thickness and the thermal resistance. The average liquid film thickness had no obvious association with the temperature glide. The liquid film fluctuation frequency was most strongly affected by the vapor-liquid interface shear force with the liquid film thickness determining the fluctuation range. Larger mass fluxes weakened the thinning effect of the mass flux. With increasing R134a mass fraction, the impact of mass flux was much obvious. With increasing R134a mass fraction, the liquid film thermal resistance increased. The laminar liquid film momentum equation was used to develop a simple method to predict the mean liquid film thickness.

Thermal Characterization of Metal-Oxide Interfaces Using Time-Domain Thermoreflectance with Nanograting Transducers.

Metal-oxide thermal boundary conductance (TBC) strongly influences the temperature rise in nanostructured systems, such as dense interconnects, when its value is comparable to the thermal conductance of the amorphous dielectric oxide. However, the thermal characterization of metal-amorphous oxide TBC is often hampered by the measurement insensitivity of techniques such as time-domain thermoreflectance (TDTR). Here, we use metal nanograting structures as opto-thermal transducers in TDTR to measure the TBC of metal-oxide interfaces. Combined with an ultrafast pump-probe laser measurement approach, the nanopatterned structures amplify the contribution of the thermal boundary resistance (TBR), the inverse of TBC, over the thermal resistance of the adjacent material, thereby enhancing measurement sensitivity. For demonstration purposes, we report the TBC between Al and SiO2 films. We then compare the impact of Al grating dimensions on the measured TBC values, sensitivities, and uncertainties. The grating periods L used in this study range from 150 to 300 nm, and the bridge widths w range from 72 to 205 nm. With the narrowest grating transducers (72 nm), the TBC of Al-SiO2 interfaces is measured to be 159-48+61 MW m-2 K-1, with the experimental sensitivity being 5× higher than that of a blanket Al film. This improvement is attributed to the reduced contribution of the SiO2 film thermal resistance to the temperature signal from TDTR response. The nanograting measurement approach described here is promising for the thermal characterization of a variety of nanostructured metal-amorphous passivation systems and interfaces common in semiconductor technology.

Simulation and experimental validation of pulsating heat pipes

• Numerical model improvements for the thermal performance prediction of pulsating heat pipes. • Model validation with new experimental data for vertical and horizontal orientation. • Flow behavior analysis on the simulated results. The one-dimensional transient numerical code of JJ Cooling Innovation has been significantly improved to simulate the thermal/hydraulic performance of pulsating heat pipes (PHPs). Using a mechanistic approach, the liquid slug and vapor plug flows and their interaction with the surrounding wall are modeled. The heat transfer is predicted using the Three-Zone Model of flow boiling in microchannels, which includes liquid film evaporation and liquid film condensation of vapor plugs and convection of liquid slugs. Discretizing the entire PHP serpentine into one continuous grid, the code solves all variables based on local conditions. The code allows the user to define the working fluid, the channel’s shape, material and wall roughness, the serpentine’s pitch, the geometrical parameters of evaporator, adiabatic region and condenser zones, and the operating parameters. The boundary conditions in the evaporator zone can either be constant heat flux or constant temperature, while on the condenser side, the coolant temperature is constant as well as the heat transfer coefficient. The code works without any fitting factor and predicts all local variables in the 1D grid as a function of time, including the liquid film thickness and the onset of boiling for the formation of new vapor plugs within the evaporating and adiabatic zones, if local nucleation conditions are reached. Growth, collapse and coalescence of generated bubbles are taken into account. The film thermal resistance is corrected to a radial conduction model. The implementation of the initial liquid film thickness laid behind a liquid slug is updated to include the effect of the bubble velocity and acceleration as well as the length of the leading slug. The nucleation of new vapor plug has also been updated. The onset of nucleation is only dependent on the local thermodynamic state. If the threshold is reached, a new method is used to simulate micro-bubbles formation and coalescence to a channel-size vapor plug. These modifications greatly improve the code accuracy and stability allowing simulations with high pressure fluid rather than ethanol only. Furthermore, in the on-going EU project Pulsating Heat Pipes for Hybrid Propulsion Systems (PHP2), a new PHP test bench has been designed and built at Provides Metalmeccanica. A copper tube PHP with a 19-turn of 2.0 mm internal diameter and 12 mm tube pitch was tested over a wide range of imposed heat loads. A microchannel water-cooling plate was used at the condenser side with an inlet temperature of 20 °C. Then, tests were done for vertical and horizontal orientations with R1233zd(E) as the working fluid. The code, which was previously validated for ethanol PHP test data from KAIST, is now successfully validated for the present experimental data points. Accurate results were obtained from low heat loads up to 250 W for a set of 49 data points, predicting 97% within an error bandwidth of 30%.

Synthesis and fabrication of films including graphene oxide functionalized with chitosan for regenerative medicine applications

Graphene oxide (GO) has recently gained attention as a scaffold reinforcing agent for tissue engineering. Biomechanical and biological properties through a synergistic effect can be strengthened when combined with other materials such as chitosan (CS). For that reason, chitosan was used for Graphene Oxide (GO) functionalization through an amide group whose formation was evident by bands around 1600 cm−1 in the FTIR analysis. Furthermore, bands located at 1348 cm−1 (D band), 1593 cm−1 (G band), and 2416 cm−1 (2D band) in the RAMAN spectrum, and the displacement of the signal at 87.03 ppm (C5) in solid-state 13C-NMR confirmed the amide formation. Films including the CS-GO compound were prepared and characterized by thermogravimetric analysis (TGA), where CS-GO film presented a lighter mass loss (~10% less loosed) than CS due probably to the covalent functionalization with GO, providing film thermal resistance. The CS-GO films synthesized were implanted in Wistar rats' subdermal tissue as a first approximation to the biological response. In vivo tests showed a low inflammatory response, good cicatrization, and advanced resorption at 60 days of implantation, as indicated by histological images. It was evidenced that the covalent union between CS and GO increased biocompatibility and the degradation/resorption capacity, demonstrating tissue regeneration with typical characteristics and tiny remnants of implanted material surrounded by a type III collagen capsule. These results show the potential application of the new synthesized films, including the CS-GO compound, in tissue engineering.

Implementation of a CFD model for wall condensation in the presence of non-condensable gas mixtures

In this paper, we discuss a CFD model to predict vapor condensation on walls in the presence of non-condensable gases, with a specific focus on large scale applications, such as accidental flows in a nuclear reactor containment. It is conclusive from the previous works that the heat and mass transport resistance due to the diffusion boundary layer in the gas phase overwhelms the liquid film thermal resistance. Therefore, the two-phase wall condensation phenomenon is treated with a single-phase (gas) model. For the numerical implementation, the containmentFOAM CFD package, based on OpenFOAM is used. For the first time, the model implementation is discussed for arbitrary multi-component mixtures, and performances of two commonly used approaches – Volumetric source terms and Face-fluxes – are compared; the Face-flux model proved to be more accurate, computationally cheaper, and less grid-dependent. Concluding, the Face-flux approach was validated against the experimental database for forced convection flows, obtained at the SETCOM facility in Forschungzentrum Jülich, Germany. The results demonstrate the model’s predictiveness and robustness for a wide range of cases in the forced convection regime.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ МОЛЕКУЛЯРНОЙ МАССЫ ЭПОКСИДНЫХ ОЛИГОМЕРОВ И ОТВЕРДИТЕЛЕЙ НА ЭКСПЛУАТАЦИОННЫЕ СВОЙСТВА ЛАКОКРАСОЧНЫХ ПОКРЫТИЙ

The paper provides the results of studies of lacquer coatings made on the basis of epoxy oligomers of different molecular mass hardened by the amine type hardeners. Thermal resistance, erosion resistance, strength and deformation characteristics of free lacquer films, as well as their physical and mechanical properties have been examined. It has been determined that the properties of epoxy lacquer coatings are significantly influenced by the molecular mass of the oligomer and hardener used to produce these coatings. It is shown that with the increase in the molecular mass used to obtain coatings epoxy oligomers improve their operational properties, such as heat resistance, erosion resistance, physical and mechanical properties.

Numerical modeling of vapor condensation over a wide range of non-condensable gas concentrations

This paper presents a numerical model to study the process of vapor condensation on surfaces characterized by film-wise condensation with the presence of Non-condensable gases (NCG). State variables in both the condensate film and the diffusion layer were solved separately and the condensation interface was used to couple the two solutions. The solution of the condensate film was obtained using well-established solutions of laminar film condensation of pure vapor. In contrast to other models surveyed, this work provides a inexpensive and accurate predictions of heat and mass transfer characteristics. We validated the work against two classical condensation problems. The model was first validated against empirical correlations and experimental work, resulting in a very good agreement. We then assessed the applicability of ignoring the condensate film effect, as performed in previous models, on the condensation processes by observing the thermal resistances of both the condensate film and diffusion layer. Results indicated that for the studied cases of NCG mass fractions above 20%, the condensate thermal resistance was at least an order of magnitude lower than that of the diffusion layer. However, the two thermal resistances seem to approach each other as NCG mass fraction becomes smaller. On another front, we observed that models that ignore the condensate film thermal resistance underestimate the interfacial temperature albeit accurately predicting the overall heat transfer rate. To simulate even lower NCG mass fractions, we validated our model to the classical analytical work of Sparrow and co-workers. Results showed a striking agreement between the two solutions at different NCG mass fractions (0.5%–10%) and subcooling degrees (5∘F–40∘F). Finally, we found a good agreement between results of our model and the heat/mass transfer analogy. The heat/mass transfer analogy is a semi-empirical method therefore, is limited to the existing correlations and their uncertainties. On the other hand, our model does not use any empiricism and relies on the available solutions of laminar condensate film of pure vapor in predicting the liquid side heat transfer coefficient.

CFD Analysis of Falling Film Hydrodynamics for a Lithium Bromide (LiBr) Solution over a Horizontal Tube

Falling film evaporators are used in applications where high heat transfer coefficients are required for low liquid load and temperature difference. One such application is the lithium bromide (LiBr)-based absorber and generator. The concentration of the aqueous LiBr solution changes within the absorber and generator because of evaporation and vapor absorption. This causes the thermophysical properties to differ and affects the film distribution, heat, and mass transfer mechanisms. For thermal performance improvement of LiBr-based falling film evaporators, in-depth analysis at the micro level is required for film distribution and hydrodynamics. In this work, a 2D numerical model was constructed using the commercial CFD software Ansys Fluent v18.0. The influence of the liquid load corresponding to droplet and jet mode, and the concentration, on film hydrodynamics was examined. It was found that the jet mode was more stable at a higher concentration of 0.65 with ±0.5% variation compared to lower concentrations. The recirculation was stronger at a low concentration of 0.45 and existed until the angular position (θ) = 10°, whereas at 0.65 concentration it diminished after θ = 5°. The improved heat transfer is expected at lower concentrations due to lower film thickness and thermal resistance, more recirculation, and a higher velocity field.

Experimental study of R600a/oil/MWCNT nano-refrigerant condensing flow inside micro-fin tubes

The present experimental study aims to investigate condensation heat transfer characteristics of R600a/oil/multi-walled carbon nanotube (MWCNT) nano-refrigerant flow inside a horizontal micro-fin tube. The test condenser is a horizontal double-pipe heat exchanger consists of a copper micro-fin tube with 14.18 mm inner diameter which is installed in a polyethylene shell with a diameter of 6 cm. The experiments cover a wide range of parameters, including mass velocity of 54 to 90 kg/m2 s, vapor quality of 0.03 to 0.76, and condensation pressure of 550 to 700 kPa. The investigations are conducted in three parts, including the characteristics of pure R600a condensing flow inside micro-fin tubes, the effect of adding lubricating oil with concentration of 1%, and the impact of adding nano-oil with nanoparticles compactness of 0.1, 0.2, and 0.3%. Comparison of the experimental data for the pure refrigerant flow with three well-known correlations shows the maximum deviation of ±20% which validates the test procedure. Based on the results, R600a/oil heat transfer coefficient is higher than pure R600a in low and medium vapor qualities, while at high qualities the pure R600a shows higher coefficient due to the impact of lubricating oil on the condensate liquid film thermal resistance. In addition, adding nanoparticles is more effective at low and medium vapor qualities and high mass velocity. The results showed that using MWCNT nanoparticles with the compactness of 0.3% increases the heat transfer coefficient up to 74.8% in comparison to the pure refrigerant.

Thermal Conductivity and Thermal Boundary Resistances of ALD Al $$_{2}$$ 2 O $$_{3}$$ 3 Films on Si and Sapphire

On Si and sapphire substrates, 6–45 nm thick films of atomic layer-deposited Al $$_{2}$$ O $$_{3}$$ were grown. The thermal conductivity of ALD films has been determined from a linear relation between film thickness and thermal resistance measured by the 3 $$\omega $$ method. ALD films on Si and sapphire showed almost same thermal conductivity in the temperature range of 50–350 K. Residual thermal resistance was also obtained by extrapolation of the linear fit and was modeled as a sum of the thermal boundary resistances at heater–film and film–substrate interfaces. The total thermal resistance addenda for films on sapphire was close to independently measured thermal boundary resistance of heater–sapphire interface. From the result, it was deduced that the thermal boundary resistance at ALD Al $$_{2}$$ O $$_{3}$$ –sapphire interface was much lower than that of heater–film. By contrast, the films on Si showed significantly larger thermal boundary resistance than films on sapphire. Data of $$< 30$$ nm films on Si were excluded because an AC coupling of electrical heating voltage to semiconductive Si complicated the relation between 3 $$\omega $$ voltage and temperature.

Mold Simulator Study of Heat Transfer Phenomenon During the Initial Solidification in Continuous Casting Mold

In this paper, mold simulator trials were firstly carried out to study the phenomena of the initial shell solidification of molten steel and the heat transfer across the initial shell to the infiltrated mold/shell slag film and mold. Second, a one-dimensional inverse heat transfer problem for solidification (1DITPS) was built to determine the temperature distribution and the heat transfer behavior through the solidifying shell from the measured shell thickness. Third, the mold wall temperature field was recovered by a 2DIHCP mathematical model from the measured in-mold wall temperatures. Finally, coupled with the measured slag film thickness and the calculations of 1DITPS and 2DIHCP, the thermal resistance and the thickness of liquid slag film in the vicinity of the meniscus were evaluated. The experiment results show that: the total mold/shell thermal resistance, the mold/slag interfacial thermal resistance, the liquid film thermal resistance, and the solid film thermal resistance is 8.0 to 14.9 × 10−4, 2.7 to 4.8 × 10−4, 1.5 to 4.6 × 10−4, and 3.9 to 6.8 × 10−4 m2 K/W, respectively. The percentage of mold/slag interfacial thermal resistance, liquid film thermal resistance, and solid film thermal resistance over the total mold/shell thermal resistance is 27.5 to 34.4, 17.2 to 34.0, and 38.5 to 48.8 pct, respectively. The ratio of radiation heat flux is around 14.1 to 51.9 pct in the liquid slag film.

Variations in Optical Properties of ZnS/Cu/ZnS Nanostructures Due to Thickness Change of ZnS Cap Layer

Nanostructures of ZnS/Cu/ZnS were deposited on glass substrate using physical vapor deposition technique. The thickness of the first and last ZnS layers was altered, while the thickness of the embedded Cu layer was fixed at 50 nm. The produced nanostructures were of good quality. Spectrophotometric measurements were carried out on the nanostructures to investigate the optical properties. The transmission and reflectivity spectra were recorded and studied in details. ZnS was selected due to its high refractive index, ease of deposition, and low cost. The copper layer was used because of its low absorption in the visible part of the spectrum and its thermal stability. The ZnS layer was found not only to anti-reflective the Cu layer, but also to stabilize the nanostructure, improve its adherence on glass substrate, and increase the film thermal resistance up to 240 °C. Furthermore, all the samples exhibit good thermal stability up to 240 °C upon annealing for two hours.

Influence of heat source size and film thickness on phonon transport in a two-dimensional thin film

Abstract. Phonon transport in a two-dimensional thin silicon film is considered and the effect of heat source size and the film thickness on the transport characteristics is examined. Frequency dependent Boltzmann equation is incorporated in the analysis to account for the contribution of the ballistic phonons to the energy transport. Equivalent equilibrium temperature is introduced to assess the thermal resistance during the phonon transport in the film. The numerical scheme with the appropriate boundary conditions is used to predict the transport properties, including the effective thermal conductivity, of the thin film. It is found that the heat source size and the film thickness influence the thermal resistance of the film almost equally. The ballistic phonons reduce the film thermal resistance while suppressing the effective thermal conductivity in the thin film.

Stagnant Effective Thermal Conductivity of Agro-Industrial Residues for Solid-State Fermentation

The stagnant effective thermal conductivities (K0) of sugar cane bagasse (SCB), wheat bran (WB), orange pulp and peel (OPP) and their combination (weight proportion 1:2:2 SCB/OPP/WB) were obtained using the line heat source method. These solid materials were applied to pectinase production via solid-state fermentation. The moisture content ranged from 4 to 80% (w.b.). A conduction mechanism through the porous media was observed, along with conduction through a liquid film and contact thermal resistance between the samples and the probe. K0 was low for intermediate moisture contents and approached the molecular conductivity of water for high moisture contents.

A dynamic parameter to describe the thermal response of buildings to radiant heat gains

This papers deals with the surface factor, a dynamic parameter that describes the thermal response of a wall to a cyclic radiant heat flux absorbed on its inner surface. Despite it was available since the Seventies in the framework of the admittance procedure, the surface factor has not been fully exploited and, unlike other dynamic thermal properties, it has been very rarely dealt with in the scientific literature.After a concise presentation of the mathematical background, the paper proposes the calculation of the surface factor for common single-layered walls, in order to investigate its sensitivity to the thickness and the thermophysical properties of the slab. Two graphs are presented for an easy and precise determination of the amplitude and the time shift of the surface factor, as a function of the properties of the material. The effect of an insulating layer is also addressed, by varying both its position and thickness. Furthermore, the investigation shows that the values of the film thermal resistance suggested by current Standards are not always appropriate, and may introduce significant inaccuracy.The results provide very useful information for optimizing the response of a wall to periodic heat fluxes acting on its internal surface.

Comparative Analysis of Heat Transfer Characteristics for CO&lt;sub&gt;2&lt;/sub&gt; and Conventional Refrigerants

s: The obvious characteristics of transcritical CO2 cycle are that the heat rejection process takes place in the supercritical region (about 8-12Mpa). The heat transfer features of CO2 under supercritical pressure are different from those of the conventional refrigerants. And the heat transfer performances comparison study for supercritical CO2 fluid and the conventional refrigerants are carried out by means of thermo-physical properties analog analysis and experimental results quantitative comparison. The special properties variation of supercritical CO2 fluid makes its heat transfer performance different from the conventional fluids. From the view of properties analysis and quantitative comparison, the heat transfer performance of supercritical CO2 is equivalent to the condensation heat transfer of conventional refrigerants. Although the condensation coefficient is very large since there is phase change and latent heat variation in the condensation process, there is liquid film thermal resistance. While in the supercritical CO2 cooling process, there is no liquid film in existence and the thickness of the boundary layer is very thin. The heat transfer temperature difference is very large, so the heat transfer performance in the supercritical CO2 cooling process is equivalent to that of the condensation heat transfer.

Effect of film thickness on the thermal resistance of confined semiconductor thin films

The thermal resistance of semiconductor thin films is predicted using lattice dynamics (LD) calculations and molecular dynamics (MD) simulations. We consider Si and Ge films with thicknesses, LF, between 0.2 and 30 nm that are confined between larger extents of the other species (i.e., Ge/Si/Ge and Si/Ge/Si structures). The LD predictions are made in the classical limit for comparison to the classical MD simulations, which are performed at a temperature of 500 K. For structures with LF&amp;lt;2 nm, the thin film thermal resistance increases rapidly with increasing film thickness, a trend we attribute to changes in the allowed vibrational states in the film. These changes are found to affect the dependence of the phonon transmission coefficient on incidence angle for the Ge/Si/Ge structures and on frequency for the Si/Ge/Si structures. When LF&amp;gt;2 nm, the MD-predicted thermal resistances are independent of the film thickness for the Ge/Si/Ge structures and increase with increasing film thickness for the Si/Ge/Si structures. We attribute these results to phonon transport that is ballistic in the Ge/Si/Ge structures and more diffusive in the Si/Ge/Si structures based on comparisons to the LD predictions, which assume ballistic phonon transport. We find that this difference between the structures cannot be predicted by comparing the mode-averaged phonon mean free path to the film thickness. It can be predicted, however, by considering the frequency dependence of the phonon mean free paths.

Mechanical properties and morphology of the clay/waterborne polyurethane nanocomposite

Stable clay/waterborne polyurethane nanocompostie dispersions were synthesized by sulfonated poly (butylene adipate) diol, 4,4-diphenylmethane diisocyanate, dimethyl propionic acid, 1,4-butanediol, triethyl amine and clay-water dispersion through a route named prepolymer acetone mixing progress. The reinforced mechanical properties and thermal resistance of films casting from it were examined by dynamic mechanical analyses (DMA), thermogravimetric analyses (TGA) and tensile tests. Furthermore, the morphology of these nanocompostie films and dispersions were observed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), wide-angle X-ray diffraction analyses (WXRD). The experimental results reveal that the clay could be predominantly dispersed in the pristine polymer forming nanocomposties, and evidently enhanced the tensile properties and modulus of it. Additionally, the best-reinforced effect could occur when the clay content was near 1 wt%.